Direct induction of molecular alignment in liquid crystal polymer network film by photopolymerization

NASA Astrophysics Data System (ADS)

Hisano, K.; Aizawa, M.; Ishizu, M.; Kurata, Y.; Shishido, A.

2016-09-01

Liquid crystal (LC) is the promising material for the fabrication of high-performance soft, flexible devices. The fascinating and useful properties arise from their cooperative effect that inherently allows the macroscopic integration and control of molecular alignment through various external stimuli. To date, light-matter interaction is the most attractive stimuli and researchers developed photoalignment through photochemical or photophysical reactions triggered by linearly polarized light. Here we show the new choice based on molecular diffusion by photopolymerization. We found that photopolymerization of a LC monomer and a crosslinker through a photomask enables to direct molecular alignment in the resultant LC polymer network film. The key generating the molecular alignment is molecular diffusion due to the difference of chemical potentials between irradiated and unirradiated regions. This concept is applicable to various shapes of photomask and two-dimensional molecular alignments can be fabricated depending on the spatial design of photomask. By virtue of the inherent versatility of molecular diffusion in materials, the process would shed light on the fabrication of various high-performance flexible materials with molecular alignment having controlled patterns.

Composite Nature of Layered Hybrid Perovskites: Assessment on Quantum and Dielectric Confinements and Band Alignment

DOE PAGES

Traore, Boubacar; Pedesseau, Laurent; Assam, Linda; ...

2018-02-26

Layered hybrid organic–inorganic perovskites (HOPs) have re-emerged as potential technological solutions for next-generation photovoltaic and optoelectronic applications. Their two-dimensional (2D) nature confers them a significant flexibility and results in the appearance of quantum and dielectric confinements. Such confinements are at the origin of their fascinating properties, and understanding them from a fundamental level is of paramount importance for optimization. Here, we provide an in-depth investigation of band alignments of 2D HOP allowing access to carriers’ confinement potentials. 2D HOPs are conceptualized as composite materials in which pseudoinorganic and -organic components are defined. In this way, computational modeling of band alignmentsmore » becomes affordable using first-principles methods. First, we show that the composite approach is suitable to study the position-dependent dielectric profiles and enables clear differentiation of the respective contributions of inorganic and organic components. Then we apply the composite approach to a variety of 2D HOPs, assessing the impact on the confinement potentials of well and barrier thickness, of the nature of the inorganic well, and of structural transitions. Using the deduced potentials, we further discuss the limitations of the effective mass approximation, scrutinizing the electronic properties of this family of composite materials. Our simulations demonstrate type-I dominant band alignment in 2D HOPs. Finally, we outline design principles on band alignment toward achieving specific optoelectronic properties. Furthermore, we present alternative theoretical methods to inspect the properties of 2D hybrid perovskites and expect that the composite approach will be applicable to other classes of layered materials.« less

Composite Nature of Layered Hybrid Perovskites: Assessment on Quantum and Dielectric Confinements and Band Alignment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Traore, Boubacar; Pedesseau, Laurent; Assam, Linda

Layered hybrid organic–inorganic perovskites (HOPs) have re-emerged as potential technological solutions for next-generation photovoltaic and optoelectronic applications. Their two-dimensional (2D) nature confers them a significant flexibility and results in the appearance of quantum and dielectric confinements. Such confinements are at the origin of their fascinating properties, and understanding them from a fundamental level is of paramount importance for optimization. Here, we provide an in-depth investigation of band alignments of 2D HOP allowing access to carriers’ confinement potentials. 2D HOPs are conceptualized as composite materials in which pseudoinorganic and -organic components are defined. In this way, computational modeling of band alignmentsmore » becomes affordable using first-principles methods. First, we show that the composite approach is suitable to study the position-dependent dielectric profiles and enables clear differentiation of the respective contributions of inorganic and organic components. Then we apply the composite approach to a variety of 2D HOPs, assessing the impact on the confinement potentials of well and barrier thickness, of the nature of the inorganic well, and of structural transitions. Using the deduced potentials, we further discuss the limitations of the effective mass approximation, scrutinizing the electronic properties of this family of composite materials. Our simulations demonstrate type-I dominant band alignment in 2D HOPs. Finally, we outline design principles on band alignment toward achieving specific optoelectronic properties. Furthermore, we present alternative theoretical methods to inspect the properties of 2D hybrid perovskites and expect that the composite approach will be applicable to other classes of layered materials.« less

Enhanced pyroelectric and piezoelectric properties of PZT with aligned porosity for energy harvesting applications† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7ta00967d Click here for additional data file.

PubMed Central

Zhang, Yan; Xie, Mengying; Roscow, James; Bao, Yinxiang; Zhou, Kechao

2017-01-01

This paper demonstrates the significant benefits of exploiting highly aligned porosity in piezoelectric and pyroelectric materials for improved energy harvesting performance. Porous lead zirconate (PZT) ceramics with aligned pore channels and varying fractions of porosity were manufactured in a water-based suspension using freeze-casting. The aligned porous PZT ceramics were characterized in detail for both piezoelectric and pyroelectric properties and their energy harvesting performance figures of merit were assessed parallel and perpendicular to the freezing direction. As a result of the introduction of porosity into the ceramic microstructure, high piezoelectric and pyroelectric harvesting figures of merits were achieved for porous freeze-cast PZT compared to dense PZT due to the reduced permittivity and volume specific heat capacity. Experimental results were compared to parallel and series analytical models with good agreement and the PZT with porosity aligned parallel to the freezing direction exhibited the highest piezoelectric and pyroelectric harvesting response; this was a result of the enhanced interconnectivity of the ferroelectric material along the poling direction and reduced fraction of unpoled material that leads to a higher polarization. A complete thermal energy harvesting system, composed of a parallel-aligned PZT harvester element and an AC/DC converter, was successfully demonstrated by charging a storage capacitor. The maximum energy density generated by the 60 vol% porous parallel-connected PZT when subjected to thermal oscillations was 1653 μJ cm–3, which was 374% higher than that of the dense PZT with an energy density of 446 μJ cm–3. The results are beneficial for the design and manufacture of high performance porous pyroelectric and piezoelectric materials in devices for energy harvesting and sensor applications. PMID:28580142

Enhanced pyroelectric and piezoelectric properties of PZT with aligned porosity for energy harvesting applications.

PubMed

Zhang, Yan; Xie, Mengying; Roscow, James; Bao, Yinxiang; Zhou, Kechao; Zhang, Dou; Bowen, Chris R

2017-04-14

This paper demonstrates the significant benefits of exploiting highly aligned porosity in piezoelectric and pyroelectric materials for improved energy harvesting performance. Porous lead zirconate (PZT) ceramics with aligned pore channels and varying fractions of porosity were manufactured in a water-based suspension using freeze-casting. The aligned porous PZT ceramics were characterized in detail for both piezoelectric and pyroelectric properties and their energy harvesting performance figures of merit were assessed parallel and perpendicular to the freezing direction. As a result of the introduction of porosity into the ceramic microstructure, high piezoelectric and pyroelectric harvesting figures of merits were achieved for porous freeze-cast PZT compared to dense PZT due to the reduced permittivity and volume specific heat capacity. Experimental results were compared to parallel and series analytical models with good agreement and the PZT with porosity aligned parallel to the freezing direction exhibited the highest piezoelectric and pyroelectric harvesting response; this was a result of the enhanced interconnectivity of the ferroelectric material along the poling direction and reduced fraction of unpoled material that leads to a higher polarization. A complete thermal energy harvesting system, composed of a parallel-aligned PZT harvester element and an AC/DC converter, was successfully demonstrated by charging a storage capacitor. The maximum energy density generated by the 60 vol% porous parallel-connected PZT when subjected to thermal oscillations was 1653 μJ cm -3 , which was 374% higher than that of the dense PZT with an energy density of 446 μJ cm -3 . The results are beneficial for the design and manufacture of high performance porous pyroelectric and piezoelectric materials in devices for energy harvesting and sensor applications.

Controlling the electronic properties of van der Waals heterostructures by applying electrostatic design

NASA Astrophysics Data System (ADS)

Winkler, Christian; Harivyasi, Shashank S.; Zojer, Egbert

2018-07-01

Van der Waals heterostructures based on the heteroassembly of 2D materials represent a recently developed class of materials with promising properties especially for optoelectronic applications. The alignment of electronic energy bands between consecutive layers of these heterostructures crucially determines their functionality. In the present paper, relying on dispersion-corrected density-functional theory calculations, we present electrostatic design as a promising tool for manipulating this band alignment. The latter is achieved by inserting a layer of aligned polar molecules between consecutive transition-metal dichalcogenide (TMD) sheets. As a consequence, collective electrostatic effects induce a shift of as much as 0.3 eV in the band edges of successive TMD layers. Building on that, the proposed approach can be used to design electronically more complex systems, like quantum cascades or quantum wells, or to change the type of band lineup between type II and type I.

Electromechanical modeling and experimental verification of a directly printed nanocomposite

NASA Astrophysics Data System (ADS)

Nafari, Alireza; Sodano, Henry A.

2018-03-01

Piezoelectric materials are currently among the most promising building blocks of sensing, actuating and energy harvesting systems. However, these materials are limited in applications due to difficulty in machining and casting it on to curve surfaces. To mitigate this issue, one method is through additive manufacturing (direct printing) of piezoelectric nanocomposite in which piezoelectric nanomaterials are embedded into a polymer matrix. Although significant progress has been recently made in this area, modeling the electromechanical response of a directly printed nanocomposite remains a challenge. Thus the objective of this study is to develop robust micromechanical and finite element models that allows the study of the electroelastic properties of a directly printed nanocomposite containing piezoelectric inclusions. Furthermore, the dependence of these properties on geometrical parameters such as aspect ratio and alignment of the active phase are investigated. The focus of this work is a demonstration of the effect gradual alignment of piezoelectric nanowires in a nanocomposite from randomly oriented to purely aligned improves the electroelastic properties of a directly printed nanocomposite. Finally, these models are verified through experimental measurement of electroelastic properties of the nanocomposites containing barium titanate nanowires in Polydimethylsiloxane (PDMS) polymer.

Preparation of Nanocomposite Plasmonic Films Made from Cellulose Nanocrystals or Mesoporous Silica Decorated with Unidirectionally Aligned Gold Nanorods.

PubMed

Campbell, Michael G; Liu, Qingkun; Sanders, Aric; Evans, Julian S; Smalyukh, Ivan I

2014-04-11

Using liquid crystalline self-assembly of cellulose nanocrystals, we achieve long-range alignment of anisotropic metal nanoparticles in colloidal nanocrystal dispersions that are then used to deposit thin structured films with ordering features highly dependent on the deposition method. These hybrid films are comprised of gold nanorods unidirectionally aligned in a matrix that can be made of ordered cellulose nanocrystals or silica nanostructures obtained by using cellulose-based nanostructures as a replica. The ensuing long-range alignment of gold nanorods in both cellulose-based and nanoporous silica films results in a polarization-sensitive surface plasmon resonance. The demonstrated device-scale bulk nanoparticle alignment may enable engineering of new material properties arising from combining the orientational ordering of host nanostructures and properties of the anisotropic plasmonic metal nanoparticles. Our approach may also allow for scalable fabrication of plasmonic polarizers and nanoporous silica structures with orientationally ordered anisotropic plasmonic nanoinclusions.

Biodegradable scaffolds designed to mimic fascia-like properties for the treatment of pelvic organ prolapse and stress urinary incontinence.

PubMed

Roman, Sabiniano; Mangir, Naside; Bissoli, Julio; Chapple, Christopher R; MacNeil, Sheila

2016-05-01

There is an urgent clinical need for better synthetic materials to be used in surgical support of the pelvic floor. The aim of the current study was to construct biodegradable synthetic scaffolds that mimic the three-dimensional architecture of human fascia, which can integrate better into host tissues both mechanically and biologically. Therefore, four different polylactic acid (PLA) scaffolds with various degrees of fibre alignment were electrospun by modifying the electrospinning parameters. Physical and mechanical properties were assessed using a BOSE electroforce tensiometer. The attachment, viability and extracellular matrix production of adipose-derived stem cells cultured on the polylactic acid scaffolds were evaluated. The bulk density of the scaffolds decreased as the proportion of aligned fibres increased. Scaffolds became stronger and stiffer with increasing amounts of aligned fibres as measured along the axis parallel to the fibre alignment. In addition, more total collagen was produced on scaffolds with aligned fibres and was organised in the direction of the aligned fibres. In conclusion, the electrospinning technique can be easily modified to develop biodegradable scaffolds with a spectrum of mechanical properties allowing extracellular matrix organisation towards human-like fascia. © The Author(s) 2016.

Strain-Induced Alignment in Collagen Gels

PubMed Central

Vader, David; Kabla, Alexandre; Weitz, David; Mahadevan, Lakshminarayana

2009-01-01

Collagen is the most abundant extracellular-network-forming protein in animal biology and is important in both natural and artificial tissues, where it serves as a material of great mechanical versatility. This versatility arises from its almost unique ability to remodel under applied loads into anisotropic and inhomogeneous structures. To explore the origins of this property, we develop a set of analysis tools and a novel experimental setup that probes the mechanical response of fibrous networks in a geometry that mimics a typical deformation profile imposed by cells in vivo. We observe strong fiber alignment and densification as a function of applied strain for both uncrosslinked and crosslinked collagenous networks. This alignment is found to be irreversibly imprinted in uncrosslinked collagen networks, suggesting a simple mechanism for tissue organization at the microscale. However, crosslinked networks display similar fiber alignment and the same geometrical properties as uncrosslinked gels, but with full reversibility. Plasticity is therefore not required to align fibers. On the contrary, our data show that this effect is part of the fundamental non-linear properties of fibrous biological networks. PMID:19529768

Finite element analyses of two dimensional, anisotropic heat transfer in wood

Treesearch

John F. Hunt; Hongmei Gu

2004-01-01

The anisotropy of wood creates a complex problem for solving heat and mass transfer problems that require analyses be based on fundamental material properties of the wood structure. Inputting basic orthogonal properties of the wood material alone are not sufficient for accurate modeling because wood is a combination of porous fiber cells that are aligned and mis-...

Coated carbon nanotube array electrodes

DOEpatents

Ren, Zhifeng; Wen, Jian; Chen, Jinghua; Huang, Zhongping; Wang, Dezhi

2006-12-12

The present invention provides conductive carbon nanotube (CNT) electrode materials comprising aligned CNT substrates coated with an electrically conducting polymer, and the fabrication of electrodes for use in high performance electrical energy storage devices. In particular, the present invention provides conductive CNTs electrode material whose electrical properties render them especially suitable for use in high efficiency rechargeable batteries. The present invention also provides methods for obtaining surface modified conductive CNT electrode materials comprising an array of individual linear, aligned CNTs having a uniform surface coating of an electrically conductive polymer such as polypyrrole, and their use in electrical energy storage devices.

Coated carbon nanotube array electrodes

DOEpatents

Ren, Zhifeng [Newton, MA; Wen, Jian [Newton, MA; Chen, Jinghua [Chestnut Hill, MA; Huang, Zhongping [Belmont, MA; Wang, Dezhi [Wellesley, MA

2008-10-28

The present invention provides conductive carbon nanotube (CNT) electrode materials comprising aligned CNT substrates coated with an electrically conducting polymer, and the fabrication of electrodes for use in high performance electrical energy storage devices. In particular, the present invention provides conductive CNTs electrode material whose electrical properties render them especially suitable for use in high efficiency rechargeable batteries. The present invention also provides methods for obtaining surface modified conductive CNT electrode materials comprising an array of individual linear, aligned CNTs having a uniform surface coating of an electrically conductive polymer such as polypyrrole, and their use in electrical energy storage devices.

Weak reversible cross links may decrease the strength of aligned fiber bundles.

PubMed

Nabavi, S Soran; Hartmann, Markus A

2016-02-21

Reversible cross-linking is an effective strategy to specifically tailor the mechanical properties of polymeric materials that can be found in a variety of biological as well as man-made materials. Using a simple model in this paper the influence of weak, reversible cross-links on the mechanical properties of aligned fiber bundles is investigated. Special emphasis in this analysis is put on the strength of the investigated structures. Using Monte Carlo methods two topologies of cross-links exceeding the strength of the covalent backbone are studied. Most surprisingly only two cross-links are sufficient to break the backbone of a multi chain system, resulting in a reduced strength of the material. The found effect crucially depends on the ratio of inter- to intra-chain cross-links and, thus, on the grafting density that determines this ratio.

Large deformation analysis of axisymmetric inhomogeneities including coupled elastic and plastic anisotropy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brannon, R.M.

1996-12-31

A mathematical framework is developed for the study of materials containing axisymmetric inclusions or flaws such as ellipsoidal voids, penny-shaped cracks, or fibers of circular cross-section. The general case of nonuniform statistical distributions of such heterogeneities is attacked by first considering a spatially uniform distribution of flaws that are all oriented in the same direction. Assuming an isotropic substrate, the macroscopic material properties of this simpler microstructure naturally should be transversely isotropic. An orthogonal basis for the linear subspace consisting of all double-symmetric transversely-isotropic fourth-order tensors associated with a given material vector is applied to deduce the explicit functional dependencemore » of the material properties of these aligned materials on the shared symmetry axis. The aligned and uniform microstructure seems geometrically simple enough that the macroscopic transversely isotropic properties could be derived in closed form. Since the resulting properties are transversely isotropic, the analyst must therefore be able to identify the appropriate coefficients of the transverse basis. Once these functions are identified, a principle of superposition of strain rates ay be applied to define an expectation integral for the composite properties of a material containing arbitrary anisotropic distributions of axisymmetric inhomogeneities. A proposal for coupling plastic anisotropy to the elastic anisotropy is presented in which the composite yield surface is interpreted as a distortion of the isotropic substrate yield surface; the distortion directions are coupled to the elastic anisotropy directions. Finally, some commonly assumed properties (such as major symmetry) of the Cauchy tangent stiffness tensor are shown to be inappropriate for large distortions of anisotropic materials.« less

Effect of the carbonyl iron particles on acoustic absorption properties of magnetic polyurethane foam

NASA Astrophysics Data System (ADS)

Geng, Jialu; Wang, Caiping; Zhu, Honglang; Wang, Xiaojie

2018-03-01

Elastomeric matrix embedded with magnetic micro-sized particles has magnetically controllable properties, which has been investigated extensively in the last decades. In this study we develop a new magnetically controllable elastomeric material for acoustic applications at lower frequencies. The soft polyurethane foam is used as matrix material due to its extraordinary elastic and acoustic absorption properties. One-step method is used to synthesize polyurethane foam, in which all components including polyether polyols 330N, MDI, deionized water, silicone oil, carbonyl iron particle (CIP) and catalyst are put into one container for curing. Changing any component can induce the change of polyurethane foam's properties, such as physical and acoustic properties. The effect of the content of MDI on acoustic absorption is studied. The CIPs are aligned under extra magnetic field during the foaming process. And the property of polyurethane foam with aligned CIPs is also investigated. Scanning electron microscope (SEM) is used to observe the structure of pore and particle-chain. The two-microphone impedance tube and the transfer function method are used to test acoustic absorption property of the magnetic foams.

Effect of Alignment on Transport Properties of Carbon Nanotube/Metallic Junctions

NASA Technical Reports Server (NTRS)

Wincheski, Buzz; Namkung, Min; Smits, Jan; Williams, Phillip; Harvey, Robert

2003-01-01

Ballistic and spin coherent transport in single walled carbon nanotubes (SWCNT) are predicted to enable high sensitivity single-nanotube devices for strain and magnetic field sensing. Based upon these phenomena, electron beam lithography procedures have been developed to study the transport properties of purified HiPCO single walled carbon nanotubes for development into sensory materials for nondestructive evaluation. Purified nanotubes are dispersed in solvent suspension and then deposited on the device substrate before metallic contacts are defined and deposited through electron beam lithography. This procedure produces randomly dispersed ropes, typically 2 - 20 nm in diameter, of single walled carbon nanotubes. Transport and scanning probe microscopy studies have shown a good correlation between the junction resistance and tube density, alignment, and contact quality. In order to improve transport properties of the junctions a technique has been developed to align and concentrate nanotubes at specific locations on the substrate surface. Lithographic techniques are used to define local areas where high frequency electric fields are to be concentrated. Application of the fields while the substrate is exposed to nanotube-containing solution results in nanotube arrays aligned with the electric field lines. A second electron beam lithography layer is then used to deposit metallic contacts across the aligned tubes. Experimental measurements are presented showing the increased tube alignment and improvement in the transport properties of the junctions.

Tunable Band Alignment with Unperturbed Carrier Mobility of On-Surface Synthesized Organic Semiconducting Wires

PubMed Central

2016-01-01

The tunable properties of molecular materials place them among the favorites for a variety of future generation devices. In addition, to maintain the current trend of miniaturization of those devices, a departure from the present top-down production methods may soon be required and self-assembly appears among the most promising alternatives. On-surface synthesis unites the promises of molecular materials and of self-assembly, with the sturdiness of covalently bonded structures: an ideal scenario for future applications. Following this idea, we report the synthesis of functional extended nanowires by self-assembly. In particular, the products correspond to one-dimensional organic semiconductors. The uniaxial alignment provided by our substrate templates allows us to access with exquisite detail their electronic properties, including the full valence band dispersion, by combining local probes with spatial averaging techniques. We show how, by selectively doping the molecular precursors, the product’s energy level alignment can be tuned without compromising the charge carrier’s mobility. PMID:26841052

Using naturally occurring polysaccharides to align molecules with nonlinear optical activity

NASA Technical Reports Server (NTRS)

Prasthofer, Thomas

1996-01-01

The Biophysics and Advanced Materials Branch of the Microgravity Science and Applications Division at Marshall Space Flight Center has been investigating polymers with the potential for nonlinear optical (NLO) applications for a number of years. Some of the potential applications for NLO materials include optical communications, computing, and switching. To this point the branch's research has involved polydiacetylenes, phthalocyanins, and other synthetic polymers which have inherent NLO properties. The aim of the present research is to investigate the possibility of using naturally occurring polymers such as polysaccharides or proteins to trap and align small organic molecules with useful NLO properties. Ordering molecules with NLO properties enhances 3rd order nonlinear effects and is required for 2nd order nonlinear effects. Potential advantages of such a system are the flexibility to use different small molecules with varying chemical and optical properties, the stability and cost of the polymers, and the ability to form thin, optically transparent films. Since the quality of any polymer films depends on optimizing ordering and minimizing defects, this work is particularly well suited for microgravity experiments. Polysaccharide and protein polymers form microscopic crystallites which must align to form ordered arrays. The ordered association of crystallites is disrupted by gravity effects and NASA research on protein crystal growth has demonstrated that low gravity conditions can improve crystal quality.

Crystallization of Stretched Polyimides: A Structure-Property Study

NASA Technical Reports Server (NTRS)

Hinkley, Jeffrey A.; Dezern, James F.

2002-01-01

A simple rotational isomeric state model was used to detect the degree to which polyimide repeat units might align to give an extended crystal. It was found experimentally that the hallmarks of stretch-crystallization were more likely to occur in materials whose molecules could readily give extended, aligned conformations. A proposed screening criterion was 84% accurate in selecting crystallizing molecules.

Constitutive Modeling of Crosslinked Nanotube Materials

NASA Technical Reports Server (NTRS)

Odegard, G. M.; Frankland, S. J. V.; Herzog, M. N.; Gates, T. S.; Fay, C. C.

2004-01-01

A non-linear, continuum-based constitutive model is developed for carbon nanotube materials in which bundles of aligned carbon nanotubes have varying amounts of crosslinks between the nanotubes. The model accounts for the non-linear elastic constitutive behavior of the material in terms of strain, and is developed using a thermodynamic energy approach. The model is used to examine the effect of the crosslinking on the overall mechanical properties of variations of the crosslinked carbon nanotube material with varying degrees of crosslinking. It is shown that the presence of the crosslinks has significant effects on the mechanical properties of the carbon nanotube materials. An increase in the transverse shear properties is observed when the nanotubes are crosslinked. However, this increase is accompanied by a decrease in axial mechanical properties of the nanotube material upon crosslinking.

Energy band alignment of antiferroelectric (Pb,La)(Zr,Sn,Ti)O3

NASA Astrophysics Data System (ADS)

Klein, Andreas; Lohaus, Christian; Reiser, Patrick; Dimesso, Lucangelo; Wang, Xiucai; Yang, Tongqing

2017-06-01

The energy band alignment of antiferroelectric (Pb,La)(Zr,Sn,Ti)O3 is studied with photoelectron spectroscopy using interfaces with high work function RuO2 and low work function Sn-doped In2O3 (ITO). It is demonstrated how spectral deconvolution can be used to determine absolute Schottky barrier heights for insulating materials with a high accuracy. Using this approach it is found that the valence band maximum energy of (Pb,La)(Zr,Sn,Ti)O3 is found to be comparable to that of Pb- and Bi-containing ferroelectric materials, which is ∼1 eV higher than that of BaTiO3. The results provide additional evidence for the occupation of the 6s orbitals as origin of the higher valence band maximum, which is directly related to the electrical properties of such compounds. The results also verify that the energy band alignment determined by photoelectron spectroscopy of as-deposited electrodes is not influenced by polarisation. The electronic structure of (Pb,La)(Zr,Sn,Ti)O3 should enable doping of the material without strongly modifying its insulating properties, which is crucial for high energy density capacitors. Moreover, the position of the energy bands should result in a great freedom of selecting electrode materials in terms of avoiding charge injection.

Metal Decorated Multi-Walled Carbon Nanotube/Polyimide Composites with High Dielectric Constants and Low Loss Factors

NASA Technical Reports Server (NTRS)

Elliott, Holly A.; Dudley, Kenneth L.; Smith, Joseph G.; Connell, John W.; Ghose, Sayata; Watson, Kent A.; Sun, Keun J.

2009-01-01

The measurement of observable electromagnetic phenomena in materials and their derived intrinsic electrical material properties are of prime importance in the discovery and development of material systems for electronic and aerospace applications. Nanocomposite materials comprised of metal decorated multi-walled carbon nanotubes (MWCNTs) were prepared by a facile method and characterized. Metal particles such as silver(Ag), platinum(Pt) and palladium(Pd) with diameters ranging from less than 5 to over 50 nanometers were distributed randomly on the MWCNTs. The present study is focused on silver decorated MWCNTs dispersed in a polyimide matrix. The Ag-containing MWCNTs were melt mixed into Ultem(TradeMark) and the mixture extruded as ribbons. The extruded ribbons exhibited a moderate to high degree of MWCNT alignment as determined by HRSEM. These ribbons were then fabricated into test specimens while maintaining MWCNT alignment and subsequently characterized for electrical and electromagnetic properties at 8-12 GHz. The results of the electromagnetic characterization showed that certain sample configurations exhibited a decoupling of the permittivity (epsilon ) and loss factor (epsilon") indicating that these properties could be tailored within certain limits. The decoupling and independent control of these fundamental electrical material parameters offers a new class of materials with potential applications in electronics, microwave engineering and optics.

Metal Decorated Multi-Walled Carbon Nanotube/Polyimide Composites with High Dielectric Constants and Low Loss Factors

NASA Technical Reports Server (NTRS)

Ghose, Sayata; Watson, Kent A.; Dudley, Kenneth L.; Elliott, Holly A.; Smith, Joseph G.; Connell, John W.

2009-01-01

The measurement of observable electromagnetic phenomena in materials and their derived intrinsic electric material properties are of prime importance in the discovery and development of material systems for electronic and aerospace applications. Nanocomposite materials comprised of metal decorated multi-walled carbon nanotubes (MWCNTs) were prepared by a facile method and characterized. Metal particles such as silver, platinum and palladium with diameters ranging from less than 5 to over 50 nanometers were distributed randomly on the MWCNTs. The metal-containing MWCNTs were then melt mixed into a polymer matrix and the mixture extruded as ribbons. These extruded ribbons exhibited a moderate to high degree of MWCNT alignment as determined by HRSEM. These ribbons were then fabricated into test specimens while maintaining MWCNT alignment and subsequently characterized for electromagnetic properties at 8-12 GHz. The present study is focused on silver decorated MWCNTs dispersed in an Ultem polyimide matrix. The results of the electromagnetic characterization showed that certain sample configurations exhibited a decoupling of the permittivity and loss factor (?? and ??) indicating that these properties could be tailored within certain limits. The decoupling and independent control of these fundamental electrical material parameters offer a new class of materials with potential applications in electronics, microwave engineering and optics.

Phase-field model simulation of ferroelectric/antiferroelectric materials microstructure evolution under multiphysics loading

NASA Astrophysics Data System (ADS)

Zhang, Jingyi

Ferroelectric (FE) and closely related antiferroelectric (AFE) materials have unique electromechanical properties that promote various applications in the area of capacitors, sensors, generators (FE) and high density energy storage (AFE). These smart materials with extensive applications have drawn wide interest in the industrial and scientific world because of their reliability and tunable property. However, reliability issues changes its paradigms and requires guidance from detailed mechanism theory as the materials applications are pushed for better performance. A host of modeling work were dedicated to study the macro-structural behavior and microstructural evolution in FE and AFE material under various conditions. This thesis is focused on direct observation of domain evolution under multiphysics loading for both FE and AFE material. Landau-Devonshire time-dependent phase field models were built for both materials, and were simulated in finite element software Comsol. In FE model, dagger-shape 90 degree switched domain was observed at preexisting crack tip under pure mechanical loading. Polycrystal structure was tested under same condition, and blocking effect of the growth of dagger-shape switched domain from grain orientation difference and/or grain boundary was directly observed. AFE ceramic model was developed using two sublattice theory, this model was used to investigate the mechanism of energy efficiency increase with self-confined loading in experimental tests. Consistent results was found in simulation and careful investigation of calculation results gave confirmation that origin of energy density increase is from three aspects: self-confinement induced inner compression field as the cause of increase of critical field, fringe leak as the source of elevated saturation polarization and uneven defects distribution as the reason for critical field shifting and phase transition speed. Another important affecting aspect in polycrystalline materials is the texture of material, textured materials have better alignment and the alignment reorganization is associated with inelastic strain. We developed a vector field of alignment to describe texture degree and introduced the alignment vector into our FE and AFE model. The model with alignment field gave quantatively results for the well-recognized irreversible strain in AFE virgin ceramics during the first poling process. The texture field also shows a shielding zone under mechanical loading around existing crack tip. In conclusion, this thesis developed working models of FE and AFE material and systematically studied their behavior under multiphysics loading in a finite element analysis approach. Materials structure of polycrystal materials including grain orientation, grain boundary, defects and materials texture were tested for their effect on hysteresis and switched domain growth. Detailed microstructure development in domain switching and alignment was directly observed in this simulation.

Biomimetic Materials by Freeze Casting

NASA Astrophysics Data System (ADS)

Porter, Michael M.; Mckittrick, Joanna; Meyers, Marc A.

2013-06-01

Natural materials, such as bone and abalone nacre, exhibit exceptional mechanical properties, a product of their intricate microstructural organization. Freeze casting is a relatively simple, inexpensive, and adaptable materials processing method to form porous ceramic scaffolds with controllable microstructural features. After infiltration of a second polymeric phase, hybrid ceramic-polymer composites can be fabricated that closely resemble the architecture and mechanical performance of natural bone and nacre. Inspired by the narwhal tusk, magnetic fields applied during freeze casting can be used to further control architectural alignment, resulting in freeze-cast materials with enhanced mechanical properties.

Hydrodynamic alignment and assembly of nanofibrils resulting in strong cellulose filaments

PubMed Central

Håkansson, Karl M. O.; Fall, Andreas B.; Lundell, Fredrik; Yu, Shun; Krywka, Christina; Roth, Stephan V.; Santoro, Gonzalo; Kvick, Mathias; Prahl Wittberg, Lisa; Wågberg, Lars; Söderberg, L. Daniel

2014-01-01

Cellulose nanofibrils can be obtained from trees and have considerable potential as a building block for biobased materials. In order to achieve good properties of these materials, the nanostructure must be controlled. Here we present a process combining hydrodynamic alignment with a dispersion–gel transition that produces homogeneous and smooth filaments from a low-concentration dispersion of cellulose nanofibrils in water. The preferential fibril orientation along the filament direction can be controlled by the process parameters. The specific ultimate strength is considerably higher than previously reported filaments made of cellulose nanofibrils. The strength is even in line with the strongest cellulose pulp fibres extracted from wood with the same degree of fibril alignment. Successful nanoscale alignment before gelation demands a proper separation of the timescales involved. Somewhat surprisingly, the device must not be too small if this is to be achieved. PMID:24887005

Temperature dependence of ferromagnet-antiferromagnet spin alignment and coercivity in epitaxial micromagnet bilayers

DOE PAGES

Lee, Michael S.; Wynn, Thomas A.; Folven, Erik; ...

2017-06-26

In this paper, soft x-ray photoemission electron microscopy with an in situ magnetic field has been used to study the relationship between ferromagnetic and antiferromagnetic spin alignment and the switching/reversal field of epitaxial micromagnetic structures. We investigated a model system consisting of a bilayer of ferromagnetic La 0.7Sr 0.3MnO 3 and antiferromagnetic LaFeO 3 where the spin axes in each layer can be driven from mutually perpendicular (spin-flop) to parallel alignment by varying the temperature between 30 and 300 K. Results show that not only does this spin alignment noticeably influence the bilayer micromagnet coercivity compared to La 0.7Sr 0.3MnOmore » 3 single-layer micromagnets, but the coercivity within this materials system can be tuned over a wide range by careful balance of material properties.« less

Temperature dependence of ferromagnet-antiferromagnet spin alignment and coercivity in epitaxial micromagnet bilayers

NASA Astrophysics Data System (ADS)

Lee, Michael S.; Wynn, Thomas A.; Folven, Erik; Chopdekar, Rajesh V.; Scholl, Andreas; Retterer, Scott T.; Grepstad, Jostein K.; Takamura, Yayoi

2017-06-01

Soft x-ray photoemission electron microscopy with an in situ magnetic field has been used to study the relationship between ferromagnetic and antiferromagnetic spin alignment and the switching/reversal field of epitaxial micromagnetic structures. We investigated a model system consisting of a bilayer of ferromagnetic L a0.7S r0.3Mn O3 and antiferromagnetic LaFe O3 where the spin axes in each layer can be driven from mutually perpendicular (spin-flop) to parallel alignment by varying the temperature between 30 and 300 K. Results show that not only does this spin alignment noticeably influence the bilayer micromagnet coercivity compared to L a0.7S r0.3Mn O3 single-layer micromagnets, but the coercivity within this materials system can be tuned over a wide range by careful balance of material properties.

Ultrasonic alignment of microparticles in nozzle-like geometries

NASA Astrophysics Data System (ADS)

Whittaker, Molly A.; Dauson, Erin R.; Parra-Raad, Jaime; Heard, Robert A.; Oppenheim, Irving J.

2018-03-01

Additive manufacturing (3-D printing) is presently limited by the mechanical properties of the materials, such as polymer resins, that are otherwise efficient and economical for part-forming. Reinforcing the resin with microscale fibers and/or particles would be an effective mechanism to achieve desired mechanical properties such as strength and ductility. Our work combines standing wave ultrasonics and microfluidics to align microparticles in devices that can act as print nozzles, based in part on our prior work with cell sorting. In this paper three different approaches are presented illustrating different engineering tradeoffs, and demonstrating laboratory results of particle alignment. First acoustic resonators are discussed, in which the ultrasonic standing waves result mostly from the mechanical properties of the microfluidic structure, excited by a piezoceramic transducer. Next non-resonant microfluidic structures are discussed, in which ultrasonic standing waves are produced directly by symmetrical transducer deployment. Finally, devices that combine nozzle-like structures, which themselves are suitable acoustic resonators, subjected to symmetrical ultrasonic excitation are presented. We will show that all three configurations will align microparticles, and discuss the tradeoffs among them for subsequent configuration of a print nozzle.

Rhombohedral cubic semiconductor materials on trigonal substrate with single crystal properties and devices based on such materials

NASA Technical Reports Server (NTRS)

Park, Yeonjoon (Inventor); Choi, Sang Hyouk (Inventor); King, Glen C. (Inventor); Elliott, James R. (Inventor)

2012-01-01

Growth conditions are developed, based on a temperature-dependent alignment model, to enable formation of cubic group IV, group II-V and group II-VI crystals in the [111] orientation on the basal (0001) plane of trigonal crystal substrates, controlled such that the volume percentage of primary twin crystal is reduced from about 40% to about 0.3%, compared to the majority single crystal. The control of stacking faults in this and other embodiments can yield single crystalline semiconductors based on these materials that are substantially without defects, or improved thermoelectric materials with twinned crystals for phonon scattering while maintaining electrical integrity. These methods can selectively yield a cubic-on-trigonal epitaxial semiconductor material in which the cubic layer is substantially either directly aligned, or 60 degrees-rotated from, the underlying trigonal material.

Bioglass incorporation improves mechanical properties and enhances cell-mediated mineralization on electrochemically aligned collagen threads.

PubMed

Nijsure, Madhura P; Pastakia, Meet; Spano, Joseph; Fenn, Michael B; Kishore, Vipuil

2017-09-01

Bone tissue engineering mandates the development of a functional scaffold that mimics the physicochemical properties of native bone. Bioglass 45S5 (BG) is a highly bioactive material known to augment bone formation and restoration. Hybrid scaffolds fabricated using collagen type I and BG resemble the organic and inorganic composition of the bone extracellular matrix and hence have been extensively investigated for bone tissue engineering applications. However, collagen-BG scaffolds developed thus far do not recapitulate the aligned structure of collagen found in native bone. In this study, an electrochemical fabrication method was employed to synthesize BG-incorporated electrochemically aligned collagen (BG-ELAC) threads that are compositionally similar to native bone. Further, aligned collagen fibrils within BG-ELAC threads mimic the anisotropic arrangement of collagen fibrils in native bone. The effect of BG incorporation on the mechanical properties and cell-mediated mineralization on ELAC threads was investigated. The results indicated that BG can be successfully incorporated within ELAC threads, without disturbing collagen fibril alignment. Further, BG incorporation significantly increased the ultimate tensile stress (UTS) and modulus of ELAC threads (p < 0.05). SBF conditioning showed extensive mineralization on BG-ELAC threads that increased over time demonstrating the bone bioactivity of BG-ELAC threads. Additionally, BG incorporation into ELAC threads resulted in increased cell proliferation (p < 0.05) and deposition of a highly dense and continuous mineralized matrix. In conclusion, incorporation of BG into ELAC threads is a viable strategy for the development of an osteoconductive material for bone tissue engineering applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2429-2440, 2017. © 2017 Wiley Periodicals, Inc.

Align and random electrospun mat of PEDOT:PSS and PEDOT:PSS/RGO

NASA Astrophysics Data System (ADS)

Sarabi, Ghazale Asghari; Latifi, Masoud; Bagherzadeh, Roohollah

2018-01-01

In this research work we fabricated two ultrafine conductive nanofibrous layers to investigate the materilas composition and their properties for the preparation of supercapacitor materials application. In first layer, a polymer and a conductive polymer were used and second layer was a composition of polymer, conductive polymer and carbon-base material. In both cases align and randomized mat of conductive nanofibers were fabricated using electrospinning set up. Conductive poly (3,4-ethylenedioxythiophene)/ polystyrene sulfonate (PEDOT:PSS) nanofibers were electrospun by dissolving fiber-forming polymer and polyvinyl alcohol (PVA) in an aqueous dispersion of PEDOT:PSS. The effect of addition of reduced graphene oxide (RGO) was considered for nanocomposite layer. The ultrafine conductive polymer fibers and conductive nanocomposite fibrous materials were also fabricated using an electrospinning process. A fixed collector and a rotating drum were used for random and align nanofibers production, respectively. The resulted fibers were characterized and analyzed by SEM, FTIR and two-point probe conductivity test. The average diameter of nanofibers measured by ImageJ software indicated that the average fiber diameter for first layer was 100 nm and for nanocomposite layer was about 85 nm. The presence of PEDOT:PSS and RGO in the nanofibers was confirmed by FT-IR spectroscopy. The conductivity of align and random layers was characterized. The conductivity of PEDOT:PSS nanofibers showed higher enhancement by addition of RGO in aqueous dispersion. The obtained results showed that alignment of fibrous materials can be considered as an engineering tool for tuning the conductivity of fibrous materials for many different applications such as supercapacitors, conductive and transparent materials.

Pinning down high-performance Cu-chalcogenides as thin-film solar cell absorbers: A successive screening approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yubo; Zhang, Wenqing, E-mail: wqzhang@mail.sic.ac.cn, E-mail: pzhang3@buffalo.edu; State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050

2016-05-21

Photovoltaic performances of Cu-chalcogenides solar cells are strongly correlated with the absorber fundamental properties such as optimal bandgap, desired band alignment with window material, and high photon absorption ability. According to these criteria, we carry out a successive screening for 90 Cu-chalcogenides using efficient theoretical approaches. Besides the well-recognized CuInSe{sub 2} and Cu{sub 2}ZnSnSe{sub 4} materials, several novel candidates are identified to have optimal bandgaps of around 1.0–1.5 eV, spike-like band alignments with CdS window layer, sharp photon absorption edges, and high absorption coefficients. These new systems have great potential to be superior absorbers for photovolatic applications if their carrriermore » transport and defect properties are properly optimized.« less

Synchrotron x-ray scattering measurements of bulk structural properties in superconducting (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}{endash}Ag tapes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thurston, T.R.; Wildgruber, U.; Jisrawi, N.

The structural properties of superconducting (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}{endash}Ag (2223) tapes have been measured using synchrotron x-ray scattering techniques. The x-ray photon energy was tuned just below the silver {ital K} absorption edge so the penetration depth was large, which allowed the measurements to be performed in a transmission geometry without removing the silver cladding. Analysis of the peaks in 2{theta} scans indicates that residual (Bi,Pb){sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (2212) superconductor starting material is present in all samples studied. The amount of 2212 varied widely among the tapes, and was not homogeneous along the length of eachmore » individual tape. Residual 2212 content increased near the ends of most samples, suggesting that 2223 phase development is sensitive to whether the superconducting material is encased in silver or not. The bulk {ital c}-axis alignment was measured in {approximately}100 mono- and multifilament samples, and correlations between {ital c}-axis alignment and current carrying capacity at 77 K were found. Multifilament samples generally had better alignment than monofilament samples. The {ital c}-axis alignment along the length of the tapes was uniform, and the superconducting material within {approximately}1 {mu}m of the Ag was better textured than the bulk of the sample. Intermediate pressings were directly shown to have an adverse affect on {ital c}-axis alignment. Finally, the evolution of texture and phase development was examined in a series of samples annealed for varying times. The 2212 starting material acquired the final {ital c}-axis alignment state after brief heating times, and only after much longer heating times did the 2212 transform into the 2223 phase. These results and their implications for improving processing procedures are discussed. {copyright} {ital 1996 American Institute of Physics.}« less

Two dimensional finite element heat transfer models for softwood

Treesearch

Hongmei Gu; John F. Hunt

2004-01-01

The anisotropy of wood creates a complex problem for solving heat and mass transfer problems that require analyses be based on fundamental material properties of the wood structure. Most heat transfer models use average thermal properties across either the radial or tangential directions and have not differentiated the effects of cellular alignment, earlywood/latewood...

Electrochemical tuning of vertically aligned MoS2 nanofilms and its application in improving hydrogen evolution reaction

PubMed Central

Wang, Haotian; Lu, Zhiyi; Xu, Shicheng; Kong, Desheng; Cha, Judy J.; Zheng, Guangyuan; Hsu, Po-Chun; Yan, Kai; Bradshaw, David; Prinz, Fritz B.; Cui, Yi

2013-01-01

The ability to intercalate guest species into the van der Waals gap of 2D layered materials affords the opportunity to engineer the electronic structures for a variety of applications. Here we demonstrate the continuous tuning of layer vertically aligned MoS2 nanofilms through electrochemical intercalation of Li+ ions. By scanning the Li intercalation potential from high to low, we have gained control of multiple important material properties in a continuous manner, including tuning the oxidation state of Mo, the transition of semiconducting 2H to metallic 1T phase, and expanding the van der Waals gap until exfoliation. Using such nanofilms after different degree of Li intercalation, we show the significant improvement of the hydrogen evolution reaction activity. A strong correlation between such tunable material properties and hydrogen evolution reaction activity is established. This work provides an intriguing and effective approach on tuning electronic structures for optimizing the catalytic activity. PMID:24248362

Improved mechanical and electrical properties in electrospun polyimide/multiwalled carbon nanotubes nanofibrous composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zha, Jun-Wei; Sun, Fang; Wang, Si-Jiao

2014-10-07

Highly aligned polyimide (PI) and PI/multi-walled carbon nanotubes (PI/MWCNTs) nanofibrous composites by incorporating poly(ethylene oxide) as the dispersing medium were fabricated using electrospinning technique. The morphology, mechanical, and electrical properties of the electrospun nanofibrous composites were investigated. Scanning electron microscope showed that the functionalized MWCNTs (f-MWCNTs) were well dispersed and oriented along the nanofiber axis. Analysis of electrical properties indicated a remarkable improvement on the alternating current conductivity by introduction of the aligned f-MWCNTs. Besides, with addition of 3 vol. % f-MWCNTs, the obvious enhancement of tensile modulus and strength was achieved. Thus, the electrospun PI/MWCNTs nanofibrous composites have greatmore » potential applications in multifunctional engineering materials.« less

Controlling band alignments by artificial interface dipoles at perovskite heterointerfaces

DOE PAGES

Yajima, Takeaki; Hikita, Yasuyuki; Minohara, Makoto; ...

2015-04-07

The concept ‘the interface is the device' is embodied in a wide variety of interfacial electronic phenomena and associated applications in oxide materials, ranging from catalysts and clean energy systems to emerging multifunctional devices. Many device properties are defined by the band alignment, which is often influenced by interface dipoles. On the other hand, the ability to purposefully create and control interface dipoles is a relatively unexplored degree of freedom for perovskite oxides, which should be particularly effective for such ionic materials. Here we demonstrate tuning the band alignment in perovskite metal-semiconductor heterojunctions over a broad range of 1.7 eV.more » This is achieved by the insertion of positive or negative charges at the interface, and the resultant dipole formed by the induced screening charge. This approach can be broadly used in applications where decoupling the band alignment from the constituent work functions and electron affinities can enhance device functionality.« less

Homeotropic alignment of multiple bent-core liquid crystal phases using a polydimethylsiloxane alignment layer

NASA Astrophysics Data System (ADS)

Carlson, Eric D.; Foley, Lee M.; Guzman, Edward; Korblova, Eva D.; Visvanathan, Rayshan; Ryu, SeongHo; Gim, Min-Jun; Tuchband, Michael R.; Yoon, Dong Ki; Clark, Noel A.; Walba, David M.

2017-08-01

The control of the molecular orientation of liquid crystals (LCs) is important in both understanding phase properties and the continuing development of new LC technologies including displays, organic transistors, and electro-optic devices. Many techniques have been developed for successfully inducing alignment of calamitic LCs, though these techniques typically do not translate to the alignment of bent-core liquid crystals (BCLCs). Some techniques have been utilized to align various phases of BCLCs, but these techniques are often unsuccessful for general alignment of multiple materials and/or multiple phases. Here, we demonstrate that glass cells treated with polydimethylsiloxane (PDMS) thin films induce high quality homeotropic alignment of multiple mesophases of four BCLCs. On cooling to the lowest temperature phase the homeotropic alignment is lost, and spherulitic growth is seen in crystal and crystal-like phases including the dark conglomerate (DC) and helical nanofilament (HNF) phases. Evidence of homeotropic alignment is observed using polarized optical microscopy. We speculate that the methyl groups on the surface of the PDMS films strongly interact with the aliphatic tails of each mesogens, resulting in homeotropic alignment.

Growth of multiwalled-carbon nanotubes using vertically aligned carbon nanofibers as templates/scaffolds and improved field-emission properties

NASA Astrophysics Data System (ADS)

Cui, H.; Yang, X.; Baylor, L. R.; Lowndes, D. H.

2005-01-01

Multiwalled-carbon nanotubes (MWCNTs) are grown on top of vertically aligned carbon nanofibers (VACNFs) via microwave plasma-enhanced chemical vapor deposition (MPECVD). The VACNFs are first grown in a direct-current plasma-enhanced chemical vapor deposition reactor using nickel catalyst. A layer of carbon-silicon materials is then deposited on the VACNFs and the nickel catalyst particle is broken down into smaller nanoparticles during an intermediate reactive-ion-plasma deposition step. These nickel nanoparticles nucleate and grow MWCNTs in the following MPECVD process. Movable-probe measurements show that the MWCNTs have greatly improved field-emission properties relative to the VACNFs.

Mean Green operators of deformable fiber networks embedded in a compliant matrix and property estimates

NASA Astrophysics Data System (ADS)

Franciosi, Patrick; Spagnuolo, Mario; Salman, Oguz Umut

2018-04-01

Composites comprising included phases in a continuous matrix constitute a huge class of meta-materials, whose effective properties, whether they be mechanical, physical or coupled, can be selectively optimized by using appropriate phase arrangements and architectures. An important subclass is represented by "network-reinforced matrices," say those materials in which one or more of the embedded phases are co-continuous with the matrix in one or more directions. In this article, we present a method to study effective properties of simple such structures from which more complex ones can be accessible. Effective properties are shown, in the framework of linear elasticity, estimable by using the global mean Green operator for the entire embedded fiber network which is by definition through sample spanning. This network operator is obtained from one of infinite planar alignments of infinite fibers, which the network can be seen as an interpenetrated set of, with the fiber interactions being fully accounted for in the alignments. The mean operator of such alignments is given in exact closed form for isotropic elastic-like or dielectric-like matrices. We first exemplify how these operators relevantly provide, from classic homogenization frameworks, effective properties in the case of 1D fiber bundles embedded in an isotropic elastic-like medium. It is also shown that using infinite patterns with fully interacting elements over their whole influence range at any element concentration suppresses the dilute approximation limit of these frameworks. We finally present a construction method for a global operator of fiber networks described as interpenetrated such bundles.

Two-dimensional finite element heat transfer model of softwood. Part I, Effective thermal conductivity

Treesearch

John F. Hunt; Hongmei Gu

2006-01-01

The anisotropy of wood complicates solution of heat and mass transfer problems that require analyses be based on fundamental material properties of the wood structure. Most heat transfer models use average thermal properties across either the radial or tangential direction and do not differentiate the effects of cellular alignment, earlywood/latewood differences, or...

A Study of Production of Miscibility Gap Alloys with Controlled Structures

NASA Technical Reports Server (NTRS)

Parr, R. A.; Johnston, M. H.; Burka, J. A.; Davis, J. H.; Lee, J. A.

1983-01-01

Composite materials were directionally solidified using a new technique to align the constituents longitudinally along the length of the specimen. In some instances a tin coating was applied and diffused into the sample to form a high transition temperature superconducting phase. The superconducting properties were measured and compared with the properties obtained for powder composites and re-directionally solidified powder compacts. The samples which were compacted and redirectionally solidified showed the highest transition temperature and wildest transition range. This indicates that both steps, powder compaction and resolidification, determine the final superconducting properties of the material.

Scalable alignment of CdS nanowires based on efficient roll-on transfer technique.

PubMed

Yan, Shancheng; Shi, Yi; Xiao, Zhongdang; Wang, Junzhuan; Hu, Dong; Xul, Xin; Lu, Tao; Liu, Aili; Gao, Fan

2013-06-01

A roll-on transfer strategy is developed to enable large-scale and uniform assembly of CdS nanowires on various rigid and flexible substrate materials. In this method, the CdS nanowires were synthesized by the hydrothermal method. The dispersed CdS NWs could be firstly aligned and selectively deposited at the micro/nanochannels between aligned nanofibers on the surface of the donor roller as a result of evaporation-induced flow and capillary action, and then the directional and aligned transfer of the CdS NWs from the donor roller to a receiver substrate via roll-on transfer technique. Finally, a device structures consisting of the nanowire channel and two metal electrodes was fabricated. The electrical property of this device was observed.

Viscoelastic properties of dendrimers in the melt from nonequlibrium molecular dynamics

NASA Astrophysics Data System (ADS)

Bosko, Jaroslaw T.; Todd, B. D.; Sadus, Richard J.

2004-12-01

The viscoelastic properties of dendrimers of generation 1-4 are studied using nonequilibrium molecular dynamics. Flow properties of dendrimer melts under shear are compared to systems composed of linear chain polymers of the same molecular weight, and the influence of molecular architecture is discussed. Rheological material properties, such as the shear viscosity and normal stress coefficients, are calculated and compared for both systems. We also calculate and compare the microscopic properties of both linear chain and dendrimer molecules, such as their molecular alignment, order parameters and rotational velocities. We find that the highly symmetric shape of dendrimers and their highly constrained geometry allows for substantial differences in their material properties compared to traditional linear polymers of equivalent molecular weight.

Layer by Layer Growth of 2D Quantum Superlattices (NBIT III)

DTIC Science & Technology

2017-02-28

building quantum superlatticies using 2D materials as the building blocks. Specifically, we develop methods that allow i) large-scale growth of aligned...superlattice and heterostructures, iii) lateral and clean patterning of 2D materials for atomically-thin circuitry and iv) novel physical properties...high precision and flexibility beyond conventional methods. Moreover, it provides the solutions for current major barrier for 2D materials (e.g

The role of water on the structure and mechanical properties of a thermoplastic natural block co-polymer from squid sucker ring teeth.

PubMed

Rieu, Clément; Bertinetti, Luca; Schuetz, Roman; Salinas-Zavala, Cesar Ca; Weaver, James C; Fratzl, Peter; Miserez, Ali; Masic, Admir

2016-09-02

Hard biological polymers exhibiting a truly thermoplastic behavior that can maintain their structural properties after processing are extremely rare and highly desirable for use in advanced technological applications such as 3D-printing, biodegradable plastics and robust composites. One exception are the thermoplastic proteins that comprise the sucker ring teeth (SRT) of the Humboldt jumbo squid (Dosidicus gigas). In this work, we explore the mechanical properties of reconstituted SRT proteins and demonstrate that the material can be re-shaped by simple processing in water and at relatively low temperature (below 100 °C). The post-processed material maintains a high modulus in the GPa range, both in the dry and the wet states. When transitioning from low to high humidity, the material properties change from brittle to ductile with an increase in plastic deformation, where water acts as a plasticizer. Using synchrotron x-ray scattering tools, we found that water mostly influences nano scale structure, whereas at the molecular level, the protein structure remains largely unaffected. Furthermore, through simultaneous in situ x-ray scattering and mechanical tests, we show that the supramolecular network of the reconstituted SRT material exhibits a progressive alignment along the strain direction, which is attributed to chain alignment of the amorphous domains of SRT proteins. The high modulus in both dry and wet states, combined with their efficient thermal processing characteristics, make the SRT proteins promising substitutes for applications traditionally reserved for petroleum-based thermoplastics.

Quantum-dot-in-perovskite solids.

PubMed

Ning, Zhijun; Gong, Xiwen; Comin, Riccardo; Walters, Grant; Fan, Fengjia; Voznyy, Oleksandr; Yassitepe, Emre; Buin, Andrei; Hoogland, Sjoerd; Sargent, Edward H

2015-07-16

Heteroepitaxy-atomically aligned growth of a crystalline film atop a different crystalline substrate-is the basis of electrically driven lasers, multijunction solar cells, and blue-light-emitting diodes. Crystalline coherence is preserved even when atomic identity is modulated, a fact that is the critical enabler of quantum wells, wires, and dots. The interfacial quality achieved as a result of heteroepitaxial growth allows new combinations of materials with complementary properties, which enables the design and realization of functionalities that are not available in the single-phase constituents. Here we show that organohalide perovskites and preformed colloidal quantum dots, combined in the solution phase, produce epitaxially aligned 'dots-in-a-matrix' crystals. Using transmission electron microscopy and electron diffraction, we reveal heterocrystals as large as about 60 nanometres and containing at least 20 mutually aligned dots that inherit the crystalline orientation of the perovskite matrix. The heterocrystals exhibit remarkable optoelectronic properties that are traceable to their atom-scale crystalline coherence: photoelectrons and holes generated in the larger-bandgap perovskites are transferred with 80% efficiency to become excitons in the quantum dot nanocrystals, which exploit the excellent photocarrier diffusion of perovskites to produce bright-light emission from infrared-bandgap quantum-tuned materials. By combining the electrical transport properties of the perovskite matrix with the high radiative efficiency of the quantum dots, we engineer a new platform to advance solution-processed infrared optoelectronics.

Electroconductive PET/SWNT Films by Solution Casting

NASA Technical Reports Server (NTRS)

Steinert, Brian W.; Dean, Derrick R.

2008-01-01

The market for electrically conductive polymers is rapidly growing, and an emerging pathway for attaining these materials is via polymer-carbon nanotube (CNT) nanocomposites, because of the superior properties of CNTs. Due to their excellent electrical properties and anisotropic magnetic susceptibility, we expect CNTs could be easily aligned to maximize their effectiveness in imparting electrical conductivity to the polymer matrix. Single-walled carbon nanotubes (SWNT) were dispersed in a polyethylene terephthalate (PET) matrix by solution blending then cast onto a glass substrate to create thin, flexible films. Various SWNT loading concentrations were implemented (0.5, 1.0, and 3.0 wt.%) to study the effect of additive density. The processing method was repeated to produce films in the presence of magnetic fields (3 and 9.4 Tesla). The SWNTs showed a high susceptibility to the magnetic field and were effectively aligned in the PET matrix. The alignment was characterized with Raman spectroscopy. Impedance spectroscopy was utilized to study the electrical behavior of the films. Concentration and dispersion seemed to play very important roles in improving electrical conductivity, while alignment played a secondary and less significant role. The most interesting result proved to be the effect of a magnetic field during processing. It appears that a magnetic field may improve dispersion of unmodified SWNTs, which seems to be more important than alignment. It was concluded that SWNTs offer a good option as conductive, nucleating filler for electroconductive polymer applications, and the utilization of a magnetic field may prove to be a novel method for CNT dispersion that could lead to improved nanocomposite materials.

An anisotropic hydrogel with electrostatic repulsion between cofacially aligned nanosheets

NASA Astrophysics Data System (ADS)

Liu, Mingjie; Ishida, Yasuhiro; Ebina, Yasuo; Sasaki, Takayoshi; Hikima, Takaaki; Takata, Masaki; Aida, Takuzo

2015-01-01

Machine technology frequently puts magnetic or electrostatic repulsive forces to practical use, as in maglev trains, vehicle suspensions or non-contact bearings. In contrast, materials design overwhelmingly focuses on attractive interactions, such as in the many advanced polymer-based composites, where inorganic fillers interact with a polymer matrix to improve mechanical properties. However, articular cartilage strikingly illustrates how electrostatic repulsion can be harnessed to achieve unparalleled functional efficiency: it permits virtually frictionless mechanical motion within joints, even under high compression. Here we describe a composite hydrogel with anisotropic mechanical properties dominated by electrostatic repulsion between negatively charged unilamellar titanate nanosheets embedded within it. Crucial to the behaviour of this hydrogel is the serendipitous discovery of cofacial nanosheet alignment in aqueous colloidal dispersions subjected to a strong magnetic field, which maximizes electrostatic repulsion and thereby induces a quasi-crystalline structural ordering over macroscopic length scales and with uniformly large face-to-face nanosheet separation. We fix this transiently induced structural order by transforming the dispersion into a hydrogel using light-triggered in situ vinyl polymerization. The resultant hydrogel, containing charged inorganic structures that align cofacially in a magnetic flux, deforms easily under shear forces applied parallel to the embedded nanosheets yet resists compressive forces applied orthogonally. We anticipate that the concept of embedding anisotropic repulsive electrostatics within a composite material, inspired by articular cartilage, will open up new possibilities for developing soft materials with unusual functions.

An anisotropic hydrogel with electrostatic repulsion between cofacially aligned nanosheets.

PubMed

Liu, Mingjie; Ishida, Yasuhiro; Ebina, Yasuo; Sasaki, Takayoshi; Hikima, Takaaki; Takata, Masaki; Aida, Takuzo

2015-01-01

Machine technology frequently puts magnetic or electrostatic repulsive forces to practical use, as in maglev trains, vehicle suspensions or non-contact bearings. In contrast, materials design overwhelmingly focuses on attractive interactions, such as in the many advanced polymer-based composites, where inorganic fillers interact with a polymer matrix to improve mechanical properties. However, articular cartilage strikingly illustrates how electrostatic repulsion can be harnessed to achieve unparalleled functional efficiency: it permits virtually frictionless mechanical motion within joints, even under high compression. Here we describe a composite hydrogel with anisotropic mechanical properties dominated by electrostatic repulsion between negatively charged unilamellar titanate nanosheets embedded within it. Crucial to the behaviour of this hydrogel is the serendipitous discovery of cofacial nanosheet alignment in aqueous colloidal dispersions subjected to a strong magnetic field, which maximizes electrostatic repulsion and thereby induces a quasi-crystalline structural ordering over macroscopic length scales and with uniformly large face-to-face nanosheet separation. We fix this transiently induced structural order by transforming the dispersion into a hydrogel using light-triggered in situ vinyl polymerization. The resultant hydrogel, containing charged inorganic structures that align cofacially in a magnetic flux, deforms easily under shear forces applied parallel to the embedded nanosheets yet resists compressive forces applied orthogonally. We anticipate that the concept of embedding anisotropic repulsive electrostatics within a composite material, inspired by articular cartilage, will open up new possibilities for developing soft materials with unusual functions.

The influence of fiber orientation on the equilibrium properties of neutral and charged biphasic tissues.

PubMed

Nagel, Thomas; Kelly, Daniel J

2010-11-01

Constitutive models facilitate investigation into load bearing mechanisms of biological tissues and may aid attempts to engineer tissue replacements. In soft tissue models, a commonly made assumption is that collagen fibers can only bear tensile loads. Previous computational studies have demonstrated that radially aligned fibers stiffen a material in unconfined compression most by limiting lateral expansion while vertically aligned fibers buckle under the compressive loads. In this short communication, we show that in conjunction with swelling, these intuitive statements can be violated at small strains. Under such conditions, a tissue with fibers aligned parallel to the direction of load initially provides the greatest resistance to compression. The results are further put into the context of a Benninghoff architecture for articular cartilage. The predictions of this computational study demonstrate the effects of varying fiber orientations and an initial tare strain on the apparent material parameters obtained from unconfined compression tests of charged tissues.

Applications for carbon fibre recovered from composites

NASA Astrophysics Data System (ADS)

Pickering; Liu, Z.; Turner, TA; Wong, KH

2016-07-01

Commercial operations to recover carbon fibre from waste composites are now developing and as more recovered fibre becomes available new applications for recovered fibre are required. Opportunities to use recovered carbon fibre as a structural reinforcement are considered involving the use of wet lay processes to produce nonwoven mats. Mats with random in-plane fibre orientation can readily be produced using existing commercial processes. However, the fibre volume fraction, and hence the mechanical properties that can be achieved, result in composites with limited mechanical properties. Fibre volume fractions of 40% can be achieved with high moulding pressures of over 100 bar, however, moulding at these pressures results in substantial fibre breakage which reduces the mean fibre length and the properties of the composite manufactured. Nonwoven mats made from aligned, short carbon fibres can achieve higher fibre volume fractions with lower fibre breakage even at high moulding pressure. A process for aligning short fibres is described and a composite of over 60% fibre volume fraction has been manufactured at a pressures up to 100 bar with low fibre breakage. Further developments of the alignment process have been undertaken and a composite of 46% fibre volume fraction has been produced moulded at a pressure of 7 bar in an autoclave, exhibiting good mechanical properties that compete with higher grade materials. This demonstrates the potential for high value applications for recovered carbon fibre by fibre alignment.

Colour stabilities of three types of orthodontic clear aligners exposed to staining agents

PubMed Central

Liu, Chen-Lu; Sun, Wen-Tian; Liao, Wen; Lu, Wen-Xin; Li, Qi-Wen; Jeong, Yunho; Liu, Jun; Zhao, Zhi-He

2016-01-01

The aim of this study was to evaluate and compare the colour stabilities of three types of orthodontic clear aligners exposed to staining agents in vitro. Sixty clear orthodontic aligners produced by three manufacturers (Invisalign, Angelalign, and Smartee) were immersed in three staining solutions (coffee, black tea, and red wine) and one control solution (distilled water). After 12-h and 7-day immersions, the aligners were washed in an ultrasonic cleaner and measured with a colourimeter. The colour changes (ΔE*) were calculated on the basis of the Commission Internationale de I'Eclairage L*a*b* colour system (CIE L*a*b*), and the results were then converted into National Bureau of Standards (NBS) units. Fourier transformation infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) were conducted to observe the molecular and morphologic alterations to the aligner surfaces, respectively. The three types of aligners exhibited slight colour changes after 12 h of staining, with the exception of the Invisalign aligners stained with coffee. The Invisalign aligners exhibited significantly higher ΔE* values (ranging from 0.30 to 27.81) than those of the Angelalign and Smartee aligners (ΔE* values ranging from 0.33 to 1.89 and 0.32 to 1.61, respectively, P<0.05). FT-IR analysis confirmed that the polymer-based structure of aligners did not exhibit significant chemical differences before and after the immersions. The SEM results revealed different surface alterations to the three types of aligner materials after the 7-day staining. The three types of aesthetic orthodontic appliances exhibited colour stability after the 12-h immersion, with the exception of the Invisalign aligners stained by coffee. The Invisalign aligners were more prone than the Angelalign and Smartee aligners to pigmentation. Aligner materials may be improved by considering aesthetic colour stability properties. PMID:27660048

Colour stabilities of three types of orthodontic clear aligners exposed to staining agents.

PubMed

Liu, Chen-Lu; Sun, Wen-Tian; Liao, Wen; Lu, Wen-Xin; Li, Qi-Wen; Jeong, Yunho; Liu, Jun; Zhao, Zhi-He

2016-12-16

The aim of this study was to evaluate and compare the colour stabilities of three types of orthodontic clear aligners exposed to staining agents in vitro. Sixty clear orthodontic aligners produced by three manufacturers (Invisalign, Angelalign, and Smartee) were immersed in three staining solutions (coffee, black tea, and red wine) and one control solution (distilled water). After 12-h and 7-day immersions, the aligners were washed in an ultrasonic cleaner and measured with a colourimeter. The colour changes (ΔE*) were calculated on the basis of the Commission Internationale de I'Eclairage L*a*b* colour system (CIE L*a*b*), and the results were then converted into National Bureau of Standards (NBS) units. Fourier transformation infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) were conducted to observe the molecular and morphologic alterations to the aligner surfaces, respectively. The three types of aligners exhibited slight colour changes after 12 h of staining, with the exception of the Invisalign aligners stained with coffee. The Invisalign aligners exhibited significantly higher ΔE* values (ranging from 0.30 to 27.81) than those of the Angelalign and Smartee aligners (ΔE* values ranging from 0.33 to 1.89 and 0.32 to 1.61, respectively, P<0.05). FT-IR analysis confirmed that the polymer-based structure of aligners did not exhibit significant chemical differences before and after the immersions. The SEM results revealed different surface alterations to the three types of aligner materials after the 7-day staining. The three types of aesthetic orthodontic appliances exhibited colour stability after the 12-h immersion, with the exception of the Invisalign aligners stained by coffee. The Invisalign aligners were more prone than the Angelalign and Smartee aligners to pigmentation. Aligner materials may be improved by considering aesthetic colour stability properties.

Induction and quantification of collagen fiber alignment in a three-dimensional hydroxyapatite-collagen composite scaffold.

PubMed

Banglmaier, Richard F; Sander, Edward A; VandeVord, Pamela J

2015-04-01

Hydroxyapatite-collagen composite scaffolds are designed to serve as a regenerative load bearing replacement that mimics bone. However, the material properties of these scaffolds are at least an order of magnitude less than that of bone and subject to fail under physiological loading conditions. These scaffolds compositionally resemble bone but they do not possess important structural attributes such as an ordered arrangement of collagen fibers, which is a correlate to the mechanical properties in bone. Furthermore, it is unclear how much ordering of structure is satisfactory to mimic bone. Therefore, quantitative methods are needed to characterize collagen fiber alignment in these scaffolds for better correlation between the scaffold structure and the mechanical properties. A combination of extrusion and compaction was used to induce collagen fiber alignment in composite scaffolds. Collagen fiber alignment, due to extrusion and compaction, was quantified from polarized light microscopy images with a Fourier transform image processing algorithm. The Fourier transform method was capable of resolving the degree of collagen alignment from polarized light images. Anisotropy indices of the image planes ranged from 0.08 to 0.45. Increases in the degree of fiber alignment induced solely by extrusion (0.08-0.25) or compaction (0.25-0.44) were not as great as those by the combination of extrusion and compaction (0.35-0.45). Additional measures of randomness and fiber direction corroborate these anisotropy findings. This increased degree of collagen fiber alignment was induced in a preferred direction that is consistent with the extrusion direction and parallel with the compacted plane. Copyright © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Reduced graphene oxide and vertically aligned carbon nanotubes superhydrophilic films for supercapacitors devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zanin, H., E-mail: hudsonzanin@gmail.com; Departamento de Semicondutores, Instrumentos e Fotônica, Faculdade de Engenharia Elétrica e Computação, Universidade Estadual de Campinas, UNICAMP, Campinas 13083-970; Saito, E., E-mail: esaito135@gmail.com

2014-01-01

Graphical abstract: - Highlights: • Graphene nanosheets were produced onto wire rods. • RGO and VACNT-O were evaluated and compared as supercapacitor electrode. • RGO and VACNT-O have structural and electrochemical properties quite similars. • The materials present good specific capacitance, energy storage and power delivery. - Abstract: Reduced graphene oxide (RGO) and vertically aligned carbon nanotubes (VACNT) superhydrophilic films were prepared by chemical vapor deposition techniques for electrical energy storage investigations. These electrodes were characterized in terms of their material and electrochemical properties by scanning electron microscopy (SEM), surface wettability, Fourier transform infrared spectroscopy (FTIR), energy dispersive and Ramanmore » spectroscopies, cyclic voltammetry (CV) and galvanostatic charge–discharge. We observed several physical structural and electrochemical similarities between these carbon-based materials with particular attention to very good specific capacitance, ultra-high energy storage and fast power delivery. Our results showed that the main difference between specific capacitance values is attributed to pseudocapacitive contribution and high density of multiwall nanotubes tips. In this work we have tested a supercapacitor device using the VACNT electrodes.« less

Electronic Chemical Potentials of Porous Metal–Organic Frameworks

PubMed Central

2014-01-01

The binding energy of an electron in a material is a fundamental characteristic, which determines a wealth of important chemical and physical properties. For metal–organic frameworks this quantity is hitherto unknown. We present a general approach for determining the vacuum level of porous metal–organic frameworks and apply it to obtain the first ionization energy for six prototype materials including zeolitic, covalent, and ionic frameworks. This approach for valence band alignment can explain observations relating to the electrochemical, optical, and electrical properties of porous frameworks. PMID:24447027

Nanostructured Block Copolymer Solutions and Composites: Mechanical and Structural Properties

NASA Astrophysics Data System (ADS)

Walker, Lynn

2015-03-01

Self-assembled block copolymer templates are used to control the nanoscale structure of materials that would not otherwise order in solution. In this work, we have developed a technique to use close-packed cubic and cylindrical mesophases of a thermoreversible block copolymer (PEO-PPO-PEO) to impart spatial order on dispersed nanoparticles. The thermoreversible nature of the template allows for the dispersion of particles synthesized outside the template. This feature extends the applicability of this templating method to many particle-polymer systems, including proteins, and also permits a systematic evaluation of the impact of design parameters on the structure and mechanical properties of the nanocomposites. The criteria for forming co-crystals have been characterized using small-angle scatting and the mechanical properties of these soft crystals determined. Numerous crystal structures have been reported for the block copolymer system and we have taken advantage of several to generate soft co-crystals. The result of this templating is spatially ordered nanoparticle arrays embedded within the block copolymer nanostructure. These soft materials can be shear aligned into crystals with long range order and this shear alignment is discussed. Finally, the dynamics of nanoparticles within the nanostructured material are characterized with fluorescence recovery after photobleaching (FRAP). The applications and general behavior of these nanostructured hydrogels are outlined.

Frontiers of controlling energy levels at interfaces

NASA Astrophysics Data System (ADS)

Koch, Norbert

The alignment of electron energy levels at interfaces between semiconductors, dielectrics, and electrodes determines the function and efficiency of all electronic and optoelectronic devices. Reliable guidelines for predicting the level alignment for a given material combination and methods to adjust the intrinsic energy landscape are needed to enable efficient engineering approaches. These are sufficiently understood for established electronic materials, e.g., Si, but for the increasing number of emerging materials, e.g., organic and 2D semiconductors, perovskites, this is work in progress. The intrinsic level alignment and the underlying mechanisms at interfaces between organic and inorganic semiconductors are discussed first. Next, methods to alter the level alignment are introduced, which all base on proper charge density rearrangement at a heterojunction. As interface modification agents we use molecular electron acceptors and donors, as well as molecular photochromic switches that add a dynamic aspect and allow device multifunctionality. For 2D semiconductors surface transfer doping with molecular acceptors/donors transpires as viable method to locally tune the Fermi-level position in the energy gap. The fundamental electronic properties of a prototypical 1D interface between intrinsic and p-doped 2D semiconductor regions are derived from local (scanning probe) and area-averaged (photoemission) spectroscopy experiments. Future research opportunities for attaining unsurpassed interface control through charge density management are discussed.

A Facile Method to Fabricate Anisotropic Hydrogels with Perfectly Aligned Hierarchical Fibrous Structures.

PubMed

Mredha, Md Tariful Islam; Guo, Yun Zhou; Nonoyama, Takayuki; Nakajima, Tasuku; Kurokawa, Takayuki; Gong, Jian Ping

2018-03-01

Natural structural materials (such as tendons and ligaments) are comprised of multiscale hierarchical architectures, with dimensions ranging from nano- to macroscale, which are difficult to mimic synthetically. Here a bioinspired, facile method to fabricate anisotropic hydrogels with perfectly aligned multiscale hierarchical fibrous structures similar to those of tendons and ligaments is reported. The method includes drying a diluted physical hydrogel in air by confining its length direction. During this process, sufficiently high tensile stress is built along the length direction to align the polymer chains and multiscale fibrous structures (from nano- to submicro- to microscale) are spontaneously formed in the bulk material, which are well-retained in the reswollen gel. The method is useful for relatively rigid polymers (such as alginate and cellulose), which are susceptible to mechanical signal. By controlling the drying with or without prestretching, the degree of alignment, size of superstructures, and the strength of supramolecular interactions can be tuned, which sensitively influence the strength and toughness of the hydrogels. The mechanical properties are comparable with those of natural ligaments. This study provides a general strategy for designing hydrogels with highly ordered hierarchical structures, which opens routes for the development of many functional biomimetic materials for biomedical applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Carbon nanotubes for thermal interface materials in microelectronic packaging

NASA Astrophysics Data System (ADS)

Lin, Wei

As the integration scale of transistors/devices in a chip/system keeps increasing, effective cooling has become more and more important in microelectronics. To address the thermal dissipation issue, one important solution is to develop thermal interface materials with higher performance. Carbon nanotubes, given their high intrinsic thermal and mechanical properties, and their high thermal and chemical stabilities, have received extensive attention from both academia and industry as a candidate for high-performance thermal interface materials. The thesis is devoted to addressing some challenges related to the potential application of carbon nanotubes as thermal interface materials in microelectronics. These challenges include: 1) controlled synthesis of vertically aligned carbon nanotubes on various bulk substrates via chemical vapor deposition and the fundamental understanding involved; 2) development of a scalable annealing process to improve the intrinsic properties of synthesized carbon nanotubes; 3) development of a state-of-art assembling process to effectively implement high-quality vertically aligned carbon nanotubes into a flip-chip assembly; 4) a reliable thermal measurement of intrinsic thermal transport property of vertically aligned carbon nanotube films; 5) improvement of interfacial thermal transport between carbon nanotubes and other materials. The major achievements are summarized. 1. Based on the fundamental understanding of catalytic chemical vapor deposition processes and the growth mechanism of carbon nanotube, fast synthesis of high-quality vertically aligned carbon nanotubes on various bulk substrates (e.g., copper, quartz, silicon, aluminum oxide, etc.) has been successfully achieved. The synthesis of vertically aligned carbon nanotubes on the bulk copper substrate by the thermal chemical vapor deposition process has set a world record. In order to functionalize the synthesized carbon nanotubes while maintaining their good vertical alignment, an in situ functionalization process has for the first time been demonstrated. The in situ functionalization renders the vertically aligned carbon nanotubes a proper chemical reactivity for forming chemical bonding with other substrate materials such as gold and silicon. 2. An ultrafast microwave annealing process has been developed to reduce the defect density in vertically aligned carbon nanotubes. Raman and thermogravimetric analyses have shown a distinct defect reduction in the CNTs annealed in microwave for 3 min. Fibers spun from the as-annealed CNTs, in comparison with those from the pristine CNTs, show increases of ˜35% and ˜65%, respectively, in tensile strength (˜0.8 GPa) and modulus (˜90 GPa) during tensile testing; an ˜20% improvement in electrical conductivity (˜80000 S m-1) was also reported. The mechanism of the microwave response of CNTs was discussed. Such a microwave annealing process has been extended to the preparation of reduced graphene oxide. 3. Based on the fundamental understanding of interfacial thermal transport and surface chemistry of metals and carbon nanotubes, two major transfer/assembling processes have been developed: molecular bonding and metal bonding. Effective improvement of the interfacial thermal transport has been achieved by the interfacial bonding. 4. The thermal diffusivity of vertically aligned carbon nanotube (VACNT, multi-walled) films was measured by a laser flash technique, and shown to be ˜30 mm2 s-1 along the tube-alignment direction. The calculated thermal conductivities of the VACNT film and the individual CNTs are ˜27 and ˜540 W m-1 K-1, respectively. The technique was verified to be reliable although a proper sampling procedure is critical. A systematic parametric study of the effects of defects, buckling, tip-to-tip contacts, packing density, and tube-tube interaction on the thermal diffusivity was carried out. Defects and buckling decreased the thermal diffusivity dramatically. An increased packing density was beneficial in increasing the collective thermal conductivity of the VACNT film; however, the increased tube-tube interaction in dense VACNT films decreased the thermal conductivity of the individual CNTs. The tip-to-tip contact resistance was shown to be ˜1x10-7 m2 K W -1. The study will shed light on the potential application of VACNTs as thermal interface materials in microelectronic packaging. 5. A combined process of in situ functionalization and microwave curing has been developed to effective enhance the interface between carbon nanotubes and the epoxy matrix. Effective medium theory has been used to analyze the interfacial thermal resistance between carbon nanotubes and polymer matrix, and that between graphite nanoplatlets and polymer matrix.

Evaluation of Georgia asphalt mixture properties using a Hamburg wheel-tracking device.

DOT National Transportation Integrated Search

2017-05-01

This study used a Hamburg Wheel-Tracking Device (HWTD) to evaluate the resistance of Georgia asphalt mixtures to rutting and stripping. It aimed to develop an HWTD test procedure and criteria aligned with GDOTs asphalt materials and mixture design...

3D-Printing of Meso-structurally Ordered Carbon Fiber/Polymer Composites with Unprecedented Orthotropic Physical Properties

NASA Astrophysics Data System (ADS)

Lewicki, James P.; Rodriguez, Jennifer N.; Zhu, Cheng; Worsley, Marcus A.; Wu, Amanda S.; Kanarska, Yuliya; Horn, John D.; Duoss, Eric B.; Ortega, Jason M.; Elmer, William; Hensleigh, Ryan; Fellini, Ryan A.; King, Michael J.

2017-03-01

Here we report the first example of a class of additively manufactured carbon fiber reinforced composite (AMCFRC) materials which have been achieved through the use of a latent thermal cured aromatic thermoset resin system, through an adaptation of direct ink writing (DIW) 3D-printing technology. We have developed a means of printing high performance thermoset carbon fiber composites, which allow the fiber component of a resin and carbon fiber fluid to be aligned in three dimensions via controlled micro-extrusion and subsequently cured into complex geometries. Characterization of our composite systems clearly show that we achieved a high order of fiber alignment within the composite microstructure, which in turn allows these materials to outperform equivalently filled randomly oriented carbon fiber and polymer composites. Furthermore, our AM carbon fiber composite systems exhibit highly orthotropic mechanical and electrical responses as a direct result of the alignment of carbon fiber bundles in the microscale which we predict will ultimately lead to the design of truly tailorable carbon fiber/polymer hybrid materials having locally programmable complex electrical, thermal and mechanical response.

3D-Printing of Meso-structurally Ordered Carbon Fiber/Polymer Composites with Unprecedented Orthotropic Physical Properties.

PubMed

Lewicki, James P; Rodriguez, Jennifer N; Zhu, Cheng; Worsley, Marcus A; Wu, Amanda S; Kanarska, Yuliya; Horn, John D; Duoss, Eric B; Ortega, Jason M; Elmer, William; Hensleigh, Ryan; Fellini, Ryan A; King, Michael J

2017-03-06

Here we report the first example of a class of additively manufactured carbon fiber reinforced composite (AMCFRC) materials which have been achieved through the use of a latent thermal cured aromatic thermoset resin system, through an adaptation of direct ink writing (DIW) 3D-printing technology. We have developed a means of printing high performance thermoset carbon fiber composites, which allow the fiber component of a resin and carbon fiber fluid to be aligned in three dimensions via controlled micro-extrusion and subsequently cured into complex geometries. Characterization of our composite systems clearly show that we achieved a high order of fiber alignment within the composite microstructure, which in turn allows these materials to outperform equivalently filled randomly oriented carbon fiber and polymer composites. Furthermore, our AM carbon fiber composite systems exhibit highly orthotropic mechanical and electrical responses as a direct result of the alignment of carbon fiber bundles in the microscale which we predict will ultimately lead to the design of truly tailorable carbon fiber/polymer hybrid materials having locally programmable complex electrical, thermal and mechanical response.

3D-Printing of Meso-structurally Ordered Carbon Fiber/Polymer Composites with Unprecedented Orthotropic Physical Properties

PubMed Central

Lewicki, James P.; Rodriguez, Jennifer N.; Zhu, Cheng; Worsley, Marcus A.; Wu, Amanda S.; Kanarska, Yuliya; Horn, John D.; Duoss, Eric B.; Ortega, Jason M.; Elmer, William; Hensleigh, Ryan; Fellini, Ryan A.; King, Michael J.

2017-01-01

Here we report the first example of a class of additively manufactured carbon fiber reinforced composite (AMCFRC) materials which have been achieved through the use of a latent thermal cured aromatic thermoset resin system, through an adaptation of direct ink writing (DIW) 3D-printing technology. We have developed a means of printing high performance thermoset carbon fiber composites, which allow the fiber component of a resin and carbon fiber fluid to be aligned in three dimensions via controlled micro-extrusion and subsequently cured into complex geometries. Characterization of our composite systems clearly show that we achieved a high order of fiber alignment within the composite microstructure, which in turn allows these materials to outperform equivalently filled randomly oriented carbon fiber and polymer composites. Furthermore, our AM carbon fiber composite systems exhibit highly orthotropic mechanical and electrical responses as a direct result of the alignment of carbon fiber bundles in the microscale which we predict will ultimately lead to the design of truly tailorable carbon fiber/polymer hybrid materials having locally programmable complex electrical, thermal and mechanical response. PMID:28262669

Ultralight anisotropic foams from layered aligned carbon nanotube sheets

NASA Astrophysics Data System (ADS)

Faraji, Shaghayegh; L. Stano, Kelly; Yildiz, Ozkan; Li, Ang; Zhu, Yuntian; Bradford, Philip D.

2015-10-01

In this work, we present large scale, ultralight aligned carbon nanotube (CNT) structures which have densities an order of magnitude lower than CNT arrays, have tunable properties and exhibit resiliency after compression. By stacking aligned sheets of carbon nanotubes and then infiltrating with a pyrolytic carbon (PyC), resilient foam-like materials were produced that exhibited complete recovery from 90% compressive strain. With density as low as 3.8 mg cm-3, the foam structure is over 500 times less dense than bulk graphite. Microscopy revealed that PyC coated the junctions among CNTs, and also increased CNT surface roughness. These changes in the morphology explain the transition from inelastic behavior to foam-like recovery of the layered CNT sheet structure. Mechanical and thermal properties of the foams were tuned for different applications through variation of PyC deposition duration while dynamic mechanical analysis showed no change in mechanical properties over a large temperature range. Observation of a large and linear electrical resistance change during compression of the aligned CNT/carbon (ACNT/C) foams makes strain/pressure sensors a relevant application. The foams have high oil absorption capacities, up to 275 times their own weight, which suggests they may be useful in water treatment and oil spill cleanup. Finally, the ACNT/C foam's high porosity, surface area and stability allow for demonstration of the foams as catalyst support structures.In this work, we present large scale, ultralight aligned carbon nanotube (CNT) structures which have densities an order of magnitude lower than CNT arrays, have tunable properties and exhibit resiliency after compression. By stacking aligned sheets of carbon nanotubes and then infiltrating with a pyrolytic carbon (PyC), resilient foam-like materials were produced that exhibited complete recovery from 90% compressive strain. With density as low as 3.8 mg cm-3, the foam structure is over 500 times less dense than bulk graphite. Microscopy revealed that PyC coated the junctions among CNTs, and also increased CNT surface roughness. These changes in the morphology explain the transition from inelastic behavior to foam-like recovery of the layered CNT sheet structure. Mechanical and thermal properties of the foams were tuned for different applications through variation of PyC deposition duration while dynamic mechanical analysis showed no change in mechanical properties over a large temperature range. Observation of a large and linear electrical resistance change during compression of the aligned CNT/carbon (ACNT/C) foams makes strain/pressure sensors a relevant application. The foams have high oil absorption capacities, up to 275 times their own weight, which suggests they may be useful in water treatment and oil spill cleanup. Finally, the ACNT/C foam's high porosity, surface area and stability allow for demonstration of the foams as catalyst support structures. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03899e

Two-dimensional finite element heat transfer model of softwood. Part III, Effect of moisture content on thermal conductivity

Treesearch

Hongmei Gu; John F. Hunt

2007-01-01

The anisotropy of wood creates a complex problem for solving heat and mass transfer problems that require analyses be based on fundamental material properties of the wood structure. Most heat transfer models for softwood use average thermal properties across either the radial or tangential direction and do not differentiate the effects of cellular alignment or...

Gas adsorption capacity in an all carbon nanomaterial composed of carbon nanohorns and vertically aligned carbon nanotubes.

PubMed

Puthusseri, Divya; Babu, Deepu J; Okeil, Sherif; Schneider, Jörg J

2017-10-04

Whereas vertically aligned carbon nanotubes (VACNTs) typically show a promising adsorption behavior at high pressures, carbon nanohorns (CNHs) exhibit superior gas adsorption properties in the low pressure regime due to their inherent microporosity. These adsorption characteristics are further enhanced when both materials are opened at their tips. The so prepared composite material allows one to investigate the effect of physical entrapment of CO 2 molecules within the specific adsorption sites of VACNTs composed of opened double walled carbon nanotubes (CNTs) and in specific adsorption sites created by spherically aggregated opened single walled carbon nanohorns. Combining 50 wt% of tip opened CNTs with tip opened CNHs increases the CO 2 adsorption capacity of this material by ∼24% at 30 bar and 298 K compared to opened CNHs alone.

Bioinspired large-scale aligned porous materials assembled with dual temperature gradients

PubMed Central

Bai, Hao; Chen, Yuan; Delattre, Benjamin; Tomsia, Antoni P.; Ritchie, Robert O.

2015-01-01

Natural materials, such as bone, teeth, shells, and wood, exhibit outstanding properties despite being porous and made of weak constituents. Frequently, they represent a source of inspiration to design strong, tough, and lightweight materials. Although many techniques have been introduced to create such structures, a long-range order of the porosity as well as a precise control of the final architecture remain difficult to achieve. These limitations severely hinder the scale-up fabrication of layered structures aimed for larger applications. We report on a bidirectional freezing technique to successfully assemble ceramic particles into scaffolds with large-scale aligned, lamellar, porous, nacre-like structure and long-range order at the centimeter scale. This is achieved by modifying the cold finger with a polydimethylsiloxane (PDMS) wedge to control the nucleation and growth of ice crystals under dual temperature gradients. Our approach could provide an effective way of manufacturing novel bioinspired structural materials, in particular advanced materials such as composites, where a higher level of control over the structure is required. PMID:26824062

Bioinspired Design: Magnetic Freeze Casting

NASA Astrophysics Data System (ADS)

Porter, Michael Martin

Nature is the ultimate experimental scientist, having billions of years of evolution to design, test, and adapt a variety of multifunctional systems for a plethora of diverse applications. Next-generation materials that draw inspiration from the structure-property-function relationships of natural biological materials have led to many high-performance structural materials with hybrid, hierarchical architectures that fit form to function. In this dissertation, a novel materials processing method, magnetic freeze casting, is introduced to develop porous scaffolds and hybrid composites with micro-architectures that emulate bone, abalone nacre, and other hard biological materials. This method uses ice as a template to form ceramic-based materials with continuously, interconnected microstructures and magnetic fields to control the alignment of these structures in multiple directions. The resulting materials have anisotropic properties with enhanced mechanical performance that have potential applications as bone implants or lightweight structural composites, among others.

Large-scale self-assembled zirconium phosphate smectic layers via a simple spray-coating process

NASA Astrophysics Data System (ADS)

Wong, Minhao; Ishige, Ryohei; White, Kevin L.; Li, Peng; Kim, Daehak; Krishnamoorti, Ramanan; Gunther, Robert; Higuchi, Takeshi; Jinnai, Hiroshi; Takahara, Atsushi; Nishimura, Riichi; Sue, Hung-Jue

2014-04-01

The large-scale assembly of asymmetric colloidal particles is used in creating high-performance fibres. A similar concept is extended to the manufacturing of thin films of self-assembled two-dimensional crystal-type materials with enhanced and tunable properties. Here we present a spray-coating method to manufacture thin, flexible and transparent epoxy films containing zirconium phosphate nanoplatelets self-assembled into a lamellar arrangement aligned parallel to the substrate. The self-assembled mesophase of zirconium phosphate nanoplatelets is stabilized by epoxy pre-polymer and exhibits rheology favourable towards large-scale manufacturing. The thermally cured film forms a mechanically robust coating and shows excellent gas barrier properties at both low- and high humidity levels as a result of the highly aligned and overlapping arrangement of nanoplatelets. This work shows that the large-scale ordering of high aspect ratio nanoplatelets is easier to achieve than previously thought and may have implications in the technological applications for similar materials.

A Unifying Perspective on Oxygen Vacancies in Wide Band Gap Oxides.

PubMed

Linderälv, Christopher; Lindman, Anders; Erhart, Paul

2018-01-04

Wide band gap oxides are versatile materials with numerous applications in research and technology. Many properties of these materials are intimately related to defects, with the most important defect being the oxygen vacancy. Here, using electronic structure calculations, we show that the charge transition level (CTL) and eigenstates associated with oxygen vacancies, which to a large extent determine their electronic properties, are confined to a rather narrow energy range, even while band gap and the electronic structure of the conduction band vary substantially. Vacancies are classified according to their character (deep versus shallow), which shows that the alignment of electronic eigenenergies and CTL can be understood in terms of the transition between cavity-like localized levels in the large band gap limit and strong coupling between conduction band and vacancy states for small to medium band gaps. We consider both conventional and hybrid functionals and demonstrate that the former yields results in very good agreement with the latter provided that band edge alignment is taken into account.

Superporous thermo-responsive hydrogels by combination of cellulose fibers and aligned micropores.

PubMed

Halake, Kantappa S; Lee, Jonghwi

2014-05-25

In the area of artificial hydrogels, simultaneous engineering of the volume transition characteristics and mechanical properties of stimuli-responsive hydrogels is an important subject. By unrestricted architecting of hierarchical structures, natural hydrogels are able to provide a wide range of swelling and mechanical properties, beyond the limits of artificial hydrogels. Herein, a combination of nanostructures and microstructures was developed to construct superporous hydrogels. Fibers of microfibrillated cellulose (MFC), an eco-friendly reinforcing material, were used as nanostructures, aligned micropores were used as microstructures, and in situ photopolymerization was used to immobilize the two structures together within the gel networks of poly(N-isopropyl acrylamide) (PNIPAm). The introduction of MFC distinctly enhanced volume transition, mainly by decreasing the swelling ratios above the transition. The introduction of directional micropores increased the swelling ratio below the transition and decreased the swelling ratio above the transition, thereby also enhancing the volume transition. Additionally, the formation of aligned micropores achieved fast water infiltration, which is beneficial for superabsorbent applications. The introduction of aligned micropores reduced the elastic modulus, but this could partially be compensated for by reinforcement with MFC. This combination of crystalline nanofibers and aligned micropores has great potential for the development of stimuli-responsive superporous hydrogels outperforming current artificial hydrogels. Copyright © 2014 Elsevier Ltd. All rights reserved.

Age Dependent Differences in Collagen Alignment of Glutaraldehyde Fixed Bovine Pericardium

PubMed Central

Sizeland, Katie H.; Wells, Hannah C.; Higgins, John; Cunanan, Crystal M.; Kirby, Nigel; Hawley, Adrian; Mudie, Stephen T.; Haverkamp, Richard G.

2014-01-01

Bovine pericardium is used for heart valve leaflet replacement where the strength and thinness are critical properties. Pericardium from neonatal animals (4–7 days old) is advantageously thinner and is considered as an alternative to that from adult animals. Here, the structures of adult and neonatal bovine pericardium tissues fixed with glutaraldehyde are characterized by synchrotron-based small angle X-ray scattering (SAXS) and compared with the mechanical properties of these materials. Significant differences are observed between adult and neonatal tissue. The glutaraldehyde fixed neonatal tissue has a higher modulus of elasticity (83.7 MPa) than adult pericardium (33.5 MPa) and a higher normalised ultimate tensile strength (32.9 MPa) than adult pericardium (19.1 MPa). Measured edge on to the tissue, the collagen in neonatal pericardium is significantly more aligned (orientation index (OI) 0.78) than that in adult pericardium (OI 0.62). There is no difference in the fibril diameter between neonatal and adult pericardium. It is shown that high alignment in the plane of the tissue provides the mechanism for the increased strength of the neonatal material. The superior strength of neonatal compared with adult tissue supports the use of neonatal bovine pericardium in heterografts. PMID:25295250

Whole Wafer Design and Fabrication for the Alignment of Nanostructures for Chemical Sensor Applications

NASA Technical Reports Server (NTRS)

Biaggi-Labiosa, Azlin M.; Hunter, Gary W.

2013-01-01

A major objective in aerospace sensor development is to produce sensors that are small in size, easy to batch fabricate and low in cost, and have low power consumption The fabrication of chemical sensors involving nanostructured materials can provide these properties as well as the potential for the development of sensor systems with unique properties and improved performance. However, the fabrication and processing of nanostructures for sensor applications currently is limited in the ability to control their location on the sensor. Currently, our group at NASA Glenn Research Center has demonstrated the controlled placement of nanostructures in sensors using a sawtooth patterned electrode design. With this design the nanostructures are aligned between opposing sawtooth electrodes by applying an alternating current.

Electronic and magnetic properties of bare armchair BC2N nanoribbons

NASA Astrophysics Data System (ADS)

Li, Hong; Xiao, Xiang; Tie, Jun; Lu, Jing

2017-03-01

We present the electronic and magnetic properties of bare armchair BC2N nanoribbons (ABC2NNRs) in the view of density functional calculations. We consider three types of edge terminations with a width of 0.75 2.10 nm. All the investigated ribbons exhibit magnetic ground states with the magnetic moments mainly located on the edge C atoms. Room temperature accessible magnetic stabilities are obtained for ABC2NNRs with NC-NC and NC-BC edge alignments. We find the ABC2NNRs have various electronic structures, where half-metal, metal, and semiconductor are all acquired depend on the edge alignment and magnetic coupling state. The results show the ABC2NNRs can be a promising candidate material in nanoelectronics and nanospintronics.

Elastic Characterization of Transversely Isotropic Soft Materials by Dynamic Shear and Asymmetric Indentation

PubMed Central

Namani, R.; Feng, Y.; Okamoto, R. J.; Jesuraj, N.; Sakiyama-Elbert, S. E.; Genin, G. M.; Bayly, P. V.

2012-01-01

The mechanical characterization of soft anisotropic materials is a fundamental challenge because of difficulties in applying mechanical loads to soft matter and the need to combine information from multiple tests. A method to characterize the linear elastic properties of transversely isotropic soft materials is proposed, based on the combination of dynamic shear testing (DST) and asymmetric indentation. The procedure was demonstrated by characterizing a nearly incompressible transversely isotropic soft material. A soft gel with controlled anisotropy was obtained by polymerizing a mixture of fibrinogen and thrombin solutions in a high field magnet (B = 11.7 T); fibrils in the resulting gel were predominantly aligned parallel to the magnetic field. Aligned fibrin gels were subject to dynamic (20–40 Hz) shear deformation in two orthogonal directions. The shear storage modulus was 1.08 ± 0. 42 kPa (mean ± std. dev.) for shear in a plane parallel to the dominant fiber direction, and 0.58 ± 0.21 kPa for shear in the plane of isotropy. Gels were indented by a rectangular tip of a large aspect ratio, aligned either parallel or perpendicular to the normal to the plane of transverse isotropy. Aligned fibrin gels appeared stiffer when indented with the long axis of a rectangular tip perpendicular to the dominant fiber direction. Three-dimensional numerical simulations of asymmetric indentation were used to determine the relationship between direction-dependent differences in indentation stiffness and material parameters. This approach enables the estimation of a complete set of parameters for an incompressible, transversely isotropic, linear elastic material. PMID:22757501

Analytical, numerical, and experimental investigations on effective mechanical properties and performances of carbon nanotubes and nanotube based nanocomposites with novel three dimensional nanostructures

NASA Astrophysics Data System (ADS)

Askari, Davood

The theoretical objectives and accomplishment of this work are the analytical and numerical investigation of material properties and mechanical behavior of carbon nanotubes (CNTs) and nanotube nanocomposites when they are subjected to various loading conditions. First, the finite element method is employed to investigate numerically the effective Young's modulus and Poisson's ratio of a single-walled CNT. Next, the effects of chirality on the effective Young's modulus and Poisson's ratio are investigated and then variations of their effective coefficient of thermal expansions and effective thermal conductivities are studied for CNTs with different structural configurations. To study the influence of small vacancy defects on mechanical properties of CNTs, finite element analyses are performed and the behavior of CNTs with various structural configurations having different types of vacancy defects is studied. It is frequently reported that nano-materials are excellent candidates as reinforcements in nanocomposites to change or enhance material properties of polymers and their nanocomposites. Second, the inclusion of nano-materials can considerably improve electrical, thermal, and mechanical properties of the bonding agent, i.e., resin. Note that, materials atomic and molecular level do not usually show isotropic behaviour, rather they have orthotropic properties. Therefore, two-phase and three-phase cylindrically orthotropic composite models consisting of different constituents with orthotropic properties are developed and introduced in this work to analytically predict the effective mechanical properties and mechanical behavior of such structures when they are subjected to various external loading conditions. To verify the analytically obtained exact solutions, finite element analyses of identical cylindrical structures are also performed and then results are compared with those obtained analytically, and excellent agreement is achieved. The third part of this dissertation investigates the growth of vertically aligned, long, and high density arrays of CNTs and novel 3-D carbon nanotube nano-forests. A Chemical vapor deposition technique is used to grow radially aligned CNTs on various types of fibrous materials such as silicon carbide, carbon, Kevlar, and glass fibers and clothes that can be used for the fabrication of multifunctional high performing laminated nanocomposite structures. Using the CNTs nano-forest clothes, nanocomposite samples are prepared and tested giving promising results for the improvement of mechanical properties and performance of composites structures.

Vertically aligned carbon nanotubes as cytocompatible material for enhanced adhesion and proliferation of osteoblast-like cells.

PubMed

Giannona, Suna; Firkowska, Izabela; Rojas-Chapana, José; Giersig, Michael

2007-01-01

In this study, we describe the spatial organization of CAL-72 osteoblast-like cells on arrays of vertically aligned multi-walled carbon nanotubes (VACNTs). It was observed that, unlike cell growth on non-patterned surfaces, the cell attachment and spreading process on VACNTs was significantly enhanced. Additionally, since carbon nanotubes are known to possess resilient mechanical properties and are chemically stable, the effect of periodic arrays of VACNTs on CAL-72 osteoblast-like cells was also studied. The periodicity and alignment of VACNTs considerably influenced growth, shape and orientation of the cells by steering toward the nanopattern. This situation is of great interest for the potential application of VACNTs in bone bioenginnering. This data provides evidence that CAL-72 osteoblast-like cells can sense physical features at the nanoscale. These results give a fascinating insight into the ways in which cell growth can be influenced by man-made nanostructures and could provide a framework for achieving controlled cell guidance with controlled organization and special physical properties.

Gelatin freeze casting of biomimetic titanium alloy with anisotropic and gradient pore structure.

PubMed

Zhang, Lei; Le Coz-Botrel, Ronan; Beddoes, Charlotte; Sjöström, Terje; Su, Bo

2017-01-17

Titanium is a material commonly used for dental and orthopaedic implants. However, due to large differences in properties between the titanium metal and the natural bone, stress shielding has been observed in the surrounding area, resulting in bone atrophy, and thus has raised concerns of the use of this material. Ideally implant materials should possess similar properties to the surrounding tissues in order to distribute the load as the joint would naturally, while also possessing a similar porous structure to the bone to enable interaction with the surrounding material. In this paper we report the formation of aligned porous titanium alloy scaffolds with the use of unidirectional freeze casting with a temperature gradient. The resulting scaffolds had a dense bottom part with sufficient strength for loading, while the top part remaining porous in order to allow bone growth in the scaffold and fully integrating with the surrounding tissue. The anisotropic nature of the pores within the titanium alloy samples were observed via micro computed tomography, where a gradient structure similar to bone was observed. The compressive strength of the fabricated scaffolds was found to be up to 427 MPa when measured with the pores aligned with the applied load, depending on the pore density. This is within the range of cortical bone.

Enhancing Mechanical and Thermal Properties of Epoxy Nanocomposites via Alignment of Magnetized SiC Whiskers.

PubMed

Townsend, James; Burtovyy, Ruslan; Aprelev, Pavel; Kornev, Konstantin G; Luzinov, Igor

2017-07-12

This research is focused on the fabrication and properties of epoxy nanocomposites containing magnetized SiC whiskers (MSiCWs). To this end, we report an original strategy for fabrication of magnetically active SiCWs by decorating the whiskers with magnetic (iron oxide) nanoparticles via polymer-polymer (poly(acrylic acid)/poly(2-vinyl pyridine)) complexation. The obtained whiskers demonstrated a substantial magnetic response in the polymerizing epoxy resin, with application of only a 20 mT (200 G) magnetic field. We also found that the whiskers chemically reacted with the epoxy resin, causing formation of an extended interphase near the boundary of the whiskers. The SiC whiskers oriented with the magnetic field demonstrated positive effects on the behavior of epoxy-based nanocomposites. Namely, the aligned MSiCWs enhanced the thermomechanical properties of the materials significantly above that of the neat epoxy and epoxy nanocomposite, with randomly oriented whiskers.

Ultralight anisotropic foams from layered aligned carbon nanotube sheets.

PubMed

Faraji, Shaghayegh; Stano, Kelly L; Yildiz, Ozkan; Li, Ang; Zhu, Yuntian; Bradford, Philip D

2015-10-28

In this work, we present large scale, ultralight aligned carbon nanotube (CNT) structures which have densities an order of magnitude lower than CNT arrays, have tunable properties and exhibit resiliency after compression. By stacking aligned sheets of carbon nanotubes and then infiltrating with a pyrolytic carbon (PyC), resilient foam-like materials were produced that exhibited complete recovery from 90% compressive strain. With density as low as 3.8 mg cm(-3), the foam structure is over 500 times less dense than bulk graphite. Microscopy revealed that PyC coated the junctions among CNTs, and also increased CNT surface roughness. These changes in the morphology explain the transition from inelastic behavior to foam-like recovery of the layered CNT sheet structure. Mechanical and thermal properties of the foams were tuned for different applications through variation of PyC deposition duration while dynamic mechanical analysis showed no change in mechanical properties over a large temperature range. Observation of a large and linear electrical resistance change during compression of the aligned CNT/carbon (ACNT/C) foams makes strain/pressure sensors a relevant application. The foams have high oil absorption capacities, up to 275 times their own weight, which suggests they may be useful in water treatment and oil spill cleanup. Finally, the ACNT/C foam's high porosity, surface area and stability allow for demonstration of the foams as catalyst support structures.

Synthesis, transfer printing, electrical and optical properties, and applications of materials composed of self-assembled, aligned single-walled carbon nanotubes

NASA Astrophysics Data System (ADS)

Pint, Cary L.

Super growth of single-walled carbon nanotubes (SWNTs) has emerged as a unique method for synthesizing self-assembled, pristine, aligned SWNT materials composed of ultra-long (millimeter-long) nanotubes. This thesis focuses on novel routes of synthesizing such self-assembled SWNTs and the challenges that arise in integrating this material into next-generation applications. First of all, this work provides unique insight into growth termination of aligned SWNTs, emphasizing the mechanism that inhibits the growth of infinitely long nanotubes. Exhaustive real-time growth studies, combined with ex-situ and in-situ TEM characterization emphasizes that Ostwald ripening and subsurface diffusion of catalyst particles play a key role in growth termination. As a result, rational steps to solving this problem can enhance growth, and may ultimately lead to the meter or kilometer-long SWNTs that are necessary for a number of applications. In addition, other novel synthesis routes are discussed, such as the ability to form macroscopic fibrils of SWNTs, called "flying carpets" from 40 nm thick substrates, and the ability to achieve supergrowth of SWNTs that are controllably doped with nitrogen. In the latter case, molecular heterojunctions of doped and undoped sections in a single strand of ultralong SWNTs are demonstrated Secondly, as supergrowth is conducted on alumina coated SiO2 substrates, any applications will require that one can transfer the SWNTs to host surfaces with minimal processing. This work demonstrates a unique contact transfer route by which both patterned arrays of SWNTs, or homogenous SWNT carpets, can be transferred to any host surface. In the first case, the SWNTs are grown vertically aligned, and transferred in patterns of horizontally aligned SWNT. This transfer process relies on simple water-vapor etching of amorphous carbons at the catalyst following growth, and strong van der Waals adhesion of the high surface-area SWNT to host surfaces (gecko effect). Next, as the SWNTs produced in supergrowth are notably large in diameter (2-5 nm), this work provides the first characterization of these SWNTs using combined microscopy and infrared polarized absorption studies. Perfectly aligned SWNTs are transferred to infrared optical windows and mounted in a rotatable vacuum cell in which polarization dependent characterization is carried out. By modeling features observed in absorption to expected optical excitonic transition energies, diameter distributions are rapidly extracted. In addition, other concepts of optical characterization in ultra-long aligned SWNTs are explored. For example, the concept of using polarized near-IR characterization for such SWNT samples is inadequate to characterize the bulk alignment due to the mismatch of the excitation wavelength and the SWNT length. Therefore, comparing anisotropy in polarized near-IR Raman or absorption gives substantially different results than anisotropic electrical transport measurements. In addition to optical characterization, this work uniquely finds that the electrical transport properties of SWNTs is ultimately limited by SWNT-SWNT junctions. This is evident in temperature-dependent DC and AC conductivity measurements that emphasize localization-induced transport characteristics. A number of non-classical electrical transport features are observed that can simply be related to the sensitivity of electrical transport to SWNT-SWNT junctions. This means that despite the incredible electrical properties of individual SWNTs, it is necessary to focus on the growth and processing of ultra-long SWNTs in order to realistically make nanotube-based materials comparable in transport characteristics to conventional materials. Finally, this work concludes by demonstrating progress on the fabrication of new SWNT-based applications. First of all, a new type of solid-state supercapacitor material is fabricated where vertically aligned SWNT are coated with metal-oxide dielectric and counterelectrode layers to form efficient supercapacitors. This design benefits from the ultra-high surface area available in SWNT arrays, the intrinsic ultra-high current carrying capacity of ultra-long SWNT (1000 times copper), the high breakdown voltages one can achieve using solid dielectric layers, and the lightweight and temperature insensitive design of this capacitor. As a result, performance comparable to current electric-double layer capacitor devices is reported, and energy densities significant larger are predicted by material optimization. In addition, progress on other applications are discussed, including devices utilizing self-assembled molecular heterojunction arrays, and terahertz polarizers made from perfectly aligned transferred SWNT films. This work demonstrates a bottom-up route toward the synthesis of new materials for novel characterization and applications.

Effect of metallic silver nanoparticles on the alignment and relaxation behaviour of liquid crystalline material in smectic C* phase

NASA Astrophysics Data System (ADS)

Vimal, Tripti; Kumar Gupta, Swadesh; Katiyar, Rohit; Srivastava, Atul; Czerwinski, Michal; Krup, Katarzyna; Kumar, Sandeep; Manohar, Rajiv

2017-09-01

The influence of silver nanoparticles dispersed in a Ferroelectric Liquid Crystal (FLC) on the properties of the resultant composite system has been investigated by thermal, electro-optical, and dielectric methods. We show that the concentration of thiol capped silver nanoparticles is a critical factor in governing the alignment of nanoparticles (NPs) in the host FLC. The orientation of NPs in composite samples affects the ordering of the LC (Liquid Crystal) phase and consequently changes the various phase transition temperatures of the host LC. Formation of self-assembled 2D (two dimensional) arrays of nanoparticles is observed for high concentration of dopant in the LC, oriented perpendicular to the direction of rubbing. We propose that the molecular interaction between the thiol capped NPs and LC molecules is the key factor behind such an arrangement of NPs. Orientation of NPs has affected the relaxation behaviour and various other material parameters, significantly. A noteworthy change in DC conductivity articulates our proposed idea of the formation of 2D array of NPs perpendicular to the direction of rubbing. This comprehensive study endorses the importance of dopant concentration in modifying the properties of the host LC material.

Engineered plant biomass feedstock particles

DOEpatents

Dooley, James H [Federal Way, WA; Lanning, David N [Federal Way, WA; Broderick, Thomas F [Lake Forest Park, WA

2012-04-17

A new class of plant biomass feedstock particles characterized by consistent piece size and shape uniformity, high skeletal surface area, and good flow properties. The particles of plant biomass material having fibers aligned in a grain are characterized by a length dimension (L) aligned substantially parallel to the grain and defining a substantially uniform distance along the grain, a width dimension (W) normal to L and aligned cross grain, and a height dimension (H) normal to W and L. In particular, the L.times.H dimensions define a pair of substantially parallel side surfaces characterized by substantially intact longitudinally arrayed fibers, the W.times.H dimensions define a pair of substantially parallel end surfaces characterized by crosscut fibers and end checking between fibers, and the L.times.W dimensions define a pair of substantially parallel top and bottom surfaces. The L.times.W surfaces of particles with L/H dimension ratios of 4:1 or less are further elaborated by surface checking between longitudinally arrayed fibers. The length dimension L is preferably aligned within 30.degree. parallel to the grain, and more preferably within 10.degree. parallel to the grain. The plant biomass material is preferably selected from among wood, agricultural crop residues, plantation grasses, hemp, bagasse, and bamboo.

Wrinkled, wavelength-tunable graphene-based surface topographies for directing cell alignment and morphology

PubMed Central

Wang, Zhongying; Tonderys, Daniel; Leggett, Susan E.; Williams, Evelyn Kendall; Kiani, Mehrdad T.; Steinberg, Ruben Spitz; Qiu, Yang; Wong, Ian Y.; Hurt, Robert H.

2015-01-01

Textured surfaces with periodic topographical features and long-range order are highly attractive for directing cell-material interactions. They mimic physiological environments more accurately than planar surfaces and can fundamentally alter cell alignment, shape, gene expression, and cellular assembly into superstructures or microtissues. Here we demonstrate for the first time that wrinkled graphene-based surfaces are suitable as textured cell attachment substrates, and that engineered wrinkling can dramatically alter cell alignment and morphology. The wrinkled surfaces are fabricated by graphene oxide wet deposition onto pre-stretched elastomers followed by relaxation and mild thermal treatment to stabilize the films in cell culture medium. Multilayer graphene oxide films form periodic, delaminated buckle textures whose wavelengths and amplitudes can be systematically tuned by variation in the wet deposition process. Human and murine fibroblasts attach to these textured films and remain viable, while developing pronounced alignment and elongation relative to those on planar graphene controls. Compared to lithographic patterning of nanogratings, this method has advantages in the simplicity and scalability of fabrication, as well as the opportunity to couple the use of topographic cues with the unique conductive, adsorptive, or barrier properties of graphene materials for functional biomedical devices. PMID:25848137

Nanorobotic System iTRo for Controllable 1D Micro/nano Material Twisting Test.

PubMed

Lu, Haojian; Shang, Wanfeng; Wei, Xueyong; Yang, Zhan; Fukuda, Toshio; Shen, Yajing

2017-06-08

In-situ micro/nano characterization is an indispensable methodology for material research. However, the precise in-situ SEM twisting of 1D material with large range is still challenge for current techniques, mainly due to the testing device's large size and the misalignment between specimen and the rotation axis. Herein, we propose an in-situ twist test robot (iTRo) to address the above challenges and realize the precise in-situ SEM twisting test for the first time. Firstly, we developed the iTRo and designed a series of control strategies, including assembly error initialization, triple-image alignment (TIA) method for rotation axis alignment, deformation-based contact detection (DCD) method for sample assembly, and switch control for robots cooperation. After that, we chose three typical 1D material, i.e., magnetic microwire Fe 74 B 13 Si 11 C 2 , glass fiber, and human hair, for twisting test and characterized their properties. The results showed that our approach is able to align the sample to the twisting axis accurately, and it can provide large twisting range, heavy load and high controllability. This work fills the blank of current in-situ mechanical characterization methodologies, which is expected to give significant impact in the fundamental nanomaterial research and practical micro/nano characterization.

Mesocrystals in Biominerals and Colloidal Arrays.

PubMed

Bergström, Lennart; Sturm née Rosseeva, Elena V; Salazar-Alvarez, German; Cölfen, Helmut

2015-05-19

Mesocrystals, which originally was a term to designate superstructures of nanocrystals with a common crystallographic orientation, have now evolved to a materials concept. The discovery that many biominerals are mesocrystals generated a large research interest, and it was suggested that mesocrystals result in better mechanical performance and optical properties compared to single crystalline structures. Mesocrystalline biominerals are mainly found in spines or shells, which have to be mechanically optimized for protection or as a load-bearing skeleton. Important examples include red coral and sea urchin spine as well as bones. Mesocrystals can also be formed from purely synthetic components. Biomimetic mineralization and assembly have been used to produce mesocrystals, sometimes with complex hierarchical structures. Important examples include the fluorapatite mesocrystals with gelatin as the structural matrix, and mesocrystalline calcite spicules with impressive strength and flexibility that could be synthesized using silicatein protein fibers as template for calcium carbonate deposition. Self-assembly of nanocrystals can also result in mesocrystals if the nanocrystals have a well-defined size and shape and the assembly conditions are tuned to allow the nanoparticles to align crystallographically. Mesocrystals formed by assembly of monodisperse metallic, semiconducting, and magnetic nanocrystals are a type of colloidal crystal with a well-defined structure on both the atomic and mesoscopic length scale.Mesocrystals typically are hybrid materials between crystalline nanoparticles and interspacing amorphous organic or inorganic layers. This structure allows to combine disparate materials like hard but brittle nanocrystals with a soft and ductile amorphous material, enabling a mechanically optimized structural design as realized in the sea urchin spicule. Furthermore, mesocrystals can combine the properties of individual nanocrystals like the optical quantum size effect, surface plasmon resonance, and size dependent magnetic properties with a mesostructure and morphology tailored for specific applications. Indeed, mesocrystals composed of crystallographically aligned polyhedral or rodlike nanocrystals with anisotropic properties can be materials with strongly directional properties and novel collective emergent properties. An additional advantage of mesocrystals is that they can combine the properties of nanoparticles with a structure on the micro- or macroscale allowing for much easier handling.

Aligned Single Wall Carbon Nanotube Polymer Composites Using an Electric Field

NASA Technical Reports Server (NTRS)

Park, Cheol; Wiklinson, John; Banda, Sumanth; Ounaies, Zoubeida; Wise, Kristopher E.; Sauti, Godfrey; Lillehei, Peter T.; Harrison, Joycelyn S.

2005-01-01

While high shear alignment has been shown to improve the mechanical properties of single wall carbon nanotubes (SWNT)-polymer composites, it is difficult to control and often results in degradation of the electrical and dielectric properties of the composite. Here, we report a novel method to actively align SWNTs in a polymer matrix, which allows for control over the degree of alignment of SWNTs without the side effects of shear alignment. In this process, SWNTs are aligned via field-induced dipolar interactions among the nanotubes under an AC electric field in a liquid matrix followed by immobilization by photopolymerization while maintaining the electric field. Alignment of SWNTs was controlled as a function of magnitude, frequency, and application time of the applied electric field. The degree of SWNT alignment was assessed using optical microscopy and polarized Raman spectroscopy and the morphology of the aligned nanocomposites was investigated by high resolution scanning electron microscopy. The structure of the field induced aligned SWNTs is intrinsically different from that of shear aligned SWNTs. In the present work, SWNTs are not only aligned along the field, but also migrate laterally to form thick, aligned SWNT percolative columns between the electrodes. The actively aligned SWNTs amplify the electrical and dielectric properties in addition to improving the mechanical properties of the composite. All of these properties of the aligned nanocomposites exhibited anisotropic characteristics, which were controllable by tuning the applied field conditions.

Effects of geometry and cell-matrix interactions on the mechanics of 3D engineered microtissues

NASA Astrophysics Data System (ADS)

Bose, Prasenjit; Eyckmans, Jeroen; Chen, Christopher; Reich, Daniel

Approaches to measure and control cell-extracellular matrix (ECM) interactions in a dynamic mechanical environment are important both for studies of mechanobiology and for tissue design for bioengineering applications. We have developed a microtissue-based platform capable of controlling the ECM alignment of 3D engineered microtissues while simultaneously permitting measurement of cellular contractile forces and the tissues' mechanical properties. The tissues self-assemble from cell-laden collagen gels placed in micro-fabricated wells containing sets of flexible elastic pillars. Tissue geometry and ECM alignment are controlled by the pillars' number, shape and location. Optical tracking of the pillars provides readout of the tissues' contractile forces. Magnetic materials bound to selected pillars allow quasi-static or dynamic stretching of the tissue, and together with simultaneous measurements of the tissues' local dynamic strain field, enable characterization of the mechanical properties of the system, including their degree of anisotropy. Results on the effects of symmetry and degree of ECM alignment and organization on the role of cell-ECM interactions in determining tissue mechanical properties will be discussed. This work is supported by NSF CMMI-1463011 and CMMI-1462710.

Directionally Antagonistic Graphene Oxide-Polyurethane Hybrid Aerogel as a Sound Absorber.

PubMed

Oh, Jung-Hwan; Kim, Jieun; Lee, Hyeongrae; Kang, Yeonjune; Oh, Il-Kwon

2018-06-21

Innovative sound absorbers, the design of which is based on carbon nanotubes and graphene derivatives, could be used to make more efficient sound absorbing materials because of their excellent intrinsic mechanical and chemical properties. However, controlling the directional alignments of low-dimensional carbon nanomaterials, such as restacking, alignment, and dispersion, has been a challenging problem when developing sound absorbing forms. Herein, we present the directionally antagonistic graphene oxide-polyurethane hybrid aerogel we developed as a sound absorber, the physical properties of which differ according to the alignment of the microscopic graphene oxide sheets. This porous graphene sound absorber has a microporous hierarchical cellular structure with adjustable stiffness and improved sound absorption performance, thereby overcoming the restrictions of both geometric and function-orientated functions. Furthermore, by controlling the inner cell size and aligned structure of graphene oxide layers in this study, we achieved remarkable improvement of the sound absorption performance at low frequency. This improvement is attributed to multiple scattering of incident and reflection waves on the aligned porous surfaces, and air-viscous resistance damping inside interconnected structures between the urethane foam and the graphene oxide network. Two anisotropic sound absorbers based on the directionally antagonistic graphene oxide-polyurethane hybrid aerogels were fabricated. They show remarkable differences owing to the opposite alignment of graphene oxide layers inside the polyurethane foam and are expected to be appropriate for the engineering design of sound absorbers in consideration of the wave direction.

Magnetic preferential orientation of metal oxide superconducting materials

DOEpatents

Capone, D.W.; Dunlap, B.D.; Veal, B.W.

1990-07-17

A superconductor comprised of a polycrystalline metal oxide such as YBa[sub 2]Cu[sub 3]O[sub 7[minus]X] (where 0 < X < 0.5) exhibits superconducting properties and is capable of conducting very large current densities. By aligning the two-dimensional Cu-O layers which carry the current in the superconducting state in the a- and b-directions, i.e., within the basal plane, a high degree of crystalline axes alignment is provided between adjacent grains permitting the conduction of high current densities. The highly anisotropic diamagnetic susceptibility of the polycrystalline metal oxide material permits the use of an applied magnetic field to orient the individual crystals when in the superconducting state to substantially increase current transport between adjacent grains. In another embodiment, the anisotropic paramagnetic susceptibility of rare-earth ions substituted into the oxide material is made use of as an applied magnetic field orients the particles in a preferential direction. This latter operation can be performed with the material in the normal (non-superconducting) state. 4 figs.

Magnetic preferential orientation of metal oxide superconducting materials

DOEpatents

Capone, Donald W.; Dunlap, Bobby D.; Veal, Boyd W.

1990-01-01

A superconductor comprised of a polycrystalline metal oxide such as YBa.sub.2 Cu.sub.3 O.sub.7-X (where 0

Aligned Carbon Nanotubes for High-Performance Films and Composites

NASA Astrophysics Data System (ADS)

Zhang, Liwen

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Specimen's plane misaligned installation solution based on charge fluctuation inside SEM

NASA Astrophysics Data System (ADS)

Lu, Haojian; Liu, Yanting; Yang, Yuanyuan; Wang, Panbing; Shen, Yajing

2018-04-01

Precise specimen's installation is a sticking point to ensure the characterization accuracy of the in-situ material property test. Although it is common knowledge that specimen's plane misaligned installation (PMI) would cause extra force loading during mechanical testing, there are few effective solutions available to deal with it at the current stage, especially during the in-situ scanning electron microscopy (SEM) test. Taking into consideration the charge fluctuation phenomenon under SEM, this paper proposes a highlight area variation (HAV) method for specimen deformation judgment, i.e., the specimen deformation is defined when the highlight area changes greater than 20% of the initial value of the specimen surface. Three types of specimens with different resistivities, i.e., human hair (electrical resistivity ˜3 × 1012 Ω cm), optical fiber (electrical resistivity ˜1017 Ω cm), and magnetic wire (electrical resistivity ˜2 × 10-5 Ω cm), are chosen to verify the effectiveness of the HAV method. Furthermore, combined with the developed robot-aided alignment system, the specimen's PMI problem can also be solved. In the demonstration, the human hair specimen is installed across two specimen stages and its in-situ twisting (in 360°) test is implemented. The results clearly indicate that the HAV method and the robot-aided alignment system are practical and reliable, and the specimen can be aligned on the same plane and installed precisely with accuracy up to 3 μm. This method will benefit the in-situ SEM material mechanical property test and has a significant impact in fundamental material research.

Extracting material response from simple mechanical tests on hardening-softening-hardening viscoplastic solids

NASA Astrophysics Data System (ADS)

Mohan, Nisha

Compliant foams are usually characterized by a wide range of desirable mechanical properties. These properties include viscoelasticity at different temperatures, energy absorption, recoverability under cyclic loading, impact resistance, and thermal, electrical, acoustic and radiation-resistance. Some foams contain nano-sized features and are used in small-scale devices. This implies that the characteristic dimensions of foams span multiple length scales, rendering modeling their mechanical properties difficult. Continuum mechanics-based models capture some salient experimental features like the linear elastic regime, followed by non-linear plateau stress regime. However, they lack mesostructural physical details. This makes them incapable of accurately predicting local peaks in stress and strain distributions, which significantly affect the deformation paths. Atomistic methods are capable of capturing the physical origins of deformation at smaller scales, but suffer from impractical computational intensity. Capturing deformation at the so-called meso-scale, which is capable of describing the phenomenon at a continuum level, but with some physical insights, requires developing new theoretical approaches. A fundamental question that motivates the modeling of foams is `how to extract the intrinsic material response from simple mechanical test data, such as stress vs. strain response?' A 3D model was developed to simulate the mechanical response of foam-type materials. The novelty of this model includes unique features such as the hardening-softening-hardening material response, strain rate-dependence, and plastically compressible solids with plastic non-normality. Suggestive links from atomistic simulations of foams were borrowed to formulate a physically informed hardening material input function. Motivated by a model that qualitatively captured the response of foam-type vertically aligned carbon nanotube (VACNT) pillars under uniaxial compression [2011,"Analysis of Uniaxial Compression of Vertically Aligned Carbon Nanotubes," J. Mech.Phys. Solids, 59, pp. 2227--2237, Erratum 60, 1753-1756 (2012)], the property space exploration was advanced to three types of simple mechanical tests: 1) uniaxial compression, 2) uniaxial tension, and 3) nanoindentation with a conical and a flat-punch tip. The simulations attempt to explain some of the salient features in experimental data, like 1) The initial linear elastic response. 2) One or more nonlinear instabilities, yielding, and hardening. The model-inherent relationships between the material properties and the overall stress-strain behavior were validated against the available experimental data. The material properties include the gradient in stiffness along the height, plastic and elastic compressibility, and hardening. Each of these tests was evaluated in terms of their efficiency in extracting material properties. The uniaxial simulation results proved to be a combination of structural and material influences. Out of all deformation paths, flat-punch indentation proved to be superior since it is the most sensitive in capturing the material properties.

Electronic Properties of Free-Standing Surfactant-Capped Lead Halide Perovskite Nanocrystals Isolated in Vacuo.

PubMed

Milosavljevic, Aleksandar R; Bozanic, Dusan; Sadhu, Subha; Vukmirovic, Nenad; Dojcilovic, Radovan; Sapkota, Pitambar; Huang, Weixin; Bozek, John D; Nicolas, Christophe; Nahon, Laurent; Ptasinska, Sylwia

2018-06-14

We report an investigation of lead halide perovskite CH3NH3PbBr3 nanocrystals and associated ligand molecules, by combining several different state-of-the-art experimental techniques, including synchrotron radiation based XPS and VUV PES of free-standing nanocrystals isolated in vacuum. By using this novel approach for perovskite materials we could directly obtain a complete band alignment to vacuum of both CH3NH3PbBr3 nanocrystals and the ligands widely used in their preparation. We discuss possible influence of the ligand molecules to apparent perovskite properties, and we compare the electronic properties of nanocrystals to that of bulk material. The experimental results were supported by DFT calculations.

Magnetic properties of permalloy-coated organic tubules

NASA Astrophysics Data System (ADS)

Krebs, J. J.; Rubinstein, M.; Lubitz, P.; Harford, M. Z.; Baral, S.; Shashidar, R.; Ho, Y. S.; Chow, G. M.; Qadri, S.

1991-11-01

An initial investigation is presented of the ferromagnetic properties of a novel type of magnetic composite, viz., permalloy-coated submicron diameter hollow cylinders or tubules. The tubules form spontaneously from an organic material, a diacetylenic phosopholipid, and were used as templates on which the ferromagnetic material was deposited by electroless deposition. The permalloy-coated tubules were dispersed in an epoxy matrix to measure the magnetization and ferromagnetic resonance (FMR) properties of individual tubules. The nature of the magnetic anisotropy and the FMR spectra observed confirmed that the tubules are well aligned by a magnetic field during the epoxy curing. The FMR spectra are interpreted in terms of a powder pattern distribution of thin-film spectra consistent with the large diameter-to-thickness ratio.

EMTA-NLA

DOE Office of Scientific and Technical Information (OSTI.GOV)

2009-10-14

EMTA-NLA is a computer program for analyzing the nonlinear stiffness, strength, and thermo-elastic properties of discontinuous fiber composite materials. Discontinuous fiber composites are chopped-fiber reinforced polymer materials that are formed by injection molding or compression molding techniques. The fibers tend to align during forming as the composite flows and fills the mold. EMTA-NLA can read the fiber orientation data from the molding software, Autodesk Moldflow Plastics Insight, and calculate the local material properties for accurately analyzing the warpage, stiffness, and strength of the as-formed composite part using the commercial NLA software. Therefore, EMTA-NLA is a unique assembly of mathematical algorithmsmore » that provide a one-of-a-kind composites constitutive model that links these two powerful commercial software packages.« less

Enhanced graphitization of carbon around carbon nanotubes during the formation of carbon nanotube/graphite composites by pyrolysis of carbon nanotube/polyaniline composites.

PubMed

Nam, Dong Hoon; Cha, Seung Il; Jeong, Yong Jin; Hong, Soon Hyung

2013-11-01

The carbon nanotubes (CNTs) are actively applied to the reinforcements for composite materials during last decade. One of the attempts is development of CNT/Carbon composites. Although there are some reports on the enhancement of mechanical properties by addition of CNTs in carbon or carbon fiber, it is far below the expectation. Considering the microstructure of carbon materials such as carbon fiber, the properties of them can be modified and enhanced by control of graphitization and alignment of graphene planes. In this study, enhanced graphitization of carbon has been observed the vicinity of CNTs during the pyrolysis of CNT/Polyaniline composites. As a result, novel types of composite, consisting of treading CNTs and coated graphite, can be fabricated. High-resolution transmission electron microscopy revealed a specific orientation relationship between the graphene layers and the CNTs, with an angle of 110 degrees between the layers and the CNT axis. The possibility of graphene alignment control in the carbon by the addition of CNTs is demonstrated.

Freeze cast porous barium titanate for enhanced piezoelectric energy harvesting

NASA Astrophysics Data System (ADS)

Roscow, J. I.; Zhang, Y.; Kraśny, M. J.; Lewis, R. W. C.; Taylor, J.; Bowen, C. R.

2018-06-01

Energy harvesting is an important developing technology for a new generation of self-powered sensor networks. This paper demonstrates the significant improvement in the piezoelectric energy harvesting performance of barium titanate by forming highly aligned porosity using freeze casting. Firstly, a finite element model demonstrating the effect of pore morphology and angle with respect to poling field on the poling behaviour of porous ferroelectrics was developed. A second model was then developed to understand the influence of microstructure-property relationships on the poling behaviour of porous freeze cast ferroelectric materials and their resultant piezoelectric and energy harvesting properties. To compare with model predictions, porous barium titanate was fabricated using freeze casting to form highly aligned microstructures with excellent longitudinal piezoelectric strain coefficients, d 33. The freeze cast barium titanate with 45 vol.% porosity had a d 33  =  134.5 pC N‑1 compared to d 33  =  144.5 pC N‑1 for dense barium titanate. The d 33 coefficients of the freeze cast materials were also higher than materials with uniformly distributed spherical porosity due to improved poling of the aligned microstructures, as predicted by the models. Both model and experimental data indicated that introducing porosity provides a large reduction in the permittivity () of barium titanate, which leads to a substantial increase in energy harvesting figure of merit, , with a maximum of 3.79 pm2 N‑1 for barium titanate with 45 vol.% porosity, compared to only 1.40 pm2 N‑1 for dense barium titanate. Dense and porous barium titanate materials were then used to harvest energy from a mechanical excitation by rectification and storage of the piezoelectric charge on a capacitor. The porous barium titanate charged the capacitor to a voltage of 234 mV compared to 96 mV for the dense material, indicating a 2.4-fold increase that was similar to that predicted by the energy harvesting figures of merit.

Studies on in situ magnetic alignment of bonded anisotropic Nd-Fe-B alloy powders

DOE PAGES

Nlebedim, I. C.; Ucar, Huseyin; Hatter, Christine B.; ...

2016-08-30

We presented some considerations for achieving high degree of alignment in polymer bonded permanent magnets via the results of a study on in situ magnetic alignment of anisotropic Nd-Fe-B magnet powders. Contributions from effect of the alignment temperature, alignment magnetic field and the properties of the polymer on the hard magnetic properties of the bonded magnet were considered. Moreover, the thermo-rheological properties of the polymer and the response of the magnet powders to the applied magnetic field indicate that hard magnetic properties were optimized at an alignment temperature just above the melting temperature of the EVA co-polymer. This agrees withmore » an observed correlation between the change in magnetization due to improved magnetic alignment of the anisotropic powders and the change in viscosity of the binder. Finally, manufacturing cost can be minimized by identifying optimum alignment temperatures and magnetic field strengths.« less

Studies on in situ magnetic alignment of bonded anisotropic Nd-Fe-B alloy powders

NASA Astrophysics Data System (ADS)

Nlebedim, I. C.; Ucar, Huseyin; Hatter, Christine B.; McCallum, R. W.; McCall, Scott K.; Kramer, M. J.; Paranthaman, M. Parans

2017-01-01

Considerations for achieving high degree of alignment in polymer bonded permanent magnets are presented via the results of a study on in situ magnetic alignment of anisotropic Nd-Fe-B magnet powders. Contributions from effect of the alignment temperature, alignment magnetic field and the properties of the polymer on the hard magnetic properties of the bonded magnet were considered. The thermo-rheological properties of the polymer and the response of the magnet powders to the applied magnetic field indicate that hard magnetic properties were optimized at an alignment temperature just above the melting temperature of the EVA co-polymer. This agrees with an observed correlation between the change in magnetization due to improved magnetic alignment of the anisotropic powders and the change in viscosity of the binder. Manufacturing cost can be minimized by identifying optimum alignment temperatures and magnetic field strengths.

Complex Anisotropic Structure of the Mantle Wedge Beneath Kamchatka Volcanoes

NASA Astrophysics Data System (ADS)

Levin, V.; Park, J.; Gordeev, E.; Droznin, D.

2002-12-01

A wedge of mantle material above the subducting lithospheric plate at a convergent margin is among the most dynamic environments of the Earth's interior. Deformation and transport of solid and volatile phases within this region control the fundamental process of elemental exchange between the surficial layers and the interior of the planet. A helpful property in the study of material deformation and transport within the upper mantle is seismic anisotropy, which may reflect both microscopic effects of preferentialy aligned crystals of olivine and orthopyroxene and macroscopic effects of systematic cracks, melt lenses, layering etc. Through the mapping of anisotropic properties within the mantle wedge we can establish patterns of deformation. Volatile content affects olivine alignment, so regions of anomalous volatile content may be evident. Indicators of seismic anisotropy commonly employed in upper mantle studies include shear wave birefringence and mode-conversion between compressional and shear body waves. When combined together, these techniques offer complementary constraints on the location and intensity of anisotropic properties. The eastern coast of southern Kamchatka overlies a vigorous convergent margin where the Pacific plate descends at a rate of almost 80 mm/yr towards the northwest. We extracted seismic anisotropy indicators from two data sets sensitive to the anisotropic properties of the uppermost mantle. Firstly, we evaluated teleseismic receiver functions for a number of sites, and found ample evidence for anisotropicaly-influenced P-to-S mode conversion. Secondly, we measured splitting in S waves of earthquakes with sources within the downgoing slab. The first set of observations provides constraints on the depth ranges where strong changes in anisotropic properties take place. The local splitting data provides constraints on the cumulative strength of anisotropic properties along specific pathways through the mantle wedge and possibly parts of the slab. To explain the vertical stratification of anisotropy implied from receiver functions, and the strong lateral dependence of shear-wave splitting observations, we cannot rely on simple models of mantle wedge behaviour e.g., olivine-crystal alignment through subduction-driven corner flow. Diverse mechanisms can contribute to the observed pattern of anisotropic properties, with volatiles likely being a key influence. For instance, we find evidence in favor of a slow-symmetry-axis anisotropy within the uppermost 10-20 km of the mantle wedge, implying either excessive hydration of the mantle or else a presence of systematically aligned volatile-filled cracks or lenses. Also, shear-wave splitting is weak beneath the Avachinsky-Koryaksky volcanic center, suggesting either vertical flow or the influence of volatiles and/or thermally-enhanced diffusion creep.

Vertically aligned carbon nanofibers and related structures: Controlled synthesis and directed assembly

NASA Astrophysics Data System (ADS)

Melechko, A. V.; Merkulov, V. I.; McKnight, T. E.; Guillorn, M. A.; Klein, K. L.; Lowndes, D. H.; Simpson, M. L.

2005-02-01

The controlled synthesis of materials by methods that permit their assembly into functional nanoscale structures lies at the crux of the emerging field of nanotechnology. Although only one of several materials families is of interest, carbon-based nanostructured materials continue to attract a disproportionate share of research effort, in part because of their wide-ranging properties. Additionally, developments of the past decade in the controlled synthesis of carbon nanotubes and nanofibers have opened additional possibilities for their use as functional elements in numerous applications. Vertically aligned carbon nanofibers (VACNFs) are a subclass of carbon nanostructured materials that can be produced with a high degree of control using catalytic plasma-enhanced chemical-vapor deposition (C-PECVD). Using C-PECVD the location, diameter, length, shape, chemical composition, and orientation can be controlled during VACNF synthesis. Here we review the CVD and PECVD systems, growth control mechanisms, catalyst preparation, resultant carbon nanostructures, and VACNF properties. This is followed by a review of many of the application areas for carbon nanotubes and nanofibers including electron field-emission sources, electrochemical probes, functionalized sensor elements, scanning probe microscopy tips, nanoelectromechanical systems (NEMS), hydrogen and charge storage, and catalyst support. We end by noting gaps in the understanding of VACNF growth mechanisms and the challenges remaining in the development of methods for an even more comprehensive control of the carbon nanofiber synthesis process.

Structural properties of H13 tool steel parts produced with use of selective laser melting technology

NASA Astrophysics Data System (ADS)

Šafka, J.; Ackermann, M.; Voleský, L.

2016-04-01

This paper deals with establishing of building parameters for 1.2344 (H13) tool steel processed using Selective Laser Melting (SLM) technology with layer thickness of 50 µm. In the first part of the work, testing matrix of models in the form of a cube with chamfered edge were built under various building parameters such as laser scanning speed and laser power. Resulting models were subjected to set of tests including measurement of surface roughness, inspection of inner structure with aid of Light Optical Microscopy and Scanning Electron Microscopy and evaluation of micro-hardness. These tests helped us to evaluate an influence of changes in building strategy to the properties of the resulting model. In the second part of the work, mechanical properties of the H13 steel were examined. For this purpose, the set of samples in the form of “dog bone” were printed under three different alignments towards the building plate and tested on universal testing machine. Mechanical testing of the samples should then reveal if the different orientation and thus different layering of the material somehow influence its mechanical properties. For this type of material, the producer provides the parameters for layer thickness of 30 µm only. Thus, our 50 µm building strategy brings shortening of the building time which is valuable especially for large models. Results of mechanical tests show slight variation in mechanical properties for various alignment of the sample.

Synthesis and supramolecular assembly of biomimetic polymers

NASA Astrophysics Data System (ADS)

Marciel, Amanda Brittany

A grand challenge in materials chemistry is the synthesis of macromolecules and polymers with precise shapes and architectures. Polymer microstructure and architecture strongly affect the resulting functionality of advanced materials, yet understanding the static and dynamic properties of these complex macromolecules in bulk has been difficult due to their inherit polydispersity. Single molecule studies have provided a wealth of information on linear flexible and semi-flexible polymers in dilute solutions. However, few investigations have focused on industrially relevant complex topologies (e.g., star, comb, hyperbranched polymers) in industrially relevant solution conditions (e.g., semi-dilute, concentrated). Therefore, from this perspective there is a strong need to synthesize precision complex architectures for bulk studies as well as complex architectures compatible with current single molecule techniques to study static and dynamic polymer properties. In this way, we developed a hybrid synthetic strategy to produce branched polymer architectures based on chemically modified DNA. Overall, this approach enables control of backbone length and flexibility, as well as branch grafting density and chemical identity. We utilized a two-step scheme based on enzymatic incorporation of non-natural nucleotides containing bioorthogonal dibenzocyclooctyne (DBCO) functional groups along the main polymer backbone, followed by copper-free "click" chemistry to graft synthetic polymer branches or oligonucleotide branches to the DNA backbone, thereby allowing for the synthesis of a variety of polymer architectures, including three-arm stars, H-polymers, graft block copolymers, and comb polymers for materials assembly and single molecule studies. Bulk materials properties are also affected by industrial processing conditions that alter polymer morphology. Therefore, in an alternative strategy we developed a microfluidic-based approach to assemble highly aligned synthetic oligopeptides nanostructures using microscale extensional flows. This strategy enabled reproducible, reliable fabrication of aligned hierarchical constructs that do not form spontaneously in solution. In this way, fluidic-directed assembly of supramolecular structures allows for unprecedented manipulation at the nano- and mesoscale, which has the potential to provide rapid and efficient control of functional materials properties.

Anisotropic, lightweight, strong, and super thermally insulating nanowood with naturally aligned nanocellulose

PubMed Central

Li, Tian; Song, Jianwei; Zhao, Xinpeng; Yang, Zhi; Pastel, Glenn; Xu, Shaomao; Jia, Chao; Dai, Jiaqi; Chen, Chaoji; Gong, Amy; Jiang, Feng; Yao, Yonggang; Fan, Tianzhu; Yang, Bao; Wågberg, Lars; Yang, Ronggui; Hu, Liangbing

2018-01-01

There has been a growing interest in thermal management materials due to the prevailing energy challenges and unfulfilled needs for thermal insulation applications. We demonstrate the exceptional thermal management capabilities of a large-scale, hierarchal alignment of cellulose nanofibrils directly fabricated from wood, hereafter referred to as nanowood. Nanowood exhibits anisotropic thermal properties with an extremely low thermal conductivity of 0.03 W/m·K in the transverse direction (perpendicular to the nanofibrils) and approximately two times higher thermal conductivity of 0.06 W/m·K in the axial direction due to the hierarchically aligned nanofibrils within the highly porous backbone. The anisotropy of the thermal conductivity enables efficient thermal dissipation along the axial direction, thereby preventing local overheating on the illuminated side while yielding improved thermal insulation along the backside that cannot be obtained with isotropic thermal insulators. The nanowood also shows a low emissivity of <5% over the solar spectrum with the ability to effectively reflect solar thermal energy. Moreover, the nanowood is lightweight yet strong, owing to the effective bonding between the aligned cellulose nanofibrils with a high compressive strength of 13 MPa in the axial direction and 20 MPa in the transverse direction at 75% strain, which exceeds other thermal insulation materials, such as silica and polymer aerogels, Styrofoam, and wool. The excellent thermal management, abundance, biodegradability, high mechanical strength, low mass density, and manufacturing scalability of the nanowood make this material highly attractive for practical thermal insulation applications. PMID:29536048

Self-Assembled Epitaxial Au–Oxide Vertically Aligned Nanocomposites for Nanoscale Metamaterials

DOE PAGES

Li, Leigang; Sun, Liuyang; Gomez-Diaz, Juan Sebastian; ...

2016-05-17

Metamaterials made of nanoscale inclusions or artificial unit cells exhibit exotic optical properties that do not exist in natural materials. Promising applications, such as super-resolution imaging, cloaking, hyperbolic propagation, and ultrafast phase velocities have been demonstrated based on mostly micrometer-scale metamaterials and few nanoscale metamaterials. To date, most metamaterials are created using costly and tedious fabrication techniques with limited paths toward reliable large-scale fabrication. In this work, we demonstrate the one-step direct growth of self-assembled epitaxial metal–oxide nanocomposites as a drastically different approach to fabricating large-area nanostructured metamaterials. Using pulsed laser deposition, we fabricated nanocomposite films with vertically aligned goldmore » (Au) nanopillars (~20 nm in diameter) embedded in various oxide matrices with high epitaxial quality. Strong, broad absorption features in the measured absorbance spectrum are clear signatures of plasmon resonances of Au nanopillars. By tuning their densities on selected substrates, anisotropic optical properties are demonstrated via angular dependent and polarization resolved reflectivity measurements and reproduced by full-wave simulations and effective medium theory. Our model predicts exotic properties, such as zero permittivity responses and topological transitions. In conclusion, our studies suggest that these self-assembled metal–oxide nanostructures provide an exciting new material platform to control and enhance optical response at nanometer scales.« less

Nonhomogeneous morphology and the elastic modulus of aligned carbon nanotube films

NASA Astrophysics Data System (ADS)

Won, Yoonjin; Gao, Yuan; Guzman de Villoria, Roberto; Wardle, Brian L.; Xiang, Rong; Maruyama, Shigeo; Kenny, Thomas W.; Goodson, Kenneth E.

2015-11-01

Carbon nanotube (CNT) arrays offer the potential to develop nanostructured materials that leverage their outstanding physical properties. Vertically aligned carbon nanotubes (VACNTs), also named CNT forests, CNT arrays, or CNT turfs, can provide high heat conductivity and sufficient mechanical compliance to accommodate thermal expansion mismatch for use as thermal interface materials (TIMs). This paper reports measurements of the in-plane moduli of vertically aligned, single-walled CNT (SWCNT) and multi-walled CNT (MWCNT) films. The mechanical response of these films is related to the nonhomogeneous morphology of the grown nanotubes, such as entangled nanotubes of a top crust layer, aligned CNTs in the middle region, and CNTs in the bottom layer. To investigate how the entanglements govern the overall mechanical moduli of CNT films, we remove the crust layer consisting of CNT entanglements by etching the CNT films from the top. A microfabricated cantilever technique shows that crust removal reduces the resulting moduli of the etched SWCNT films by as much as 40%, whereas the moduli of the etched MWCNT films do not change significantly, suggesting a minimal crust effect on the film modulus for thick MWCNT films (>90 μm). This improved understanding will allow us to engineer the mechanical moduli of CNT films for TIMs or packaging applications.

Thermal Conductivity of Polymer Copoly(Ethylene Vinyl Acetate)/Nano-Filler Blends

NASA Technical Reports Server (NTRS)

Ghose, S.; Watson, K. A.; Working, D. C.; Connell, J. W.; Smith, J. G., Jr.; Lin, Y.; Sun, Y. P.

2007-01-01

The development of flexible, thermally conductive fabrics and plastic tubes for the Liquid Cooling and Ventilation Garment (LCVG) are needed to reduce weight and improve the mobility, comfort, and performance of future spacesuits. Such improvements would allow astronauts to operate more efficiently and safely for extended extravehicular activities. As a continuation of our work on the improvement of thermal conductivity (TC) of polymeric materials, nanocomposites were prepared from copoly(ethylene vinyl acetate), trade name Elvax 260 , metallized carbon nanofibers (CNFs), nickel (Ni) nanostrands, boron nitride both alone and as mixtures with aluminum powder. The nanocomposites were prepared by melt mixing at various loading levels and subsequently fabricated into several material forms (i.e., ribbons, tubes, and compression molded plaques) for analysis. Ribbons and tubes were extruded to form samples in which the nanoparticles were aligned in the direction of flow. The degree of dispersion and alignment of the nanoparticles were investigated using high-resolution scanning electron microscopy. Tensile properties of the aligned samples were determined at room temperature. TC measurements were performed using a laser flash (Nanoflash ) technique. The TC of the samples was measured in both the direction of alignment as well as transverse. Tubing of comparable dimensions to that used in the LCVG was extruded from select compositions and the thermal conductivities of the tubes measured.

Quasi-one dimensional (Q1D) nanostructures: Synthesis, integration and device application

NASA Astrophysics Data System (ADS)

Chien, Chung-Jen

Quasi-one-dimensional (Q1D) nanostructures such as nanotubes and nanowires have been widely regarded as the potential building blocks for nanoscale electronic, optoelectronic and sensing devices. In this work, the content can be divided into three categories: Nano-material synthesis and characterizations, alignment and integration, physical properties and application. The dissertation consists of seven chapters as following. Chapter 1 will give an introduction to low dimensional nano-materials. Chapter 2 explains the mechanism how Q1D nanostructure grows. Chapter 3 describes the methods how we horizontally and vertically align the Q1D nanostructure. Chapter 4 and 5 are the electrical and optical device characterization respectively. Chapter 6 demonstrates the integration of Q1D nanostructures and the device application. The last chapter will discuss the future work and conclusion of the thesis.

Loading mode dependent effective properties of octet-truss lattice structures using 3D-printing

NASA Astrophysics Data System (ADS)

Challapalli, Adithya

Cellular materials, often called lattice materials, are increasingly receiving attention for their ultralight structures with high specific strength, excellent impact absorption, acoustic insulation, heat dissipation media and compact heat exchangers. In alignment with emerging additive manufacturing (AM) technology, realization of the structural applications of the lattice materials appears to be becoming faster. Considering the direction dependent material properties of the products with AM, by directionally dependent printing resolution, effective moduli of lattice structures appear to be directionally dependent. In this paper, a constitutive model of a lattice structure, which is an octet-truss with a base material having an orthotropic material property considering AM is developed. In a case study, polyjet based 3D printing material having an orthotropic property with a 9% difference in the principal direction provides difference in the axial and shear moduli in the octet-truss by 2.3 and 4.6%. Experimental validation for the effective properties of a 3D printed octet-truss is done for uniaxial tension and compression test. The theoretical value based on the micro-buckling of truss member are used to estimate the failure strength. Modulus value appears a little overestimate compared with the experiment. Finite element (FE) simulations for uniaxial compression and tension of octettruss lattice materials are conducted. New effective properties for the octet-truss lattice structure are developed considering the observed behavior of the octet-truss structure under macroscopic compression and tension trough simulations.

Enhanced piezoresponse of highly aligned electrospun poly(vinylidene fluoride) nanofibers

NASA Astrophysics Data System (ADS)

Kang, Sung Bum; Won, Sang Hyuk; Im, Min Ji; Kim, Chan Ul; Park, Won Il; Baik, Jeong Min; Choi, Kyoung Jin

2017-09-01

Well-ordered nanostructure arrays with controlled densities can potentially improve material properties; however, their fabrication typically involves the use of complicated processing techniques. In this work, we demonstrate a uniaxial alignment procedure for fabricating poly(vinylidene fluoride) (PVDF) electrospun nanofibers (NFs) by introducing collectors with additional steps. The mechanism of the observed NF alignment, which occurs due to the concentration of lateral electric field lines around collector steps, has been elucidated via finite-difference time-domain simulations. The membranes composed of well-aligned PVDF NFs are characterized by a higher content of the PVDF β-phase, as compared to those manufactured from randomly orientated fibers. The piezoelectric energy harvester, which was fabricated by transferring well-aligned PVDF NFs onto flexible substrates with Ag electrodes attached to both sides, exhibited a 2-fold increase in the output voltage and a 3-fold increase in the output current as compared to the corresponding values obtained for the device manufactured from randomly oriented NFs. The enhanced piezoresponse observed for the aligned PVDF NFs is due to their higher β-phase content, denser structure, smaller effective radius of curvature during bending, greater applied strain, and higher fraction of contributing NFs.

Structure-Property Relations in Carbon Nanotube Fibers by Downscaling Solution Processing.

PubMed

Headrick, Robert J; Tsentalovich, Dmitri E; Berdegué, Julián; Bengio, Elie Amram; Liberman, Lucy; Kleinerman, Olga; Lucas, Matthew S; Talmon, Yeshayahu; Pasquali, Matteo

2018-03-01

At the microscopic scale, carbon nanotubes (CNTs) combine impressive tensile strength and electrical conductivity; however, their macroscopic counterparts have not met expectations. The reasons are variously attributed to inherent CNT sample properties (diameter and helicity polydispersity, high defect density, insufficient length) and manufacturing shortcomings (inadequate ordering and packing), which can lead to poor transmission of stress and current. To efficiently investigate the disparity between microscopic and macroscopic properties, a new method is introduced for processing microgram quantities of CNTs into highly oriented and well-packed fibers. CNTs are dissolved into chlorosulfonic acid and processed into aligned films; each film can be peeled and twisted into multiple discrete fibers. Fibers fabricated by this method and solution-spinning are directly compared to determine the impact of alignment, twist, packing density, and length. Surprisingly, these discrete fibers can be twice as strong as their solution-spun counterparts despite a lower degree of alignment. Strength appears to be more sensitive to internal twist and packing density, while fiber conductivity is essentially equivalent among the two sets of samples. Importantly, this rapid fiber manufacturing method uses three orders of magnitude less material than solution spinning, expanding the experimental parameter space and enabling the exploration of unique CNT sources. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Static dielectric properties of an ensemble of restricted one-dimensional oscillators

NASA Astrophysics Data System (ADS)

Tjipto Margo, Broto

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Flexible and Lightweight Pressure Sensor Based on Carbon Nanotube/Thermoplastic Polyurethane-Aligned Conductive Foam with Superior Compressibility and Stability.

PubMed

Huang, Wenju; Dai, Kun; Zhai, Yue; Liu, Hu; Zhan, Pengfei; Gao, Jiachen; Zheng, Guoqiang; Liu, Chuntai; Shen, Changyu

2017-12-06

Flexible and lightweight carbon nanotube (CNT)/thermoplastic polyurethane (TPU) conductive foam with a novel aligned porous structure was fabricated. The density of the aligned porous material was as low as 0.123 g·cm -3 . Homogeneous dispersion of CNTs was achieved through the skeleton of the foam, and an ultralow percolation threshold of 0.0023 vol % was obtained. Compared with the disordered foam, mechanical properties of the aligned foam were enhanced and the piezoresistive stability of the flexible foam was improved significantly. The compression strength of the aligned TPU foam increases by 30.7% at the strain of 50%, and the stress of the aligned foam is 22 times that of the disordered foam at the strain of 90%. Importantly, the resistance variation of the aligned foam shows a fascinating linear characteristic under the applied strain until 77%, which would benefit the application of the foam as a desired pressure sensor. During multiple cyclic compression-release measurements, the aligned conductive CNT/TPU foam represents excellent reversibility and reproducibility in terms of resistance. This nice capability benefits from the aligned porous structure composed of ladderlike cells along the orientation direction. Simultaneously, the human motion detections, such as walk, jump, squat, etc. were demonstrated by using our flexible pressure sensor. Because of the lightweight, flexibility, high compressibility, excellent reversibility, and reproducibility of the conductive aligned foam, the present study is capable of providing new insights into the fabrication of a high-performance pressure sensor.

Enhancing the value of commodity polymers: Part 1. Structure-property relationships in composite materials based on maleated polypropylene/inorganic phosphate glasses. Part 2. New value-added applications for polyesters

NASA Astrophysics Data System (ADS)

Gupta, Mohit

The first part of the thesis (Chapters 2 & 3) describes a new class of organic polymer/inorganic glass composite materials with property improvements that are impossible to achieve with classical polymer blends or composites. These materials exhibit good processability, superior mechanical performance, good thermal stability, and have excellent gas barrier properties. Low glass transition temperature phosphate glasses (Pglass) are used as inorganic fillers and slightly maleated polypropylene is used as the organic polymer matrix. The Pglass, which was dispersed as spherical droplets in the unoriented composites can be elongated into high aspect ratio platelets during the biaxial stretching process. Biaxially oriented films exhibited a brick wall type microstructure with highly aligned inorganic platelets in a ductile organic matrix and the oxygen barrier properties are significantly improved due to presence of Pglass platelets as impermeable inclusions. Mechanical properties of the biaxially oriented films showed significant improvements compared to neat polymer due to uniform dispersion of the Pglass platelets. Properly dispersed and aligned platelets have proven to be very effective for increasing the composite modulus. These developed materials therefore show promise to help fulfill the ever increasing demand for new advanced materials for a wide variety of advanced packaging applications because of their gas barrier properties, flexibility, transparency, mechanical strength and performance under humid conditions. The second part of the thesis (Chapters 4 & 5) describes new value-added applications for polyesters. Chapter 4 reports a novel process for the decolorization of green and blue colored PET bottle flakes using hydrogen peroxide. The decolorized flakes were characterized for color, intrinsic viscosity values. Decolorized flakes exhibited color values similar to those of colorless recycled PET and even though IV values decreased, bleached flakes still exhibit useful molecular weight. The consumption of H2O2 during the bleaching process was quantified by titrating the residual peroxide using a standard solution of potassium permanganate. Chapter 5 reports synthesis of ductile amorphous polymers which change their color as a function of mechanical deformation. Cyano--OPV moieties were covalently incorporated into the backbone of amorphous polyester PETG. The materials exhibit a significant color change upon compression consistent with efficient breakup of the dye aggregates upon deformation and therefore can be useful for technological applications that require smart coatings with integrated scratch detectors.

Magnet-assisted device-level alignment for the fabrication of membrane-sandwiched polydimethylsiloxane microfluidic devices

NASA Astrophysics Data System (ADS)

Lu, J.-C.; Liao, W.-H.; Tung, Y.-C.

2012-07-01

Polydimethylsiloxane (PDMS) microfluidic device is one of the most essential techniques that advance microfluidics research in recent decades. PDMS is broadly exploited to construct microfluidic devices due to its unique and advantageous material properties. To realize more functionalities, PDMS microfluidic devices with multi-layer architectures, especially those with sandwiched membranes, have been developed for various applications. However, existing alignment methods for device fabrication are mainly based on manual observations, which are time consuming, inaccurate and inconsistent. This paper develops a magnet-assisted alignment method to enhance device-level alignment accuracy and precision without complicated fabrication processes. In the developed alignment method, magnets are embedded into PDMS layers at the corners of the device. The paired magnets are arranged in symmetric positions at each PDMS layer, and the magnetic attraction force automatically pulls the PDMS layers into the aligned position during assembly. This paper also applies the method to construct a practical microfluidic device, a tunable chaotic micromixer. The results demonstrate the successful operation of the device without failure, which suggests the accurate alignment and reliable bonding achieved by the method. Consequently, the fabrication method developed in this paper is promising to be exploited to construct various membrane-sandwiched PDMS microfluidic devices with more integrated functionalities to advance microfluidics research.

Designing Semiconductor Heterostructures Using Digitally Accessible Electronic-Structure Data

NASA Astrophysics Data System (ADS)

Shapera, Ethan; Schleife, Andre

Semiconductor sandwich structures, so-called heterojunctions, are at the heart of modern applications with tremendous societal impact: Light-emitting diodes shape the future of lighting and solar cells are promising for renewable energy. However, their computer-based design is hampered by the high cost of electronic structure techniques used to select materials based on alignment of valence and conduction bands and to evaluate excited state properties. We describe, validate, and demonstrate an open source Python framework which rapidly screens existing online databases and user-provided data to find combinations of suitable, previously fabricated materials for optoelectronic applications. The branch point energy aligns valence and conduction bands of different materials, requiring only the bulk density functional theory band structure. We train machine learning algorithms to predict the dielectric constant, electron mobility, and hole mobility with material descriptors available in online databases. Using CdSe and InP as emitting layers for LEDs and CH3NH3PbI3 and nanoparticle PbS as absorbers for solar cells, we demonstrate our broadly applicable, automated method.

Programmable and electrically controllable light scattering from surface-polymer stabilized liquid crystals.

PubMed

Bédard-Arcand, Jean-Philippe; Galstian, Tigran

2012-08-01

We report the creation and study of a polarization independent light scattering material system based on surface-polymer stabilized liquid crystals. Originally isotropic cell substrates with thin nonpolymerized reactive mesogen layers are used for the alignment of pure nonreactive nematic liquid crystals. The partial interdiffusion of the two materials followed by the application of orienting external electric and magnetic fields and the photo polymerization of the reactive mesogen allow us the control of electro-optic scattering properties of obtained cells.

Directly measuring of thermal pulse transfer in one-dimensional highly aligned carbon nanotubes

PubMed Central

Zhang, Guang; Liu, Changhong; Fan, Shoushan

2013-01-01

Using a simple and precise instrument system, we directly measured the thermo-physical properties of one-dimensional highly aligned carbon nanotubes (CNTs). A kind of CNT-based macroscopic materials named super aligned carbon nanotube (SACNT) buckypapers was measured in our experiment. We defined a new one-dimensional parameter, the “thermal transfer speed” to characterize the thermal damping mechanisms in the SACNT buckypapers. Our results indicated that the SACNT buckypapers with different densities have obviously different thermal transfer speeds. Furthermore, we found that the thermal transfer speed of high-density SACNT buckypapers may have an obvious damping factor along the CNTs aligned direction. The anisotropic thermal diffusivities of SACNT buckypapers could be calculated by the thermal transfer speeds. The thermal diffusivities obviously increase as the buckypaper-density increases. For parallel SACNT buckypapers, the thermal diffusivity could be as high as 562.2 ± 55.4 mm2/s. The thermal conductivities of these SACNT buckypapers were also calculated by the equation k = Cpαρ. PMID:23989589

Directly measuring of thermal pulse transfer in one-dimensional highly aligned carbon nanotubes.

PubMed

Zhang, Guang; Liu, Changhong; Fan, Shoushan

2013-01-01

Using a simple and precise instrument system, we directly measured the thermo-physical properties of one-dimensional highly aligned carbon nanotubes (CNTs). A kind of CNT-based macroscopic materials named super aligned carbon nanotube (SACNT) buckypapers was measured in our experiment. We defined a new one-dimensional parameter, the "thermal transfer speed" to characterize the thermal damping mechanisms in the SACNT buckypapers. Our results indicated that the SACNT buckypapers with different densities have obviously different thermal transfer speeds. Furthermore, we found that the thermal transfer speed of high-density SACNT buckypapers may have an obvious damping factor along the CNTs aligned direction. The anisotropic thermal diffusivities of SACNT buckypapers could be calculated by the thermal transfer speeds. The thermal diffusivities obviously increase as the buckypaper-density increases. For parallel SACNT buckypapers, the thermal diffusivity could be as high as 562.2 ± 55.4 mm(2)/s. The thermal conductivities of these SACNT buckypapers were also calculated by the equation k = Cpαρ.

Band alignment and optical response of facile grown NiO/ZnO nano-heterojunctions

NASA Astrophysics Data System (ADS)

Sultan, Muhammad; Mumtaz, Sundas; Ali, Asad; Khan, Muhammad Yaqoob; Iqbal, Tahir

2017-12-01

ZnO nanorods decorated by NiO nanostructures were fabricated using facile chemical route. The nanorods of ZnO were prepared by using chemical bath deposition technique and subsequently decorated by NiO using sol-gel spin coating. The density and orientation of the ZnO nanorods was controlled through the seed layer with preferential growth along c-axis and hexagonal face. X-Ray Photoelectron Spectroscopy (XPS) analysis was used to confirm stoichiometry of the materials and band alignment study of the heterostructures. Type-II band alignment was observed from the experimental results. The IV characteristics of the device depicting rectifying behavior at different temperatures were observed with photocurrent generation in response to light excitation. The electrical properties reported in this study are in line with earlier work where heterojunctions were fabricated by physical deposition techniques.

Fabrication of high temperature superconductors

DOEpatents

Balachandran, Uthamalingam; Dorris, Stephen E.; Ma, Beihai; Li, Meiya

2003-06-17

A method of forming a biaxially aligned superconductor on a non-biaxially aligned substrate substantially chemically inert to the biaxially aligned superconductor comprising is disclosed. A non-biaxially aligned substrate chemically inert to the superconductor is provided and a biaxially aligned superconductor material is deposited directly on the non-biaxially aligned substrate. A method forming a plume of superconductor material and contacting the plume and the non-biaxially aligned substrate at an angle greater than 0.degree. and less than 90.degree. to deposit a biaxially aligned superconductor on the non-biaxially aligned substrate is also disclosed. Various superconductors and substrates are illustrated.

Development of Smart Optical Gels with Highly Magnetically Responsive Bicelles.

PubMed

Isabettini, Stéphane; Stucki, Sandro; Massabni, Sarah; Baumgartner, Mirjam E; Reckey, Pernille Q; Kohlbrecher, Joachim; Ishikawa, Takashi; Windhab, Erich J; Fischer, Peter; Kuster, Simon

2018-03-14

Hydrogels delivering on-demand tailorable optical properties are formidable smart materials with promising perspectives in numerous fields, including the development of modern sensors and switches, the essential quality criterion being a defined and readily measured response to environmental changes. Lanthanide ion (Ln 3+ )-chelating bicelles are interesting building blocks for such materials because of their magnetic responsive nature. Imbedding these phospholipid-based nanodiscs in a magnetically aligned state in gelatin permits an orientation-dependent retardation of polarized light. The resulting tailorable anisotropy gives the gel a well-defined optical signature observed as a birefringence signal. These phenomena were only reported for a single bicelle-gelatin pair and required high magnetic field strengths of 8 T. Herein, we demonstrate the versatility and enhance the viability of this technology with a new generation of aminocholesterol (Chol-NH 2 )-doped bicelles imbedded in two different types of gelatin. The highly magnetically responsive nature of the bicelles allowed to gel the anisotropy at commercially viable magnetic field strengths between 1 and 3 T. Thermoreversible gels with a unique optical signature were generated by exposing the system to various temperature conditions and external magnetic field strengths. The resulting optical properties were a signature of the gel's environmental history, effectively acting as a sensor. Solutions containing the bicelles simultaneously aligning parallel and perpendicular to the magnetic field directions were obtained by mixing samples chelating Tm 3+ and Dy 3+ . These systems were successfully gelled, providing a material with two distinct temperature-dependent optical characteristics. The high degree of tunability in the magnetic response of the bicelles enables encryption of the gel's optical properties. The proposed gels are viable candidates for temperature tracking of sensitive goods and provide numerous perspectives for future development of tomorrow's smart materials and technologies.

Chain alignment for improved properties - Optimization of PLA and PHB-V by crystallization and reinforcement

NASA Astrophysics Data System (ADS)

Moser, K.; Bergmann, B.; Diemert, J.; Elsner, P.

2014-05-01

In this paper two promising ways to improve the material characteristics of PLA and PHB-V are presented by showing their positive effects on mechanical, optical, and thermal properties. The optimization is achieved by increasing the crystallization from the melt of the polymer chains and the other by means of a reinforcement of the matrices by bio-based materials. In the case of crystallization specific nucleating agents and optimized process parameters promote optimized crystallization conditions and lead particularly in toughness to significant improvements. In addition to crystallization the introduction of cellulose-based reinforcing materials is also a good alternative to improve the ductility of a biopolymer matrix considerably. Due to their polar surface structure cellulose fibres are favouring a very good interaction to the also polar biopolymers. In addition, the polar surfaces of both materials results in very homogeneous dispersion within the compound.

Photoactive devices including porphyrinoids with coordinating additives

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forrest, Stephen R; Zimmerman, Jeramy; Yu, Eric K

Coordinating additives are included in porphyrinoid-based materials to promote intermolecular organization and improve one or more photoelectric characteristics of the materials. The coordinating additives are selected from fullerene compounds and organic compounds having free electron pairs. Combinations of different coordinating additives can be used to tailor the characteristic properties of such porphyrinoid-based materials, including porphyrin oligomers. Bidentate ligands are one type of coordinating additive that can form coordination bonds with a central metal ion of two different porphyrinoid compounds to promote porphyrinoid alignment and/or pi-stacking. The coordinating additives can shift the absorption spectrum of a photoactive material toward higher wavelengths,more » increase the external quantum efficiency of the material, or both.« less

Hierarchical micro-architectures of electrodes for energy storage

NASA Astrophysics Data System (ADS)

Yue, Yuan; Liang, Hong

2015-06-01

The design of electrodes for the electrochemical energy storage devices, particularly Lithium ion batteries (LIBs) and Supercapacitors (SCs), has extraordinary importance in optimization of electrochemical performance. Regardless of the materials used, the architecture of electrodes is crucial for charge transport efficiency and electrochemical interactions. This report provides a critical review of the prototype architectural design and micro- and nano-material properties designated to electrodes of LIBs and SCs. An alternative classification criterion is proposed that divides reported hierarchical architectures into two categories: aligned and unaligned structures. The structures were evaluated and it was found that the aligned architectures are superior to the unaligned in the following characteristics: 1) highly-organized charger pathways, 2) tunable interspaces between architecture units, and 3) good electric-contacted current collectors prepared along with electrodes. Based on these findings, challenges and potential routes to resolve those are provided for future development.

Thin randomly aligned hierarchical carbon nanotube arrays as ultrablack metamaterials

NASA Astrophysics Data System (ADS)

De Nicola, Francesco; Hines, Peter; De Crescenzi, Maurizio; Motta, Nunzio

2017-07-01

Ultrablack metamaterials are artificial materials able to harvest all the incident light regardless of wavelength, angle, or polarization. Here, we show the ultrablack properties of randomly aligned hierarchical carbon nanotube arrays with thicknesses below 200 nm. The thin coatings are realized by solution processing and dry-transfer deposition on different substrates. The hierarchical surface morphology of the coatings is biomimetic and provides a large effective area that improves the film optical absorption. Also, such a morphology is responsible for the moth-eye effect, which leads to the omnidirectional and polarization-independent suppression of optical reflection. The films exhibit an emissivity up to 99.36% typical of an ideal black body, resulting in the thinnest ultrablack metamaterial ever reported. Such a material may be exploited for thermal, optical, and optoelectronic devices such as heat sinks, optical shields, solar cells, light and thermal sensors, and light-emitting diodes.

Methods and instruments for materials testing

NASA Technical Reports Server (NTRS)

Hansma, Paul (Inventor); Drake, Barney (Inventor); Rehn, Douglas (Inventor); Adams, Jonathan (Inventor); Lulejian, Jason (Inventor)

2011-01-01

Methods and instruments for characterizing a material, such as the properties of bone in a living human subject, using a test probe constructed for insertion into the material and a reference probe aligned with the test probe in a housing. The housing is hand held or placed so that the reference probe contacts the surface of the material under pressure applied either by hand or by the weight of the housing. The test probe is inserted into the material to indent the material while maintaining the reference probe substantially under the hand pressure or weight of the housing allowing evaluation of a property of the material related to indentation of the material by the probe. Force can be generated by a voice coil in a magnet structure to the end of which the test probe is connected and supported in the magnet structure by a flexure, opposing flexures, a linear translation stage, or a linear bearing. Optionally, a measurement unit containing the test probe and reference probe is connected to a base unit with a wireless connection, allowing in the field material testing.

Thermoelectricity in fullerene-metal heterojunctions.

PubMed

Yee, Shannon K; Malen, Jonathan A; Majumdar, Arun; Segalman, Rachel A

2011-10-12

Thermoelectricty in heterojunctions, where a single-molecule is trapped between metal electrodes, has been used to understand transport properties at organic-inorganic interfaces. (1) The transport in these systems is highly dependent on the energy level alignment between the molecular orbitals and the Fermi level (or work function) of the metal contacts. To date, the majority of single-molecule measurements have focused on simple small molecules where transport is dominated through the highest occupied molecular orbital. (2, 3) In these systems, energy level alignment is limited by the absence of electrode materials with low Fermi levels (i.e., large work functions). Alternatively, more controllable alignment between molecular orbitals and the Fermi level can be achieved with molecules whose transport is dominated by the lowest unoccupied molecular orbital (LUMO) because of readily available metals with lower work functions. Herein, we report molecular junction thermoelectric measurements of fullerene molecules (i.e., C(60), PCBM, and C(70)) trapped between metallic electrodes (i.e., Pt, Au, Ag). Fullerene junctions demonstrate the first strongly n-type molecular thermopower corresponding to transport through the LUMO, and the highest measured magnitude of molecular thermopower to date. While the electronic conductance of fullerenes is highly variable, due to fullerene's variable bonding geometries with the electrodes, the thermopower shows predictable trends based on the alignment of the LUMO with the work function of the electrodes. Both the magnitude and trend of the thermopower suggest that heterostructuring organic and inorganic materials at the nanoscale can further enhance thermoelectric performance, therein providing a new pathway for designing thermoelectric materials.

Characterization of assembled MEMS

NASA Astrophysics Data System (ADS)

Jandric, Zoran; Randall, John N.; Saini, Rahul; Nolan, Michael; Skidmore, George

2004-12-01

Zyvex is developing a low-cost high-precision method for manufacturing MEMS-based three-dimensional structures/assemblies. The assembly process relies on compliant properties of the interconnecting components. The sockets and connectors are designed to benefit from their compliant nature by allowing the mechanical component to self-align, i.e. reposition themselves to their designed, stable position, independent of the initial placement of the part by the external robot. Thus, the self-aligning property guarantees the precision of the assembled structure to be very close to, or the same, as the precision of the lithography process itself. A three-dimensional (3D) structure is achieved by inserting the connectors into the sockets through the use of a passive end-effector. We have developed the automated, high-yield, assembly procedure which permits connectors to be picked up from any location within the same die, or a separate die. This general procedure allows for the possibility to assemble parts of dissimilar materials. We have built many 3D MEMS structures, including several 3D MEMS devices such as a scanning electron microscope (SEM) micro column, mass-spectrometer column, variable optical attenuator. For these 3D MEMS structures we characterize their mechanical strength through finite element simulation, dynamic properties by finite-element analysis and experimentally with UMECH"s MEMS motion analyzer (MMA), alignment accuracy by using an in-house developed dihedral angle measurement laser autocollimator, and impact properties by performing drop tests. The details of the experimental set-ups, the measurement procedures, and the experimental data are presented in this paper.

Characterization of assembled MEMS

NASA Astrophysics Data System (ADS)

Jandric, Zoran; Randall, John N.; Saini, Rahul; Nolan, Michael; Skidmore, George

2005-01-01

Zyvex is developing a low-cost high-precision method for manufacturing MEMS-based three-dimensional structures/assemblies. The assembly process relies on compliant properties of the interconnecting components. The sockets and connectors are designed to benefit from their compliant nature by allowing the mechanical component to self-align, i.e. reposition themselves to their designed, stable position, independent of the initial placement of the part by the external robot. Thus, the self-aligning property guarantees the precision of the assembled structure to be very close to, or the same, as the precision of the lithography process itself. A three-dimensional (3D) structure is achieved by inserting the connectors into the sockets through the use of a passive end-effector. We have developed the automated, high-yield, assembly procedure which permits connectors to be picked up from any location within the same die, or a separate die. This general procedure allows for the possibility to assemble parts of dissimilar materials. We have built many 3D MEMS structures, including several 3D MEMS devices such as a scanning electron microscope (SEM) micro column, mass-spectrometer column, variable optical attenuator. For these 3D MEMS structures we characterize their mechanical strength through finite element simulation, dynamic properties by finite-element analysis and experimentally with UMECH"s MEMS motion analyzer (MMA), alignment accuracy by using an in-house developed dihedral angle measurement laser autocollimator, and impact properties by performing drop tests. The details of the experimental set-ups, the measurement procedures, and the experimental data are presented in this paper.

Elongational Flow Assists with the Assembly of Protein Nanofibrils

NASA Astrophysics Data System (ADS)

Mittal, Nitesh; Kamada, Ayaka; Lendel, Christofer; Lundell, Fredrik; Soderberg, Daniel

2016-11-01

Controlling the aggregation process of protein-based macromolecular structures in a confined environment using small-scale flow devices and understanding their assembly mechanisms is essential to develop bio-based materials. Whey protein, a protein mixture with β-lactoglobulin as main component, is able to self-assemble into amyloid-like protein nanofibers which are stabilized by hydrogen bonds. The conditions at which the fibrillation process occurs can affect the properties and morphology of the fibrils. Here, we show that the morphology of protein nanofibers greatly affects their assembly. We used elongational flow based double flow-focusing device for this study. In-situ behavior of the straight and flexible fibrils in the flow channel is determined using small-angle X-ray scattering (SAXS) technique. Our process combines hydrodynamic alignment with dispersion to gel-transition that produces homogeneous and smooth fibers. Moreover, successful alignment before gelation demands a proper separation of the time-scales involved, which we tried to identify in the current study. The presented approach combining small scale flow devices with in-situ synchrotron X-ray studies and protein engineering is a promising route to design high performance protein-based materials with controlled physical and chemical properties. We acknowledge the support from Wallenberg Wood Science Center.

Technical feasibility and economical viability of remote hybrid power systems in Northern Ontario

NASA Astrophysics Data System (ADS)

Gubbels, Jason Matthew

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Evaluation of remotely sensed wetland mapping

NASA Astrophysics Data System (ADS)

Gluck, Michael J.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Effects of propagational factors on quantum wires in close parallel proximity

NASA Astrophysics Data System (ADS)

Wilson, David A.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Tectonic magnetic fabrics in pure and simple shear: Experimental investigations

NASA Astrophysics Data System (ADS)

Alford, Craig Steven

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Use of a single epiphyte lichen species Hypogymnia physodes as an indicator of air quality in northern Ontario

NASA Astrophysics Data System (ADS)

Pfeiffer, Helmut Nickolaus

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Gravity study of an Archaen crustal segment near Thunder Bay, Ontario

NASA Astrophysics Data System (ADS)

Cheadle, Scott Philip

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Northern lights: A history of Thunder Bay Hydro

NASA Astrophysics Data System (ADS)

Black, David Leo

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Photoluminescence and Raman characterization of PLEE and MBE grown semiconductor epilayers

NASA Astrophysics Data System (ADS)

Harrison, Dale A.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Development of nonlinear 3-D, and novel 2-D optical microscope imaging systems for time-lapse imaging

NASA Astrophysics Data System (ADS)

Girardin, Robert Joseph

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Simple route to new palladium-carbonyl-bis(diphenylphosphino)methane complexes

NASA Astrophysics Data System (ADS)

Krysa, Elizabeth

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Impurity band conduction in reduced samples of bismuth iron molybdate

NASA Astrophysics Data System (ADS)

McIntyre, Shawn M.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Photon number density operator

NASA Astrophysics Data System (ADS)

Melde, Thomas

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Dielectric and infrared studies of radio frequency processes in some alcohols

NASA Astrophysics Data System (ADS)

Mandal, Humayun

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Real-time implementation of some attitude estimation algorithms on a quadrotor UAV

NASA Astrophysics Data System (ADS)

Nayak, Siddhant

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Ordered supramolecular oligothiophene structures on passivated silicon surfaces

NASA Astrophysics Data System (ADS)

Liu, Renjie

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Synthesis and electrochemical study of PtIr and PtRu nanomaterials

NASA Astrophysics Data System (ADS)

Alammari, Walaa S.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

P-type gallium nitride semiconductor development and characterization for LEDs and other devices

NASA Astrophysics Data System (ADS)

Togtema, Gregorey L.

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Incorporation of a Decorin Biomimetic Enhances the Mechanical Properties of Electrochemically Aligned Collagen Threads

PubMed Central

Kishore, Vipuil; Paderi, John E.; Akkus, Anna; Smith, Katie M.; Balachandran, Dave; Beaudoin, Stephen; Panitch, Alyssa; Akkus, Ozan

2011-01-01

Orientational anisotropy of collagen molecules is integral for the mechanical strength of collagen-rich tissues. We have previously reported a novel methodology to synthesize highly oriented electrochemically aligned collagen (ELAC) threads with mechanical properties converging upon those of native tendon. Decorin, a small leucine rich proteoglycan (SLRP), binds to fibrillar collagen and has been suggested to enhance the mechanical properties of tendon. Based on the structure of natural decorin, we have previously designed and synthesized a peptidoglycan (DS-SILY) that mimics decorin both structurally and functionally. In this study, we investigated the effect of the incorporation of DS-SILY on the mechanical properties and structural organization of ELAC threads. The results indicated that the addition of DS-SILY at a molar ratio of 30:1 (Collagen:DS-SILY) significantly enhanced the ultimate stress and ultimate strain of the ELAC threads. Furthermore, differential scanning calorimetry revealed that the addition of DS-SILY at a molar ratio of 30:1 resulted in a more thermally stable collagen structure. However, addition of DS-SILY at a higher concentration (10:1 Collagen:DS-SILY) yielded weaker threads with mechanical properties comparable to collagen control threads. Transmission emission microscopy revealed that the addition of DS-SILY at a higher concentration (10:1) resulted in pronounced aggregation of collagen fibrils. More importantly, these aggregates were not aligned along the long axis of the ELAC thereby compromising on the overall tensile properties of the material. We conclude that incorporation of an optimal amount of DS-SILY is a promising approach to synthesize mechanically competent collagen based biomaterials for tendon tissue engineering applications. PMID:21356334

Thermal Conductivity of Copoly(ethylene vinyl acetate)/Nano-Filler Blends

NASA Technical Reports Server (NTRS)

Ghose, S.; Watson, K. A.; Working, D. C.; Connell, J. W.; Smith, J. G.; Lin, Y.; Sun, Y. P.

2007-01-01

The development of flexible, thermally conductive fabrics and plastic tubes for the Liquid Cooling and Ventilation Garment (LCVG) are needed to reduce weight and improve the mobility, comfort, and performance of future spacesuits. Such improvements would allow astronauts to operate more efficiently and safely for extended extravehicular activities. As a continuation of our work on the improvement of thermal conductivity (TC) of polymeric materials, nanocomposites were prepared from copoly(ethylene vinyl acetate), trade name Elvax 260TradeMark), metallized carbon nanofibers (CNFs), nickel (Ni) nanostrands, boron nitride both alone and as mixtures with aluminum powder. The nanocomposites were prepared by melt mixing at various loading levels and subsequently fabricated into several material forms (i.e., ribbons, tubes, and compression molded plaques) for analysis. Ribbons and tubes were extruded to form samples in which the nanoparticles were aligned in the direction of flow. The degree of dispersion and alignment of the nanoparticles were investigated using high-resolution scanning electron microscopy. Tensile properties of the aligned samples were determined at room temperature. TC measurements were performed using a laser flash (Nanoflash(TradeMark) technique. The TC of the samples was measured in both the direction of alignment as well as transverse. Tubing of comparable dimensions to that used in the LCVG was extruded from select compositions and the thermal conductivities of the tubes measured.

Magnetic Properties of Restacked 2D Spin 1/2 honeycomb RuCl3 Nanosheets.

PubMed

Weber, Daniel; Schoop, Leslie M; Duppel, Viola; Lippmann, Judith M; Nuss, Jürgen; Lotsch, Bettina V

2016-06-08

Spin 1/2 honeycomb materials have gained substantial interest due to their exotic magnetism and possible application in quantum computing. However, in all current materials out-of-plane interactions are interfering with the in-plane order, hence a true 2D magnetic honeycomb system is still in demand. Here, we report the exfoliation of the magnetic semiconductor α-RuCl3 into the first halide monolayers and the magnetic characterization of the spin 1/2 honeycomb arrangement of turbostratically stacked RuCl3 monolayers. The exfoliation is based on a reductive lithiation/hydration approach, which gives rise to a loss of cooperative magnetism due to the disruption of the spin 1/2 state by electron injection into the layers. The restacked, macroscopic pellets of RuCl3 layers lack symmetry along the stacking direction. After an oxidative treatment, cooperative magnetism similar to the bulk is restored. The oxidized pellets of restacked single layers feature a magnetic transition at TN = 7 K if the field is aligned parallel to the ab-plane, while the magnetic properties differ from bulk α-RuCl3 if the field is aligned perpendicular to the ab-plane. The deliberate introduction of turbostratic disorder to manipulate the magnetic properties of RuCl3 is of interest for research in frustrated magnetism and complex magnetic order as predicted by the Kitaev-Heisenberg model.

Relationship between nanotopographical alignment and stem cell fate with live imaging and shape analysis

NASA Astrophysics Data System (ADS)

Newman, Peter; Galenano-Niño, Jorge Luis; Graney, Pamela; Razal, Joselito M.; Minett, Andrew I.; Ribas, João; Ovalle-Robles, Raquel; Biro, Maté; Zreiqat, Hala

2016-12-01

The topography of a biomaterial regulates cellular interactions and determine stem cell fate. A complete understanding of how topographical properties affect cell behavior will allow the rational design of material surfaces that elicit specified biological functions once placed in the body. To this end, we fabricate substrates with aligned or randomly organized fibrous nanostructured topographies. Culturing adipose-derived stem cells (ASCs), we explore the dynamic relationship between the alignment of topography, cell shape and cell differentiation to osteogenic and myogenic lineages. We show aligned topographies differentiate cells towards a satellite cell muscle progenitor state - a distinct cell myogenic lineage responsible for postnatal growth and repair of muscle. We analyze cell shape between the different topographies, using fluorescent time-lapse imaging over 21 days. In contrast to previous work, this allows the direct measurement of cell shape at a given time rather than defining the morphology of the underlying topography and neglecting cell shape. We report quantitative metrics of the time-based morphological behaviors of cell shape in response to differing topographies. This analysis offers insights into the relationship between topography, cell shape and cell differentiation. Cells differentiating towards a myogenic fate on aligned topographies adopt a characteristic elongated shape as well as the alignment of cells.

Ion Conduction in Microphase-Separated Block Copolymer Electrolytes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kambe, Yu; Arges, Christopher G.; Patel, Shrayesh

2017-01-01

Microphase separation of block copolymers provides a promising route towards engineering a mechanically robust ion conducting film for electrochemical devices. The separation into two different nano-domains enables the film to simultaneously exhibit both high ion conductivity and mechanical robustness, material properties inversely related in most homopolymer and random copolymer electrolytes. To exhibit the maximum conductivity and mechanical robustness, both domains would span across macroscopic length scales enabling uninterrupted ion conduction. One way to achieve this architecture is through external alignment fields that are applied during the microphase separation process. In this review, we present the progress and challenges for aligningmore » the ionic domains in block copolymer electrolytes. A survey of alignment and characterization is followed by a discussion of how the nanoscale architecture affects the bulk conductivity and how alignment may be improved to maximize the number of participating conduction domains.« less

Layered and scrolled nanocomposites with aligned semi-infinite graphene inclusions at the platelet limit

NASA Astrophysics Data System (ADS)

Liu, Pingwei; Jin, Zhong; Katsukis, Georgios; Drahushuk, Lee William; Shimizu, Steven; Shih, Chih-Jen; Wetzel, Eric D.; Taggart-Scarff, Joshua K.; Qing, Bo; Van Vliet, Krystyn J.; Li, Richard; Wardle, Brian L.; Strano, Michael S.

2016-07-01

Two-dimensional (2D) materials can uniquely span the physical dimensions of a surrounding composite matrix in the limit of maximum reinforcement. However, the alignment and assembly of continuous 2D components at high volume fraction remain challenging. We use a stacking and folding method to generate aligned graphene/polycarbonate composites with as many as 320 parallel layers spanning 0.032 to 0.11 millimeters in thickness that significantly increases the effective elastic modulus and strength at exceptionally low volume fractions of only 0.082%. An analogous transverse shear scrolling method generates Archimedean spiral fibers that demonstrate exotic, telescoping elongation at break of 110%, or 30 times greater than Kevlar. Both composites retain anisotropic electrical conduction along the graphene planar axis and transparency. These composites promise substantial mechanical reinforcement, electrical, and optical properties at highly reduced volume fraction.

Layered and scrolled nanocomposites with aligned semi-infinite graphene inclusions at the platelet limit.

PubMed

Liu, Pingwei; Jin, Zhong; Katsukis, Georgios; Drahushuk, Lee William; Shimizu, Steven; Shih, Chih-Jen; Wetzel, Eric D; Taggart-Scarff, Joshua K; Qing, Bo; Van Vliet, Krystyn J; Li, Richard; Wardle, Brian L; Strano, Michael S

2016-07-22

Two-dimensional (2D) materials can uniquely span the physical dimensions of a surrounding composite matrix in the limit of maximum reinforcement. However, the alignment and assembly of continuous 2D components at high volume fraction remain challenging. We use a stacking and folding method to generate aligned graphene/polycarbonate composites with as many as 320 parallel layers spanning 0.032 to 0.11 millimeters in thickness that significantly increases the effective elastic modulus and strength at exceptionally low volume fractions of only 0.082%. An analogous transverse shear scrolling method generates Archimedean spiral fibers that demonstrate exotic, telescoping elongation at break of 110%, or 30 times greater than Kevlar. Both composites retain anisotropic electrical conduction along the graphene planar axis and transparency. These composites promise substantial mechanical reinforcement, electrical, and optical properties at highly reduced volume fraction. Copyright © 2016, American Association for the Advancement of Science.

Aligning Curriculum Materials with the Australian Curriculum: What Is Happening in the Field and What Needs to Be Done?

ERIC Educational Resources Information Center

Watt, Michael

2016-01-01

The purpose of this study was to inform the deliberations of a policymakers' working group by investigating what key actors in the materials' marketplace are doing to align digital and print-based materials with the Australian Curriculum and what steps need to be taken to deliver aligned materials to schools. Content analysis method was used to…

Large-scale horizontally aligned ZnO microrod arrays with controlled orientation, periodic distribution as building blocks for chip-in piezo-phototronic LEDs.

PubMed

Guo, Zhen; Li, Haiwen; Zhou, Lianqun; Zhao, Dongxu; Wu, Yihui; Zhang, Zhiqiang; Zhang, Wei; Li, Chuanyu; Yao, Jia

2015-01-27

A novel method of fabricating large-scale horizontally aligned ZnO microrod arrays with controlled orientation and periodic distribution via combing technology is introduced. Horizontally aligned ZnO microrod arrays with uniform orientation and periodic distribution can be realized based on the conventional bottom-up method prepared vertically aligned ZnO microrod matrix via the combing method. When the combing parameters are changed, the orientation of horizontally aligned ZnO microrod arrays can be adjusted (θ = 90° or 45°) in a plane and a misalignment angle of the microrods (0.3° to 2.3°) with low-growth density can be obtained. To explore the potential applications based on the vertically and horizontally aligned ZnO microrods on p-GaN layer, piezo-phototronic devices such as heterojunction LEDs are built. Electroluminescence (EL) emission patterns can be adjusted for the vertically and horizontally aligned ZnO microrods/p-GaN heterojunction LEDs by applying forward bias. Moreover, the emission color from UV-blue to yellow-green can be tuned by investigating the piezoelectric properties of the materials. The EL emission mechanisms of the LEDs are discussed in terms of band diagrams of the heterojunctions and carrier recombination processes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sensing surface morphology of biofibers by decorating spider silk and cellulosic filaments with nematic microdroplets

PubMed Central

Aguirre, Luis E.; de Oliveira, Alexandre; Seč, David; Čopar, Simon; Almeida, Pedro L.; Ravnik, Miha; Godinho, Maria Helena; Žumer, Slobodan

2016-01-01

Probing the surface morphology of microthin fibers such as naturally occurring biofibers is essential for understanding their structural properties, biological function, and mechanical performance. The state-of-the-art methods for studying the surfaces of biofibers are atomic force microscopy imaging and scanning electron microscopy, which well characterize surface geometry of the fibers but provide little information on the local interaction potential of the fibers with the surrounding material. In contrast, complex nematic fluids respond very well to external fields and change their optical properties upon such stimuli. Here we demonstrate that liquid crystal droplets deposited on microthin biofibers—including spider silk and cellulosic fibers—reveal characteristics of the fibers’ surface, performing as simple but sensitive surface sensors. By combining experiments and numerical modeling, different types of fibers are identified through the fiber-to-nematic droplet interactions, including perpendicular and axial or helicoidal planar molecular alignment. Spider silks align nematic molecules parallel to fibers or perpendicular to them, whereas cellulose aligns the molecules unidirectionally or helicoidally along the fibers, indicating notably different surface interactions. The nematic droplets as sensors thus directly reveal chirality of cellulosic fibers. Different fiber entanglements can be identified by depositing droplets exactly at the fiber crossings. More generally, the presented method can be used as a simple but powerful approach for probing the surface properties of small-size bioobjects, opening a route to their precise characterization. PMID:26768844

Sensing surface morphology of biofibers by decorating spider silk and cellulosic filaments with nematic microdroplets.

PubMed

Aguirre, Luis E; de Oliveira, Alexandre; Seč, David; Čopar, Simon; Almeida, Pedro L; Ravnik, Miha; Godinho, Maria Helena; Žumer, Slobodan

2016-02-02

Probing the surface morphology of microthin fibers such as naturally occurring biofibers is essential for understanding their structural properties, biological function, and mechanical performance. The state-of-the-art methods for studying the surfaces of biofibers are atomic force microscopy imaging and scanning electron microscopy, which well characterize surface geometry of the fibers but provide little information on the local interaction potential of the fibers with the surrounding material. In contrast, complex nematic fluids respond very well to external fields and change their optical properties upon such stimuli. Here we demonstrate that liquid crystal droplets deposited on microthin biofibers--including spider silk and cellulosic fibers--reveal characteristics of the fibers' surface, performing as simple but sensitive surface sensors. By combining experiments and numerical modeling, different types of fibers are identified through the fiber-to-nematic droplet interactions, including perpendicular and axial or helicoidal planar molecular alignment. Spider silks align nematic molecules parallel to fibers or perpendicular to them, whereas cellulose aligns the molecules unidirectionally or helicoidally along the fibers, indicating notably different surface interactions. The nematic droplets as sensors thus directly reveal chirality of cellulosic fibers. Different fiber entanglements can be identified by depositing droplets exactly at the fiber crossings. More generally, the presented method can be used as a simple but powerful approach for probing the surface properties of small-size bioobjects, opening a route to their precise characterization.

Highly anisotropic magneto-transport and field orientation dependent oscillations in aligned carbon nanotube/epoxy composites

NASA Astrophysics Data System (ADS)

Wells, Brian; Kumar, Raj; Reynolds, C. Lewis; Peters, Kara; Bradford, Philip D.

2017-12-01

Carbon nanotubes (CNTs) have been widely investigated as additive materials for composites with potential applications in electronic devices due to their extremely large electrical conductivity and current density. Here, highly aligned CNT composite films were created using a sequential layering fabrication technique. The degree of CNT alignment leads to anisotropic resistance values which varies >400× in orthogonal directions. Similarly, the magnetoresistance (MR) of the CNT composite differs depending upon the relative direction of current and the applied magnetic field. A suppression of negative to positive MR crossover was also observed. More importantly, an overall positive magnetoresistance behavior with localized +/- oscillations was discovered at low fields which persists up to room temperature when the current (I) and in-plane magnetic field (B) were parallel to the axis of CNT (B∥I∥CNT), which is consistent with Aharonov-Bohm oscillations in our CNT/epoxy composites. When the current, applied magnetic field, and nanotube axis are aligned, the in-plane MR is positive instead of negative as observed for all other field, current, and tube orientations. Here, we provide in-depth analysis of the conduction mechanism and anisotropy in the magneto-transport properties of these aligned CNT-epoxy composites.

Measurement of material mechanical properties in microforming

NASA Astrophysics Data System (ADS)

Yun, Wang; Xu, Zhenying; Hui, Huang; Zhou, Jianzhong

2006-02-01

As the rapid market need of micro-electro-mechanical systems engineering gives it the wide development and application ranging from mobile phones to medical apparatus, the need of metal micro-parts is increasing gradually. Microforming technology challenges the plastic processing technology. The findings have shown that if the grain size of the specimen remains constant, the flow stress changes with the increasing miniaturization, and also the necking elongation and the uniform elongation etc. It is impossible to get the specimen material properties in conventional tensile test machine, especially in the high precision demand. Therefore, one new measurement method for getting the specimen material-mechanical property with high precision is initiated. With this method, coupled with the high speed of Charge Coupled Device (CCD) camera and high precision of Coordinate Measuring Machine (CMM), the elongation and tensile strain in the gauge length are obtained. The elongation, yield stress and other mechanical properties can be calculated from the relationship between the images and CCD camera movement. This measuring method can be extended into other experiments, such as the alignment of the tool and specimen, micro-drawing process.

Near-Infrared Chromophore Functionalized Soft Actuator with Ultrafast Photoresponsive Speed and Superior Mechanical Property.

PubMed

Liu, Li; Liu, Mei-Hua; Deng, Lin-Lin; Lin, Bao-Ping; Yang, Hong

2017-08-23

In this Communication, we develop a two-step acyclic diene metathesis in situ polymerization/cross-linking method to synthesize uniaxially aligned main-chain liquid crystal elastomers with chemically bonded near-infrared absorbing four-alkenyl-tailed croconaine-core cross-linkers. Because of the extraordinary photothermal conversion property, such a soft actuator material can raise its local temperature from 18 to 260 °C in 8 s, and lift up burdens 5600 times heavier than its own weight, under 808 nm near-infrared irradiation.

Preferential growth of short aligned, metallic-rich single-walled carbon nanotubes from perpendicular layered double hydroxide film.

PubMed

Zhao, Meng-Qiang; Tian, Gui-Li; Zhang, Qiang; Huang, Jia-Qi; Nie, Jing-Qi; Wei, Fei

2012-04-07

Direct bulk growth of single-walled carbon nanotubes (SWCNTs) with required properties, such as diameter, length, and chirality, is the first step to realize their advanced applications in electrical and optical devices, transparent conductive films, and high-performance field-effect transistors. Preferential growth of short aligned, metallic-rich SWCNTs is a great challenge to the carbon nanotube community. We report the bulk preferential growth of short aligned SWCNTs from perpendicular Mo-containing FeMgAl layered double hydroxide (LDH) film by a facile thermal chemical vapor deposition with CH(4) as carbon source. The growth of the short aligned SWCNTs showed a decreased growth velocity with an initial value of 1.9 nm s(-1). Such a low growth velocity made it possible to get aligned SWCNTs shorter than 1 μm with a growth duration less than 15 min. Raman spectra with different excitation wavelengths indicated that the as-grown short aligned SWCNTs showed high selectivity of metallic SWCNTs. Various kinds of materials, such as mica, quartz, Cu foil, and carbon fiber, can serve as the substrates for the growth of perpendicular FeMoMgAl LDH films and also the growth of the short aligned SWCNTs subsequently. These findings highlight the easy route for bulk preferential growth of aligned metallic-rich SWCNTs with well defined length for further bulk characterization and applications. This journal is © The Royal Society of Chemistry 2012

Effect of tow alignment on the mechanical performance of 3D woven textile composites

NASA Technical Reports Server (NTRS)

Norman, Timothy L.; Allison, Patti; Baldwin, Jack W.; Gracias, Brian K.; Seesdorf, Dave

1993-01-01

Three-dimensional (3D) woven preforms are currently being considered for use as primary structural components. Lack of technology to properly manufacture, characterize and predict mechanical properties, and predict damage mechanisms leading to failure are problems facing designers of textile composite materials. Two material systems with identical specifications but different manufacturing approaches are investigated. One manufacturing approach resulted in an irregular (nonuniform) preform geometry. The other approach yielded the expected preform geometry (uniform). The objectives are to compare the mechanical properties of the uniform and nonuniform angle interlock 3D weave constructions. The effect of adding layers of laminated tape to the outer surfaces of the textile preform is also examined. Damage mechanisms are investigated and test methods are evaluated.

Studies of anisotropic in-plane aligned a-axis oriented YBa(2)Cu(3)O(7-x) thin films

NASA Astrophysics Data System (ADS)

Trajanovic, Zoran

1997-12-01

Due to their layered planar structure, cuprate oxide superconductors possess remarkable anisotropic properties which may be related to their high transition temperatures. In-plane aligned a-axis YBa2Cu3O7 (YBCO) films are good candidates for such anisotropic studies. Furthermore, the full advantage of favorable material characteristics can be then utilized in applications such as vertical SNS junctions with the leads along the b-direction of YBCO and other novel junction configurations. High quality, smooth, in-plane aligned films are obtained on (100) LaSrGaO4. Form x-ray data, the films show complete b- and c-axes separation for the measured a-axis orientation. The anisotropic resistivity ratio (ρ c/ρ b), measured along the two crystallographic axes of single films gives ρ c/ρ b of ≈20 near the transition, with T cs near 90 K. In such films the grain boundary effects can be decoupled from the intrinsic anisotropic properties of YBCO. From oxygen annealing studies it was estimated that the CuO chains supply about 60% of the carriers. From J c measurements it is determined that the orientation of magnetic field with respect to the crystallographic film axes is the primary factor governing the J c values. The angular dependence of J c on the applied magnetic field is compared against various theoretical models showing the best agreement with the modified Ginzburg-Landau's anisotropic mass model (at T ≈ T c) and Tinkham's thin film model (at T < T c). By utilizing the Co-dopant, the coupling between CuO2 planes and the resulting enhancement of the intrinsic anisotropy of YBCO can be studied. Deposition and cooling conditions are shown to be the primary factor that influence the quality of dopant incorporation and the resulting oxygen ordering within the YBCO lattice. Various complex structures and devices utilizing in-plane aligned, a-axis films are presented. Other materials exhibiting in-plane alignment and a-axis growth are described. Optional substrates for achieving such films are also discussed.

Semiconductor tunnel junction with enhancement layer

DOEpatents

Klem, John F.; Zolper, John C.

1997-01-01

The incorporation of a pseudomorphic GaAsSb layer in a runnel diode structure affords a new degree of freedom in designing runnel junctions for p-n junction device interconnects. Previously only doping levels could be varied to control the tunneling properties. This invention uses the valence band alignment band of the GaAsSb with respect to the surrounding materials to greatly relax the doping requirements for tunneling.

3D-Printing of Meso-structurally Ordered Carbon Fiber/Polymer Composites with Unprecedented Orthotropic Physical Properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lewicki, James P.; Rodriguez, Jennifer N.; Zhu, Cheng

Here we report the first example of a class of additively manufactured carbon fiber reinforced composite (AMCFRC) materials which have been achieved through the use of a latent thermal cured aromatic thermoset resin system, through an adaptation of direct ink writing (DIW) 3D-printing technology. We have developed a means of printing high performance thermoset carbon fiber composites, which allow the fiber component of a resin and carbon fiber fluid to be aligned in three dimensions via controlled micro-extrusion and subsequently cured into complex geometries. Characterization of our composite systems clearly show that we achieved a high order of fiber alignmentmore » within the composite microstructure, which in turn allows these materials to outperform equivalently filled randomly oriented carbon fiber and polymer composites. Moreover, our AM carbon fiber composite systems exhibit highly orthotropic mechanical and electrical responses as a direct result of the alignment of carbon fiber bundles in the microscale which we predict will ultimately lead to the design of truly tailorable carbon fiber/polymer hybrid materials having locally programmable complex electrical, thermal and mechanical response.« less

3D-Printing of Meso-structurally Ordered Carbon Fiber/Polymer Composites with Unprecedented Orthotropic Physical Properties

DOE PAGES

Lewicki, James P.; Rodriguez, Jennifer N.; Zhu, Cheng; ...

2017-03-06

Here we report the first example of a class of additively manufactured carbon fiber reinforced composite (AMCFRC) materials which have been achieved through the use of a latent thermal cured aromatic thermoset resin system, through an adaptation of direct ink writing (DIW) 3D-printing technology. We have developed a means of printing high performance thermoset carbon fiber composites, which allow the fiber component of a resin and carbon fiber fluid to be aligned in three dimensions via controlled micro-extrusion and subsequently cured into complex geometries. Characterization of our composite systems clearly show that we achieved a high order of fiber alignmentmore » within the composite microstructure, which in turn allows these materials to outperform equivalently filled randomly oriented carbon fiber and polymer composites. Moreover, our AM carbon fiber composite systems exhibit highly orthotropic mechanical and electrical responses as a direct result of the alignment of carbon fiber bundles in the microscale which we predict will ultimately lead to the design of truly tailorable carbon fiber/polymer hybrid materials having locally programmable complex electrical, thermal and mechanical response.« less

Epitaxial hexagonal materials on IBAD-textured substrates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matias, Vladimir; Yung, Christopher

2017-08-15

A multilayer structure including a hexagonal epitaxial layer, such as GaN or other group III-nitride (III-N) semiconductors, a <111> oriented textured layer, and a non-single crystal substrate, and methods for making the same. The textured layer has a crystalline alignment preferably formed by the ion-beam assisted deposition (IBAD) texturing process and can be biaxially aligned. The in-plane crystalline texture of the textured layer is sufficiently low to allow growth of high quality hexagonal material, but can still be significantly greater than the required in-plane crystalline texture of the hexagonal material. The IBAD process enables low-cost, large-area, flexible metal foil substratesmore » to be used as potential alternatives to single-crystal sapphire and silicon for manufacture of electronic devices, enabling scaled-up roll-to-roll, sheet-to-sheet, or similar fabrication processes to be used. The user is able to choose a substrate for its mechanical and thermal properties, such as how well its coefficient of thermal expansion matches that of the hexagonal epitaxial layer, while choosing a textured layer that more closely lattice matches that layer.« less

Final Report: Nanoscale Dynamical Heterogeneity in Complex Magnetic Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kevan, Stephen

2016-05-27

A magnetic object can be demagnetized by dropping it on a hard surface, but what does ‘demagnetized’ actually mean? In 1919 Heinrich Barkhausen proved the existence of magnetic domains, which are regions of uniform magnetization that are much larger than atoms but much smaller than a macroscopic object. A material is fully magnetized when domain magnetizations are aligned, while it is demagnetized when the domain magnetizations are randomly oriented and the net magnetization is zero. The heterogeneity of a demagnetized object leads to interesting questions. Magnets are unstable when their poles align, and stable when their poles anti-align, so whymore » is the magnetized state ever stable? What do domains look like? What is the structure of a domain wall? How does the magnetized state transform to the demagnetized state? How do domains appear and disappear? What are the statistical properties of domains and how do these vary as the domain pattern evolves? Some of these questions remain the focus of intense study nearly a century after Barkhausen’s discovery. For example, just a few years ago a new kind of magnetic texture called a skyrmion was discovered. A skyrmion is a magnetic domain that is a nanometer-scale, topologically protected vortex. ‘Topologically protected’ means that skyrmions are hard to destroy and so are stable for extended periods. Skyrmions are characterized by integral quantum numbers and are observed to move with little dissipation and so could store and process information with very low power input. Our research project uses soft x-rays, which offer very high magnetic contrast, to probe magnetic heterogeneity and to measure how it evolves in time under external influences. We will condition a soft x-ray beam so that the wave fronts will be coherent, that is, they will be smooth and well-defined. When coherent soft x-ray beam interacts with a magnetic material, the magnetic heterogeneity is imprinted onto the wave fronts and projected into a diffraction pattern. These patterns will be analyzed to understand the structure, motion, and statistical properties of magnetic textures and their boundaries. Over the period covered by this grant we will study a) the structure, phase behaviors, and motion of skyrmions in various thin film materials, and 2) the statistical properties of Barkhausen cascades, which are a key factor in how magnetization varies.« less

Fiber-coupled thermal microscope for solid materials based on thermoreflectance method

NASA Astrophysics Data System (ADS)

Miyake, Shugo; Hatori, Kimihito; Ohtsuki, Tetsuya; Awano, Takaaki; Sekine, Makoto

2018-06-01

Measurement of the thermal properties of solid-state materials, including high- and low-thermal-conductivity materials in electronic devices, is very important to improve thermal design. The thermoreflectance method is well known as a powerful technique for measuring a wide range of thermal conductivity. However, in order to precisely determine the thermoreflectance signal, the alignment between two laser beams should be perfectly coaxial, similar to that in the numerical calculation model. In this paper, a developed fiber-coupled thermal microscope based on the thermoreflectance method is demonstrated, which we use to determine the frequency dependence of the temperature responses of silicon, sapphire, zirconium, and Pyrex glass samples.

SU-F-I-59: Quality Assurance Phantom for PET/CT Alignment and Attenuation Correction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, T; Hamacher, K

2016-06-15

Purpose: This study utilizes a commercial PET/CT phantom to investigate two specific properties of a PET/CT system: the alignment accuracy of PET images with those from CT used for attenuation correction and the accuracy of this correction in PET images. Methods: A commercial PET/CT phantom consisting of three aluminum rods, two long central cylinders containing uniform activity, and attenuating materials such as air, water, bone and iodine contrast was scanned using a standard PET/CT protocol. Images reconstructed with 2 mm slice thickness and a 512 by 512 matrix were obtained. The center of each aluminum rod in the PET andmore » CT images was compared to evaluate alignment accuracy. ROIs were drawn on transaxial images of the central rods at each section of attenuating material to determine the corrected activity (in BQML). BQML values were graphed as a function of slice number to provide a visual representation of the attenuation-correction throughout the whole phantom. Results: Alignment accuracy is high between the PET and CT images. The maximum deviation between the two in the axial plane is less than 1.5 mm, which is less than the width of a single pixel. BQML values measured along different sections of the large central rods are similar among the different attenuating materials except iodine contrast. Deviation of BQML values in the air and bone sections from the water section is less than 1%. Conclusion: Accurate alignment of PET and CT images is critical to ensure proper calculation and application of CT-based attenuation correction. This study presents a simple and quick method to evaluate the two with a single acquisition. As the phantom also includes spheres of increasing diameter, this could serve as a straightforward means to annually evaluate the status of a modern PET/CT system.« less

Hybrid density functional study of band alignment in ZnO-GaN and ZnO-(Ga(1-x)Zn(x))(N(1-x)O(x))-GaN heterostructures.

PubMed

Wang, Zhenhai; Zhao, Mingwen; Wang, Xiaopeng; Xi, Yan; He, Xiujie; Liu, Xiangdong; Yan, Shishen

2012-12-05

The band alignment in ZnO-GaN and related heterostructures is crucial for uses in solar harvesting technology. Here, we report our density functional calculations of the band alignment and optical properties of ZnO-GaN and ZnO-(Ga(1-x)Zn(x))(N(1-x)O(x))-GaN heterostructures using a Heyd-Scuseria-Ernzerhof (HSE) hybrid functional. We found that the conventional GGA functionals underestimate not only the band gap but also the band offset of these heterostructures. Using the hybrid functional calculations, we show that the (Ga(1-x)Zn(x))(N(1-x)O(x)) solid solution has a direct band gap of about 2.608 eV, in good agreement with the experimental data. More importantly, this solid solution forms type-II band alignment with the host materials. A GaN-(Ga(1-x)Zn(x))(N(1-x)O(x))-ZnO core-shell solar cell model is presented to improve the visible light absorption ability and carrier collection efficiency.

Achievable flatness in a large microwave power transmitting antenna

NASA Technical Reports Server (NTRS)

Ried, R. C.

1980-01-01

A dual reference SPS system with pseudoisotropic graphite composite as a representative dimensionally stable composite was studied. The loads, accelerations, thermal environments, temperatures and distortions were calculated for a variety of operational SPS conditions along with statistical considerations of material properties, manufacturing tolerances, measurement accuracy and the resulting loss of sight (LOS) and local slope distributions. A LOS error and a subarray rms slope error of two arc minutes can be achieved with a passive system. Results show that existing materials measurement, manufacturing, assembly and alignment techniques can be used to build the microwave power transmission system antenna structure. Manufacturing tolerance can be critical to rms slope error. The slope error budget can be met with a passive system. Structural joints without free play are essential in the assembly of the large truss structure. Variations in material properties, particularly for coefficient of thermal expansion from part to part, is more significant than actual value.

Amperometric Detection in Microchip Electrophoresis Devices: Effect of Electrode Material and Alignment on Analytical Performance

PubMed Central

Fischer, David J.; Hulvey, Matthew K.; Regel, Anne R.; Lunte, Susan M.

2012-01-01

The fabrication and evaluation of different electrode materials and electrode alignments for microchip electrophoresis with electrochemical (EC) detection is described. The influences of electrode material, both metal and carbon-based, on sensitivity and limits of detection (LOD) were examined. In addition, the effects of working electrode alignment on analytical performance (in terms of peak shape, resolution, sensitivity, and LOD) were directly compared. Using dopamine (DA), norepinephrine (NE), and catechol (CAT) as test analytes, it was found that pyrolyzed photoresist electrodes with end-channel alignment yielded the lowest limit of detection (35 nM for DA). In addition to being easier to implement, end-channel alignment also offered better analytical performance than off-channel alignment for the detection of all three analytes. In-channel electrode alignment resulted in a 3.6-fold reduction in peak skew and reduced peak tailing by a factor of 2.1 for catechol in comparison to end-channel alignment. PMID:19802847

Hierarchically structured carbon nanotubes for energy conversion and storage

NASA Astrophysics Data System (ADS)

Du, Feng

As the world population continues to increase, large amounts of energy are consumed. Reality pushes us to find new energy or use our current energy more efficiently. Researches on energy conversion and storage have become increasingly important and essential. This grand challenge research has led to a recent focus on nanostructured materials. Carbon nanomaterials such as carbon nanotubes (CNTs) play a critical role in all of these nanotechnology challenges. CNTs have a very large surface area, a high electrochemical accessibility, high electronic conductivity and strong mechanical properties. This combination of properties makes them promising materials for energy device applications, such as FETs, supercapacitors, fuel cells, and lithium batteries. This study focuses on exploring the possibility of using vertically aligned carbon nanotubes (VA-CNTs) as the electrode materials in these energy applications. For the application of electrode materials, electrical conductive, vertically aligned CNTs with controllable length and diameter were synthesized. Several CVD methods for VA-CNT growth have been explored, although the iron / aluminum pre-coated catalyst CVD system was the main focus. A systematic study of several factors, including growth time, temperature, gas ratio, catalyst coating was conducted. The mechanism of VA-CNTs was discussed and a model for VA-CNT length / time was proposed to explain the CNT growth rate. Furthermore, the preferential growth of semiconducting (up to 96 atom% carbon) VA-SWNTs by using a plasma enhanced CVD process combined with fast heating was also explored, and these semiconducting materials have been directly used for making FETs using simple dispersion in organic solvent, without any separation and purification. Also, by inserting electron-accepting nitrogen atoms into the conjugated VA-CNT structure during the growth process, we synthesized vertically aligned nitrogen containing carbon nanotubes (VA-NCNTs). After purification of the metal catalyst, these metal-free VA-NCNTs have shown even better oxidation reduction reaction (ORR) performance than commercially available platinum based electrodes in many aspects, including electrocatalytic activity, long-term operation stability, and tolerance to fuel-molecule crossover. Quantum mechanics calculations and electrochemical experimental results indicate that the charge-deficient carbon atoms around the electron-rich nitrogen atoms improve the ORR reaction and the action of the electrochemical cycling. Finally, by growing vertically aligned carbon nanotubes between graphitic layers in thermally-expanded HOPG, we developed a novel, controlled orientation 3D VA-CNT-graphene architecture, which could allow free transport of electrons and ions. These 3D architectures with a tunable pillar length were demonstrated to be excellent electrode materials for energy related devices. Further, these 3D structures were functionalized with nickel hydroxide by electrodeposition, and the resultant hybrid materials could deliver a high energy density (e.g., ~35 Wh/kg) at a high power density (e.g., ~8 kW/kg), which would significantly outperform many currently available electrode materials.

Electrospun Collagen/Silk Tissue Engineering Scaffolds: Fiber Fabrication, Post-Treatment Optimization, and Application in Neural Differentiation of Stem Cells

NASA Astrophysics Data System (ADS)

Zhu, Bofan

Biocompatible scaffolds mimicking the locally aligned fibrous structure of native extracellular matrix (ECM) are in high demand in tissue engineering. In this thesis research, unidirectionally aligned fibers were generated via a home-built electrospinning system. Collagen type I, as a major ECM component, was chosen in this study due to its support of cell proliferation and promotion of neuroectodermal commitment in stem cell differentiation. Synthetic dragline silk proteins, as biopolymers with remarkable tensile strength and superior elasticity, were also used as a model material. Good alignment, controllable fiber size and morphology, as well as a desirable deposition density of fibers were achieved via the optimization of solution and electrospinning parameters. The incorporation of silk proteins into collagen was found to significantly enhance mechanical properties and stability of electrospun fibers. Glutaraldehyde (GA) vapor post-treatment was demonstrated as a simple and effective way to tune the properties of collagen/silk fibers without changing their chemical composition. With 6-12 hours GA treatment, electrospun collagen/silk fibers were not only biocompatible, but could also effectively induce the polarization and neural commitment of stem cells, which were optimized on collagen rich fibers due to the unique combination of biochemical and biophysical cues imposed to cells. Taken together, electrospun collagen rich composite fibers are mechanically strong, stable and provide excellent cell adhesion. The unidirectionally aligned fibers can accelerate neural differentiation of stem cells, representing a promising therapy for neural tissue degenerative diseases and nerve injuries.

Structure and magnetic fabric of the Quetico metasedimentary rocks in the Calm Lake - Perch Lake area, near Atikokan, Northwestern Ontario

NASA Astrophysics Data System (ADS)

Sarvas, Perry

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Fire disturbance mapping in a northern boreal forest using AVHRR/NDVI imagery: Comparing techniques of change detection and substrate correction

NASA Astrophysics Data System (ADS)

Remmel, Tarmo Kaarel

Carbon nanotubes (CNTs) with extraordinary properties and thus many potential applications have been predicted to be the best reinforcements for the next-generation multifunctional composite materials. Difficulties exist in transferring the most use of the unprecedented properties of individual CNTs to macroscopic forms of CNT assemblies. Therefore, this thesis focuses on two main goals: 1) discussing the issues that influence the performance of bulk CNT products, and 2) fabricating high-performance dry CNT films and composite films with an understanding of the fundamental structure-property relationship in these materials. Dry CNT films were fabricated by a winding process using CNT arrays with heights of 230 mum, 300 im and 360 mum. The structures of the as-produced films, as well as their mechanical and electrical properties were examined in order to find out the effects of different CNT lengths. It was found that the shorter CNTs synthesized by shorter time in the CVD furnace exhibited less structural defects and amorphous carbon, resulting in more compact packing and better nanotube alignment when made into dry films, thus, having better mechanical and electrical performance. A novel microcombing approach was developed to mitigate the CNT waviness and alignment in the dry films, and ultrahigh mechanical properties and exceptional electrical performance were obtained. This method utilized a pair of sharp surgical blades with microsized features at the blade edges as micro-combs to, for the first time, disentangle and straighten the wavy CNTs in the dry-drawn CNT sheet at single-layer level. The as-combed CNT sheet exhibited high level of nanotube alignment and straightness, reduced structural defects, and enhanced nanotube packing density. The dry CNT films produced by microcombing had a very high Young's modulus of 172 GPa, excellent tensile strength of 3.2 GPa, and unprecedented electrical conductivity of 1.8x10 5 S/m, which were records for CNT films or buckypapers. This novel technique could construct CNT films with reproducible properties, which also had the potential to be scale-up for industrial mass production. Based on the microcombing approach, dispersion issue of the long, straight, and highly aligned CNTs was investigated by adding PVA matrix into the microcombed CNT sheets. It was found although microcombing promoted the formation of agglomerated strands of the long, straight, and aligned CNTs, this was not an adverse problem in impairing the composite performance. When matrix was added, those agglomerated strands were wrapped together which maintained a more stable and better contact between nanotubes than those in the dry films. The as-produced CNT/PVA composite films exhibit an electrical conductivity of 1.84x105 S/m, Young's modulus of 119 GPa, tensile strength of 2.9 GPa, and toughness of 52.4 J/cm3, which represent improvements over those of uncombed samples by 300%, 100%, 120%, and 200%, respectively, demonstrating the effectiveness and reliability of microcombing in producing high-performance CNT/polymer composite films.

Semiconductor tunnel junction with enhancement layer

DOEpatents

Klem, J.F.; Zolper, J.C.

1997-10-21

The incorporation of a pseudomorphic GaAsSb layer in a runnel diode structure affords a new degree of freedom in designing runnel junctions for p-n junction device interconnects. Previously only doping levels could be varied to control the tunneling properties. This invention uses the valence band alignment band of the GaAsSb with respect to the surrounding materials to greatly relax the doping requirements for tunneling. 5 figs.

Photoemission Spectroscopy Studies of Methylammonium Lead Iodide Perovskite Thin Films and Interfaces

NASA Astrophysics Data System (ADS)

Thibau, Emmanuel S.

Organometal halide perovskites have recently emerged as promising materials for fundamentally low-cost, high-performance optoelectronics. In this thesis, we utilize thermal co-evaporation of PbI2 and CH3NH 3 I to fabricate thin films of CH3NH3PbI 3. We first investigate the effect of stoichiometry on some of its structural, optical and electronic properties. Then, we study the energy level alignment of CH3NH3PbI3 with 6 organic semiconductors, revealing good agreement between the data and the theory of vacuum level alignment. Finally, the interface formed between CH3NH 3PbI3 and MoO3 is examined. The findings suggest migration of iodide species into the oxide layer, resulting in deterioration of its chemical and electronic properties. Insertion of an organic interlayer is shown to mitigate these undesirable effects. The results of this work could be of use in device engineering, where knowledge of such interfacial phenomena is of utmost importance in achieving optimized device structures.

Plasma fluorination of vertically aligned carbon nanotubes: functionalization and thermal stability.

PubMed

Struzzi, Claudia; Scardamaglia, Mattia; Hemberg, Axel; Petaccia, Luca; Colomer, Jean-François; Snyders, Rony; Bittencourt, Carla

2015-01-01

Grafting of fluorine species on carbon nanostructures has attracted interest due to the effective modification of physical and chemical properties of the starting materials. Various techniques have been employed to achieve a controlled fluorination yield; however, the effect of contaminants is rarely discussed, although they are often present. In the present work, the fluorination of vertically aligned multiwalled carbon nanotubes was performed using plasma treatment in a magnetron sputtering chamber with fluorine diluted in an argon atmosphere with an Ar/F2 ratio of 95:5. The effect of heavily diluted fluorine in the precursor gas mixture is investigated by evaluating the modifications in the nanotube structure and the electronic properties upon plasma treatment. The existence of oxygen-based grafted species is associated with background oxygen species present in the plasma chamber in addition to fluorine. The thermal stability and desorption process of the fluorine species grafted on the carbon nanotubes during the fluorine plasma treatment were evaluated by combining different spectroscopic techniques.

Two-dimensional n -InSe/p -GeSe(SnS) van der Waals heterojunctions: High carrier mobility and broadband performance

NASA Astrophysics Data System (ADS)

Xia, Cong-xin; Du, Juan; Huang, Xiao-wei; Xiao, Wen-bo; Xiong, Wen-qi; Wang, Tian-xing; Wei, Zhong-ming; Jia, Yu; Shi, Jun-jie; Li, Jing-bo

2018-03-01

Recently, constructing van der Waals (vdW) heterojunctions by stacking different two-dimensional (2D) materials has been considered to be effective strategy to obtain the desired properties. Here, through first-principles calculations, we find theoretically that the 2D n -InSe/p -GeSe(SnS) vdW heterojunctions are the direct-band-gap semiconductor with typical type-II band alignment, facilitating the effective separation of photogenerated electron and hole pairs. Moreover, they possess the high optical absorption strength (˜105 ), broad spectrum width, and excellent carrier mobility (˜103c m2V-1s-1 ). Interestingly, under the influences of the interlayer coupling and external electric field, the characteristics of type-II band alignment is robust, while the band-gap values and band offset are tunable. These results indicate that 2D n -InSe/p -GeSe(SnS) heterojunctions possess excellent optoelectronic and transport properties, and thus can become good candidates for next-generation optoelectronic nanodevices.

Plasmonic Gold Nanorod Dispersions with Electrical and Optical Tunability

NASA Astrophysics Data System (ADS)

Grabowski, Christopher; Mahoney, Clare; Park, Kyoungweon; Jawaid, Ali; White, Timothy; Vaia, Richard

The transmissive, absorptive, electrical, and thermal properties of plasmonic gold nanorods (NRs) have led to their employment in a broad range of applications. These electro-optical properties - governed by their size, shape, and composition - are widely and precisely tunable during synthesis. Gold NRs show promise for large scale optical elements as they have been demonstrated to align faster than liquid crystal films (μs) at low fields (1 V/ μm). Successfully dispersing a high volume fraction of gold NRs requires a strategy to control particle-particle separation and thus avoid aggregation. Herein, we discuss the role of theta temperature and the ability to swell or collapse the chains of polymer-grafted gold NRs to alter the interaction potential between particles. UV-Vis spectroscopy, scattering, and electrical susceptibility characterization methods were employed to determine nanoparticle dispersion along with the degree of gold NR alignment. The development of new agile photonic materials, controllable with both light and electric fields, will help address emerging needs in laser hardening (agile filters) and variable transmission visors.

Effect of Terminal Modification on the Molecular Assembly and Mechanical Properties of Protein-Based Block Copolymers.

PubMed

Jacobsen, Matthew M; Tokareva, Olena S; Ebrahimi, Davoud; Huang, Wenwen; Ling, Shengjie; Dinjaski, Nina; Li, David; Simon, Marc; Staii, Cristian; Buehler, Markus J; Kaplan, David L; Wong, Joyce Y

2017-09-01

Accurate prediction and validation of the assembly of bioinspired peptide sequences into fibers with defined mechanical characteristics would aid significantly in designing and creating materials with desired properties. This process may also be utilized to provide insight into how the molecular architecture of many natural protein fibers is assembled. In this work, computational modeling and experimentation are used in tandem to determine how peptide terminal modification affects a fiber-forming core domain. Modeling shows that increased terminal molecular weight and hydrophilicity improve peptide chain alignment under shearing conditions and promote consolidation of semicrystalline domains. Mechanical analysis shows acute improvements to strength and elasticity, but significantly reduced extensibility and overall toughness. These results highlight an important entropic function that terminal domains of fiber-forming peptides exhibit as chain alignment promoters, which ultimately has notable consequences on the mechanical behavior of the final fiber products. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Directional Solidification and Mechanical Properties of NiAl-NiAlTa Alloys

NASA Technical Reports Server (NTRS)

Johnson, D. R.; Chen, X. F.; Oliver, B. F.; Noebe, R. D.; Whittenberger, J. D.

1995-01-01

Directional solidification of eutectic alloys is a promising technique for producing in-situ composite materials exhibiting a balance of properties. Consequently, the microstructure, creep strength and fracture toughness of directionally solidified NiAl-NiAlTa alloys were investigated. Directional solidification was performed by containerless processing techniques to minimize alloy contamination. The eutectic composition was found to be NiAl-15.5 at% Ta and well-aligned microstructures were produced at this composition. A near-eutectic alloy of NiAl-14.5Ta was also investigated. Directional solidification of the near-eutectic composition resulted in microstructures consisting of NiAl dendrites surrounded by aligned eutectic regions. The off-eutectic alloy exhibited promising compressive creep strengths compared to other NiAl-based intermetallics, while preliminary testing indicated that the eutectic alloy was competitive with Ni-base single crystal superalloys. The room temperature toughness of these two-phase alloys was similar to that of polycrystalline NiAl even with the presence of the brittle Laves phase NiAlTa.

Roll-to-Roll Continuous Manufacturing Multifunctional Nanocomposites by Electric-Field-Assisted "Z" Direction Alignment of Graphite Flakes in Poly(dimethylsiloxane).

PubMed

Guo, Yuanhao; Chen, Yuwei; Wang, Enmin; Cakmak, Miko

2017-01-11

A roll-to-roll continuous process was developed to manufacture large-scale multifunctional poly(dimethylsiloxane) (PDMS) films embedded with thickness direction ("Z" direction) aligned graphite nanoparticles by application of electric field. The kinetics of particle "Z" alignment and chain formation was studied by tracking the real-time change of optical light transmission through film thickness direction. Benefiting from the anisotropic structure of aligned particle chains, the electrical and thermal properties of the nanocomposites were dramatically enhanced through the thickness direction as compared to those of the nanocomposites containing the same particle loading without electrical field alignment. With 5 vol % graphite loading, 250 times higher electrical conductivity, 43 times higher dielectric permittivity, and 1.5 times higher thermal conductivity was achieved in the film thickness direction after the particles were aligned under electrical field. Moreover, the aligned nanocomposites with merely 2 vol % graphite particles exhibit even higher electric conductivity and dielectric permittivity than those of the nonaligned nanocomposites at random percolation threshold (10 vol % particles), as the "electric-field-directed" percolation threshold concentration is substantially decreased using this process. As the graphite loading increases to 20 vol %, the aligned nanocomposites exhibit thermal conductivity as high as 6.05 W/m·K, which is 35 times the thermal conductivity of pure matrix. This roll-to-roll electric field continuous process provides a simple, low-cost, and commercially viable method to manufacture multifunctional nanocomposites for applications as embedded capacitor, electromagnetic (EM) shielding, and thermal interface materials.

Guiding the orientation of smooth muscle cells on random and aligned polyurethane/collagen nanofibers.

PubMed

Jia, Lin; Prabhakaran, Molamma P; Qin, Xiaohong; Ramakrishna, Seeram

2014-09-01

Fabricating scaffolds that can simulate the architecture and functionality of native extracellular matrix is a huge challenge in vascular tissue engineering. Various kinds of materials are engineered via nano-technological approaches to meet the current challenges in vascular tissue regeneration. During this study, nanofibers from pure polyurethane and hybrid polyurethane/collagen in two different morphologies (random and aligned) and in three different ratios of polyurethane:collagen (75:25; 50:50; 25:75) are fabricated by electrospinning. The fiber diameters of the nanofibrous scaffolds are in the range of 174-453 nm and 145-419 for random and aligned fibers, respectively, where they closely mimic the nanoscale dimensions of native extracellular matrix. The aligned polyurethane/collagen nanofibers expressed anisotropic wettability with mechanical properties which is suitable for regeneration of the artery. After 12 days of human aortic smooth muscle cells culture on different scaffolds, the proliferation of smooth muscle cells on hybrid polyurethane/collagen (3:1) nanofibers was 173% and 212% higher than on pure polyurethane scaffolds for random and aligned scaffolds, respectively. The results of cell morphology and protein staining showed that the aligned polyurethane/collagen (3:1) scaffold promote smooth muscle cells alignment through contact guidance, while the random polyurethane/collagen (3:1) also guided cell orientation most probably due to the inherent biochemical composition. Our studies demonstrate the potential of aligned and random polyurethane/collagen (3:1) as promising substrates for vascular tissue regeneration. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Freestanding Aligned Multi-walled Carbon Nanotubes for Supercapacitor Devices

NASA Astrophysics Data System (ADS)

Moreira, João Vitor Silva; Corat, Evaldo José; May, Paul William; Cardoso, Lays Dias Ribeiro; Lelis, Pedro Almeida; Zanin, Hudson

2016-11-01

We report on the synthesis and electrochemical properties of multi-walled carbon nanotubes (MWCNTs) for supercapacitor devices. Freestanding vertically-aligned MWCNTs and MWCNT powder were grown concomitantly in a one-step chemical vapour deposition process. Samples were characterized by scanning and transmission electron microscopies and Fourier transform infrared and Raman spectroscopies. At similar film thicknesses and surface areas, the freestanding MWCNT electrodes showed higher electrochemical capacitance and gravimetric specific energy and power than the randomly-packed nanoparticle-based electrodes. This suggests that more ordered electrode film architectures facilitate faster electron and ion transport during the charge-discharge processes. Energy storage and supply or supercapacitor devices made from these materials could bridge the gap between rechargeable batteries and conventional high-power electrostatic capacitors.

Embedded Aligned Carbon Nanotube Sheets for Strain and Damage sensing in Composite Structures

NASA Astrophysics Data System (ADS)

Aly, Karim Aly Abdelomoaty Elsayed

The world demand for fiber reinforced composite materials has been steadily increasing because of the widespread adoption of this class of material in many markets. The automotive, aerospace, marine and energy sectors account for a large percentage of this grow. Outstanding fatigue performance, high specific stiffness and strength, and low density are among the most important properties that fiber reinforced polymer composites offer. Furthermore, their properties can be tailored to meet the specific needs of the final applications. However, this class of material is composed of multiple layers of inhomogeneous and anisotropic constituents, i.e. fibers and matrix. Therefore, this laminated nature make the composite material prone to intrinsic damage including interfacial debonding and delamination and their strength and failure are dependent on the fiber architecture and direction of the applied stresses. Consequently, it is of prime importance to monitor the health of these structures. New and improved methods for early detection of damage and structural health monitoring of composite materials may allow for enhanced reliability, lifetime and performance while minimizing maintenance time during a composite part's service life. Over the last few decades different non-destructive methods and materials have been investigated for use as strain sensors. Since the discovery of carbon nanotubes (CNTs), they have attracted much research interest due to their superior electrical, thermal and mechanical properties as well as their high aspect ratio. In this context, CNTs have been used in the recent years to enable sensing capabilities. In this dissertation, the usage of CNTs for performing strain and damage sensing in composites is evaluated. This was enabled by embedding aligned sheets of two millimeters long, interconnected CNTs into laminated structures that were then subjected to different forms of mechanical loading. The localization of the CNT sheets inside the host structure was done using a novel technique that allowed for carrying out the embedment task conveniently and repeatedly. The real-time electrical resistance change of the CNT sheets in response to the applied mechanical stresses was measured in-situ so that the electromechnical behavior of the CNTs could be linked to the strain change and damage in the host structure. The quasi-static and dynamic flexural, axial tensile and compression loadings of the composite structures revealed that the CNT sheets exhibited sensitivity, stability and repeatability which are vital properties for any successful health monitoring technique. (Abstract shortened by ProQuest.).

Buckling of Carbon Nanotube-Reinforced Polymer Laminated Composite Materials Subjected to Axial Compression and Shear Loadings

NASA Technical Reports Server (NTRS)

Riddick, J. C.; Gates, T. S.; Frankland, S.-J. V.

2005-01-01

A multi-scale method to predict the stiffness and stability properties of carbon nanotube-reinforced laminates has been developed. This method is used in the prediction of the buckling behavior of laminated carbon nanotube-polyethylene composites formed by stacking layers of carbon nanotube-reinforced polymer with the nanotube alignment axes of each layer oriented in different directions. Linking of intrinsic, nanoscale-material definitions to finite scale-structural properties is achieved via a hierarchical approach in which the elastic properties of the reinforced layers are predicted by an equivalent continuum modeling technique. Solutions for infinitely long symmetrically laminated nanotube-reinforced laminates with simply-supported or clamped edges subjected to axial compression and shear loadings are presented. The study focuses on the influence of nanotube volume fraction, length, orientation, and functionalization on finite-scale laminate response. Results indicate that for the selected laminate configurations considered in this study, angle-ply laminates composed of aligned, non-functionalized carbon nanotube-reinforced lamina exhibit the greatest buckling resistance with 1% nanotube volume fraction of 450 nm uniformly-distributed carbon nanotubes. In addition, hybrid laminates were considered by varying either the volume fraction or nanotube length through-the-thickness of a quasi-isotropic laminate. The ratio of buckling load-to-nanotube weight percent for the hybrid laminates considered indicate the potential for increasing the buckling efficiency of nanotube-reinforced laminates by optimizing nanotube size and proportion with respect to laminate configuration.

Vertically Aligned and Interconnected Boron Nitride Nanosheets for Advanced Flexible Nanocomposite Thermal Interface Materials.

PubMed

Chen, Jin; Huang, Xingyi; Sun, Bin; Wang, Yuxin; Zhu, Yingke; Jiang, Pingkai

2017-09-13

The continuous evolution toward semiconductor technology in the "more-than-Moore" era and rapidly increasing power density of modern electronic devices call for advanced thermal interface materials (TIMs). Here, we report a novel strategy to construct flexible polymer nanocomposite TIMs for advanced thermal management applications. First, aligned polyvinyl alcohol (PVA) supported and interconnected 2D boron nitride nanosheets (BNNSs) composite fiber membranes were fabricated by electrospinning. Then, the nanocomposite TIMs were constructed by rolling the PVA/BNNS composite fiber membranes to form cylinders and subsequently vacuum-assisted impregnation of polydimethylsiloxane (PDMS) into the porous cylinders. The nanocomposite TIMs not only exhibit a superhigh through-plane thermal conductivity enhancement of about 10 times at a low BNNS loading of 15.6 vol % in comparison with the pristine PDMS but also show excellent electrical insulating property (i.e., high volume electrical resistivity). The outstanding thermal management capability of the nanocomposite TIMs was practically confirmed by capturing the surface temperature variations of a working LED chip integrated with the nanocomposite TIMs.

Tunable band alignment in two-phase-coexistence Nb3O7F nanocrystals with enhanced light harvesting and photocatalytic performance

NASA Astrophysics Data System (ADS)

Li, Zhen; Huang, Fei; Feng, Xin; Yan, Aihua; Dong, Haiming; Hu, Miao; Li, Qi

2018-06-01

A two-phase-coexistence technique offers intriguing variables to maneuver novel and enhanced functionality in a single-component material. Most importantly, new band alignment and perfect interfaces between two phases can strongly affect local photoelectronic properties. However, previous efforts to achieve two-phase coexistence were mainly restricted to specific systems and methods. Here we demonstrate a phase-transition route to acquire two-phase-coexistence niobium oxyfluoride (Nb3O7F) nanocrystals for the first time. Based on key distinguishing features of the experimental results and theoretical analysis, the phase transition of Nb3O7F involves an organic/inorganic hybrid, heat treating, Al-doping, lattice deformation and structural rearrangement. The band gap can be effectively tuned from 3.03 eV to 2.84 eV, and the VBM can be tuned from 1.49 eV to 1.69 eV according to the phase proportion. Benefiting from uniform nanocrystal size, tunable band alignment and an optimized interfacial structure, the two-phase coexistence markedly enhances visible-light harvesting and the photocatalytic performance of Nb3O7F nanocrystals. The results not only demonstrate an opportunity to explore two-phase coexistence of novel nanocrystals, but also illustrate the role of two-phase coexistence in achieving enhanced photoelectronic properties.

Tunable band alignment in two-phase-coexistence Nb3O7F nanocrystals with enhanced light harvesting and photocatalytic performance.

PubMed

Li, Zhen; Huang, Fei; Feng, Xin; Yan, Aihua; Dong, Haiming; Hu, Miao; Li, Qi

2018-06-01

A two-phase-coexistence technique offers intriguing variables to maneuver novel and enhanced functionality in a single-component material. Most importantly, new band alignment and perfect interfaces between two phases can strongly affect local photoelectronic properties. However, previous efforts to achieve two-phase coexistence were mainly restricted to specific systems and methods. Here we demonstrate a phase-transition route to acquire two-phase-coexistence niobium oxyfluoride (Nb 3 O 7 F) nanocrystals for the first time. Based on key distinguishing features of the experimental results and theoretical analysis, the phase transition of Nb 3 O 7 F involves an organic/inorganic hybrid, heat treating, Al-doping, lattice deformation and structural rearrangement. The band gap can be effectively tuned from 3.03 eV to 2.84 eV, and the VBM can be tuned from 1.49 eV to 1.69 eV according to the phase proportion. Benefiting from uniform nanocrystal size, tunable band alignment and an optimized interfacial structure, the two-phase coexistence markedly enhances visible-light harvesting and the photocatalytic performance of Nb 3 O 7 F nanocrystals. The results not only demonstrate an opportunity to explore two-phase coexistence of novel nanocrystals, but also illustrate the role of two-phase coexistence in achieving enhanced photoelectronic properties.

High voltage electrophoretic deposition for electrochemical energy storage and other applications

NASA Astrophysics Data System (ADS)

Santhanagopalan, Sunand

High voltage electrophoretic deposition (HVEPD) has been developed as a novel technique to obtain vertically aligned forests of one-dimensional nanomaterials for efficient energy storage. The ability to control and manipulate nanomaterials is critical for their effective usage in a variety of applications. Oriented structures of one-dimensional nanomaterials provide a unique opportunity to take full advantage of their excellent mechanical and electrochemical properties. However, it is still a significant challenge to obtain such oriented structures with great process flexibility, ease of processing under mild conditions and the capability to scale up, especially in context of efficient device fabrication and system packaging. This work presents HVEPD as a simple, versatile and generic technique to obtain vertically aligned forests of different one-dimensional nanomaterials on flexible, transparent and scalable substrates. Improvements on material chemistry and reduction of contact resistance have enabled the fabrication of high power supercapacitor electrodes using the HVEPD method. The investigations have also paved the way for further enhancements of performance by employing hybrid material systems and AC/DC pulsed deposition. Multi-walled carbon nanotubes (MWCNTs) were used as the starting material to demonstrate the HVEPD technique. A comprehensive study of the key parameters was conducted to better understand the working mechanism of the HVEPD process. It has been confirmed that HVEPD was enabled by three key factors: high deposition voltage for alignment, low dispersion concentration to avoid aggregation and simultaneous formation of holding layer by electrodeposition for reinforcement of nanoforests. A set of suitable parameters were found to obtain vertically aligned forests of MWCNTs. Compared with their randomly oriented counterparts, the aligned MWCNT forests showed better electrochemical performance, lower electrical resistance and a capability to achieve superhydrophpbicity, indicating their potential in a broad range of applications. The versatile and generic nature of the HVEPD process has been demonstrated by achieving deposition on flexible and transparent substrates, as well as aligned forests of manganese dioxide (MnO2) nanorods. A continuous roll-printing HVEPD approach was then developed to obtain aligned MWCNT forest with low contact resistance on large, flexible substrates. Such large-scale electrodes showed no deterioration in electrochemical performance and paved the way for practical device fabrication. The effect of a holding layer on the contact resistance between aligned MWCNT forests and the substrate was studied to improve electrochemical performance of such electrodes. It was found that a suitable precursor salt like nickel chloride could be used to achieve a conductive holding layer which helped to significantly reduce the contact resistance. This in turn enhanced the electrochemical performance of the electrodes. High-power scalable redox capacitors were then prepared using HVEPD. Very high power/energy densities and excellent cyclability have been achieved by synergistically combining hydrothermally synthesized, highly crystalline α-MnO 2 nanorods, vertically aligned forests and reduced contact resistance. To further improve the performance, hybrid electrodes have been prepared in the form of vertically aligned forest of MWCNTs with branches of α-MnO 2 nanorods on them. Large- scale electrodes with such hybrid structures were manufactured using continuous HVEPD and characterized, showing further improved power and energy densities. The alignment quality and density of MWCNT forests were also improved by using an AC/DC pulsed deposition technique. In this case, AC voltage was first used to align the MWCNTs, followed by immediate DC voltage to deposit the aligned MWCNTs along with the conductive holding layer. Decoupling of alignment from deposition was proven to result in better alignment quality and higher electrochemical performance.

Effects of Matrix Alignment and Mechanical Constraints on Cellular Behavior in 3D Engineered Microtissues

NASA Astrophysics Data System (ADS)

Bose, Prasenjit; Eyckmans, Jeroen; Chen, Christopher; Reich, Daniel

The adhesion of cells to the extracellular matrix (ECM) plays a crucial role in a variety of cellular functions. The main building blocks of the ECM are 3D networks of fibrous proteins whose structure and alignments varies with tissue type. However, the impact of ECM alignment on cellular behaviors such as cell adhesion, spreading, extension and mechanics remains poorly understood. We present results on the development of a microtissue-based system that enables control of the structure, orientation, and degree of fibrillar alignment in 3D fibroblast-populated collagen gels. The tissues self-assemble from cell-laden collagen gels placed in micro-fabricated wells containing sets of elastic pillars. The contractile action of the cells leads to controlled alignment of the fibrous collagen, depending on the number and location of the pillars in each well. The pillars are elastic, and are utilized to measure the contractile forces of the microtissues, and by incorporating magnetic material in selected pillars, time-varying forces can be applied to the tissues for dynamic stimulation and measurement of mechanical properties. Results on the effects of varying pillar shape, spacing, location, and stiffness on microtissue organization and contractility will be presented. This work is supported by NSF CMMI-1463011.

Synergistic structures from magnetic freeze casting with surface magnetized alumina particles and platelets.

PubMed

Frank, Michael B; Hei Siu, Sze; Karandikar, Keyur; Liu, Chin-Hung; Naleway, Steven E; Porter, Michael M; Graeve, Olivia A; McKittrick, Joanna

2017-12-01

Magnetic freeze casting utilizes the freezing of water, a low magnetic field and surface magnetized materials to make multi-axis strengthened porous scaffolds. A much greater magnetic moment was measured for larger magnetized alumina platelets compared with smaller particles, which indicated that more platelet aggregation occurred within slurries. This led to more lamellar wall alignment along the magnetic field direction during magnetic freeze casting at 75 mT. Slurries with varying ratios of magnetized particles to platelets (0:1, 1:3, 1:1, 3:1, 7:1, 1:0) produced porous scaffolds with different structural features and degrees of lamellar wall alignment. The greatest mechanical enhancement in the magnetic field direction was identified in the synergistic condition with the highest particle to platelet ratio (7:1). Magnetic freeze casting with varying ratios of magnetized anisotropic and isotropic alumina provided insights about how heterogeneous morphologies aggregate within lamellar walls that impact mechanical properties. Fabrication of strengthened scaffolds with multi-axis aligned porosity was achieved without introducing different solid materials, freezing agents or additives. Resemblance of 7:1 particle to platelet scaffold microstructure to wood light-frame house construction is framed in the context of assembly inspiration being derived from both natural and synthetic sources. Copyright © 2017 Elsevier Ltd. All rights reserved.

Thin Crystal Film Polarizer for Display Application

NASA Astrophysics Data System (ADS)

Paukshto, Michael

2003-03-01

Optiva Inc. has pioneered the development of nano-thin crystalline film (TCF) optical coatings for use in information displays and other applications. TCF is a material based on water-based dichroic dye solutions. Disk-like dye molecules aggregate in a ``plane-to-plane" manner; this self-assembly results in formation of highly anisometric rod-like stacks. These stacks have an aspect ratio of approximately 200:1. At a certain threshold of dye concentration, a nematic ordering of the rod-like stacks appears. Such a system acquires polarizing properties according to the following mechanism. Flow-induced alignment is known to occur in the lyotropic systems in a shear flow. In our case, the material undergoes shear alignment while being coated onto a glass or plastic substrate. In the coated thin film, the long molecular stacks are oriented in the flow direction parallel to the flow direction and substrate plane. The planes of the dye molecules are perpendicular to the substrate plane with the optical transition oscillators lying in the molecule plane. After the coating, as the thin film dries, crystallization occurs due to water evaporation. In a dry film, the molecular planes maintain their orthogonal orientation with respect to the substrate surface. TCF is known to possess properties of an E-mode polarizer. TCF technology has now migrated out of the R stage into manufacturing and is currently being incorporated into new display products. This presentation will provide an overview of TCF technology. The first part of the presentation will describe material structure, optical properties and characterization, material processing and associated coating equipment. This will be followed by a presentation on optical modeling and simulation of display performance with TCF components. Comparisons of display performance will be made for exemplar configurations of a variety of LCDs, including TN, STN and AMLCD designs in both transmissive and reflective modes.

Electric-dipole effect of defects on the energy band alignment of rutile and anatase TiO₂.

PubMed

Zhang, Daoyu; Yang, Minnan; Dong, Shuai

2015-11-21

Titanium dioxide materials have been studied intensively and extensively for photocatalytic applications. A long-standing open question is the energy band alignment of rutile and anatase TiO2 phases, which can affect the photocatalytic process in the composite system. There are basically two contradictory viewpoints about the alignment of these two TiO2 phases supported by the respective experiments: (1) straddling type and (2) staggered type. In this work, our DFT plus U calculations show that the perfect rutile(110) and anatase(101) surfaces have the straddling type band alignment, whereas the surfaces with defects can turn the band alignment into the staggered type. The electric dipoles induced by defects are responsible for the reversal of band alignment. Thus the defects introduced during the preparation and post-treatment processes of materials are probably the answer to the above open question regarding the band alignment, which can be considered in real practice to tune the photocatalytic activity of materials.

Flexible polymeric rib waveguide with self-align couplers system

PubMed Central

Huang, Cheng-Sheng; Wang, Wei-Chih

2011-01-01

The authors report a polymeric based rib waveguide with U shape self-align fiber couplers system using a simple micromolding process with SU8 as a molding material and polydimethysiloxane as a waveguide material. The material is used for its good optical transparency, low surface tension, biocompatibility, and durability. Furthermore, the material is highly formable. This unique fabrication molding technique provides a means of keeping the material and manufacturing costs to a minimum. The self-align fiber couplers system also proves a fast and simple means of light coupling. The flexible nature of the waveguide material makes this process ideal for a potential wearable optical sensor. PMID:22171151

Aligning flaky FeSiAl particles with a two-dimensional rotating magnetic field to improve microwave-absorbing and shielding properties of composites

NASA Astrophysics Data System (ADS)

Liu, Chang; Cai, Jun; Duan, Yubing; Li, Xinghao; Zhang, Deyuan

2018-07-01

In order to enhance the microwave-absorbing and shielding properties of the composites, the flaky FeSiAl particles embedded in an epoxy polymer were aligned with a two-dimensional rotating magnetic field. The morphologies, electromagnetic (EM) characteristics, and microwave-absorbing and shielding properties of the unaligned and aligned FeSiAl/epoxy composites were investigated. The results showed that after alignment treatment, the flaky FeSiAl particles tend to orient uniformly in the rotating magnetic field, and the permittivity and permeability of the aligned composites were increased in the frequency range of 1-18 GHz compared with that of randomly distributed composites. The calculated microwave-absorbing properties indicated that the peak value of the return loss (RL) of the aligned composites can reach 8.8 dB, compared with 5.8 dB of the unaligned composites of 2.5 mm in thickness (60 wt%); and the bandwidth with RL value more than 6 dB is in a wider frequency range from 1 to 2.8 GHz. And the calculated shielding effectiveness (SE) of the aligned composites is 1.1-3 times higher than that of unaligned one in every thickness, and the maximum SE of the aligned one is 31.8 dB at 18 GHz with a thickness of 2.5 mm.

Multifunctional Nanotube Polymer Nanocomposites for Aerospace Applications: Adhesion between SWCNT and Polymer Matrix

NASA Technical Reports Server (NTRS)

Park, Cheol; Wise, Kristopher E.; Kang, Jin Ho; Kim, Jae-Woo; Sauti, Godfrey; Lowther, Sharon E.; Lillehei, Peter T.; Smith, Michael W.; Siochi, Emilie J.; Harrison, Joycelyn S.;

Growth and applications of GeSn-related group-IV semiconductor materials

PubMed Central

Zaima, Shigeaki; Nakatsuka, Osamu; Taoka, Noriyuki; Kurosawa, Masashi; Takeuchi, Wakana; Sakashita, Mitsuo

2015-01-01

We review the technology of Ge1−xSnx-related group-IV semiconductor materials for developing Si-based nanoelectronics. Ge1−xSnx-related materials provide novel engineering of the crystal growth, strain structure, and energy band alignment for realising various applications not only in electronics, but also in optoelectronics. We introduce our recent achievements in the crystal growth of Ge1−xSnx-related material thin films and the studies of the electronic properties of thin films, metals/Ge1−xSnx, and insulators/Ge1−xSnx interfaces. We also review recent studies related to the crystal growth, energy band engineering, and device applications of Ge1−xSnx-related materials, as well as the reported performances of electronic devices using Ge1−xSnx related materials. PMID:27877818

Growth and applications of GeSn-related group-IV semiconductor materials.

PubMed

Zaima, Shigeaki; Nakatsuka, Osamu; Taoka, Noriyuki; Kurosawa, Masashi; Takeuchi, Wakana; Sakashita, Mitsuo

2015-08-01

We review the technology of Ge 1- x Sn x -related group-IV semiconductor materials for developing Si-based nanoelectronics. Ge 1- x Sn x -related materials provide novel engineering of the crystal growth, strain structure, and energy band alignment for realising various applications not only in electronics, but also in optoelectronics. We introduce our recent achievements in the crystal growth of Ge 1- x Sn x -related material thin films and the studies of the electronic properties of thin films, metals/Ge 1- x Sn x , and insulators/Ge 1- x Sn x interfaces. We also review recent studies related to the crystal growth, energy band engineering, and device applications of Ge 1- x Sn x -related materials, as well as the reported performances of electronic devices using Ge 1- x Sn x related materials.

Large-area, lightweight and thick biomimetic composites with superior material properties via fast, economic, and green pathways.

PubMed

Walther, Andreas; Bjurhager, Ingela; Malho, Jani-Markus; Pere, Jaakko; Ruokolainen, Janne; Berglund, Lars A; Ikkala, Olli

2010-08-11

Although remarkable success has been achieved to mimic the mechanically excellent structure of nacre in laboratory-scale models, it remains difficult to foresee mainstream applications due to time-consuming sequential depositions or energy-intensive processes. Here, we introduce a surprisingly simple and rapid methodology for large-area, lightweight, and thick nacre-mimetic films and laminates with superior material properties. Nanoclay sheets with soft polymer coatings are used as ideal building blocks with intrinsic hard/soft character. They are forced to rapidly self-assemble into aligned nacre-mimetic films via paper-making, doctor-blading or simple painting, giving rise to strong and thick films with tensile modulus of 45 GPa and strength of 250 MPa, that is, partly exceeding nacre. The concepts are environmentally friendly, energy-efficient, and economic and are ready for scale-up via continuous roll-to-roll processes. Excellent gas barrier properties, optical translucency, and extraordinary shape-persistent fire-resistance are demonstrated. We foresee advanced large-scale biomimetic materials, relevant for lightweight sustainable construction and energy-efficient transportation.

Polar Nature of Biomimetic Fluorapatite/Gelatin Composites: A Comparison of Bipolar Objects and the Polar State of Natural Tissue.

PubMed

Burgener, Matthias; Putzeys, Tristan; Gashti, Mazeyar Parvinzadeh; Busch, Susanne; Aboulfadl, Hanane; Wübbenhorst, Michael; Kniep, Rüdiger; Hulliger, Jürg

2015-09-14

The correspondence of the state of alignment of macromolecules in biomimetic materials and natural tissues is demonstrated by investigating a mechanism of electrical polarity formation: An in vitro grown biomimetic FAp/gelatin composite is investigated for its polar properties by second harmonic (SHGM) and scanning pyroelectric microscopy (SPEM). Hexagonal prismatic seed crystals formed in gelatin gels represent a monodomain polar state, due to aligned mineralized gelatin molecules. Later growth stages, showing dumbbell morphologies, develop into a bipolar state because of surface recognition by gelatin functionality: A reversal of the polar alignment of macromolecules, thus, takes place close to that basal plane of the seed. In natural hard tissues (teeth and bone investigated by SPEM) and the biomimetic FAp/gelatin composite, we find a surprising analogy in view of growth-induced states of polarity: The development of polarity in vivo and in vitro can be explained by a Markov-type mechanism of molecular recognition during the attachment of macromolecules.

A comparative study of zirconium and titanium implants in rat: osseointegration and bone material quality.

PubMed

Hoerth, Rebecca M; Katunar, María R; Gomez Sanchez, Andrea; Orellano, Juan C; Ceré, Silvia M; Wagermaier, Wolfgang; Ballarre, Josefina

2014-02-01

Permanent metal implants are widely used in human medical treatments and orthopedics, for example as hip joint replacements. They are commonly made of titanium alloys and beyond the optimization of this established material, it is also essential to explore alternative implant materials in view of improved osseointegration. The aim of our study was to characterize the implant performance of zirconium in comparison to titanium implants. Zirconium implants have been characterized in a previous study concerning material properties and surface characteristics in vitro, such as oxide layer thickness and surface roughness. In the present study, we compare bone material quality around zirconium and titanium implants in terms of osseointegration and therefore characterized bone material properties in a rat model using a multi-method approach. We used light and electron microscopy, micro Raman spectroscopy, micro X-ray fluorescence and X-ray scattering techniques to investigate the osseointegration in terms of compositional and structural properties of the newly formed bone. Regarding the mineralization level, the mineral composition, and the alignment and order of the mineral particles, our results show that the maturity of the newly formed bone after 8 weeks of implantation is already very high. In conclusion, the bone material quality obtained for zirconium implants is at least as good as for titanium. It seems that the zirconium implants can be a good candidate for using as permanent metal prosthesis for orthopedic treatments.

Effect of electric field induced alignment and dispersion of functionalized carbon nanotubes on properties of natural rubber

NASA Astrophysics Data System (ADS)

Gao, Jiangshan; He, Yan; Gong, Xiubin

2018-06-01

The original equipment and method for orienting multi-walled carbon nanotubes (MWCNTs) in natural rubber (NR) by alternating current (AC) electric field were reported in the present study. MWCNTs with various volume fractions were dispersed in the mixture latex which composed of natural rubber, additives and methylbenzene. The application of AC electric field during nanocomposites curing process was used to induce the formation of aligned conductive nanotube networks between the electrodes. The aligned MWCNTs in the composites have a better orientation performance and dispersion quality than these of random MWCNTs by analyzing TEM and SEM images. The effects of MWCNTs anisotropy on thermal conductivity, dielectric properties, and dynamic mechanical properties of NR were studied. The mean value of thermal conductivity of composites loading with aligned MWCNTs was 8.67% higher than that of composites with random MWCNTs due to the anisotropy of aligned MWCNTs. The compounds with aligned MWCNTs possessed low dielectric constant, loss tangents and conductivity, namely a good insulativity. The compounds loading with aligned MWCNTs had lower loss modulus and better dynamic mechanical properties than those with random MWCNTs. This method can make full use of the high thermal conductivity of MWCNTs axis, and expand the application areas of natural rubber like conducting heat in a certain direction with a high efficiency.

Two-dimensional metal-organic frameworks with high thermoelectric efficiency through metal ion selection.

PubMed

He, Yuping; Spataru, Catalin D; Léonard, Francois; Jones, Reese E; Foster, Michael E; Allendorf, Mark D; Alec Talin, A

2017-07-26

Two-dimensional (2D) materials have attracted much attention due to their novel properties. An exciting new class of 2D materials based on metal-organic frameworks (MOFs) has recently emerged, displaying high electrical conductivity, a rarity among organic nanoporous materials. The emergence of these materials raises intriguing questions about their fundamental electronic, optical, and thermal properties, but few studies exist in this regard. Here we present an atomistic study of the thermoelectric properties of crystalline 2D MOFs X 3 (HITP) 2 with X = Ni, Pd or Pt, and HITP = 2,3,6,7,10,11-hexaiminotriphenylene, using both ab initio transport models and classical molecular dynamics simulations. We find that these materials have a high Seebeck coefficient and low thermal conductivity, making them promising for thermoelectric applications. Furthermore, we explore the dependence of thermoelectric transport properties on the atomic structure by comparing the calculated band structure, band alignment, and electronic density of states of the three 2D MOFs, and find that the thermoelectric transport properties strongly depend on both the interaction between the ligands and the metal ions, and the d orbital splitting of the metal ions induced by the ligands. This demonstrates that selection of the metal ion is a powerful approach to control and enhance the thermoelectric properties. Interestingly we reveal an unexpected effect where, unlike for electrons, the thermal and electrical current may not be equally carried by the holes, leading to a significant deviation from the Wiedemann-Franz law. The results of this work provide fundamental guidance to optimize the existing 2D MOFs, and to design and discover new families of MOF-like materials for thermoelectric applications.

Laser beam alignment apparatus and method

DOEpatents

Gruhn, C.R.; Hammond, R.B.

The disclosure related to an apparatus and method for laser beam alignment. Thermoelectric properties of a disc in a laser beam path are used to provide an indication of beam alignment and/or automatic laser alignment.

Laser beam alignment apparatus and method

DOEpatents

Gruhn, Charles R.; Hammond, Robert B.

1981-01-01

The disclosure relates to an apparatus and method for laser beam alignment. Thermoelectric properties of a disc in a laser beam path are used to provide an indication of beam alignment and/or automatic laser alignment.

Manipulation and control of the interfacial polarization in organic light-emitting diodes by dipolar doping

NASA Astrophysics Data System (ADS)

Jäger, Lars; Schmidt, Tobias D.; Brütting, Wolfgang

2016-09-01

Most of the commonly used electron transporting materials in organic light-emitting diodes exhibit interfacial polarization resulting from partially aligned permanent dipole moments of the molecules. This property modifies the internal electric field distribution of the device and therefore enables an earlier flat band condition for the hole transporting side, leading to improved charge carrier injection. Recently, this phenomenon was studied with regard to different materials and degradation effects, however, so far the influence of dilution has not been investigated. In this paper we focus on dipolar doping of the hole transporting material 4,4-bis[N-(1-naphthyl)-N-phenylamino]-biphenyl (NPB) with the polar electron transporting material tris-(8-hydroxyquinolate) aluminum (Alq3). Impedance spectroscopy reveals that changes of the hole injection voltage do not scale in a simple linear fashion with the effective thickness of the doped layer. In fact, the measured interfacial polarization reaches a maximum value for a 1:1 blend. Taking the permanent dipole moment of Alq3 into account, an increasing degree of dipole alignment is found for decreasing Alq3 concentration. This observation can be explained by the competition between dipole-dipole interactions leading to dimerization and the driving force for vertical orientation of Alq3 dipoles at the surface of the NPB layer.

Near Field Scanning Optical Microscopy (NSOM) of Nano Devices

DTIC Science & Technology

2008-12-01

FEATURES OF GaN NANOWIRES Gallium Nitride (GaN) nanowires are semiconductor wires of great interest lately for its some of its unique properties. These...via chemical vapour deposition (CVD) [19] or even with gas source molecular beam epitaxy (MBE) [20] The GaN nanowires growth techniques will not be...Denlinger, and Peidong Yang, Crystallographic alignment of high-density gallium nitride nanowire arrays, Nature Materials, Issue 3 Vol 8, pg 524

Nanoscale characterization of the electrical properties of oxide electrodes at the organic semiconductor-oxide electrode interface in organic solar cells

NASA Astrophysics Data System (ADS)

MacDonald, Gordon Alex

This dissertation focuses on characterizing the nanoscale and surface averaged electrical properties of transparent conducting oxide electrodes such as indium tin oxide (ITO) and transparent metal-oxide (MO) electron selective interlayers (ESLs), such as zinc oxide (ZnO), the ability of these materials to rapidly extract photogenerated charges from organic semiconductors (OSCs) used in organic photovoltaic (OPV) cells, and evaluating their impact on the power conversion efficiency (PCE) of OPV devices. In Chapter 1, we will introduce the fundamental principles, benefits, and the key innovations that have advanced this technology. In Chapter 2 of this dissertation, we demonstrate an innovative application of conductive probe atomic force microscopy (CAFM) to map the nanoscale electrical heterogeneity at the interface between ITO, and a well-studied OSC, copper phthalocyanine (CuPc).(MacDonald et al. (2012) ACS Nano, 6, p. 9623) In this work we collected arrays of current-voltage (J-V) curves, using a CAFM probe as the top contact of CuPc/ITO systems, to map the local J-V responses. By comparing J-V responses to known models for charge transport, we were able to determine if the local rate-limiting-step for charge transport is through the OSC (ohmic) or the CuPc/ITO interface (non-ohmic). Chapter 3 focus on the electrical property characterization of RF-magnetron sputtered ZnO (sp-ZnO) ESL films on ITO substrates. We have shown that the energetic alignment of ESLs and the OSC active materials plays a critical role in determining the PCE of OPV devices and UV light soaking sensitivity. We have used a combination of device testing, modeling, and impedance spectroscopy to characterize the effects that energetic alignment has on the charge carrier transport and distribution within the OPV device. In Chapter 4 we demonstrate that the local properties of sp-ZnO films varies as a function of the underlying ITO crystal face. We show that the local ITO crystal face determines the local nucleation and growth of the sp-ZnO films and, in turn, affects the nanoscale distribution of electrical and chemical properties. These studies have contributed to a detailed understanding of the role that electrical heterogeneity, insulating barriers and energetic alignment at MO/OSC interfaces play in OPV PCE.

Electrical properties of 0.4 cm long single walled nanotubes

NASA Astrophysics Data System (ADS)

Yu, Zhen

2005-03-01

Centimeter scale aligned carbon nanotube arrays are grown from nanoparticle/metal catalyst pads[1]. We find the nanotubes grow both with and ``against the wind.'' A metal underlayer provides in-situ electrical contact to these long nanotubes with no post growth processing needed. Using the electrically contacted nanotubes, we study electrical transport of 0.4 cm long nanotubes[2]. Using this data, we are able to determine the resistance of a nanotube as a function of length quantitatively, since the contact resistance is negligible in these long nanotubes. The source drain I-V curves are quantitatively described by a classical, diffusive model. Our measurements show that the outstanding transport properties of nanotubes can be extended to the cm scale and open the door to large scale integrated nanotube circuits with macroscopic dimensions. These are the longest electrically contacted single walled nanotubes measured to date. [1] Zhen Yu, Shengdong Li, Peter J. Burke, ``Synthesis of Aligned Arrays of Millimeter Long, Straight Single-Walled Carbon Nanotubes,'' Chemistry of Materials, 16(18), 3414-3416 (2004). [2] Shengdong Li, Zhen Yu, Christopher Rutherglen, Peter J. Burke, ``Electrical properties of 0.4 cm long single-walled carbon nanotubes'' Nano Letters, 4(10), 2003-2007 (2004).

Pseudocapacitive and hierarchically ordered porous electrode materials supercapacitors

NASA Astrophysics Data System (ADS)

Saruhan, B.; Gönüllü, Y.; Arndt, B.

2013-05-01

Commercially available double layer capacitors store energy in an electrostatic field. This forms in the form of a double layer by charged particles arranged on two electrodes consisting mostly of active carbon. Such double layer capacitors exhibit a low energy density, so that components with large capacity according to large electrode areas are required. Our research focuses on the development of new electrode materials to realize the production of electrical energy storage systems with high energy density and high power density. Metal oxide based electrodes increase the energy density and the capacitance by addition of pseudo capacitance to the static capacitance present by the double layer super-capacitor electrodes. The so-called hybrid asymmetric cell capacitors combine both types of energy storage in a single component. In this work, the production routes followed in our laboratories for synthesis of nano-porous and aligned metal oxide electrodes using the electrochemical and sputter deposition as well as anodization methods will be described. Our characterisation studies concentrate on electrodes having redox metal-oxides (e.g. MnOx and WOx) and hierarchically aligned nano-porous Li-doped TiO2-NTs. The material specific and electrochemical properties achieved with these electrodes will be presented.

Strain-induced vertical self-organization of semiconductor quantum dots: A computational study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shtinkov, N., E-mail: nshtinkov@uottawa.ca

Atomistic strain simulations based on the valence force field method are employed to study the vertical arrangements of semiconductor quantum dot (QD) multilayers. The effects of the QD shape, dimensions, and materials parameters are systematically investigated, varying independently the following parameters: spacer width H, QD lateral spacing D, base b, and height h, slope of the side facets, elastic properties of the dot and the substrate materials, and lattice mismatch between the dot and the substrate. The transition between vertically aligned and anti-aligned structures is found to be determined mainly by the ratios H/D and b/D, as well as bymore » the strain anisotropy of the substrate and to a lesser extent of the QD. The dependence on the QD height h is significant only for steep side facets and large aspect ratios h/b, and the effects of the lattice mismatch strain and the bulk elastic moduli are found to be negligible. The comparison with experimental data shows an excellent agreement with the results from the simulations, demonstrating that the presented analysis results in precise theoretical predictions for the vertical self-organization regime in a wide range of QD materials systems.« less

Direct observation of the alignment of ferromagnetic spins by antiferromagnetic spins

NASA Astrophysics Data System (ADS)

Nolting, F.; Scholl, A.; Stöhr, J.; Seo, J. W.; Fompeyrine, J.; Siegwart, H.; Locquet, J.-P.; Anders, S.; Lüning, J.; Fullerton, E. E.; Toney, M. F.; Scheinfein, M. R.; Padmore, H. A.

2000-06-01

The arrangement of spins at interfaces in a layered magnetic material often has an important effect on the properties of the material. One example of this is the directional coupling between the spins in an antiferromagnet and those in an adjacent ferromagnet, an effect first discovered in 1956 and referred to as exchange bias. Because of its technological importance for the development of advanced devices such as magnetic read heads and magnetic memory cells, this phenomenon has received much attention. Despite extensive studies, however, exchange bias is still poorly understood, largely due to the lack of techniques capable of providing detailed information about the arrangement of magnetic moments near interfaces. Here we present polarization-dependent X-ray magnetic dichroism spectro-microscopy that reveals the micromagnetic structure on both sides of a ferromagnetic-antiferromagnetic interface. Images of thin ferromagnetic Co films grown on antiferromagnetic LaFeO3 show a direct link between the arrangement of spins in each material. Remanent hysteresis loops, recorded for individual ferromagnetic domains, show a local exchange bias. Our results imply that the alignment of the ferromagnetic spins is determined, domain by domain, by the spin directions in the underlying antiferromagnetic layer.

Overcoming low-alignment signal contrast induced alignment failure by alignment signal enhancement

NASA Astrophysics Data System (ADS)

Lee, Byeong Soo; Kim, Young Ha; Hwang, Hyunwoo; Lee, Jeongjin; Kong, Jeong Heung; Kang, Young Seog; Paarhuis, Bart; Kok, Haico; de Graaf, Roelof; Weichselbaum, Stefan; Droste, Richard; Mason, Christopher; Aarts, Igor; de Boeij, Wim P.

2016-03-01

Overlay is one of the key factors which enables optical lithography extension to 1X node DRAM manufacturing. It is natural that accurate wafer alignment is a prerequisite for good device overlay. However, alignment failures or misalignments are commonly observed in a fab. There are many factors which could induce alignment problems. Low alignment signal contrast is one of the main issues. Alignment signal contrast can be degraded by opaque stack materials or by alignment mark degradation due to processes like CMP. This issue can be compounded by mark sub-segmentation from design rules in combination with double or quadruple spacer process. Alignment signal contrast can be improved by applying new material or process optimization, which sometimes lead to the addition of another process-step with higher costs. If we can amplify the signal components containing the position information and reduce other unwanted signal and background contributions then we can improve alignment performance without process change. In this paper we use ASML's new alignment sensor (as was introduced and released on the NXT:1980Di) and sample wafers with special stacks which can induce poor alignment signal to demonstrate alignment and overlay improvement.

Tailoring Thermal Radiative Properties with Doped-Silicon Nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Zhuomin

Aligned doped-silicon nanowire (D-SiNW) arrays form a hyperbolic metamaterial in the mid-infrared and have unique thermal radiative properties, such as broadband omnidirectional absorption, low-loss negative refraction, etc. A combined theoretical and experimental investigation will be performed to characterize D-SiNW arrays and other metamaterials for tailoring thermal radiative properties. Near-field thermal radiation between anisotropic materials with hyperbolic dispersions will also be predicted for potential application in energy harvesting. A new kind of anisotropic metamaterial with a hyperbolic dispersion in a broad infrared region has been proposed and demonstrated based on aligned doped-silicon nanowire (D-SiNW) arrays. D-SiNW-based metamaterials have unique thermal radiativemore » properties, such as broadband omnidirectional absorption whose width and location can be tuned by varying the filling ratio and/or doping level. Furthermore, high figure of merit (FOM) can be achieved in a wide spectral region, suggesting that D-SiNW arrays may be used as a negative refraction material with much less loss than other structured materials, such as layered semiconductor materials. We have also shown that D-SiNWs and other nanostructures can significantly enhance near-field thermal radiation. The study of near-field radiative heat transfer between closely spaced objects and the electromagnetic wave interactions with micro/nanostructured materials has become an emerging multidisciplinary field due to its importance in advanced energy systems, manufacturing, local thermal management, and high spatial resolution thermal sensing and mapping. We have performed extensive study on the energy streamlines involving anisotropic metamaterials and the applicability of the effective medium theory for near-field thermal radiation. Graphene as a 2D material has attracted great attention in nanoelectronics, plasmonics, and energy harvesting. We have shown that graphene can be used to tailor the transmittance, reflectance, and absorptance of nanostructured materials. Furthermore, graphene can be used to enhance near-field coupling to increase the phonon tunneling probability. We have performed analysis of near-field thermophotovoltaic devices with backside reflecting mirror and with tungsten gratings. We have predicted a large enhancement of electroluminescent refrigeration at a separation distance down to 10 nm due to near-field thermal radiation effect. A heat flux measurement system is developed to measure the near-field radiation in vacuum. We have fabricated doped Si plates separated by sparsely distributed posts to create a 200-800 nm vacuum gap. Our measurement results demonstrate that 11 times enhancement of near-field thermal radiation between parallel doped-Si plates with a lateral dimension 1 cm by 1 cm.« less

Characterization of Polyester Matrix Reinforced with Banana Fibers Thermal Properties by Photoacoustic Technique

NASA Astrophysics Data System (ADS)

de Assis, Foluke S.; Netto, Pedro A.; Margem, Frederico M.; Monteiro, Artur R. P. Junior Sergio N.

Synthetic fibers are being replaced gradually by natural materials such as lignocellulosic fibers. Compared to synthetic fibers, natural fibers have shown advantages in technical aspects such as environmental and economic. So there is a growing international interest in the use of those fibers. The banana fiber presents significant properties to be studied, but until now few thermal properties on banana fiber as reinforcement of polyester matrix were performed. The present work had as its objective to investigate, by photoacoustic spectroscopy and photothermal techniques the thermal properties of diffusivity, specific heat capacity and conductivity for polyester composites reinforced with banana fibers. In the polyester matrix will be added up to 30% in volume of continuous and aligned banana fibers. These values show that the incorporation of banana fibers in the polyester matrix changes its thermal properties.

Antimicrobial Properties of 2D MnO2 and MoS2 Nanomaterials Vertically Aligned on Graphene Materials and Ti3C2 MXene.

PubMed

Alimohammadi, Farbod; Sharifian Gh, Mohammad; Attanayake, Nuwan H; Thenuwara, Akila C; Gogotsi, Yury; Anasori, Babak; Strongin, Daniel R

2018-06-07

Two-dimensional (2D) nanomaterials have attracted considerable attention in biomedical and environmental applications due to their antimicrobial activity. In the interest of investigating the primary antimicrobial mode-of-action of 2D nanomaterials, we studied the antimicrobial properties of MnO 2 and MoS 2 , toward Gram-positive and Gram-negative bacteria. Bacillus subtilis and Escherichia coli bacteria were treated individually with 100 μg/mL of randomly oriented and vertically aligned nanomaterials for ∼3 h in the dark. The vertically aligned 2D MnO 2 and MoS 2 were grown on 2D sheets of graphene oxide, reduced graphene oxide, and Ti 3 C 2 MXene. Measurements to determine the viability of bacteria in the presence of the 2D nanomaterials performed by using two complementary techniques, flow cytometry, and fluorescence imaging showed that, while MnO 2 and MoS 2 nanosheets show different antibacterial activities, in both cases, Gram-positive bacteria show a higher loss in membrane integrity. Scanning electron microscopy images suggest that the 2D nanomaterials, which have a detrimental effect on bacteria viability, compromise the cell wall, leading to significant morphological changes. We propose that the peptidoglycan mesh (PM) in the bacterial wall is likely the primary target of the 2D nanomaterials. Vertically aligned 2D MnO 2 nanosheets showed the highest antimicrobial activity, suggesting that the edges of the nanosheets were likely compromising the cell walls upon contact.

Toolkit for Evaluating Alignment of Instructional and Assessment Materials to the Common Core State Standards

ERIC Educational Resources Information Center

Achieve, Inc., 2014

2014-01-01

In joint partnership, Achieve, The Council of Chief State School Officers, and Student Achievement Partners have developed a Toolkit for Evaluating the Alignment of Instructional and Assessment Materials to the Common Core State Standards. The Toolkit is a set of interrelated, freely available instruments for evaluating alignment to the CCSS; each…

Extrinsic polarization-controlled optical anisotropy in plasmon-black phosphorus coupled system

NASA Astrophysics Data System (ADS)

Liu, Zizhuo; Wells, Spencer A.; Butun, Serkan; Palacios, Edgar; Hersam, Mark C.; Aydin, Koray

2018-07-01

Two-dimensional black phosphorus (BP) has drawn extensive research interest due to its promising anisotropic photonic and electronic properties. Here, we study anisotropic optical absorption and photoresponse of exfoliated BP flakes at visible frequencies. We enhance this intrinsic optical anisotropy in BP flakes by coupling plasmonic rectangular nanopatch arrays that support localized surface plasmon resonances. In particular, by combining extrinsic anisotropic plasmonic nanostructures lithographically aligned with intrinsically anisotropic BP flakes, we demonstrate for the first time a combined anisotropic plasmonic-semiconductor coupling that provides significant control over the polarization-dependent optical properties of the plasmon-BP hybrid material system, enhancing polarization-sensitive responses to a larger degree. This hybrid material system not only unveils the plasmon-enhanced mechanisms in BP, but also provides novel controllable functionalities in optoelectronic device applications involving polarization-sensitive optical and electrical responses.

Extrinsic polarization-controlled optical anisotropy in plasmon-black phosphorus coupled system.

PubMed

Liu, Zizhuo; Wells, Spencer A; Butun, Serkan; Palacios, Edgar; Hersam, Mark C; Aydin, Koray

2018-07-13

Two-dimensional black phosphorus (BP) has drawn extensive research interest due to its promising anisotropic photonic and electronic properties. Here, we study anisotropic optical absorption and photoresponse of exfoliated BP flakes at visible frequencies. We enhance this intrinsic optical anisotropy in BP flakes by coupling plasmonic rectangular nanopatch arrays that support localized surface plasmon resonances. In particular, by combining extrinsic anisotropic plasmonic nanostructures lithographically aligned with intrinsically anisotropic BP flakes, we demonstrate for the first time a combined anisotropic plasmonic-semiconductor coupling that provides significant control over the polarization-dependent optical properties of the plasmon-BP hybrid material system, enhancing polarization-sensitive responses to a larger degree. This hybrid material system not only unveils the plasmon-enhanced mechanisms in BP, but also provides novel controllable functionalities in optoelectronic device applications involving polarization-sensitive optical and electrical responses.

Controle de l'alignement des nanotubes de carbone multiparois a l'interieur d'un polymere et d''un materiau composite multi-echelles a l'aide d'un champ electrique

NASA Astrophysics Data System (ADS)

Arguin, Maxime

Composite materials are lightweight and have very good mechanical properties which make them a good alternative to metallic structures traditionally used in aircraft. However, these materials have a very low electrical conductivity compared to metal which limits their use for electrical application such as current return network. For example, carbon fiber composites have relatively good in-plane conductivity but a resistance between each ply, generated by the epoxy, reduced the conductivity through the thickness of the material by a thousand. The anisotropy results in a poor current diffusion through each layer of the composite and heat generation at surface when an electric current is applied on a composite panel. For this reason, the electrical conductivity of carbon fibers composite must be improved to be used for electrical applications. This thesis shows a new procedure to enhance the electrical conductivity of composite material in a preferential way (i.e., through the thickness). Multi-walled carbon nanotubes (MWCNTs) were added to the epoxy matrix of a composite to create multiscale composite. An electric field was also used to control the global distribution of the NTCs. Alignment results made on a UV epoxy reinforced with 0.01wt.% of MWCNTs showed a decrease of the resistivity by four orders of magnitude. This decrease of resistivity was also associated with formation of a filamentary microstructure that goes from one electrode to the others creating preferential conduction pathways. Afterwards, a hand lay-up process was modified to incorporate electric field alignment during the manufacturing of the composite. An improvement of the conductivity of 36% and 99% were obtained when an electric of 60V/mm were used to align the nanoparticles in multiscale composites containing 0.01wt.% and 0.1wt.% of MWCNTs, respectively. However, these modest improvements were still not enough to reach a complete current diffusion through the thickness but this technique is still a potential way to achieve it. Finally, the project shows the potential of using electric field induced alignment of the MWCNTs to improve the conductivity of multiscale composite. Furthermore, this technique has the advantage to be suitable to other common manufacturing processes using in the industry.

Shear wave propagation in anisotropic soft tissues and gels

PubMed Central

Namani, Ravi; Bayly, Philip V.

2013-01-01

The propagation of shear waves in soft tissue can be visualized by magnetic resonance elastography (MRE) [1] to characterize tissue mechanical properties. Dynamic deformation of brain tissue arising from shear wave propagation may underlie the pathology of blast-induced traumatic brain injury. White matter in the brain, like other biological materials, exhibits a transversely isotropic structure, due to the arrangement of parallel fibers. Appropriate mathematical models and well-characterized experimental systems are needed to understand wave propagation in these structures. In this paper we review the theory behind waves in anisotropic, soft materials, including small-amplitude waves superimposed on finite deformation of a nonlinear hyperelastic material. Some predictions of this theory are confirmed in experimental studies of a soft material with controlled anisotropy: magnetically-aligned fibrin gel. PMID:19963987

Enhanced Raman Scattering on In-plane Anisotropic Layered Materials

DOE PAGES

Liang, Liangbo; Meunier, Vincent; Sumpter, Bobby G.; ...

2015-11-19

Surface-enhanced Raman scattering (SERS) on two-dimensional (2D) layered materials has provided a unique platform to study the chemical mechanism (CM) of the enhancement due to its natural separation from electromagnetic enhancement. The CM stems from the basic charge interactions between the substrate and molecules. Despite the extensive studies of the energy alignment between 2D materials and molecules, an understanding of how the electronic properties of the substrate are explicitly involved in the charge interaction is still unclear. Lately, a new group of 2D layered materials with anisotropic structure, including orthorhombic black phosphorus (BP) and triclinic rhenium disulphide (ReS2), has attractedmore » great interest due to their unique anisotropic electrical and optical properties. Herein, we report a unique anisotropic Raman enhancement on few-layered BP and ReS2 using copper phthalocyanine (CuPc) molecules as a Raman probe, which is absent on isotropic graphene and h-BN. According to detailed Raman tensor analysis and density functional theory calculations, anisotropic charge interactions due to the anisotropic carrier mobilities of the 2D materials are responsible for the angular dependence of the Raman enhancement. Our findings not only provide new insights into the CM process in SERS, but also open up new avenues for the exploration and application of the electronic properties of anisotropic 2D layered materials.« less

A Sustainable Substitute for Ivory: the Jarina Seed from the Amazon

NASA Astrophysics Data System (ADS)

Chu, Yinghao; Meyers A, Marc A.; Wang, Bin; Yang, Wen; Jung, Jae-Young; Coimbra, Carlos F. M.

2015-09-01

The dried endosperm of the seed of Phytelephas sp is widely used for artisanal work in the Amazon region due to its favorable mechanical properties and pleasant appearance that resemble elephant ivory. While the seeds have enjoyed popularity and limited use by selected industries (e.g., military uniform buttons and piano keys) and handicraft applications, little is known about the mechanical properties and structure of this sustainable material. This work is the first to characterize the dried Jarina endosperm and to investigate its functionality as a viable substitute for elephant ivory. Structural analysis of typical seeds reveals the prevalence of tubules that align in rings and radiate from the (usually hollow) core of the seed. This seed, in the absence of a reinforcement structure or mineral phase, possesses mechanical properties slightly inferior to elephant ivory and selected plastics, while retaining the visual appeal of a naturally occurring material. A synthetic structure inspired on the seed is created and suggestions for further development are discussed.

A Sustainable Substitute for Ivory: the Jarina Seed from the Amazon

PubMed Central

Chu, Yinghao; Meyers A, Marc A.; Wang, Bin; Yang, Wen; Jung, Jae-Young; Coimbra, Carlos F. M.

2015-01-01

The dried endosperm of the seed of Phytelephas sp is widely used for artisanal work in the Amazon region due to its favorable mechanical properties and pleasant appearance that resemble elephant ivory. While the seeds have enjoyed popularity and limited use by selected industries (e.g., military uniform buttons and piano keys) and handicraft applications, little is known about the mechanical properties and structure of this sustainable material. This work is the first to characterize the dried Jarina endosperm and to investigate its functionality as a viable substitute for elephant ivory. Structural analysis of typical seeds reveals the prevalence of tubules that align in rings and radiate from the (usually hollow) core of the seed. This seed, in the absence of a reinforcement structure or mineral phase, possesses mechanical properties slightly inferior to elephant ivory and selected plastics, while retaining the visual appeal of a naturally occurring material. A synthetic structure inspired on the seed is created and suggestions for further development are discussed. PMID:26399626

The Effects of Fluid Absorption on the Mechanical Properties of Joint Prostheses Components

NASA Astrophysics Data System (ADS)

Yarbrough, David; Viano, Ann

2010-02-01

Ultra-high-molecular-weight polyethylene (UHMWPE) is the material playing the role of cartilage in human prosthetic joints. Wear debris from UHMWPE is a common reason for joint arthroplasty failure, and the exact mechanism responsible for wear remains an area of investigation. In this study, the microstructure of UHMWPE was examined as a function of fluid absorption. Samples with varying exposure to e-beam radiation (as part of the manufacturing process) were soaked for forty days in saline or artificial synovial fluid, under zero or 100 lbs load. Samples were then tensile-tested according to ASTM D-3895. The post-stressed material was then examined by transmission electron microscopy to evaluate the molecular response to stress, which correlates with macroscopic mechanical properties. Three parameters of the crystalline lamellae were measured: thickness, stacking ratio, and alignment to stress direction. Results indicate that fluid absorption does affect the mechanical properties of UHMWPE at both the microscopic and microscopic levels. )

Self-assembly 2D zinc-phthalocyanine heterojunction: An ideal platform for high efficiency solar cell

NASA Astrophysics Data System (ADS)

Jiang, Xue; Jiang, Zhou; Zhao, Jijun

2017-12-01

As an alternative to silicon-based solar cells, organic photovoltaic cells emerge for their easy manufacture, low cost, and light weight but are limited by their less stability, low power conversion efficiencies, and low charge carrier mobilities. Here, we design a series of two-dimensional (2D) organic materials incorporating zinc-phthalocyanine (ZnPc) based building blocks which can inherit their excellent intrinsic properties but overcome those shortcomings. Our first-principles calculation shows that such 2D ZnPc-based materials exhibit excellent thermal stabilities, suitable bandgaps, small effective masses, and good absorption properties. The additional benzene rings and nitrogen atoms incorporated between ZnPc molecules are mainly responsible for the modifications of electronic and optical properties. Moreover, some heterojunction solar cells constructed using those 2D ZnPc monolayers as the donor and acceptor have an appropriate absorber gap and interface band alignment. Among them, a power conversion efficiency up to 14.04% is achieved, which is very promising for the next-generation organic solar cells.

Analyzing the Curriculum Alignment of Teachers

ERIC Educational Resources Information Center

Turan-Özpolat, Esen; Bay, Erdal

2017-01-01

The purpose of this research was to analyze the curriculum alignment of teachers in secondary education 5th grade Science course. Alignment levels of teachers in dimensions of acquisition, content, teaching methods and techniques, activity, material and measurement - assessment, and the reasons for their alignment/non-alignment to the curriculum…

Control of the hierarchical assembly of π-conjugated optoelectronic peptides by pH and flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mansbach, Rachael A.; Ferguson, Andrew L.

Self-assembled nanoaggregates of p-conjugated peptides possess optoelectronic properties due to electron delocalization over the conjugated peptide groups that make them attractive candidates for the fabrication of bioelectronic materials. We present a computational and theoretical study to resolve the microscopic effects of pH and flow on the non-equilibrium morphology and kinetics of early-stage assembly of an experimentally-realizable optoelectronic peptide that displays pH triggerable assembly. Employing coarse-grained molecular dynamics simulations, we probe the effects of pH on growth kinetics and aggregate morphology to show that control of the peptide protonation state by pH can be used to modulate the assembly rates, degreemore » of molecular alignment, and resulting morphologies within the self-assembling nanoaggregates. We also quantify the time and length scales at which convective flows employed in directed assembly compete with microscopic diffusion to show that flow influences cluster alignment and assembly rate during early-stage assembly only at extremely high shear rates. This suggests that observed improvements in optoelectronic properties at experimentally-accessible shear rates are due to the alignment of large aggregates of hundreds of monomers on time scales in excess of hundreds of nanoseconds. Lastly, our work provides new fundamental understanding of the effects of pH and flow to control the morphology and kinetics of early-stage assembly of p-conjugated peptides and lays the groundwork for the rational manipulation of environmental conditions to direct assembly and the attendant emergent optoelectronic properties.« less

Control of the hierarchical assembly of π-conjugated optoelectronic peptides by pH and flow

DOE PAGES

Mansbach, Rachael A.; Ferguson, Andrew L.

2017-01-01

Self-assembled nanoaggregates of p-conjugated peptides possess optoelectronic properties due to electron delocalization over the conjugated peptide groups that make them attractive candidates for the fabrication of bioelectronic materials. We present a computational and theoretical study to resolve the microscopic effects of pH and flow on the non-equilibrium morphology and kinetics of early-stage assembly of an experimentally-realizable optoelectronic peptide that displays pH triggerable assembly. Employing coarse-grained molecular dynamics simulations, we probe the effects of pH on growth kinetics and aggregate morphology to show that control of the peptide protonation state by pH can be used to modulate the assembly rates, degreemore » of molecular alignment, and resulting morphologies within the self-assembling nanoaggregates. We also quantify the time and length scales at which convective flows employed in directed assembly compete with microscopic diffusion to show that flow influences cluster alignment and assembly rate during early-stage assembly only at extremely high shear rates. This suggests that observed improvements in optoelectronic properties at experimentally-accessible shear rates are due to the alignment of large aggregates of hundreds of monomers on time scales in excess of hundreds of nanoseconds. Lastly, our work provides new fundamental understanding of the effects of pH and flow to control the morphology and kinetics of early-stage assembly of p-conjugated peptides and lays the groundwork for the rational manipulation of environmental conditions to direct assembly and the attendant emergent optoelectronic properties.« less

Fabrication of high thermal conductivity arrays of carbon nanotubes and their composites

DOEpatents

Geohegan, David B [Knoxville, TN; Ivanov, Ilya N [Knoxville, TN; Puretzky, Alexander A [Knoxville, TN

2010-07-27

Methods and apparatus are described for fabrication of high thermal conductivity arrays of carbon nanotubes and their composites. A composition includes a vertically aligned nanotube array including a plurality of nanotubes characterized by a property across substantially all of the vertically aligned nanotube array. A method includes depositing a vertically aligned nanotube array that includes a plurality of nanotubes; and controlling a deposition rate of the vertically aligned nanotubes array as a function of an in situ monitored property of the plurality of nanotubes.

Band alignment and charge transfer predictions of ZnO/ZnX (X = S, Se or Te) interfaces applied to solar cells: a PBE+U theoretical study.

PubMed

Flores, Efracio Mamani; Gouvea, Rogério Almeida; Piotrowski, Maurício Jeomar; Moreira, Mário Lucio

2018-02-14

The engineering of semiconductor materials for the development of solar cells is of great importance today. Two topics are considered to be of critical importance for the efficiency of Grätzel-type solar cells, the efficiency of charge separation and the efficiency of charge carrier transfer. Thus, one research focus is the combination of semiconductor materials with the aim of reducing charge recombination, which occurs by spatial charge separation. From an experimental point of view, the combining of materials can be achieved by decorating a core with a shell of another material resulting in a core-shell system, which allows control of the desired photoelectronic properties. In this context, a computational simulation is mandatory for the atomistic understanding of possible semiconductor combinations and for the prediction of their properties. Considering the construction of ZnO/ZnX (X = S, Se or Te) interfaces, we seek to investigate the electronic influence of the shell (ZnX) on the core (ZnO) and, consequently, find out which of the interfaces would present the appropriate properties for (Grätzel-type) solar cell applications. To perform this study, we have employed density functional theory (DFT) calculations, considering the Perdew-Burke-Ernzerhof (PBE) functional. However, it is well-known that plain DFT fails to describe strong electronic correlated materials where, in general, an underestimation of the band gap is obtained. Thus, to obtain the correct description of the electronic properties, a Hubbard correction was employed, i.e. PBE+U calculations. The PBE+U methodology provided the correct electronic structure properties for bulk ZnO in good agreement with experimental values (99.4%). The ZnO/ZnX interfaces were built and were composed of six ZnO layers and two ZnX layers, which represents the decoration process. The core-shell band gap was 2.2 eV for ZnO/ZnS, ∼1.71 eV for ZnO/ZnSe and ∼0.95 eV for ZnO/ZnTe, which also exhibited a type-II band alignment. Bader charge analysis showed an accumulation of charges in the 6th layer of ZnO for the three ZnO/ZnX interfaces. On the basis of these results, we have proposed that ZnO/ZnS and ZnO/ZnSe core-shell structures can be applied as good candidates (with better efficiency) for photovoltaic devices.

Optical properties of II-VI structures for solar energy utilization

NASA Astrophysics Data System (ADS)

Schrier, Joshua; Demchenko, Denis; Wang, Lin-Wang

2007-03-01

Although II-VI semiconductor materials are abundant, stable, and have direct band gaps, the band gaps are too large for optimal photovoltaic efficiency. However, staggered band alignments of pairs of these materials, and also the formation of intermediate impurity levels in the band gap (which has been demonstrated to increase the efficiency as compared to both single-junction devices), could be utilized to improve the suitability of these materials for solar energy utilization. Previous theoretical studies of these materials are limited, due to the well-known band gap underestimation by density-functional theory. To calculate the absorption spectra, we utilize a band-corrected planewave pseudopotential approach, which gives agreements of within 0.1 eV of the bulk optical gaps values. In this talk, I will present our work on predicting the optical properties of ZnO/ZnS and ZnO/ZnTe heterostructures, nanostructures, and alloys. This work was supported by U.S. Department of Energy under Contract No.DE-AC02-05CH11231 and used the resources of the National Energy Research Scientific Computing Center.

Molecular self-assembly approaches for supramolecular electronic and organic electronic devices

NASA Astrophysics Data System (ADS)

Yip, Hin-Lap

Molecular self-assembly represents an efficient bottom-up strategy to generate structurally well-defined aggregates of semiconducting pi-conjugated materials. The capability of tuning the chemical structures, intermolecular interactions and nanostructures through molecular engineering and novel materials processing renders it possible to tailor a large number of unprecedented properties such as charge transport, energy transfer and light harvesting. This approach does not only benefit traditional electronic devices based on bulk materials, but also generate a new research area so called "supramolecular electronics" in which electronic devices are built up with individual supramolecular nanostructures with size in the sub-hundred nanometers range. My work combined molecular self-assembly together with several novel materials processing techniques to control the nucleation and growth of organic semiconducting nanostructures from different type of pi-conjugated materials. By tailoring the interactions between the molecules using hydrogen bonds and pi-pi stacking, semiconducting nanoplatelets and nanowires with tunable sizes can be fabricated in solution. These supramolecular nanostructures were further patterned and aligned on solid substrates through printing and chemical templating methods. The capability to control the different hierarchies of organization on surface provides an important platform to study their structural-induced electronic properties. In addition to using molecular self-assembly to create different organic nanostructures, functional self-assembled monolayer (SAM) formed by spontaneous chemisorption on surfaces was used to tune the interfacial property in organic solar cells. Devices showed dramatically improved performance when appropriate SAMs were applied to optimize the contact property for efficiency charge collection.

Effect of Age and Proteoglycan Deficiency on Collagen Fiber Re-Alignment and Mechanical Properties in Mouse Supraspinatus Tendon

PubMed Central

Connizzo, Brianne K.; Sarver, Joseph J.; Iozzo, Renato V.; Birk, David E.; Soslowsky, Louis J.

2013-01-01

Collagen fiber realignment is one mechanism by which tendon responds to load. Re-alignment is altered when the structure of tendon is altered, such as in the natural process of aging or with alterations of matrix proteins, such as proteoglycan expression. While changes in re-alignment and mechanical properties have been investigated recently during development, they have not been studied in (1) aged tendons, or (2) in the absence of key proteoglycans. Collagen fiber re-alignment and the corresponding mechanical properties are quantified throughout tensile mechanical testing in both the insertion site and the midsubstance of mouse supraspinatus tendons in wild type (WT), decorin-null (Dcn-/-), and biglycan-null (Bgn-/-) mice at three different ages (90 days, 300 days, and 570 days). Percent relaxation was significantly decreased with age in the WT and Dcn-/- tendons, but not in the Bgn-/- tendons. Changes with age were found in the linear modulus at the insertion site where the 300 day group was greater than the 90 day and 570 day group in the Bgn-/- tendons and the 90 day group was smaller than the 300 day and 570 day groups in the Dcn-/- tendons. However, no changes in modulus were found across age in WT tendons were found. The midsubstance fibers of the WT and Bgn-/- tendons were initially less aligned with increasing age. The re-alignment was significantly altered with age in the WT tendons, with older groups responding to load later in the mechanical test. This was also seen in the Dcn-/- midsubstance and the Bgn-/- insertion, but not in the other locations. Although some studies have found changes in the WT mechanical properties with age, this study did not support those findings. However, it did show fiber re-alignment changes at both locations with age, suggesting a breakdown of tendon′s ability to respond to load in later ages. In the proteoglycan-null tendons however, there were changes in the mechanical properties, accompanied only by location-dependent re-alignment changes, suggesting a site-specific role for these molecules in loading. Finally, changes in the mechanical properties did not occur in concert with changes in re-alignment, suggesting that typical mechanical property measurements alone are insufficient to describe how structural alterations affect tendon′s response to load. PMID:23445064

A machine-learning approach reveals that alignment properties alone can accurately predict inference of lateral gene transfer from discordant phylogenies.

PubMed

Roettger, Mayo; Martin, William; Dagan, Tal

2009-09-01

Among the methods currently used in phylogenomic practice to detect the presence of lateral gene transfer (LGT), one of the most frequently employed is the comparison of gene tree topologies for different genes. In cases where the phylogenies for different genes are incompatible, or discordant, for well-supported branches there are three simple interpretations for the result: 1) gene duplications (paralogy) followed by many independent gene losses have occurred, 2) LGT has occurred, or 3) the phylogeny is well supported but for reasons unknown is nonetheless incorrect. Here, we focus on the third possibility by examining the properties of 22,437 published multiple sequence alignments, the Bayesian maximum likelihood trees for which either do or do not suggest the occurrence of LGT by the criterion of discordant branches. The alignments that produce discordant phylogenies differ significantly in several salient alignment properties from those that do not. Using a support vector machine, we were able to predict the inference of discordant tree topologies with up to 80% accuracy from alignment properties alone.

Fabrication of nanoscale to macroscale nickel-multiwall carbon nanotube hybrid materials with tunable material properties

NASA Astrophysics Data System (ADS)

Abdalla, Ahmed M.; Majdi, Tahereh; Ghosh, Suvojit; Puri, Ishwar K.

2016-12-01

To utilize their superior properties, multiwall carbon nanotubes (MWNTs) must be manipulated and aligned end-to-end. We describe a nondestructive method to magnetize MWNTs and provide a means to remotely manipulate them through the electroless deposition of magnetic nickel nanoparticles on their surfaces. The noncovalent bonds between Ni nanoparticles and MWNTs produce a Ni-MWNT hybrid material (NiCH) that is electrically conductive and has an enhanced magnetic susceptibility and elastic modulus. Our experiments show that MWNTs can be plated with Ni for Ni:MWNT weight ratios of γ = 1, 7, 14 and 30, to control the material properties. The phase, atom-level, and morphological information from x-ray diffraction, energy dispersive x-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, dark field STEM, and atomic force microscopy clarify the plating process and reveal the mechanical properties of the synthesized material. Ni metalizes at the surface of the Pd catalyst, forming a continuous wavy layer that encapsulates the MWNT surfaces. Subsequently, Ni acts as an autocatalyst, allowing the plating to continue even after the original Pd catalyst has been completely covered. Raising γ increases the coating layer thickness from 10 to 150 nm, which influences the NiCH magnetic properties and tunes its elastic modulus from 12.5 to 58.7 GPa. The NiCH was used to fabricate Ni-MWNT macrostructures and tune their morphologies by changing the direction of an applied magnetic field. Leveraging the hydrophilic Ni-MWNT outer surface, a water-based conductive ink was created and used to print a conductive path that had an electrical resistivity of 5.9 Ω m, illustrating the potential of this material for printing electronic circuits.

Strontium ruthenate-anatase titanium dioxide heterojunctions from first-principles: Electronic structure, spin, and interface dipoles

NASA Astrophysics Data System (ADS)

Ferdous, Naheed; Ertekin, Elif

2016-07-01

The epitaxial integration of functional oxides with wide band gap semiconductors offers the possibility of new material systems for electronics and energy conversion applications. We use first principles to consider an epitaxial interface between the correlated metal oxide SrRuO3 and the wide band gap semiconductor TiO2, and assess energy level alignment, interfacial chemistry, and interfacial dipole formation. Due to the ferromagnetic, half-metallic character of SrRuO3, according to which only one spin is present at the Fermi level, we demonstrate the existence of a spin dependent band alignment across the interface. For two different terminations of SrRuO3, the interface is found to be rectifying with a Schottky barrier of ≈1.3-1.6 eV, in good agreement with experiment. In the minority spin, SrRuO3 exhibits a Schottky barrier alignment with TiO2 and our calculated Schottky barrier height is in excellent agreement with previous experimental measurements. For majority spin carriers, we find that SrRuO3 recovers its exchange splitting gap and bulk-like properties within a few monolayers of the interface. These results demonstrate a possible approach to achieve spin-dependent transport across a heteroepitaxial interface between a functional oxide material and a conventional wide band gap semiconductor.

Probing interfacial energetics and charge transfer kinetics in semiconductor nanocomposites: New insights into heterostructured TiO 2/BiVO 4 photoanodes

DOE PAGES

Hess, Lucas H.; Cooper, Jason K.; Loiudice, Anna; ...

2017-02-28

Heterostructured nanocomposites offer promise for creating systems exhibiting functional properties that exceed those of the isolated components. For solar energy conversion, such combinations of semiconducting nanomaterials can be used to direct charge transfer along pathways that reduce recombination and promote efficient charge extraction. However, interfacial energetics and associated kinetic pathways often differ significantly from predictions derived from the characteristics of pure component materials, particularly at the nanoscale. Here, the emergent properties of TiO 2/BiVO 4 nanocomposite photoanodes are explored using a combination of X-ray and optical spectroscopies, together with photoelectrochemical (PEC) characterization. Application of these methods to both the puremore » components and the fully assembled nanocomposites reveals unpredicted interfacial energetic alignment, which promotes ultrafast injection of electrons from BiVO 4 into TiO 2. Physical charge separation yields extremely long-lived photoexcited states and correspondingly enhanced photoelectrochemical functionality. This work highlights the importance of probing emergent interfacial energetic alignment and kinetic processes for understanding mechanisms of solar energy conversion in complex nanocomposites.« less

Effect of degumming time on silkworm silk fibre for biodegradable polymer composites

NASA Astrophysics Data System (ADS)

Ho, Mei-po; Wang, Hao; Lau, Kin-tak

2012-02-01

Recently, many studies have been conducted on exploitation of natural materials for modern product development and bioengineering applications. Apart from plant-based materials (such as sisal, hemp, jute, bamboo and palm fibre), animal-based fibre is a kind of sustainable natural materials for making novel composites. Silkworm silk fibre extracted from cocoon has been well recognized as a promising material for bio-medical engineering applications because of its superior mechanical and bioresorbable properties. However, when producing silk fibre reinforced biodegradable/bioresorbable polymer composites, hydrophilic sericin has been found to cause poor interfacial bonding with most polymers and thus, it results in affecting the resultant properties of the composites. Besides, sericin layers on fibroin surface may also cause an adverse effect towards biocompatibility and hypersensitivity to silk for implant applications. Therefore, a proper pre-treatment should be done for sericin removal. Degumming is a surface modification process which allows a wide control of the silk fibre's properties, making the silk fibre possible to be used for the development and production of novel bio-composites with unique/specific mechanical and biodegradable properties. In this paper, a cleaner and environmentally friendly surface modification technique for tussah silk in polymer based composites is proposed. The effectiveness of different degumming parameters including degumming time and temperature on tussah silk is discussed through the analyses of their mechanical and morphological properties. Based on results obtained, it was found that the mechanical properties of tussah silk are affected by the degumming time due to the change of the fibre structure and fibroin alignment.

Field-Induced Alignment of Polar Bent-Ccore Smectic A Liquid Crystals

NASA Astrophysics Data System (ADS)

Shen, Yongqiang; Goodhew, Lisa; Shao, Renfan; Maclennan, Joseph; Clark, Noel; Rudquist, Per

2014-03-01

The SmAPF phase is a promising phase modulator mode. To use the SmAPF materials for applications, we need to obtain uniform, large-area alignment of the samples. However, bent-core liquid crystals are notoriously difficult to align with conventional surface treatment methods because most of them have no nematic phase. We have developed a powerful, new method using in-plane applied electric fields that allows us to create a perfect bookshelf alignment of orthogonal bent-core smectics. By using an interdigitated, finger-like electrode arrangement on one of the cell surfaces, we can align the materials by applying in-plane electric fields. This stripe geometry, which produces curved field lines, allows for only one smectic layer orientation, normal both to the cell walls and to the finger electrodes. After alignment, the cell can be operated in the conventional way by connecting the finger electrodes together to make one effective electrode, opposing continuous, common electrode on the opposite side of the cell. This alignment method opens up the use of these materials in perfectly aligned cells for both amplitude and phase-only modulation applications. This work was supported by NSF MRSEC Grant No. DMR-0820579, by NSF Grant No. DMR-1008300, and by Swedish Research Council (VR) Grant No. 621-2009-3621.

Creating Polymer Hydrogel Microfibres with Internal Alignment via Electrical and Mechanical Stretching

PubMed Central

Zhang, Shuming; Liu, Xi; Barreto-Ortiz, Sebastian F.; Yu, Yixuan; Ginn, Brian; DeSantis, Nicholas; Hutton, Daphne L; Grayson, Warren; Cui, Fu-Zhai; Korgel, Brian A.; Gerecht, Sharon; Mao, Hai-Quan

2014-01-01

Hydrogels have been widely used for 3-dimensional (3D) cell culture and tissue regeneration due to their tunable biochemical and physicochemical properties as well as their high water content, which resembles the aqueous microenvironment of the natural extracellular matrix. While many properties of natural hydrogel matrices are modifiable, their intrinsic isotropic structure limits the control over cellular organization, which is critical to restore tissue function. Here we report a generic approach to incorporate alignment topography inside the hydrogel matrix using a combination of electrical and mechanical stretching. Hydrogel fibres with uniaxial alignment were prepared from aqueous solutions of natural polymers such as alginate, fibrin, gelatin, and hyaluronic acid under ambient conditions. The unique internal alignment feature drastically enhances the mechanical properties of the hydrogel microfibres. Furthermore, the facile, organic solvent-free processing conditions are amenable to the incorporation of live cells within the hydrogel fibre or on the fibre surface; both approaches effectively induce cellular alignment. This work demonstrates a versatile and scalable strategy to create aligned hydrogel microfibres from various natural polymers. PMID:24439410

Mechanical properties of nanostructure of biological materials

NASA Astrophysics Data System (ADS)

Ji, Baohua; Gao, Huajian

2004-09-01

Natural biological materials such as bone, teeth and nacre are nanocomposites of protein and mineral with superior strength. It is quite a marvel that nature produces hard and tough materials out of protein as soft as human skin and mineral as brittle as classroom chalk. What are the secrets of nature? Can we learn from this to produce bio-inspired materials in the laboratory? These questions have motivated us to investigate the mechanics of protein-mineral nanocomposite structure. Large aspect ratios and a staggered alignment of mineral platelets are found to be the key factors contributing to the large stiffness of biomaterials. A tension-shear chain (TSC) model of biological nanostructure reveals that the strength of biomaterials hinges upon optimizing the tensile strength of the mineral crystals. As the size of the mineral crystals is reduced to nanoscale, they become insensitive to flaws with strength approaching the theoretical strength of atomic bonds. The optimized tensile strength of mineral crystals thus allows a large amount of fracture energy to be dissipated in protein via shear deformation and consequently enhances the fracture toughness of biocomposites. We derive viscoelastic properties of the protein-mineral nanostructure and show that the toughness of biocomposite can be further enhanced by the viscoelastic properties of protein.

Development of high J c Bi2223/Ag thick film materials prepared by heat treatment under low P O2

NASA Astrophysics Data System (ADS)

Takeda, Y.; Shimoyama, J.; Motoki, T.; Nakamura, S.; Nakashima, T.; Kobayashi, S.; Kato, T.

2018-07-01

In general, a dense and c-axis grain-oriented microstructure is desirable in order to achieve the high critical current properties of Bi2223 polycrystalline materials. On the other hand, our recent studies have shown that precise control of the chemical compositions of Bi2223 is also effective for the enhancement of intergrain J c. In this study, the development of Bi2223 thick film materials with high critical current properties was attempted by controlling both the microstructure and the chemical compositions. A high intergrain J c of ∼8 kA cm‑2 at 77 K of a film with ∼40 μm t was achieved by increasing the Pb substitution level for the Bi site and controlling the nonstoichiometric chemical compositions. Furthermore, it was revealed that an increase in the thickness enabled us to obtain high I c films suitable for practical applications. In contrast, there are still issues, especially in controlling the grain alignment at the inner part of the film, which suggests that the J c properties of thick film materials could be further improved by forming a more ideal microstructure, as realized in the Bi2223 filaments of multi-filamentary Ag-sheathed tapes.

Properties of Retinal Precursor Cells Grown on Vertically Aligned Multiwalled Carbon Nanotubes Generated for the Modification of Retinal Implant-Embedded Microelectrode Arrays

PubMed Central

Johnen, Sandra; Meißner, Frank; Krug, Mario; Baltz, Thomas; Endler, Ingolf; Mokwa, Wilfried; Walter, Peter

2016-01-01

Background. To analyze the biocompatibility of vertically aligned multiwalled carbon nanotubes (MWCNT), used as nanomodification to optimize the properties of prostheses-embedded microelectrodes that induce electrical stimulation of surviving retinal cells. Methods. MWCNT were synthesized on silicon wafers. Their growth was achieved by iron particles (Fe) or mixtures of iron-platinum (Fe-Pt) and iron-titanium (Fe-Ti) acting as catalysts. Viability, growth, adhesion, and gene expression of L-929 and retinal precursor (R28) cells were analyzed after nondirect and direct contact. Results. Nondirect contact had almost no influence on cell growth, as measured in comparison to reference materials with defined levels of cytotoxicity. Both cell types exhibited good proliferation properties on each MWCNT-coated wafer. Viability ranged from 95.9 to 99.8%, in which better survival was observed for nonfunctionalized MWCNT generated with the Fe-Pt and Fe-Ti catalyst mixtures. R28 cells grown on the MWCNT-coated wafers showed a decreased gene expression associated with neural and glial properties. Expression of the cell cycle-related genes CCNC, MYC, and TP53 was slightly downregulated. Cultivation on plasma-treated MWCNT did not lead to additional changes. Conclusions. All tested MWCNT-covered slices showed good biocompatibility profiles, confirming that this nanotechnology is a promising tool to improve prostheses bearing electrodes which connect with retinal tissue. PMID:27200182

Properties of Retinal Precursor Cells Grown on Vertically Aligned Multiwalled Carbon Nanotubes Generated for the Modification of Retinal Implant-Embedded Microelectrode Arrays.

PubMed

Johnen, Sandra; Meißner, Frank; Krug, Mario; Baltz, Thomas; Endler, Ingolf; Mokwa, Wilfried; Walter, Peter

2016-01-01

Background. To analyze the biocompatibility of vertically aligned multiwalled carbon nanotubes (MWCNT), used as nanomodification to optimize the properties of prostheses-embedded microelectrodes that induce electrical stimulation of surviving retinal cells. Methods. MWCNT were synthesized on silicon wafers. Their growth was achieved by iron particles (Fe) or mixtures of iron-platinum (Fe-Pt) and iron-titanium (Fe-Ti) acting as catalysts. Viability, growth, adhesion, and gene expression of L-929 and retinal precursor (R28) cells were analyzed after nondirect and direct contact. Results. Nondirect contact had almost no influence on cell growth, as measured in comparison to reference materials with defined levels of cytotoxicity. Both cell types exhibited good proliferation properties on each MWCNT-coated wafer. Viability ranged from 95.9 to 99.8%, in which better survival was observed for nonfunctionalized MWCNT generated with the Fe-Pt and Fe-Ti catalyst mixtures. R28 cells grown on the MWCNT-coated wafers showed a decreased gene expression associated with neural and glial properties. Expression of the cell cycle-related genes CCNC, MYC, and TP53 was slightly downregulated. Cultivation on plasma-treated MWCNT did not lead to additional changes. Conclusions. All tested MWCNT-covered slices showed good biocompatibility profiles, confirming that this nanotechnology is a promising tool to improve prostheses bearing electrodes which connect with retinal tissue.

Anisotropic thermal conductivity in epoxy-bonded magnetocaloric composites

NASA Astrophysics Data System (ADS)

Weise, Bruno; Sellschopp, Kai; Bierdel, Marius; Funk, Alexander; Bobeth, Manfred; Krautz, Maria; Waske, Anja

2016-09-01

Thermal management is one of the crucial issues in the development of magnetocaloric refrigeration technology for application. In order to ensure optimal exploitation of the materials "primary" properties, such as entropy change and temperature lift, thermal properties (and other "secondary" properties) play an important role. In magnetocaloric composites, which show an increased cycling stability in comparison to their bulk counterparts, thermal properties are strongly determined by the geometric arrangement of the corresponding components. In the first part of this paper, the inner structure of a polymer-bonded La(Fe, Co, Si)13-composite was studied by X-ray computed tomography. Based on this 3D data, a numerical study along all three spatial directions revealed anisotropic thermal conductivity of the composite: Due to the preparation process, the long-axis of the magnetocaloric particles is aligned along the xy plane which is why the in-plane thermal conductivity is larger than the thermal conductivity along the z-axis. Further, the study is expanded to a second aspect devoted to the influence of particle distribution and alignment within the polymer matrix. Based on an equivalent ellipsoids model to describe the inner structure of the composite, numerical simulation of the thermal conductivity in different particle arrangements and orientation distributions were performed. This paper evaluates the possibilities of microstructural design for inducing and adjusting anisotropic thermal conductivity in magnetocaloric composites.

Simulation of exposure and alignment for nanoimprint lithography

NASA Astrophysics Data System (ADS)

Deng, Yunfei; Neureuther, Andrew R.

2002-07-01

Rigorous electromagnetic simulation with TEMPEST is used to examine the exposure and alignment processes for nano-imprint lithography with attenuating thin-film molds. Parameters in the design of topographical features of the nano-imprint system and material choices of the components are analyzed. The small feature size limits light transmission through the feature. While little can be done with auxiliary structures to attract light into small holes, the use of an absorbing material with a low real part of the refractive index such as silver helps mitigates the problem. Results on complementary alignment marks shows that the small transmission through the metal layer and the vertical separation of two alignment marks create the leakage equivalent to 1 nm misalignment but satisfactory alignment can be obtained by measuring alignment signals over a +/- 30 nm range.

Fundamental and progress of Bi2Te3-based thermoelectric materials

NASA Astrophysics Data System (ADS)

Hong, Min; Chen, Zhi-Gang; Zou, Jin

2018-04-01

Thermoelectric materials, enabling the directing conversion between heat and electricity, are one of the promising candidates for overcoming environmental pollution and the upcoming energy shortage caused by the over-consumption of fossil fuels. Bi2Te3-based alloys are the classical thermoelectric materials working near room temperature. Due to the intensive theoretical investigations and experimental demonstrations, significant progress has been achieved to enhance the thermoelectric performance of Bi2Te3-based thermoelectric materials. In this review, we first explored the fundamentals of thermoelectric effect and derived the equations for thermoelectric properties. On this basis, we studied the effect of material parameters on thermoelectric properties. Then, we analyzed the features of Bi2Te3-based thermoelectric materials, including the lattice defects, anisotropic behavior and the strong bipolar conduction at relatively high temperature. Then we accordingly summarized the strategies for enhancing the thermoelectric performance, including point defect engineering, texture alignment, and band gap enlargement. Moreover, we highlighted the progress in decreasing thermal conductivity using nanostructures fabricated by solution grown method, ball milling, and melt spinning. Lastly, we employed modeling analysis to uncover the principles of anisotropy behavior and the achieved enhancement in Bi2Te3, which will enlighten the enhancement of thermoelectric performance in broader materials.

Assembly of Layered Monetite-Chitosan Nanocomposite and Its Transition to Organized Hydroxyapatite.

PubMed

Ruan, Qichao; Liberman, David; Zhang, Yuzheng; Ren, Dongni; Zhang, Yunpeng; Nutt, Steven; Moradian-Oldak, Janet

2016-06-13

Bioinspired synthesis of hierarchically structured calcium phosphate (CaP) material is a highly promising strategy for developing improved bone substitute materials. However, synthesis of CaP materials with outstanding mechanical properties still remains an ongoing challenge. Inspired by the formation of lamellar structure in nacre, we designed an organic matrix composed of chitosan and cis-butenediolic acid (maleic acid, MAc) that could assemble into a layered complex and further guide the mineralization of monetite crystals, resulting in the formation of organized and parallel arrays of monetite platelets with a brick-and-mortar structure. Using the layered monetite-chitosan composite as a precursor, we were able to synthesize hydroxyapatite (HAp) with multiscale hierarchically ordered structure via a topotactic phase transformation process. On the nanoscale, needlelike HAp crystallites assembled into organized bundles that aligned to form highly oriented plates on the microscale. On the large-scale level, these plates with different crystal orientations were stacked together to form a layered structure. The organized structures and composite feature yielded CaP materials with improved mechanical properties close to those of bone. Our study introduces a biomimetic approach that may be practical for the design of advanced, mechanically robust materials for biomedical applications.

Co-dispersion of plasmonic nanorods in thermotropic nematic liquid crystals

NASA Astrophysics Data System (ADS)

Sheetah, Ghadah; Liu, Qinkun; Smalukh, Ivan

Colloidal dispersions of plasmonic metal nanoparticles in liquid crystals promise the capability of pre-engineering tunable optical properties of mesostructured metal-dielectric composites. Recently, concentrated dispersions of anisotropic gold, silver, and metal alloy nanoparticles in nematic hosts have been achieved and successfully controlled by low-voltage fields. However, to enable versatile designs of material behavior of the composites, simultaneous co-dispersion of anisotropic particles with different shapes, alignment properties, and compositions are often needed. We achieve such co-dispersions and explore their switching characteristics in response to external stimuli like light and electric fields. We demonstrated that spectral characteristics of co-dispersions of multiple types of anisotropic nanoparticles in a common nematic host provides unprecedented variety of electrically- and optically-tunable material behavior, with a host of potential practical applications in electro-optic devices and displays Ghadah acknowledges support from the King Faisal University (KFU) graduate fellowship.

Pressure sensor based on pristine multi-walled carbon nanotubes forest

NASA Astrophysics Data System (ADS)

Yasar, M.; Mohamed, N. M.; Hamid, N. H.; Shuaib, M.

2016-11-01

In the course of the most recent decade, carbon nanotubes (CNTs) have been developed as alternate material for many sensing applications because of their interesting properties. Their outstanding electromechanical properties make them suitable for pressure/strain sensing application. Other than in view of their structure and number of walls (i.e. Single-Walled CNTs and MultiWalled CNTs), carbon nanotubes can likewise be classified based on their orientation and combined arrangement. One such classification is vertically aligned Multi-Walled Carbon Nanotubes (VA-MWCNTs), regularly termed as CNTs arrays, foam or forest which is macro scale form of CNTs. Elastic behavior alongside exceptional electromechanical (high gauge factor) make it suitable for pressure sensing applications. This paper presents pressure sensor based on such carbon nanotubes forest in pristine form which enables it to perform over wider temperature range as compared to pressure sensors based on conventional materials such as Silicon.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Fei; Zhang, Shujun; Yang, Tiannan

The discovery of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution single crystals is a breakthrough in ferroelectric materials. A key signature of relaxor-ferroelectric solid solutions is the existence of polar nanoregions, a nanoscale inhomogeneity, that coexist with normal ferroelectric domains. Despite two decades of extensive studies, the contribution of polar nanoregions to the underlying piezoelectric properties of relaxor ferroelectrics has yet to be established. Here we quantitatively characterize the contribution of polar nanoregions to the dielectric/piezoelectric responses of relaxor-ferroelectric crystals using a combination of cryogenic experiments and phase-field simulations. The contribution of polar nanoregions to the room-temperature dielectric and piezoelectric propertiesmore » is in the range of 50–80%. A mesoscale mechanism is proposed to reveal the origin of the high piezoelectricity in relaxor ferroelectrics, where the polar nanoregions aligned in a ferroelectric matrix can facilitate polarization rotation. This mechanism emphasizes the critical role of local structure on the macroscopic properties of ferroelectric materials.« less

Nonlinear Optical Properties of Organic and Polymeric Thin Film Materials of Potential for Microgravity Processing Studies

NASA Technical Reports Server (NTRS)

Abdeldayem, Hossin; Frazier, Donald O.; Paley, Mark S.; Penn, Benjamin; Witherow, William K.; Bank, Curtis; Shields, Angela; Hicks, Rosline; Ashley, Paul R.

1996-01-01

In this paper, we will take a closer look at the state of the art of polydiacetylene, and metal-free phthalocyanine films, in view of the microgravity impact on their optical properties, their nonlinear optical properties and their potential advantages for integrated optics. These materials have many attractive features with regard to their use in integrated optical circuits and optical switching. Thin films of these materials processed in microgravity environment show enhanced optical quality and better molecular alignment than those processed in unit gravity. Our studies of these materials indicate that microgravity can play a major role in integrated optics technology. Polydiacetylene films are produced by UV irradiation of monomer solution through an optical window. This novel technique of forming polydiacetylene thin films has been modified for constructing sophisticated micro-structure integrated optical patterns using a pre-programmed UV-Laser beam. Wave guiding through these thin films by the prism coupler technique has been demonstrated. The third order nonlinear parameters of these films have been evaluated. Metal-free phthalocyanine films of good optical quality are processed in our laboratories by vapor deposition technique. Initial studies on these films indicate that they have excellent chemical, laser, and environmental stability. They have large nonlinear optical parameters and show intrinsic optical bistability. This bistability is essential for optical logic gates and optical switching applications. Waveguiding and device making investigations of these materials are underway.

Enhanced room temperature gas sensing of aligned Mn3O4 nanorod assemblies functionalized by aluminum anodic membranes.

PubMed

John, Neetha; Thomas, Paulose; Divya, K V; Abraham, K E

2018-08-17

The study includes a conductometric chemical sensor design using aligned Mn 3 O 4 nanorods. Nanostructuring is an emerging field of prominence due to its capacity to introduce unprecedented properties in materials with potential applications. A hydrothermally prepared in situ Mn 3 O 4 sample appears with an urchin rod-like morphology, which changes to a spherical shape upon annealing. An aluminum anodic membrane/template (AAO) is used for the growth of the nanorods and also as a medium to support the sensor. The aligned Mn 3 O 4 nanorods are formed in the pores of the AAO by vacuum infiltration approach, which is later on annealed. The gold electrical contacts are deposited on the top or bottom ends of the Mn 3 O 4 -embedded AAO to ensure conductometric sensing along the length of the Mn 3 O 4 nanorods. In comparison to the Mn 3 O 4 film-based sensor, the Mn 3 O 4 nanorods in the AAO template have enhanced sensitivity for detecting ethanol and acetone vapor at room temperature. The novel property observed is a result of the large surface area and number of oxygen vacancies of the uniformly aligned and parallel assemblies of the nanorods. The sensor exhibits the lowest response time at 4 s for ethanol and 2 s for acetone at room temperature with a concentration of 50 ppm. The response time is 7 and 5 s, respectively, for 25 ppm. The maximum sensitivities of the sensor at room temperature for ethanol and acetone gases are 67% and 68%, respectively, for 50 ppm concentration. The growth mechanism of the aligned nanorods formed in the AAO template is well established through FESEM analysis. The XPS and HRTEM study give additional evidence for the presence of oxidation states and structure of the prepared nanostructures, respectively.

Outside-the-(Cavity-prep)-Box Thinking

PubMed Central

Thompson, V.P.; Watson, T.F.; Marshall, G.W.; Blackman, B.R.K.; Stansbury, J.W.; Schadler, L.S.; Pearson, R.A.; Libanori, R.

2013-01-01

Direct placement restorative materials must interface with tooth structures that are often compromised by caries or trauma. The material must seal the interface while providing sufficient strength and wear resistance to assure function of the tooth for, ideally, the lifetime of the patient. Needed are direct restorative materials that are less technique-sensitive than current resin-based composite systems while having improved properties. The ideal material could be successfully used in areas of the world with limited infrastructure. Advances in our understanding of the interface between the restoration adhesive system and the stages of carious dentin can be used to promote remineralization. Application of fracture mechanics to adhesion at the tooth-restoration interface can provide insights for improvement. Research in polymer systems suggests alternatives to current composite resin matrix systems to overcome technique sensitivity, while advances in nano- and mesoparticle reinforcement and alignment in composite systems can increase material strength, toughness, and wear resistance, foreshadowing dental application. PMID:24129814

A black body absorber from vertically aligned single-walled carbon nanotubes

PubMed Central

Mizuno, Kohei; Ishii, Juntaro; Kishida, Hideo; Hayamizu, Yuhei; Yasuda, Satoshi; Futaba, Don N.; Yumura, Motoo; Hata, Kenji

2009-01-01

Among all known materials, we found that a forest of vertically aligned single-walled carbon nanotubes behaves most similarly to a black body, a theoretical material that absorbs all incident light. A requirement for an object to behave as a black body is to perfectly absorb light of all wavelengths. This important feature has not been observed for real materials because materials intrinsically have specific absorption bands because of their structure and composition. We found a material that can absorb light almost perfectly across a very wide spectral range (0.2–200 μm). We attribute this black body behavior to stem from the sparseness and imperfect alignment of the vertical single-walled carbon nanotubes. PMID:19339498

Poly(L-lactide) and poly(butylene succinate) immiscible blends: from electrospinning to biologically active materials.

PubMed

Stoyanova, Nikoleta; Paneva, Dilyana; Mincheva, Rosica; Toncheva, Antoniya; Manolova, Nevena; Dubois, Philippe; Rashkov, Iliya

2014-08-01

For the first time the preparation of defect-free fibers from immiscible blends of high molar mass poly(lactic acid) (PLA) and poly(butylene succinate) (PBS) in the whole range of the polyester weight ratios is shown. Electrospinning using the solvent-nonsolvent approach proved most appropriate. Moreover, electrospinning revealed crucial for the obtaining of PLA/PBS materials maintaining integrity. DSC and XRD analyses attested for a plasticizing effect and for increased PLA crystallinity at PBS addition to PLA. The mechanical properties of the PLA/PBS mats were controlled by the alignment of the fibers and changed from plastic to brittle materials upon increasing the PBS content. Drug loading and tests against pathogenic microorganisms suggested that the obtained mats can find application as antibacterial fibrous materials. Copyright © 2014 Elsevier B.V. All rights reserved.

Controlled growth of well-aligned GaS nanohornlike structures and their field emission properties.

PubMed

Sinha, Godhuli; Panda, Subhendu K; Datta, Anuja; Chavan, Padmakar G; Shinde, Deodatta R; More, Mahendra A; Joag, D S; Patra, Amitava

2011-06-01

Here, we report the synthesis of vertically aligned gallium sulfide (GaS) nanohorn arrays using simple vapor-liquid-solid (VLS) method. The morphologies of GaS nano and microstructures are tuned by controlling the temperature and position of the substrate with respect to the source material. A plausible mechanism for the controlled growth has been proposed. It is important to note that the turn-on field value of GaS nanohorns array is found to be the low turn-on field 4.2 V/μm having current density of 0.1 μA/cm(2). The striking feature of the field emission behavior of the GaS nanohorn arrays is that the average emission current remains nearly constant over long time without any degradation. © 2011 American Chemical Society

A Study on Reactive Ion Etching of Barium Strontium Titanate Films Using Mixtures of Argon (Ar), Carbon Tetrafluoride (CF4), and Sulfur Hexafluoride (SF6)

DTIC Science & Technology

2014-07-01

BST) is a complex oxide material with ferroic properties which has been considered for applications ranging from non-volatile memory to microwave...utilizing self-aligned etching to create metal-insulator-metal (MIM) varactors . As part of this method we employed reactive ion etching (RIE) to remove BST...of BST removed vs. etch time for Ar:SF6. .........................................................4 Figure 3. SEM cross-section of varactor showing

Micromechanical Properties of Beryllium and Other Instrument Materials.

DTIC Science & Technology

1981-12-01

in microcreep testing is to maintain the -4 precision of alignment at 10" radians. Repeated unloading to zero stress, as is sometimes done in...a bit uneven, with the only evident trend being a zero slope. This type of record is arbitrarily designated "Type U". Type U records are not quite as...the annealing temperature of 1450OF at a rate of 50 Farenheit degrees per hour, held for one hour, then cooled to room temperature at 50 Farenheit

Laser-driven coating of vertically aligned carbon nanotubes with manganese oxide from metal organic precursors for energy storage.

PubMed

Pérez Del Pino, A; György, E; Alshaikh, I; Pantoja-Suárez, F; Andújar, J L; Pascual, E; Amade, R; Bertran-Serra, E

2017-09-29

Carbon nanotubes-transition metal oxide systems are intensively studied due to their excellent properties for electrochemical applications. In this work, an innovative procedure is developed for the synthesis of vertically aligned multi-walled carbon nanotubes (VACNTs) coated with transition metal oxide nanostructures. VACNTs are grown by plasma enhanced chemical vapor deposition and coated with a manganese-based metal organic precursor (MOP) film based on manganese acetate solution. Subsequent UV pulsed laser irradiation induces the effective heating-decomposition of the MOP leading to the crystallization of manganese oxide nanostructures on the VACNT surface. The study of the morphology, structure and composition of the synthesized materials shows the formation of randomly oriented MnO 2 crystals, with few nanometers in size, and to their alignment in hundreds of nm long filament-like structures, parallel to the CNT's long axis. Electrochemical measurements reveal a significant increase of the specific capacitance of the MnO 2 -VACNT system (100 F g -1 ) as compared to the initial VACNT one (21 F g -1 ).

Laser-driven coating of vertically aligned carbon nanotubes with manganese oxide from metal organic precursors for energy storage

NASA Astrophysics Data System (ADS)

Pérez del Pino, A.; György, E.; Alshaikh, I.; Pantoja-Suárez, F.; Andújar, J. L.; Pascual, E.; Amade, R.; Bertran-Serra, E.

2017-09-01

Carbon nanotubes-transition metal oxide systems are intensively studied due to their excellent properties for electrochemical applications. In this work, an innovative procedure is developed for the synthesis of vertically aligned multi-walled carbon nanotubes (VACNTs) coated with transition metal oxide nanostructures. VACNTs are grown by plasma enhanced chemical vapor deposition and coated with a manganese-based metal organic precursor (MOP) film based on manganese acetate solution. Subsequent UV pulsed laser irradiation induces the effective heating-decomposition of the MOP leading to the crystallization of manganese oxide nanostructures on the VACNT surface. The study of the morphology, structure and composition of the synthesized materials shows the formation of randomly oriented MnO2 crystals, with few nanometers in size, and to their alignment in hundreds of nm long filament-like structures, parallel to the CNT’s long axis. Electrochemical measurements reveal a significant increase of the specific capacitance of the MnO2-VACNT system (100 F g-1) as compared to the initial VACNT one (21 F g-1).

Modulation of gene expression using electrospun scaffolds with templated architecture.

PubMed

Karchin, A; Wang, Y-N; Sanders, J E

2012-06-01

The fabrication of biomimetic scaffolds is a critical component to fulfill the promise of functional tissue-engineered materials. We describe herein a simple technique, based on printed circuit board manufacturing, to produce novel templates for electrospinning scaffolds for tissue-engineering applications. This technique facilitates fabrication of electrospun scaffolds with templated architecture, which we defined as a scaffold's bulk mechanical properties being driven by its fiber architecture. Electrospun scaffolds with templated architectures were characterized with regard to fiber alignment and mechanical properties. Fast Fourier transform analysis revealed a high degree of fiber alignment along the conducting traces of the templates. Mechanical testing showed that scaffolds demonstrated tunable mechanical properties as a function of templated architecture. Fibroblast-seeded scaffolds were subjected to a peak strain of 3 or 10% at 0.5 Hz for 1 h. Exposing seeded scaffolds to the low strain magnitude (3%) significantly increased collagen I gene expression compared to the high strain magnitude (10%) in a scaffold architecture-dependent manner. These experiments indicate that scaffolds with templated architectures can be produced, and modulation of gene expression is possible with templated architectures. This technology holds promise for the long-term goal of creating tissue-engineered replacements with the biomechanical and biochemical make-up of native tissues. Copyright © 2012 Wiley Periodicals, Inc.

Comprehensive analyses of how tubule occlusion and advanced glycation end-products diminish strength of aged dentin

NASA Astrophysics Data System (ADS)

Shinno, Yuko; Ishimoto, Takuya; Saito, Mitsuru; Uemura, Reo; Arino, Masumi; Marumo, Keishi; Nakano, Takayoshi; Hayashi, Mikako

2016-01-01

In clinical dentistry, since fracture is a major cause of tooth loss, better understanding of mechanical properties of teeth structures is important. Dentin, the major hard tissue of teeth, has similar composition to bone. In this study, we investigated the mechanical properties of human dentin not only in terms of mineral density but also using structural and quality parameters as recently accepted in evaluating bone strength. Aged crown and root dentin (age ≥ 40) exhibited significantly lower flexural strength and toughness than young dentin (age < 40). Aged dentin, in which the dentinal tubules were occluded with calcified material, recorded the highest mineral density; but showed significantly lower flexural strength than young dentin. Dentin with strong alignment of the c-axis in hydroxyapatite exhibited high fracture strength, possibly because the aligned apatite along the collagen fibrils may reinforce the intertubular dentin. Aged dentin, showing a high advanced glycation end-products (AGEs) level in its collagen, recorded low flexural strength. We first comprehensively identified significant factors, which affected the inferior mechanical properties of aged dentin. The low mechanical strength of aged dentin is caused by the high mineral density resulting from occlusion of dentinal tubules and accumulation of AGEs in dentin collagen.

Derivation of Multiple Covarying Material and Process Parameters Using Physics-Based Modeling of X-ray Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khaira, Gurdaman; Doxastakis, Manolis; Bowen, Alec

There is considerable interest in developing multimodal characterization frameworks capable of probing critical properties of complex materials by relying on distinct, complementary methods or tools. Any such framework should maximize the amount of information that is extracted from any given experiment and should be sufficiently powerful and efficient to enable on-the-fly analysis of multiple measurements in a self-consistent manner. Such a framework is demonstrated in this work in the context of self-assembling polymeric materials, where theory and simulations provide the language to seamlessly mesh experimental data from two different scattering measurements. Specifically, the samples considered here consist of diblock copolymersmore » (BCP) that are self-assembled on chemically nanopatterned surfaces. The copolymers microphase separate into ordered lamellae with characteristic dimensions on the scale of tens of nanometers that are perfectly aligned by the substrate over macroscopic areas. These aligned lamellar samples provide ideal standards with which to develop the formalism introduced in this work and, more generally, the concept of high-information-content, multimodal experimentation. The outcomes of the proposed analysis are then compared to images generated by 3D scanning electron microscopy tomography, serving to validate the merit of the framework and ideas proposed here.« less

Field alignment of bent-core smectic liquid crystals for analog optical phase modulation

NASA Astrophysics Data System (ADS)

Shen, Y.; Goodhew, L.; Shao, R.; Moran, M.; Korblova, E.; Walba, D. M.; Clark, N. A.; Maclennan, J. E.; Rudquist, P.

2015-05-01

A general method for aligning bent-core smectic liquid crystal materials is described. Alternating electric fields between interdigitated electrodes patterned on one cell surface create torques on the liquid crystal that result in uniform "bookshelf" orientation of the smectic layers. The aligned cell can then be driven in the conventional way by applying an electric field between all of the stripe electrodes connected together and a monolithic electrode on the other cell surface. Fast, analog, optical phase-only modulation is demonstrated in a device containing a polar, bent-core SmAPF material aligned using this technique.

Approximate static condensation algorithm for solving multi-material diffusion problems on meshes non-aligned with material interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kikinzon, Evgeny; Kuznetsov, Yuri; Lipnikov, Konstatin

In this study, we describe a new algorithm for solving multi-material diffusion problem when material interfaces are not aligned with the mesh. In this case interface reconstruction methods are used to construct approximate representation of interfaces between materials. They produce so-called multi-material cells, in which materials are represented by material polygons that contain only one material. The reconstructed interface is not continuous between cells. Finally, we suggest the new method for solving multi-material diffusion problems on such meshes and compare its performance with known homogenization methods.

Approximate static condensation algorithm for solving multi-material diffusion problems on meshes non-aligned with material interfaces

DOE PAGES

Kikinzon, Evgeny; Kuznetsov, Yuri; Lipnikov, Konstatin; ...

2017-07-08

In this study, we describe a new algorithm for solving multi-material diffusion problem when material interfaces are not aligned with the mesh. In this case interface reconstruction methods are used to construct approximate representation of interfaces between materials. They produce so-called multi-material cells, in which materials are represented by material polygons that contain only one material. The reconstructed interface is not continuous between cells. Finally, we suggest the new method for solving multi-material diffusion problems on such meshes and compare its performance with known homogenization methods.

Sensitivity of corneal biomechanical and optical behavior to material parameters using design of experiments method.

PubMed

Xu, Mengchen; Lerner, Amy L; Funkenbusch, Paul D; Richhariya, Ashutosh; Yoon, Geunyoung

2018-02-01

The optical performance of the human cornea under intraocular pressure (IOP) is the result of complex material properties and their interactions. The measurement of the numerous material parameters that define this material behavior may be key in the refinement of patient-specific models. The goal of this study was to investigate the relative contribution of these parameters to the biomechanical and optical responses of human cornea predicted by a widely accepted anisotropic hyperelastic finite element model, with regional variations in the alignment of fibers. Design of experiments methods were used to quantify the relative importance of material properties including matrix stiffness, fiber stiffness, fiber nonlinearity and fiber dispersion under physiological IOP. Our sensitivity results showed that corneal apical displacement was influenced nearly evenly by matrix stiffness, fiber stiffness and nonlinearity. However, the variations in corneal optical aberrations (refractive power and spherical aberration) were primarily dependent on the value of the matrix stiffness. The optical aberrations predicted by variations in this material parameter were sufficiently large to predict clinically important changes in retinal image quality. Therefore, well-characterized individual variations in matrix stiffness could be critical in cornea modeling in order to reliably predict optical behavior under different IOPs or after corneal surgery.

Recent advances in photonics packaging materials

NASA Astrophysics Data System (ADS)

Zweben, Carl

2006-02-01

There are now over a dozen low-CTE materials with thermal conductivities between that of copper (400 w/m-K) and over 4X copper (1700 W/m-K). Most have low densities. For comparison, traditional low-CTE packaging materials like copper/tungsten have thermal conductivities that are little or no better than that of aluminum (200 W/m-K) and high densities. There are also low-density thermal insulators with low CTEs. Some advanced materials are low cost. Most do not outgas. They have a wide range of electrical properties that can be used to minimize electromagnetic emissions or provide EMI shielding. Several are now in commercial and aerospace applications, including laser diode packages; light-emitting diode (LED) packages; thermoelectric cooler bases, plasma displays; power modules; servers; laptops; heat sinks; thermally conductive, low-CTE printed circuit boards; and printed circuit board cold plates. Advanced material payoffs include: improved thermal performance, reliability, alignment and manufacturing yield; reduced thermal stresses and heating power requirements; simplified thermal design; enablement of hard solder direct attach; weight savings up to 85%; size reductions up to 65%; and lower cost. This paper discusses the large and increasing number of advanced packaging materials, including properties, development status, applications, increasing manufacturing yield, cost, lessons learned and future directions, including nanocomposites.

Tailorable Dielectric Material with Complex Permittivity Characteristics

NASA Technical Reports Server (NTRS)

Smith, Joseph G. (Inventor); Watson, Kent A. (Inventor); Elliott, Holly A (Inventor); Delozier, Donavon Mark (Inventor); Connell, John W. (Inventor); Ghose, Sayata (Inventor); Dudley, Kenneth L. (Inventor)

2014-01-01

A dielectric material includes a network of nanosubstrates, such as but not limited to nanotubes, nanosheets, or other nanomaterials or nanostructures, a polymer base material or matrix, and nanoparticles constructed at least partially of an elemental metal. The network has a predetermined nanosubstrate loading percentage by weight with respect to a total weight of the dielectric material, and a preferential or predetermined longitudinal alignment with respect to an orientation of an incident electrical field. A method of forming the dielectric material includes depositing the metal-based nanoparticles onto the nanosubstrates and subsequently mixing these with a polymer matrix. Once mixed, alignment can be achieved by melt extrusion or a similar mechanical shearing process. Alignment of the nanosubstrate may be in horizontal or vertical direction with respect to the orientation of an incident electrical field.

Ternary eutectic growth of nanostructured thermoelectric Ag-Pb-Te materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Hsin-jay; Chen, Sinn-wen; Foo, Wei-jian

2012-07-09

Nanostructured Ag-Pb-Te thermoelectric materials were fabricated by unidirectionally solidifying the ternary Ag-Pb-Te eutectic and near-eutectic alloys using the Bridgeman method. Specially, the Bridgman-grown eutectic alloy exhibited a partially aligned lamellar microstructure, which consisted of Ag{sub 5}Te{sub 3} and Te phases, with additional 200-600 nm size particles of PbTe. The self-assembled interfaces altered the thermal and electronic transport properties in the bulk Ag-Pb-Te eutectic alloy. Presumably due to phonon scattering from the nanoscale microstructure, a low thermal conductivity ({kappa} = 0.3 W/mK) was achieved of the eutectic alloy, leading to a zT peak of 0.41 at 400 K.

Relative properties of smooth terminating bands

NASA Astrophysics Data System (ADS)

Afanasjev, A. V.; Ragnarsson, I.

1998-01-01

The relative properties of smooth terminating bands observed in the A ∼ 110 mass region are studied within the effective alignment approach. Theoretical values of ietf are calculated using the configuration-dependent shell-correction model with the cranked Nilsson potential. Reasonable agreement with experiment shows that previous interpretations of these bands are consistent with the present study. Contrary to the case of superdeformed bands, the effective alignments of these bands deviate significantly from the pure single-particle alignments of the corresponding orbitals. This indicates that in the case of smooth terminating bands, the effects associated with changes in equilibrium deformations contribute significantly to the effective alignment.

Fibrin gels exhibit improved biological, structural, and mechanical properties compared with collagen gels in cell-based tendon tissue-engineered constructs.

PubMed

Breidenbach, Andrew P; Dyment, Nathaniel A; Lu, Yinhui; Rao, Marepalli; Shearn, Jason T; Rowe, David W; Kadler, Karl E; Butler, David L

2015-02-01

The prevalence of tendon and ligament injuries and inadequacies of current treatments is driving the need for alternative strategies such as tissue engineering. Fibrin and collagen biopolymers have been popular materials for creating tissue-engineered constructs (TECs), as they exhibit advantages of biocompatibility and flexibility in construct design. Unfortunately, a few studies have directly compared these materials for tendon and ligament applications. Therefore, this study aims at determining how collagen versus fibrin hydrogels affect the biological, structural, and mechanical properties of TECs during formation in vitro. Our findings show that tendon and ligament progenitor cells seeded in fibrin constructs exhibit improved tenogenic gene expression patterns compared with their collagen-based counterparts for approximately 14 days in culture. Fibrin-based constructs also exhibit improved cell-derived collagen alignment, increased linear modulus (2.2-fold greater) compared with collagen-based constructs. Cyclic tensile loading, which promotes the maturation of tendon constructs in a previous work, exhibits a material-dependent effect in this study. Fibrin constructs show trending reductions in mechanical, biological, and structural properties, whereas collagen constructs only show improved tenogenic expression in the presence of mechanical stimulation. These findings highlight that components of the mechanical stimulus (e.g., strain amplitude or time of initiation) need to be tailored to the material and cell type. Given the improvements in tenogenic expression, extracellular matrix organization, and material properties during static culture, in vitro findings presented here suggest that fibrin-based constructs may be a more suitable alternative to collagen-based constructs for tissue-engineered tendon/ligament repair.

Fibrin Gels Exhibit Improved Biological, Structural, and Mechanical Properties Compared with Collagen Gels in Cell-Based Tendon Tissue-Engineered Constructs

PubMed Central

Dyment, Nathaniel A.; Lu, Yinhui; Rao, Marepalli; Shearn, Jason T.; Rowe, David W.; Kadler, Karl E.; Butler, David L.

2015-01-01

The prevalence of tendon and ligament injuries and inadequacies of current treatments is driving the need for alternative strategies such as tissue engineering. Fibrin and collagen biopolymers have been popular materials for creating tissue-engineered constructs (TECs), as they exhibit advantages of biocompatibility and flexibility in construct design. Unfortunately, a few studies have directly compared these materials for tendon and ligament applications. Therefore, this study aims at determining how collagen versus fibrin hydrogels affect the biological, structural, and mechanical properties of TECs during formation in vitro. Our findings show that tendon and ligament progenitor cells seeded in fibrin constructs exhibit improved tenogenic gene expression patterns compared with their collagen-based counterparts for approximately 14 days in culture. Fibrin-based constructs also exhibit improved cell-derived collagen alignment, increased linear modulus (2.2-fold greater) compared with collagen-based constructs. Cyclic tensile loading, which promotes the maturation of tendon constructs in a previous work, exhibits a material-dependent effect in this study. Fibrin constructs show trending reductions in mechanical, biological, and structural properties, whereas collagen constructs only show improved tenogenic expression in the presence of mechanical stimulation. These findings highlight that components of the mechanical stimulus (e.g., strain amplitude or time of initiation) need to be tailored to the material and cell type. Given the improvements in tenogenic expression, extracellular matrix organization, and material properties during static culture, in vitro findings presented here suggest that fibrin-based constructs may be a more suitable alternative to collagen-based constructs for tissue-engineered tendon/ligament repair. PMID:25266738

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang Shumin; Tian Hongwei; Pei Yanhui

A novel hedgehog-like core/shell structure, consisting of a high density of vertically aligned graphene sheets and a thin graphene shell/a copper core (VGs-GS/CC), has been synthesized via a simple one-step synthesis route using radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD). Scanning and transmission electron microscopy investigations show that the morphology of this core/shell material could be controlled by deposition time. For a short deposition time, only multilayer graphene shell tightly surrounds the copper particle, while as the deposition time is relative long, graphene sheets extend from the surface of GS/CC. The GS can protect CC particles from oxidation. The growth mechanismmore » for the obtained GS/CC and VGs-GS/CC has been revealed. Compared to VGs, VGs-GS/CC material exhibits a better electron field emission property. This investigation opens a possibility for designing a core/shell structure of different carbon-metal hybrid materials for a wide variety of practical applications. - Graphical abstract: With increasing deposition time, graphene sheets extend from the surface of GS/CC, causing the multilayer graphene encapsulated copper to be converted into vertically aligned graphene sheets-graphene shell/copper core structure. Highlights: Black-Right-Pointing-Pointer A novel hedgehog-like core/shell structure has been synthesized. Black-Right-Pointing-Pointer The structure consists of vertical graphene sheets-graphene shell and copper core. Black-Right-Pointing-Pointer The morphology of VGs-GS/CC can be controlled by choosing a proper deposition time. Black-Right-Pointing-Pointer With increasing deposition time, graphene sheets extend from the surface of GS/CC. Black-Right-Pointing-Pointer VGs-GS/CC exhibits a better electron field emission property as compared with VGs.« less

Optical properties and band alignments in ZnTe nanoparticles/MoS2 layer hetero-interface using SE and KPFM studies

NASA Astrophysics Data System (ADS)

Sharma, Intu; Mehta, B. R.

2017-11-01

Integration of a layered two-dimensional (2D) material with a non-2D material provides a platform where one can modulate and achieve the properties desired for various next-generation electronic and opto-electronic applications. Here, we investigated ZnTe nanoparticles/MoS2 hetero-interfaces with the thickness of the MoS2 varying from few to multilayer. High-resolution transmission electron microscopy was used to observe the crystalline behaviour of the ZnTe nanoparticles, while the number of MoS2 layers was investigated using Raman measurements. Spectroscopic ellipsometry (SE) analysis based on the five-layer fitting model was used to analyse the optical behaviour of the heterojunction, where the excitonic features corresponding to the MoS2 layers and absorption features due to the ZnTe nanoparticles are observed. From the Kelvin probe force microscopy (KPFM) measurements, the surface potential (SP) of the ZnTe nanoparticles/MoS2 is found to be different in comparison with the SP of the ZnTe nanoparticles and MoS2, which is indicative of the charge transfer at the ZnTe nanoparticles/MoS2 hetero-interface. Various parameters obtained using SE and KPFM measurements were used to propose energy band alignments at the ZnTe nanoparticles/MoS2 hetero-interface. In addition, an interface photovoltage of 193 mV was obtained by carrying out KPFM measurements under illuminating condition.

Thermal Conduction in Vertically Aligned Copper Nanowire Arrays and Composites.

PubMed

Barako, Michael T; Roy-Panzer, Shilpi; English, Timothy S; Kodama, Takashi; Asheghi, Mehdi; Kenny, Thomas W; Goodson, Kenneth E

2015-09-02

The ability to efficiently and reliably transfer heat between sources and sinks is often a bottleneck in the thermal management of modern energy conversion technologies ranging from microelectronics to thermoelectric power generation. These interfaces contribute parasitic thermal resistances that reduce device performance and are subjected to thermomechanical stresses that degrade device lifetime. Dense arrays of vertically aligned metal nanowires (NWs) offer the unique combination of thermal conductance from the constituent metal and mechanical compliance from the high aspect ratio geometry to increase interfacial heat transfer and device reliability. In the present work, we synthesize copper NW arrays directly onto substrates via templated electrodeposition and extend this technique through the use of a sacrificial overplating layer to achieve improved uniformity. Furthermore, we infiltrate the array with an organic phase change material and demonstrate the preservation of thermal properties. We use the 3ω method to measure the axial thermal conductivity of freestanding copper NW arrays to be as high as 70 W m(-1) K(-1), which is more than an order of magnitude larger than most commercial interface materials and enhanced-conductivity nanocomposites reported in the literature. These arrays are highly anisotropic, and the lateral thermal conductivity is found to be only 1-2 W m(-1) K(-1). We use these measured properties to elucidate the governing array-scale transport mechanisms, which include the effects of morphology and energy carrier scattering from size effects and grain boundaries.

Enhanced optoelectronic performances of vertically aligned hexagonal boron nitride nanowalls-nanocrystalline diamond heterostructures

NASA Astrophysics Data System (ADS)

Sankaran, Kamatchi Jothiramalingam; Hoang, Duc Quang; Kunuku, Srinivasu; Korneychuk, Svetlana; Turner, Stuart; Pobedinskas, Paulius; Drijkoningen, Sien; van Bael, Marlies K.; D' Haen, Jan; Verbeeck, Johan; Leou, Keh-Chyang; Lin, I.-Nan; Haenen, Ken

2016-07-01

Field electron emission (FEE) properties of vertically aligned hexagonal boron nitride nanowalls (hBNNWs) grown on Si have been markedly enhanced through the use of nitrogen doped nanocrystalline diamond (nNCD) films as an interlayer. The FEE properties of hBNNWs-nNCD heterostructures show a low turn-on field of 15.2 V/μm, a high FEE current density of 1.48 mA/cm2 and life-time up to a period of 248 min. These values are far superior to those for hBNNWs grown on Si substrates without the nNCD interlayer, which have a turn-on field of 46.6 V/μm with 0.21 mA/cm2 FEE current density and life-time of 27 min. Cross-sectional TEM investigation reveals that the utilization of the diamond interlayer circumvented the formation of amorphous boron nitride prior to the growth of hexagonal boron nitride. Moreover, incorporation of carbon in hBNNWs improves the conductivity of hBNNWs. Such a unique combination of materials results in efficient electron transport crossing nNCD-to-hBNNWs interface and inside the hBNNWs that results in enhanced field emission of electrons. The prospective application of these materials is manifested by plasma illumination measurements with lower threshold voltage (370 V) and longer life-time, authorizing the role of hBNNWs-nNCD heterostructures in the enhancement of electron emission.

Growth, strain relaxation properties and high-κ dielectric integration of mixed-anion GaAs{sub 1-y}Sb{sub y} metamorphic materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Y.; Clavel, M.; Goley, P.

Mixed-anion, GaAs{sub 1-y}Sb{sub y} metamorphic materials with a wide range of antimony (Sb) compositions extending from 15% to 62%, were grown by solid source molecular beam epitaxy (MBE) on GaAs substrates. The impact of different growth parameters on the Sb composition in GaAs{sub 1-y}Sb{sub y} materials was systemically investigated. The Sb composition was well-controlled by carefully optimizing the As/Ga ratio, the Sb/Ga ratio, and the substrate temperature during the MBE growth process. High-resolution x-ray diffraction demonstrated a quasi-complete strain relaxation within each composition of GaAs{sub 1-y}Sb{sub y}. Atomic force microscopy exhibited smooth surface morphologies across the wide range of Sbmore » compositions in the GaAs{sub 1-y}Sb{sub y} structures. Selected high-κ dielectric materials, Al{sub 2}O{sub 3}, HfO{sub 2}, and Ta{sub 2}O{sub 5} were deposited using atomic layer deposition on the GaAs{sub 0.38}Sb{sub 0.62} material, and their respective band alignment properties were investigated by x-ray photoelectron spectroscopy (XPS). Detailed XPS analysis revealed a valence band offset of >2 eV for all three dielectric materials on GaAs{sub 0.38}Sb{sub 0.62}, indicating the potential of utilizing these dielectrics on GaAs{sub 0.38}Sb{sub 0.62} for p-type metal-oxide-semiconductor (MOS) applications. Moreover, both Al{sub 2}O{sub 3} and HfO{sub 2} showed a conduction band offset of >2 eV on GaAs{sub 0.38}Sb{sub 0.62}, suggesting these two dielectrics can also be used for n-type MOS applications. The well-controlled Sb composition in several GaAs{sub 1-y}Sb{sub y} material systems and the detailed band alignment analysis of multiple high-κ dielectric materials on a fixed Sb composition, GaAs{sub 0.38}Sb{sub 0.62}, provides a pathway to utilize GaAs{sub 1-y}Sb{sub y} materials in future microelectronic and optoelectronic applications.« less

Fabrication and characterization of biomimetic ceramic/polymer composite materials for dental restoration.

PubMed

Petrini, Morena; Ferrante, Maurizio; Su, Bo

2013-04-01

Conventional dental composites with randomly dispersed inorganic particles within a polymer matrix fail to recapitulate the aligned and anisotropic structure of the dentin and enamel. The aim of the study was to produce a biomimetic composite consisting of a ceramic preform with graded and continuously aligned open pores, infiltrated with epoxy resin. The freeze casting technique was used to obtain the hierarchically structured architecture of the ceramic preforms. Optical and scanning electron microscopy (SEM) and differential thermal analysis and thermogravimetry (TG-DTA) were used to characterize the samples. Three point bending test and compression test were also performed. All analysis confirmed that the biomimetic composite was characterized by a multi-level hierarchical structure along the freezing direction. In the bottom layers close to the cooling plate (up to 2mm thick), a randomly packed ceramic with closed pores were formed, which resulted in incomplete infiltration with resin and resultant poor mechanical propertiesof the composite. Above 2mm, all ceramic samples showed an aligned structure with an increasing lamellae spacing (wavelength) and a decreasing wall thickness. Mechanical tests showed that the properties of the composites made from ceramic preforms above 2mm from cooling plate are similar to those of the dentin. The fabrication processing reported in this work offers a viable route for the fabrication of biomimetic composites, which could be potentially used in a range of dental restorations to compete with the current dental composites and ceramics. Copyright © 2012 Academy of Dental Materials. All rights reserved.

Electronic structures and enhanced optical properties of blue phosphorene/transition metal dichalcogenides van der Waals heterostructures.

PubMed

Peng, Qiong; Wang, Zhenyu; Sa, Baisheng; Wu, Bo; Sun, Zhimei

2016-08-24

As a fast emerging topic, van der Waals (vdW) heterostructures have been proposed to modify two-dimensional layered materials with desired properties, thus greatly extending the applications of these materials. In this work, the stacking characteristics, electronic structures, band edge alignments, charge density distributions and optical properties of blue phosphorene/transition metal dichalcogenides (BlueP/TMDs) vdW heterostructures were systematically studied based on vdW corrected density functional theory. Interestingly, the valence band maximum and conduction band minimum are located in different parts of BlueP/MoSe2, BlueP/WS2 and BlueP/WSe2 heterostructures. The MoSe2, WS2 or WSe2 layer can be used as the electron donor and the BlueP layer can be used as the electron acceptor. We further found that the optical properties under visible-light irradiation of BlueP/TMDs vdW heterostructures are significantly improved. In particular, the predicted upper limit energy conversion efficiencies of BlueP/MoS2 and BlueP/MoSe2 heterostructures reach as large as 1.16% and 0.98%, respectively, suggesting their potential applications in efficient thin-film solar cells and optoelectronic devices.

Interfacial energetics of two-dimensional colloidal clusters generated with a tunable anharmonic interaction potential

NASA Astrophysics Data System (ADS)

Hilou, Elaa; Du, Di; Kuei, Steve; Biswal, Sibani Lisa

2018-02-01

Interfacial characteristics are critical to various properties of two-dimensional (2D) materials such as band alignment at a heterojunction and nucleation kinetics in a 2D crystal. Despite the desire to harness these enhanced interfacial properties for engineering new materials, unexpected phase transitions and defects, unique to the 2D morphology, have left a number of open questions. In particular, the effects of configurational anisotropy, which are difficult to isolate experimentally, and their influence on interfacial properties are not well understood. In this work, we begin to probe this structure-thermodynamic relationship, using a rotating magnetic field to generate an anharmonic interaction potential in a 2D system of paramagnetic particles. At low magnetic field strengths, weakly interacting colloidal particles form non-close-packed, fluidlike droplets, whereas, at higher field strengths, crystallites with hexagonal ordering are observed. We examine spatial and interfacial properties of these 2D colloidal clusters by measuring the local bond orientation order parameter and interfacial stiffness as a function of the interaction strength. To our knowledge, this is the first study to measure the tunable interfacial stiffness of a 2D colloidal cluster by controlling particle interactions using external fields.

Integrated three-dimensional shape and reflection properties measurement system.

PubMed

Krzesłowski, Jakub; Sitnik, Robert; Maczkowski, Grzegorz

2011-02-01

Creating accurate three-dimensional (3D) digitalized models of cultural heritage objects requires that information about surface geometry be integrated with measurements of other material properties like color and reflectance. Up until now, these measurements have been performed in laboratories using manually integrated (subjective) data analyses. We describe an out-of-laboratory bidirectional reflectance distribution function (BRDF) and 3D shape measurement system that implements shape and BRDF measurement in a single setup with BRDF uncertainty evaluation. The setup aligns spatial data with the angular reflectance distribution, yielding a better estimation of the surface's reflective properties by integrating these two modality measurements into one setup using a single detector. This approach provides a better picture of an object's intrinsic material features, which in turn produces a higher-quality digitalized model reconstruction. Furthermore, this system simplifies the data processing by combining structured light projection and photometric stereo. The results of our method of data analysis describe the diffusive and specular attributes corresponding to every measured geometric point and can be used to render intricate 3D models in an arbitrarily illuminated scene.

Poling of PVDF matrix composites for integrated structural load sensing

NASA Astrophysics Data System (ADS)

Haghiashtiani, Ghazaleh; Greminger, Michael A.; Zhao, Ping

2014-03-01

The purpose of this study is to create and evaluate a smart composite structure that can be used for integrated load sensing and structural health monitoring. In this structure, PVDF films are used as the matrix material instead of epoxy resin or other thermoplastics. The reinforcements are two layers of carbon fiber with one layer of Kevlar separating them. Due to the electrical conductivity properties of carbon fiber and the dielectric effect of Kevlar, the structure acts as a capacitor. Furthermore, the piezoelectric properties of the PVDF matrix can be used to monitor the response of the structure under applied loads. In order to exploit the piezoelectric properties of PVDF, the PVDF material must be polarized to align the dipole moments of its crystalline structure. The optimal condition for poling the structure was found by performing a 23 factorial design of experiment (DoE). The factors that were studied in DoE were temperature, voltage, and duration of poling. Finally, the response of the poled structure was monitored by exposing the samples to an applied load.

Compositions for directed alignment of conjugated polymers

DOEpatents

Kim, Jinsang; Kim, Bong-Gi; Jeong, Eun Jeong

2016-04-19

Conjugated polymers (CPs) achieve directed alignment along an applied flow field and a dichroic ratio of as high as 16.67 in emission from well-aligned thin films and fully realized anisotropic optoelectronic properties of CPs in field-effect transistor (FET).

SU-F-E-10: Student-Driven Exploration of Radiographic Material Properties, Phantom Construction, and Clinical Workflows Or: The Extraordinary Life of CANDY MAN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahon, RN; Riblett, MJ; Hugo, GD

Purpose: To develop a hands-on learning experience that explores the radiological and structural properties of everyday items and applies this knowledge to design a simple phantom for radiotherapy exercises. Methods: Students were asked to compile a list of readily available materials thought to have radiation attenuation properties similar to tissues within the human torso. Participants scanned samples of suggested materials and regions of interest (ROIs) were used to characterize bulk attenuation properties. Properties of each material were assessed via comparison to a Gammex Tissue characterization phantom and used to construct a list of inexpensive near-tissue-equivalent materials. Critical discussions focusing onmore » samples found to differ from student expectations were used to revise and narrow the comprehensive list. From their newly acquired knowledge, students designed and constructed a simple thoracic phantom for use in a simulated clinical workflow. Students were tasked with setting up the phantom and acquiring planning CT images for use in treatment planning and dose delivery. Results: Under engineer and physicist supervision, students were trained to use a CT simulator and acquired images for approximately 60 different foodstuffs, candies, and household items. Through peer discussion, students gained valuable insights and were made to review preconceptions about radiographic material properties. From a subset of imaged materials, a simple phantom was successfully designed and constructed to represent a human thorax. Students received hands-on experience with clinical treatment workflows by learning how to perform CT simulation, create a treatment plan for an embedded tumor, align the phantom for treatment, and deliver a treatment fraction. Conclusion: In this activity, students demonstrated their ability to reason through the radiographic material selection process, construct a simple phantom to specifications, and exercise their knowledge of clinical workflows. Furthermore, the enjoyable and inexpensive nature of this project proved to attract participant interest and drive creative exploration. Mahon and Riblett have nothing to disclose; Hugo has a research agreement with Phillips Medical systems, a license agreement with Varian Medical Systems, research grants from the National Institute of Health. Authors do not have any potential conflicts of interest to disclose.« less

Exotic quantum properties under high magnetic fields and pressure-induced superconductivity in layered ZrTe5 and pyrite PtBi2

NASA Astrophysics Data System (ADS)

Tian, Mingliang; Tian, Zhaorong; Ning, Wei; Mingliang Tian Team

Topological Dirac semimetal is a newly discovered class of materials which has attracted intense attention. This material can be viewed as a three-dimensional (3D) analog of graphene and has linear energy dispersion in bulk, leading to a range of exotic transport properties. Here we report direct quantum transport evidence of the 3D Dirac semimetal phase of semimetallic materials ZrTe5 and pyrite PtBi2 by angular-dependent magnetoresistance measurements under high magnetic fields up to 35 T, as well as the pressure-induced superconductivity. We observed very clear negative longitudinal magnetoresistance in ZrTe5 induced by chiral anomaly under the condition of the magnetic field aligned only along the current direction, and the extreme large unsaturated magnetoresistance in pyrite PtBi2 up to 11.2 million percent at T = 1.8 K and 33 T, which surpasses the previously reported Dirac materials, such as LaSb, WTe2 and NbP. Analysis of the Shubnikov de Haas oscillations suggest that both ZrTe5 and PtBi2\\ are likely a new topological semimetals.

Computational Search for Specific Magnetoelectronic Characteristics

NASA Astrophysics Data System (ADS)

Pickett, Warren E.

1997-08-01

Many aspects of the coupling between magnetic state (ferro- or antiferromagnetic) and the electronic properties of a material can be predicted reliably from local spin density (LSD) calculations. Such calculations are routinely used to interpret data, but so far little actual prediction of new materials has been attempted. We present here the application of LSD methods to look for half-metallic (HM) antiferromagnetic (AFM) compounds. These materials will have unusual properties, such as 100% spin-polarized transport with no net magnetic field, and the possibility of a novel type of superconductivity. The double perovskite crystal structure was chosen, due to some experience with it and its simplicity, and magnetic ions M',M'' were chosen in the expectation that their moments in the La_2M'M''O6 compound would be equal in magnitude and could be induced to align in an antiparallel manner, giving zero total magnetization. Results for six compounds, with magnetic ions chosen from the 3d transition series, will be described. Three HM AFM states have been found, as well as several HM ferromagnetic states.

Ordered materials for organic electronics and photonics.

PubMed

O'Neill, Mary; Kelly, Stephen M

2011-02-01

We present a critical review of semiconducting/light emitting, liquid crystalline materials and their use in electronic and photonic devices such as transistors, photovoltaics, OLEDs and lasers. We report that annealing from the mesophase improves the order and packing of organic semiconductors to produce state-of-the-art transistors. We discuss theoretical models which predict how charge transport and light emission is affected by the liquid crystalline phase. Organic photovoltaics and OLEDs require optimization of both charge transport and optical properties and we identify the various trade-offs involved for ordered materials. We report the crosslinking of reactive mesogens to give pixellated full-colour OLEDs and distributed bi-layer photovoltaics. We show how the molecular organization inherent to the mesophase can control the polarization of light-emitting devices and the gain in organic, thin-film lasers and can also provide distributed feedback in chiral nematic mirrorless lasers. We update progress on the surface alignment of liquid crystalline semiconductors to obtain monodomain devices without defects or devices with spatially varying properties. Finally the significance of all of these developments is assessed. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sub-5 nm, globally aligned graphene nanoribbons on Ge(001)

DOE PAGES

Kiraly, Brian; Mannix, Andrew J.; Jacobberger, Robert M.; ...

2016-05-23

Graphene nanoribbons (GNRs) hold great promise for future electronics because of their edge and width dependent electronic bandgaps and exceptional transport properties. While significant progress toward such devices has been made, the field has been limited by difficulties achieving narrow widths, global alignment, and atomically pristine GNR edges on technologically relevant substrates. A recent advance has challenged these limits by using Ge(001) substrates to direct the bottom-up growth of GNRs with nearly pristine armchair edges and widths near ~10 nm via atmospheric pressure chemical vapor deposition. In this work, we extend the growth of GNRs on Ge(001) to ultra-high vacuummore » conditions and realize GNRs narrower than 5 nm. Armchair graphene nanoribbons directed along the Ge <110> surface directions are achieved with excellent width control and relatively large bandgaps. As a result, the bandgap magnitude and electronic uniformity make these new materials excellent candidates for future developments in nanoelectronics.« less

Growth of well-aligned ZnO nanorods using auge catalyst by vapor phase transportation.

PubMed

Ha, S Y; Jung, M N; Park, S H; Ko, H J; Ko, H; Oh, D C; Yao, T; Chang, J H

2006-11-01

Well-aligned ZnO nanorods have been achieved using new alloy (AuGe) catalyst. Zn powder was used as a source material and it was transported in a horizontal tube furnace onto an AuGe deposited Si substrates. The structural and optical properties of ZnO nanorods were characterized by scanning electron microscopy, high resolution X-ray diffraction, and photoluminescence. ZnO nanorods grown at 650 degrees C on 53 nm thick AuGe layer show uniform shape with the length of 8 +/- 0.5 microm and the diameter of 150 +/- 5 nm. Also, the tilting angle of ZnO nanorods (+/- 5.5 degrees) is confirmed by HRXRD. High structural quality of the nanorods is conformed by the photoluminescence measurement. All samples show strong UV emission without considerable deep level emission. However, weak deep level emission appears at high (700 degrees C) temperature due to the increase of oxygen desertion.

Alteration of architecture of MoO₃ nanostructures on arbitrary substrates: growth kinetics, spectroscopic and gas sensing properties.

PubMed

Illyaskutty, Navas; Sreedhar, Sreeja; Sanal Kumar, G; Kohler, Heinz; Schwotzer, Matthias; Natzeck, Carsten; Pillai, V P Mahadevan

2014-11-21

MoO3 nanostructures have been grown in thin film form on five different substrates by RF magnetron sputtering and subsequent annealing; non-aligned nanorods, aligned nanorods, bundled nanowires, vertical nanorods and nanoslabs are formed respectively on the glass, quartz, wafer, alumina and sapphire substrates. The nanostructures formed on these substrates are characterized by AFM, SEM, GIXRD, XPS, micro-Raman, diffuse reflectance and photoluminescence spectroscopy. A detailed growth model for morphology alteration with respect to substrates has been discussed by considering various aspects such as surface roughness, lattice parameters and the thermal expansion coefficient, of both substrates and MoO3. The present study developed a strategy for the choice of substrates to materialize different types MoO3 nanostructures for future thin film applications. The gas sensing tests point towards using these MoO3 nanostructures as principal detection elements in gas sensors.

Anisotropic Mechanical Properties of Magnetically Aligned Fibrin Gels Measured by Magnetic Resonance Elastography

PubMed Central

Namani, Ravi; Wood, Matthew D.; Sakiyama-Elbert, Shelly E.; Bayly, Philip V.

2009-01-01

The anisotropic mechanical properties of magnetically aligned fibrin gels were measured by magnetic resonance elastography (MRE) and by a standard mechanical test: unconfined compression. Soft anisotropic biomaterials are notoriously difficult to characterize, especially in vivo. MRE is well-suited for efficient, non-invasive, and nondestructive assessment of shear modulus. Direction-dependent differences in shear modulus were found to be statistically significant for gels polymerized at magnetic fields of 11.7T and 4.7T compared to control gels. Mechanical anisotropy was greater in the gels polymerized at the higher magnetic field. These observations were consistent with results from unconfined compression tests. Analysis of confocal microscopy images of gels showed measurable alignment of fibrils in gels polymerized at 11.7T. This study provides direct, quantitative measurements of the anisotropy in mechanical properties that accompanies fibril alignment in fibrin gels. PMID:19656516

Navigating neurites utilize cellular topography of Schwann cell somas and processes for optimal guidance

PubMed Central

Lopez-Fagundo, Cristina; Mitchel, Jennifer A.; Ramchal, Talisha D.; Dingle, Yu-Ting L.; Hoffman-Kim, Diane

2013-01-01

The path created by aligned Schwann cells (SCs) after nerve injury underlies peripheral nerve regeneration. We developed geometric bioinspired substrates to extract key information needed for axon guidance by deconstructing the topographical cues presented by SCs. We have previously reported materials that directly replicate SC topography with micro- and nanoscale resolution, but a detailed explanation of the means of directed axon extension on SC topography has not yet been described. Here, using neurite tracing and time-lapse microscopy, we analyzed the SC features that influence axon guidance. Novel poly(dimethylsiloxane) materials, fabricated via photolithography, incorporated bioinspired topographical components with the shapes and sizes of aligned SCs, namely somas and processes, where the length of the processes were varied but the soma geometry and dimensions were kept constant. Rat dorsal root ganglia neurites aligned to all materials presenting bioinspired topography after a 5 days in culture and to bioinspired materials presenting soma and process features after only 17 hours in culture. Key findings of this study were: Neurite response to underlying bioinspired topographical features was time dependent, where at 5 days, neurites aligned most strongly to materials presenting combinations of soma and process features, with higher than average density of either process or soma features; but at 17 hours they aligned more strongly to materials presenting average densities of soma and process features and to materials presenting process features only. These studies elucidate the influence of SC topography on axon guidance in a time-dependent setting and have implications for the optimization of nerve regeneration strategies. PMID:23557939

Single-Axis Accelerometer

NASA Technical Reports Server (NTRS)

Tucker, Dennis Stephen (Inventor); Capo-Lugo, Pedro A. (Inventor)

2016-01-01

A single-axis accelerometer includes a housing defining a sleeve. An object/mass is disposed in the sleeve for sliding movement therein in a direction aligned with the sleeve's longitudinal axis. A first piezoelectric strip, attached to a first side of the object and to the housing, is longitudinally aligned with the sleeve's longitudinal axis. The first piezoelectric strip includes a first strip of a piezoelectric material with carbon nanotubes substantially aligned along a length thereof. A second piezoelectric strip, attached to a second side of the object and to the housing, is longitudinally aligned with the sleeve's longitudinal axis. The second piezoelectric strip includes a second strip of the piezoelectric material with carbon nanotubes substantially aligned along a length thereof. A voltage sensor is electrically coupled to at least one of the first and second piezoelectric strips.

Study of flowability effect on self-planarization performance at SOC materials

NASA Astrophysics Data System (ADS)

Yun, Huichan; Kim, Jinhyung; Park, Youjung; Kim, Yoona; Jeong, Seulgi; Baek, Jaeyeol; Yoon, Byeri; Lim, Sanghak

2017-03-01

For multilayer process, importance of carbon-based spin-on hardmask material that replaces amorphous carbon layer (ACL) is ever increasing. Carbon-based spin-on hardmask is an organic polymer with high carbon content formulated in organic solvents for spin-coating application that is cured through baking. In comparison to CVD process for ACL, carbon-based spin-on hardmask material can offer several benefits: lower cost of ownership (CoO) and improved process time, as well as better gap-fill and planarization performances. Thus carbon-based spin-on hardmask material of high etch resistance, good gap-fill properties and global planarization performances over various pattern topographies are desired to achieve the fine patterning and high aspect ratio (A/R). In particular, good level of global planarization of spin coated layer over the underlying pattern topographies is important for self-aligned double patterning (SADP) process as it dictates the photolithographic margin. Herein, we report a copolymer carbon-based spin-on hardmask resin formulation that exhibits favorable film shrinkage profile and good etch resistance properties. By combining the favorable characteristics of each resin - one resin with good shrinkage property and the other with excellent etch resistance into the copolymer, it was possible to achieve a carbonbased spin-on hardmask formulation with desirable level of etch resistance and the planarization performances across various underlying substrate pattern topographies.

Examination of rapid phase change in copper wires to improve material models and understanding of burst

NASA Astrophysics Data System (ADS)

Olles, Joseph; Garasi, Christopher; Ball, J. Patrick

2017-11-01

Electrically-pulsed wires undergo multiple phase changes including a postulated metastable phase resulting in explosive wire growth. Simulations using the MHD approximation attempt to account for the governing physics, but lack the material properties (equations-of-state and electrical conductivity) to accurately predict the phase evolution of the exploding (bursting) wire. To explore the dynamics of an exploding copper wire (in water), we employ a digital micro-Schlieren streak photography technique. This imaging quantifies wire expansion and shock waves emitted from the wire during phase changes. Using differential voltage probes, a Rogowski coil, and timing fiducials, the phase change of the wire is aligned with electrical power and energy deposition. Time-correlated electrical diagnostics and imaging allow for detailed validation of MHD simulations, comparing observed phases with phase change details found in the material property descriptions. In addition to streak imaging, a long exposure image is taken to capture axial striations along the length of the wire. These images are used to compare with results from 3D MHD simulations which propose that these perturbations impact the rate of wire expansion and temporal change in phases. If successful, the experimental data will identify areas for improvement in the material property models, and modeling results will provide insight into the details of phase change in the wire with correlation to variations in the electrical signals.

Amorphous carbon for photovoltaics

NASA Astrophysics Data System (ADS)

Risplendi, Francesca; Grossman, Jeffrey C.

2015-03-01

All-carbon solar cells have attracted attention as candidates for innovative photovoltaic devices. Carbon-based materials such as graphene, carbon nanotubes (CNT) and amorphous carbon (aC) have the potential to present physical properties comparable to those of silicon-based materials with advantages such as low cost and higher thermal stability.In particular a-C structures are promising systems in which both sp2 and sp3 hybridization coordination are present in different proportions depending on the specific density, providing the possibility of tuning their optoelectronic properties and achieving comparable sunlight absorption to aSi. In this work we employ density functional theory to design suitable device architectures, such as bulk heterojunctions (BHJ) or pn junctions, consisting of a-C as the active layer material.Regarding BHJ, we study interfaces between aC and C nanostructures (such as CNT and fullerene) to relate their optoelectronic properties to the stoichiometry of aC. We demonstrate that the energy alignment between the a-C mobility edges and the occupied and unoccupied states of the CNT or C60 can be widely tuned by varying the aC density to obtain a type II interface.To employ aC in pn junctions we analyze the p- and n-type doping of a-C focusingon an evaluation of the Fermi level and work function dependence on doping.Our results highlight promising features of aC as the active layer material of thin-film solar cells.

Elastic and Piezoelectric Properties of Boron Nitride Nanotube Composites. Part II; Finite Element Model

NASA Technical Reports Server (NTRS)

Kim, H. Alicia; Hardie, Robert; Yamakov, Vesselin; Park, Cheol

2015-01-01

This paper is the second part of a two-part series where the first part presents a molecular dynamics model of a single Boron Nitride Nanotube (BNNT) and this paper scales up to multiple BNNTs in a polymer matrix. This paper presents finite element (FE) models to investigate the effective elastic and piezoelectric properties of (BNNT) nanocomposites. The nanocomposites studied in this paper are thin films of polymer matrix with aligned co-planar BNNTs. The FE modelling approach provides a computationally efficient way to gain an understanding of the material properties. We examine several FE models to identify the most suitable models and investigate the effective properties with respect to the BNNT volume fraction and the number of nanotube walls. The FE models are constructed to represent aligned and randomly distributed BNNTs in a matrix of resin using 2D and 3D hollow and 3D filled cylinders. The homogenisation approach is employed to determine the overall elastic and piezoelectric constants for a range of volume fractions. These models are compared with an analytical model based on Mori-Tanaka formulation suitable for finite length cylindrical inclusions. The model applies to primarily single-wall BNNTs but is also extended to multi-wall BNNTs, for which preliminary results will be presented. Results from the Part 1 of this series can help to establish a constitutive relationship for input into the finite element model to enable the modeling of multiple BNNTs in a polymer matrix.

Self-alignment of plasmonic gold nanorods in reconfigurable anisotropic fluids for tunable bulk metamaterial applications.

PubMed

Liu, Qingkun; Cui, Yanxia; Gardner, Dennis; Li, Xin; He, Sailing; Smalyukh, Ivan I

2010-04-14

We demonstrate the bulk self-alignment of dispersed gold nanorods imposed by the intrinsic cylindrical micelle self-assembly in nematic and hexagonal liquid crystalline phases of anisotropic fluids. External magnetic field and shearing allow for alignment and realignment of the liquid crystal matrix with the ensuing long-range orientational order of well-dispersed plasmonic nanorods. This results in a switchable polarization-sensitive plasmon resonance exhibiting stark differences from that of the same nanorods in isotropic fluids. The device-scale bulk nanoparticle alignment may enable optical metamaterial mass production and control of properties arising from combining the switchable nanoscale structure of anisotropic fluids with the surface plasmon resonance properties of the plasmonic nanorods.

p-i-n heterojunctions with BiFeO3 perovskite nanoparticles and p- and n-type oxides: photovoltaic properties.

PubMed

Chatterjee, Soumyo; Bera, Abhijit; Pal, Amlan J

2014-11-26

We formed p-i-n heterojunctions based on a thin film of BiFeO3 nanoparticles. The perovskite acting as an intrinsic semiconductor was sandwiched between a p-type and an n-type oxide semiconductor as hole- and electron-collecting layer, respectively, making the heterojunction act as an all-inorganic oxide p-i-n device. We have characterized the perovskite and carrier collecting materials, such as NiO and MoO3 nanoparticles as p-type materials and ZnO nanoparticles as the n-type material, with scanning tunneling spectroscopy; from the spectrum of the density of states, we could locate the band edges to infer the nature of the active semiconductor materials. The energy level diagram of p-i-n heterojunctions showed that type-II band alignment formed at the p-i and i-n interfaces, favoring carrier separation at both of them. We have compared the photovoltaic properties of the perovskite in p-i-n heterojunctions and also in p-i and i-n junctions. From current-voltage characteristics and impedance spectroscopy, we have observed that two depletion regions were formed at the p-i and i-n interfaces of a p-i-n heterojunction. The two depletion regions operative at p-i-n heterojunctions have yielded better photovoltaic properties as compared to devices having one depletion region in the p-i or the i-n junction. The results evidenced photovoltaic devices based on all-inorganic oxide, nontoxic, and perovskite materials.

Development of New Supramolecular Lyotropic Liquid Crystals and Their Application as Alignment Media for Organic Compounds.

PubMed

Leyendecker, Martin; Meyer, Nils-Christopher; Thiele, Christina M

2017-09-11

Most alignment media for the residual dipolar coupling (RDC) based molecular structure determination of small organic compounds consist of rod-like polymers dissolved in organic solvents or of swollen cross-linked polymer gels. Thus far, the synthesis of polymer-based alignment media has been a challenging process, which is often followed by a time-consuming sample preparation. We herein propose the use of non-polymeric alignment media based on benzenetricarboxamides (BTAs), which self-assemble into rod-like supramolecules. Our newly found supramolecular lyotropic liquid crystals (LLCs) are studied in terms of their LLC properties and their suitability as alignment media in NMR spectroscopy. Scalable enantiodifferentiating properties are introduced through a sergeant-and-soldier principle by blending achiral with chiral substituted BTAs. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Optical bandgap modelling from the structural arrangement of carbon nanotubes.

PubMed

Butler, Timothy P; Rashid, Ijaz; Montelongo, Yunuen; Amaratunga, Gehan A J; Butt, Haider

2018-06-14

The optical bandgap properties of vertically-aligned carbon nanotube (VACNT) arrays were probed through their interaction with white light, with the light reflected from the rotating arrays measured with a spectrometer. The precise deterministic control over the structure of vertically-aligned carbon nanotube arrays through electron beam lithography and well-controlled growth conditions brings with it the ability to produce exotic photonic crystals over a relatively large area. The characterisation of the behaviour of these materials in the presence of light is a necessary first step toward application. Relatively large area array structures of high-quality VACNTs were fabricated in square, hexagonal, circular and pseudorandom patterned arrays with length scales on the order of those of visible light for the purpose of investigating how they may be used to manipulate an impinging light beam. In order to investigate the optical properties of these arrays a set of measurement apparatus was designed which allowed the accurate measurement of their optical bandgap characteristics. The patterned samples were rotated under the illuminating white light beam, revealing interesting optical bandgap results caused by the changing patterns and relative positions of the scattering elements (VACNTs).

Effects of specimen preparation on the electromagnetic property measurements of solid materials with an automatic network analyzer

NASA Technical Reports Server (NTRS)

Long, E. R., Jr.

1986-01-01

Effects of specimen preparation on measured values of an acrylic's electomagnetic properties at X-band microwave frequencies, TE sub 1,0 mode, utilizing an automatic network analyzer have been studied. For 1 percent or less error, a gap between the specimen edge and the 0.901-in. wall of the specimen holder was the most significant parameter. The gap had to be less than 0.002 in. The thickness variation and alignment errors in the direction parallel to the 0.901-in. wall were equally second most significant and had to be less than 1 degree. Errors in the measurement f the thickness were third most significant. They had to be less than 3 percent. The following parameters caused errors of 1 percent or less: ratios of specimen-holder thicknesses of more than 15 percent, gaps between the specimen edge and the 0.401-in. wall less than 0.045 in., position errors less than 15 percent, surface roughness, hickness variation in the direction parallel to the 0.401-in. wall less than 35 percent, and specimen alignment in the direction parallel to the 0.401-in. wall mass than 5 degrees.

Fabrication and mechanical behavior of dye-doped polymer optical fiber

NASA Astrophysics Data System (ADS)

Jiang, Changhong; Kuzyk, Mark G.; Ding, Jow-Lian; Johns, William E.; Welker, David J.

2002-07-01

The purpose of this article is to study the materials physics behind dye-doped polymethyl metharcylate (PMMA) that is important for the optical fiber drawing process. We report effects of the fabrication process on the mechanical properties of the final fiber. The qualitative degree of polymer chain alignment is found to increase with the drawing force, which in turn decreases with the drawing temperature and increases with the drawing ratio. The chain alignment relaxes when the fibers are annealed at 95 degC with a commensurate decrease in fiber length and increase in diameter. The annealed fiber has higher ductility but lower strength than the unannealed fiber. Both the yield and tensile strengths are dependent on the strain rate. The relationship between tensile strength, sigmab, and fiber diameter, d, is found empirically to be sigmab[is proportional to]d-0.5. The yield strength appears to be less sensitive to the fiber diameter than the tensile strength. For PMMA doped with disperse red 1 azo dye, the yield strength, tensile strength, and Young's modulus peak at a dye concentration of 0.0094 wt %. These results are useful for designing polymer optical fibers with well-defined mechanical properties.

Optical properties of orthodontic aligners--spectrophotometry analysis of three types before and after aging.

PubMed

Lombardo, Luca; Arreghini, Angela; Maccarrone, Roberta; Bianchi, Anna; Scalia, Santo; Siciliani, Giuseppe

2015-01-01

The aim was to assess and compare absorbance and transmittance values of three types of clear orthodontic aligners before and after two cycles of in vitro aging. Nine samples of orthodontic aligners from three different manufacturers (Invisalign, Align Technology, Santa Clara, CA, USA; All-In, Micerium, Avegno, GE, Italy; F22 Aligner, Sweden & Martina, Due Carrare, PD, Italy) were selected, and each sample was subjected to spectrophotometry analysis of both its transmittance and absorbance a total of 27 times. Samples were subsequently aged in vitro at a constant temperature in artificial saliva supplemented with food colouring for two cycles of 14 days each. The spectrophotometry protocol was then repeated, and the resulting data were analysed and compared by means of ANOVA (p < 0.05). All types of aligners tested yielded lower transmittance and higher absorbance values after aging, but the difference was not significant in any case. That being said, the F22 aligners were found to be most transparent, both before and after aging, followed by Invisalign and All-In, and these differences were statistically significant. Commercial aligners possess significantly different optical, and therefore aesthetic, properties, both as delivered and following aging.

High-density carbon nanotube buckypapers with superior transport and mechanical properties.

PubMed

Zhang, Ling; Zhang, Guang; Liu, Changhong; Fan, Shoushan

2012-09-12

High-density buckypapers were obtained by using well-aligned carbon nanotube arrays. The density of the buckypapers was as high as 1.39 g cm(-3), which is close to the ultimate density of ideal buckypapers. Then we measured the transport and mechanical properties of the buckypapers. Our results demonstrated that its electrical and thermal conductivities could be almost linearly improved by increasing its density. In particular, its superior thermal conductivity is nearly twice that of common metals, which enables it a lightweight and more efficient heat-transfer materials. The Young's modulus of the buckypapers could reach a magnitude over 2 GPa, which is greatly improved compared with previous reported results. In view of this, our work provided a simple and convenient method to prepare high-density buckypapers with excellent transport and mechanical properties.

Hybrid hydrogels containing vertically aligned carbon nanotubes with anisotropic electrical conductivity for muscle myofiber fabrication.

PubMed

Ahadian, Samad; Ramón-Azcón, Javier; Estili, Mehdi; Liang, Xiaobin; Ostrovidov, Serge; Shiku, Hitoshi; Ramalingam, Murugan; Nakajima, Ken; Sakka, Yoshio; Bae, Hojae; Matsue, Tomokazu; Khademhosseini, Ali

2014-03-19

Biological scaffolds with tunable electrical and mechanical properties are of great interest in many different fields, such as regenerative medicine, biorobotics, and biosensing. In this study, dielectrophoresis (DEP) was used to vertically align carbon nanotubes (CNTs) within methacrylated gelatin (GelMA) hydrogels in a robust, simple, and rapid manner. GelMA-aligned CNT hydrogels showed anisotropic electrical conductivity and superior mechanical properties compared with pristine GelMA hydrogels and GelMA hydrogels containing randomly distributed CNTs. Skeletal muscle cells grown on vertically aligned CNTs in GelMA hydrogels yielded a higher number of functional myofibers than cells that were cultured on hydrogels with randomly distributed CNTs and horizontally aligned CNTs, as confirmed by the expression of myogenic genes and proteins. In addition, the myogenic gene and protein expression increased more profoundly after applying electrical stimulation along the direction of the aligned CNTs due to the anisotropic conductivity of the hybrid GelMA-vertically aligned CNT hydrogels. We believe that platform could attract great attention in other biomedical applications, such as biosensing, bioelectronics, and creating functional biomedical devices.

Hybrid hydrogels containing vertically aligned carbon nanotubes with anisotropic electrical conductivity for muscle myofiber fabrication

PubMed Central

Ahadian, Samad; Ramón-Azcón, Javier; Estili, Mehdi; Liang, Xiaobin; Ostrovidov, Serge; Shiku, Hitoshi; Ramalingam, Murugan; Nakajima, Ken; Sakka, Yoshio; Bae, Hojae; Matsue, Tomokazu; Khademhosseini, Ali

2014-01-01

Biological scaffolds with tunable electrical and mechanical properties are of great interest in many different fields, such as regenerative medicine, biorobotics, and biosensing. In this study, dielectrophoresis (DEP) was used to vertically align carbon nanotubes (CNTs) within methacrylated gelatin (GelMA) hydrogels in a robust, simple, and rapid manner. GelMA-aligned CNT hydrogels showed anisotropic electrical conductivity and superior mechanical properties compared with pristine GelMA hydrogels and GelMA hydrogels containing randomly distributed CNTs. Skeletal muscle cells grown on vertically aligned CNTs in GelMA hydrogels yielded a higher number of functional myofibers than cells that were cultured on hydrogels with randomly distributed CNTs and horizontally aligned CNTs, as confirmed by the expression of myogenic genes and proteins. In addition, the myogenic gene and protein expression increased more profoundly after applying electrical stimulation along the direction of the aligned CNTs due to the anisotropic conductivity of the hybrid GelMA-vertically aligned CNT hydrogels. We believe that platform could attract great attention in other biomedical applications, such as biosensing, bioelectronics, and creating functional biomedical devices. PMID:24642903

Hybrid hydrogels containing vertically aligned carbon nanotubes with anisotropic electrical conductivity for muscle myofiber fabrication

NASA Astrophysics Data System (ADS)

Ahadian, Samad; Ramón-Azcón, Javier; Estili, Mehdi; Liang, Xiaobin; Ostrovidov, Serge; Shiku, Hitoshi; Ramalingam, Murugan; Nakajima, Ken; Sakka, Yoshio; Bae, Hojae; Matsue, Tomokazu; Khademhosseini, Ali

2014-03-01

Biological scaffolds with tunable electrical and mechanical properties are of great interest in many different fields, such as regenerative medicine, biorobotics, and biosensing. In this study, dielectrophoresis (DEP) was used to vertically align carbon nanotubes (CNTs) within methacrylated gelatin (GelMA) hydrogels in a robust, simple, and rapid manner. GelMA-aligned CNT hydrogels showed anisotropic electrical conductivity and superior mechanical properties compared with pristine GelMA hydrogels and GelMA hydrogels containing randomly distributed CNTs. Skeletal muscle cells grown on vertically aligned CNTs in GelMA hydrogels yielded a higher number of functional myofibers than cells that were cultured on hydrogels with randomly distributed CNTs and horizontally aligned CNTs, as confirmed by the expression of myogenic genes and proteins. In addition, the myogenic gene and protein expression increased more profoundly after applying electrical stimulation along the direction of the aligned CNTs due to the anisotropic conductivity of the hybrid GelMA-vertically aligned CNT hydrogels. We believe that platform could attract great attention in other biomedical applications, such as biosensing, bioelectronics, and creating functional biomedical devices.

A Grand Challenge for CMOS Scaling: Alternate Gate Dielectrics

NASA Astrophysics Data System (ADS)

Wallace, Robert M.

2001-03-01

Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.13 um complementary metal oxide semiconductor (CMOS) technology. The prospect of replacing SiO2 is a formidable task because the alternate gate dielectric must provide many properties that are, at a minimum, comparable to those of SiO2 yet with a much higher permittivity. A systematic examination of the required performance of gate dielectrics suggests that the key properties to consider in the selection an alternative gate dielectric candidate are (a) permittivity, band gap and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. We will review the performance requirements for materials associated with CMOS scaling, the challenges associated with these requirements, and the state-of-the-art in current research for alternate gate dielectrics. The requirements for process integration compatibility are remarkably demanding, and any serious candidates will emerge only through continued, intensive investigation.

DC Plasma Synthesis of Vertically Aligned Carbon Nanofibers for Biointerfacing

NASA Astrophysics Data System (ADS)

Pearce, Ryan Christopher

Vertically aligned carbon nanofibers (VACNFs) are a class of materials whose nanoscale dimensions and physical properties makes them uniquely suitable as functional elements in many applications for biodetection and biointerfacing on a cellular level. Control of VACNF synthesis by catalytic plasma enhanced chemical vapor deposition (PECVD) presents many challenges in integration into devices and structures designed for biointerfacing, such as transparent or flexible substrates. This dissertation addresses ways to overcome many of these issues in addition to deepening the fundamental understanding of nano-synthesis in catalytic PECVD. First, a survey of the field of VACNF synthesis and biointerfacing is presented, identifying the present challenges and greatest experimental applications. It is followed by experimental observations that elucidate the underlying mechanism to fiber alignment during synthesis, a critical step for deterministic control of fiber growth. Using a grid of electrodes patterned by photolithography on an insulating substrate, it was found that the alignment of the fibers is controlled by the anisotropic etching provided by ions during dc-PECVD synthesis. The VACNFs that have been utilized for many cellular interfacing experiments have unique mechanical and fluorescent properties due to a SiNx coating. The mechanism for SiNx deposition to VACNF sidewalls during synthesis is explored in addition to a detailed study of the optical properties of the coating. To explain the optical properties of this coating it is proposed that the source of photoluminescence for the SiNx coated VACNFs is quantum confinement effects due to the presence of silicon nanoclusters embedded in a Si3N4 matrix. These luminescent fibers have proven useful as registry markers in cell impalefection studies. To realize VACNF arrays used as an inflatable angioplasty balloon with embedded fibers to deliver drugs across the blood-brain barrier, a method for transferring fibers to flexible polydimethylesiloxane (PDMS) is presented. A process has been developed that involves synthesizing fibers on aluminum, followed by spin coating a thin layer of PDMS and then dissolving the underlying aluminum with KOH. Finally, a method of fiber synthesis using just air and acetone as the process gases is presented, enabling the possibility of inatmosphere, large scale VACNF synthesis. It is envisioned that these advancements should assist the viability of large scale VACNF related technologies and will help to bridge the gap between experimental applications and industrial adoption.

Synthesis and properties of SiN coatings as stable fluorescent markers on vertically aligned carbon nanofibers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pearce, Ryan; Klein, Kate L; Ivanov, Ilia N

2014-01-01

The growth of vertically aligned carbon nanofibers (VACNFs) in a catalytic dc ammonia/acetylene plasma process on silicon substrates is often accompanied by sidewall deposition of material that contains mostly Si and N. In fluorescent microscopy experiments, imaging VACNF interfacing to live cell cultures it turned out that this material is broadly fluorescent, which made VACNFs useful as spatial markers, or created nuisance when DNA-labeling got masked. In this paper we provide insight into nature of this silicon/nitrogen in situ coatings. Here we have proposed a potential mechanism for deposition of SiNx coating on the sidewalls of VACNFs during PECVD synthesismore » in addition to exploring the origin of the coatings fluorescence. It seems most likely that the substrate reacts with the process gases through both processes similar to reactive sputtering and CVD to form silane and other silicon bearing compounds before being deposited isotropically as a SiNx coating onto the VACNFs. The case for the presence of Si-NCs is made strong through a combination of the strong fluorescence and elemental analysis of the samples. These broadly luminescent fibers can prove useful as registry markers in fluorescent cellular studies.« less

Multifunctional composites for energy storage

NASA Astrophysics Data System (ADS)

Shuvo, Mohammad Arif I.; Karim, Hasanul; Rajib, Md; Delfin, Diego; Lin, Yirong

2014-03-01

Electrochemical super-capacitors have become one of the most important topics in both academia and industry as novel energy storage devices because of their high power density, long life cycles, and high charge/discharge efficiency. Recently, there has been an increasing interest in the development of multifunctional structural energy storage devices such as structural super-capacitors for applications in aerospace, automobiles and portable electronics. These multifunctional structural super-capacitors provide lighter structures combining energy storage and load bearing functionalities. Due to their superior materials properties, carbon fiber composites have been widely used in structural applications for aerospace and automotive industries. Besides, carbon fiber has good electrical conductivity which will provide lower equivalent series resistance; therefore, it can be an excellent candidate for structural energy storage applications. Hence, this paper is focused on performing a pilot study for using nanowire/carbon fiber hybrids as building materials for structural energy storage materials; aiming at enhancing the charge/discharge rate and energy density. This hybrid material combines the high specific surface area of carbon fiber and pseudo-capacitive effect of metal oxide nanowires which were grown hydrothermally in an aligned fashion on carbon fibers. The aligned nanowire array could provide a higher specific surface area that leads to high electrode-electrolyte contact area and fast ion diffusion rates. Scanning Electron Microscopy (SEM) and XRay Diffraction (XRD) measurements were used for the initial characterization of this nanowire/carbon fiber hybrid material system. Electrochemical testing has been performed using a potentio-galvanostat. The results show that gold sputtered nanowire hybrid carbon fiber provides 65.9% better performance than bare carbon fiber cloth as super-capacitor.

Self-aligned block technology: a step toward further scaling

NASA Astrophysics Data System (ADS)

Lazzarino, Frédéric; Mohanty, Nihar; Feurprier, Yannick; Huli, Lior; Luong, Vinh; Demand, Marc; Decoster, Stefan; Vega Gonzalez, Victor; Ryckaert, Julien; Kim, Ryan Ryoung Han; Mallik, Arindam; Leray, Philippe; Wilson, Chris; Boemmels, Jürgen; Kumar, Kaushik; Nafus, Kathleen; deVilliers, Anton; Smith, Jeffrey; Fonseca, Carlos; Bannister, Julie; Scheer, Steven; Tokei, Zsolt; Piumi, Daniele; Barla, Kathy

2017-04-01

In this work, we present and compare two integration approaches to enable self-alignment of the block suitable for the 5- nm technology node. The first approach is exploring the insertion of a spin-on metal-based material to memorize the first block and act as an etch stop layer in the overall integration. The second approach is evaluating the self-aligned block technology employing widely used organic materials and well-known processes. The concept and the motivation are discussed considering the effects on design and mask count as well as the impact on process complexity and EPE budget. We show the integration schemes and discuss the requirements to enable self-alignment. We present the details of materials and processes selection to allow optimal selective etches and we demonstrate the proof of concept using a 16- nm half-pitch BEOL vehicle. Finally, a study on technology insertion and cost estimation is presented.

Overview on the Surface Functionalization Mechanism and Determination of Surface Functional Groups of Plasma Treated Carbon Nanotubes.

PubMed

Saka, Cafer

2018-01-02

The use of carbon materials for many applications is due to the unique diversity of structures and properties ranging from chemical bonds between the carbon atoms of the materials to nanostructures, crystallite alignment, and microstructures. Carbon nanotubes and other nanoscale carbonaceous materials draw much attention due to their physical and chemical properties, such as high strength, high resistance to corrosion, electrical and thermal conductivity, stability and a qualified adsorbent. Carbon-based nanomaterials, which have a relatively large specific area and layered structure, can be used as an adsorbent for efficient removal of organic and inorganic contaminants. However, one of the biggest obstacles to the development of carbon-based nanomaterials adsorbents is insolubility and the lack of functional groups on the surface. There are several approaches to introduce functional groups on carbon nanotubes. One of these approaches, plasma applications, now has an important place in the creation of surface functional groups as a flexible, fast, and environmentally friendly method. This review focuses on recent information concerning the surface functionalization and modification of plasma treated carbon nanotube. This review considers the surface properties, advantages, and disadvantages of plasma-applied carbon nanotubes. It also examines the reaction mechanisms involved in the functional groups on the surface.

Effects of interfacial alignments on the stability of graphene on Ru(0001) substrate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Lei; Liu, Yanmin; Ma, Tianbao, E-mail: mtb@mail.tsinghua.edu.cn

2016-06-27

Structure and electronic properties of two-dimensional materials could be tuned by interfacial misfit or orientation angles. However, graphene grown on Ru(0001) substrate usually shows stable moiré superlattice with a periodicity of 3.0 nm indicating an aligned geometry. The reason for the absence of misaligned structure is still unknown. We have performed first-principles calculation to investigate the microstructure and morphology of graphene on Ru(0001) substrate in both aligned and misaligned geometries with rotation angles of 0°, 7.6°, and 23.4°, respectively. Our results indicate that both the graphene corrugation and moiré superlattice periodicity decrease as the rotation angle increases. Meanwhile the interaction energymore » between graphene and Ru(0001) substrate also becomes weakened with the rotation angle, as the decrease and discretization of intense charge transfer sites at the graphene/Ru interface, which is closely related to the interface stacking structure. Counterintuitively, the strain energy in graphene also increases anomalously with the rotation angle, which is attributed to the highly distorted local deformation of graphene due to the strong but discrete covalent bonding with Ru substrate. The simultaneous increase in both the interaction energy and strain energy in graphene/Ru(0001) heterostructure with rotation angle contributes to the preferred configuration in the aligned state.« less

From Wood to Textiles: Top-Down Assembly of Aligned Cellulose Nanofibers.

PubMed

Jia, Chao; Chen, Chaoji; Kuang, Yudi; Fu, Kun; Wang, Yilin; Yao, Yonggang; Kronthal, Spencer; Hitz, Emily; Song, Jianwei; Xu, Fujun; Liu, Boyang; Hu, Liangbing

2018-06-07

Advanced textiles made of macroscopic fibers are usually prepared from synthetic fibers, which have changed lives over the past century. The shortage of petrochemical resources, however, greatly limits the development of the textile industry. Here, a facile top-down approach for fabricating macroscopic wood fibers for textile applications (wood-textile fibers) comprising aligned cellulose nanofibers directly from natural wood via delignification and subsequent twisting is demonstrated. Inherently aligned cellulose nanofibers are well retained, while the microchannels in the delignified wood are squeezed and totally removed by twisting, resulting in a dense structure with approximately two times higher mechanical strength (106.5 vs 54.9 MPa) and ≈20 times higher toughness (7.70 vs 0.36 MJ m -3 ) than natural wood. Dramatically different from natural wood, which is brittle in nature, the resultant wood-textile fibers are highly flexible and bendable, likely due to the twisted structures. The wood-textile fibers also exhibit excellent knitting properties and dyeability, which are critical for textile applications. Furthermore, functional wood-textile fibers can be achieved by preinfiltrating functional materials in the delignified wood film before twisting. This top-down approach of fabricating aligned macrofibers is simple, scalable, and cost-effective, representing a promising direction for the development of smart textiles and wearable electronics. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Minerals and aligned collagen fibrils in tilapia fish scales: structural analysis using dark-field and energy-filtered transmission electron microscopy and electron tomography.

PubMed

Okuda, Mitsuhiro; Ogawa, Nobuhiro; Takeguchi, Masaki; Hashimoto, Ayako; Tagaya, Motohiro; Chen, Song; Hanagata, Nobutaka; Ikoma, Toshiyuki

2011-10-01

The mineralized structure of aligned collagen fibrils in a tilapia fish scale was investigated using transmission electron microscopy (TEM) techniques after a thin sample was prepared using aqueous techniques. Electron diffraction and electron energy loss spectroscopy data indicated that a mineralized internal layer consisting of aligned collagen fibrils contains hydroxyapatite crystals. Bright-field imaging, dark-field imaging, and energy-filtered TEM showed that the hydroxyapatite was mainly distributed in the hole zones of the aligned collagen fibrils structure, while needle-like materials composed of calcium compounds including hydroxyapatite existed in the mineralized internal layer. Dark-field imaging and three-dimensional observation using electron tomography revealed that hydroxyapatite and needle-like materials were mainly found in the matrix between the collagen fibrils. It was observed that hydroxyapatite and needle-like materials were preferentially distributed on the surface of the hole zones in the aligned collagen fibrils structure and in the matrix between the collagen fibrils in the mineralized internal layer of the scale.

Polarization properties of below-threshold harmonics from aligned molecules H2+ in linearly polarized laser fields.

PubMed

Dong, Fulong; Tian, Yiqun; Yu, Shujuan; Wang, Shang; Yang, Shiping; Chen, Yanjun

2015-07-13

We investigate the polarization properties of below-threshold harmonics from aligned molecules in linearly polarized laser fields numerically and analytically. We focus on lower-order harmonics (LOHs). Our simulations show that the ellipticity of below-threshold LOHs depends strongly on the orientation angle and differs significantly for different harmonic orders. Our analysis reveals that this LOH ellipticity is closely associated with resonance effects and the axis symmetry of the molecule. These results shed light on the complex generation mechanism of below-threshold harmonics from aligned molecules.

Preparation and characterization of green-nano-composite material based on polyaniline, multiwalled carbon nano tubes and carboxymethyl cellulose: For electrochemical sensor applications.

PubMed

Gautam, Vineeta; Singh, Karan Pratap; Yadav, Vijay Laxmi

2018-06-01

In this paper, we are presenting the preparation and characterization of "polyaniline/multiwalled carbon nanotubes/carboxymethyl cellulose" based novel composite material. It's morphological, thermal, structural, and electrochemical properties were investigated by using different instrumental techniques. During the in-situ chemical polymerization of aniline in the aqueous suspension of CMC and MWCNTs, the particle size change in two different ways "top to bottom" (low molecular weight oligomers grows in size) and "bottom to top" (long fibers of CMC fragmented in the reaction mixture). The combination of these two processes facilitated the fabrication of an integrated green-nano-composite material. In addition, a little amount of conductive nanofillers (MWCNTs) boosts the electrical and electrocatalytic properties of the material. Electron-rich centers of benzenoid rings exhibited π-π stacking with sp 2 carbon of MWCNTs. CMC dominantly impact on the properties of PANI, negatively charged carboxylate group of CMC ionically bonded with protonated amine/imine. FTIR and Raman analysis confirmed that the material has dominated quinoid units and effective charge transfer. Hydroxyl and carboxyl groups and bonded water molecules of CMC results in a network of hydrogen bonds (which induced directional property). PANI/MWCNTs/CMC have nanobead-like structures (TEM analysis), large surface area, large pore volume, small pore diameter (BET and BJH studies) and good dispersion ability in the aqueous phase. Nanostructures of aligned PANI exhibited excellent electrochemical properties have attracted increasing attention. Modified carbon paste electrode was used for electrocatalytic detection of ascorbic acid (as a model analyte). The sensor exhibited a linear range 0.05 mM-5 mM, sensitivity 100.63 μA mM -1  cm -2 , and limit of detection 0.01 mM. PANI/MWCNTs/CMC is suitable nanocomposite material for apply electroactive/conducting ink and membrane (which could be used in electrochemical sensor applications). Copyright © 2018 Elsevier Ltd. All rights reserved.

Delamination toughness characterization of out-of-autoclave vacuum-bag-only polymer matrix composites enhanced by z-aligned carbon nanofibers

NASA Astrophysics Data System (ADS)

Brewer, John S.

Brewer, John S., M. S., University of South Alabama, May 2015. Delamination Toughness Characterization of Out-of-Autoclave Vacuum-Bag-Only Polymer Matrix Composites Enhanced by z-aligned Carbon Nanofibers. Chair of Committee: Kuang-Ting Hsiao, Ph.D. In the last few decades, the use of composite materials has revolutionized materials manufacturing. Now, carbon fiber materials are at the forefront of engineering and manufacturing technology. One of the chief failure modes of composite materials is delamination. For this reason, this study employed the Mode-I Interlaminar Fracture Toughness Test (ASTM D 5528-01) to characterize how the inclusion of z-aligned carbon nanofibers (CNF) in Carbon Fiber Reinforced Polymers (CFRP) affects delamination strength. CFRP with z-aligned CNF in concentrations of 0.3% and 0.6% by weight were compared to control CFRP samples and CFRP samples modified with 0.3 weight percent unaligned CNF. The largest improvement was seen in the 0.3 weight percent aligned composite with a mean interlaminar fracture toughness increase of over 35%, while the uncertainty was decreased. A standard deviation of 3.3% was observed which equates to an uncertainty value 30% better than the control samples. Data and microscopy are included and discussed.

Controlled Deposition and Alignment of Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Smits, Jan M. (Inventor); Wincheski, Russell A. (Inventor); Ingram, JoAnne L. (Inventor); Watkins, Anthony Neal (Inventor); Jordan, Jeffrey D. (Inventor)

2009-01-01

A carbon nanotube (CNT) attraction material is deposited on a substrate in the gap region between two electrodes on the . substrate. An electric potential is applied to the two electrodes. The CNT attraction material is wetted with a solution defined by a carver liquid having carbon nanotubes (CNTs) suspended therein. A portion of the CNTs align with the electric field and adhere to The CNT attraction material. The carrier liquid and any CNTs not adhered to the CNT attraction material are then removed.

Controlled Deposition and Alignment of Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Patry, JoAnne L. (Inventor); Smits, Jan M. (Inventor); Watkins, Anthony Neal (Inventor); Jordan, Jeffrey D. (Inventor); Wincheski, Russell A. (Inventor)

2012-01-01

A carbon nanotube (CNT) attraction material is deposited on a substrate in the gap region between two electrodes on the substrate. An electric potential is applied to the two electrodes. The CNT attraction material is wetted with a solution defined by a carrier liquid having carbon nanotubes (CNTs) suspended therein. A portion of the CNTs align with the electric field and adhere to the CNT attraction material. The carrier liquid and any CNTs not adhered to the CNT attraction material are then removed.

Single- and Multilayered Nanostructures via Laser-Induced Block Copolymer Self-Assembly

NASA Astrophysics Data System (ADS)

Majewski, Pawel; Yager, Kevin; Rahman, Atikur; Black, Charles

We present a novel method of accelerated self-assembly of block copolymer thin films utilizing laser light, called Laser Zone Annealing (LZA). In our approach, steep temperature transients are induced in block copolymer films by rastering narrowly focused laser line over the light-absorbing substrate. Extremely steep temperature gradients accelerate the process of self-assembly by several orders-of-magnitude compared to conventional oven annealing, and, when coupled to photo-thermal shearing, lead to global alignment of block copolymer domains assessed by GISXAS diffraction studies and real-space SEM imaging. We demonstrate monolithic alignment of various block-copolymer thin films including PS-b-PMMA, PS-b-PEO, PS-b-P2VP, PS-b-PI and observe different responsiveness to the shearing rate depending on the characteristic relaxation timescale of the particular material. Subsequently, we use the aligned polymeric films as templates for synthesis of single- and multi-layered arrays of inorganic, metallic or semiconducting nanowires and nanomeshes and investigate their anisotropic electro-optical properties. Research carried out in part at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

Spectroscopic characterizations of a mixed surfactant mesophase and its application in materials synthesis

NASA Astrophysics Data System (ADS)

Liu, Limin

A viscous lyotropic crystalline mesophase containing bis (2-ethylhexyl) sodium sulfosuccinate (AOT), alpha-phosphatidylcholine (lecithin), with comparable volume fractions of isooctane and water was characterized by Fourier-transform 31P and 1H nuclear magnetic resonance (NMR) spectroscopy. Shear alignment on the reverse hexagonal mesophase was reflected through both 31P NMR and 1H NMR spectra. A complicated 31P spectrum was observed as a result of superposition of chemical shifts according to the distribution of crystalline domains prior to shear. The initially disordered samples with polydomain structures became macroscopically aligned after Couette shear and the alignment retained for a long period of time. 31P NMR chemical shift anisotropy characteristics were used to elucidate orientation of the hexagonal phase. Interestingly, 1H NMR of the water, methyl and methylene groups exhibited spectral changes upon shear alignment closely corresponding with that of 31P NMR spectra. A reverse hexagonal to lamellar phase transition was manifested as an expanding of the expressed 31P NMR chemical shift anisotropy and an apparent reversal of the powder pattern with increasing water content and/or temperature. Correspondingly, 1H NMR spectra also experienced a spectral pattern transition as the water content or temperature was increased. These observations complement the findings of mesophase alignment obtained using small angle neutron scattering (SANS) and imply that 31P and 1H NMR spectroscopy can be used as probes to define microstructure and monitor orientation changes in this binary surfactant system. This is especially beneficial if these mesophases are used as templates for materials synthesis. The mesophase retains its alignment for extended periods allowing materials synthesis to be decoupled from the application of shear. Highly aligned string-like silica nanostructures were obtained through templated synthesis in the columnar hexagonal structure of the viscous lyotropic crystalline mesophase. A two-step procedure was used to first shear-align the surfactant mesophase, and then conduct synthesis under quiescent conditions in the mesophase. Polystyrene was post-grafted to the silica surface without disturbing its nanostring morphology. The coupling of materials synthesis in surfactant mesophases with processing techniques (e.g. extrusion) may result in functional materials, such as new catalyst support and membrane nanoarchitectures.

Nanowire modified carbon fibers for enhanced electrical energy storage

NASA Astrophysics Data System (ADS)

Shuvo, Mohammad Arif Ishtiaque; (Bill) Tseng, Tzu-Liang; Ashiqur Rahaman Khan, Md.; Karim, Hasanul; Morton, Philip; Delfin, Diego; Lin, Yirong

2013-09-01

The study of electrochemical super-capacitors has become one of the most attractive topics in both academia and industry as energy storage devices because of their high power density, long life cycles, and high charge/discharge efficiency. Recently, there has been increasing interest in the development of multifunctional structural energy storage devices such as structural super-capacitors for applications in aerospace, automobiles, and portable electronics. These multifunctional structural super-capacitors provide structures combining energy storage and load bearing functionalities, leading to material systems with reduced volume and/or weight. Due to their superior materials properties, carbon fiber composites have been widely used in structural applications for aerospace and automotive industries. Besides, carbon fiber has good electrical conductivity which will provide lower equivalent series resistance; therefore, it can be an excellent candidate for structural energy storage applications. Hence, this paper is focused on performing a pilot study for using nanowire/carbon fiber hybrids as building materials for structural energy storage materials; aiming at enhancing the charge/discharge rate and energy density. This hybrid material combines the high specific surface area of carbon fiber and pseudo-capacitive effect of metal oxide nanowires, which were grown hydrothermally in an aligned fashion on carbon fibers. The aligned nanowire array could provide a higher specific surface area that leads to high electrode-electrolyte contact area thus fast ion diffusion rates. Scanning Electron Microscopy and X-Ray Diffraction measurements are used for the initial characterization of this nanowire/carbon fiber hybrid material system. Electrochemical testing is performed using a potentio-galvanostat. The results show that gold sputtered nanowire carbon fiber hybrid provides 65.9% higher energy density than bare carbon fiber cloth as super-capacitor.

Squid pen-inspired chitinous functional materials: Hierarchical chitin fibers by centrifugal jet-spinning and transparent chitin fiber-reinforced composite

NASA Astrophysics Data System (ADS)

Jeong, Seung-Hwan; Kim, Joong-Kwon; Lim, Young-Woo; Hwang, Hyun-Bin; Kwon, Hee-Young; Bae, Byeong-Soo; Jin, Jungho

2018-01-01

Here, inspired by the fibrous composite structure of a squid pen, we introduce hierarchical chitin fibers (herein, termed "Chiber") and their transparent composites and demonstrate the potential of these chitinous functional materials as a sustainable separation-membrane and reinforcing filler for composites. We employ a centrifugal jet-spinning process to fabricate Chiber with aligned chitin nanofibrillar architectures, for which we discuss the processing-morphology relationship. A nonwoven fiber-mat made of Chiber exhibits excellent adsorbing performance for a toxic ionic dye (Congo Red), and has a low coefficient of thermal expansion comparable to that of glass fibers. Finally, we demonstrate a squid pen-mimetic transparent composite using Chiber and investigate its optical property.

Enhancement of Local Piezoresponse in Polymer Ferroelectrics via Nanoscale Control of Microstructure

DOE PAGES

Choi, Yoon-Young; Sharma, Pankaj; Phatak, Charudatta; ...

2015-02-01

Polymer ferroelectrics are flexible and lightweight electromechanical materials that are widely studied due to their potential application as sensors, actuators, and energy harvesters. However, one of the biggest challenges is their low piezoelectric coefficient. Here, we report a mechanical annealing effect based on local pressure induced by a nanoscale tip that enhances the local piezoresponse. This process can control the nanoscale material properties over a microscale area at room temperature. We attribute this improvement to the formation and growth of beta-phase extended chain crystals via sliding diffusion and crystal alignment along the scan axis under high mechanical stress. We believemore » that this technique can be useful for local enhancement of piezoresponse in ferroelectric polymer thin films.« less

Rotational superstructure in van der Waals heterostructure of self-assembled C 60 monolayer on the WSe 2 surface

DOE PAGES

Santos, Elton J. G.; Scullion, Declan; Chu, Ximo S.; ...

2017-08-23

Hybrid van der Waals (vdW) heterostructures composed of two-dimensional (2D) layered materials and self-assembled organic molecules are promising systems for electronic and optoelectronic applications with enhanced properties and performance. Control of molecular assembly is therefore paramount to fundamentally understand the nucleation, ordering, alignment, and electronic interaction of organic molecules with 2D materials. Here, we report the formation and detailed study of highly ordered, crystalline monolayers of C 60 molecules self-assembled on the surface of WSe 2 in well-ordered arrays with large grain sizes (~5 μm). Using high-resolution scanning tunneling microscopy (STM), we observe a periodic 2 × 2 superstructure inmore » the C 60 monolayer and identify four distinct molecular appearances. Using vdW-corrected ab initio density functional theory (DFT) simulations, we determine that the interplay between vdW and Coulomb interactions as well as adsorbate–adsorbate and adsorbate–substrate interactions results in specific rotational arrangements of the molecules forming the superstructure. The orbital ordering through the relative positions of bonds in adjacent molecules creates a charge redistribution that links the molecule units in a long-range network. Furthermore, this rotational superstructure extends throughout the self-assembled monolayer and opens a pathway towards engineering aligned hybrid organic/inorganic vdW heterostructures with 2D layered materials in a precise and controlled way.« less

Rotational superstructure in van der Waals heterostructure of self-assembled C 60 monolayer on the WSe 2 surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Santos, Elton J. G.; Scullion, Declan; Chu, Ximo S.

Hybrid van der Waals (vdW) heterostructures composed of two-dimensional (2D) layered materials and self-assembled organic molecules are promising systems for electronic and optoelectronic applications with enhanced properties and performance. Control of molecular assembly is therefore paramount to fundamentally understand the nucleation, ordering, alignment, and electronic interaction of organic molecules with 2D materials. Here, we report the formation and detailed study of highly ordered, crystalline monolayers of C 60 molecules self-assembled on the surface of WSe 2 in well-ordered arrays with large grain sizes (~5 μm). Using high-resolution scanning tunneling microscopy (STM), we observe a periodic 2 × 2 superstructure inmore » the C 60 monolayer and identify four distinct molecular appearances. Using vdW-corrected ab initio density functional theory (DFT) simulations, we determine that the interplay between vdW and Coulomb interactions as well as adsorbate–adsorbate and adsorbate–substrate interactions results in specific rotational arrangements of the molecules forming the superstructure. The orbital ordering through the relative positions of bonds in adjacent molecules creates a charge redistribution that links the molecule units in a long-range network. Furthermore, this rotational superstructure extends throughout the self-assembled monolayer and opens a pathway towards engineering aligned hybrid organic/inorganic vdW heterostructures with 2D layered materials in a precise and controlled way.« less

Mesocrystalline calcium silicate hydrate: A bioinspired route toward elastic concrete materials

PubMed Central

Picker, Andreas; Nicoleau, Luc; Burghard, Zaklina; Bill, Joachim; Zlotnikov, Igor; Labbez, Christophe; Nonat, André; Cölfen, Helmut

2017-01-01

Calcium silicate hydrate (C-S-H) is the binder in concrete, the most used synthetic material in the world. The main weakness of concrete is the lack of elasticity and poor flexural strength considerably limiting its potential, making reinforcing steel constructions necessary. Although the properties of C-S-H could be significantly improved in organic hybrids, the full potential of this approach could not be reached because of the random C-S-H nanoplatelet structure. Taking inspiration from a sea urchin spine with highly ordered nanoparticles in the biomineral mesocrystal, we report a bioinspired route toward a C-S-H mesocrystal with highly aligned C-S-H nanoplatelets interspaced with a polymeric binder. A material with a bending strength similar to nacre is obtained, outperforming all C-S-H–based materials known to date. This strategy could greatly benefit future construction processes because fracture toughness and elasticity of brittle cementitious materials can be largely enhanced on the nanoscale. PMID:29209660

Experimental findings on the underwater measurements uncertainty of speed of sound and the alignment system

NASA Astrophysics Data System (ADS)

Santos, T. Q.; Alvarenga, A. V.; Oliveira, D. P.; Mayworm, R. C.; Souza, R. M.; Costa-Félix, R. P. B.

2016-07-01

Speed of sound is an important quantity to characterize reference materials for ultrasonic applications, for instance. The alignment between the transducer and the test body is an key activity in order to perform reliable and consistent measurement. The aim of this work is to evaluate the influence of the alignment system to the expanded uncertainty of such measurement. A stainless steel cylinder was previously calibrated on an out of water system typically used for calibration of non-destructive blocks. Afterwards, the cylinder was calibrated underwater with two distinct alignment system: fixed and mobile. The values were statistically compared to the out-of-water measurement, considered the golden standard for such application. For both alignment systems, the normalized error was less than 0.8, leading to conclude that the both measurement system (under and out-of-water) do not diverge significantly. The gold standard uncertainty was 2.7 m-s-1, whilst the fixed underwater system resulted in 13 m-s-1, and the mobile alignment system achieved 6.6 m-s-1. After the validation of the underwater system for speed of sound measurement, it will be applied to certify Encapsulated Tissue Mimicking Material as a reference material for biotechnology application.

Apparatus for monitoring X-ray beam alignment

DOEpatents

Steinmeyer, Peter A.

1991-10-08

A self-contained, hand-held apparatus is provided for minitoring alignment of an X-ray beam in an instrument employing an X-ray source. The apparatus includes a transducer assembly containing a photoresistor for providing a range of electrical signals responsive to a range of X-ray beam intensities from the X-ray beam being aligned. A circuit, powered by a 7.5 VDC power supply and containing an audio frequency pulse generator whose frequency varies with the resistance of the photoresistor, is provided for generating a range of audible sounds. A portion of the audible range corresponds to low X-ray beam intensity. Another portion of the audible range corresponds to high X-ray beam intensity. The transducer assembly may include an a photoresistor, a thin layer of X-ray fluorescent material, and a filter layer transparent to X-rays but opaque to visible light. X-rays from the beam undergoing alignment penetrate the filter layer and excite the layer of fluorescent material. The light emitted from the fluorescent material alters the resistance of the photoresistor which is in the electrical circuit including the audio pulse generator and a speaker. In employing the apparatus, the X-ray beam is aligned to a complete alignment by adjusting the X-ray beam to produce an audible sound of the maximum frequency.

Apparatus for monitoring X-ray beam alignment

DOEpatents

Steinmeyer, P.A.

1991-10-08

A self-contained, hand-held apparatus is provided for monitoring alignment of an X-ray beam in an instrument employing an X-ray source. The apparatus includes a transducer assembly containing a photoresistor for providing a range of electrical signals responsive to a range of X-ray beam intensities from the X-ray beam being aligned. A circuit, powered by a 7.5 VDC power supply and containing an audio frequency pulse generator whose frequency varies with the resistance of the photoresistor, is provided for generating a range of audible sounds. A portion of the audible range corresponds to low X-ray beam intensity. Another portion of the audible range corresponds to high X-ray beam intensity. The transducer assembly may include an a photoresistor, a thin layer of X-ray fluorescent material, and a filter layer transparent to X-rays but opaque to visible light. X-rays from the beam undergoing alignment penetrate the filter layer and excite the layer of fluorescent material. The light emitted from the fluorescent material alters the resistance of the photoresistor which is in the electrical circuit including the audio pulse generator and a speaker. In employing the apparatus, the X-ray beam is aligned to a complete alignment by adjusting the X-ray beam to produce an audible sound of the maximum frequency. 2 figures.

New Materials for the Undergraduate Classroom to Build Pre-Service Teachers' NGSS Skills and Knowledge

NASA Astrophysics Data System (ADS)

Egger, A. E.; Awad, A. A.; Baldwin, K. A.; Birnbaum, S. J.; Bruckner, M. Z.; DeBari, S. M.; Dechaine, J.; Ebert, J. R.; Gray, K. R.; Hauge, R.; Linneman, S. R.; Monet, J.; Thomas, J.; Varrella, G.

2014-12-01

As part of InTeGrate, teams of 3 instructors at 3 different institutions developed modules that help prepare pre-service teachers to teach Earth science aligned with the NGSS. Modules were evaluated against a rubric, which addresses InTeGrate's five guiding principles, learning objectives and outcomes, assessment and measurement, resources and materials, instructional strategies and alignment. As all modules must address one or more Earth-related grand challenge facing society, develop student ability to address interdisciplinary problems, improve student understanding of the methods of geoscience, use authentic geoscience data, and incorporate systems thinking, they align well with the NGSS. Once modules passed the rubric, they were tested by the authors in their classrooms. Testing included pre- and post-assessment of geoscience literacy and assessment of student learning towards the module goal; materials were revised based on the results of testing. In "Exploring Geoscience Methods with Secondary Education Students," pre-service science teachers compare geoscientific thinking with the classic (experimental) scientific method, investigate global climate change and its impacts on human systems, and prepare an interdisciplinary lesson plan that addresses geoscience methods in context of a socioscientific issue. In "Soils and Society," pre-service elementary teachers explore societal issues where soil is important, develop skills to describe and test soil properties, and create a standards-based Soils and Society Kit that consists of lessons and supporting materials to teach K-8 students about a soil-and-society issue. In "Interactions between Water, Earth's Surface, and Human Activity," students explore the effects of running water on shaping Earth's surface both over geologic time and through short-term flooding events, and produce a brochure to inform citizens of the impact of living near a river. The modules are freely available at http://serc.carleton.edu/integrate/teaching_materials/modules_courses.html and include Instructor Stories, where each author describes how they adapted the module to their teaching environment. The goal of showing different implementations of the materialst is to facilitate adoption and adaption beyond the team of authors.

Single-domain multiferroic BiFeO 3 films

DOE PAGES

Kuo, Chang -Yang; Hu, Z.; Yang, J. C.; ...

2016-09-01

The strong coupling between antiferromagnetism and ferroelectricity at room temperature found in BiFeO 3 generates high expectations for the design and development of technological devices with novel functionalities. However, the multi-domain nature of the material tends to nullify the properties of interest and complicates the thorough understanding of the mechanisms that are responsible for those properties. Here we report the realization of a BiFeO 3 material in thin film form with single-domain behaviour in both its magnetism and ferroelectricity: the entire film shows its antiferromagnetic axis aligned along the crystallographic b axis and its ferroelectric polarization along the c axis.more » With this we are able to reveal that the canted ferromagnetic moment due to the Dzyaloshinskii–Moriya interaction is parallel to the a axis. Moreover, by fabricating a Co/BiFeO 3 heterostructure, we demonstrate that the ferromagnetic moment of the Co film does couple directly to the canted moment of BiFeO 3.« less

Electrical response of liquid crystal cells doped with multi-walled carbon nanotubes.

PubMed

García-García, Amanda; Vergaz, Ricardo; Algorri, José Francisco; Quintana, Xabier; Otón, José Manuel

2015-01-01

The inclusion of nanoparticles modifies a number of fundamental properties of many materials. Doping of nanoparticles in self-organized materials such as liquid crystals may be of interest for the reciprocal interaction between the matrix and the nanoparticles. Elongated nanoparticles and nanotubes can be aligned and reoriented by the liquid crystal, inducing noticeable changes in their optical and electrical properties. In this work, cells of liquid crystal doped with high aspect ratio multi-walled carbon nanotubes have been prepared, and their characteristic impedance has been studied at different frequencies and excitation voltages. The results demonstrate alterations in the anisotropic conductivity of the samples with the applied electric field, which can be followed by monitoring the impedance evolution with the excitation voltage. Results are consistent with a possible electric contact between the coated substrates of the LC cell caused by the reorientation of the nanotubes. The reversibility of the doped system upon removal of the electric field is quite low.

The origin of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Fei; Zhang, Shujun; Yang, Tiannan

The discovery of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution single crystals is a breakthrough in ferroelectric materials. A key signature of relaxor-ferroelectric solid solutions is the existence of polar nanoregions, a nanoscale inhomogeneity, that coexist with normal ferroelectric domains. Despite two decades of extensive studies, the contribution of polar nanoregions to the underlying piezoelectric properties of relaxor ferroelectrics has yet to be established. Here we quantitatively characterize the contribution of polar nanoregions to the dielectric/piezoelectric responses of relaxor-ferroelectric crystals using a combination of cryogenic experiments and phase-field simulations. The contribution of polar nanoregions to the room-temperature dielectric and piezoelectric propertiesmore » is in the range of 50–80%. A mesoscale mechanism is proposed to reveal the origin of the high piezoelectricity in relaxor ferroelectrics, where the polar nanoregions aligned in a ferroelectric matrix can facilitate polarization rotation. This mechanism emphasizes the critical role of local structure on the macroscopic properties of ferroelectric materials.« less

The origin of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution crystals

DOE PAGES

Li, Fei; Zhang, Shujun; Yang, Tiannan; ...

2016-12-19

The discovery of ultrahigh piezoelectricity in relaxor-ferroelectric solid solution single crystals is a breakthrough in ferroelectric materials. A key signature of relaxor-ferroelectric solid solutions is the existence of polar nanoregions, a nanoscale inhomogeneity, that coexist with normal ferroelectric domains. Despite two decades of extensive studies, the contribution of polar nanoregions to the underlying piezoelectric properties of relaxor ferroelectrics has yet to be established. Here we quantitatively characterize the contribution of polar nanoregions to the dielectric/piezoelectric responses of relaxor-ferroelectric crystals using a combination of cryogenic experiments and phase-field simulations. The contribution of polar nanoregions to the room-temperature dielectric and piezoelectric propertiesmore » is in the range of 50–80%. A mesoscale mechanism is proposed to reveal the origin of the high piezoelectricity in relaxor ferroelectrics, where the polar nanoregions aligned in a ferroelectric matrix can facilitate polarization rotation. This mechanism emphasizes the critical role of local structure on the macroscopic properties of ferroelectric materials.« less

Mesohysteresis model for ferromagnetic materials by minimization of the micromagnetic free energy

NASA Astrophysics Data System (ADS)

van den Berg, A.; Dupré, L.; Van de Wiele, B.; Crevecoeur, G.

2009-04-01

To study the connection between macroscopic hysteretic behavior and the microstructural properties, this paper presents and validates a new material dependent three-dimensional mesoscopic magnetic hysteresis model. In the presented mesoscopic description, the different micromagnetic energy terms are reformulated on the space scale of the magnetic domains. The sample is discretized in cubic cells, each with a local stress state, local bcc crystallographic axes, etc. The magnetization is assumed to align with one of the three crystallographic axes, in positive or negative sense, defining six volume fractions within each cell. The micromagnetic Gibbs free energy is described in terms of these volume fractions. Hysteresis loops are computed by minimizing the mesoscopic Gibbs free energy using a modified gradient search for a sequence of external applied fields. To validate the mesohysteresis model, we studied the magnetic memory properties. Numerical experiments reveal that (1) minor hysteresis loops are indeed closed and (2) the closed minor loops are erased from the memory.

Nanomaterials in the construction industry: a review of their applications and environmental health and safety considerations.

PubMed

Lee, Jaesang; Mahendra, Shaily; Alvarez, Pedro J J

2010-07-27

The extraordinary chemical and physical properties of materials at the nanometer scale enable novel applications ranging from structural strength enhancement and energy conservation to antimicrobial properties and self-cleaning surfaces. Consequently, manufactured nanomaterials (MNMs) and nanocomposites are being considered for various uses in the construction and related infrastructure industries. To achieve environmentally responsible nanotechnology in construction, it is important to consider the lifecycle impacts of MNMs on the health of construction workers and dwellers, as well as unintended environmental effects at all stages of manufacturing, construction, use, demolition, and disposal. Here, we review state-of-the-art applications of MNMs that improve conventional construction materials, suggest likely environmental release scenarios, and summarize potential adverse biological and toxicological effects and their mitigation. Aligned with multidisciplinary assessment of the environmental implications of emerging technologies, this review seeks to promote awareness of potential benefits of MNMs in construction and stimulate the development of guidelines to regulate their use and disposal to mitigate potential adverse effects on human and environmental health.

Nanotransfer and nanoreplication using deterministically grown sacrificial nanotemplates

DOEpatents

Melechko, Anatoli V [Oak Ridge, TN; McKnight, Timothy E. , Guillorn, Michael A.; Ilic, Bojan [Ithaca, NY; Merkulov, Vladimir I [Knoxville, TN; Doktycz, Mitchel J [Knoxville, TN; Lowndes, Douglas H [Knoxville, TN; Simpson, Michael L [Knoxville, TN

2011-05-17

Methods, manufactures, machines and compositions are described for nanotransfer and nanoreplication using deterministically grown sacrificial nanotemplates. A method includes depositing a catalyst particle on a surface of a substrate to define a deterministically located position; growing an aligned elongated nanostructure on the substrate, an end of the aligned elongated nanostructure coupled to the substrate at the deterministically located position; coating the aligned elongated nanostructure with a conduit material; removing a portion of the conduit material to expose the catalyst particle; removing the catalyst particle; and removing the elongated nanostructure to define a nanoconduit.

High-κ gate dielectrics: Current status and materials properties considerations

NASA Astrophysics Data System (ADS)

Wilk, G. D.; Wallace, R. M.; Anthony, J. M.

2001-05-01

Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal-oxide-semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward successful integration into the expected processing conditions for future CMOS technologies, especially due to their tendency to form at interfaces with Si (e.g. silicates). These pseudobinary systems also thereby enable the use of other high-κ materials by serving as an interfacial high-κ layer. While work is ongoing, much research is still required, as it is clear that any material which is to replace SiO2 as the gate dielectric faces a formidable challenge. The requirements for process integration compatibility are remarkably demanding, and any serious candidates will emerge only through continued, intensive investigation.

Synthesis and Fabrication of Nanocomposite Fibers of Collagen-Cellulose Nanocrystals by Coelectrocompaction.

PubMed

Cudjoe, Elvis; Younesi, Mousa; Cudjoe, Edward; Akkus, Ozan; Rowan, Stuart J

2017-04-10

An electrochemical process has been used to compact cellulose nanocrystals (CNC) and access aligned micron-sized CNC fibers. Placing a current across aqueous solutions of carboxylic acid functionalized CNCs (t-CNC-COOH) or carboxylic acid/primary amine functionalized CNCs (t-CNC-COOH-NH 2 ) creates a pH gradient between the electrodes, which results in the migration and concentration of the CNC fibers at their isoelectric point. By matching the carboxylic acid/amine ratio of CNCs and collagen (ca. 30:70 carboxylic acid:amine ratio), it is possible to coelectrocompact both nanofibers and access aligned nanocomposite fibers. t-CNC-COOH-NH 2 /collagen fibers showed a maximum increase in mechanical properties at 5 wt % of t-CNC-COOH-NH 2 . Compared to collagen/CNC films which have no alignment in the plane of the films, the tensile properties of the aligned fibers show a significant enhancement in the wet mechanical properties (40 MPa vs 230 MPa) for the 5 wt % of t-CNC-COOH-NH 2 /collagen films and fiber, respectively.

Silicon Alignment Pins: An Easy Way to Realize a Wafer-To-Wafer Alignment

NASA Technical Reports Server (NTRS)

Peralta, Alejandro (Inventor); Gill, John J. (Inventor); Toda, Risaku (Inventor); Lin, Robert H. (Inventor); Jung-Kubiak, Cecile (Inventor); Reck, Theodore (Inventor); Thomas, Bertrand (Inventor); Siles, Jose V. (Inventor); Lee, Choonsup (Inventor); Chattopadhyay, Goutam (Inventor)

2016-01-01

A silicon alignment pin is used to align successive layers of components made in semiconductor chips and/or metallic components to make easier the assembly of devices having a layered structure. The pin is made as a compressible structure which can be squeezed to reduce its outer diameter, have one end fit into a corresponding alignment pocket or cavity defined in a layer of material to be assembled into a layered structure, and then allowed to expand to produce an interference fit with the cavity. The other end can then be inserted into a corresponding cavity defined in a surface of a second layer of material that mates with the first layer. The two layers are in registry when the pin is mated to both. Multiple layers can be assembled to create a multilayer structure. Examples of such devices are presented.

Fabrication of a Highly Aligned Neural Scaffold via a Table Top Stereolithography 3D Printing and Electrospinning^.

PubMed

Lee, Se-Jun; Nowicki, Margaret; Harris, Brent; Zhang, Lijie Grace

2017-06-01

Three-dimensional (3D) bioprinting is a rapidly emerging technique in the field of tissue engineering to fabricate extremely intricate and complex biomimetic scaffolds in the range of micrometers. Such customized 3D printed constructs can be used for the regeneration of complex tissues such as cartilage, vessels, and nerves. However, the 3D printing techniques often offer limited control over the resolution and compromised mechanical properties due to short selection of printable inks. To address these limitations, we combined stereolithography and electrospinning techniques to fabricate a novel 3D biomimetic neural scaffold with a tunable porous structure and embedded aligned fibers. By employing two different types of biofabrication methods, we successfully utilized both synthetic and natural materials with varying chemical composition as bioink to enhance biocompatibilities and mechanical properties of the scaffold. The resulting microfibers composed of polycaprolactone (PCL) polymer and PCL mixed with gelatin were embedded in 3D printed hydrogel scaffold. Our results showed that 3D printed scaffolds with electrospun fibers significantly improve neural stem cell adhesion when compared to those without the fibers. Furthermore, 3D scaffolds embedded with aligned fibers showed an enhancement in cell proliferation relative to bare control scaffolds. More importantly, confocal microscopy images illustrated that the scaffold with PCL/gelatin fibers greatly increased the average neurite length and directed neurite extension of primary cortical neurons along the fiber. The results of this study demonstrate the potential to create unique 3D neural tissue constructs by combining 3D bioprinting and electrospinning techniques.

Enhancement of hole mobility in InSe monolayer via an InSe and black phosphorus heterostructure.

PubMed

Ding, Yi-Min; Shi, Jun-Jie; Xia, Congxin; Zhang, Min; Du, Juan; Huang, Pu; Wu, Meng; Wang, Hui; Cen, Yu-Lang; Pan, Shu-Hang

2017-10-05

To enhance the low hole mobility (∼40 cm 2 V -1 s -1 ) of InSe monolayer, a novel two-dimensional (2D) van der Waals heterostructure made of InSe and black phosphorus (BP) monolayers with high hole mobility (∼10 3 cm 2 V -1 s -1 ) has been constructed and its structural and electronic properties are investigated using first-principles calculations. We find that the InSe/BP heterostructure exhibits a direct band gap of 1.39 eV and type-II band alignment with electrons (holes) located in the InSe (BP) layer. The band offsets of InSe and BP are 0.78 eV for the conduction band minimum and 0.86 eV for the valence band maximum, respectively. Surprisingly, the hole mobility in the InSe/BP heterostructure exceeds 10 4 cm 2 V -1 s -1 , which is one order of magnitude larger than the hole mobility of BP and three orders larger than that of the InSe monolayer. The electron mobility is also increased to 3 × 10 3 cm 2 V -1 s -1 . The physical reason has been analyzed deeply, and a universal method is proposed to improve the carrier mobility of 2D materials by forming heterostructures with them and other 2D materials with complementary properties. The InSe/BP heterostructure can thus be widely used in nanoscale InSe-based field-effect transistors, photodetectors and photovoltaic devices due to its type-II band alignment and high carrier mobility.

A novel post-weld-shift measurement and compensation technique in butterfly-type laser module packages

NASA Astrophysics Data System (ADS)

Hsu, Yi-Cheng, Sr.; Tsai, Y. C.; Hung, Y. S.; Cheng, W. H.

2005-08-01

One of the greatest challenges in the packaging of laser modules using laser welding technique is to use a reliable and accurate joining process. However, during welding, due to the material property difference between welded components, the rapid solidification of the welded region and the associated material shrinkage often introduced a post-weld-shift (PWS) between welded components. For a typical single-mode fiber application, if the PWS induced fiber alignment shift by the laser welding joining process is even a few micrometers, up to 50 % or greater loss in the coupled power may occur. The fiber alignment shift of the PWS effect in the laser welding process has a significant impact on the laser module package yield. Therefore, a detailed understanding of the effects of PWS on the fiber alignment shifts in laser-welded laser module packages and then the compensation of the fiber alignment shifts due to PWS effects are the key research subjects in laser welding techniques for optoelectronic packaging applications. Previously, the power losses due to PWS in butterfly-type laser module packages have been qualitatively corrected by applying the laser hammering technique to the direction of the detected shift. Therefore, by applying an elastic deformation to the welded components and by observing the corresponding power variation, the direction and magnitude of the PWS may be predicted. Despite numerous studies on improving the fabrication yields of laser module packaging using the PWS correction in laser welding techniques by a qualitative estimate, limited information is available for the quantitative understanding of the PWS induced fiber alignment shift which can be useful in designing and fabricating high-yield and high-performance laser module packages. The purpose of this paper is to present a quantitative probing of the PWS induced fiber alignment shift in laser-welded butterfly-type laser module packaging by employing a novel technique of a high-magnification camera with image capture system (HMCICS). The benefit of using the HMCICS technique to determine the fiber alignment shift are quantitatively measure and compensate the PWS direction and magnitude during the laser-welded laser module packages. This study makes it possible to probe the nonlinear behavior of the PWS by using a novel HMCICS technique that results in a real time quantitative compensation of the PWS in butterfly-type laser module packages, when compared to the currently available qualitatively estimated techniques to correct the PWS2. Therefore, the reliable butterfly-type laser modules with high yield and high performance used in lightwave transmission systems may thus be developed and fabricated.

Optical and structural properties of amorphous Se x Te100- x aligned nanorods

NASA Astrophysics Data System (ADS)

Al-Agel, Faisal A.

2013-12-01

In the present work, we report studies on optical and structural phenomenon in as-deposited thin films composed of aligned nanorods of amorphous Se x Te100- x ( x = 3, 6, 9, and 12). In structural studies, field emission scanning electron microscopic (FESEM) images suggest that these thin films contain high yield of aligned nanorods. These nanorods show a completely amorphous nature, which is verified by X-ray diffraction patterns of these thin films. Optical studies include the measurement of spectral dependence of absorption, reflection, and transmission of these thin films, respectively. On the basis of optical absorption data, a direct optical band gap is observed. This observation of a direct optical band gap in these nanorods is interesting as chalcogenides normally show an indirect band gap, and due to this reason, these materials could not become very popular for semiconducting devices. Therefore, this is an important report and will open up new directions for the application of these materials in semiconducting devices. The value of this optical band gap is found to decrease with the increase in selenium (Se) concentration. The reflection and absorption data are employed to estimate the values of optical constants (extinction coefficient ( k) and refractive index ( n)). From the spectral dependence of these optical constants, it is found that the values of refractive index ( n) increase, whereas the values of extinction coefficient ( k) decrease with the increase in photon energy. The real and imaginary parts of dielectric constants calculated with the values of extinction coefficient ( k) and refractive index ( n), are found to vary with photon energy and dopant concentration.

A Semi-Automatic Alignment Method for Math Educational Standards Using the MP (Materialization Pattern) Model

ERIC Educational Resources Information Center

Choi, Namyoun

2010-01-01

Educational standards alignment, which matches similar or equivalent concepts of educational standards, is a necessary task for educational resource discovery and retrieval. Automated or semi-automated alignment systems for educational standards have been recently available. However, existing systems frequently result in inconsistency in…

Hydrostatic self-aligning axial/torsional mechanism

DOEpatents

O'Connor, Daniel G.; Gerth, Howard L.

1990-01-01

The present invention is directed to a self-aligning axial/torsional loading mechanism for testing the strength of brittle materials which are sensitive to bending moments. Disposed inside said self-aligning loading mechanism is a frictionless hydrostatic ball joint with a flexure ring to accommodate torsional loads through said ball joint.

A material sensitivity study on the accuracy of deformable organ registration using linear biomechanical models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chi, Y.; Liang, J.; Yan, D.

2006-02-15

Model-based deformable organ registration techniques using the finite element method (FEM) have recently been investigated intensively and applied to image-guided adaptive radiotherapy (IGART). These techniques assume that human organs are linearly elastic material, and their mechanical properties are predetermined. Unfortunately, the accurate measurement of the tissue material properties is challenging and the properties usually vary between patients. A common issue is therefore the achievable accuracy of the calculation due to the limited access to tissue elastic material constants. In this study, we performed a systematic investigation on this subject based on tissue biomechanics and computer simulations to establish the relationshipsmore » between achievable registration accuracy and tissue mechanical and organ geometrical properties. Primarily we focused on image registration for three organs: rectal wall, bladder wall, and prostate. The tissue anisotropy due to orientation preference in tissue fiber alignment is captured by using an orthotropic or a transversely isotropic elastic model. First we developed biomechanical models for the rectal wall, bladder wall, and prostate using simplified geometries and investigated the effect of varying material parameters on the resulting organ deformation. Then computer models based on patient image data were constructed, and image registrations were performed. The sensitivity of registration errors was studied by perturbating the tissue material properties from their mean values while fixing the boundary conditions. The simulation results demonstrated that registration error for a subvolume increases as its distance from the boundary increases. Also, a variable associated with material stability was found to be a dominant factor in registration accuracy in the context of material uncertainty. For hollow thin organs such as rectal walls and bladder walls, the registration errors are limited. Given 30% in material uncertainty, the registration error is limited to within 1.3 mm. For a solid organ such as the prostate, the registration errors are much larger. Given 30% in material uncertainty, the registration error can reach 4.5 mm. However, the registration error distribution for prostates shows that most of the subvolumes have a much smaller registration error. A deformable organ registration technique that uses FEM is a good candidate in IGART if the mean material parameters are available.« less

Multi-Scale CNT-Based Reinforcing Polymer Matrix Composites for Lightweight Structures

NASA Technical Reports Server (NTRS)

Eberly, Daniel; Ou, Runqing; Karcz, Adam; Skandan, Ganesh; Mather, Patrick; Rodriguez, Erika

2013-01-01

Reinforcing critical areas in carbon polymer matrix composites (PMCs), also known as fiber reinforced composites (FRCs), is advantageous for structural durability. Since carbon nanotubes (CNTs) have extremely high tensile strength, they can be used as a functional additive to enhance the mechanical properties of FRCs. However, CNTs are not readily dispersible in the polymer matrix, which leads to lower than theoretically predicted improvement in mechanical, thermal, and electrical properties of CNT composites. The inability to align CNTs in a polymer matrix is also a known issue. The feasibility of incorporating aligned CNTs into an FRC was demonstrated using a novel, yet commercially viable nanofiber approach, termed NRMs (nanofiber-reinforcing mats). The NRM concept of reinforcement allows for a convenient and safe means of incorporating CNTs into FRC structural components specifically where they are needed during the fabrication process. NRMs, fabricated through a novel and scalable process, were incorporated into FRC test panels using layup and vacuum bagging techniques, where alternating layers of the NRM and carbon prepreg were used to form the reinforced FRC structure. Control FRC test panel coupons were also fabricated in the same manner, but comprised of only carbon prepreg. The FRC coupons were machined to size and tested for flexural, tensile, and compression properties. This effort demonstrated that FRC structures can be fabricated using the NRM concept, with an increased average load at break during flexural testing versus that of the control. The NASA applications for the developed technologies are for lightweight structures for in-space and launch vehicles. In addition, the developed technologies would find use in NASA aerospace applications such as rockets, aircraft, aircraft/spacecraft propulsion systems, and supporting facilities. The reinforcing aspect of the technology will allow for more efficient joining of fiber composite parts, thus offering additional weight savings. More robust structures capable of withstanding micrometeoroid and space debris impacts will be possible with the enhanced mechanical properties imparted by the aligned CNTs incorporated into the fiber composite structure, as well as the potential for improved electrical and thermal properties. The materials fabrication approach developed in the present effort is a platform for customer applications where additional reinforcement is required or would be beneficial, especially in FRC structures and component parts. Depending upon the specific customer application, the NRM could be tailored to the specific matrix resin and desired property enhancement.

Thermal Conductivity of Polyimide/Carbon Nanofiller Blends

NASA Technical Reports Server (NTRS)

Ghose, S.; Watson, K. A.; Delozier, D. M.; Working, D. C.; Connell, J. W.; Smith, J. G.; Sun, Y. P.; Lin, Y.

2007-01-01

In efforts to improve the thermal conductivity (TC) of Ultem(TM) 1000, it was compounded with three carbon based nano-fillers. Multiwalled carbon nanotubes (MWCNT), vapor grown carbon nanofibers (CNF) and expanded graphite (EG) were investigated. Ribbons were extruded to form samples in which the nano-fillers were aligned. Samples were also fabricated by compression molding in which the nano-fillers were randomly oriented. The thermal properties were evaluated by DSC and TGA, and the mechanical properties of the aligned samples were determined by tensile testing. The degree of dispersion and alignment of the nanoparticles were investigated with high-resolution scanning electron microscopy. The thermal conductivity of the samples was measured in both the direction of alignment as well as perpendicular to that direction using the Nanoflash technique. The results of this study will be presented.

Thermal Conductivity of Polyimide/Nanofiller Blends

NASA Technical Reports Server (NTRS)

Ghose, S.; Watson, K. A.; Delozier, D. M.; Working, D. c.; Connell, J. W.; Smith, J. G.; Sun, Y. P.; Lin, Y.

2006-01-01

In efforts to improve the thermal conductivity of Ultem(TM) 1000, it was compounded with three carbon based nano-fillers. Multiwalled carbon nanotubes (MWCNT), vapor grown carbon nanofibers (CNF) and expanded graphite (EG) were investigated. Ribbons were extruded to form samples in which the nano-fillers were aligned. Samples were also fabricated by compression molding in which the nano-fillers were randomly oriented. The thermal properties were evaluated by DSC and TGA, and the mechanical properties of the aligned samples were determined by tensile testing. The degree of dispersion and alignment of the nanoparticles were investigated with high-resolution scanning electron microscopy. The thermal conductivity of the samples was measured in both the direction of alignment as well as perpendicular to that direction using the Nanoflash technique. The results of this study will be presented.

High-resolution Earth-based lunar radar studies: Applications to lunar resource assessment

NASA Technical Reports Server (NTRS)

Stacy, N. J. S.; Campbell, D. B.

1992-01-01

The lunar regolith will most likely be a primary raw material for lunar base construction and resource extraction. High-resolution radar observations of the Moon provide maps of radar backscatter that have intensity variations generally controlled by the local slope, material, and structural properties of the regolith. The properties that can be measured by the radar system include the dielectric constant, density, loss tangent, and wavelength scale roughness. The radar systems currently in operation at several astronomical observatories provide the ability to image the lunar surface at spatial resolutions approaching 30 m at 3.8 cm and 12.6 cm wavelengths and approximately 500 m at 70 cm wavelength. The radar signal penetrates the lunar regolith to a depth of 10-20 wavelengths so the measured backscatter contains contributions from the vacuum-regolith interface and from wavelength-scale heterogeneities in the electrical properties of the subsurface material. The three wavelengths, which are sensitive to different scale structures and scattering volumes, provide complementary information on the regolith properties. Aims of the previous and future observations include (1) analysis of the scattering properties associated with fresh impact craters, impact crater rays, and mantled deposits; (2) analysis of high-incidence-angle observations of the lunar mare to investigate measurement of the regolith dielectric constant and hence porosity; (3) investigation of interferometric techniques using two time-delayed observations of the same site, observations that require a difference in viewing geometry less than 0.05 deg and, hence, fortuitous alignment of the Earth-Moon system when visible from Arecibo Observatory.

Magnetic field effect for cellulose nanofiber alignment

NASA Astrophysics Data System (ADS)

Kim, Jaehwan; Chen, Yi; Kang, Kwang-Sun; Park, Young-Bin; Schwartz, Mark

2008-11-01

Regenerated cellulose formed into cellulose nanofibers under strong magnetic field and aligned perpendicularly to the magnetic field. Well-aligned microfibrils were found as the exposure time of the magnetic field increased. Better alignment and more crystalline structure of the cellulose resulted in the increased decomposition temperature of the material. X-ray crystallograms showed that crystallinity index of the cellulose increased as the exposure time of the magnetic field increased.

Prospects of Nanotechnology in Clinical Immunodiagnostics

PubMed Central

Ansari, Anees A.; Alhoshan, Mansour; Alsalhi, Mohamad S.; Aldwayyan, Abdullah S.

2010-01-01

Nanostructured materials are promising compounds that offer new opportunities as sensing platforms for the detection of biomolecules. Having micrometer-scale length and nanometer-scale diameters, nanomaterials can be manipulated with current nanofabrication methods, as well as self-assembly techniques, to fabricate nanoscale bio-sensing devices. Nanostructured materials possess extraordinary physical, mechanical, electrical, thermal and multifunctional properties. Such unique properties advocate their use as biomimetic membranes to immobilize and modify biomolecules on the surface of nanoparticles. Alignment, uniform dispersion, selective growth and diameter control are general parameters which play critical roles in the successful integration of nanostructures for the fabrication of bioelectronic sensing devices. In this review, we focus on different types and aspects of nanomaterials, including their synthesis, properties, conjugation with biomolecules and their application in the construction of immunosensing devices. Some key results from each cited article are summarized by relating the concept and mechanism behind each sensor, experimental conditions and the behavior of the sensor under different conditions, etc. The variety of nanomaterial-based bioelectronic devices exhibiting novel functions proves the unique properties of nanomaterials in such sensing devices, which will surely continue to expand in the future. Such nanomaterial based devices are expected to have a major impact in clinical immunodiagnostics, environmental monitoring, security surveillance and for ensuring food safety. PMID:22163566

Polarization holograms in a bifunctional amorphous polymer exhibiting equal values of photoinduced linear and circular birefringences.

PubMed

Provenzano, Clementina; Pagliusi, Pasquale; Cipparrone, Gabriella; Royes, Jorge; Piñol, Milagros; Oriol, Luis

2014-10-09

Light-controlled molecular alignment is a flexible and useful strategy introducing novelty in the fields of mechanics, self-organized structuring, mass transport, optics, and photonics and addressing the development of smart optical devices. Azobenzene-containing polymers are well-known photocontrollable materials with large and reversible photoinduced optical anisotropies. The vectorial holography applied to these materials enables peculiar optical devices whose properties strongly depend on the relative values of the photoinduced birefringences. Here is reported a polarization holographic recording based on the interference of two waves with orthogonal linear polarization on a bifunctional amorphous polymer that, exceptionally, exhibits equal values of linear and circular birefringence. The peculiar photoresponse of the material coupled with the holographic technique demonstrates an optical device capable of decomposing the light into a set of orthogonally polarized linear components. The holographic structures are theoretically described by the Jones matrices method and experimentally investigated.

Synthesis of monoclinic potassium niobate nanowires that are stable at room temperature.

PubMed

Kim, Seungwook; Lee, Ju-Hyuck; Lee, Jaeyeon; Kim, Sang-Woo; Kim, Myung Hwa; Park, Sungnam; Chung, Haegeun; Kim, Yong-Il; Kim, Woong

2013-01-09

We report the synthesis of KNbO(3) nanowires (NWs) with a monoclinic phase, a phase not observed in bulk KNbO(3) materials. The monoclinic NWs can be synthesized via a hydrothermal method using metallic Nb as a precursor. The NWs are metastable, and thermal treatment at ∼450 °C changed the monoclinic phase into the orthorhombic phase, which is the most stable phase of KNbO(3) at room temperature. Furthermore, we fabricated energy-harvesting nanogenerators by vertically aligning the NWs on SrTiO(3) substrates. The monoclinic NWs showed significantly better energy conversion characteristics than orthorhombic NWs. Moreover, the frequency-doubling efficiency of the monoclinic NWs was ∼3 times higher than that of orthorhombic NWs. This work may contribute to the synthesis of materials with new crystalline structures and hence improve the properties of the materials for various applications.

Regionally variant collagen alignment correlates with viscoelastic properties of the disc of the human temporomandibular joint.

PubMed

Gutman, Shawn; Kim, Daniel; Tarafder, Solaiman; Velez, Sergio; Jeong, Julia; Lee, Chang H

2018-02-01

To determine the regionally variant quality of collagen alignment in human TMJ discs and its statistical correlation with viscoelastic properties. For quantitative analysis of the quality of collagen alignment, horizontal sections of human TMJ discs with Pricrosirius Red staining were imaged under circularly polarized microscopy. Mean angle and angular deviation of collagen fibers in each region were analyzed using a well-established automated image-processing for angular gradient. Instantaneous and relaxation moduli of each disc region were measured under stress-relaxation test both in tensile and compression. Then Spearman correlation analysis was performed between the angular deviation and the moduli. To understand the effect of glycosaminoglycans on the correlation, TMJ disc samples were treated by chondroitinase ABC (C-ABC). Our imaging processing analysis showed the region-variant direction of collagen alignment, consistently with previous findings. Interestingly, the quality of collagen alignment, not only the directions, was significantly different in between the regions. The angular deviation of fiber alignment in the anterior and intermediate regions were significantly smaller than the posterior region. Medial and lateral regions showed significantly bigger angular deviation than all the other regions. The regionally variant angular deviation values showed statistically significant correlation with the tensile instantaneous modulus and the relaxation modulus, partially dependent on C-ABC treatment. Our findings suggest the region-variant degree of collagen fiber alignment is likely attributed to the heterogeneous viscoelastic properties of TMJ disc that may have significant implications in development of regenerative therapy for TMJ disc. Copyright © 2017 Elsevier Ltd. All rights reserved.

Development of a reinforced electrochemically aligned collagen bioscaffold for tendon tissue engineering applications

NASA Astrophysics Data System (ADS)

Uquillas Paredes, Jorge Alfredo

Type-I collagen is a promising biomaterial that can be used to synthesize bioscaffolds as a strategy to regenerate and repair damaged tendons. The existing in vitro prepared collagen bioscaffolds are in the form of gels, foams, or extruded fibers. These bioscaffolds readily present sites for attachment of biological factors and cells; however, they have extremely poor biomechanical properties in comparison to the properties of native tendons. The biomechanical function of type-I collagen bioscaffolds needs to be elevated to the level of natural tissues for this biomaterial to replace mechanically challenged tendons in a functionally meaningful way. The overall goal of this dissertation is to develop a reinforced electrochemically aligned collagenous bioscaffold for applications in tendon tissue engineering. The bioscaffold is synthesized by a unique electrochemical process via isoelectric focusing (IEF) to attain a very high degree of molecular alignment and packing density. This dissertation presents progress made on four aims: A) development of simple and descriptive electrochemical theory via the mathematical model of IEF and the forces acting on collagen alignment under an electric field; B) optimization of the post-alignment PBS treatment step to achieve d- banding pattern in uncrosslinked electrochemically aligned collagen (ELAC) bioscaffolds; C) optimization of the best crosslinking protocol to produce the strongest possible ELAC biomaterial with excellent cellular compatibility; and D) in vivo evaluation of the biocompatibility and biodegradability properties of electronically aligned collagen bioscaffolds. The results of this dissertation provide strong evidence showing that reinforced ELAC bioscaffolds could be used clinically in the future to repair damaged tendons.

Effect of Eu magnetism on the electronic properties of the candidate Dirac material EuMnBi2

NASA Astrophysics Data System (ADS)

May, Andrew F.; McGuire, Michael A.; Sales, Brian C.

2014-08-01

The crystal structure and physical properties of the layered material EuMnBi2 have been characterized by measurements on single crystals. EuMnBi2 is isostructural with the Dirac material SrMnBi2 based on single-crystal x-ray diffraction, crystallizing in the I4/mmm space group (No. 139). Magnetic susceptibility measurements suggest antiferromagnetic (AFM) ordering of moments on divalent Eu ions near TN=22 K. For low fields, the ordered Eu moments are aligned along the c axis, and a spin flop is observed near 5.4 T at 5 K. The moment is not saturated in an applied field of 13 T at 5 K, which is uncommon for compounds containing Eu2+. The magnetic behavior suggests an anisotropy enhancement via interaction between Eu and the Mn moments that appear to be ordered antiferromagnetically below ≈310 K. A large increase in the magnetoresistance is observed across the spin flop, with absolute magnetoresistance reaching ≈650% at 5 K and 12 T. Hall effect measurements reveal a decrease in the carrier density below TN, which implies a manipulation of the Fermi surface by magnetism on the sites surrounding the Bi square nets that lead to Dirac cones in this family of materials.

Setting Directions: Anisotropy in Hierarchically Organized Porous Silica

PubMed Central

2017-01-01

Structural hierarchy, porosity, and isotropy/anisotropy are highly relevant factors for mechanical properties and thereby the functionality of porous materials. However, even though anisotropic and hierarchically organized, porous materials are well known in nature, such as bone or wood, producing the synthetic counterparts in the laboratory is difficult. We report for the first time a straightforward combination of sol–gel processing and shear-induced alignment to create hierarchical silica monoliths exhibiting anisotropy on the levels of both, meso- and macropores. The resulting material consists of an anisotropic macroporous network of struts comprising 2D hexagonally organized cylindrical mesopores. While the anisotropy of the mesopores is an inherent feature of the pores formed by liquid crystal templating, the anisotropy of the macropores is induced by shearing of the network. Scanning electron microscopy and small-angle X-ray scattering show that the majority of network forming struts is oriented towards the shearing direction; a quantitative analysis of scattering data confirms that roughly 40% of the strut volume exhibits a preferred orientation. The anisotropy of the material’s macroporosity is also reflected in its mechanical properties; i.e., the Young’s modulus differs by nearly a factor of 2 between the directions of shear application and perpendicular to it. Unexpectedly, the adsorption-induced strain of the material exhibits little to no anisotropy. PMID:28989232

Scanning wave photopolymerization enables dye-free alignment patterning of liquid crystals

PubMed Central

Hisano, Kyohei; Aizawa, Miho; Ishizu, Masaki; Kurata, Yosuke; Nakano, Wataru; Akamatsu, Norihisa; Barrett, Christopher J.; Shishido, Atsushi

2017-01-01

Hierarchical control of two-dimensional (2D) molecular alignment patterns over large areas is essential for designing high-functional organic materials and devices. However, even by the most powerful current methods, dye molecules that discolor and destabilize the materials need to be doped in, complicating the process. We present a dye-free alignment patterning technique, based on a scanning wave photopolymerization (SWaP) concept, that achieves a spatial light–triggered mass flow to direct molecular order using scanning light to propagate the wavefront. This enables one to generate macroscopic, arbitrary 2D alignment patterns in a wide variety of optically transparent polymer films from various polymerizable mesogens with sufficiently high birefringence (>0.1) merely by single-step photopolymerization, without alignment layers or polarized light sources. A set of 150,000 arrays of a radial alignment pattern with a size of 27.4 μm × 27.4 μm were successfully inscribed by SWaP, in which each individual pattern is smaller by a factor of 104 than that achievable by conventional photoalignment methods. This dye-free inscription of microscopic, complex alignment patterns over large areas provides a new pathway for designing higher-performance optical and mechanical devices. PMID:29152567

Magnetic field alignment of coil-coil diblock copolymers and blends via intrinsic chain anisotropy

NASA Astrophysics Data System (ADS)

Rokhlenko, Yekaterina; Majewski, Pawel; Larson, Steven; Yager, Kevin; Gopalan, Padma; Avgeropoulos, Apostolos; Chan, Edwin; Osuji, Chinedum

Magnetic fields can control alignment of self-assembled soft materials such as block copolymers provided there is a suitably large magnetic susceptibility anisotropy present in the system. Recent results have highlighted the existence of a non-trivial intrinsic anisotropy in coil-coil diblock copolymers, specifically in lamellar-forming PS-b-P4VP, which enables alignment at field strengths of a few tesla in systems lacking mesogenic components. Alignment is predicated on correlation in the orientation of end-end vectors implied by the localization of block junctions at the microdomain interface and is observed on cooling across the order-disorder transition in the presence of the field. For appropriate combinations of field strength and grain size, we can leverage intrinsic chain anisotropy to magnetically direct self-assembly of many non-mesogenic systems, including other coil-coil BCPs like PS-b-PDMS and PS-b-PMMA, blends of BCPs of disparate morphologies and MWs, and blends of BCPs with homopolymers. This is noteworthy as blends of PS-b-P4VP with PEO provide a route to form functional materials such as nanoporous films by dissolution of PEO, or aligned ion conduction materials. We survey these various systems using TEM and in-situ X-ray scattering to study the phase behavior and temperature-, time- and field- dependent dynamics of alignment.

Large format focal plane array integration with precision alignment, metrology and accuracy capabilities

NASA Astrophysics Data System (ADS)

Neumann, Jay; Parlato, Russell; Tracy, Gregory; Randolph, Max

2015-09-01

Focal plane alignment for large format arrays and faster optical systems require enhanced precision methodology and stability over temperature. The increase in focal plane array size continues to drive the alignment capability. Depending on the optical system, the focal plane flatness of less than 25μm (.001") is required over transition temperatures from ambient to cooled operating temperatures. The focal plane flatness requirement must also be maintained in airborne or launch vibration environments. This paper addresses the challenge of the detector integration into the focal plane module and housing assemblies, the methodology to reduce error terms during integration and the evaluation of thermal effects. The driving factors influencing the alignment accuracy include: datum transfers, material effects over temperature, alignment stability over test, adjustment precision and traceability to NIST standard. The FPA module design and alignment methodology reduces the error terms by minimizing the measurement transfers to the housing. In the design, the proper material selection requires matched coefficient of expansion materials minimizes both the physical shift over temperature as well as lowering the stress induced into the detector. When required, the co-registration of focal planes and filters can achieve submicron relative positioning by applying precision equipment, interferometry and piezoelectric positioning stages. All measurements and characterizations maintain traceability to NIST standards. The metrology characterizes the equipment's accuracy, repeatability and precision of the measurements.

Strain-induced alignment and phase behavior of blue phase liquid crystals confined to thin films.

PubMed

Bukusoglu, Emre; Martinez-Gonzalez, Jose A; Wang, Xiaoguang; Zhou, Ye; de Pablo, Juan J; Abbott, Nicholas L

2017-12-06

We report on the influence of surface confinement on the phase behavior and strain-induced alignment of thin films of blue phase liquid crystals (BPs). Confining surfaces comprised of bare glass, dimethyloctadecyl [3-(trimethoxysilyl)propyl] ammonium chloride (DMOAP)-functionalized glass, or polyvinyl alcohol (PVA)-coated glass were used with or without mechanically rubbing to influence the azimuthal anchoring of the BPs. These experiments reveal that confinement can change the phase behavior of the BP films. For example, in experiments performed with rubbed-PVA surfaces, we measured the elastic strain of the BPs to change the isotropic-BPII phase boundary, suppressing formation of BPII for film thicknesses incommensurate with the BPII lattice. In addition, we observed strain-induced alignment of the BPs to exhibit a complex dependence on both the surface chemistry and azimuthal alignment of the BPs. For example, when using bare glass surfaces causing azimuthally degenerate and planar anchoring, BPI oriented with (110) planes of the unit cell parallel to the contacting surfaces for thicknesses below 3 μm but transitioned to an orientation with (200) planes aligned parallel to the contacting surfaces for thicknesses above 4 μm. In contrast, BPI aligned with (110) planes parallel to confining surfaces for all other thicknesses and surface treatments, including bare glass with uniform azimuthal alignment. Complementary simulations based on minimization of the total free energy (Landau-de Gennes formalism) confirmed a thickness-dependent reorientation due to strain of BPI unit cells within a window of surface anchoring energies and in the absence of uniform azimuthal alignment. In contrast to BPI, BPII did not exhibit thickness-dependent orientations but did exhibit orientations that were dependent on the surface chemistry, a result that was also captured in simulations by varying the anchoring energies. Overall, the results in this paper reveal that the orientations assumed by BPs in thin films reflect a complex interplay of surface interactions and elastic energies associated with strain of the BP lattice. The results also provide new principles and methods to control the structure and properties of BP thin films, which may find use in BP-templated material synthesis, and BP-based optical and electronic devices.

Vertically-aligned BCN Nanotube Arrays with Superior Performance in Electrochemical capacitors

PubMed Central

Zhou, Junshuang; Li, Na; Gao, Faming; Zhao, Yufeng; Hou, Li; Xu, Ziming

2014-01-01

Electrochemical capacitors (EC) have received tremendous interest due to their high potential to satisfy the urgent demand in many advanced applications. The development of new electrode materials is considered to be the most promising approach to enhance the EC performance substantially. Herein, we present a high-capacity capacitor material based on vertically-aligned BC2N nanotube arrays (VA-BC2NNTAs) synthesized by low temperature solvothermal route. The obtained VA-BC2NNTAs display the good aligned nonbuckled tubular structure, which could indeed advantageously enhance capacitor performance. VA-BC2NNTAs exhibit an extremely high specific capacitance, 547 Fg−1, which is about 2–6 times larger than that of the presently available carbon-based materials. Meanwhile, VA-BC2NNTAs maintain an excellent rate capability and high durability. All these characteristics endow VA-BC2NNTAs an alternative promising candidate for an efficient electrode material for electrochemical capacitors (EC). PMID:25124300

Study for new hardmask process scheme

NASA Astrophysics Data System (ADS)

Lee, Daeyoup; Tatti, Phillip; Lee, Richard; Chang, Jack; Cho, Winston; Bae, Sanggil

2017-03-01

Hardmask processes are a key technique to enable low-k semiconductors, but they can have an impact on patterning control, influencing defectivity, alignment, and overlay. Specifically, amorphous carbon layer (ACL) hardmask schemes can negatively affect overlay by creating distorted alignment signals. A new scheme needs to be developed that can be inserted where amorphous carbon is used but provide better alignment performance. Typical spin-on carbon (SOC) materials used in other hardmask schemes have issues with DCD-FCD skew. In this paper we will evaluate new spin-on carbon material with a higher carbon content that could be a candidate to replace amorphous carbon.

Gas-Phase Functionalization of Macroscopic Carbon Nanotube Fiber Assemblies: Reaction Control, Electrochemical Properties, and Use for Flexible Supercapacitors.

PubMed

Iglesias, Daniel; Senokos, Evgeny; Alemán, Belén; Cabana, Laura; Navío, Cristina; Marcilla, Rebeca; Prato, Maurizio; Vilatela, Juan J; Marchesan, Silvia

2018-02-14

The assembly of aligned carbon nanotubes (CNTs) into fibers (CNTFs) is a convenient approach to exploit and apply the unique physico-chemical properties of CNTs in many fields. CNT functionalization has been extensively used for its implementation into composites and devices. However, CNTF functionalization is still in its infancy because of the challenges associated with preservation of CNTF morphology. Here, we report a thorough study of the gas-phase functionalization of CNTF assemblies using ozone which was generated in situ from a UV source. In contrast with liquid-based oxidation methods, this gas-phase approach preserves CNTF morphology, while notably increasing its hydrophilicity. The functionalized material is thoroughly characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy. Its newly acquired hydrophilicity enables CNTF electrochemical characterization in aqueous media, which was not possible for the pristine material. Through comparison of electrochemical measurements in aqueous electrolytes and ionic liquids, we decouple the effects of functionalization on pseudocapacitive reactions and quantum capacitance. The functionalized CNTF assembly is successfully used as an active material and a current collector in all-solid supercapacitor flexible devices with an ionic liquid-based polymer electrolyte.

Incorporation of New Benzofulvene Derivatives Into Polymers to Give New NLO Materials

NASA Technical Reports Server (NTRS)

Bowens, Andrea D.; Bu, Xiu; Mintz, Eric A.; Zhang, Yue

1996-01-01

The need for fast electro-optic switches and modulators for optical communication, and laser frequency conversion has created a demand for new second-order non-linear optical materials. One approach to produce such materials is to align chromophores with large molecular hyperpolarizabilities in polymers. Recently fulvenes and benzofulvenes which contain electron donating groups have been shown to exhibit large second-order non-linear optical properties. The resonance structures shown below suggest that intramolecular charge transfer (ICT) should be favorable in omega - (hydroxyphenyl)benzofulvenes and even more favorable in omega-omega - (phenoxy)benzofulvenes because of the enhanced donor properties of the O group. This ICT should lead to enormously enhanced second-order hyperpolarizability. We have prepared all three new omega - (hydroxyphenyl)benzofulvenes by the condensation of indene with the appropriate hydroxyaryl aldehyde in MeOH or MeOH/H2O under base catalysis. In a similar fashion we have prepared substituted benzofulvenes with multipal donor groups. Preliminary studies show that some of our benzofulvene derivatives exhibit second order harmonic generation (SHG). Measurements were carried out by preparing host-guest polymers. The results of our work on benzofulvene derivatives in host-guest polymers when covalently bonded in the polymer will be described.

Mechanics and Physics of Solids, Uncertainy, and the Archetype-Genome Exemplar

NASA Astrophysics Data System (ADS)

Greene, M. Steven

This dissertation argues that the mechanics and physics of solids rely on a fundamental exemplar: the apparent properties of a system depend on the building blocks that comprise it. Building blocks are referred to as archetypes and apparent system properties as the system genome. Three entities are of importance: the archetype properties, the conformation of archetypes, and the properties of interactions activated by that conformation. The combination of these entities into the system genome is called assembly. To show the utility of the archetype-genome exemplar, the dissertation presents the mathematical construction and computational implementation of a new theory for solid mechanics that is a continuum manifestation of the assembly process. The so-called archetype-blending continuum theory aligns the form of globally valid balance laws with physics evolving in a material's composite constitutive response so that, by rethinking conventional micromechanics, the theory accounts naturally for each piece of the genome assembly triplet: archetypes, interactions, and their conformation. With the pieces of the triplet isolated in the theory, materials genome design concepts that separately control microstructure and property may be gleaned from exploration of the constitutive parameter space. A suite of simulations that apply the new theory to polymer nanocomposite materials demonstrate the ability of the theory to predict a robust material genome that includes damping properties, modulus weakening, local strain amplification, and size effects. The dissertation also presents a theoretical assessment of the importance of uncertainty propagation in the archetype-genome exemplar. The findings from a set of computational experiments on instances of a general class of microstructured materials suggest that when overlap occurs between the size of the system geometry and the features of the conformation, material genomes become less certain. Increasing nonuniformity of boundary conditions and the size of random field correlation lengths exacerbate this conclusion. These criteria are combined into a scalar metric used to assess the impact of archetype-level uncertainties on the material genome for general scenarios in solid mechanics. Exemplary benchmark problems include bending in elastoplasticity and instability-induced pattern transition in porous elastomer. The contributions of this dissertation are threefold: (1) the mathematical construction of a new continuum theory for mechanics and physics of solids, (2) implementation of the theory, and (3) theoretical assessment of the scenarios in which material genomes deviate from determinism.

Alignment of Teacher-Developed Curricula and National Standards in Qatar's National Education Reform

ERIC Educational Resources Information Center

Nasser, Ramzi; Zaki, Eman; Allen, Nancy; Al Mula, Badria; Al Mutawaha, Fatma; Al Bin Ali, Hessa; Kerr, Tricia

2014-01-01

This study investigated the degree to which teacher developed curriculum was aligned with the national standards in Qatar. Three sources of data included teacher response to a questionnaire, teacher interviews and expert rating of the alignment of teacher-developed materials with curriculum standards. A survey and interview questions measured…

Boron Nitride Coated Carbon Nanotube Arrays with Enhanced Compressive Mechanical Property

NASA Astrophysics Data System (ADS)

Jing, Lin; Tay, Roland Yingjie; Li, Hongling; Tsang, Siu Hon; Tan, Dunlin; Zhang, Bowei; Tok, Alfred Iing Yoong; Teo, Edwin Hang Tong

Vertically aligned carbon nanotube (CNT) array is one of the most promising energy dissipating materials due to its excellent temperature invariant mechanical property. However, the CNT arrays with desirable recoverability after compression is still a challenge. Here, we report on the mechanical enhancement of the CNT arrays reinforced by coating with boron nitride (BN) layers. These BN coated CNT (BN/CNT) arrays exhibit excellent compressive strength and recoverability as compared to those of the as-prepared CNT arrays which totally collapsed after compression. In addition, the BN coating also provides better resistance to oxidation due to its intrinsic thermal stability. This work presented here opens a new pathway towards tuning mechanical behavior of any arbitrary CNT arrays for promising potential such as damper, vibration isolator and shock absorber applications.

Magnetic properties of hybrid elastomers with magnetically hard fillers: rotation of particles

NASA Astrophysics Data System (ADS)

Stepanov, G. V.; Borin, D. Yu; Bakhtiiarov, A. V.; Storozhenko, P. A.

2017-03-01

Hybrid magnetic elastomers belonging to the family of magnetorheological elastomers contain magnetically hard components and are of the utmost interest for the development of semiactive and active damping devices as well as actuators and sensors. The processes of magnetizing of such elastomers are accompanied by structural rearrangements inside the material. When magnetized, the elastomer gains its own magnetic moment resulting in changes of its magneto-mechanical properties, which remain permanent, even in the absence of external magnetic fields. Influenced by the magnetic field, magnetized particles move inside the matrix forming chain-like structures. In addition, the magnetically hard particles can rotate to align their magnetic moments with the new direction of the external field. Such an elastomer cannot be demagnetized by the application of a reverse field.

First principles investigations of the electronic structure and chemical bonding of U3Si2C2 - A uranium silicide-carbide with the rare [SiC] unit

NASA Astrophysics Data System (ADS)

Matar, S. F.; Pöttgen, R.

2012-10-01

The electronic structure of U3Si2C2, with the rare [SiC] unit is examined from ab initio with an assessment of the properties of chemical bonding. We show that plain GGA fails describing the experimental lattice parameters and the electronic structure. A better agreement with experiment (crystal determination and magnetic properties) is obtained with the GGA + U method and U = 4 eV. The energy-volume equation of state and the set of elastic constants are obtained showing incompressibility along the c-axis with U-C-Si alignment and a brittle material. Bonding of U1 and U2 selectively with Si and C and Si-C bonds are remarkable

Supporting Excellence: A Framework for Developing, Implementing, and Sustaining a High-Quality District Curriculum. First Edition

ERIC Educational Resources Information Center

Council of the Great City Schools, 2017

2017-01-01

In the ongoing effort to improve instructional standards in our nation's urban public schools, the Council of the Great City Schools has released resources to help districts determine the quality and alignment of instructional materials at each grade level; to ensure that materials for English language learners are rigorous and aligned to district…

Effect of cadmium telluride quantum dots on the dielectric and electro-optical properties of ferroelectric liquid crystals.

PubMed

Kumar, A; Biradar, A M

2011-04-01

We present here the dielectric and electro-optical studies of cadmium telluride quantum dots (CdTe QDs) doped ferroelectric liquid crystals (FLCs). It has been observed that the doping of CdTe QDs not only induced a pronounced memory effect but also affected the physical parameters of FLC material (LAHS19). The modifications in the physical parameters and memory effect of LAHS19 are found to depend on the concentration ratio of CdTe QDs. The lower concentration of CdTe QDs (1-3 wt%) enhanced the values of spontaneous polarization and rotational viscosity of LAHS19 material but did not favor the memory effect, whereas a higher concentration of CdTe QDs (>5 wt%) degraded the alignment of LAHS19 material. The doping of ∼5 wt% of CdTe QDs is found to be the most suitable for achieving good memory effect without significantly affecting the material parameters. ©2011 American Physical Society

Mechanical Design of Carbon Ion Optics

NASA Technical Reports Server (NTRS)

Haag, Thomas

2005-01-01

Carbon Ion Optics are expected to provide much longer thruster life due to their resistance to sputter erosion. There are a number of different forms of carbon that have been used for fabricating ion thruster optics. The mechanical behavior of carbon is much different than that of most metals, and poses unique design challenges. In order to minimize mission risk, the behavior of carbon must be well understood, and components designed within material limitations. Thermal expansion of the thruster structure must be compatible with thermal expansion of the carbon ion optics. Specially designed interfaces may be needed so that grid gap and aperture alignment are not adversely affected by dissimilar material properties within the thruster. The assembled thruster must be robust and tolerant of launch vibration. The following paper lists some of the characteristics of various carbon materials. Several past ion optics designs are discussed, identifying strengths and weaknesses. Electrostatics and material science are not emphasized so much as the mechanical behavior and integration of grid electrodes into an ion thruster.

Interface Engineering of Monolayer MoS2/GaN Hybrid Heterostructure: Modified Band Alignment for Photocatalytic Water Splitting Application by Nitridation Treatment.

PubMed

Zhang, Zhaofu; Qian, Qingkai; Li, Baikui; Chen, Kevin J

2018-05-23

Interface engineering is a key strategy to deal with the two-dimensional (2D)/three-dimensional (3D) hybrid heterostructure, since the properties of this atomic-layer-thick 2D material can easily be impacted by the substrate environment. In this work, the structural, electronic, and optical properties of the 2D/3D heterostructure of monolayer MoS 2 on wurtzite GaN surface without and with nitridation interfacial layer are systematically investigated by first-principles calculation and experimental analysis. The nitridation interfacial layer can be introduced into the 2D/3D heterostructure by remote N 2 plasma treatment to GaN sample surface prior to stacking monolayer MoS 2 on top. The calculation results reveal that the 2D/3D integrated heterostructure is energetically favorable with a negative formation energy. Both interfaces demonstrate indirect band gap, which is a benefit for longer lifetime of the photoexcited carriers. Meanwhile, the conduction band edge and valence band edge of the MoS 2 side increases after nitridation treatment. The modification to band alignment is then verified by X-ray photoelectron spectroscopy measurement on MoS 2 /GaN heterostructures constructed by a modified wet-transfer technique, which indicates that the MoS 2 /GaN heterostructure without nitridation shows a type-II alignment with a conduction band offset (CBO) of only 0.07 eV. However, by the deployment of interface nitridation, the band edges of MoS 2 move upward for ∼0.5 eV as a result of the nitridized substrate property. The significantly increased CBO could lead to better electron accumulation capability at the GaN side. The nitridized 2D/3D heterostructure with effective interface treatment exhibits a clean band gap and substantial optical absorption ability and could be potentially used as practical photocatalyst for hydrogen generation by water splitting using solar energy.

Superior Thermal Interface via Vertically Aligned Carbon Nanotubes Grown on Graphite Foils

DTIC Science & Technology

2012-01-01

accepted 12 November 2012) In an attempt to study the thermal transport at the interface between nanotubes and graphene, vertically aligned multiwalled...tually increases the thermal barrier in a significant manner. On the other hand, thermal transport properties of thermal tapes and thermally conductive...aforementioned study achieved superior thermal transport properties, the processing and scale-up of the developed process would be prohibitively

Phosphorene quantum dot-fullerene nanocomposites for solar energy conversion: An unexplored inorganic-organic nanohybrid with novel photovoltaic properties

NASA Astrophysics Data System (ADS)

Rajbanshi, Biplab; Kar, Moumita; Sarkar, Pallavi; Sarkar, Pranab

2017-10-01

Using the self-consistent charge density-functional based tight-binding (SCC-DFTB) method, coupled with time-dependent density functional theory (TDDFT) calculations, for the first time we explore the possibility of use of phosphorene quantum dots in solar energy harvesting devices. The phosphorene quantum dots-fullerene (PQDs-PCBA) nanocomposites show type-II band alignment indicating spatial separation of charge carriers. The TDDFT calculations also show that the PQD-fullerene nanocomposites seem to be exciting material for future generation solar energy harvester, with extremely fast charge transfer and very poor recombination rate.

Transverse thermal conductivity of porous materials made from aligned nano- and microcylindrical pores

NASA Astrophysics Data System (ADS)

Prasher, Ravi

2006-09-01

Nanoporous and microporous materials made from aligned cylindrical pores play important roles in present technologies and will play even bigger roles in future technologies. The insight into the phonon thermal conductivity of these materials is important and relevant in many technologies and applications. Since the mean free path of phonons can be comparable to the pore size and interpore distance, diffusion-approximation based effective medium models cannot be used to predict the thermal conductivity of these materials. Strictly speaking, the Boltzmann transport equation (BTE) must be solved to capture the ballistic nature of thermal transport; however, solving BTE in such a complex network of pores is impractical. As an alternative, we propose an approximate ballistic-diffusive microscopic effective medium model for predicting the thermal conductivity of phonons in two-dimensional nanoporous and microporous materials made from aligned cylindrical pores. The model captures the size effects due to the pore diameter and the interpore distance and reduces to diffusion-approximation based models for macroporous materials. The results are in good agreement with experimental data.

Probing photoresponse of aligned single-walled carbon nanotube doped ultrathin MoS2.

PubMed

Wang, Rui; Wang, Tianjiao; Hong, Tu; Xu, Ya-Qiong

2018-08-24

We report a facile method to produce ultrathin molybdenum disulfide (MoS 2 ) hybrids with polarized near-infrared (NIR) photoresponses, in which horizontally-aligned single-walled carbon nanotubes (SWNTs) are integrated with single- and few-layer MoS 2 through a two-step chemical vapor deposition process. The photocurrent generation mechanisms in SWNT-MoS 2 hybrids are systematically investigated through wavelength- and polarization-dependent scanning photocurrent measurements. When the incident photon energy is above the direct bandgap of MoS 2 , isotropic photocurrent signals are observed, which can be primarily attributed to the direct bandgap transition in MoS 2 . In contrast, if the incident photon energy in the NIR region is below the direct bandgap of MoS 2 , the maximum photocurrent response occurs when the incident light is polarized in the direction along the SWNTs, indicating that photocurrent signals mainly result from the anisotropic absorption of SWNTs. More importantly, these two-dimensional (2D) hybrid structures inherit the electrical transport properties from MoS 2 , displaying n-type characteristics at a zero gate voltage. These fundamental studies provide a new way to produce ultrathin MoS 2 hybrids with inherited electrical properties and polarized NIR photoresponses, opening doors for engineering various 2D hybrid materials for future broadband optoelectronic applications.

Silk Fibroin Degradation Related to Rheological and Mechanical Properties.

PubMed

Partlow, Benjamin P; Tabatabai, A Pasha; Leisk, Gary G; Cebe, Peggy; Blair, Daniel L; Kaplan, David L

2016-05-01

Regenerated silk fibroin has been proposed as a material substrate for biomedical, optical, and electronic applications. Preparation of the silk fibroin solution requires extraction (degumming) to remove contaminants, but results in the degradation of the fibroin protein. Here, a mechanism of fibroin degradation is proposed and the molecular weight and polydispersity is characterized as a function of extraction time. Rheological analysis reveals significant changes in the viscosity of samples while mechanical characterization of cast and drawn films shows increased moduli, extensibility, and strength upon drawing. Fifteen minutes extraction time results in degraded fibroin that generates the strongest films. Structural analysis by wide angle X-ray scattering (WAXS) and Fourier transform infrared spectroscopy (FTIR) indicates molecular alignment in the drawn films and shows that the drawing process converts amorphous films into the crystalline, β-sheet, secondary structure. Most interesting, by using selected extraction times, films with near-native crystallinity, alignment, and molecular weight can be achieved; yet maximal mechanical properties for the films from regenerated silk fibroin solutions are found with solutions subjected to some degree of degradation. These results suggest that the regenerated solutions and the film casting and drawing processes introduce more complexity than native spinning processes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Template-free synthesis of multifunctional carbonaceous microcone forests

NASA Astrophysics Data System (ADS)

Wang, Qiang; Yang, Lei; Dai, Bing; Bai, Jie; Yang, Zhenhuai; Guo, Shuai; He, Yurong; Han, Jiecai; Zhu, Jiaqi

2018-01-01

Forests of vertically aligned carbonaceous microcones are fabricated directly on a nickel mesh by microwave-plasma-assisted chemical vapor deposition. The microstructure is formed through a simple one-step process involving self-assembly. The fabricated composite exhibits superhydrophobicity and superoleophilicity as well as low density, owing to which it floats on water and can be used for the in-situ separation of oil from water at the oil/water interface. Furthermore, the composite exhibits pH responsivity, and its water permeability can be varied simply by altering the pH of the aqueous solution. In addition, the composite is suitable for use as an electrode material for supercapacitors owing to its large geometric surface area, porous structure, and superior electrical properties, which allow for fast ion and electron transportation. Thus, this composite consisting of forests of vertically aligned carbonaceous microcones on a nickel mesh is expected to find use in a wide range of fields and applications, including in environmental cleanup, flow switches, and energy storage devices.

Patterned Well-Aligned ZnO Nanorods Assisted with Polystyrene Monolayer by Oxygen Plasma Treatment.

PubMed

Choi, Hyun Ji; Lee, Yong-Min; Yu, Jung-Hoon; Hwang, Ki-Hwan; Boo, Jin-Hyo

2016-08-05

Zinc oxide is known as a promising material for sensing devices due to its piezoelectric properties. In particular, the alignment of ZnO nanostructures into ordered nanoarrays is expected to improve the device sensitivity due to the large surface area which can be utilized to capture significant quantities of gas particles. However, ZnO nanorods are difficult to grow on the quartz substrate with well-ordered shape. So, we investigated nanostructures by adjusting the interval distance of the arranged ZnO nanorods using polystyrene (PS) spheres of various sizes (800 nm, 1300 nm and 1600 nm). In addition, oxygen plasma treatment was used to specify the nucleation site of round, patterned ZnO nanorod growth. Therefore, ZnO nanorods were grown on a quartz substrate with a patterned polystyrene monolayer by the hydrothermal method after oxygen plasma treatment. The obtained ZnO nanostructures were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscope (FE-SEM).

Acoustic plane wave preferential orientation of metal oxide superconducting materials

DOEpatents

Tolt, Thomas L.; Poeppel, Roger B.

1991-01-01

A polycrystalline metal oxide such as YBa.sub.2 Cu.sub.3 O.sub.7-X (where 0

Correlation between micrometer-scale ripple alignment and atomic-scale crystallographic orientation of monolayer graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Jin Sik; Chang, Young Jun; Woo, Sungjong

Deformation normal to the surface is intrinsic in two-dimensional materials due to phononic thermal fluctuations at finite temperatures. Graphene's negative thermal expansion coefficient is generally explained by such an intrinsic property. Recently, friction measurements on graphene exfoliated on a silicon oxide surface revealed an anomalous anisotropy whose origin was believed to be the formation of ripple domains. Here, we uncover the atomistic origin of the observed friction domains using a cantilever torsion microscopy in conjunction with angle-resolved photoemission spectroscopy. We experimentally demonstrate that ripples on graphene are formed along the zigzag direction of the hexagonal lattice. The formation of zigzagmore » directional ripple is consistent with our theoretical model that takes account of the atomic-scale bending stiffness of carbon-carbon bonds and the interaction of graphene with the substrate. Lastly, the correlation between micrometer-scale ripple alignment and atomic-scale arrangement of exfoliated monolayer graphene is first discovered and suggests a practical tool for measuring lattice orientation of graphene.« less

Correlation between micrometer-scale ripple alignment and atomic-scale crystallographic orientation of monolayer graphene

DOE PAGES

Choi, Jin Sik; Chang, Young Jun; Woo, Sungjong; ...

2014-12-01

Deformation normal to the surface is intrinsic in two-dimensional materials due to phononic thermal fluctuations at finite temperatures. Graphene's negative thermal expansion coefficient is generally explained by such an intrinsic property. Recently, friction measurements on graphene exfoliated on a silicon oxide surface revealed an anomalous anisotropy whose origin was believed to be the formation of ripple domains. Here, we uncover the atomistic origin of the observed friction domains using a cantilever torsion microscopy in conjunction with angle-resolved photoemission spectroscopy. We experimentally demonstrate that ripples on graphene are formed along the zigzag direction of the hexagonal lattice. The formation of zigzagmore » directional ripple is consistent with our theoretical model that takes account of the atomic-scale bending stiffness of carbon-carbon bonds and the interaction of graphene with the substrate. Lastly, the correlation between micrometer-scale ripple alignment and atomic-scale arrangement of exfoliated monolayer graphene is first discovered and suggests a practical tool for measuring lattice orientation of graphene.« less

Correlation between micrometer-scale ripple alignment and atomic-scale crystallographic orientation of monolayer graphene.

PubMed

Choi, Jin Sik; Chang, Young Jun; Woo, Sungjong; Son, Young-Woo; Park, Yeonggu; Lee, Mi Jung; Byun, Ik-Su; Kim, Jin-Soo; Choi, Choon-Gi; Bostwick, Aaron; Rotenberg, Eli; Park, Bae Ho

2014-12-01

Deformation normal to the surface is intrinsic in two-dimensional materials due to phononic thermal fluctuations at finite temperatures. Graphene's negative thermal expansion coefficient is generally explained by such an intrinsic property. Recently, friction measurements on graphene exfoliated on a silicon oxide surface revealed an anomalous anisotropy whose origin was believed to be the formation of ripple domains. Here, we uncover the atomistic origin of the observed friction domains using a cantilever torsion microscopy in conjunction with angle-resolved photoemission spectroscopy. We experimentally demonstrate that ripples on graphene are formed along the zigzag direction of the hexagonal lattice. The formation of zigzag directional ripple is consistent with our theoretical model that takes account of the atomic-scale bending stiffness of carbon-carbon bonds and the interaction of graphene with the substrate. The correlation between micrometer-scale ripple alignment and atomic-scale arrangement of exfoliated monolayer graphene is first discovered and suggests a practical tool for measuring lattice orientation of graphene.

Synergistic toughening of composite fibres by self-alignment of reduced graphene oxide and carbon nanotubes.

PubMed

Shin, Min Kyoon; Lee, Bommy; Kim, Shi Hyeong; Lee, Jae Ah; Spinks, Geoffrey M; Gambhir, Sanjeev; Wallace, Gordon G; Kozlov, Mikhail E; Baughman, Ray H; Kim, Seon Jeong

2012-01-31

The extraordinary properties of graphene and carbon nanotubes motivate the development of methods for their use in producing continuous, strong, tough fibres. Previous work has shown that the toughness of the carbon nanotube-reinforced polymer fibres exceeds that of previously known materials. Here we show that further increased toughness results from combining carbon nanotubes and reduced graphene oxide flakes in solution-spun polymer fibres. The gravimetric toughness approaches 1,000 J g(-1), far exceeding spider dragline silk (165 J g(-1)) and Kevlar (78 J g(-1)). This toughness enhancement is consistent with the observed formation of an interconnected network of partially aligned reduced graphene oxide flakes and carbon nanotubes during solution spinning, which act to deflect cracks and allow energy-consuming polymer deformation. Toughness is sensitive to the volume ratio of the reduced graphene oxide flakes to the carbon nanotubes in the spinning solution and the degree of graphene oxidation. The hybrid fibres were sewable and weavable, and could be shaped into high-modulus helical springs.

Deformation behavior and mechanical analysis of vertically aligned carbon nanotube (VACNT) bundles

NASA Astrophysics Data System (ADS)

Hutchens, Shelby B.

Vertically aligned carbon nanotubes (VACNTs) serve as integral components in a variety of applications including MEMS devices, energy absorbing materials, dry adhesives, light absorbing coatings, and electron emitters, all of which require structural robustness. It is only through an understanding of VACNT's structural mechanical response and local constitutive stress-strain relationship that future advancements through rational design may take place. Even for applications in which the structural response is not central to device performance, VACNTs must be sufficiently robust and therefore knowledge of their microstructure-property relationship is essential. This thesis first describes the results of in situ uniaxial compression experiments of 50 micron diameter cylindrical bundles of these complex, hierarchical materials as they undergo unusual deformation behavior. Most notably they deform via a series of localized folding events, originating near the bundle base, which propagate laterally and collapse sequentially from bottom to top. This deformation mechanism accompanies an overall foam-like stress-strain response having elastic, plateau, and densification regimes with the addition of undulations in the stress throughout the plateau regime that correspond to the sequential folding events. Microstructural observations indicate the presence of a strength gradient, due to a gradient in both tube density and alignment along the bundle height, which is found to play a key role in both the sequential deformation process and the overall stress-strain response. Using the complicated structural response as both motivation and confirmation, a finite element model based on a viscoplastic solid is proposed. This model is characterized by a flow stress relation that contains an initial peak followed by strong softening and successive hardening. Analysis of this constitutive relation results in capture of the sequential buckling phenomenon and a strength gradient effect. This combination of experimental and modeling approaches motivates discussion of the particular microstructural mechanisms and local material behavior that govern the non-trivial energy absorption via sequential, localized buckle formation in the VACNT bundles.

Surface-restrained growth of vertically aligned carbon nanotube arrays with excellent thermal transport performance.

PubMed

Ping, Linquan; Hou, Peng-Xiang; Liu, Chang; Li, Jincheng; Zhao, Yang; Zhang, Feng; Ma, Chaoqun; Tai, Kaiping; Cong, Hongtao; Cheng, Hui-Ming

2017-06-22

A vertically aligned carbon nanotube (VACNT) array is a promising candidate for a high-performance thermal interface material in high-power microprocessors due to its excellent thermal transport property. However, its rough and entangled free tips always cause poor interfacial contact, which results in serious contact resistance dominating the total thermal resistance. Here, we employed a thin carbon cover to restrain the disorderly growth of the free tips of a VACNT array. As a result, all the free tips are seamlessly connected by this thin carbon cover and the top surface of the array is smoothed. This unique structure guarantees the participation of all the carbon nanotubes in the array in the heat transport. Consequently the VACNT array grown on a Cu substrate shows a record low thermal resistance of 0.8 mm 2 K W -1 including the two-sided contact resistances, which is 4 times lower than the best result previously reported. Remarkably, the VACNT array can be easily peeled away from the Cu substrate and act as a thermal pad with excellent flexibility, adhesive ability and heat transport capability. As a result the CNT array with a thin carbon cover shows great potential for use as a high-performance flexible thermal interface material.

Dry contact transfer printing of aligned carbon nanotube patterns and characterization of their optical properties for diameter distribution and alignment.

PubMed

Pint, Cary L; Xu, Ya-Qiong; Moghazy, Sharief; Cherukuri, Tonya; Alvarez, Noe T; Haroz, Erik H; Mahzooni, Salma; Doorn, Stephen K; Kono, Junichiro; Pasquali, Matteo; Hauge, Robert H

2010-02-23

A scalable and facile approach is demonstrated where as-grown patterns of well-aligned structures composed of single-walled carbon nanotubes (SWNT) synthesized via water-assisted chemical vapor deposition (CVD) can be transferred, or printed, to any host surface in a single dry, room-temperature step using the growth substrate as a stamp. We demonstrate compatibility of this process with multiple transfers for large-scale device and specifically tailored pattern fabrication. Utilizing this transfer approach, anisotropic optical properties of the SWNT films are probed via polarized absorption, Raman, and photoluminescence spectroscopies. Using a simple model to describe optical transitions in the large SWNT species present in the aligned samples, polarized absorption data are demonstrated as an effective tool for accurate assignment of the diameter distribution from broad absorption features located in the infrared. This can be performed on either well-aligned samples or unaligned doped samples, allowing simple and rapid feedback of the SWNT diameter distribution that can be challenging and time-consuming to obtain in other optical methods. Furthermore, we discuss challenges in accurately characterizing alignment in structures of long versus short carbon nanotubes through optical techniques, where SWNT length makes a difference in the information obtained in such measurements. This work provides new insight to the efficient transfer and optical properties of an emerging class of long, large diameter SWNT species typically produced in the CVD process.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reigel, M. M.; Fowley, M. D.; Pickenheim, B. R.

A soft metal with low wear resistance (6000 series aluminum), was used to minimize run time while maximizing wear rate. Two paddle configurations were tested, with the first four paddles after the augers replaced by the wear paddles. The first configuration was all flat paddles, with the first paddle not aligned with the augers and is consistent with present SPF mixer. The second configuration had helical paddles for the first three stages after the augers and a flat paddle at the fourth stage. The first helical paddle was aligned with the auger flight for the second configuration. The all flatmore » paddle configuration wear rate was approximately double the wear rate of the helical paddles for the first two sets of paddles after the augers. For both configurations, there was little or no wear on the third and fourth paddle sets based on mass change, indicating that the fully wetted premix materials are much less abrasive than the un-wetted or partially wetted premix. Additionally, inspection of the wear surface of the paddles at higher magnification showed the flat paddles were worn much more than the helical and is consistent with the wear rates. Aligning the auger discharge flight with the first set of helical paddles was effective in reducing the wear rate as compared to the flat paddle configuration. Changing the paddle configuration from flat to helical resulted in a slight increase in rheological properties. Although, both tests produced grout-like material that is within the processing rage of the SPF, it should be noted that cement is not included in the premix and water was used rather than salt solution, which does affect the rheology of the fresh grout. The higher rheological properties from the helical wear test are most likely due to the reduced number of shearing paddles in the mixer. In addition, there is variation in the rheological data for each wear test. This is most likely due to the way that the dry feeds enter the mixer from the dry feeder. The premix is discharged from the hopper in an unsteady fashion, where irregular sized clumps were observed leaving the discharge of the auger, though the auger speed is constant.« less

An anisotropically and heterogeneously aligned patterned electrospun scaffold with tailored mechanical property and improved bioactivity for vascular tissue engineering.

PubMed

Xu, He; Li, Haiyan; Ke, Qinfei; Chang, Jiang

2015-04-29

The development of vascular scaffolds with controlled mechanical properties and stimulatory effects on biological activities of endothelial cells still remains a significant challenge to vascular tissue engineering. In this work, we reported an innovative approach to prepare a new type of vascular scaffolds with anisotropically and heterogeneously aligned patterns using electrospinning technique with unique wire spring templates, and further investigated the structural effects of the patterned electrospun scaffolds on mechanical properties and angiogenic differentiation of human umbilical vein endothelial cells (HUVECs). Results showed that anisotropically aligned patterned nanofibrous structure was obtained by depositing nanofibers on template in a structurally different manner, one part of nanofibers densely deposited on the embossments of wire spring and formed cylindrical-like structures in the transverse direction, while others loosely suspended and aligned along the longitudinal direction, forming a three-dimensional porous microstructure. We further found that such structures could efficiently control the mechanical properties of electrospun vascular scaffolds in both longitudinal and transverse directions by altering the interval distances between the embossments of patterned scaffolds. When HUVECs were cultured on scaffolds with different microstructures, the patterned scaffolds distinctively promoted adhesion of HUVECs at early stage and proliferation during the culture period. Most importantly, cells experienced a large shape change associated with cell cytoskeleton and nuclei remodeling, leading to a stimulatory effect on angiogenesis differentiation of HUVECs by the patterned microstructures of electrospun scaffolds, and the scaffolds with larger distances of intervals showed a higher stimulatory effect. These results suggest that electrospun scaffolds with the anisotropically and heterogeneously aligned patterns, which could efficiently control the mechanical properties and bioactivities of the scaffolds, might have great potential in vascular tissue engineering application.

Piezoelectric Response of Aligned Electrospun Polyvinylidene Fluoride/Carbon Nanotube Nanofibrous Membranes.

PubMed

Wu, Chang-Mou; Chou, Min-Hui; Zeng, Wun-Yuan

2018-06-10

Polyvinylidene fluoride (PVDF) shows piezoelectricity related to its β-phase content and mechanical and electrical properties influenced by its morphology and crystallinity. Electrospinning (ES) can produce ultrafine and well-aligned PVDF nanofibers. In this study, the effects of the presence of carbon nanotubes (CNT) and optimized ES parameters on the crystal structures and piezoelectric properties of aligned PVDF/CNT nanofibrous membranes were examined. The optimal β content and piezoelectric coefficient (d 33 ) of the aligned electrospun PVDF reached 88% and 27.4 pC/N; CNT addition increased the β-phase content to 89% and d 33 to 31.3 pC/N. The output voltages of piezoelectric units with aligned electrospun PVDF/CNT membranes increased linearly with applied loading and showed good stability during cyclic dynamic compression and tension. The sensitivities of the piezoelectric units with the membranes under dynamic compression and tension were 2.26 mV/N and 4.29 mV/%, respectively. In bending tests, the output voltage increased nonlinearly with bending angle because complicated forces were involved. The output of the aligned membrane-based piezoelectric unit with CNT was 1.89 V at the bending angle of 100°. The high electric outputs indicate that the aligned electrospun PVDF/CNT membranes are potentially effective for flexible wearable sensor application with high sensitivity.

Mechanically Oriented 3D Collagen Hydrogel for Directing Neurite Growth.

PubMed

Antman-Passig, Merav; Levy, Shahar; Gartenberg, Chaim; Schori, Hadas; Shefi, Orit

2017-05-01

Recent studies in the field of neuro-tissue engineering have demonstrated the promising effects of aligned contact guidance cue to scaffolds of enhancement and direction of neuronal growth. In vivo, neurons grow and develop neurites in a complex three-dimensional (3D) extracellular matrix (ECM) surrounding. Studies have utilized hydrogel scaffolds derived from ECM molecules to better simulate natural growth. While many efforts have been made to control neuronal growth on 2D surfaces, the development of 3D scaffolds with an elaborate oriented topography to direct neuronal growth still remains a challenge. In this study, we designed a method for growing neurons in an aligned and oriented 3D collagen hydrogel. We aligned collagen fibers by inducing controlled uniaxial strain on gels. To examine the collagen hydrogel as a suitable scaffold for neuronal growth, we evaluated the physical properties of the hydrogel and measured collagen fiber properties. By combining the neuronal culture in 3D collagen hydrogels with strain-induced alignment, we were able to direct neuronal growth in the direction of the aligned collagen matrix. Quantitative evaluation of neurite extension and directionality within aligned gels was performed. The analysis showed neurite growth aligned with collagen matrix orientation, while maintaining the advantageous 3D growth.

Processing and characterization of phase boundaries in ceramic and metallic materials

NASA Astrophysics Data System (ADS)

Zeng, Liang

The goal of this dissertation work was to explore and describe advanced characterization of novel materials processing. These characterizations were carried out using scanning and transmission electron microscopy (SEM and TEM), and X-ray diffraction techniques. The materials studied included ceramics and metallic materials. The first part of this dissertation focuses on the processing, and the resulting interfacial microstructure of ceramics joined using spin-on interlayers. SEM, TEM, and indentation tests were used to investigate the interfacial microstructural and mechanical property evolution of polycrystalline zirconia bonded to glass ceramic MaCor(TM), and polycrystalline alumina to single crystal alumina. Interlayer assisted specimens were joined using a thin amorphous silica interlayer. This interlayer was produced by spin coating an organic based silica bond material precursor and curing at 200°C, followed by joining in a microwave cavity or conventional electric furnace. Experimental results indicate that in the joining of the zirconia and MaCor(TM) no significant interfacial microstructural and mechanical property differences developed between materials joined either with or without interlayers, due to the glassy nature of MaCor(TM). The bond interface was non-planar, as a result of the strong wetting of MaCor(TM) and silica and dissolution of the zirconia. However, without the aid of a silica interlayer, sapphire and 98% polycrystalline alumina failed to join under the experimental conditions under this study. A variety of interfacial morphologies have been observed, including amorphous regions, fine crystalline alumina, and intimate contact between the sapphire and polycrystalline alumina. In addition, the evolution of the joining process from the initial sputter-cure to the final joining state and joining mechanisms were characterized. The second part of this dissertation focused on the effects of working and heat treatment on microstructure, texture, phase boundary movement, and mechanical property evolution in Ti-6Al-4V wire. The as-received wire consisted of equilibrium a and metastable beta phases and had a moderately strong fiber texture with prism plane normals aligned with the wire axis. The wire was worked by extrusion, solution heat-treatment and water quenching, and aging. The extrusion process strengthened the as-received texture. After solutionization and quenching, microstrucual observations showed the presence of many needlelike martensitic platelets in the prior beta phase regions. Texture analysis revealed that a secondary fiber with basal plane normals aligned with the wire axis emerged at the expense of the initial texture, indicating that highly preferred phase boundary motion (variant selection) occurred during the beta → alpha transformation. The strength of the variant selection consistently increased with solutionization temperature and time. In addition, the effects of dislocation type and density on variant selections were further investigated. This implies that strategic prior deformation and heat treatment can be exploited to design the resulting texture and microstructure and consequently optimize the properties of titanium products.

Vertically aligned single-walled carbon nanotubes by chemical assembly--methodology, properties, and applications.

PubMed

Diao, Peng; Liu, Zhongfan

2010-04-06

Single-walled carbon nanotubes (SWNTs), as one of the most promising one-dimension nanomaterials due to its unique structure, peculiar chemical, mechanical, thermal, and electronic properties, have long been considered as an important building block to construct ordered alignments. Vertically aligned SWNTs (v-SWNTs) have been successfully prepared by using direct growth and chemical assembly strategies. In this review, we focus explicitly on the v-SWNTs fabricated via chemical assembly strategy. We provide the readers with a full and systematic summary covering the advances in all aspects of this area, including various approaches for the preparation of v-SWNTs using chemical assembly techniques, characterization, assembly kinetics, and electrochemical properties of v-SWNTs. We also review the applications of v-SWNTs in electrochemical and bioelectrochemical sensors, photoelectric conversion, and scanning probe microscopy.

Preparation of Monodomain Liquid Crystal Elastomers and Liquid Crystal Elastomer Nanocomposites.

PubMed

Kim, Hojin; Zhu, Bohan; Chen, Huiying; Adetiba, Oluwatomiyin; Agrawal, Aditya; Ajayan, Pulickel; Jacot, Jeffrey G; Verduzco, Rafael

2016-02-06

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and as soft robots. Here, we demonstrate the preparation of shape-responsive liquid crystal elastomers (LCEs) and LCE nanocomposites along with characterization of their shape-responsiveness, mechanical properties, and microstructure. Two types of LCEs - polysiloxane-based and epoxy-based - are synthesized, aligned, and characterized. Polysiloxane-based LCEs are prepared through two crosslinking steps, the second under an applied load, resulting in monodomain LCEs. Polysiloxane LCE nanocomposites are prepared through the addition of conductive carbon black nanoparticles, both throughout the bulk of the LCE and to the LCE surface. Epoxy-based LCEs are prepared through a reversible esterification reaction. Epoxy-based LCEs are aligned through the application of a uniaxial load at elevated (160 °C) temperatures. Aligned LCEs and LCE nanocomposites are characterized with respect to reversible strain, mechanical stiffness, and liquid crystal ordering using a combination of imaging, two-dimensional X-ray diffraction measurements, differential scanning calorimetry, and dynamic mechanical analysis. LCEs and LCE nanocomposites can be stimulated with heat and/or electrical potential to controllably generate strains in cell culture media, and we demonstrate the application of LCEs as shape-responsive substrates for cell culture using a custom-made apparatus.

Band Alignment and Charge Transfer in Complex Oxide Interfaces

NASA Astrophysics Data System (ADS)

Zhong, Zhicheng; Hansmann, Philipp

2017-01-01

The synthesis of transition metal heterostructures is currently one of the most vivid fields in the design of novel functional materials. In this paper, we propose a simple scheme to predict band alignment and charge transfer in complex oxide interfaces. For semiconductor heterostructures, band-alignment rules like the well-known Anderson or Schottky-Mott rule are based on comparison of the work function or electron affinity of the bulk components. This scheme breaks down for oxides because of the invalidity of a single work-function approximation as recently shown in [Phys. Rev. B 93, 235116 (2016), 10.1103/PhysRevB.93.235116; Adv. Funct. Mater. 26, 5471 (2016), 10.1002/adfm.201600243]. Here, we propose a new scheme that is built on a continuity condition of valence states originating in the compounds' shared network of oxygen. It allows for the prediction of sign and relative amplitude of the intrinsic charge transfer, taking as input only information about the bulk properties of the components. We support our claims by numerical density functional theory simulations as well as (where available) experimental evidence. Specific applications include (i) controlled doping of SrTiO3 layers with the use of 4 d and 5 d transition metal oxides and (ii) the control of magnetic ordering in manganites through tuned charge transfer.

Collagen-PVA aligned nanofiber on collagen sponge as bi-layered scaffold for surface cartilage repair.

PubMed

Lin, Hsin-Yi; Tsai, Wen-Chi; Chang, Shih-Hsing

2017-05-01

Researchers have made bi-layered scaffolds but mostly for osteochondral repairs. The anatomic structure of human cartilage has different zones and that each has varying matrix morphology and mechanical properties is often overlooked. Two bi-layered collagen-based composites were made to replicate the superficial and transitional zones of an articular cartilage. Aligned and random collagen-PVA nanofibers were electrospun onto a freeze-dried collagen sponge to make the aligned and random composites, respectively. The morphology, swelling ratio, degradation and tensile properties of the two composites were examined. Primary porcine chondrocytes were cultured on the composites for three weeks and their proliferation and secretion of glycosaminoglycan (GAG) and type II collagen were measured. The influences of the cell culture on the tensile properties of the composites were studied. The nanofiber layer remained adhered to the sponge after three weeks of cell culture. Both composites lost 30-35% of their total weight in a saline buffer after three weeks. The tensile strength and Young's modulus of both composites increased after three weeks of chondrocyte culture (p < 0.05). The aligned composite with extracellular matrix deposition had a Young's modulus (0.35 MPa) similar to that of articular cartilage reported in literature (0.36-0.8 MPa). The chondrocytes on both aligned and random composites proliferated and secreted similar amounts of GAG and type II collagen. They were seen embedded in lacunae after three weeks. The aligned composite may be more suitable for articular cartilage repair because of the higher tensile strength from the aligned nanofibers on the surface that can better resist wear.

Low-temperature growth of aligned ZnO nanorods: effect of annealing gases on the structural and optical properties.

PubMed

Umar, Ahmad; Hahn, Yoon-Bong; Al-Hajry, A; Abaker, M

2014-06-01

Aligned ZnO nanorods were grown on ZnO/Si substrate via simple aqueous solution process at low-temperature of - 65 degrees C by using zinc nitrate and hexamethylenetetramine (HMTA). The detailed morphological and structural properties measured by FESEM, XRD, EDS and TEM confirmed that the as-grown nanorods are vertically aligned, well-crystalline possessing wurtzite hexagonal phase and grown along the [0001] direction. The room-temperature photoluminescence spectrum of the grown nanorods exhibited a strong and broad green emission and small ultraviolet emission. The as-prepared ZnO nanorods were post-annealed in nitrogen (N2) and oxygen (O2) environments and further characterized in terms of their morphological, structural and optical properties. After annealing the nanorods exhibit well-crystallinity and wurtzite hexagonal phase. Moreover, by annealing the PL spectra show the enhancement in the UV emission and suppression in the green emission. The presented results demonstrate that simply by post-annealing process, the optical properties of ZnO nanostructures can be controlled.

High volume production of nanostructured materials

DOEpatents

Ripley, Edward B [Knoxville, TN; Morrell, Jonathan S [Knoxville, TN; Seals, Roland D [Oak Ridge, TN; Ludtka, Gerard M [Oak Ridge, TN

2009-10-13

A system and method for high volume production of nanoparticles, nanotubes, and items incorporating nanoparticles and nanotubes. Microwave, radio frequency, or infrared energy vaporizes a metal catalyst which, as it condenses, is contacted by carbon or other elements such as silicon, germanium, or boron to form agglomerates. The agglomerates may be annealed to accelerate the production of nanotubes. Magnetic or electric fields may be used to align the nanotubes during their production. The nanotubes may be separated from the production byproducts in aligned or non-aligned configurations. The agglomerates may be formed directly into tools, optionally in compositions that incorporate other materials such as abrasives, binders, carbon-carbon composites, and cermets.

Methods for high volume production of nanostructured materials

DOEpatents

Ripley, Edward B [Knoxville, TN; Morrell, Jonathan S [Knoxville, TN; Seals, Roland D [Oak Ridge, TN; Ludtka, Gerald M [Oak Ridge, TN

2011-03-22

A system and method for high volume production of nanoparticles, nanotubes, and items incorporating nanoparticles and nanotubes. Microwave, radio frequency, or infrared energy vaporizes a metal catalyst which, as it condenses, is contacted by carbon or other elements such as silicon, germanium, or boron to form agglomerates. The agglomerates may be annealed to accelerate the production of nanotubes. Magnetic or electric fields may be used to align the nanotubes during their production. The nanotubes may be separated from the production byproducts in aligned or non-aligned configurations. The agglomerates may be formed directly into tools, optionally in compositions that incorporate other materials such as abrasives, binders, carbon-carbon composites, and cermets.

Impact of materials engineering on edge placement error (Conference Presentation)

NASA Astrophysics Data System (ADS)

Freed, Regina; Mitra, Uday; Zhang, Ying

2017-04-01

Transistor scaling has transitioned from wavelength scaling to multi-patterning techniques, due to the resolution limits of immersion of immersion lithography. Deposition and etch have enabled scaling in the by means of SADP and SAQP. Spacer based patterning enables extremely small linewidths, sufficient for several future generations of transistors. However, aligning layers in Z-direction, as well as aligning cut and via patterning layers, is becoming a road-block due to global and local feature variation and fidelity. This presentation will highlight the impact of deposition and etch on this feature alignment (EPE) and illustrate potential paths toward lowering EPE using material engineering.

Simultaneous ultrasound and photoacoustics based flow cytometry

NASA Astrophysics Data System (ADS)

Gnyawali, Vaskar; Strohm, Eric M.; Tsai, Scott S. H.; Kolios, Michael C.

2018-04-01

We have developed a flow cytometer based on simultaneous detection of ultrasound and photoacoustic waves from individual particles/cells flowing in a microfluidic channel. Our polydimethylsiloxane (PDMS) based hydrodynamic 3-dimensional (3D) flow-focusing microfluidic device contains a cross-junction channel, a micro-needle (ID 100 μm and OD 200 μm) insert, and a 3D printed frame to hold and align a high frequency (center frequency 375 MHz) ultrasound transducer. The focused flow passes through a narrow focal zone with lateral and axial focal lengths of 6-8 μm and 15-20 μm, respectively. Both the lateral and axial alignments are achieved by screwing the transducer to the frame onto the PDMS device. Individual particles pass through an interrogation zone in the microfluidic channel with a collinearly aligned ultrasound transducer and a focused 532 nm wavelength laser beam. The particles are simultaneously insonified by high-frequency ultrasound and irradiated by a laser beam. The ultrasound backscatter and laser generated photoacoustic waves are detected for each passing particle. The backscattered ultrasound and photoacoustic signal are strongly dependent on the size, morphology, mechanical properties, and material properties of the flowing particles; these parameters can be extracted by analyzing unique features in the power spectrum of the signals. Frequencies less than 100 MHz do not have these unique spectral signatures. We show that we can reliably distinguish between different particles in a sample using the acoustic-based flow cytometer. This technique, when extended to biomedical applications, allows us to rapidly analyze the spectral signatures from individual single cells of a large cell population, with applications towards label-free detection and characterization of healthy and diseased cells.

Electrospun Polycaprolactone Scaffolds for Small-Diameter Tissue Engineered Blood Vessels

NASA Astrophysics Data System (ADS)

Lee, Carol Hsiu-Yueh

Cardiovascular disease is the leading cause of death in the United States with many patients requiring coronary artery bypass grafting. The current standard is using autografts such as the saphenous vein or intimal mammary artery, however creating a synthetic graft could eliminate this painful and inconvenient procedure. Large diameter grafts have long been established with materials such as DacronRTM and TeflonRTM, however these materials have not proved successful in small-diameter (< 6 mm) grafts where thrombosis and intimal hyperplasia are common in graft failure. With the use of a synthetic biodegradable polymer (polycaprolactone) we utilize our expertise in electrospinning and femtosecond laser ablation to create a novel tri-layered tissue engineered blood vessel containing microchannels. The benefits of creating a tri-layer is to mimic native arteries that contain an endothelium to prevent thrombosis in the inner layer, aligned smooth muscle cells in the middle to control vasodilation and constriction, and a mechanically robust outer layer. The following work evaluates the mechanical properties of such a graft (tensile, fatigue, burst pressure, and suture retention strength), the ability to rapidly align cells in laser ablated microchannels in PCL scaffolds, and the biological integration (co-culture of endothelial and smooth muscle cells) with electrospun PCL scaffolds. The conclusions from this work establish that the electrospun tri-layers provide adequate mechanical strength as a tissue engineered blood vessel, that laser ablated microchannels are able to contain the smooth muscle cells, and that cells are able to adhere to PCL fibers. However, future work includes adjusting microchannel dimensions to properly align smooth muscle cells along with perfect co-cultures of endothelial and smooth muscle cells on the electrospun tri-layer.

Intrinsic alignments in redMaPPer clusters - I. Central galaxy alignments and angular segregation of satellites

NASA Astrophysics Data System (ADS)

Huang, Hung-Jin; Mandelbaum, Rachel; Freeman, Peter E.; Chen, Yen-Chi; Rozo, Eduardo; Rykoff, Eli; Baxter, Eric J.

2016-11-01

The shapes of cluster central galaxies are not randomly oriented, but rather exhibit coherent alignments with the shapes of their parent clusters as well as with the surrounding large-scale structures. In this work, we aim to identify the galaxy and cluster quantities that most strongly predict the central galaxy alignment phenomenon among a large parameter space with a sample of 8237 clusters and 94 817 members within 0.1 < z < 0.35, based on the red-sequence Matched-filter Probabilistic Percolation cluster catalogue constructed from the Sloan Digital Sky Survey. We first quantify the alignment between the projected central galaxy shapes and the distribution of member satellites, to understand what central galaxy and cluster properties most strongly correlate with these alignments. Next, we investigate the angular segregation of satellites with respect to their central galaxy major axis directions, to identify the satellite properties that most strongly predict their angular segregation. We find that central galaxies are more aligned with their member galaxy distributions in clusters that are more elongated and have higher richness, and for central galaxies with larger physical size, higher luminosity and centring probability, and redder colour. Satellites with redder colour, higher luminosity, located closer to the central galaxy, and with smaller ellipticity show a stronger angular segregation towards their central galaxy major axes. Finally, we provide physical explanations for some of the identified correlations, and discuss the connection to theories of central galaxy alignments, the impact of primordial alignments with tidal fields, and the importance of anisotropic accretion.

Intrinsic alignments in redMaPPer clusters – I. Central galaxy alignments and angular segregation of satellites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Hung -Jin; Mandelbaum, Rachel; Freeman, Peter E.

The shapes of cluster central galaxies are not randomly oriented, but rather exhibit coherent alignments with the shapes of their parent clusters as well as with the surrounding large-scale structures. In this work, we aim to identify the galaxy and cluster quantities that most strongly predict the central galaxy alignment phenomenon among a large parameter space with a sample of 8237 clusters and 94 817 members within 0.1 < z < 0.35, based on the red-sequence Matched-filter Probabilistic Percolation cluster catalogue constructed from the Sloan Digital Sky Survey. We first quantify the alignment between the projected central galaxy shapes andmore » the distribution of member satellites, to understand what central galaxy and cluster properties most strongly correlate with these alignments. Next, we investigate the angular segregation of satellites with respect to their central galaxy major axis directions, to identify the satellite properties that most strongly predict their angular segregation. We find that central galaxies are more aligned with their member galaxy distributions in clusters that are more elongated and have higher richness, and for central galaxies with larger physical size, higher luminosity and centring probability, and redder colour. Satellites with redder colour, higher luminosity, located closer to the central galaxy, and with smaller ellipticity show a stronger angular segregation towards their central galaxy major axes. Lastly, we provide physical explanations for some of the identified correlations, and discuss the connection to theories of central galaxy alignments, the impact of primordial alignments with tidal fields, and the importance of anisotropic accretion.« less

Intrinsic alignments in redMaPPer clusters – I. Central galaxy alignments and angular segregation of satellites

DOE PAGES

Huang, Hung -Jin; Mandelbaum, Rachel; Freeman, Peter E.; ...

2016-08-11

The shapes of cluster central galaxies are not randomly oriented, but rather exhibit coherent alignments with the shapes of their parent clusters as well as with the surrounding large-scale structures. In this work, we aim to identify the galaxy and cluster quantities that most strongly predict the central galaxy alignment phenomenon among a large parameter space with a sample of 8237 clusters and 94 817 members within 0.1 < z < 0.35, based on the red-sequence Matched-filter Probabilistic Percolation cluster catalogue constructed from the Sloan Digital Sky Survey. We first quantify the alignment between the projected central galaxy shapes andmore » the distribution of member satellites, to understand what central galaxy and cluster properties most strongly correlate with these alignments. Next, we investigate the angular segregation of satellites with respect to their central galaxy major axis directions, to identify the satellite properties that most strongly predict their angular segregation. We find that central galaxies are more aligned with their member galaxy distributions in clusters that are more elongated and have higher richness, and for central galaxies with larger physical size, higher luminosity and centring probability, and redder colour. Satellites with redder colour, higher luminosity, located closer to the central galaxy, and with smaller ellipticity show a stronger angular segregation towards their central galaxy major axes. Lastly, we provide physical explanations for some of the identified correlations, and discuss the connection to theories of central galaxy alignments, the impact of primordial alignments with tidal fields, and the importance of anisotropic accretion.« less

Functional Alignment of Metabolic Networks.

PubMed

Mazza, Arnon; Wagner, Allon; Ruppin, Eytan; Sharan, Roded

2016-05-01

Network alignment has become a standard tool in comparative biology, allowing the inference of protein function, interaction, and orthology. However, current alignment techniques are based on topological properties of networks and do not take into account their functional implications. Here we propose, for the first time, an algorithm to align two metabolic networks by taking advantage of their coupled metabolic models. These models allow us to assess the functional implications of genes or reactions, captured by the metabolic fluxes that are altered following their deletion from the network. Such implications may spread far beyond the region of the network where the gene or reaction lies. We apply our algorithm to align metabolic networks from various organisms, ranging from bacteria to humans, showing that our alignment can reveal functional orthology relations that are missed by conventional topological alignments.

Functionalization of vertically aligned carbon nanotubes.

PubMed

Van Hooijdonk, Eloise; Bittencourt, Carla; Snyders, Rony; Colomer, Jean-François

2013-01-01

This review focuses and summarizes recent studies on the functionalization of carbon nanotubes oriented perpendicularly to their substrate, so-called vertically aligned carbon nanotubes (VA-CNTs). The intrinsic properties of individual nanotubes make the VA-CNTs ideal candidates for integration in a wide range of devices, and many potential applications have been envisaged. These applications can benefit from the unidirectional alignment of the nanotubes, the large surface area, the high carbon purity, the outstanding electrical conductivity, and the uniformly long length. However, practical uses of VA-CNTs are limited by their surface characteristics, which must be often modified in order to meet the specificity of each particular application. The proposed approaches are based on the chemical modifications of the surface by functionalization (grafting of functional chemical groups, decoration with metal particles or wrapping of polymers) to bring new properties or to improve the interactions between the VA-CNTs and their environment while maintaining the alignment of CNTs.

Functionalization of vertically aligned carbon nanotubes

PubMed Central

Snyders, Rony; Colomer, Jean-François

2013-01-01

Summary This review focuses and summarizes recent studies on the functionalization of carbon nanotubes oriented perpendicularly to their substrate, so-called vertically aligned carbon nanotubes (VA-CNTs). The intrinsic properties of individual nanotubes make the VA-CNTs ideal candidates for integration in a wide range of devices, and many potential applications have been envisaged. These applications can benefit from the unidirectional alignment of the nanotubes, the large surface area, the high carbon purity, the outstanding electrical conductivity, and the uniformly long length. However, practical uses of VA-CNTs are limited by their surface characteristics, which must be often modified in order to meet the specificity of each particular application. The proposed approaches are based on the chemical modifications of the surface by functionalization (grafting of functional chemical groups, decoration with metal particles or wrapping of polymers) to bring new properties or to improve the interactions between the VA-CNTs and their environment while maintaining the alignment of CNTs. PMID:23504581

Investigation of the magnetic properties of Nd-Fe-B based hard magnetic materials

NASA Astrophysics Data System (ADS)

Grössinger, R.; Hilscher, G.; Kirchmayr, H.; Sassik, H.; Strnat, R.; Wiesinger, G.

1985-05-01

Nd-Fe-B type magnets were prepared by a melt spinning technique. The resulting ribbons were used as starting material for plastic bonded aligned powder magnets. The hard magnetic properties were studied in static fields up to 50 kG as well as in pulsed fields up to 150 kG. The coercivity measured on ribbons ( 1H' c) was found for high values to be larger than that obtained from the plastic bonded magnets ( 1Hc), which we attribute to the influence of the grinding procedure. The anisotropy field HA determined by applying the SPD (Singular Point Detection) technique, was found (for υ < 13 m/s) to depend strongly on the wheel velocity υ, however for velocities exceeding this value, HA remained essentially constant (∼ 75 kG). Mössbauer spectra were recorded at room as well as at liquid helium temperature. The different shape of the respective spectra reflects the change of the easy axis with temperature. A phase analysis performed by computer fitting the spectra showed that the amount of Fe-precipitates influences the formation of the coercivity.

Optically Tunable Chiral Plasmonic Guest-Host Cellulose Films Weaved with Long-range Ordered Silver Nanowires.

PubMed

Chu, Guang; Wang, Xuesi; Chen, Tianrui; Gao, Jianxiong; Gai, Fangyuan; Wang, Yu; Xu, Yan

2015-06-10

Plasmonic materials with large chiroptical activity at visible wavelength have attracted considerable attention due to their potential applications in metamaterials. Here we demonstrate a novel guest-host chiral nematic liquid crystal film composed of bulk self-co-assembly of the dispersed plasmonic silver nanowires (AgNWs) and cellulose nanocrystals (CNCs). The AgNWs-CNCs composite films show strong plasmonic optical activities, that are dependent on the chiral photonic properties of the CNCs host medium and orientation of the guest AgNWs. Tunable chiral distribution of the aligned anisotropic AgNWs with long-range order is obtained through the CNCs liquid crystal mediated realignment. The chiral plasmonic optical activity of the AgNWs-CNCs composite films can be tuned by changing the interparticle electrostatic repulsion between the CNCs nanorods and AgNWs. We also observe an electromagnetic energy transfer phenomena among the plasmonic bands of AgNWs, due to the modulation of the photonic band gap of the CNCs host matrix. This facile approach for fabricating chiral macrostructured plasmonic materials with optically tunable property is of interest for a variety of advanced optics applications.

Theory of electrical conductivity and dielectric permittivity of highly aligned graphene-based nanocomposites.

PubMed

Xia, Xiaodong; Hao, Jia; Wang, Yang; Zhong, Zheng; Weng, George J

2017-05-24

Highly aligned graphene-based nanocomposites are of great interest due to their excellent electrical properties along the aligned direction. Graphene fillers in these composites are not necessarily perfectly aligned, but their orientations are highly confined to a certain angle, [Formula: see text] with 90° giving rise to the randomly oriented state and 0° to the perfectly aligned one. Recent experiments have shown that electrical conductivity and dielectric permittivity of highly aligned graphene-polymer nanocomposites are strongly dependent on this distribution angle, but at present no theory seems to exist to address this issue. In this work we present a new effective-medium theory that is derived from the underlying physical process including the effects of graphene orientation, filler loading, aspect ratio, percolation threshold, interfacial tunneling, and Maxwell-Wagner-Sillars polarization, to determine these two properties. The theory is formulated in the context of preferred orientational average. We highlight this new theory with an application to rGO/epoxy nanocomposites, and demonstrate that the calculated in-plane and out-of-plane conductivity and permittivity are in agreement with the experimental data as the range of graphene orientations changes from the randomly oriented to the highly aligned state. We also show that the percolation thresholds of highly aligned graphene nanocomposites are in general different along the planar and the normal directions, but they converge into a single one when the statistical distribution of graphene fillers is spherically symmetric.

Influence of binding material of PZT coating on microresonator's electrical and mechanical properties

NASA Astrophysics Data System (ADS)

Janusas, Giedrius; Guobiene, Asta; Palevicius, Arvydas; Brunius, Alfredas; Cekas, Elingas; Baltrusaitis, Valentinas; Sakalys, Rokas

2017-06-01

Microresonators are fundamental components integrated in hosts of MEMS applications: covering the automotive sector, the telecommunication industry, electronic equipment for surface/material characterization and motion sensing, and etc. The aim of this paper is to investigate the mechanical and electrical properties of PZT film fabricated with three binding materials: polyvinyl butyral (PVB), polymethyl methacrylate (PMMA) and polystyrene (PS) and to evaluate applicability in control of microresonators Q factor. Micro particles of PZT powder were mixed with 20% solution of PVB, PMMA and PS in benzyl alcohol. For investigation of mechanical and electrical properties multilayer cantilevers were made. Obtained PZT and polymer paste was screen printed on copper (thickness 40 μm) using polyester monofilament screen meshes (layer thickness 50 μm) and dried for 30 min at 100°C. Electric dipoles of the PZT particles in composite material were aligned using high voltage generator (5 kV) and a custom-made holder. Electric field was held for 30 min. Surfaces of the applied films were investigated by Atomic Force Microscope NanoWizard(R)3 NanoScience. Dynamic and electrical characteristics of the multilayer were investigated using laser triangular displacement sensor LK-G3000. The measured vibration amplitude and generated electrical potential was collected with USB oscilloscope PicoScope 3424. As the results showed, these cantilevers were able to transform mechanical strain energy into electric potential and, v.v. However, roughness of PZT coatings with PMMA and PS were higher, what could be the reason of the worse quality of the top electrode. However, the main advantage of the created composite piezoelectric material is the possibility to apply it on any uniform or non-uniform vibrating surface and to transform low frequency vibrations into electricity.

Line-frequency doubling of directed self-assembly patterns for single-digit bit pattern media lithography

NASA Astrophysics Data System (ADS)

Patel, K. C.; Ruiz, R.; Lille, J.; Wan, L.; Dobiz, E.; Gao, H.; Robertson, N.; Albrecht, T. R.

2012-03-01

Directed self-assembly is emerging as a promising technology to define sub-20nm features. However, a straightforward path to scale block copolymer lithography to single-digit fabrication remains challenging given the diverse material properties found in the wide spectrum of self-assembling materials. A vast amount of block copolymer research for industrial applications has been dedicated to polystyrene-b-methyl methacrylate (PS-b-PMMA), a model system that displays multiple properties making it ideal for lithography, but that is limited by a weak interaction parameter that prevents it from scaling to single-digit lithography. Other block copolymer materials have shown scalability to much smaller dimensions, but at the expense of other material properties that could delay their insertion into industrial lithographic processes. We report on a line doubling process applied to block copolymer patterns to double the frequency of PS-b-PMMA line/space features, demonstrating the potential of this technique to reach single-digit lithography. We demonstrate a line-doubling process that starts with directed self-assembly of PS-b-PMMA to define line/space features. This pattern is transferred into an underlying sacrificial hard-mask layer followed by a growth of self-aligned spacers which subsequently serve as hard-masks for transferring the 2x frequency doubled pattern to the underlying substrate. We applied this process to two different block copolymer materials to demonstrate line-space patterns with a half pitch of 11nm and 7nm underscoring the potential to reach single-digit critical dimensions. A subsequent patterning step with perpendicular lines can be used to cut the fine line patterns into a 2-D array of islands suitable for bit patterned media. Several integration challenges such as line width control and line roughness are addressed.

Preferential orientation of metal oxide superconducting materials by mechanical means

DOEpatents

Capone, Donald W.

1990-01-01

A superconductor comprised of a polycrystalline metal oxide such as YBa.sub.2 Cu.sub.3 O.sub.7-X (where 0<.times.<0.5) is capable of accommodating very large current densities. By aligning the two-dimensional Cu--O layers which carry the current in the superconducting state in the a- and b-directions, i.e., within the basal plane, a high degree of crystalline axes alignment is provided between adjacent grains permitting the metal oxide material to accommodate high current densities. The orthorhombic crystalline particles have a tendency to lie down on one of the longer sides, i.e., on the a- or b-direction. Aligning the crystals in this orientation is accomplished by mechanical working of the material such as by extrusion, tape casting or slip casting, provided a single crystal powder is used as a starting material, to provide a highly oriented, e.g., approximately 90% of the crystal particles have a common orientation, superconducting matrix capable of supporting large current densities.

Preferential orientation of metal oxide superconducting materials by mechanical means

DOEpatents

Capone, D.W.

1990-11-27

A superconductor comprised of a polycrystalline metal oxide such as YBa[sub 2]Cu[sub 3]O[sub 7[minus]X] (where 0 < X < 0.5) is capable of accommodating very large current densities. By aligning the two-dimensional Cu-O layers which carry the current in the superconducting state in the a- and b-directions, i.e., within the basal plane, a high degree of crystalline axes alignment is provided between adjacent grains permitting the metal oxide material to accommodate high current densities. The orthorhombic crystalline particles have a tendency to lie down on one of the longer sides, i.e., on the a- or b-direction. Aligning the crystals in this orientation is accomplished by mechanical working of the material such as by extrusion, tape casting or slip casting, provided a single crystal powder is used as a starting material, to provide a highly oriented, e.g., approximately 90% of the crystal particles have a common orientation, superconducting matrix capable of supporting large current densities. 3 figs.

Nucleation, Growth, and Alignment of Poly(3-hexylthiophene) Nanofibers for High-Performance OFETs.

PubMed

Persson, Nils E; Chu, Ping-Hsun; McBride, Michael; Grover, Martha; Reichmanis, Elsa

2017-04-18

Conjugated semiconducting polymers have been the subject of intense study for over two decades with promising advances toward a printable electronics manufacturing ecosystem. These materials will deliver functional electronic devices that are lightweight, flexible, large-area, and cost-effective, with applications ranging from biomedical sensors to solar cells. Synthesis of novel molecules has led to significant improvements in charge carrier mobility, a defining electrical performance metric for many applications. However, the solution processing and thin film deposition of conjugated polymers must also be properly controlled to obtain reproducible device performance. This has led to an abundance of research on the process-structure-property relationships governing the microstructural evolution of the model semicrystalline poly(3-hexylthiophene) (P3HT) as applied to organic field effect transistor (OFET) fabrication. What followed was the production of an expansive body of work on the crystallization, self-assembly, and charge transport behavior of this semiflexible polymer whose strong π-π stacking interactions allow for highly creative methods of structural control, including the modulation of solvent and solution properties, flow-induced crystallization and alignment techniques, structural templating, and solid-state thermal and mechanical processing. This Account relates recent progress in the microstructural control of P3HT thin films through the nucleation, growth, and alignment of P3HT nanofibers. Solution-based nanofiber formation allows one to develop structural order prior to thin film deposition, mitigating the need for intricate deposition processes and enabling the use of batch and continuous chemical processing steps. Fiber growth is framed as a traditional crystallization problem, with the balance between nucleation and growth rates determining the fiber size and ultimately the distribution of grain boundaries in the solid state. Control of nucleation can be accomplished through a sonication-based seeding procedure, while growth can be modulated through supersaturation control via the tuning of solvent quality, the use of UV irradiation or through aging. These principles carry over to the flow-induced growth of P3HT nanofibers in a continuous microfluidic processing system, leading to thin films with significantly enhanced mobility. Further gains can be made by promoting long-range polymer chain alignment, achieved by depositing nanofibers through shear-based coating methods that promote high fiber packing density and alignment. All of these developments in processing were carried out on a standard OFET platform, enabling us to generalize quantitative structure-property relationships from structural data sources such as UV-vis, AFM, and GIWAXS. It is shown that a linear correlation exists between mobility and the in-plane orientational order of nanofibers, as extracted from AFM images using advanced computer vision software developed by our group. Herein, we discuss data-driven approaches to the determination of process-structure-property relationships, as well as the transferability of structural control strategies for P3HT to other conjugated polymer systems and applications.

Aggregate nanostructures of organic molecular materials.

PubMed

Liu, Huibiao; Xu, Jialiang; Li, Yongjun; Li, Yuliang

2010-12-21

Conjugated organic molecules are interesting materials because of their structures and their electronic, electrical, magnetic, optical, biological, and chemical properties. However, researchers continue to face great challenges in the construction of well-defined organic compounds that aggregate into larger molecular materials such as nanowires, tubes, rods, particles, walls, films, and other structural arrays. Such nanoscale materials could serve as direct device components. In this Account, we describe our recent progress in the construction of nanostructures formed through the aggregation of organic conjugated molecules and in the investigation of the optical, electrical, and electronic properties that depend on the size or morphology of these nanostructures. We have designed and synthesized functional conjugated organic molecules with structural features that favor assembly into aggregate nanostructures via weak intermolecular interactions. These large-area ordered molecular aggregate nanostructures are based on a variety of simpler structures such as fullerenes, perylenes, anthracenes, porphyrins, polydiacetylenes, and their derivatives. We have developed new methods to construct these larger structures including organic vapor-solid phase reaction, natural growth, association via self-polymerization and self-organization, and a combination of self-assembly and electrochemical growth. These methods are both facile and reliable, allowing us to produce ordered and aligned aggregate nanostructures, such as large-area arrays of nanowires, nanorods, and nanotubes. In addition, we can synthesize nanoscale materials with controlled properties. Large-area ordered aggregate nanostructures exhibit interesting electrical, optical, and optoelectronic properties. We also describe the preparation of large-area aggregate nanostructures of charge transfer (CT) complexes using an organic solid-phase reaction technique. By this process, we can finely control the morphologies and sizes of the organic nanostructures on wires, tubes, and rods. Through field emission studies, we demonstrate that the films made from arrays of CT complexes are a new kind of cathode materials, and we systematically investigate the effects of size and morphology on electrical properties. Low-dimension organic/inorganic hybrid nanostructures can be used to produce new classes of organic/inorganic solid materials with properties that are not observed in either the individual nanosize components or the larger bulk materials. We developed the combined self-assembly and templating technique to construct various nanostructured arrays of organic and inorganic semiconductors. The combination of hybrid aggregate nanostructures displays distinct optical and electrical properties compared with their individual components. Such hybrid structures show promise for applications in electronics, optics, photovoltaic cells, and biology. In this Account, we aim to provide an intuition for understanding the structure-function relationships in organic molecular materials. Such principles could lead to new design concepts for the development of new nonhazardous, high-performance molecular materials on aggregate nanostructures.

A method to integrate patterned electrospun fibers with microfluidic systems to generate complex microenvironments for cell culture applications

PubMed Central

Wallin, Patric; Zandén, Carl; Carlberg, Björn; Hellström Erkenstam, Nina; Liu, Johan; Gold, Julie

2012-01-01

The properties of a cell’s microenvironment are one of the main driving forces in cellular fate processes and phenotype expression invivo. The ability to create controlled cell microenvironments invitro becomes increasingly important for studying or controlling phenotype expression in tissue engineering and drug discovery applications. This includes the capability to modify material surface properties within well-defined liquid environments in cell culture systems. One successful approach to mimic extra cellular matrix is with porous electrospun polymer fiber scaffolds, while microfluidic networks have been shown to efficiently generate spatially and temporally defined liquid microenvironments. Here, a method to integrate electrospun fibers with microfluidic networks was developed in order to form complex cell microenvironments with the capability to vary relevant parameters. Spatially defined regions of electrospun fibers of both aligned and random orientation were patterned on glass substrates that were irreversibly bonded to microfluidic networks produced in poly-dimethyl-siloxane. Concentration gradients obtained in the fiber containing channels were characterized experimentally and compared with values obtained by computational fluid dynamic simulations. Velocity and shear stress profiles, as well as vortex formation, were calculated to evaluate the influence of fiber pads on fluidic properties. The suitability of the system to support cell attachment and growth was demonstrated with a fibroblast cell line. The potential of the platform was further verified by a functional investigation of neural stem cell alignment in response to orientation of electrospun fibers versus a microfluidic generated chemoattractant gradient of stromal cell-derived factor 1 alpha. The described method is a competitive strategy to create complex microenvironments invitro that allow detailed studies on the interplay of topography, substrate surface properties, and soluble microenvironment on cellular fate processes. PMID:23781291

Neurogenic differentiation of human umbilical cord mesenchymal stem cells on aligned electrospun polypyrrole/polylactide composite nanofibers with electrical stimulation

NASA Astrophysics Data System (ADS)

Zhou, Junfeng; Cheng, Liang; Sun, Xiaodan; Wang, Xiumei; Jin, Shouhong; Li, Junxiang; Wu, Qiong

2016-09-01

Adult central nervous system (CNS) tissue has a limited capacity to recover after trauma or disease. Recent medical cell therapy using polymeric biomaterialloaded stem cells with the capability of differentiation to specific neural population has directed focuses toward the recovery of CNS. Fibers that can provide topographical, biochemical and electrical cues would be attractive for directing the differentiation of stem cells into electro-responsive cells such as neuronal cells. Here we report on the fabrication of an electrospun polypyrrole/polylactide composite nanofiber film that direct or determine the fate of mesenchymal stem cells (MSCs), via combination of aligned surface topography, and electrical stimulation (ES). The surface morphology, mechanical properties and electric properties of the film were characterized. Comparing with that on random surface film, expression of neurofilament-lowest and nestin of human umbilical cord mesenchymal stemcells (huMSCs) cultured on film with aligned surface topography and ES were obviously enhanced. These results suggest that aligned topography combining with ES facilitates the neurogenic differentiation of huMSCs and the aligned conductive film can act as a potential nerve scaffold.

Interplay between spherical confinement and particle shape on the self-assembly of rounded cubes.

PubMed

Wang, Da; Hermes, Michiel; Kotni, Ramakrishna; Wu, Yaoting; Tasios, Nikos; Liu, Yang; de Nijs, Bart; van der Wee, Ernest B; Murray, Christopher B; Dijkstra, Marjolein; van Blaaderen, Alfons

2018-06-08

Self-assembly of nanoparticles (NPs) inside drying emulsion droplets provides a general strategy for hierarchical structuring of matter at different length scales. The local orientation of neighboring crystalline NPs can be crucial to optimize for instance the optical and electronic properties of the self-assembled superstructures. By integrating experiments and computer simulations, we demonstrate that the orientational correlations of cubic NPs inside drying emulsion droplets are significantly determined by their flat faces. We analyze the rich interplay of positional and orientational order as the particle shape changes from a sharp cube to a rounded cube. Sharp cubes strongly align to form simple-cubic superstructures whereas rounded cubes assemble into icosahedral clusters with additionally strong local orientational correlations. This demonstrates that the interplay between packing, confinement and shape can be utilized to develop new materials with novel properties.

Wire metamaterials: physics and applications.

PubMed

Simovski, Constantin R; Belov, Pavel A; Atrashchenko, Alexander V; Kivshar, Yuri S

2012-08-16

The physics and applications of a broad class of artificial electromagnetic materials composed of lattices of aligned metal rods embedded in a dielectric matrix are reviewed. Such structures are here termed wire metamaterials. They appear in various settings and can operate from microwaves to THz and optical frequencies. An important group of these metamaterials is a wire medium possessing extreme optical anisotropy. The study of wire metamaterials has a long history, however, most of their important and useful properties have been revealed and understood only recently, especially in the THz and optical frequency ranges where the wire media correspond to the lattices of microwires and nanowires, respectively. Another group of wire metamaterials are arrays and lattices of nanorods of noble metals whose unusual properties are driven by plasmonic resonances. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Controlled growth of vertically aligned carbon nanotubes on metal substrates

NASA Astrophysics Data System (ADS)

Gao, Zhaoli

Carbon nanotube (CNT) is a fascinating material with extraordinary electrical thermal and mechanical properties. Growing vertically aligned CNT (VACNT) arrays on metal substrates is an important step in bringing CNT into practical applications such as thermal interface materials (TIMs) and microelectrodes. However, the growth process is challenging due to the difficulties in preventing catalyst diffusion and controlling catalyst dewetting on metal substrates with physical surface heterogeneity. In this work, the catalyst diffusion mechanism and catalyst dewetting theory were studied for the controlled growth of VACNTs on metal substrates. The diffusion time of the catalyst, the diffusion coefficients for the catalyst in the substrate materials and the number density of catalyst nanoparticles after dewetting are identified as the key parameters, based on which three strategies are developed. Firstly, a fast-heating catalyst pretreatment strategy was used, aiming at preserving the amount of catalyst prior to CNT growth by reducing the catalyst diffusion time. The catalyst lifetime is extended from half an hour to one hour on a patterned Al thin film and a VACNT height of 106 mum, about twenty fold of that reported in the literature, was attained. Secondly, a diffusion barrier layer strategy is employed for a reduction of catalyst diffusion into the substrate materials. Enhancement of VACNT growth on Cu substrates was achieved by adopting a conformal Al2O 3 diffusion barrier layer fabricated by a specially designed atomic layer deposition (ALD) system. Lastly, a novel catalyst glancing angle deposition (GLAD) strategy is performed to manipulate the morphology of a relatively thick catalyst on metal substrates with physical surface heterogeneity, aiming to obtain uniform and dense catalyst nanoparticles after dewetting in the pretreatment process for enhanced VACNT growth. We are able to control the VACNT growth conditions on metal substrates in terms of their distribution, heights and alignments. Catalyst loss is controlled by the catalyst diffusion time and catalyst diffusion coefficients. A shorter catalyst diffusion time and smaller diffusion coefficient enhance VACNT growth on metals due to reduced catalyst loss during the pretreatment process. The dewetting behaviors of the thin film catalysts are influenced by the physical surface heterogeneity of the substrates which leads to non-uniform growth of VACNTs. The GLAD process facilitates the deposition of a relatively thick catalyst layer for the creation of dense and uniform catalyst nanoparticles. Applications of VACNT-metal structures in TIMs and microelectrodes are demonstrated. The VACNT-TIMs fabricated on Al alloy substrates have a typical thermal contact resistivity of 17.1 mm2˙K/W and their effective application in high-brightness LED thermal management was demonstrated. Electrochemical characterization was carried out on VACNT microelectrodes for the development of high resolution retinal prostheses and a satisfactory electrochemical property was again demonstrated.

Plasma treatment of p-GaN/n-ZnO nanorod light-emitting diodes

NASA Astrophysics Data System (ADS)

Leung, Yu Hang; Ng, Alan M. C.; Djurišic, Aleksandra B.; Chan, Wai Kin; Fong, Patrick W. K.; Lui, Hsien Fai; Surya, Charles

2014-03-01

Zinc oxide (ZnO) is a material of great interest for short-wavelength optoelectronic applications due to its wide band gap (3.37 eV) and high exciton binding energy (60 meV). Due to the difficulty in stable p-type doping of ZnO, other p-type materials such as gallium nitride (GaN) have been used to form heterojunctions with ZnO. p-GaN/n-ZnO heterojunction devices, in particular light-emitting diodes (LED) have been extensively studied. There was a huge variety of electronic properties and emission colors on the reported devices. It is due to the different energy alignment at the interface caused by different properties of the GaN layer and ZnO counterpart in the junction. Attempts have been made on modifying the heterojunction by various methods, such as introducing a dielectric interlayer and post-growth surface treatment, and changing the growth methods of ZnO. In this study, heterojunction LED devices with p-GaN and ZnO nanorods array are demonstrated. The ZnO nanorods were grown by a solution method. The ZnO nanorods were exposed to different kinds of plasma treatments (such as nitrogen and oxygen) after the growth. It was found that the treatment could cause significant change on the optical properties of the ZnO nanorods, as well as the electronic properties and light emissions of the resultant LED devices.

A Genome-Scale Investigation of How Sequence, Function, and Tree-Based Gene Properties Influence Phylogenetic Inference.

PubMed

Shen, Xing-Xing; Salichos, Leonidas; Rokas, Antonis

2016-09-02

Molecular phylogenetic inference is inherently dependent on choices in both methodology and data. Many insightful studies have shown how choices in methodology, such as the model of sequence evolution or optimality criterion used, can strongly influence inference. In contrast, much less is known about the impact of choices in the properties of the data, typically genes, on phylogenetic inference. We investigated the relationships between 52 gene properties (24 sequence-based, 19 function-based, and 9 tree-based) with each other and with three measures of phylogenetic signal in two assembled data sets of 2,832 yeast and 2,002 mammalian genes. We found that most gene properties, such as evolutionary rate (measured through the percent average of pairwise identity across taxa) and total tree length, were highly correlated with each other. Similarly, several gene properties, such as gene alignment length, Guanine-Cytosine content, and the proportion of tree distance on internal branches divided by relative composition variability (treeness/RCV), were strongly correlated with phylogenetic signal. Analysis of partial correlations between gene properties and phylogenetic signal in which gene evolutionary rate and alignment length were simultaneously controlled, showed similar patterns of correlations, albeit weaker in strength. Examination of the relative importance of each gene property on phylogenetic signal identified gene alignment length, alongside with number of parsimony-informative sites and variable sites, as the most important predictors. Interestingly, the subsets of gene properties that optimally predicted phylogenetic signal differed considerably across our three phylogenetic measures and two data sets; however, gene alignment length and RCV were consistently included as predictors of all three phylogenetic measures in both yeasts and mammals. These results suggest that a handful of sequence-based gene properties are reliable predictors of phylogenetic signal and could be useful in guiding the choice of phylogenetic markers. © The Author 2016. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.

Following in Real Time the Two-Step Assembly of Nanoparticles into Mesocrystals in Levitating Drops.

PubMed

Agthe, Michael; Plivelic, Tomás S; Labrador, Ana; Bergström, Lennart; Salazar-Alvarez, German

2016-11-09

Mesocrystals composed of crystallographically aligned nanocrystals are present in biominerals and assembled materials which show strongly directional properties of importance for mechanical protection and functional devices. Mesocrystals are commonly formed by complex biomineralization processes and can also be generated by assembly of anisotropic nanocrystals. Here, we follow the evaporation-induced assembly of maghemite nanocubes into mesocrystals in real time in levitating drops. Analysis of time-resolved small-angle X-ray scattering data and ex situ scanning electron microscopy together with interparticle potential calculations show that the substrate-free, particle-mediated crystallization process proceeds in two stages involving the formation and rapid transformation of a dense, structurally disordered phase into ordered mesocrystals. Controlling and tailoring the particle-mediated formation of mesocrystals could be utilized to assemble designed nanoparticles into new materials with unique functions.

Band alignment measurements at heterojunction interfaces in layered thin film solar cells & thermoelectrics

NASA Astrophysics Data System (ADS)

Fang, Fang

2011-12-01

Public awareness of the increasing energy crisis and the related serious environmental concerns has led to a significantly growing demand for alternative clean and renewable energy resources. Thin film are widely applied in multiple renewable energy devices owing to the reduced amount of raw materials and increase flexibility of choosing from low-cost candidates, which translates directly into reduced capital cost. This is a key driving force to make renewable technology competitive in the energy market. This thesis is focused on the measurement of energy level alignments at interfaces of thin film structures for renewable energy applications. There are two primary foci: II -VI semiconductor ZnSe/ZnTe thin film solar cells and Bi2Te3/Sb2Te3 thin film structures for thermoelectric applications. In both cases, the electronic structure and energy band alignment at interfaces usually controls the carrier transport behavior and determines the quality of the device. High-resolution photoemission spectroscopy (lab-based XPS & synchrotron-based UPS) was used to investigate the chemical and electronic properties of epitaxial Bi2Te3 and Sb2Te3 thin films, in order to validate the anticipated band alignment at interfaces in Bi 2Te3/Sb2Te3 superlattices as one favoring electron-transmission. A simple, thorough two-step treatment of a chemical etching in dilute hydrochloric acid solution and a subsequent annealing at ˜150°C under ultra-high vacuum environment is established to remove the surface oxides completely. It is an essential step to ensure the measurements on electronic states are acquired on stoichimetric, oxide-free clean surface of Bi 2Te3 and Sb2Te3 films. The direct measurement of valence band offsets (VBO) at a real Sb 2Te3/Bi2Te3 interface is designed based on the Kraut model; a special stacking film structure is prepared intentionally: sufficiently thin Sb2Te3 film on top of Bi2Te 3 that photoelectrons from both of them are collected simultaneously. From a combination of core levels and valence band ultraviolet photoemission spectra of the bulk materials as well as the heterojunction (Sb2Te 3/Bi2Te3), the VBO at p-type Sb2Te 3 and n-type Bi2Te3 is determined as 0.04 +/- 0.10 eV. Such a small energy offset is within the same magnitude of the thermal energy of kT, at room temperature. The motivation for the II-VI ZnTe-based thin film solar cell derives from the need to identify and overcome performance-limiting properties related to the processing of film deposition using close space sublimation (CSS). Chemical and electronic properties of the CSS grown ZnTe/ZnSe films were studied in x-ray diffraction, scanning electron microscopy and photoemission spectroscopy. Specifically, Se oxide was observed on the ZnSe surface, the removal of this oxide generated apparent offsets in the valence band and hence the alignment at the heterojunction energy diagram. Processing steps to mitigate oxidation yielded the best cells. Film structure was studied on the dependence of growth time; physical film damage is found during the initial stages when depositing ZnTe on a grown ZnSe film. Preliminary studies of films grown by evaporation and their characterizations are presented at last. In this thesis, a better understanding of the electronic structure at interfaces is built in two different thin film devices, and the resulting band energy diagram of the corresponding devices offered effective feedback in materials and device.The problem of energy equilibrium in the human body has received a great deal.

Materials science research in microgravity

NASA Technical Reports Server (NTRS)

Perepezko, John H.

1992-01-01

There are several important attributes of an extended duration microgravity environment that offer a new dimension in the control of the microstructure, processing, and properties of materials. First, when gravitational effects are minimized, buoyancy driven convection flows are also minimized. The flows due to density differences, brought about either by composition or temperature gradients will then be reduced or eliminated to permit a more precise control of the temperature and the composition of a melt which is critical in achieving high quality crystal growth of electronic materials or alloy structures. Secondly, body force effects such as sedimentation, hydrostatic pressure, and deformation are similarly reduced. These effects may interfere with attempts to produce uniformly dispersed or aligned second phases during melt solidification. Thirdly, operating in a microgravity environment will facilitate the containerless processing of melts to eliminate the limitations of containment for reactive melts. The noncontacting forces such as those developed from electromagnet, electrostatic, or acoustic fields can be used to position samples. With this mode of operation, contamination can be minimized to enable the study of reactive melts and to eliminate extraneous crystal nucleation so that novel crystalline structures and new glass compositions may be produced. In order to take advantage of the microgravity environment for materials research, it has become clear that reliable processing models based on a sound ground based experimental experience and an established thermophysical property data base are essential.

Cognitive training transfer using a personal computer-based game: A close quarters battle case study

NASA Astrophysics Data System (ADS)

Woodman, Michael D.

In this dissertation, liquid crystal (LC) materials and devices are investigated in order to meet the challenges for photonics and displays applications. We have studied three kinds of liquid crystal materials: positive dielectric anisotropic LCs, negative dielectric anisotropic LCs, and dual-frequency LCs. For the positive dielectric anisotropic LCs, we have developed some high birefringence isothiocyanato tolane LC compounds with birefringence ˜0.4, and super high birefringence isothiocyanato biphenyl-bistolane LC compounds with birefringence as high as ˜0.7. Moreover, we have studied the photostability of several high birefringence LC compounds, mixtures, and LC alignment layers in order to determine the failure mechanism concerning the lifetime of LC devices. Although cyano and isothiocyanato LC compounds have similar absorption peaks, the isothiocyanato compounds are more stable than their cyano counterparts under the same illumination conditions. This ultraviolet-durable performance of isothiocyanato compounds originates from its molecular structure and the delocalized electron distribution. We have investigated the alignment performance of negative dielectric anisotropic LCs in homeotropic (vertical aligned, VA) LC cell. Some (2, 3) laterally difluorinated biphenyls, terphenyls and tolanes are selected for this study. Due to the strong repulsive force between LCs and alignment layer, (2,3) laterally difluorinated terphenyls and tolanes do not align well in a VA cell resulting in a poor contrast ratio for the LC panel. We have developed a novel method to suppress the light leakage at dark state. By doping positive Deltaepsilon or non-polar LC compounds or mixtures into the host negative LC mixtures, the repulsive force is reduced and the cell exhibits an excellent dark state. In addition, these dopants increase the birefringence and reduce the viscosity of the host LCs which leads to a faster response time. In this dissertation, we investigate the dielectric heating effect of dual-frequency LCs. Because the absorption peak of imaginary dielectric constant occurs at high frequency region (˜ MHz), there is a heat generated when the LC cell is operated at a high frequency voltage. We have formulated a new dual-frequency LC mixture which greatly reduces the dielectric heating effect while maintaining good physical properties. Another achievement in this thesis is that we have developed a polarization independent phase modulator by using a negative dielectric anisotropic LC gel. (Abstract shortened by UMI.)

Controlled Synthesis and Functionalization of Vertically-Aligned Carbon Nanotubes for Multifunctional Applications

DTIC Science & Technology

2015-05-07

6 1.6 Lithium - Ion Batteries Based on Vertically-Aligned Carbon Nanotube Electrodes and Ionic...Cl, Br, or I) Prepared by Ball-Milling and Used as Anode Materials for Lithium - Ion Batteries ……………....................23 3.4 Well-Defined Two...9 1.6 Lithium - Ion Batteries Based on Vertically-Aligned Carbon Nanotube Electrodes and Ionic Liquid Electrolytes

Mercury-Cadmium-Telluride Focal Plane Array Performance Under Non-Standard Operating Conditions

NASA Technical Reports Server (NTRS)

Richardson, Brandon S.; Eastwood, Michael L.; Bruce, Carl F.; Green, Robert O.; Coles, J. B.

2011-01-01

This paper highlights a new technique that allows the Teledyne Scientific & Imaging LLC TCM6604A Mercury-Cadmium-Telluride (MCT) Focal Plane Array (FPA) to operate at room temperature. The Teledyne MCT FPA has been a standard in Imaging Spectroscopy since its creation in the 1980's. This FPA has been used in applications ranging from space instruments such as CRISM, M3 and ARTEMIS to airborne instruments such as MaRS and the Next Generation AVIRIS Instruments1. Precise focal plane alignment is always a challenge for such instruments. The current FPA alignment process results in multiple cold cycles requiring week-long durations, thereby increasing the risk and cost of a project. These alignment cycles are necessary because optimal alignment is approached incrementally and can only be measured with the FPA and Optics at standard operating conditions, requiring a cold instrument. Instruments using this FPA are normally cooled to temperatures below 150K for the MCT FPA to properly function. When the FPA is run at higher temperatures the dark current increases saturating the output. This paper covers the prospect of warm MCT FPA operation from a theoretical and experimental perspective. We discuss the empirical models and physical laws that govern MCT material properties and predict the optimal settings that will result in the best MCT PA performance at 300K. Theoretical results are then calculated for the proposed settings. We finally present the images and data obtained using the actual system with the warm MCT FPA settings. The paper concludes by emphasizing the strong positive correlation between the measured values and the theoretical results.

Extending the Cutoff Wavelength of Thermophotovoltaic Devices via Band Structure Engineering

NASA Astrophysics Data System (ADS)

Lee, Michael Steven

Complex oxides, solid-state compounds comprised of oxygen and at least two metal cations, are an intriguing class of materials for implementation into future microelectronic devices. They possess a wide range of functional properties, such as magnetism, ferroelectricity, and superconductivity, that can all be readily modified by their sensitivity to lattice strain, electronic and magnetic fields, chemical doping, and other external stimuli. This sensitivity makes complex oxides highly capable materials, but also introduces many technical challenges. The work of this dissertation has focused on extending our current knowledge of the magnetic materials properties and interfacial effects present in epitaxial films into micro- and nanoscale features. Ferromagnetic (FM) spin textures are arrangements of magnetic moments within such patterned features. Their switching behaviors are essential components of current data storage applications, and complex oxides are ideal candidates for future designs. In any materials system, the deviation from bulk or thin film properties when scaling down to nanostructures can be difficult to predict due to either size induced effects or consequences of the fabrication process itself. Therefore, these magnetic films and multilayers must be studied in the modified state to understand the challenges and opportunities associated with designing practical structures. Soft x-ray photoemission electron microscopy (X-PEEM) was used to observe and characterize the evolution of magnetic domain structure as a function of temperature in micromagnets patterned into epitaxial films of La0.7 Sr0.3MnO3 (LSMO). These images reveal the formation of novel spin textures that are a hybridization of well-described configurations, vortex and Landau, and emerge from the balance between fundamental materials parameters, micromagnet geometries, and epitaxial strain. Furthermore, slight perturbations to the lattice near the lithographically defined microstructure edges are shown to induce long range suppression of the magnetocrystalline anisotropy while other magnetic parameters, such as the saturation magnetization, remain unchanged. The results demonstrate how the magnetic domain state can be tailored through careful incorporation of these factors. Additional complexity is added to the system by interfacing LSMO with antiferromagnetic (AFM) LaFeO3 (LFO) or La0.7Sr 0.3FeO3 (LSFO). In unpatterned bilayers and superlattices, exchange coupling across the FM/AFM interface promotes a perpendicular alignment of the FM and AFM spin axes. Within patterned bilayers the alignment can be driven into a parallel configuration through changes in the micromagnet width, crystallographic orientation, and temperature. The importance of FM/AFM spin alignment is emphasized by magnetic reversal experiments of individual magnetic bits that demonstrate the coercivity can be adjusted over a wide range relative to LSMO single-layer micromagnets. In a superlattice of FM/AFM interfaces, the relative influence of the LSMO is reduced as the TC drops from 360 K to 80 K due to the ultra-thin sublayer thickness. Like the initial study on LSMO, the magnetocrystalline anisotropy of the LSFO layer is fully suppressed near microstructure edges, and the AFM domain configuration is entirely dictated by a magnetostatic-type effect in that region. This behavior persists both above and below the TC (with spin-flop coupling preserved) suggesting a new method to control AFM spin textures which are typically pinned to stochastic structural domains and defects and require large fields to manipulate.

Mechanical design of multiple zone plates precision alignment apparatus for hard X-ray focusing in twenty-nanometer scale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shu, Deming; Liu, Jie; Gleber, Sophie C.

An enhanced mechanical design of multiple zone plates precision alignment apparatus for hard x-ray focusing in a twenty-nanometer scale is provided. The precision alignment apparatus includes a zone plate alignment base frame; a plurality of zone plates; and a plurality of zone plate holders, each said zone plate holder for mounting and aligning a respective zone plate for hard x-ray focusing. At least one respective positioning stage drives and positions each respective zone plate holder. Each respective positioning stage is mounted on the zone plate alignment base frame. A respective linkage component connects each respective positioning stage and the respectivemore » zone plate holder. The zone plate alignment base frame, each zone plate holder and each linkage component is formed of a selected material for providing thermal expansion stability and positioning stability for the precision alignment apparatus.« less

Vertically aligned carbon nanotubes black coatings from roll-to-roll deposition process

NASA Astrophysics Data System (ADS)

Goislard de Monsabert, Thomas; Papciak, L.; Sangar, A.; Descarpentries, J.; Vignal, T.; de Longiviere, Xavier; Porterat, D.; Mestre, Q.; Hauf, H.

2017-09-01

Vertically aligned carbon nanotubes (VACNTs) have recently attracted growing interest as a very efficient light absorbing material over a broad spectral range making them a superior coating in space optics applications such as radiometry, optical calibration, and stray light elimination. However, VACNT coatings available to-date most often result from batch-to-batch deposition processes thus potentially limiting the manufacturing repeatability, substrate size and cost efficiency of this material.

Materials Science and Device Physics of 2-Dimensional Semiconductors

NASA Astrophysics Data System (ADS)

Fang, Hui

Materials and device innovations are the keys to future technology revolution. For MOSFET scaling in particular, semiconductors with ultra-thin thickness on insulator platform is currently of great interest, due to the potential of integrating excellent channel materials with the industrially mature Si processing. Meanwhile, ultra-thin thickness also induces strong quantum confinement which in turn affect most of the material properties of these 2-dimensional (2-D) semiconductors, providing unprecedented opportunities for emerging technologies. In this thesis, multiple novel 2-D material systems are explored. Chapter one introduces the present challenges faced by MOSFET scaling. Chapter two covers the integration of ultrathin III V membranes with Si. Free standing ultrathin III-V is studied to enable high performance III-V on Si MOSFETs with strain engineering and alloying. Chapter three studies the light absorption in 2-D membranes. Experimental results and theoretical analysis reveal that light absorption in the 2-D quantum membranes is quantized into a fundamental physical constant, where we call it the quantum unit of light absorption, irrelevant of most of the material dependent parameters. Chapter four starts to focus on another 2-D system, atomic thin layered chalcogenides. Single and few layered chalcogenides are first explored as channel materials, with focuses in engineering the contacts for high performance MOSFETs. Contact treatment by molecular doping methods reveals that many layered chalcogenides other than MoS2 exhibit good transport properties at single layer limit. Finally, Chapter five investigated 2-D van der Waals heterostructures built from different single layer chalcogenides. The investigation in a WSe2/MoS2 hetero-bilayer shows a large Stokes like shift between photoluminescence peak and lowest absorption peak, as well as strong photoluminescence intensity, consistent with spatially indirect transition in a type II band alignment in this van der Waals heterostructure. This result enables new family of semiconductor heterostructures having tunable optoelectronic properties with customized composite layers and highlights the ability to build van der Waals semiconductor heterostructure lasers/LEDs.

Minimizing performance degradation induced by interfacial recombination in perovskite solar cells through tailoring of the transport layer electronic properties

NASA Astrophysics Data System (ADS)

Xu, Liang; Molaei Imenabadi, Rouzbeh; Vandenberghe, William G.; Hsu, Julia W. P.

2018-03-01

The performance of hybrid organic-inorganic metal halide perovskite solar cells is investigated using one-dimensional drift-diffusion device simulations. We study the effects of interfacial defect density, doping concentration, and electronic level positions of the charge transport layer (CTL). Choosing CTLs with a favorable band alignment, rather than passivating CTL-perovskite interfacial defects, is shown to be beneficial for maintaining high power-conversion efficiency, due to reduced minority carrier density arising from a favorable local electric field profile. Insights from this study provide theoretical guidance on practical selection of CTL materials for achieving high-performance perovskite solar cells.

Graded junction termination extensions for electronic devices

NASA Technical Reports Server (NTRS)

Merrett, J. Neil (Inventor); Isaacs-Smith, Tamara (Inventor); Sheridan, David C. (Inventor); Williams, John R. (Inventor)

2006-01-01

A graded junction termination extension in a silicon carbide (SiC) semiconductor device and method of its fabrication using ion implementation techniques is provided for high power devices. The properties of silicon carbide (SiC) make this wide band gap semiconductor a promising material for high power devices. This potential is demonstrated in various devices such as p-n diodes, Schottky diodes, bipolar junction transistors, thyristors, etc. These devices require adequate and affordable termination techniques to reduce leakage current and increase breakdown voltage in order to maximize power handling capabilities. The graded junction termination extension disclosed is effective, self-aligned, and simplifies the implementation process.

Graded junction termination extensions for electronic devices

NASA Technical Reports Server (NTRS)

Merrett, J. Neil (Inventor); Isaacs-Smith, Tamara (Inventor); Sheridan, David C. (Inventor); Williams, John R. (Inventor)

2007-01-01

A graded junction termination extension in a silicon carbide (SiC) semiconductor device and method of its fabrication using ion implementation techniques is provided for high power devices. The properties of silicon carbide (SiC) make this wide band gap semiconductor a promising material for high power devices. This potential is demonstrated in various devices such as p-n diodes, Schottky diodes, bipolar junction transistors, thyristors, etc. These devices require adequate and affordable termination techniques to reduce leakage current and increase breakdown voltage in order to maximize power handling capabilities. The graded junction termination extension disclosed is effective, self-aligned, and simplifies the implementation process.

A Robust Method to Generate Mechanically Anisotropic Vascular Smooth Muscle Cell Sheets for Vascular Tissue Engineering.

PubMed

Backman, Daniel E; LeSavage, Bauer L; Shah, Shivem B; Wong, Joyce Y

2017-06-01

In arterial tissue engineering, mimicking native structure and mechanical properties is essential because compliance mismatch can lead to graft failure and further disease. With bottom-up tissue engineering approaches, designing tissue components with proper microscale mechanical properties is crucial to achieve the necessary macroscale properties in the final implant. This study develops a thermoresponsive cell culture platform for growing aligned vascular smooth muscle cell (VSMC) sheets by photografting N-isopropylacrylamide (NIPAAm) onto micropatterned poly(dimethysiloxane) (PDMS). The grafting process is experimentally and computationally optimized to produce PNIPAAm-PDMS substrates optimal for VSMC attachment. To allow long-term VSMC sheet culture and increase the rate of VSMC sheet formation, PNIPAAm-PDMS surfaces were further modified with 3-aminopropyltriethoxysilane yielding a robust, thermoresponsive cell culture platform for culturing VSMC sheets. VSMC cell sheets cultured on patterned thermoresponsive substrates exhibit cellular and collagen alignment in the direction of the micropattern. Mechanical characterization of patterned, single-layer VSMC sheets reveals increased stiffness in the aligned direction compared to the perpendicular direction whereas nonpatterned cell sheets exhibit no directional dependence. Structural and mechanical anisotropy of aligned, single-layer VSMC sheets makes this platform an attractive microstructural building block for engineering a vascular graft to match the in vivo mechanical properties of native arterial tissue. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ultraviolet-ozone surface modification for non-wetting hole transport materials based inverted planar perovskite solar cells with efficiency exceeding 18%

NASA Astrophysics Data System (ADS)

Xu, Xiuwen; Ma, Chunqing; Cheng, Yuanhang; Xie, Yue-Min; Yi, Xueping; Gautam, Bhoj; Chen, Shengmei; Li, Ho-Wa; Lee, Chun-Sing; So, Franky; Tsang, Sai-Wing

2017-08-01

Non-wetting hole transport materials (HTMs) have great potential in facilitating large-sized perovskite crystal growth and enhancing device stability by opposing moisture ingress, However, the severe non-wetting issue limits the wide application of these materials in low-temperature solution-processed inverted planar perovskite solar cells (PVSCs), and corresponding devices are rarely reported. Here, a facile ultraviolet-ozone (UVO) modification method is demonstrated to overcome this issue. By carefully controlling the UVO modification time, the surface wettability of poly-TPD can be tuned without affecting the bulk properties of the film, hence perovskite films with desired grain size and excellent coverage can be deposited via a one-step spin-coating method. Benefiting from the high-quality perovskite, well-matched energy level alignment and hydrophobic property of poly-TPD, the resulting PVSCs show a champion power conversion efficiency of 18.19% with significantly enhanced stability as compared to the PEDOT:PSS counterparts. Moreover, the UVO modification approach also demonstrates its validity when being extended to other hydrophobic HTMs. This work not only provides a general strategy to broaden the selection pool of HTMs for solution-processed inverted planar PVSCs, but also may triggers the exploration of more advanced strategies to make non-wetting HTMs applicable in solution-processed inverted planar PVSCs.

Structure and electrical properties of Pb(ZrxTi1-x)O3 deposited on textured Pt thin films

NASA Astrophysics Data System (ADS)

Hong, Jongin; Song, Han Wook; Lee, Hee Chul; Lee, Won Jong; No, Kwangsoo

2001-08-01

The texturing of the bottom electrode plays a key role in the structure and electrical properties of Pb(Zr, Ti)O3 (PZT) thin films. We fabricated Pt bottom electrodes having a different thickness on MgO single crystals at 600 °C by rf magnetron sputtering. As the thickness of platinum (Pt) thin film increased, the preferred orientation of Pt thin film changed from (200) to (111). PZT thin films were fabricated at 450 °C by electron cyclotron resonance-plasma enhanced metal organic chemical vapor deposition on the textured Pt thin films. The texturing of the bottom electrode caused drastic changes in the C-V characteristics, P-E characteristics, and fatigue characteristics of metal/ferroelectric material/metal (MFM) capacitors. The difference of the electrical properties between the PZT thin films having different texturing was discussed in terms-of the x-y alignment and the interface between electrode and PZT in MFM capacitors.

Tuning the structural and electronic properties of heterogeneous chalcogenide nanostructures

NASA Astrophysics Data System (ADS)

Giberti, Federico; Voros, Marton; Galli, Giulia

Heterogeneous nanostructures, such as quantum dots (QDs) embedded in solid matrices, are promising platforms for solar energy conversion. Unfortunately, there is scarce information on the structure of the interface between the dots and their embedding matrix, thus hampering the design of functional materials with desired optoelectronic properties. Here, we developed a hierarchical computational strategy to obtain realistic models of semiconductor QDs embedded in matrices using enhanced sampling classical molecular dynamics simulations and predicted their electronic structure using first-principles electronic structure methods. We investigated PbSe/CdSe systems which are promising materials for solar cell applications and found a favorable quasi-type-II band alignments both for PbSe QDs in CdSe matrices and for CdSe embedded in PbSe. However, in the former case, we found the presence of detrimental intra-gap states, while in the latter no defect states are present. Hence we predict that embedding CdSe in PbSe leads to a more efficient platform for solar energy conversion. In addition, we showed that the structure of CdSe QD and in turn its band gap might be tuned by applying pressure to the PbSe matrix, providing a way to engineer the properties of new functional materials. Work by F. Giberti was supported by MICCoM funded by the U.S. Department of Energy (DOE), DOE/BES 5J-30161-0010A; work by M. Voros was supported by the U.S. DOE, under Award DE-AC02-06CH11357.

The Influence of Component Alignment and Ligament Properties on Tibiofemoral Contact Forces in Total Knee Replacement.

PubMed

Smith, Colin R; Vignos, Michael F; Lenhart, Rachel L; Kaiser, Jarred; Thelen, Darryl G

2016-02-01

The study objective was to investigate the influence of coronal plane alignment and ligament properties on total knee replacement (TKR) contact loads during walking. We created a subject-specific knee model of an 83-year-old male who had an instrumented TKR. The knee model was incorporated into a lower extremity musculoskeletal model and included deformable contact, ligamentous structures, and six degrees-of-freedom (DOF) tibiofemoral and patellofemoral joints. A novel numerical optimization technique was used to simultaneously predict muscle forces, secondary knee kinematics, ligament forces, and joint contact pressures from standard gait analysis data collected on the subject. The nominal knee model predictions of medial, lateral, and total contact forces during gait agreed well with TKR measures, with root-mean-square (rms) errors of 0.23, 0.22, and 0.33 body weight (BW), respectively. Coronal plane component alignment did not affect total knee contact loads, but did alter the medial-lateral load distribution, with 4 deg varus and 4 deg valgus rotations in component alignment inducing +17% and -23% changes in the first peak medial tibiofemoral contact forces, respectively. A Monte Carlo analysis showed that uncertainties in ligament stiffness and reference strains induce ±0.2 BW uncertainty in tibiofemoral force estimates over the gait cycle. Ligament properties had substantial influence on the TKR load distributions, with the medial collateral ligament and iliotibial band (ITB) properties having the largest effects on medial and lateral compartment loading, respectively. The computational framework provides a viable approach for virtually designing TKR components, considering parametric uncertainty and predicting the effects of joint alignment and soft tissue balancing procedures on TKR function during movement.

The Influence of Component Alignment and Ligament Properties on Tibiofemoral Contact Forces in Total Knee Replacement

PubMed Central

Smith, Colin R.; Vignos, Michael F.; Lenhart, Rachel L.; Kaiser, Jarred; Thelen, Darryl G.

2016-01-01

The study objective was to investigate the influence of coronal plane alignment and ligament properties on total knee replacement (TKR) contact loads during walking. We created a subject-specific knee model of an 83-year-old male who had an instrumented TKR. The knee model was incorporated into a lower extremity musculoskeletal model and included deformable contact, ligamentous structures, and six degrees-of-freedom (DOF) tibiofemoral and patellofemoral joints. A novel numerical optimization technique was used to simultaneously predict muscle forces, secondary knee kinematics, ligament forces, and joint contact pressures from standard gait analysis data collected on the subject. The nominal knee model predictions of medial, lateral, and total contact forces during gait agreed well with TKR measures, with root-mean-square (rms) errors of 0.23, 0.22, and 0.33 body weight (BW), respectively. Coronal plane component alignment did not affect total knee contact loads, but did alter the medial–lateral load distribution, with 4 deg varus and 4 deg valgus rotations in component alignment inducing +17% and −23% changes in the first peak medial tibiofemoral contact forces, respectively. A Monte Carlo analysis showed that uncertainties in ligament stiffness and reference strains induce ±0.2 BW uncertainty in tibiofemoral force estimates over the gait cycle. Ligament properties had substantial influence on the TKR load distributions, with the medial collateral ligament and iliotibial band (ITB) properties having the largest effects on medial and lateral compartment loading, respectively. The computational framework provides a viable approach for virtually designing TKR components, considering parametric uncertainty and predicting the effects of joint alignment and soft tissue balancing procedures on TKR function during movement. PMID:26769446

Atom by atom: HRTEM insights into inorganic nanotubes and fullerene-like structures

PubMed Central

Sadan, Maya Bar; Houben, Lothar; Enyashin, Andrey N.; Seifert, Gotthard; Tenne, Reshef

2008-01-01

The characterization of nanostructures down to the atomic scale is essential to understand some physical properties. Such a characterization is possible today using direct imaging methods such as aberration-corrected high-resolution transmission electron microscopy (HRTEM), when iteratively backed by advanced modeling produced by theoretical structure calculations and image calculations. Aberration-corrected HRTEM is therefore extremely useful for investigating low-dimensional structures, such as inorganic fullerene-like particles and inorganic nanotubes. The atomic arrangement in these nanostructures can lead to new insights into the growth mechanism or physical properties, where imminent commercial applications are unfolding. This article will focus on two structures that are symmetric and reproducible. The first structure that will be dealt with is the smallest stable symmetric closed-cage structure in the inorganic system, a MoS2 nanooctahedron. It is investigated by means of aberration-corrected microscopy which allowed validating the suggested DFTB-MD model. It will be shown that structures diverging from the energetically most stable structures are present in the laser ablated soot and that the alignment of the different shells is parallel, unlike the bulk material where the alignment is antiparallel. These findings correspond well with the high-energy synthetic route and they provide more insight into the growth mechanism. The second structure studied is WS2 nanotubes, which have already been shown to have a unique structure with very desirable mechanical properties. The joint HRTEM study combined with modeling reveals new information regarding the chirality of the different shells and provides a better understanding of their growth mechanism. PMID:18838681

Atom by atom: HRTEM insights into inorganic nanotubes and fullerene-like structures.

PubMed

Bar Sadan, Maya; Houben, Lothar; Enyashin, Andrey N; Seifert, Gotthard; Tenne, Reshef

2008-10-14

The characterization of nanostructures down to the atomic scale is essential to understand some physical properties. Such a characterization is possible today using direct imaging methods such as aberration-corrected high-resolution transmission electron microscopy (HRTEM), when iteratively backed by advanced modeling produced by theoretical structure calculations and image calculations. Aberration-corrected HRTEM is therefore extremely useful for investigating low-dimensional structures, such as inorganic fullerene-like particles and inorganic nanotubes. The atomic arrangement in these nanostructures can lead to new insights into the growth mechanism or physical properties, where imminent commercial applications are unfolding. This article will focus on two structures that are symmetric and reproducible. The first structure that will be dealt with is the smallest stable symmetric closed-cage structure in the inorganic system, a MoS(2) nanooctahedron. It is investigated by means of aberration-corrected microscopy which allowed validating the suggested DFTB-MD model. It will be shown that structures diverging from the energetically most stable structures are present in the laser ablated soot and that the alignment of the different shells is parallel, unlike the bulk material where the alignment is antiparallel. These findings correspond well with the high-energy synthetic route and they provide more insight into the growth mechanism. The second structure studied is WS(2) nanotubes, which have already been shown to have a unique structure with very desirable mechanical properties. The joint HRTEM study combined with modeling reveals new information regarding the chirality of the different shells and provides a better understanding of their growth mechanism.

Synthesis and viscoelastic characterization of microstructurally aligned Silk fibroin sponges.

PubMed

Panda, Debojyoti; Konar, Subhajit; Bajpai, Saumendra K; Arockiarajan, A

2017-07-01

Silk fibroin (SF) is a model candidate for use in tissue engineering and regenerative medicine owing to its bio-compatible mechanochemical properties. Despite numerous advances made in the fabrication of various biomimetic substrates using SF, relatively few clinical applications have been designed, primarily due to the lack of complete understanding of its constitutive properties. Here we fabricate microstructurally aligned SF sponge using the unidirectional freezing technique wherein a novel solvent-processing technique involving Acetic acid is employed, which obviates the post-treatment of the sponges to induce their water-stability. Subsequently, we quantify the anisotropic, viscoelastic response of the bulk SF sponge samples by performing a series of mechanical tests under uniaxial compression over a wide range of strain rates. Results for these uniaxial compression tests in the finite strain regime through ramp strain and ramp-relaxation loading histories applied over two orders of strain rate magnitude show that microstructural anisotropy is directly manifested in the bulk viscoelastic solid-like response. Furthermore, the experiments reveal a high degree of volume compressibility of the sponges during deformation, and also evince for their remarkable strain recovery capacity under large compressive strains during strain recovery tests. Finally, in order to predict the bulk viscoelastic material properties of the fabricated and pre-characterized SF sponges, a finite strain kinematics-based, nonlinear, continuum model developed within a thermodynamically-consistent framework in a parallel investigation, was successfully employed to capture the viscoelastic solid-like, transversely isotropic, and compressible response of the sponges macroscopically. Copyright © 2017 Elsevier Ltd. All rights reserved.

Three-Dimensional Structure Analysis and Percolation Properties of a Barrier Marine Coating

PubMed Central

Chen, Bo; Guizar-Sicairos, Manuel; Xiong, Gang; Shemilt, Laura; Diaz, Ana; Nutter, John; Burdet, Nicolas; Huo, Suguo; Mancuso, Joel; Monteith, Alexander; Vergeer, Frank; Burgess, Andrew; Robinson, Ian

2013-01-01

Artificially structured coatings are widely employed to minimize materials deterioration and corrosion, the annual direct cost of which is over 3% of the gross domestic product (GDP) for industrial countries. Manufacturing higher performance anticorrosive coatings is one of the most efficient approaches to reduce this loss. However, three-dimensional (3D) structure of coatings, which determines their performance, has not been investigated in detail. Here we present a quantitative nano-scale analysis of the 3D spatial structure of an anticorrosive aluminium epoxy barrier marine coating obtained by serial block-face scanning electron microscopy (SBFSEM) and ptychographic X-ray computed tomography (PXCT). We then use finite element simulations to demonstrate how percolation through this actual 3D structure impedes ion diffusion in the composite materials. We found the aluminium flakes align within 15° of the coating surface in the material, causing the perpendicular diffusion resistance of the coating to be substantially higher than the pure epoxy. PMID:23378910

Multi-Material Tissue Engineering Scaffold with Hierarchical Pore Architecture.

PubMed

Morgan, Kathy Ye; Sklaviadis, Demetra; Tochka, Zachary L; Fischer, Kristin M; Hearon, Keith; Morgan, Thomas D; Langer, Robert; Freed, Lisa E

2016-08-23

Multi-material polymer scaffolds with multiscale pore architectures were characterized and tested with vascular and heart cells as part of a platform for replacing damaged heart muscle. Vascular and muscle scaffolds were constructed from a new material, poly(limonene thioether) (PLT32i), which met the design criteria of slow biodegradability, elastomeric mechanical properties, and facile processing. The vascular-parenchymal interface was a poly(glycerol sebacate) (PGS) porous membrane that met different criteria of rapid biodegradability, high oxygen permeance, and high porosity. A hierarchical architecture of primary (macroscale) and secondary (microscale) pores was created by casting the PLT32i prepolymer onto sintered spheres of poly(methyl methacrylate) (PMMA) within precisely patterned molds followed by photocuring, de-molding, and leaching out the PMMA. Pre-fabricated polymer templates were cellularized, assembled, and perfused in order to engineer spatially organized, contractile heart tissue. Structural and functional analyses showed that the primary pores guided heart cell alignment and enabled robust perfusion while the secondary pores increased heart cell retention and reduced polymer volume fraction.

Water-Soluble Polymeric Interfacial Material for Planar Perovskite Solar Cells.

PubMed

Zheng, Lingling; Ma, Yingzhuang; Xiao, Lixin; Zhang, Fengyan; Wang, Yuanhao; Yang, Hongxing

2017-04-26

Interfacial materials play a critical role in photoelectric conversion properties as well as the anomalous hysteresis phenomenon of the perovskite solar cells (PSCs). In this article, a water-soluble polythiophene PTEBS was employed as a cathode interfacial material for PSCs. Efficient energy level aligning and improved film morphology were obtained due to an ultrathin coating of PTEBS. Better ohmic contact between the perovskite layer and the cathode also benefits the charge transport and extraction of the device. Moreover, less charge accumulation at the interface weakens the polarization of the perovskite resulting in a relatively quick response of the modified device. The ITO/PTEBS/CH 3 NH 3 PbI 3 /spiro-MeOTAD/Au cells by an all low-temperature process achieved power conversion efficiencies of up to 15.4% without apparent hysteresis effect. Consequently, the utilization of this water-soluble polythiophene is a practical approach for the fabrication of highly efficient, large-area, and low-cost PSCs and compatible with low-temperature solution process, roll-to-roll manufacture, and flexible application.

Elevated-temperature application of the IITRI compression test fixture for graphite/polyimide filamentary composites

NASA Technical Reports Server (NTRS)

Raju, B. B.; Camarda, C. J.; Cooper, P. A.

1979-01-01

Seventy-nine graphite/polyimide compression specimens were tested to investigate experimentally the IITRI test method for determining compressive properties of composite materials at room and elevated temperatures (589 K (600 F)). Minor modifications were made to the standard IITRI fixture and a high degree of precision was maintained in specimen fabrication and load alignment. Specimens included four symmetric laminate orientations. Various widths were tested to evaluate the effect of width on measured modulus and strength. In most cases three specimens of each width were tested at room and elevated temperature and a polynomial regression analysis was used to reduce the data. Scatter of replicate tests and back-to-back strain variations were low, and no specimens failed by instability. Variation of specimen width had a negligible effect on the measured ultimate strengths and initial moduli of the specimens. Measured compressive strength and stiffness values were sufficiently high for the material to be considered a usable structural material at temperatures as high as 589 K (600 F).

Effects of Structural Variations on the Cellular Response and Mechanical Properties of Biocompatible, Biodegradable, and Porous Smectic Liquid Crystal Elastomers.

PubMed

Sharma, Anshul; Mori, Taizo; Mahnen, Cory J; Everson, Heather R; Leslie, Michelle T; Nielsen, Alek D; Lussier, Laurent; Zhu, Chenhui; Malcuit, Christopher; Hegmann, Torsten; McDonough, Jennifer A; Freeman, Ernest J; Korley, LaShanda T J; Clements, Robert J; Hegmann, Elda

2017-02-01

The authors report on series of side-chain smectic liquid crystal elastomer (LCE) cell scaffolds based on star block-copolymers featuring 3-arm, 4-arm, and 6-arm central nodes. A particular focus of these studies is placed on the mechanical properties of these LCEs and their impact on cell response. The introduction of diverse central nodes allows to alter and custom-modify the mechanical properties of LCE scaffolds to values on the same order of magnitude of various tissues of interest. In addition, it is continued to vary the position of the LC pendant group. The central node and the position of cholesterol pendants in the backbone of ε-CL blocks (alpha and gamma series) affect the mechanical properties as well as cell proliferation and particularly cell alignment. Cell directionality tests are presented demonstrating that several LCE scaffolds show cell attachment, proliferation, narrow orientational dispersion of cells, and highly anisotropic cell growth on the as-synthesized LCE materials. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of packing density and surface roughness of vertically-aligned carbon nanotubes on adhesive properties of gecko-inspired mimetics.

PubMed

Chen, Bingan; Zhong, Guofang; Oppenheimer, Pola Goldberg; Zhang, Can; Tornatzky, Hans; Esconjauregui, Santiago; Hofmann, Stephan; Robertson, John

2015-02-18

We have systematically studied the macroscopic adhesive properties of vertically aligned nanotube arrays with various packing density and roughness. Using a tensile setup in shear and normal adhesion, we find that there exists a maximum packing density for nanotube arrays to have adhesive properties. Too highly packed tubes do not offer intertube space for tube bending and side-wall contact to surfaces, thus exhibiting no adhesive properties. Likewise, we also show that the surface roughness of the arrays strongly influences the adhesion properties and the reusability of the tubes. Increasing the surface roughness of the array strengthens the adhesion in the normal direction, but weakens it in the shear direction. Altogether, these results allow progress toward mimicking the gecko's vertical mobility.

Magnetism variations and susceptibility hysteresis at the metal-insulator phase transition temperature of VO2 in a composite film containing vanadium and tungsten oxides

NASA Astrophysics Data System (ADS)

Akande, Amos A.; Rammutla, Koena E.; Moyo, Thomas; Osman, Nadir S. E.; Nkosi, Steven S.; Jafta, Charl J.; Mwakikunga, Bonex W.

2015-02-01

We report on the magnetic property of 0.67-WO3+0.33-VOx mixture film deposit on the corning glass substrate using the chemical sol-gel and atmospheric pressure chemical vapor deposition (APCVD) methods. The XRD and Raman spectroscopy confirm species of both materials, and the morphological studies with FIB-SEM and TEM reveal segregation of W and V atoms. XPS reveals that V4+ from VO2 forms only 11% of the film; V3+ in the form of V2O3 form 1% of the film, 21% is V5+ from V2O5 and 67% is given to W6+ from WO3. The analysis of the ESR data shows some sharp changes in the magnetism near the metal-to-insulator (MIT), which could be theoretically interpreted as the ordering or alignment of electron spins from net moment nature to parallel alignment of magnetic moment. The derivatives of magnetic susceptibility established the thermally induced magnetic property: two distinct transitions of 339 K for heating data and 338 K for cooling data for 151.2 mT field were obtained. Similar results were also obtained for 308.7 mT field, 336 K for heating data and 335 K for cooling data. VSM results confirm a paramagnetic phase with a small amount of magnetically ordered phase.

Interfacial Molecular Packing Determines Exciton Dynamics in Molecular Heterostructures: The Case of Pentacene-Perfluoropentacene.

PubMed

Rinn, Andre; Breuer, Tobias; Wiegand, Julia; Beck, Michael; Hübner, Jens; Döring, Robin C; Oestreich, Michael; Heimbrodt, Wolfram; Witte, Gregor; Chatterjee, Sangam

2017-12-06

The great majority of electronic and optoelectronic devices depend on interfaces between p-type and n-type semiconductors. Finding matching donor-acceptor systems in molecular semiconductors remains a challenging endeavor because structurally compatible molecules may not necessarily be suitable with respect to their optical and electronic properties, and the large exciton binding energy in these materials may favor bound electron-hole pairs rather than free carriers or charge transfer at an interface. Regardless, interfacial charge-transfer exciton states are commonly considered as an intermediate step to achieve exciton dissociation. The formation efficiency and decay dynamics of such states will strongly depend on the molecular makeup of the interface, especially the relative alignment of donor and acceptor molecules. Structurally well-defined pentacene-perfluoropentacene heterostructures of different molecular orientations are virtually ideal model systems to study the interrelation between molecular packing motifs at the interface and their electronic properties. Comparing the emission dynamics of the heterosystems and the corresponding unitary films enables accurate assignment of every observable emission signal in the heterosystems. These heterosystems feature two characteristic interface-specific luminescence channels at around 1.4 and 1.5 eV that are not observed in the unitary samples. Their emission strength strongly depends on the molecular alignment of the respective donor and acceptor molecules, emphasizing the importance of structural control for device construction.

Vertically aligned carbon nanotube electrodes for lithium-ion batteries

NASA Astrophysics Data System (ADS)

Welna, Daniel T.; Qu, Liangti; Taylor, Barney E.; Dai, Liming; Durstock, Michael F.

As portable electronics become more advanced and alternative energy demands become more prevalent, the development of advanced energy storage technologies is becoming ever more critical in today's society. In order to develop higher power and energy density batteries, innovative electrode materials that provide increased storage capacity, greater rate capabilities, and good cyclability must be developed. Nanostructured materials are gaining increased attention because of their potential to mitigate current electrode limitations. Here we report on the use of vertically aligned multi-walled carbon nanotubes (VA-MWNTs) as the active electrode material in lithium-ion batteries. At low specific currents, these VA-MWNTs have shown high reversible specific capacities (up to 782 mAh g -1 at 57 mA g -1). This value is twice that of the theoretical maximum for graphite and ten times more than their non-aligned equivalent. Interestingly, at very high discharge rates, the VA-MWNT electrodes retain a moderate specific capacity due to their aligned nature (166 mAh g -1 at 26 A g -1). These results suggest that VA-MWNTs are good candidates for lithium-ion battery electrodes which require high rate capability and capacity.

Evaluation of transition metal oxide as carrier-selective contacts for silicon heterojunction solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ding, L.; Boccard, Matthieu; Holman, Zachary

2015-04-06

"Reducing light absorption in the non-active solar cell layers, while enabling the extraction of the photogenerated minority carriers at quasi-Fermi levels are two key factors to improve current generation and voltage, and therefore efficiency of silicon heterojunction solar devices. To address these two critical aspects, transition metal oxide materials have been proposed as alternative to the n- and p-type amorphous silicon used as electron and hole selective contacts, respectively. Indeed, transition metal oxides such as molybdenum oxide, titanium oxide, nickel oxide or tungsten oxide combine a wide band gap typically over 3 eV with a band structure and theoretical bandmore » alignment with silicon that results in high transparency to the solar spectrum and in selectivity for the transport of only one carrier type. Improving carrier extraction or injection using transition metal oxide has been a topic of investigation in the field of organic solar cells and organic LEDs; from these pioneering works a lot of knowledge has been gained on materials properties, ways to control these during synthesis and deposition, and their impact on device performance. Recently, the transfer of some of this knowledge to silicon solar cells and the successful application of some metal oxide to contact heterojunction devices have gained much attention. In this contribution, we investigate the suitability of various transition metal oxide films (molybdenum oxide, titanium oxide, and tungsten oxide) deposited either by thermal evaporation or sputtering as transparent hole or electron selective transport layer for silicon solar cells. In addition to systematically characterize their optical and structural properties, we use photoemission spectroscopy to relate compound stoichiometry to band structure and characterize band alignment to silicon. The direct silicon/metal oxide interface is further analyzed by quasi-steady state photoconductance decay method to assess the quality of surface passivation. In complement, we construct full device structures incorporating in some cases surface passivation schemes, with measured initial conversion efficiency over 15% and evaluate the carrier transport properties using temperature-dependent current-voltage and capacitance-voltage measurements. With this detailed characterization study, we aim at providing the framework to assess the potential of a material as a carrier selective contact and the understanding of how each of the aforementioned parameters on the metal oxide films influence the full solar cell operating performances.« less

Mechanical function near defects in an aligned nanofiber composite is preserved by inclusion of disorganized layers: Insight into meniscus structure and function.

PubMed

Bansal, Sonia; Mandalapu, Sai; Aeppli, Céline; Qu, Feini; Szczesny, Spencer E; Mauck, Robert L; Zgonis, Miltiadis H

2017-07-01

The meniscus is comprised of circumferentially aligned fibers that resist the tensile forces within the meniscus (i.e., hoop stress) that develop during loading of the knee. Although these circumferential fibers are severed by radial meniscal tears, tibial contact stresses do not increase until the tear reaches ∼90% of the meniscus width, suggesting that the severed circumferential fibers still bear load and maintain the mechanical functionality of the meniscus. Recent data demonstrates that the interfibrillar matrix can transfer strain energy to disconnected fibrils in tendon fascicles. In the meniscus, interdigitating radial tie fibers, which function to stabilize and bind the circumferential fibers together, are hypothesized to function in a similar manner by transmitting load to severed circumferential fibers near a radial tear. To test this hypothesis, we developed an engineered fibrous analog of the knee meniscus using poly(ε-caprolactone) to create aligned scaffolds with variable amounts of non-aligned elements embedded within the scaffold. We show that the tensile properties of these scaffolds are a function of the ratio of aligned to non-aligned elements, and change in a predictable fashion following a simple mixture model. When measuring the loss of mechanical function in scaffolds with a radial tear, compared to intact scaffolds, the decrease in apparent linear modulus was reduced in scaffolds containing non-aligned layers compared to purely aligned scaffolds. Increased strains in areas adjacent to the defect were also noted in composite scaffolds. These findings indicate that non-aligned (disorganized) elements interspersed within an aligned network can improve overall mechanical function by promoting strain transfer to nearby disconnected fibers. This finding supports the notion that radial tie fibers may similarly promote tear tolerance in the knee meniscus, and will direct changes in clinical practice and provide guidance for tissue engineering strategies. The meniscus is a complex fibrous tissue, whose architecture includes radial tie fibers that run perpendicular to and interdigitate with the predominant circumferential fibers. We hypothesized that these radial elements function to preserve mechanical function in the context of interruption of circumferential bundles, as would be the case in a meniscal tear. To test this hypothesis, we developed a biomaterial analog containing disorganized layers enmeshed regularly throughout an otherwise aligned network. Using this material formulation, we showed that strain transmission is improved in the vicinity of defects when disorganized fiber layers were present. This supports the idea that radial elements within the meniscus improve function near a tear, and will guide future clinical interventions and the development of engineered replacements. Copyright © 2017 Acta Materialia Inc. All rights reserved.