Naturally occurring reverse tilt domains in a high-pretilt alignment nematic liquid crystal

NASA Astrophysics Data System (ADS)

Wang, Ruiting; Atherton, Timothy J.; Zhu, Minhua; Petschek, Rolfe G.; Rosenblatt, Charles

2007-08-01

A cell whose substrates were coated with the polyamic acid SE1211 (Nissan Chemical Industries) and baked at high temperatures was filled with a nematic liquid crystal in the isotropic phase. On cooling into the nematic phase, naturally occurring and temporally and thermally robust reverse tilt domains separated by thin filamentlike walls were observed. The properties of these structures are reported.

Trends on band alignments: Validity of Anderson's rule in SnS2- and SnSe2-based van der Waals heterostructures

NASA Astrophysics Data System (ADS)

Koda, Daniel S.; Bechstedt, Friedhelm; Marques, Marcelo; Teles, Lara K.

2018-04-01

Van der Waals (vdW) heterostructures are promising candidates for building blocks in novel electronic and optoelectronic devices with tailored properties, since their electronic action is dominated by the band alignments upon their contact. In this work, we analyze 10 vdW heterobilayers based on tin dichalcogenides by first-principles calculations. Structural studies show that all systems are stable, and that commensurability leads to smaller interlayer distances. Using hybrid functional calculations, we derive electronic properties and band alignments for all the heterosystems and isolated two-dimensional (2D) crystals. Natural band offsets are derived from calculated electron affinities and ionization energies of 11 freestanding 2D crystals. They are compared with band alignments in true heterojunctions, using a quantum mechanical criterion, and available experimental data. For the hBN/SnSe 2 system, we show that hBN suffers an increase in band gap, while leaving almost unchanged the electronic properties of SnSe2. Similarly, MX2 (M = Mo, W; X = S, Se) over SnX2 preserve the natural discontinuities from each side of the heterobilayer. Significant charge transfer occurs in junctions with graphene, which becomes p-doped and forms an Ohmic contact with SnX2. Zirconium and hafnium dichalcogenides display stronger interlayer interactions, leading to larger shifts in band alignments with tin dichalcogenides. Significant orbital overlap is found, which creates zero conduction band offset systems. The validity of the Anderson electron affinity rule is discussed. Failures of this model are traced back to interlayer interaction, band hybridization, and quantum dipoles. The systematic work sheds light on interfacial engineering for future vdW electronic and optoelectronic devices.

Uniaxial alignment of triisopropylsilylethynyl pentacene via zone-casting technique.

PubMed

Su, Yajun; Gao, Xiang; Liu, Jiangang; Xing, Rubo; Han, Yanchun

2013-09-14

Uniaxially aligned triisopropylsilylethynyl pentacene (TIPS-pentacene) crystals over a large area were fabricated using zone-casting technique. The array of TIPS-pentacene displayed a high orientation degree with a dichroic ratio (DR) of 0.80. The crystals were arranged with c axis perpendicular to the substrate and the long axis of the ribbon corresponded to the a axis of TIPS-pentacene. The properties of the solutions and the processing parameters were shown to influence the formation of the oriented TIPS-pentacene crystalline array. Solvent with a low boiling point (such as chloroform) favoured the orientation of the ribbon-like crystals. The concentration of the solution should be appropriate, ensuring the crystallization velocity of TIPS-pentacene matching with the receding of the meniscus. Besides, we proved that the casting speed should be large enough to induce a sufficient concentration gradient. The orientation mechanism of TIPS-pentacene was attributed to a synergy of the ordered nuclei and a match between the crystallization velocity and the casting speed. Field effect transistors (FETs) based on the oriented TIPS-pentacene crystalline array showed a mobility of 0.67 cm(2) V(-1) s(-1).

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.

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.

Mineral crystal alignment in mineralized fracture callus determined by 3D small-angle X-ray scattering

NASA Astrophysics Data System (ADS)

Liu, Yifei; Manjubala, Inderchand; Roschger, Paul; Schell, Hanna; Duda, Georg N.; Fratzl, Peter

2010-10-01

Callus tissue formed during bone fracture healing is a mixture of different tissue types as revealed by histological analysis. But the structural characteristics of mineral crystals within the healing callus are not well known. Since two-dimensional (2D) scanning small-angle X-ray scattering (sSAXS) patterns showed that the size and orientation of callus crystals vary both spatially and temporally [1] and 2D electron microscopic analysis implies an anisotropic property of the callus morphology, the mineral crystals within the callus are also expected to vary in size and orientation in 3D. Three-dimensional small-angle X-ray scattering (3D SAXS), which combines 2D SAXS patterns collected at different angles of sample tilting, has been previously applied to investigate bone minerals in horse radius [2] and oim/oim mouse femur/tibia [3]. We implement a similar 3D SAXS method but with a different way of data analysis to gather information on the mineral alignment in fracture callus. With the proposed accurate yet fast assessment of 3D SAXS information, it was shown that the plate shaped mineral particles in the healing callus were aligned in groups with their predominant orientations occurring as a fiber texture.

Topographically induced homeotropic alignment of liquid crystals on self-assembled opal crystals.

PubMed

Kumar, Pankaj; Oh, Su Yeon; Baliyan, Vijay K; Kundu, Sudarshan; Lee, Seung Hee; Kang, Shin-Woong

2018-04-02

The surface of multilayered opal crystals resulted in homeotropic alignment of liquid crystal (LC), originated from the surface topography of opal crystals rather than a chemical nature of the nanoparticles. The polar anchoring energy (5.51 × 10 -5 J/m 2 ) of the crystal surface for nematic LC molecules was in a similar range to the conventional polyimide alignment layer (2.11 × 10 -5 J/m 2 ) used for commercial applications. The critical length scale for anchoring transition was approximately Lw = ~1 μm. If a diameter of particle d < 1 μm for opal crystals, LC molecules preferred to anchor vertically to the surface to minimize elastic free energy of bulk LCs. The LC favored a planar anchoring if d > 1 μm. The results provide crucial insights to understand the homeotropic alignment of LCs on solid surfaces and therefore offer opportunities to develop novel materials for a vertical alignment of LCs.

Photoluminescence analysis of self induced planer alignment in azo dye dispersed nematic liquid crystal complex

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

Kumar, Rishi, E-mail: kkraina@gmail.com; Sood, Srishti, E-mail: kkraina@gmail.com; Raina, K. K., E-mail: kkraina@gmail.com

2014-04-24

We have developed azo dye doped nematic liquid crystal complex for advanced photonic liquid crystal display technology aspects. Disperse orange azo dye self introduced planer alignment in the nematic liquid crystal without any surface anchoring treatment. Planer alignment was characterized by optical polarizing microscopy. The electro-optical switching response of dye disperse planer aligned nematic cell was investigated as a function of applied voltage with the help of photoluminescence spectrophotometer for the tuning of photoluminescence contrast.

Apparatus and methods for using achromatic phase matching at high orders of dispersion

DOEpatents

Richman, Bruce; Trebino, Rick; Bisson, Scott; Sidick, Erkin

2001-01-01

Achromatic phase-matching (APM) is used for efficiently multiplying the frequency of broad bandwidth light by using a nonlinear optical medium comprising a second-harmonic generation (SHG) crystal. Stationary optical elements whose configuration, properties, and arrangement have been optimized to match the dispersion characteristics of the SHG crystal to at least the second order. These elements include a plurality of prismatic elements for directing an input light beam onto the SHG crystal such that each ray wavelength is aligned to match the phase-matching angle for the crystal at each wavelength of light to at least the second order and such that every ray wavelength overlap within the crystal.

Ultra-stiff large-area carpets of carbon nanotubes

NASA Astrophysics Data System (ADS)

Meysami, Seyyed Shayan; Dallas, Panagiotis; Britton, Jude; Lozano, Juan G.; Murdock, Adrian T.; Ferraro, Claudio; Gutierrez, Eduardo Saiz; Rijnveld, Niek; Holdway, Philip; Porfyrakis, Kyriakos; Grobert, Nicole

2016-06-01

Herewith, we report the influence of post-synthesis heat treatment (<=2350 °C and plasma temperatures) on the crystal structure, defect density, purity, alignment and dispersibility of free-standing large-area (several cm2) carpets of ultra-long (several mm) vertically aligned multi-wall carbon nanotubes (VA-MWCNTs). VA-MWCNTs were produced in large quantities (20-30 g per batch) using a semi-scaled-up aerosol-assisted chemical vapour deposition (AACVD) setup. Electron and X-ray diffraction showed that the heat treatment at 2350 °C under inert atmosphere purifies, removes residual catalyst particles, and partially aligns adjacent single crystals (crystallites) in polycrystalline MWCNTs. The purification and improvement in the crystallites alignment within the MWCNTs resulted in reduced dispersibility of the VA-MWCNTs in liquid media. High-resolution microscopy revealed that the crystallinity is improved in scales of few tens of nanometres while the point defects remain largely unaffected. The heat treatment also had a marked benefit on the mechanical properties of the carpets. For the first time, we report compression moduli as high as 120 MPa for VA-MWCNT carpets, i.e. an order of magnitude higher than previously reported figures. The application of higher temperatures (arc-discharge plasma, >=4000 °C) resulted in the formation of a novel graphite-matrix composite reinforced with CVD and arc-discharge-like carbon nanotubes.Herewith, we report the influence of post-synthesis heat treatment (<=2350 °C and plasma temperatures) on the crystal structure, defect density, purity, alignment and dispersibility of free-standing large-area (several cm2) carpets of ultra-long (several mm) vertically aligned multi-wall carbon nanotubes (VA-MWCNTs). VA-MWCNTs were produced in large quantities (20-30 g per batch) using a semi-scaled-up aerosol-assisted chemical vapour deposition (AACVD) setup. Electron and X-ray diffraction showed that the heat treatment at 2350 °C under inert atmosphere purifies, removes residual catalyst particles, and partially aligns adjacent single crystals (crystallites) in polycrystalline MWCNTs. The purification and improvement in the crystallites alignment within the MWCNTs resulted in reduced dispersibility of the VA-MWCNTs in liquid media. High-resolution microscopy revealed that the crystallinity is improved in scales of few tens of nanometres while the point defects remain largely unaffected. The heat treatment also had a marked benefit on the mechanical properties of the carpets. For the first time, we report compression moduli as high as 120 MPa for VA-MWCNT carpets, i.e. an order of magnitude higher than previously reported figures. The application of higher temperatures (arc-discharge plasma, >=4000 °C) resulted in the formation of a novel graphite-matrix composite reinforced with CVD and arc-discharge-like carbon nanotubes. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01660j

Computational aspects of the smectization process in liquid crystals: An example study of a perfectly aligned two-dimensional hard-boomerang system

NASA Astrophysics Data System (ADS)

Chrzanowska, Agnieszka

2017-06-01

A replica method for calculation of smectic liquid crystal properties within the Onsager theory has been presented and applied to an exemplary case of two-dimensional perfectly aligned needlelike boomerangs. The method allows one to consider the complete influence of the interaction terms in contrast to the Fourier expansion method which uses mostly first or second order terms of expansion. The program based on the replica algorithm is able to calculate a single representative layer as an equivalent set of layers, depending on the size of the considered width of the sample integration interval. It predicts successfully smectic density distributions, energies, and layer thicknesses for different types of layer arrangement—of the antiferroelectric or of the smectic A order type. Specific features of the algorithm performance and influence of the numerical accuracy on the physical properties are presented. Future applications of the replica method to freely rotating molecules are discussed.

Computational aspects of the smectization process in liquid crystals: An example study of a perfectly aligned two-dimensional hard-boomerang system.

PubMed

Chrzanowska, Agnieszka

2017-06-01

A replica method for calculation of smectic liquid crystal properties within the Onsager theory has been presented and applied to an exemplary case of two-dimensional perfectly aligned needlelike boomerangs. The method allows one to consider the complete influence of the interaction terms in contrast to the Fourier expansion method which uses mostly first or second order terms of expansion. The program based on the replica algorithm is able to calculate a single representative layer as an equivalent set of layers, depending on the size of the considered width of the sample integration interval. It predicts successfully smectic density distributions, energies, and layer thicknesses for different types of layer arrangement-of the antiferroelectric or of the smectic A order type. Specific features of the algorithm performance and influence of the numerical accuracy on the physical properties are presented. Future applications of the replica method to freely rotating molecules are discussed.

Blazed vector grating liquid crystal cells with photocrosslinkable polymeric alignment films fabricated by one-step polarizer rotation method

NASA Astrophysics Data System (ADS)

Kawai, Kotaro; Kuzuwata, Mitsuru; Sasaki, Tomoyuki; Noda, Kohei; Kawatsuki, Nobuhiro; Ono, Hiroshi

2014-12-01

Blazed vector grating liquid crystal (LC) cells, in which the directors of low-molar-mass LCs are antisymmetrically distributed, were fabricated by one-step exposure of an empty glass cell inner-coated with a photocrosslinkable polymer LC (PCLC) to UV light. By adopting a LC cell structure, twisted nematic (TN) and homogeneous (HOMO) alignments were obtained in the blazed vector grating LC cells. Moreover, the diffraction efficiency of the blazed vector grating LC cells was greatly improved by increasing the thickness of the device in comparison with that of a blazed vector grating with a thin film structure obtained in our previous study. In addition, the diffraction efficiency and polarization states of ±1st-order diffracted beams from the resultant blazed vector grating LC cells were controlled by designing a blazed pattern in the alignment films, and these diffraction properties were well explained on the basis of Jones calculus and the elastic continuum theory of nematic LCs.

Versatile alignment layer method for new types of liquid crystal photonic devices

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

Finnemeyer, V.; Bryant, D.; Lu, L.

2015-07-21

Liquid crystal photonic devices are becoming increasingly popular. These devices often present a challenge when it comes to creating a robust alignment layer in pre-assembled cells. In this paper, we describe a method of infusing a dye into a microcavity to produce an effective photo-definable alignment layer. However, previous research on such alignment layers has shown that they have limited stability, particularly against subsequent light exposure. As such, we further describe a method of utilizing a pre-polymer, infused into the microcavity along with the liquid crystal, to provide photostability. We demonstrate that the polymer layer, formed under ultraviolet irradiation ofmore » liquid crystal cells, has been effectively localized to a thin region near the substrate surface and provides a significant improvement in the photostability of the liquid crystal alignment. This versatile alignment layer method, capable of being utilized in devices from the described microcavities to displays, offers significant promise for new photonics applications.« less

Twisted nematic liquid crystal cells with rubbed poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) films for active polarization control of terahertz waves

NASA Astrophysics Data System (ADS)

Sasaki, Tomoyuki; Okuyama, Hiroki; Sakamoto, Moritsugu; Noda, Kohei; Okamoto, Hiroyuki; Kawatsuki, Nobuhiro; Ono, Hiroshi

2017-04-01

We fabricated a terahertz (THz) polarization converter using a twisted nematic (TN) liquid crystal (LC) cell. Poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) films coated on quartz glass substrates were used as electrode layers in the TN LC cell. The PEDOT/PSS films were rubbed unidirectionally using a rayon cloth to align the nematic LC, thereby also serving as an alignment layer. The azimuthal surface anchoring strength of the PEDOT/PSS films was measured to be 5 × 10-4 J/m2 using the Néel wall method, which is similar to that of typical polymeric alignment layers. The optical constants of the PEDOT/PSS film in the THz range were also characterized using the Drude-Smith model, and the results indicated that the PEDOT/PSS films could be used both as transparent electrodes in the THz range and as alignment layers for the LC. The electro-optical properties of the fabricated TN LC cell were also investigated using a polarized visible laser and THz time-domain spectroscopic system. In particular, the transmission spectra and polarization conversion property of the TN LC cell in the THz range were theoretically analyzed based on a stratified model that considers optical anisotropy, absorption, and multiple interference. This work substantiates the advantages of TN LC cells with rubbed PEDOT/PSS films useful for THz polarization converters with electrical tunability.

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.

Polymer dispersed nematic liquid crystal for large area displays and light valves

NASA Astrophysics Data System (ADS)

Drzaic, Paul S.

1986-09-01

A new electro-optical material based on nematic liquid crystal dispersed in a polymer matrix has recently been introduced by Fergason. This technology (termed NCAP, for nematic curvilinear aligned phase) is suitable for making very large area (thousands of square centimeter) light valves and displays. The device consists of micron size droplets of liquid crystal dispersed in and surrounded by a polymer film. Light passing through the film in the absence of an applied field is strongly forward scattered, giving a milky, translucent film. Application of an electric field across the liquid crystal/polymer film places the film in a highly transparent state. Pleochroic dyes may be employed in the system in order to achieve controllable light absorption as well as scattering. Microscopically, it is shown that the liquid-crystal director lies preferentially parallel to the polymer wall, leading to a bipolar-like configuration of the liquid-crystal directors within the droplet. The symmetry axes of the droplets are randomly oriented in the unpowered, scattering state, but align parallel to the field in the powered, transparent state. The electric field required to reorient a given droplet varies inversely with the diameter of that droplet, and it is shown that the macroscopic electro-optical properties of the film can be modeled if the distribution of liquid-crystal droplet sizes is known.

The Role of ZnO Particle Size, Shape and Concentration on Liquid Crystal Order and Current-Voltage Properties for Potential Photovoltaic Applications

NASA Astrophysics Data System (ADS)

Martinez-Miranda, Luz J.; Branch, Janelle; Thompson, Robert; Taylor, Jefferson W.; Salamanca-Riba, Lourdes

2012-02-01

We investigate the role order plays in the transfer of charges in ZnO nanoparticle - octylcyanobiphenyl (8CB) liquid crystal system for photovoltaic applications as well as the role the nominally 7x5x5nm^3 or 20x5x5nm^3 ZnO nanoparticles play in improving that order. Our results for the 5nm nanoparticles show an improvement in the alignment of the liquid crystal with increasing weight percentage of ZnO nanoparticles^1. Our results for the 7x5x5 nm^3 sample show that the current is larger than the current obtained for the 5 nm samples. We find that order is improved for concentrations close to 35% wt ZnO for both the 7x5x5 nm^3 and 20x5x5 nm^3. We have analyzed the X-ray scans for both the 7x5x5 and the 20x5x5 nm^3 samples. The signal corresponding to the liquid crystal aligned parallel to the substrate is much smaller than the peak corresponding to the liquid crystal aligned approximately at 70 with respect to the substrate for the 7x5x5 nm^3 sample whereas this same peak is comparable or more intense for the 20x5x5 nm^3 sample. 1. L. J. Mart'inez-Miranda, Kaitlin M. Traister, Iriselies Mel'endez-Rodr'iguez, and Lourdes Salamanca-Riba, Appl. Phys. Letts, 97, 223301 (2010).

Tunable dichroic polarization beam splitter created by one-step holographic photoalignment using four-beam polarization interferometry

NASA Astrophysics Data System (ADS)

Kawai, Kotaro; Sakamoto, Moritsugu; Noda, Kohei; Sasaki, Tomoyuki; Kawatsuki, Nobuhiro; Ono, Hiroshi

2017-01-01

A tunable dichroic polarization beam splitter (tunable DPBS) simultaneously performs the follow functions: 1. Separation of a polarized incident beam into multiple pairs of orthogonally polarized beams; 2. Separation of the propagation direction of two wavelength incident beams after passing through the tunable DPBS; and 3. Control of both advanced polarization and wavelength separation capabilities by varying the temperature of the tunable DPBS. This novel complex optical property is realized by diffraction phenomena using a designed three-dimensional periodic structure of aligned liquid crystals in the tunable DPBS, which was fabricated quickly with precision in a one-step photoalignment using four-beam polarization interferometry. In experiments, we demonstrated that these diffraction properties are obtained by entering polarized beams of wavelengths 532 nm and 633 nm onto the tunable DPBS. These diffraction properties are described using the Jones calculus in a polarization propagation analysis. Of significance is that the aligned liquid crystal structure needed to obtain these diffraction properties was proposed based on a theoretical analysis, and these properties were then demonstrated experimentally. The tunable DPBS can perform several functions of a number of optical elements such as wave plates, polarization beam splitter, dichroic beam splitter, and tunable wavelength filter. Therefore, the tunable DPBS can contribute to greater miniaturization, sophistication, and cost reduction of optical systems used widely in applications, such as optical measurements, communications, and information processing.

Electrorotation of colloidal particles in liquid crystals

NASA Astrophysics Data System (ADS)

Liao, G.; Smalyukh, I. I.; Kelly, J. R.; Lavrentovich, O. D.; Jákli, A.

2005-09-01

We present the first observations of dc electric-field-induced rotational motion of finite particles in liquid crystals. We show that the electrorotation is essentially identical to the well-known Quincke rotation, which in liquid crystals triggers an additional translational motion at higher fields. In the smectic phase the translational motion is confined to the two-dimensional geometry of smectic layers, in contrast to the isotropic and nematic phases, where the particles can move in all three dimensions. We demonstrate that by a proper analysis of the electrorotation, one can determine the in-plane viscosity of smectic liquid crystals. This method needs only a small amount of material, does not require uniform alignment over large areas, and enables probing rheological properties locally.

Fabrication and Characterization of Vertically Aligned ZnO Nanorod Arrays via Inverted Monolayer Colloidal Crystals Mask

NASA Astrophysics Data System (ADS)

Chen, Cheng; Ding, Taotao; Qi, Zhiqiang; Zhang, Wei; Zhang, Jun; Xu, Juan; Chen, Jingwen; Dai, Jiangnan; Chen, Changqing

2018-04-01

The periodically ordered ZnO nanorod (NR) arrays have been successfully synthesized via a hydrothermal approach on the silicon substrates by templating of the TiO2 ring deriving from the polystyrene (PS) nanosphere monolayer colloidal crystals (MCC). With the inverted MCC mask, sol-gel-derived ZnO seeds could serve as the periodic nucleation positions for the site-specific growth of ZnO NRs. The large-scale patterned arrays of single ZnO NR with good side-orientation can be readily produced. According to the experimental results, the as-integrated ZnO NR arrays showed an excellent crystal quality and optical property, very suitable for optoelectronic applications such as stimulated emitters and ZnO photonic crystal devices.

DNA Nanotubes for NMR Structure Determination of Membrane Proteins

PubMed Central

Bellot, Gaëtan; McClintock, Mark A.; Chou, James J; Shih, William M.

2013-01-01

Structure determination of integral membrane proteins by solution NMR represents one of the most important challenges of structural biology. A Residual-Dipolar-Coupling-based refinement approach can be used to solve the structure of membrane proteins up to 40 kDa in size, however, a weak-alignment medium that is detergent-resistant is required. Previously, availability of media suitable for weak alignment of membrane proteins was severely limited. We describe here a protocol for robust, large-scale synthesis of detergent-resistant DNA nanotubes that can be assembled into dilute liquid crystals for application as weak-alignment media in solution NMR structure determination of membrane proteins in detergent micelles. The DNA nanotubes are heterodimers of 400nm-long six-helix bundles each self-assembled from a M13-based p7308 scaffold strand and >170 short oligonucleotide staple strands. Compatibility with proteins bearing considerable positive charge as well as modulation of molecular alignment, towards collection of linearly independent restraints, can be introduced by reducing the negative charge of DNA nanotubes via counter ions and small DNA binding molecules. This detergent-resistant liquid-crystal media offers a number of properties conducive for membrane protein alignment, including high-yield production, thermal stability, buffer compatibility, and structural programmability. Production of sufficient nanotubes for 4–5 NMR experiments can be completed in one week by a single individual. PMID:23518667

DNA nanotubes for NMR structure determination of membrane proteins.

PubMed

Bellot, Gaëtan; McClintock, Mark A; Chou, James J; Shih, William M

2013-04-01

Finding a way to determine the structures of integral membrane proteins using solution nuclear magnetic resonance (NMR) spectroscopy has proved to be challenging. A residual-dipolar-coupling-based refinement approach can be used to resolve the structure of membrane proteins up to 40 kDa in size, but to do this you need a weak-alignment medium that is detergent-resistant and it has thus far been difficult to obtain such a medium suitable for weak alignment of membrane proteins. We describe here a protocol for robust, large-scale synthesis of detergent-resistant DNA nanotubes that can be assembled into dilute liquid crystals for application as weak-alignment media in solution NMR structure determination of membrane proteins in detergent micelles. The DNA nanotubes are heterodimers of 400-nm-long six-helix bundles, each self-assembled from a M13-based p7308 scaffold strand and >170 short oligonucleotide staple strands. Compatibility with proteins bearing considerable positive charge as well as modulation of molecular alignment, toward collection of linearly independent restraints, can be introduced by reducing the negative charge of DNA nanotubes using counter ions and small DNA-binding molecules. This detergent-resistant liquid-crystal medium offers a number of properties conducive for membrane protein alignment, including high-yield production, thermal stability, buffer compatibility and structural programmability. Production of sufficient nanotubes for four or five NMR experiments can be completed in 1 week by a single individual.

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).

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.

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.

The Stonehenge technique. A method for aligning coherent bremsstrahlung radiators

NASA Astrophysics Data System (ADS)

Livingston, Ken

2009-05-01

This paper describes a technique for the alignment of crystal radiators used to produce high energy, linearly polarized photons via coherent bremsstrahlung scattering at electron beam facilities. In these experiments the crystal is mounted on a goniometer which is used to adjust its orientation relative to the electron beam. The angles and equations which relate the crystal lattice, goniometer and electron beam direction are presented here, and the method of alignment is illustrated with data taken at MAMI (the Mainz microtron). A practical guide to setting up a coherent bremsstrahlung facility and installing new crystals using this technique is also included.

Enhanced NH3 gas sensing properties of a QCM sensor by increasing the length of vertically orientated ZnO nanorods

NASA Astrophysics Data System (ADS)

Minh, Vu Anh; Tuan, Le Anh; Huy, Tran Quang; Hung, Vu Ngoc; Quy, Nguyen Van

2013-01-01

Vertically aligned ZnO nanorods were directly synthesised on a gold electrode of quartz crystal microbalance (QCM) by a simple low-temperature hydrothermal method for a NH3 gas sensing application. The length of vertically aligned ZnO nanorods was increased to purpose enhancement in the gas sensing response of the sensor. The length of ZnO nanorods increased with an increase in growth time. The growth time of ZnO nanorods was systematically varied in the range of 1-4 h to examine the effect of the length of the ZnO nanorods on the gas sensing properties of the fabricated sensors. The gas sensing properties of sensors with different ZnO nanorods lengths was examined at room temperature for various concentrations of NH3 (50-800 ppm) in synthetic air. Enhancement in gas sensing response by increasing the length of ZnO nanorods was observed.

Quantitative regulation of bone-mimetic, oriented collagen/apatite matrix structure depends on the degree of osteoblast alignment on oriented collagen substrates.

PubMed

Matsugaki, Aira; Isobe, Yoshihiro; Saku, Taro; Nakano, Takayoshi

2015-02-01

Bone tissue has a specific anisotropic morphology derived from collagen fiber alignment and the related apatite crystal orientation as a bone quality index. However, the precise mechanism of cellular regulation of the crystallographic orientation of apatite has not been clarified. In this study, anisotropic construction of cell-produced mineralized matrix in vitro was established by initiating organized cellular alignment and subsequent oriented bone-like matrix (collagen/apatite) production. The oriented collagen substrates with three anisotropic levels were prepared by a hydrodynamic method. Primary osteoblasts were cultured on the fabricated substrates until mineralized matrix formation is confirmed. Osteoblast alignment was successfully regulated by the level of substrate collagen orientation, with preferential alignment along the direction of the collagen fibers. Notably, both fibrous orientation of newly synthesized collagen matrix and c-axis of produced apatite crystals showed preferential orientation along the cell direction. Because the degree of anisotropy of the deposited apatite crystals showed dependency on the directional distribution of osteoblasts cultured on the oriented collagen substrates, the cell orientation determines the crystallographic anisotropy of produced apatite crystals. To the best of our knowledge, this is the first report demonstrating that bone tissue anisotropy, even the alignment of apatite crystals, is controllable by varying the degree of osteoblast alignment via regulating the level of substrate orientation. © 2014 Wiley Periodicals, Inc.

Stable azodye photo-alignment layer for liquid crystal devices achieved by "turning off" dye photosensitivity

NASA Astrophysics Data System (ADS)

McGinty, C.; Finnemeyer, V.; Reich, R.; Clark, H.; Berry, S.; Bos, P.

2017-11-01

We have previously proposed a low cost, versatile process for stabilizing azodye photo-alignment layers for liquid crystal devices by utilizing a surface localized reactive mesogen (RM) layer. The RM is applied by dissolving the monomer in a liquid crystal material prior to filling the cell. In this paper, we show the significant effect of azodye layer thickness on the long term stability of these alignment layers when exposed to polarized light. We demonstrate, surprisingly, that thin azodye layers (˜3 nm) provide improved stability over thicker (˜40 nm) layers. Using this process, we show cells which have been stable to exposure with polarized light through one month. Additionally, we demonstrate the use of a photo-alignment layer to align the liquid crystals that afterwards can be rendered insensitive to polarized light. This was accomplished by using the process described above with the additional step of eliminating the photosensitivity of the azodye layer through photo-bleaching; the result is an RM alignment layer that will be stable when exposed to polarized light in the dye absorption band.

A method to align a bent crystal for channeling experiments by using quasichanneling oscillations

NASA Astrophysics Data System (ADS)

Sytov, A. I.; Guidi, V.; Tikhomirov, V. V.; Bandiera, L.; Bagli, E.; Germogli, G.; Mazzolari, A.; Romagnoni, M.

2018-04-01

A method to calculate both the bent crystal angle of alignment and radius of curvature by using only one distribution of deflection angles has been developed. The method is based on measuring of the angular position of recently predicted and observed quasichanneling oscillations in the deflection angle distribution and consequent fitting of both the radius and angular alignment by analytic formulae. In this paper this method is applied on the example of simulated angular distributions over a wide range of values of both radius and alignment for electrons. It is carried out through the example of (111) nonequidistant planes though this technique is general and could be applied to any kind of planes. In addition, the method application constraints are also discussed. It is shown by simulations that this method, being in fact a sort of beam diagnostics, allows one in a certain case to increase the crystal alignment accuracy as well as to control precisely the radius of curvature inside an accelerator tube without vacuum breaking. In addition, it speeds up the procedure of crystal alignment in channeling experiments, reducing beamtime consuming.

Efficient room-temperature source of polarized single photons

DOEpatents

Lukishova, Svetlana G.; Boyd, Robert W.; Stroud, Carlos R.

2007-08-07

An efficient technique for producing deterministically polarized single photons uses liquid-crystal hosts of either monomeric or oligomeric/polymeric form to preferentially align the single emitters for maximum excitation efficiency. Deterministic molecular alignment also provides deterministically polarized output photons; using planar-aligned cholesteric liquid crystal hosts as 1-D photonic-band-gap microcavities tunable to the emitter fluorescence band to increase source efficiency, using liquid crystal technology to prevent emitter bleaching. Emitters comprise soluble dyes, inorganic nanocrystals or trivalent rare-earth chelates.

High-mobility, aligned crystalline domains of TIPS-pentacene with metastable polymorphs through lateral confinement of crystal growth.

PubMed

Giri, Gaurav; Park, Steve; Vosgueritchian, Michael; Shulaker, Max Marcel; Bao, Zhenan

2014-01-22

Patterns composed of solvent wetting and dewetting regions promote lateral confinement of solution-sheared and lattice-strained TIPS-pentacene crystals. This lateral confinement causes aligned crystal growth, and the smallest patterns of 0.5 μm wide solvent wetting regions promotes formation of highly strained, aligned, and single-crystalline TIPS-pentacene regions with mobility as high as 2.7 cm(2) V(-1) s(-1) . © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Third harmonic frequency generation by type-I critically phase-matched LiB3O5 crystal by means of optically active quartz crystal.

PubMed

Gapontsev, Valentin P; Tyrtyshnyy, Valentin A; Vershinin, Oleg I; Davydov, Boris L; Oulianov, Dmitri A

2013-02-11

We present a method of third harmonic generation at 355 nm by frequency mixing of fundamental and second harmonic radiation of an ytterbium nanosecond pulsed all-fiber laser in a type-I phase-matched LiB(3)O(5) (LBO) crystal where originally orthogonal polarization planes of the fundamental and second harmonic beams are aligned by an optically active quartz crystal. 8 W of ultraviolet light at 355 nm were achieved with 40% conversion efficiency from 1064 nm radiation. The conversion efficiency obtained in a type-I phase-matched LBO THG crystal was 1.6 times higher than the one achieved in a type-II LBO crystal at similar experimental conditions. In comparison to half-wave plates traditionally used for polarization alignment the optically active quartz crystal has much lower temperature dependence and requires simpler optical alignment.

Investigation of synthetic spider silk crystallinity and alignment via electrothermal, pyroelectric, literature XRD, and tensile techniques.

PubMed

Munro, Troy; Putzeys, Tristan; Copeland, Cameron G; Xing, Changhu; Lewis, Randolph V; Ban, Heng; Glorieux, Christ; Wubbenhorst, Michael

2017-04-01

The processes used to create synthetic spider silk greatly affect the properties of the produced fibers. This paper investigates the effect of process variations during artificial spinning on the thermal and mechanical properties of the produced silk. Property values are also compared to the ones of the natural dragline silk of the N. clavipes spider, and to unprocessed (as-spun) synthetic silk. Structural characterization by scanning pyroelectric microscopy is employed to provide insight into the axial orientation of the crystalline regions of the fiber and is supported by XRD data. The results show that stretching and passage through liquid baths induce crystal formation and axial alignment in synthetic fibers, but with different structural organization than natural silks. Furthermore, an increase in thermal diffusivity and elastic modulus is observed with decreasing fiber diameter, trending towards properties of natural fiber. This effect seems to be related to silk fibers being subjected to a radial gradient during production.

Investigation of synthetic spider silk crystallinity and alignment via electrothermal, pyroelectric, literature XRD, and tensile techniques

PubMed Central

Munro, Troy; Putzeys, Tristan; Copeland, Cameron G.; Xing, Changhu; Lewis, Randolph V; Ban, Heng; Glorieux, Christ; Wubbenhorst, Michael

2018-01-01

The processes used to create synthetic spider silk greatly affect the properties of the produced fibers. This paper investigates the effect of process variations during artificial spinning on the thermal and mechanical properties of the produced silk. Property values are also compared to the ones of the natural dragline silk of the N. clavipes spider, and to unprocessed (as-spun) synthetic silk. Structural characterization by scanning pyroelectric microscopy is employed to provide insight into the axial orientation of the crystalline regions of the fiber and is supported by XRD data. The results show that stretching and passage through liquid baths induce crystal formation and axial alignment in synthetic fibers, but with different structural organization than natural silks. Furthermore, an increase in thermal diffusivity and elastic modulus is observed with decreasing fiber diameter, trending towards properties of natural fiber. This effect seems to be related to silk fibers being subjected to a radial gradient during production. PMID:29430211

The effect of surface alignment on analog control of director rotation in polarization stiffened SmC* devices

NASA Astrophysics Data System (ADS)

Reznikov, Mitya; Lopatina, Lena M.; O'Callaghan, Michael J.; Bos, Philip J.

2011-03-01

The effect of surface alignment on the achievement of analog ("V"-shaped) electric field control of director rotation in SmC* liquid crystal devices is investigated experimentally and through numerical modeling. Ferroelectric SmC* liquid crystals are intrinsically analog and thresholdless, i.e. the director can be rotated freely around the tilt cone. Whether or not a SmC* liquid crystal cell exhibits thresholdless switching depends strongly on the influence of the cell's alignment layers, on the magnitude of the liquid crystal's spontaneous polarization, and on whether smectic layers adopt a bookshelf or chevron configuration. To study the effect of the surface alignment layers, we have exploited a technique for the vertical (bookshelf) alignment of the smectic layers that does not depend on surface anisotropy. The alignment technique allows an experimental study of the influence of surfaces spanning a wide range of pretilt angles, azimuthal and zenithal anchoring energies. This technique is used to study the effect of surfaces on the threshold behavior of director rotation in SmC* materials under the influence of an electric field. The alignment technique also allowed us to use a high-PS liquid crystal material having an I-A-C phase sequence and reduced layer shrinkage thought to be well suited to thresholdless switching. We show that the alignment layer has a strong effect, and that excellent analog response can be achieved for the case of alignment layers which promote homeotropic director orientation. We further model and discuss the potential effect of a thin layer of nematic at the surface and the possibility of gliding of the easy axis during switching.

Effect of annealing on the structural and optical properties of heavily carbon-doped ZnO

NASA Astrophysics Data System (ADS)

Huang, He; Deng, Z. W.; Li, D. C.; Barbir, E.; Y Jiang, W.; Chen, M. X.; Kavanagh, K. L.; Mooney, P. M.; Watkins, S. P.

2010-04-01

ZnO films grown by metalorganic vapor phase epitaxy (MOVPE) at low temperatures (~500 °C) exhibit very high levels of carbon incorporation in the range of up to several percent. Such large levels of carbon incorporation significantly affect the structural properties of the thin films resulting in broadening of symmetric (0 0 2) rocking curves as well as broadened (1 0 1) pole figures compared with films grown at high temperature. Annealing of the films under air ambient at temperatures between 800 and 1100 °C results in dramatic sharpening of symmetric (0 0 2) rocking curves, indicating improved crystal alignment along the c-axes. (1 0 1) pole figure scans also show significant sharpening in the azimuthal axis, indicating similar improvements in the in-plane crystal alignment perpendicular to the c-axis. Raman spectra for as-grown ZnO at 500 °C show strong D and G peaks at 1381 and 1578 cm-1 due to sp2 carbon clusters. Annealing at 1000 °C results in the elimination of these bands, indicating that post-growth annealing treatment is a useful method to reduce the concentration of sp2 carbon clusters.

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.

Growth Of Oriented Crystals At Polymerized Membranes

DOEpatents

Charych, Deborah H. , Berman, Amir

2000-01-25

The present invention relates to methods and compositions for the growth and alignment of crystals at biopolymeric films. The methods and compositions of the present invention provide means to generate a variety of dense crystalline ceramic films, with totally aligned crystals, at low temperatures and pressures, suitable for use with polymer and plastic substrates.

The strength of a calcified tissue depends in part on the molecular structure and organization of its constituent mineral crystals in their organic matrix

NASA Technical Reports Server (NTRS)

Landis, W. J.

1995-01-01

High-voltage electron-microscopic tomographic (3D) studies of the ultrastructural interaction between mineral and organic matrix in a variety of calcified tissues reveal different crystal structural and organizational features in association with their respective organic matrices. In brittle or weak pathologic or ectopic calcifications, including examples of osteogenesis imperfecta, calciphylaxis, calcergy, and dermatomyositis, hydroxyapatite crystals occur in various sizes and shapes and are oriented and aligned with respect to collagen in a manner which is distinct from that found in normal calcified tissues. A model of collagen-mineral interaction is proposed which may account for the observed crystal structures and organization. The results indicate that the ultimate strength, support, and other mechanical properties provided by a calcified tissue are dependent in part upon the molecular structure and arrangement of its constituent mineral crystals within their organic matrix.

The strength of a calcified tissue depends in part on the molecular structure and organization of its constituent mineral crystals in their organic matrix.

PubMed

Landis, W J

1995-05-01

High-voltage electron-microscopic tomographic (3D) studies of the ultrastructural interaction between mineral and organic matrix in a variety of calcified tissues reveal different crystal structural and organizational features in association with their respective organic matrices. In brittle or weak pathologic or ectopic calcifications, including examples of osteogenesis imperfecta, calciphylaxis, calcergy, and dermatomyositis, hydroxyapatite crystals occur in various sizes and shapes and are oriented and aligned with respect to collagen in a manner which is distinct from that found in normal calcified tissues. A model of collagen-mineral interaction is proposed which may account for the observed crystal structures and organization. The results indicate that the ultimate strength, support, and other mechanical properties provided by a calcified tissue are dependent in part upon the molecular structure and arrangement of its constituent mineral crystals within their organic matrix.

Three-dimensionally modulated anisotropic structure for diffractive optical elements created by one-step three-beam polarization holographic photoalignment

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

Kawai, Kotaro, E-mail: s135016@stn.nagaokaut.ac.jp; Sakamoto, Moritsugu; Noda, Kohei

2016-03-28

A diffractive optical element with a three-dimensional liquid crystal (LC) alignment structure for advanced control of polarized beams was fabricated by a highly efficient one-step photoalignment method. This study is of great significance because different two-dimensional continuous and complex alignment patterns can be produced on two alignment films by simultaneously irradiating an empty glass cell composed of two unaligned photocrosslinkable polymer LC films with three-beam polarized interference beam. The polarization azimuth, ellipticity, and rotation direction of the diffracted beams from the resultant LC grating widely varied depending on the two-dimensional diffracted position and the polarization states of the incident beams.more » These polarization diffraction properties are well explained by theoretical analysis based on Jones calculus.« less

A molecular design principle of lyotropic liquid-crystalline conjugated polymers with directed alignment capability for plastic electronics

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

Kim, Bong-Gi; Jeong, Eun Jeong; Chung, Jong Won

Conjugated polymers with a one-dimensional p-orbital overlap exhibit optoelectronic anisotropy. Their unique anisotropic properties can be fully realized in device applications only when the conjugated chains are aligned. Here, we report a molecular design principle of conjugated polymers to achieve concentration-regulated chain planarization, self-assembly, liquid-crystal-like good mobility and non-interdigitated side chains. As a consequence of these intra- and intermolecular attributes, chain alignment along an applied flow field occurs. This liquid-crystalline conjugated polymer was realized by incorporating intramolecular sulphur–fluorine interactions and bulky side chains linked to a tetrahedral carbon having a large form factor. By optimizing the polymer concentration and themore » flow field, we could achieve a high dichroic ratio of 16.67 in emission from conducting conjugated polymer films. Two-dimensional grazing-incidence X-ray diffraction was performed to analyse a well-defined conjugated polymer alignment. Thin-film transistors built on highly aligned conjugated polymer films showed more than three orders of magnitude faster carrier mobility along the conjugated polymer alignment direction than the perpendicular direction.« less

Dynamic and magneto-optic properties of bent-core liquid crystals

NASA Astrophysics Data System (ADS)

Salili, Seyyed Muhammad

In this work, we describe dynamic behavior of free-standing bent-core liquid crystal filaments under dilative and axial compressive stresses in the B7 phase. We found that such filaments demonstrate very complex structures depending on the filament's temperature relative to the isotropic phase, initial filament thickness, and velocity at which the filament is pulled or compressed. We also present our experimental methods, results and analysis of the rupture and recoil properties of several bent-core liquid crystal filaments, anticipating that they may serve as a model system for complex biological fibers. After that, we systematically describe rheological measurements for dimeric liquid crystal compounds. We studied the shear-induced alignment properties, measured the viscoelastic properties as a function of temperature, shear rate, stress and frequency, and compared the results with the rheological properties of conventional chiral nematic and smectic phases. Then we present results of chiral nematic liquid crystals composed of flexible dimer molecules subject to large DC magnetic fields between 0 and 31T. We observe that these fields lead to selective reflection of light depending on temperature and magnetic field. The band of reflected wavelengths can be tuned from ultraviolet to beyond the IR-C band. A similar effect induced by electric fields has been presented previously, and was explained by a field-induced oblique-heliconical director deformation in accordance with early theoretical predictions. Finally, we report an unprecedented magnetic field-induced shifts of the isotropic-nematic phase transition temperature observed in liquid crystal dimers where two rigid linear mesogens are linked by flexible chains of either even- or odd-numbered hydrocarbon groups. This effect is explained in terms of quenching of the thermal fluctuations and decrease of the average bend angle of molecules in the odd-numbered dimers.

Polarization-dependent DANES study on vertically-aligned ZnO nanorods

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

Sun, Chengjun; Park, Chang-In; Jin, Zhenlan

2016-05-01

The local structural and local density of states of vertically-aligned ZnO nanorods were examined by using a polarization-dependent diffraction anomalous near edge structure (DANES) measurements from c-oriented ZnO nanorods at the Zn K edge with the incident x-ray electric field parallel and perpendicular to the x-ray momentum transfer direction. Orientation-dependent local structures determined by DANES were comparable with polarization-dependent EXAFS results. Unlike other techniques, polarization-dependent DANES can uniquely describe the orientation-dependent local structural properties and the local density of states of a selected element in selected-phased crystals of compounds or mixed-phased structures.

Adaptable liquid crystal elastomers with transesterification-based bond exchange reactions.

PubMed

Hanzon, Drew W; Traugutt, Nicholas A; McBride, Matthew K; Bowman, Christopher N; Yakacki, Christopher M; Yu, Kai

2018-02-14

Adaptable liquid crystal elastomers (LCEs) have recently emerged to provide a new and robust method to program monodomain LCE samples. When a constant stress is applied with active bond exchange reactions (BERs), polymer chains and mesogens gradually align in the strain direction. Mesogen alignment is maintained after removing the BER stimulus (e.g. by lowering the temperature) and the programmed LCE samples exhibit free-standing two-way shape switching behavior. Here, a new adaptable main-chain LCE system was developed with thermally induced transesterification BERs. The network combines the conventional properties of LCEs, such as an isotropic phase transition and soft elasticity, with the dynamic features of adaptable network polymers, which are malleable to stress relaxation due to the BERs. Polarized Fourier transform infrared measurements confirmed the alignment of polymer chains and mesogens after strain-induced programming. The influence of the creep stress, temperature, and time on the strain amplitude of two-way shape switching was examined. The LCE network demonstrates an innovative feature of reprogrammability, where the reversible shape-switching memory of programmed LCEs is readily deleted by free-standing heating as random BERs disrupt the mesogen alignment, so LCEs are reprogrammed after returning to the polydomain state. Due to the dynamic nature of the LCE network, it also exhibits a surface welding effect and can be fully dissolved in the organic solvent, which might be utilized for green and sustainable recycling of LCEs.

Alignment of nematic liquid crystals by inhomogeneous surfaces

NASA Astrophysics Data System (ADS)

Ong, Hiap Liew; Hurd, Alan J.; Meyer, Robert B.

1985-01-01

Variable oblique alignment of nematic liquid crystals has been achieved on microscopically inhomogeneous surfaces. The surfaces consist of small patches favoring vertical (homeotropic) alignment surrounded by a matrix favoring a planar alignment. The construction of these surfaces employs randomly distributed microscopic metal islands formed by certain metals as vapor-deposited films. Larger scale periodic patterns were made as well to verify the techniques. The results are interpreted in terms of a continuum elasticity theory and azimuthal degeneracy is also discussed.

Zigzag nanoribbons of two-dimensional silicene-like crystals: magnetic, topological and thermoelectric properties.

PubMed

Wierzbicki, Michał; Barnaś, Józef; Swirkowicz, Renata

2015-12-09

The effects of electron-electron and spin-orbit interactions on the ground-state magnetic configuration and on the corresponding thermoelectric and spin thermoelectric properties in zigzag nanoribbons of two-dimensional hexagonal crystals are analysed theoretically. The thermoelectric properties of quasi-stable magnetic states are also considered. Of particular interest is the influence of Coulomb and spin-orbit interactions on the topological edge states and on the transition between the topological insulator and conventional gap insulator states. It is shown that the interplay of both interactions also has a significant impact on the transport and thermoelectric characteristics of the nanoribbons. The spin-orbit interaction also determines the in-plane magnetic easy axis. The thermoelectric properties of nanoribbons with in-plane magnetic moments are compared to those of nanoribbons with edge magnetic moments oriented perpendicularly to their plane. Nanoribbons with ferromagnetic alignment of the edge moments are shown to reveal spin thermoelectricity in addition to the conventional one.

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.

Crystallization Behavior of Poly(ethylene oxide) in Vertically Aligned Carbon Nanotube Array.

PubMed

Sheng, Jiadong; Zhou, Shenglin; Yang, Zhaohui; Zhang, Xiaohua

2018-03-27

We investigate the effect of the presence of vertically aligned multiwalled carbon nanotubes (CNTs) on the orientation of poly(ethylene oxide) (PEO) lamellae and PEO crystallinity. The high alignment of carbon nanotubes acting as templates probably governs the orientation of PEO lamellae. This templating effect might result in the lamella planes of PEO crystals oriented along a direction parallel to the long axis of the nanotubes. The presence of aligned carbon nanotubes also gives rise to the decreases in PEO crystallinity, crystallization temperature, and melting temperature due to the perturbation of carbon nanotubes to the crystallization of PEO. These effects have significant implications for controlling the orientation of PEO lamellae and decreasing the crystallinity of PEO and thickness of PEO lamellae, which have significant impacts on ion transport in PEO/CNT composite and the capacitive performance of PEO/CNT composite. Both the decreased PEO crystallinity and the orientation of PEO lamellae along the long axes of vertically aligned CNTs give rise to the decrease in the charge transfer resistance, which is associated with the improvements in the ion transport and capacitive performance of PEO/CNT composite.

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.

Electric-field-induced flow-aligning state in a nematic liquid crystal.

PubMed

Fatriansyah, Jaka Fajar; Orihara, Hiroshi

2015-04-01

The response of shear stress to a weak ac electric field as a probe is measured in a nematic liquid crystal under shear flow and dc electric fields. Two states with different responses are clearly observed when the dc electric field is changed at a constant shear rate: the flow aligning and non-flow aligning states. The director lies in the shear plane in the flow aligning state and out of the plane in the non-flow aligning state. Through application of dc electric field, the non-flow aligning state can be changed to the flow aligning state. In the transition from the flow aligning state to the non-flow aligning state, it is found that the response increases and the relaxation time becomes longer. Here, the experimental results in the flow aligning state are discussed on the basis of the Ericksen-Leslie theory.

Liquid-crystal-based tunable plasmonic waveguide filters

NASA Astrophysics Data System (ADS)

Yin, Shengtao; Liu, Yan Jun; Xiao, Dong; He, Huilin; Luo, Dan; Jiang, Shouzhen; Dai, Haitao; Ji, Wei; Sun, Xiao Wei

2018-06-01

We propose a liquid-crystal-based tunable plasmonic waveguide filter and numerically investigate its filtering properties. The filter consists of a metal-insulator-metal waveguide with a nanocavity resonator. By filling the nanocavity with birefringent liquid crystals (LCs), we could then vary the effective refractive index of the nanocavity by controlling the alignment of the LC molecules, hence making the filter tunable. The tunable filtering properties are further analyzed in details via the temporal coupled mode theory (CMT) and the finite-difference time-domain (FDTD) method. The simulation results show that the resonant wavelengths have linear redshift as the refractive index of the nanocavity increases and the coupling efficiency is more than 65% without considering the internal loss in the nanocavity and waveguides. These achieved results by the FDTD simulations can be also accurately analyzed by CMT. The compact design of our proposed plasmonic filters is especially favorable for integration, and such filters could find many important potential applications in high-density plasmonic integration circuits.

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

New developments in 3D liquid crystal elastomers scaffolds for tissue engineering: from physical template to responsive substrate

NASA Astrophysics Data System (ADS)

Prévôt, Marianne E.; Bergquist, Leah E.; Sharma, Anshul; Mori, Taizo; Gao, Yungxiang; Bera, Tanmay; Zhu, Chenhui; Leslie, Michelle T.; Cukelj, Richard; Korley, LaShanda T. J.; Freeman, Ernest J.; McDonough, Jennifer A.; Clements, Robert J.; Hegmann, Elda

2017-08-01

We report here on cell growth and proliferation within a 3D architecture created using smectic liquid crystal elastomers (LCEs) leading to a responsive scaffold for tissue engineering. The investigated LCE scaffolds exhibit biocompatibility, controlled degradability, with mechanical properties and morphologies that can match development of the extracellular matrix. Moreover, the synthetic pathway and scaffold design offer a versatility of processing, allowing modifications of the surface such as adjusting the hydrophilic/hydrophobic balance and the mobility of the LC moieties to enhance the biomaterial performance. First, we succeeded in generating LCEs whose mechanical properties mimic muscle tissue. In films, our LCEs showed cell adhesion, proliferation, and alignment. We also achieved creating 3D LCE structures using either metallic template or microsphere scaffolds. Finally, we recorded a four times higher cell proliferation capability in comparison to conventional porous films and, most importantly, anisotropic cell growth that highlights the tremendous effect of liquid crystal moieties within LCEs on the cell environment.

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

On the formation of well-aligned ZnO nanowall networks by catalyst-free thermal evaporation method

NASA Astrophysics Data System (ADS)

Yin, Zhigang; Chen, Nuofu; Dai, Ruixuan; Liu, Lei; Zhang, Xingwang; Wang, Xiaohui; Wu, Jinliang; Chai, Chunlin

2007-07-01

Two-dimensional ZnO nanowall networks were grown on ZnO-coated silicon by thermal evaporation at low temperature without catalysts or additives. All of the results from scanning electronic spectroscope, X-ray diffraction and Raman scattering confirmed that the ZnO nanowalls were vertically aligned and c-axis oriented. The room-temperature photoluminescence spectra showed a dominated UV peak at 378 nm, and a much suppressed orange emission centered at ˜590 nm. This demonstrates fairly good crystal quality and optical properties of the product. A possible three-step, zinc vapor-controlled process was proposed to explain the growth of well-aligned ZnO nanowall networks. The pre-coated ZnO template layer plays a key role during the synthesis process, which guides the growth direction of the synthesized products.

A study of substrate-liquid crystal interaction

NASA Astrophysics Data System (ADS)

Zhang, Baoshe

This thesis concerns the study of substrate-liquid crystal interaction from two different angles. In one approach, we used the IPS (in-plane switching) technique to investigate the liquid crystal alignment by rubbed polyimide films. The IPS mode of liquid crystal cell operation is facilitated through comb electrodes capable of producing planar electric field. We have fabricated comb electrodes with a periodicity of 2 mum in order to confine the planar electric field close to the liquid crystal-substrate interface. Through optical transmittance measurements and comparison with theoretical predictions based on the Ladau-de Gennes formalism, we found the experimental data to be consistent with the physical picture of soft anchoring, in which the liquid crystal director at the substrate interface is rotated azimuthally under the planar electric field. As a result, we were able to obtain the azimuthal anchoring strength as a fitting parameter of the theory. This part of the thesis thus presents evidence(s) for director switching at the liquid crystal-substrate interface, as well as a method for measuring the azimuthal anchoring strength through optical means. In the second approach, we used nano-lithographic technique to fabricate textured two dimensional periodic patterns on silicon wafers, and examined the resulting liquid crystal alignment effect of such textured substrates. It was found that with decreasing periodicity, there exists an orientational transition from a state in which the liquid crystal alignment copies the substrate pattern at larger periodicity, to a state of uniform alignment at smaller periodicity. In our system, this transition occurs at a periodicity between 0.4 mum and 0.8 mum. Through theoretical simulations based on the model of competition between the elastic distortion energy and the interfacial anchoring potential, it was found that there is indeed a first-order abrupt transition when the periodicity is decreased. This is due to the fact that the elastic distortion energy scales as the inverse of the periodicity squared. Hence when the periodicity is decreased, the elastic distortion energy increases rapidly. At the critical periodicity the elastic distortion energy crosses the interfacial anchoring potential, below which the uniform alignment becomes the lower energy state. The uniform-aligned state was confirmed by the excellent theory-experiment agreement on spectral measurements, in conjunction with the optical microscope observations. In the uniform-aligned state, a large pretilt angle (35°) was obtained.

The stonehenge technique: a new method of crystal alignment for coherent bremsstrahlung experiments

NASA Astrophysics Data System (ADS)

Livingston, Kenneth

2005-08-01

In the coherent bremsstrahlung technique a thin diamond crystal oriented correctly in an electron beam can produce photons with a high degree of linear polarization.1 The crystal is mounted on a goniometer to control its orientation and it is necessary to measure the angular offsets a) between the crystal axes and the goniometer axes and b) between the goniometer and the electron beam axis. A method for measuring these offsets and aligning the crystal was developed by Lohman et al, and has been used successfully in Mainz.2 However, recent attempts to investigate new crystals have shown that this approach has limitations which become more serious at higher beam energies where more accurate setting of the crystal angles, which scale with l/Ebeam, is required. (Eg. the recent installation of coherent bremsstrahlung facility at Jlab, with Ebeam = 6 GeV ) This paper describes a new, more general alignment technique, which overcomes these limitations. The technique is based on scans where the horizontal and vertical rotation axes of the goniometer are adjusted in a series of steps to make the normal to the crystal describe a cone of a given angle. For each step in the scan, the photon energy spectrum is measured using a tagging spectrometer, and the offsets between the electron beam and the crystal lattice are inferred from the resulting 2D plot. Using this method, it is possible to align the crystal with the beam quickly, and hence to set any desired orientation of the crystal relative to the beam. This is essential for any experiment requiring linearly polarized photons produced via coherent bremsstrahlung, and is also required for a systematic study of the channeling radiation produced by the electron beam incident on the crystal.

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.

Liquid crystal dynamic flow control by bidirectional alignment surface

NASA Astrophysics Data System (ADS)

Li, Y. W.; Lee, C. Y.; Kwok, H. S.

2009-02-01

We investigate the behavior of liquid crystal dynamic flow in a cell with a bidirectional alignment (BDA) surface. Numerical simulations show that with a BDA surface having a pitch comparable to the cell gap d, the liquid crystal dynamic flow direction can be controlled by the driving voltage. Such an effect can be applied to bistable twisted nematic displays without the need for anchoring breaking.

Ion-beam-spurted dimethyl-sulfate-doped PEDOT:PSS composite-layer-aligning liquid crystal with low residual direct-current voltage

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

Liu, Yang; Lee, Ju Hwan; Seo, Dae-Shik, E-mail: dsseo@yonsei.ac.kr

2016-09-05

Thin ion-beam (IB)-spurted dimethyl sulfate/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (DMS/PEDOT:PSS) layers with improved electro-optic performance are presented for aligning liquid crystals. IB spurting is effective for enhancing the conductivity of such layers, as well as the anchoring energy of the liquid crystals sandwiched between them. Compared with a commercial twisted-nematic cell assembled with polyimide alignment layers, the same cell assembled with 3.0-keV IB-spurted DMS/PEDOT:PSS alignment layers shows a 38% faster switching and a 93% lower residual direct current. The improved electro-optic performance here is likely due to the enhanced electric field effect and the charge-releasing ability of thin IB-spurted DMS/PEDOT:PSS layers.

Transport properties of high quality heterostructures from unstable 2D crystals prepared in inert atmosphere

NASA Astrophysics Data System (ADS)

Yu, Geliang; Yang, Cao; Khestanova, Ekaterina; Mishchenko, Artem; Kretinin, Andy; Gorbachev, Roman; Novoselov, Konstantin; Andre, Geim; Manchester Group Team

Many layered materials can be cleaved down to individual atomic planes, similar to graphene, but only a small minority of them are stable under ambient conditions. The rest reacts and decomposes in air, which has severely hindered their investigation and possible uses. Here we introduce a remedial approach based on cleavage, transfer, alignment and encapsulation of airsensitive crystals, all inside a controlled inert atmosphere. To illustrate the technology, we choose two archetypal two-dimensional crystals unstable in air: black phosphorus and niobium diselenide. Our field-effect devices made from their monolayers are conductive and fully stable under ambient conditions, in contrast to the counterparts processed in air. NbSe2 remains superconducting down to the monolayer thickness. Starting with a trilayer, phosphorene devices reach sufficiently high mobilities to exhibit Landau quantization. The approach offers a venue to significantly expand the range of experimentally accessible two-dimensional crystals and their heterostructures.

Liquid crystal Janus emulsion droplets: preparation, tumbling, and swimming.

PubMed

Jeong, Joonwoo; Gross, Adam; Wei, Wei-Shao; Tu, Fuquan; Lee, Daeyeon; Collings, Peter J; Yodh, A G

2015-09-14

This study introduces liquid crystal (LC) Janus droplets. We describe a process for the preparation of these droplets, which consist of nematic LC and polymer compartments. The process employs solvent-induced phase separation in emulsion droplets generated by microfluidics. The droplet morphology was systematically investigated and demonstrated to be sensitive to the surfactant concentration in the background phase, the compartment volume ratio, and the possible coalescence of multiple Janus droplets. Interestingly, the combination of a polymer and an anisotropic LC introduces new functionalities into Janus droplets, and these properties lead to unusual dynamical behaviors. The different densities and solubilities of the two compartments produce gravity-induced alignment, tumbling, and directional self-propelled motion of Janus droplets. LC Janus droplets with remarkable optical properties and dynamical behaviors thus offer new avenues for applications of Janus colloids and active soft matter.

Computational split-field finite-difference time-domain evaluation of simplified tilt-angle models for parallel-aligned liquid-crystal devices

NASA Astrophysics Data System (ADS)

Márquez, Andrés; Francés, Jorge; Martínez, Francisco J.; Gallego, Sergi; Álvarez, Mariela L.; Calzado, Eva M.; Pascual, Inmaculada; Beléndez, Augusto

2018-03-01

Simplified analytical models with predictive capability enable simpler and faster optimization of the performance in applications of complex photonic devices. We recently demonstrated the most simplified analytical model still showing predictive capability for parallel-aligned liquid crystal on silicon (PA-LCoS) devices, which provides the voltage-dependent retardance for a very wide range of incidence angles and any wavelength in the visible. We further show that the proposed model is not only phenomenological but also physically meaningful, since two of its parameters provide the correct values for important internal properties of these devices related to the birefringence, cell gap, and director profile. Therefore, the proposed model can be used as a means to inspect internal physical properties of the cell. As an innovation, we also show the applicability of the split-field finite-difference time-domain (SF-FDTD) technique for phase-shift and retardance evaluation of PA-LCoS devices under oblique incidence. As a simplified model for PA-LCoS devices, we also consider the exact description of homogeneous birefringent slabs. However, we show that, despite its higher degree of simplification, the proposed model is more robust, providing unambiguous and physically meaningful solutions when fitting its parameters.

Positioning and joining of organic single-crystalline wires

PubMed Central

Wu, Yuchen; Feng, Jiangang; Jiang, Xiangyu; Zhang, Zhen; Wang, Xuedong; Su, Bin; Jiang, Lei

2015-01-01

Organic single-crystal, one-dimensional materials can effectively carry charges and/or excitons due to their highly ordered molecule packing, minimized defects and eliminated grain boundaries. Controlling the alignment/position of organic single-crystal one-dimensional architectures would allow on-demand photon/electron transport, which is a prerequisite in waveguides and other optoelectronic applications. Here we report a guided physical vapour transport technique to control the growth, alignment and positioning of organic single-crystal wires with the guidance of pillar-structured substrates. Submicrometre-wide, hundreds of micrometres long, highly aligned, organic single-crystal wire arrays are generated. Furthermore, these organic single-crystal wires can be joined within controlled angles by varying the pillar geometries. Owing to the controllable growth of organic single-crystal one-dimensional architectures, we can present proof-of-principle demonstrations utilizing joined wires to allow optical waveguide through small radii of curvature (internal angles of ~90–120°). Our methodology may open a route to control the growth of organic single-crystal one-dimensional materials with potential applications in optoelectronics. PMID:25814032

Nanoimprinted ultrafine line and space nanogratings for liquid crystal alignment.

PubMed

Liu, Yan Jun; Loh, Wei Wei; Leong, Eunice Sok Ping; Kustandi, Tanu Suryadi; Sun, Xiao Wei; Teng, Jing Hua

2012-11-23

Ultrafine 50 nm line and space nanogratings were fabricated using nanoimprint lithography, and were further used as an alignment layer for liquid crystals. The surface morphologies of the nanogratings were characterized and their surface energies were estimated through the measurement of the contact angles for two different liquids. Experimental results show that the surface energies of the nanogratings are anisotropic: the surface free energy towards the direction parallel to the grating lines is higher than that in the direction perpendicular to the grating lines. Electro-optical characteristics were tested from a twisted nematic liquid crystal cell, which was assembled using two identical nanogratings. Experimental results show that such a kind of nanograting is promising as an alternative to the conventional rubbing process for liquid crystal alignment.

Red blood cells aligning inside innovative liquid crystal cell

NASA Astrophysics Data System (ADS)

Likhomanova, S. V.; Kamanin, A. A.; Kamanina, N. V.

2017-11-01

Investigation results of red blood cells (human erythrocytes) aligning and fixing inside the liquid crystal (LC) cell have been presented in the present paper. LC cells have been modified through the improved nanostructured relief and LC sensitized with intermolecular charge transfer complex COANP-C70.

Optical detection of sepsis markers using liquid crystal based biosensors

NASA Astrophysics Data System (ADS)

McCamley, Maureen K.; Artenstein, Andrew W.; Opal, Steven M.; Crawford, Gregory P.

2007-02-01

A liquid crystal based biosensor for the detection and diagnosis of sepsis is currently in development. Sepsis, a major clinical syndrome with a significant public health burden in the US due to a large elderly population, is the systemic response of the body to a localized infection and is defined as the combination of pathologic infection and physiological changes. Bacterial infections are responsible for 90% of cases of sepsis in the US. Currently there is no bedside diagnostic available to positively identify sepsis. The basic detection scheme employed in a liquid crystal biosensor contains attributes that would find value in a clinical setting, especially for the early detection of sepsis. Utilizing the unique properties of liquid crystals, such as birefringence, a bedside diagnostic is in development which will optically report the presence of biomolecules. In a septic patient, an endotoxin known as lipopolysaccharide (LPS) is released from the outer membrane of Gram-negative bacteria and can be found in the blood stream. It is hypothesized that this long chained molecule will cause local disruptions to the open surface of a sensor containing aligned liquid crystal. The bulk liquid crystal ampli.es these local changes at the surface due to the presence of the sepsis marker, providing an optical readout through polarizing microscopy images. Liquid crystal sensors consisting of both square and circular grids, 100-200 μm in size, have been fabricated and filled with a common liquid crystal material, 5CB. Homeotropic alignment was confirmed using polarizing microscopy. The grids were then contacted with either saline only (control), or saline with varying concentrations of LPS. Changes in the con.guration of the nematic director of the liquid crystal were observed through the range of concentrations tested (5mg/mL - 1pg/mL) which have been confirmed by a consulting physician as clinically relevant levels.

A mimic study on effects of fluoride on tooth enamel structures

NASA Astrophysics Data System (ADS)

Ma, Guobin; Wang, Mu; Liu, Xiang Yang

2010-03-01

Tooth enamel is the hardest tissue in human body, and this superior mechanical property is contributed by its unique microstructures, i.e., oriented growth of rod-like apatite crystals into basic structural units called the prisms Fluoride (F^-) has been recognized to have significant effects on the physical and chemical properties of tooth enamel. However, the role of F^- on microstructures of apatite crystals is not well understood yet. Here we report a detailed investigation on the topic. Mimic in vitro growth of tooth enamel structures is performed at the biophysical conditions in simulated body fluids, using belt-like hydroxyapatite crystals as substrates It shows that F^- on the order of 0.1 mM will dramatically change the morphology of the grown crystals from irregular slabs to nano-needles, and the needles are aligned along the substrate with an average misorientation of ˜12 . Branched growth of bundles of nano-needles occurs with further increase of F^-, and finally, growth of highly porous structures as well as microspheres takes place when the F^- concentration exceeds 5 mM. In comparison with real tooth enamel structures, the relationship between enamel microstructures and tooth caries as well as fluorosis is discussed.

Shear alignment and orientational order of shape-anisotropic grains

NASA Astrophysics Data System (ADS)

Stannarius, Ralf; Wegner, Sandra; Szabó, Balázs; Börzsönyi, Tamás

2014-03-01

Granular matter research was focused for a long time mainly on ensembles of spherical or irregularly shaped grains. In recent years, interest has grown in the study of anisometric, i.e. elongated or flattened particles [see e. g. Börzsönyi, Soft Matter 9, 7401 (2013)]. However, many related phenomena are still only little understood, quantitative experiments are scarce. We investigate shear induced order and alignment of macroscopic shape-anisotropic particles by means of X-ray computed tomography. Packing and orientation of individual grains in sheared ensembles of prolate and oblate objects (ellipsoids, cylinders and similar) are resolved non-invasively [T. Börzsönyi PRL 108, 228302 (2012)]. The experiments show that many observations are qualitatively and even quantitatively comparable to the behavior of well-understood molecular liquid crystals. We establish quantitative relations between aspect ratios and shear alignment. The induced orientational order influences local packing as well as macroscopic friction properties.

Anchoring energy of photo-sensitive polyimide alignment film containing methoxy cinnamate

NASA Astrophysics Data System (ADS)

Kim, Suyoung; Shin, Sung Eui; Shin, DongMyung

2010-02-01

Photosensitive polyimide containing 2-methoxy cinnamate was synthesized for photo-alignment layer of liquid crystals (LCs). 2-Methoxy cinnamic acid was confirmed photo-sensitive material by linearly polarized UV light. We studied that effect of polarized UV light on rubbed polyimide film. Anchoring energy of liquid crystal with aligning surface was measured. Irradiation of depolarized UV light on rubbed Polyimide film suppressed effective anchoring energy. Linearly polarized UV light on rubbed polyimide film controlled anchoring energy effectively. Polyimide film containing 2-methoxy cinnamate can control the photo-alignment layer easily due to its photo-sensitivity.

Progress in linear optics, non-linear optics and surface alignment of liquid crystals

NASA Astrophysics Data System (ADS)

Ong, H. L.; Meyer, R. B.; Hurd, A. J.; Karn, A. J.; Arakelian, S. M.; Shen, Y. R.; Sanda, P. N.; Dove, D. B.; Jansen, S. A.; Hoffmann, R.

We first discuss the progress in linear optics, in particular, the formulation and application of geometrical-optics approximation and its generalization. We then discuss the progress in non-linear optics, in particular, the enhancement of a first-order Freedericksz transition and intrinsic optical bistability in homeotropic and parallel oriented nematic liquid crystal cells. Finally, we discuss the liquid crystal alignment and surface effects on field-induced Freedericksz transition.

Large polar pretilt for the liquid crystal homologous series alkylcyanobiphenyl

NASA Astrophysics Data System (ADS)

Huang, Zhibin; Rosenblatt, Charles

2005-01-01

Sufficiently strong rubbing of the polyimide alignment layer SE-1211 (Nissan Chemical Industries, Ltd.) results in a large pretilt of the liquid crystal director from the homeotropic orientation. The threshold rubbing strength required to induce nonzero pretilt is found to be a monotonic function of the number of methylene units in the homologous liquid crystal series alkylcyanobiphenyl. The results are discussed in terms of the dual easy axis model for alignment.

Anisotropic Properties of Single-Crystalline CeNiGe2

NASA Astrophysics Data System (ADS)

Jung, M. H.; Harrison, N.; Lacerda, A. H.; Pagliuso, P. G.; Sarrao, J. L.; Thompson, J. D.

2002-07-01

The anisotropic properties of CeNiGe2 with a layered crystal structure have been studied by measurements of electrical resistivity, magnetic susceptibility and magnetization. It is confirmed that CeNiGe2 undergoes two-step antiferromagnetic transition at TNI = 4 K and TNII = 3 K as reported earlier on polycrystalline samples. CeNiGe2 is found to exhibit highly anisotropic properties with an easy magnetization axis along the longest crystallographic b direction. The magnetization ratio M(H//b)/M(H⊥b) is estimated to be about 15 at 5 T. The in-plane resistivity ρ⊥b(T) shows double maxima typical of that expected when an interplay of crystal-field and Kondo effects plays a role. The low-T maximum at 4 K in ρ⊥b(T) is strongly suppressed with increasing magnetic field. This negative magnetoresistance is a result of the strong reduction of magnetic scattering by the ferromagnetic alignment of Ce magnetic moments.

Fast Response and Spontaneous Alignment in Liquid Crystals Doped with 12-Hydroxystearic Acid Gelators.

PubMed

Lin, Hui-Chi; Wang, Chih-Hung; Wang, Jyun-Kai; Tsai, Sheng-Feng

2018-05-07

The spontaneous vertical alignment of liquid crystals (LCs) in gelator (12-hydroxystearic acid)-doped LC cells was studied. Gelator-induced alignment can be used in both positive and negative LC cells. The electro-optical characteristics of the gelator-doped negative LC cell were similar to those of an LC cell that contained a vertically aligned (VA) host. The rise time of the gelator-doped LC cell was two orders of magnitude shorter than that of the VA host LC cell. The experimental results indicate that the gelator-induced vertical alignment of LC molecules occurred not only on the surface of the indium tin oxide (ITO) but also on the homogeneous alignment layer. Various LC alignments (planar, hybrid, multistable hybrid, and vertical alignments) were achieved by modulating the doped gelator concentrations. The multistable characteristic of LCs doped with the gelator is also presented. The alignment by doping with a gelator reduces the manufacturing costs and provides a means of fabricating fast-responding, flexible LC displays using a low-temperature process.

Electrically switchable photonic liquid crystal devices for routing of a polarized light wave

NASA Astrophysics Data System (ADS)

Rushnova, Irina I.; Melnikova, Elena A.; Tolstik, Alexei L.; Muravsky, Alexander A.

2018-04-01

The new mode of LC alignment based on photoalignment AtA-2 azo dye where the refractive interface between orthogonal orientations of the LC director exists without voltage and disappeared or changed with critical voltage has been proposed. The technology to fabricate electrically controlled liquid crystal elements for spatial separation and switching of linearly polarized light beams on the basis of the total internal reflection effect has been significantly improved. Its distinctive feature is the application of a composite alignment material comprising two sublayers of Nylon-6 and AtA-2 photoalignment azo dye offering patterned liquid crystal director orientation with high alignment quality value q = 0 . 998. The fabricated electrically controlled spatially structured liquid crystal devices enable implementation of propagation directions separation for orthogonally polarized light beams and their switching with minimal crosstalk.

AFM and x-ray studies of buffing and uv light induced alignment of liquid crystals on SE610 polyimide films

NASA Astrophysics Data System (ADS)

Kim, Jae-Hoon; Shi, Yushan; Ha, Kiryong; West, John L.; Kumar, Satyendra

1997-03-01

We have studied the competition between the effects of mechanical buffing of and photo-induced chemical reaction in Nissan SE610 polyimide film on the director orientation of liquid crystals using atomic force microscopy (AFM) and textural study under polarizing miscroscope. It was found that the uv light exposure after buffing significantly alters the degree and the direction of alignment achieved by buffing. Results of our study show that the two techniques can be used to control and fine-tune liquid crystal alignment. A description of the microscopic changes as inferred from AFM and x-ray studies will be presented.

High-Throughput Image Analysis of Fibrillar Materials: A Case Study on Polymer Nanofiber Packing, Alignment, and Defects in Organic Field Effect Transistors.

PubMed

Persson, Nils E; Rafshoon, Joshua; Naghshpour, Kaylie; Fast, Tony; Chu, Ping-Hsun; McBride, Michael; Risteen, Bailey; Grover, Martha; Reichmanis, Elsa

2017-10-18

High-throughput discovery of process-structure-property relationships in materials through an informatics-enabled empirical approach is an increasingly utilized technique in materials research due to the rapidly expanding availability of data. Here, process-structure-property relationships are extracted for the nucleation, growth, and deposition of semiconducting poly(3-hexylthiophene) (P3HT) nanofibers used in organic field effect transistors, via high-throughput image analysis. This study is performed using an automated image analysis pipeline combining existing open-source software and new algorithms, enabling the rapid evaluation of structural metrics for images of fibrillar materials, including local orientational order, fiber length density, and fiber length distributions. We observe that microfluidic processing leads to fibers that pack with unusually high density, while sonication yields fibers that pack sparsely with low alignment. This is attributed to differences in their crystallization mechanisms. P3HT nanofiber packing during thin film deposition exhibits behavior suggesting that fibers are confined to packing in two-dimensional layers. We find that fiber alignment, a feature correlated with charge carrier mobility, is driven by increasing fiber length, and that shorter fibers tend to segregate to the buried dielectric interface during deposition, creating potentially performance-limiting defects in alignment. Another barrier to perfect alignment is the curvature of P3HT fibers; we propose a mechanistic simulation of fiber growth that reconciles both this curvature and the log-normal distribution of fiber lengths inherent to the fiber populations under consideration.

Molecular Orientation of a Terbium(III)-Phthalocyaninato Double-Decker Complex for Effective Suppression of Quantum Tunneling of the Magnetization.

PubMed

Yamabayashi, Tsutomu; Katoh, Keiichi; Breedlove, Brian K; Yamashita, Masahiro

2017-06-15

Single-molecule magnet (SMM) properties of crystals of a terbium(III)-phthalocyaninato double-decker complex with different molecular packings ( 1 : TbPc₂, 2 : TbPc₂·CH₂Cl₂) were studied to elucidate the relationship between the molecular packing and SMM properties. From single crystal X-ray analyses, the high symmetry of the coordination environment of 2 suggested that the SMM properties were improved. Furthermore, the shorter intermolecular Tb-Tb distance and relative collinear alignment of the magnetic dipole in 2 indicated that the magnetic dipole-dipole interactions were stronger than those in 1 . This was confirmed by using direct current magnetic measurements. From alternating current magnetic measurements, the activation energy for spin reversal for 1 and 2 were similar. However, the relaxation time for 2 is three orders of magnitude slower than that for 1 in the low- T region due to effective suppression of the quantum tunneling of the magnetization. These results suggest that the SMM properties of TbPc₂ highly depend on the molecular packing.

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.

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.

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

Micro-beam Laue alignment of multi-reflection Bragg coherent diffraction imaging measurements

DOE PAGES

Hofmann, Felix; Phillips, Nicholas W.; Harder, Ross J.; ...

2017-08-08

Multi-reflection Bragg coherent diffraction imaging has the potential to allow three-dimensional (3D) resolved measurements of the full lattice strain tensor in specific micro-crystals. Until now such measurements were hampered by the need for laborious, time-intensive alignment procedures. Here, in this paper, a different approach is demonstrated, using micro-beam Laue X-ray diffraction to first determine the lattice orientation of the micro-crystal. This information is then used to rapidly align coherent diffraction measurements of three or more reflections from the crystal. Based on these, 3D strain and stress fields in the crystal are successfully determined. This approach is demonstrated on a focusedmore » ion beam milled micro-crystal from which six reflections could be measured. Since information from more than three independent reflections is available, the reliability of the phases retrieved from the coherent diffraction data can be assessed. Lastly, our results show that rapid, reliable 3D coherent diffraction measurements of the full lattice strain tensor in specific micro-crystals are now feasible and can be successfully carried out even in heavily distorted samples.« less

Micro-beam Laue alignment of multi-reflection Bragg coherent diffraction imaging measurements

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

Hofmann, Felix; Phillips, Nicholas W.; Harder, Ross J.

Multi-reflection Bragg coherent diffraction imaging has the potential to allow three-dimensional (3D) resolved measurements of the full lattice strain tensor in specific micro-crystals. Until now such measurements were hampered by the need for laborious, time-intensive alignment procedures. Here, in this paper, a different approach is demonstrated, using micro-beam Laue X-ray diffraction to first determine the lattice orientation of the micro-crystal. This information is then used to rapidly align coherent diffraction measurements of three or more reflections from the crystal. Based on these, 3D strain and stress fields in the crystal are successfully determined. This approach is demonstrated on a focusedmore » ion beam milled micro-crystal from which six reflections could be measured. Since information from more than three independent reflections is available, the reliability of the phases retrieved from the coherent diffraction data can be assessed. Lastly, our results show that rapid, reliable 3D coherent diffraction measurements of the full lattice strain tensor in specific micro-crystals are now feasible and can be successfully carried out even in heavily distorted samples.« less

Micro-beam Laue alignment of multi-reflection Bragg coherent diffraction imaging measurements.

PubMed

Hofmann, Felix; Phillips, Nicholas W; Harder, Ross J; Liu, Wenjun; Clark, Jesse N; Robinson, Ian K; Abbey, Brian

2017-09-01

Multi-reflection Bragg coherent diffraction imaging has the potential to allow three-dimensional (3D) resolved measurements of the full lattice strain tensor in specific micro-crystals. Until now such measurements were hampered by the need for laborious, time-intensive alignment procedures. Here a different approach is demonstrated, using micro-beam Laue X-ray diffraction to first determine the lattice orientation of the micro-crystal. This information is then used to rapidly align coherent diffraction measurements of three or more reflections from the crystal. Based on these, 3D strain and stress fields in the crystal are successfully determined. This approach is demonstrated on a focused ion beam milled micro-crystal from which six reflections could be measured. Since information from more than three independent reflections is available, the reliability of the phases retrieved from the coherent diffraction data can be assessed. Our results show that rapid, reliable 3D coherent diffraction measurements of the full lattice strain tensor in specific micro-crystals are now feasible and can be successfully carried out even in heavily distorted samples.

Micro-beam Laue Alignment of Multi-Reflection Bragg Coherent Diffraction Imaging Measurements

PubMed Central

Hofmann, Felix; Phillips, Nicholas W.; Harder, Ross J.; Liu, Wenjun; Clark, Jesse N.; Robinson, Ian K.; Abbey, Brian

2017-01-01

Multi-reflection Bragg coherent diffraction imaging has the potential to allow 3D resolved measurements of the full lattice strain tensor in specific micro-crystals. Until now such measurements were hampered by the need for laborious, time-intensive alignment procedures. Here we demonstrate a different approach, using micro-beam Laue X-ray diffraction to first determine the lattice orientation of the micro-crystal. This information is then used to rapidly align coherent diffraction measurements of three or more reflections from the crystal. Based on these, 3D strain and stress fields in the crystal are successfully determined. This approach is demonstrated on a focussed ion beam milled micro-crystal from which six reflections could be measured. Since information from more than three independent reflections is available, the reliability of the phases retrieved from the coherent diffraction data can be assessed. Our results show that rapid, reliable 3D coherent diffraction measurements of the full lattice strain tensor in specific micro-crystals are now feasible and can be successfully carried out even in heavily distorted samples. PMID:28862628

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.

Optimizing alignment and growth of low-loss YAG single crystal fibers using laser heated pedestal growth technique.

PubMed

Bera, Subhabrata; Nie, Craig D; Soskind, Michael G; Harrington, James A

2017-12-10

The effect of misalignments of different optical components in the laser heated pedestal growth apparatus have been modeled using Zemax optical design software. By isolating the misalignments causing the non-uniformity in the melt zone, the alignment of the components was fine-tuned. Using this optimized alignment, low-loss YAG single crystal fibers of 120 μm diameter were grown, with total attenuation loss as low as 0.5 dB/m at 1064 nm.

Wide-view transflective liquid crystal display for mobile applications

NASA Astrophysics Data System (ADS)

Kim, Hyang Yul; Ge, Zhibing; Wu, Shin-Tson; Lee, Seung Hee

2007-12-01

A high optical efficiency and wide-view transflective liquid crystal display based on fringe-field switching structure is proposed. The transmissive part has a homogenous liquid crystal (LC) alignment and is driven by a fringe electric field, which exhibits excellent electro-optic characteristics. The reflective part has a hybrid LC alignment with quarter-wave phase retardation and is also driven by a fringe electric field. Consequently, the transmissive and reflective parts have similar gamma curves.

The use of a mini-κ goniometer head in macromolecular crystallography diffraction experiments

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

Brockhauser, Sandor; UJF–EMBL–CNRS UMI 3265, 6 Rue Jules Horowitz, 38043 Grenoble; Ravelli, Raimond B. G.

2013-07-01

Hardware and software solutions for MX data-collection strategies using the EMBL/ESRF miniaturized multi-axis goniometer head are presented. Most macromolecular crystallography (MX) diffraction experiments at synchrotrons use a single-axis goniometer. This markedly contrasts with small-molecule crystallography, in which the majority of the diffraction data are collected using multi-axis goniometers. A novel miniaturized κ-goniometer head, the MK3, has been developed to allow macromolecular crystals to be aligned. It is available on the majority of the structural biology beamlines at the ESRF, as well as elsewhere. In addition, the Strategy for the Alignment of Crystals (STAC) software package has been developed to facilitatemore » the use of the MK3 and other similar devices. Use of the MK3 and STAC is streamlined by their incorporation into online analysis tools such as EDNA. The current use of STAC and MK3 on the MX beamlines at the ESRF is discussed. It is shown that the alignment of macromolecular crystals can result in improved diffraction data quality compared with data obtained from randomly aligned crystals.« less

Uncovering a reconstructive solid-solid phase transition in a metal-organic framework.

PubMed

Longley, L; Li, N; Wei, F; Bennett, T D

2017-11-01

A nanoporous three-dimensional metal-organic framework (MOF), ZnPurBr undergoes a transition to a previously unreported high-temperature phase, ZnPurBr-ht. The transition, which proceeds without mass loss, is uncovered through the use of differential scanning calorimetry (DSC). The new crystal structure was solved using single-crystal X-ray diffraction, and the mechanical properties of both phases investigated by nanoindentation and density functional theory. The anisotropy of the calculated Young's moduli showed good agreement with the crystallographic alignment of the stiff purinate organic linker. The results provide a prototypical example of the importance of the use of DSC in the MOF field, where its use is not currently standard in characterization.

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.

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

Liquid crystals of carbon nanotubes and graphene.

PubMed

Zakri, Cécile; Blanc, Christophe; Grelet, Eric; Zamora-Ledezma, Camilo; Puech, Nicolas; Anglaret, Eric; Poulin, Philippe

2013-04-13

Liquid crystal ordering is an opportunity to develop novel materials and applications with spontaneously aligned nanotubes or graphene particles. Nevertheless, achieving high orientational order parameter and large monodomains remains a challenge. In addition, our restricted knowledge of the structure of the currently available materials is a limitation for fundamental studies and future applications. This paper presents recent methodologies that have been developed to achieve large monodomains of nematic liquid crystals. These allow quantification and increase of their order parameters. Nematic ordering provides an efficient way to prepare conductive films that exhibit anisotropic properties. In particular, it is shown how the electrical conductivity anisotropy increases with the order parameter of the nematic liquid crystal. The order parameter can be tuned by controlling the length and entanglement of the nanotubes. In the second part of the paper, recent results on graphene liquid crystals are reported. The possibility to obtain water-based liquid crystals stabilized by surfactant molecules is demonstrated. Structural and thermodynamic characterizations provide indirect but statistical information on the dimensions of the graphene flakes. From a general point of view, this work presents experimental approaches to optimize the use of nanocarbons as liquid crystals and provides new methodologies for the still challenging characterization of such materials.

Synthesis and structural characterization of bulk Sb2Te3 single crystal

NASA Astrophysics Data System (ADS)

Sultana, Rabia; Gahtori, Bhasker; Meena, R. S.; Awana, V. P. S.

2018-05-01

We report the growth and characterization of bulk Sb2Te3 single crystal synthesized by the self flux method via solid state reaction route from high temperature melt (850˚C) and slow cooling (2˚C/hour) of constituent elements. The single crystal X-ray diffraction pattern showed the 00l alignment and the high crystalline nature of the resultant sample. The rietveld fitted room temperature powder XRD revealed the phase purity and rhombohedral structure of the synthesized crystal. The formation and analysis of unit cell structure further verified the rhombohedral structure composed of three quintuple layers stacked one over the other. The SEM image showed the layered directional growth of the synthesized crystal carried out using the ZEISS-EVOMA-10 scanning electron microscope The electrical resistivity measurement was carried out using the conventional four-probe method on a quantum design Physical Property Measurement System (PPMS). The temperature dependent electrical resistivity plot for studied Sb2Te3 single crystal depicts metallic behaviour in the absence of any applied magnetic field. The synthesis as well as the structural characterization of as grown Sb2Te3 single crystal is reported and discussed in the present letter.

Exploiting both optical and electrical anisotropy in nanowire electrodes for higher transparency.

PubMed

Dong, Jianjin; Goldthorpe, Irene A

2018-01-26

Transparent electrodes such as indium tin oxide and random meshes of silver nanowires (AgNWs) have isotropic in-plane properties. However, we show that imparting some alignment to AgNWs can create anisotropic transparency and electrical conductivity characteristics that may benefit many applications. For example, liquid crystal displays and the touch sensors on top of them often only need to be transparent to one type of polarized light as well as predominantly conductive in only one direction. Herein, AgNWs are slightly preferentially aligned during their deposition by rod coating. Compared to randomly oriented AgNW films, the alignment boosts the transparency to perpendicularly polarized light, as well as achieves a higher transparency for a given sheet resistance in one direction compared to randomly oriented AgNWs films. These factors together increase the transparency of a 16 Ω/sq electrode by 7.3 percentage points. The alignment technique is cheap and scalable, compatible with roll-to-roll processes, and most importantly does not require extra processing steps, as rod coating is already a standard process for AgNW electrode fabrication.

Exploiting both optical and electrical anisotropy in nanowire electrodes for higher transparency

NASA Astrophysics Data System (ADS)

Dong, Jianjin; Goldthorpe, Irene A.

2018-01-01

Transparent electrodes such as indium tin oxide and random meshes of silver nanowires (AgNWs) have isotropic in-plane properties. However, we show that imparting some alignment to AgNWs can create anisotropic transparency and electrical conductivity characteristics that may benefit many applications. For example, liquid crystal displays and the touch sensors on top of them often only need to be transparent to one type of polarized light as well as predominantly conductive in only one direction. Herein, AgNWs are slightly preferentially aligned during their deposition by rod coating. Compared to randomly oriented AgNW films, the alignment boosts the transparency to perpendicularly polarized light, as well as achieves a higher transparency for a given sheet resistance in one direction compared to randomly oriented AgNWs films. These factors together increase the transparency of a 16 Ω/sq electrode by 7.3 percentage points. The alignment technique is cheap and scalable, compatible with roll-to-roll processes, and most importantly does not require extra processing steps, as rod coating is already a standard process for AgNW electrode fabrication.

Effect of grain alignment on magnetic properties of Hg(Re)-1223 superconductors

NASA Astrophysics Data System (ADS)

Sakamoto, N.; Noguchi, S.; Akune, T.; Matsumoto, Y.

2002-08-01

Alignment of HgBa 2Ca 2Cu 3Re 0.2O y (Hg(Re)-1223) powders was made in epoxy resin under a high magnetic field of 10 T to be confirmed by X-ray analysis. DC magnetizations and AC susceptibilities of the grain aligned specimen were measured by SQUID and PPMS magnetometers at temperatures of 5-110 K and under the field of 0-14 T for both field directions of B parallel and perpendicular to ab-plane. The magnetization width for B parallel to the c-axis ΔMc showed high values at low field, decreased rather rapidly with the magnetic field compared to that for B parallel to the ab-plane ΔMab and became lower than ΔMab above a crossing field Bcr. Peak-heights of the imaginary parts of the AC susceptibilities χ″ were largest at B∥ c-axis. Non-aligned samples always showed intermediate characteristics between B∥ c-axis and B∥ ab-plane. Irreversibility fields of all samples were also evaluated. Correlations of the pinning mechanism with the crystal axis orientations are discussed.

Fast Response and Spontaneous Alignment in Liquid Crystals Doped with 12-Hydroxystearic Acid Gelators

PubMed Central

Lin, Hui-Chi; Wang, Chih-Hung; Wang, Jyun-Kai; Tsai, Sheng-Feng

2018-01-01

The spontaneous vertical alignment of liquid crystals (LCs) in gelator (12-hydroxystearic acid)-doped LC cells was studied. Gelator-induced alignment can be used in both positive and negative LC cells. The electro-optical characteristics of the gelator-doped negative LC cell were similar to those of an LC cell that contained a vertically aligned (VA) host. The rise time of the gelator-doped LC cell was two orders of magnitude shorter than that of the VA host LC cell. The experimental results indicate that the gelator-induced vertical alignment of LC molecules occurred not only on the surface of the indium tin oxide (ITO) but also on the homogeneous alignment layer. Various LC alignments (planar, hybrid, multistable hybrid, and vertical alignments) were achieved by modulating the doped gelator concentrations. The multistable characteristic of LCs doped with the gelator is also presented. The alignment by doping with a gelator reduces the manufacturing costs and provides a means of fabricating fast-responding, flexible LC displays using a low-temperature process. PMID:29735937

Experiments with crystal deflectors for high energy ion beams: Electromagnetic dissociation probability for well channeled ions

NASA Astrophysics Data System (ADS)

Scandale, W.; Taratin, A. M.; Kovalenko, A. D.

2013-01-01

The paper presents the current status with the use of the crystal defectors for high energy ion beams. The channeling properties of multicharged ions are discussed. The results of the experiments on the deflection and extraction (collimation) of high energy ion beams with bent crystals performed in the accelerator centers are shortly considered. The analysis of the recent collimation experiment with a Pb nuclei of 270GeV/c per charge at the CERN Super Proton Synchrotron showed that the channeling efficiency was as large as about 90%. For Pb ions of the LHC energies a new mechanism, which can reduce the channeling efficiency, appears. The electromagnetic dissociation (ED) becomes possible for well channeled particles. However, the estimations performed in the paper show that the ED probability is small and should not visibly reduce the collimation efficiency. On the other hand, the aligned crystal gives the possibility to study the ED processes of heavy nuclei in the conditions when nuclear interactions are fully suppressed.

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.

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.

Alignment of crystal orientations of the multi-domain photonic crystals in Parides sesostris wing scales

PubMed Central

Yoshioka, S.; Fujita, H.; Kinoshita, S.; Matsuhana, B.

2014-01-01

It is known that the wing scales of the emerald-patched cattleheart butterfly, Parides sesostris, contain gyroid-type photonic crystals, which produce a green structural colour. However, the photonic crystal is not a single crystal that spreads over the entire scale, but it is separated into many small domains with different crystal orientations. As a photonic crystal generally has band gaps at different frequencies depending on the direction of light propagation, it seems mysterious that the scale is observed to be uniformly green under an optical microscope despite the multi-domain structure. In this study, we have carefully investigated the structure of the wing scale and discovered that the crystal orientations of different domains are not perfectly random, but there is a preferred crystal orientation that is aligned along the surface normal of the scale. This finding suggests that there is an additional factor during the developmental process of the microstructure that regulates the crystal orientation. PMID:24352678

Fast switchable ferroelectric liquid crystal gratings with two electro-optical modes

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

Ma, Ying; Srivastava, A. K., E-mail: abhishek-srivastava-lu@yahoo.co.in; Chigrinov, V. G.

In this article, we reveal a theoretical and experimental illustration of the Ferroelectric liquid crystal (FLC) grating fabricated by mean of patterned alignment based on photo-alignment. The complexity related to the mismatching of the predefined alignment domains on the top and bottom substrate has been avoided by incorporating only one side photo aligned substrate while the other substrate does not have any alignment layer. Depending on the easy axis in the said alignment domains and the azimuth plane of the impinging polarized light, the diffracting element can be tuned in two modes i.e. DIFF/OFF switchable and DIFF/TRANS switchable modes, whichmore » can be applied to different applications. The diffraction profile has been illustrated theoretically that fits well with the experimental finding and thus the proposed diffraction elements with fast response time and high diffraction efficiency could find application in many modern devices.« less

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.

Crystallization mechanisms of acicular crystals

NASA Astrophysics Data System (ADS)

Puel, François; Verdurand, Elodie; Taulelle, Pascal; Bebon, Christine; Colson, Didier; Klein, Jean-Paul; Veesler, Stéphane

2008-01-01

In this contribution, we present an experimental investigation of the growth of four different organic molecules produced at industrial scale with a view to understand the crystallization mechanism of acicular or needle-like crystals. For all organic crystals studied in this article, layer-by-layer growth of the lateral faces is very slow and clear, as soon as the supersaturation is high enough, there is competition between growth and surface-activated secondary nucleation. This gives rise to pseudo-twinned crystals composed of several needle individuals aligned along a crystallographic axis; this is explained by regular over- and inter-growths as in the case of twinning. And when supersaturation is even higher, nucleation is fast and random. In an industrial continuous crystallization, the rapid growth of needle-like crystals is to be avoided as it leads to fragile crystals or needles, which can be partly broken or totally detached from the parent crystals especially along structural anisotropic axis corresponding to weaker chemical bonds, thus leading to slower growing faces. When an activated mechanism is involved such as a secondary surface nucleation, it is no longer possible to obtain a steady state. Therefore, the crystal number, size and habit vary significantly with time, leading to troubles in the downstream processing operations and to modifications of the final solid-specific properties. These results provide valuable information on the unique crystallization mechanisms of acicular crystals, and show that it is important to know these threshold and critical values when running a crystallizer in order to obtain easy-to-handle crystals.

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.

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.

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.

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.

Precision mechanical structure of an ultra-high-resolution spectrometer for inelastic X-ray scattering instrument

DOEpatents

Shu, Deming; Shvydko, Yuri; Stoupin, Stanislav A.; Khachatryan, Ruben; Goetze, Kurt A.; Roberts, Timothy

2015-04-14

A method and an ultrahigh-resolution spectrometer including a precision mechanical structure for positioning inelastic X-ray scattering optics are provided. The spectrometer includes an X-ray monochromator and an X-ray analyzer, each including X-ray optics of a collimating (C) crystal, a pair of dispersing (D) element crystals, anomalous transmission filter (F) and a wavelength (W) selector crystal. A respective precision mechanical structure is provided with the X-ray monochromator and the X-ray analyzer. The precision mechanical structure includes a base plate, such as an aluminum base plate; positioning stages for D-crystal alignment; positioning stages with an incline sensor for C/F/W-crystal alignment, and the positioning stages including flexure-based high-stiffness structure.

Spontaneous liquid crystal and ferromagnetic ordering of colloidal magnetic nanoplates

PubMed Central

Shuai, M.; Klittnick, A.; Shen, Y.; Smith, G. P.; Tuchband, M. R.; Zhu, C.; Petschek, R. G.; Mertelj, A.; Lisjak, D.; Čopič, M.; Maclennan, J. E.; Glaser, M. A.; Clark, N. A.

2016-01-01

Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magnetomechanical effects. A longstanding interest and challenge has been to make such suspensions macroscopically ferromagnetic, that is having uniform magnetic alignment in the absence of a field. Here we report a fluid suspension of magnetic nanoplates that spontaneously aligns into an equilibrium nematic liquid crystal phase that is also macroscopically ferromagnetic. Its zero-field magnetization produces distinctive magnetic self-interaction effects, including liquid crystal textures of fluid block domains arranged in closed flux loops, and makes this phase highly sensitive, with it dramatically changing shape even in the Earth's magnetic field. PMID:26817823

Switchable polarization-sensitive surface plasmon resonance of highly stable gold nanorods liquid crystals composites

NASA Astrophysics Data System (ADS)

Liu, Qingkun; Qian, Jun; Cai, Fuhong; Smalyukh, Ivan I.; He, Sailing

2011-12-01

In this work, we demonstrate the bulk self-alignment of gold nanorods (GNRs) dispersed in lyotropic nematic liquid crystals (LCs) with high optical absorption coefficient at the surface plasmon resonant wavelength. The polymer-coated GNRs which show spontaneous long-range orientational ordering along the director of LC host exhibit long-term stability as well as high concentration. External magnetic field and shearing allow for alignment and realignment of the orientation of gold nanorods by changing the director of the liquid crystal matrix. This results in a switchable polarization-sensitive surface plasmon resonance exhibiting stark differences from that of the same nanorods in isotropic fluids. The devise-scale bulk nanoparticle alignment may enable optical metamaterial mass production and control of surface plasmon resonance of nanoparticles.

Alignment of CH3F in para-H2 crystal studied by IR quantum cascade laser polarization spectroscopy.

PubMed

Kawasaki, Hiroyuki; Mizoguchi, Asao; Kanamori, Hideto

2016-05-14

In order to investigate the alignment of CH3F in para-H2 crystals, high resolution polarization spectroscopy of the ν3 vibrational band is studied using a quantum cascade laser at 1040 cm(-1). It is found that the main and satellite series of peaks in the ν3 vibrational band of CH3F have the same polarization dependence. This result supports the previously proposed cluster model with ortho-H2 in first and second nearest neighbor sites. The observed polarization dependence function is well described by a simple six-axis void model in which CH3F is not aligned along the c-axis of the crystal but tilted to 64.9(3)° from it.

Direction-specific interaction forces underlying zinc oxide crystal growth by oriented attachment

DOE PAGES

Zhang, X.; Shen, Z.; Liu, J.; ...

2017-10-10

Here, crystallization by particle attachment is impacting our understanding of natural mineralization processes and holds promise for novel materials design. When particles assemble in crystallographic registry, expulsion of the intervening solvent and particle coalescence is enabled by near-perfect co-alignment via interparticle forces that remain poorly quantified. Here we report measurement and simulation of these nanoscale aligning forces for the ZnO(0001)-ZnO(000¯1) system in aqueous solution. Dynamic force spectroscopy using nanoengineered single crystal probes reveals an attractive force with 60o rotational periodicity. Calculated distance and orientation-dependent potentials of mean force show several attractive free energy wells distinguished by numbers of intervening watermore » layers, which reach a minimum when aligned. The calculated activation energy to separate the attractively bound solvated interfaces perfectly reproduces the measured 60o periodicity, revealing the key role of intervening water structuring as a basis to generate the interparticle torque that completes alignment and enables coalescence.« less

Direction-specific interaction forces underlying zinc oxide crystal growth by oriented attachment

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

Zhang, X.; Shen, Z.; Liu, J.

Here, crystallization by particle attachment is impacting our understanding of natural mineralization processes and holds promise for novel materials design. When particles assemble in crystallographic registry, expulsion of the intervening solvent and particle coalescence is enabled by near-perfect co-alignment via interparticle forces that remain poorly quantified. Here we report measurement and simulation of these nanoscale aligning forces for the ZnO(0001)-ZnO(000¯1) system in aqueous solution. Dynamic force spectroscopy using nanoengineered single crystal probes reveals an attractive force with 60o rotational periodicity. Calculated distance and orientation-dependent potentials of mean force show several attractive free energy wells distinguished by numbers of intervening watermore » layers, which reach a minimum when aligned. The calculated activation energy to separate the attractively bound solvated interfaces perfectly reproduces the measured 60o periodicity, revealing the key role of intervening water structuring as a basis to generate the interparticle torque that completes alignment and enables coalescence.« less

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

Synthetic Studies of Antimony Sulfur Iodide and Predictions/Synthesis of New Nitrogen Containing Crystal Structures.

DTIC Science & Technology

1983-02-01

Okazaki, 2 it appeared likely that well-aligned SbSI would have extremely useful piezoelectric properties. It was appreciated that a source of high purity...which often facilitate this, and may also lead to special physical effects (as with the ferroelectric behavior of SbSI). In hydroxyapatite , there are two...Fabrication of Piezoelectric Cerdmics," Ferroelectrics 41, 77-69 (1982). 3. P.E.O. Morgan, "Synthetic Studies of Antimony Sulfur Iodide," Proposal to ONR from

Formation mechanism of self-assembled polarization-dependent periodic nanostructures in β-Ga2O3

NASA Astrophysics Data System (ADS)

Nakanishi, Y.; Shimotsuma, Y.; Sakakura, M.; Shimizu, M.; Miura, K.

2018-02-01

We have successfully observed self-assembled periodic nanostructures inside Si single crystal and GaP crystal, by the femtosecond double-pulse irradiation. These results experimentally indicate that the self-assembly of the periodic nanostructures inside semiconductors triggered by ultrashort pulses irradiation are possibly associated with a direct or an indirect band gap. More recently we have also empirically classified the photoinduced bulk nanogratings into the following three types: (1) structural deficiency, (2) compressed structure, (3) partial crystallization. We have still a big question about what material properties are involved in the bulk nanograting structure formation. In this study, to expand the selectivity of the material for bulk nanograting formation, we have employed β-Ga2O3 crystals (indirect bandgap Eg 4.8 eV) as a sample for femtosecond laser irradiation. The nanograting structure inside β-Ga2O3 crystal was aligned perpendicular to the laser polarization direction. Such phenomenon is similar to the nanograting in SiO2 glass (Eg 9 eV). Moreover, to clarify the band structure, we have also investigate the photoinduced structure in Sn doped β-Ga2O3 crystals, which exhibit direct bandgap according to the first principle calculation.

Terahertz Science and Technology of Macroscopically Aligned Carbon Nanotube Films

NASA Astrophysics Data System (ADS)

Kono, Junichiro

One of the outstanding challenges in nanotechnology is how to assemble individual nano-objects into macroscopic architectures while preserving their extraordinary properties. For example, the one-dimensional character of electrons in individual carbon nanotubes leads to extremely anisotropic transport, optical, and magnetic phenomena, but their macroscopic manifestations have been limited. Here, we describe methods for preparing macroscopic films, sheets, and fibers of highly aligned carbon nanotubes and their applications to basic and applied terahertz studies. Sufficiently thick films act as ideal terahertz polarizers, and appropriately doped films operate as polarization-sensitive, flexible, powerless, and ultra-broadband detectors. Together with recently developed chirality enrichment methods, these developments will ultimately allow us to study dynamic conductivities of interacting one-dimensional electrons in macroscopic single crystals of single-chirality single-wall carbon nanotubes.

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.

Multilevel, multicomponent microarchitectures of vertically-aligned carbon nanotubes for diverse applications.

PubMed

Qu, Liangti; Vaia, Rich A; Dai, Liming

2011-02-22

A simple multiple contact transfer technique has been developed for controllable fabrication of multilevel, multicomponent microarchitectures of vertically aligned carbon nanotubes (VA-CNTs). Three dimensional (3-D) multicomponent micropatterns of aligned single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs) have been fabricated, which can be used to develop a newly designed touch sensor with reversible electrical responses for potential applications in electronic devices, as demonstrated in this study. The demonstrated dependence of light diffraction on structural transfiguration of the resultant CNT micropattern also indicates their potential for optical devices. Further introduction of various components with specific properties (e.g., ZnO nanorods) into the CNT micropatterns enabled us to tailor such surface characteristics as wettability and light response. Owing to the highly generic nature of the multiple contact transfer strategy, the methodology developed here could provide a general approach for interposing a large variety of multicomponent elements (e.g., nanotubes, nanorods/wires, photonic crystals, etc.) onto a single chip for multifunctional device applications.

Superior electro-optical properties of electrically controlled birefringence mode using solution-derived La{sub 2}O{sub 3} films

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

Jeong, Hae-Chang; Park, Hong-Gyu; Lee, Ju Hwan

2015-11-15

The authors demonstrate a high performance electrically controlled birefringence (ECB) mode with solution-derived La{sub 2}O{sub 3} films at various molar concentrations. Uniform and homogeneous liquid crystal (LC) alignment was spontaneously achieved on the La{sub 2}O{sub 3} films for lanthanum concentrations at ratios greater than and equal to 0.2. A preferred orientation of LC molecules appeared along the filling direction, and the LC alignment was maintained via van der Waals force by nanocrystals of the La{sub 2}O{sub 3} films. The LC alignment mechanism was confirmed by x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy analysis. Superior electro-optical characteristics of the ECBmore » cells constructed with solution-derived La{sub 2}O{sub 3} films were observed, which suggests that the proposed solution-derived La{sub 2}O{sub 3} films have strong potential for use in the production of advanced LC displays.« less

Enhancement of polar anchoring strength in a graphene-nematic suspension and its effect on nematic electro-optic switching

NASA Astrophysics Data System (ADS)

Basu, Rajratan

2017-07-01

A small quantity of monolayer graphene flakes is doped in a nematic liquid crystal (LC), and the effective polar anchoring strength coefficient between the LC and the alignment substrate is found to increase by an order of magnitude. The hexagonal pattern of graphene can interact with the LC's benzene rings via π -π electron stacking, enabling the LC to anchor to the graphene surface homogeneously (i.e., planar anchoring). When the LC cell is filled with the graphene-doped LC, some graphene flakes are preferentially attached to the alignment layer and modify the substrate's anchoring property. These spontaneously deposited graphene flakes promote planar anchoring at the substrate and the polar anchoring energy at alignment layer is enhanced significantly. The enhanced anchoring energy is found to impact favorably on the electro-optic response of the LC. Additional studies reveal that the nematic electro-optic switching is significantly faster in the LC-graphene hybrid than that of the pure LC.

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.

Measurement of anchoring coefficient of homeotropically aligned nematic liquid crystal using a polarizing optical microscope in reflective mode

NASA Astrophysics Data System (ADS)

Baek, Sang-In; Kim, Sung-Jo; Kim, Jong-Hyun

2015-09-01

Although the homeotropic alignment of liquid crystals is widely used in LCD TVs, no easy method exists to measure its anchoring coefficient. In this study, we propose an easy and convenient measurement technique in which a polarizing optical microscope is used in the reflective mode with an objective lens having a low depth of focus. All measurements focus on the reflection of light near the interface between the liquid crystal and alignment layer. The change in the reflected light is measured by applying an electric field. We model the response of the director of the liquid crystal to the electric field and, thus, the change in reflectance. By adjusting the extrapolation length in the calculation, we match the experimental and calculated results and obtain the anchoring coefficient. In our experiment, the extrapolation lengths were 0.31 ± 0.04 μm, 0.32 ± 0.08 μm, and 0.23 ± 0.05 μm for lecithin, AL-64168, and SE-5662, respectively.

Flexible Semitransparent Energy Harvester with High Pressure Sensitivity and Power Density Based on Laterally Aligned PZT Single-Crystal Nanowires.

PubMed

Zhao, Quan-Liang; He, Guang-Ping; Di, Jie-Jian; Song, Wei-Li; Hou, Zhi-Ling; Tan, Pei-Pei; Wang, Da-Wei; Cao, Mao-Sheng

2017-07-26

A flexible semitransparent energy harvester is assembled based on laterally aligned Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) single-crystal nanowires (NWs). Such a harvester presents the highest open-circuit voltage and a stable area power density of up to 10 V and 0.27 μW/cm 2 , respectively. A high pressure sensitivity of 0.14 V/kPa is obtained in the dynamic pressure sensing, much larger than the values reported in other energy harvesters based on piezoelectric single-crystal NWs. Furthermore, theoretical and finite element analyses also confirm that the piezoelectric voltage constant g 33 of PZT NWs is competitive to the lead-based bulk single crystals and ceramics, and the enhanced pressure sensitivity and power density are substantially linked to the flexible structure with laterally aligned PZT NWs. The energy harvester in this work holds great potential in flexible and transparent sensing and self-powered systems.

Experimental Realization of Efficient, Room Temperature Single-Photon Sources with Definite Circular and Linear Polarizations

NASA Astrophysics Data System (ADS)

Boutsidis, Christos

In this thesis I present experimental demonstrations of room-temperature, single-photon sources with definite linear and circular polarizations. Definite photon polarization increases the efficiency of quantum communication systems. In contrast with cryogenic-temperature single-photon sources based on epitaxial quantum dots requiring expensive MBE and nanofabrication, my method utilizes a mature liquid crystal technology, which I made consistent with single-emitter fluorescence microscopy. The structures I have prepared are planar-aligned cholesteric liquid crystals forming 1-D photonic bandgaps for circularly-polarized light, which were used to achieve definite circularly-polarized fluorescence of single emitters doped in this environment. I also used planar-aligned nematic liquid crystals to align single molecules with linear dipole moments and achieved definite linearly-polarized fluorescence. I used single nanocrystal quantum dots, single nanodiamond color-centers, rare-earth-doped nanocrystals, and single terrylene and DiIC18(3) dye molecules as emitters. For nanocrystal quantum dots I observed circular polarization dissymmetry factors as large as ge = --1.6. In addition, I observed circularly-polarized resonances in the fluorescence of emitters within a cholesteric microcavity, with cavity quality factors of up to Q ˜ 250. I also showed that the fluorescence of DiIC18(3) dye molecules in planar-aligned nematic cells exhibits definite linear polarization, with a degree of polarization of rho = --0.58 +/- 0.03. Distributed Bragg reflectors form another type of microcavity that can be used to realize a single-photon source. I characterized the fluorescence from nanocrystal quantum dots doped in the defect layers of such microcavites, both organic and inorganic. Finally, to demonstrate the single-photon properties of single-emitter-doped cholesteric and nematic liquid crystal structures and distributed Bragg reflector microcavities, I present observations of photon antibunching from emitters doped in each of these structures. These experimental observations include photon antibunching from: nanocrystal quantum dots and nanodiamond color-centers doped in a cholesteric microcavity; terrylene and DiIC 18(3) dye molecules doped in nematic structures, and nanocrystal quantum dots doped in the distributed Bragg reflector microcavity. A value of the zero-time second-order coherence as low as g(2)(0) = 0.001 +/- 0.03 was measured. These results represent an important step forward in the realization of room temperature single-photon sources with definite polarization for secure quantum communication.

Fast-switching chiral nematic liquid-crystal mode with polymer-sustained twisted vertical alignment.

PubMed

Chang, Kai-Han; Joshi, Vinay; Chien, Liang-Chy

2017-04-01

We demonstrate a fast-switching liquid-crystal mode with polymer-sustained twisted vertical alignment. By optimizing the polymerization condition, a polymer microstructure with controlled orientation is produced. The polymer microstructure not only synergistically suppresses the optical bounce during field-induced homeotropic-twist transition but also shortens the response time significantly. Theoretical analyses validate that the ground state free energy density is modified by the aligning field of the polymer microstructure, which affects the driving voltage of the device. The outcomes of this paper will enable the development of fast-switching and achromatic electro-optical and photonic devices.

Fast-switching chiral nematic liquid-crystal mode with polymer-sustained twisted vertical alignment

NASA Astrophysics Data System (ADS)

Chang, Kai-Han; Joshi, Vinay; Chien, Liang-Chy

2017-04-01

We demonstrate a fast-switching liquid-crystal mode with polymer-sustained twisted vertical alignment. By optimizing the polymerization condition, a polymer microstructure with controlled orientation is produced. The polymer microstructure not only synergistically suppresses the optical bounce during field-induced homeotropic-twist transition but also shortens the response time significantly. Theoretical analyses validate that the ground state free energy density is modified by the aligning field of the polymer microstructure, which affects the driving voltage of the device. The outcomes of this paper will enable the development of fast-switching and achromatic electro-optical and photonic devices.

Explicit crystal host effects on excited state properties of linear polyacenes: towards a room-temperature maser

NASA Astrophysics Data System (ADS)

Charlton, Robert; Bogatko, Stuart; Zuehlsdorff, Tim; Hine, Nicholas; Horsfield, Andrew; Haynes, Peter

Maser technology has been held back for decades by the impracticality of the operating conditions of traditional masing devices, such as cryogenic freezing and strong magnetic fields. Recently it has been experimentally demonstrated that pentacene in p-terphenyl can act as a viable solid-state room-temperature maser by exploiting the alignment of the low-lying singlet and triplet excited states of pentacene. To understand the operation of this device from first principles, an ab initio study of the excitonic properties of pentacene in p-terphenyl has been carried out using time-dependent density functional theory (TDDFT), implemented in the linear-scaling ONETEP software (www.onetep.org). In particular, we focus on the impact that the wider crystal has on the localised pentacene excitations by performing an explicit DFT treatment of the p-terphenyl environment. We demonstrate the importance of explicit crystal host effects in calculating the excitation energies of pentacene in p-terphenyl, providing important information for the operation of the maser. We then use this same approach to test the viability of other linear polyacenes as maser candidates as a screening step before experimental testing.

Microstructure and phase behavior in colloids and liquid crystals

NASA Astrophysics Data System (ADS)

Lohr, Matthew Alan

This thesis describes our investigation of microstructure and phase behavior in colloids and liquid crystals. The first set of experiments explores the phase behavior of helical packings of thermoresponsive microspheres inside glass capillaries as a function of volume fraction. Stable helical packings are observed with long-range orientational order. Some of these packings evolve abruptly to disordered states as the volume fraction is reduced. We quantify these transitions using correlation functions and susceptibilities of an orientational order parameter. The emergence of coexisting metastable packings, as well as coexisting ordered and disordered states, is also observed. These findings support the notion of phase-transition-like behavior in quasi-one-dimensional systems. The second set of experiments investigates cross-over behavior from glasses with attractive interactions to sparse gel-like states. In particular, the vibrational modes of quasi-two-dimensional disordered colloidal packings of hard colloidal spheres with short-range attractions are measured as a function of packing fraction. A crossover from glassy to sparse gel-like states is indicated by an excess of low-frequency phonon modes. This change in vibrational mode distribution appears to arise from highly localized vibrations that tend to involve individual and/or small clusters of particles with few local bonds. These mode behaviors and corresponding structural insights may serve as a useful signature for glass-gel transitions in wider classes of attractive packings. A third set of experiments explores the director structures of aqueous lyotropic chromonic liquid crystal (LCLC) films created on square lattice cylindrical-micropost substrates. The structures are manipulated by modulating of the concentration-dependent elastic properties of LCLC s via drying. Nematic LCLC films exhibit preferred bistable alignment along the diagonals of the micropost lattice. Columnar LCLC films form two distinct director and defect configurations: a diagonally aligned director pattern with local squares of defects, and an off-diagonal configuration with zig-zag defects. The formation of these patterns appears to be tied to the relative free energy costs of splay and bend deformations in the precursor nematic films. The observed nematic and columnar configurations are understood numerically using a Landau-de Gennes free energy model. This work provides first examples of quasi-2D micropatterning of LC films in the columnar phase and the first micropatterning of lyotropic LC films in general, as well as demonstrating alignment and configuration switching of typically difficult-to-align LCLC films via bulk elastic properties.

Optimization of processing parameters on the controlled growth of ZnO nanorod arrays for the performance improvement of solid-state dye-sensitized solar cells

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

Lee, Yi-Mu, E-mail: ymlee@nuu.edu.t; Yang, Hsi-Wen

2011-03-15

High-transparency and high quality ZnO nanorod arrays were grown on the ITO substrates by a two-step chemical bath deposition (CBD) method. The effects of processing parameters including reaction temperature (25-95 {sup o}C) and solution concentration (0.01-0.1 M) on the crystal growth, alignment, optical and electrical properties were systematically investigated. It has been found that these process parameters are critical for the growth, orientation and aspect ratio of the nanorod arrays, showing different structural and optical properties. Experimental results reveal that the hexagonal ZnO nanorod arrays prepared under reaction temperature of 95 {sup o}C and solution concentration of 0.03 M possessmore » highest aspect ratio of {approx}21, and show the well-aligned orientation and optimum optical properties. Moreover the ZnO nanorod arrays based heterojunction electrodes and the solid-state dye-sensitized solar cells (SS-DSSCs) were fabricated with an improved optoelectrical performance. -- Graphical abstract: The ZnO nanorod arrays demonstrate well-alignment, high aspect ratio (L/D{approx}21) and excellent optical transmittance by low-temperature chemical bath deposition (CBD). Display Omitted Research highlights: > Investigate the processing parameters of CBD on the growth of ZnO nanorod arrays. > Optimization of CBD process parameters: 0.03 M solution concentration and reaction temperature of 95 {sup o}C. > The prepared ZnO samples possess well-alignment and high aspect ratio (L/D{approx}21). > An n-ZnO/p-NiO heterojunction: great rectifying behavior and low leakage current. > SS-DSSC has J{sub SC} of 0.31 mA/cm{sup 2} and V{sub OC} of 590 mV, and an improved {eta} of 0.059%.« less

Spontaneous liquid crystal and ferromagnetic ordering of colloidal magnetic nanoplates

DOE PAGES

Shuai, M.; Klittnick, A.; Shen, Y.; ...

2016-01-28

Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magnetomechanical effects. A longstanding interest and challenge has been to make such suspensions macroscopically ferromagnetic, that is having uniform magnetic alignment in the absence of a field. Here we report a fluid suspension of magnetic nanoplates that spontaneously aligns into an equilibrium nematic liquid crystal phase that is also macroscopically ferromagnetic. We find Its zero-field magnetization produces distinctive magnetic self-interaction effects, includingmore » liquid crystal textures of fluid block domains arranged in closed flux loops, and makes this phase highly sensitive, with it dramatically changing shape even in the Earth’s magnetic field.« less

Enhanced photoluminescence and field-emission behavior of vertically well aligned arrays of In-doped ZnO Nanowires.

PubMed

Ahmad, Mashkoor; Sun, Hongyu; Zhu, Jing

2011-04-01

Vertically oriented well-aligned Indium doped ZnO nanowires (NWs) have been successfully synthesized on Au-coated Zn substrate by controlled thermal evaporation. The effect of indium dopant on the optical and field-emission properties of these well-aligned ZnO NWs is investigated. The doped NWs are found to be single crystals grown along the c-axis. The composition of the doped NWs is confirmed by X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and X-ray photospectroscopy (XPS). The photoluminescence (PL) spectra of doped NWs having a blue-shift in the UV region show a prominent tuning in the optical band gap, without any significant peak relating to intrinsic defects. The turn-on field of the field emission is found to be ∼2.4 V μm(-1) and an emission current density of 1.13 mA cm(-2) under the field of 5.9 V μm(-1). The field enhancement factor β is estimated to be 9490 ± 2, which is much higher than that of any previous report. Furthermore, the doped NWs exhibit good emission current stability with a variation of less than 5% during a 200 s under a field of 5.9 V μm(-1). The superior field emission properties are attributed to the good alignment, high aspect ratio, and better crystallinity of In-doped NWs. © 2011 American Chemical Society

Growth and dislocation studies of β-HMX.

PubMed

Gallagher, Hugh G; Sherwood, John N; Vrcelj, Ranko M

2014-01-01

The defect structure of organic materials is important as it plays a major role in their crystal growth properties. It also can play a subcritical role in "hot-spot" detonation processes of energetics and one such energetic is cyclotetramethylene-tetranitramine, in the commonly used beta form (β-HMX). The as-grown crystals grown by evaporation from acetone show prismatic, tabular and columnar habits, all with {011}, {110}, (010) and (101) faces. Etching on (010) surfaces revealed three different types of etch pits, two of which could be identified with either pure screw or pure edge dislocations, the third is shown to be an artifact of the twinning process that this material undergoes. Examination of the {011} and {110} surfaces show only one type of etch pit on each surface; however their natural asymmetry precludes the easy identification of their Burgers vector or dislocation type. Etching of cleaved {011} surfaces demonstrates that the etch pits can be associated with line dislocations. All dislocations appear randomly on the crystal surfaces and do not form alignments characteristic of mechanical deformation by dislocation slip. Crystals of β-HMX grown from acetone show good morphological agreement with that predicted by modelling, with three distinct crystal habits observed depending upon the supersaturation of the growth solution. Prismatic habit was favoured at low supersaturation, while tabular and columnar crystals were predominant at higher super saturations. The twin plane in β-HMX was identified as a (101) reflection plane. The low plasticity of β-HMX is shown by the lack of etch pit alignments corresponding to mechanically induced dislocation arrays. On untwinned {010} faces, two types of dislocations exist, pure edge dislocations with b = [010] and pure screw dislocations with b = [010]. On twinned (010) faces, a third dislocation type exists and it is proposed that these pits are associated with pure screw dislocations with b = [010]. Graphical abstractEtch pits on the twinned (010) face of β-HMX.

Micropatterned photoalignment for wavefront controlled switchable optical devices

NASA Astrophysics Data System (ADS)

Glazar, Nikolaus

Photoalignment is a well-established technique for surface alignment of the liquid crystal director. Previously, chrome masks were necessary for patterned photoalignment but were difficult to use, costly, and inflexible. To extend the capabilities of photoalignment we built an automated maskless multi-domain photoalignment device based on a DMD (digital multimirror device) projection system. The device is capable of creating arbitrary photoalignment patterns with micron-sized features. Pancharatnam-Berry phase (PB-phase) is a geometric phase that arises from cyclic change of polarization state. By varying the azimuthal anchoring angle in a hybrid-aligned liquid crystal cell we can control the spatial variation of the PB-phase shift. Using our automated photoalignment device to align the liquid crystal arbitrary wave front manipulations are possible. The PB-phase shift effect is maximized when the cell is tuned to have a half-wave retardation and disappears at full-wave retardation, so the cell can be switched on and off by applying a voltage. Two wavefront controlled devices developed using this technique will be discussed: A switchable liquid crystal phase shift mask for creating sub-diffraction sized photolithographic features, and a transparent diffractive display that utilizes a switchable liquid crystal diffraction grating.

Integrated crystal mounting and alignment system for high-throughput biological crystallography

DOEpatents

Nordmeyer, Robert A.; Snell, Gyorgy P.; Cornell, Earl W.; Kolbe, William F.; Yegian, Derek T.; Earnest, Thomas N.; Jaklevich, Joseph M.; Cork, Carl W.; Santarsiero, Bernard D.; Stevens, Raymond C.

2007-09-25

A method and apparatus for the transportation, remote and unattended mounting, and visual alignment and monitoring of protein crystals for synchrotron generated x-ray diffraction analysis. The protein samples are maintained at liquid nitrogen temperatures at all times: during shipment, before mounting, mounting, alignment, data acquisition and following removal. The samples must additionally be stably aligned to within a few microns at a point in space. The ability to accurately perform these tasks remotely and automatically leads to a significant increase in sample throughput and reliability for high-volume protein characterization efforts. Since the protein samples are placed in a shipping-compatible layered stack of sample cassettes each holding many samples, a large number of samples can be shipped in a single cryogenic shipping container.

Integrated crystal mounting and alignment system for high-throughput biological crystallography

DOEpatents

Nordmeyer, Robert A.; Snell, Gyorgy P.; Cornell, Earl W.; Kolbe, William; Yegian, Derek; Earnest, Thomas N.; Jaklevic, Joseph M.; Cork, Carl W.; Santarsiero, Bernard D.; Stevens, Raymond C.

2005-07-19

A method and apparatus for the transportation, remote and unattended mounting, and visual alignment and monitoring of protein crystals for synchrotron generated x-ray diffraction analysis. The protein samples are maintained at liquid nitrogen temperatures at all times: during shipment, before mounting, mounting, alignment, data acquisition and following removal. The samples must additionally be stably aligned to within a few microns at a point in space. The ability to accurately perform these tasks remotely and automatically leads to a significant increase in sample throughput and reliability for high-volume protein characterization efforts. Since the protein samples are placed in a shipping-compatible layered stack of sample cassettes each holding many samples, a large number of samples can be shipped in a single cryogenic shipping container.

Nanoimprinting-induced nanomorphological transition in polymer solar cells: enhanced electrical and optical performance.

PubMed

Jeong, Seonju; Cho, Changsoon; Kang, Hyunbum; Kim, Ki-Hyun; Yuk, Youngji; Park, Jeong Young; Kim, Bumjoon J; Lee, Jung-Yong

2015-03-24

We have investigated the effects of a directly nanopatterned active layer on the electrical and optical properties of inverted polymer solar cells (i-PSCs). The capillary force in confined molds plays a critical role in polymer crystallization and phase separation of the film. The nanoimprinting process induced improved crystallization and multidimensional chain alignment of polymers for more effective charge transfer and a fine phase-separation between polymers and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) to favor exciton dissociation and increase the generation rate of charge transfer excitons. Consequently, the power conversion efficiency with a periodic nanostructure was enhanced from 7.40% to 8.50% and 7.17% to 9.15% in PTB7 and PTB7-Th based i-PSCs, respectively.

Improvement of the relaxation time and the order parameter of nematic liquid crystal using a hybrid alignment mixture of carbon nanotube and polyimide

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

Lee, Hyojin; Yang, Seungbin; Lee, Ji-Hoon, E-mail: jihoonlee@jbnu.ac.kr

2014-05-12

We examined the electrooptical properties of a nematic liquid crystal (LC) sample whose substrates were coated with a mixture of carbon nanotube (CNT) and polyimide (PI). The relaxation time of the sample coated with 1.5 wt. % CNT mixture was about 35% reduced compared to the pure polyimide sample. The elastic constant and the order parameter of the CNT-mixture sample were increased and the fast relaxation of LC could be approximated to the mean-field theory. We found the CNT-mixed polyimide formed more smooth surface than the pure PI from atomic force microscopy images, indicating the increased order parameter is related to themore » smooth surface topology of the CNT-polyimide mixture.« less

Resonant optical alignment and orientation of Mn2+ spins in CdMnTe crystals

NASA Astrophysics Data System (ADS)

Baryshnikov, K. A.; Langer, L.; Akimov, I. A.; Korenev, V. L.; Kusrayev, Yu. G.; Averkiev, N. S.; Yakovlev, D. R.; Bayer, M.

2015-11-01

We report on spin orientation and alignment of Mn2 + ions in (Cd,Mn)Te diluted magnetic semiconductor crystals using resonant intracenter excitation with circular- and linear-polarized light. The resulting polarized emission of the magnetic ions is observed at low temperatures when the spin relaxation time of the Mn2 + ions is in the order of 1 ms , which considerably exceeds the photoluminescence decay time of 23 μ s . We demonstrate that the experimental data on optical orientation and alignment of Mn2 + ions can be explained using a phenomenological model that is based on the approximation of isolated centers.

Tilted Liquid Crystal Alignment on Asymmetrically Grooved Porous Alumina Film

NASA Astrophysics Data System (ADS)

Maeda, Tsuyoshi; Hiroshima, Kohki

2005-06-01

This paper reports the achievement of tilted liquid crystal (LC) alignment on an anodic porous alumina (APA) film using microgrooves with asymmetric shapes and dozens of minute pores. The microgrooves with asymmetric shapes were formed by a rubbing technique. The minute pores were then produced by anodization. The LC pretilt angle was controlled by the shapes of the microgrooves and pores. The LC director was orientated in the same inclining direction as that of a rubbed polyimide (PI) film. The pretilt angle was in the range of 20 to 90°. This tilted LC alignment remains very stable against external forces such as thermal shock and intense light.

Aligned Layers of Silver Nano-Fibers.

PubMed

Golovin, Andrii B; Stromer, Jeremy; Kreminska, Liubov

2012-02-01

We describe a new dichroic polarizers made by ordering silver nano-fibers to aligned layers. The aligned layers consist of nano-fibers and self-assembled molecular aggregates of lyotropic liquid crystals. Unidirectional alignment of the layers is achieved by means of mechanical shearing. Aligned layers of silver nano-fibers are partially transparent to a linearly polarized electromagnetic radiation. The unidirectional alignment and density of the silver nano-fibers determine degree of polarization of transmitted light. The aligned layers of silver nano-fibers might be used in optics, microwave applications, and organic electronics.

Effect of growth time on the structure, morphology and optical properties of hydrothermally synthesized TiO2 nanorod thin films

NASA Astrophysics Data System (ADS)

Mohapatra, A. K.; Nayak, J.

2018-05-01

Titanium dioxide (TiO2) nanorod thin films were deposited on fluorine doped tin oxide coated glass substrates by a single step rapid hydrothermal process. The concentration of the precursor, the temperature of the reaction mixture were optimized in order to enhance the rate of deposition. Unlike the previously reported hydrothermal treatment for 24 - 48 h, the deposition of well aligned titanium dioxide nanorods was achieved in a short time such as 3 - 8 h. The crystal structure of the films were investigated by X-rays diffraction. The morphology of the nanorod films were studied with scanning electron microscopy. The optical properties were studied by photoluminescence spectroscopy.

Efficient high repetition rate electro-optic Q-switched laser with an optically active langasite crystal

PubMed Central

Ma, Shihui; Yu, Haohai; Zhang, Huaijin; Han, Xuekun; Lu, Qingming; Ma, Changqin; Boughton, Robert I.; Wang, Jiyang

2016-01-01

With an optically active langasite (LGS) crystal as the electro-optic Q-switch, we demonstrate an efficient Q-switched laser with a repetition rate of 200 kHz. Based on the theoretical analysis of the interaction between optical activity and electro-optic property, the optical activity of the crystal has no influence on the birefringence during Q-switching if the quarter wave plate used was rotated to align with the polarization direction. With a Nd:LuVO4 crystal possessing a large emission cross-section and a short fluorescence lifetime as the gain medium, a stable LGS Q-switched laser was designed with average output power of 4.39 W, corresponding to a slope efficiency of 29.4% and with a minimum pulse width of 5.1 ns. This work represents the highest repetition rate achieved so far in a LGS Q-switched laser and it can provide a practical Q-switched laser with a tunable high repetition rates for many applications, such as materials processing, laser ranging, medicine, military applications, biomacromolecule materials, remote sensing, etc. PMID:27461819

Stokes parameter studies of spontaneous emission from chiral nematic liquid crystals as a one-dimensional photonic stopband crystal: experiment and theory.

PubMed

Woon, Kai L; O'Neill, Mary; Richards, Gary J; Aldred, Matthew P; Kelly, Stephen M

2005-04-01

The helical structure of uniformly aligned chiral nematic liquid crystals results in a photonic stopband for only one sense of circular polarization. The spectroscopic Stokes polarimeter is used to analyze spontaneous emission in the stopband. Highly polarized photoluminescence is found and the polarization properties vary with the excitation wavelength. Spontaneous emission is enhanced at the stopband edge and this Purcell effect is greater on excitation at wavelengths where the absorption coefficient is low. This is interpreted as greater overlap between the excited molecules and the electrical modal field of the resonant modes at the stopband edge. Photoluminescence detected from the excitation face of the liquid crystal cell is less polarized because of photon tunneling. Fermi's golden rule in conjunction with Stokes vectors is used to model the polarization of emission taking multiple reflections at the interfaces of the cell into account. The discrepancy between the experiment and the theoretical model is interpreted as direct experimental evidence that virtual photons, which originate from zero point fluctuations of quantum space, are randomly polarized.

Tuning the Assembly of Spherical Nanoparticles in Semicrystalline Polymers

NASA Astrophysics Data System (ADS)

Zhao, Dan; Jestin, Jacques; Zhao, Longxi; Kumar, Sanat K.; Mohammadkhani, Mohammad; Benicewicz, Brian C.

We propose a simple, novel strategy to controlling nanoparticle (NPs) dispersion states in a semi-crystalline polymer matrix exploiting the kinetics of polymer crystallization. The system consists of poly(methyl methacrylate) grafted spherical silica NPs and poly(ethylene oxide) matrices, which are thermodynamically miscible in the melt. We first show that no remarkable change was observed in the spatial dispersion of NPs upon fast crystallization. However, for slow crystallization, both TEM and X-ray/neutron scattering reveal that the system starts to be organized in a ``layer-by-layer'' architecture, where the NPs are aligned in the amorphous phases intercalated by the crystalline lamellar phases. More importantly, we have found that the resulting ``sheet-like'' NP morphology gives rise to a 2-fold increase in the storage modulus but without compromising the fracture toughness of the neat polymer. These results open pathways for creating in-situ biomimetic hierarchical structures with improved mechanical properties through a simple, single-step crystallization processing, which could lead to new applications for this largest class of commercially relevant polymeric materials.

Alignment of CH{sub 3}F in para-H{sub 2} crystal studied by IR quantum cascade laser polarization spectroscopy

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

Kawasaki, Hiroyuki; Mizoguchi, Asao; Kanamori, Hideto

In order to investigate the alignment of CH{sub 3}F in para-H{sub 2} crystals, high resolution polarization spectroscopy of the ν{sub 3} vibrational band is studied using a quantum cascade laser at 1040 cm{sup −1}. It is found that the main and satellite series of peaks in the ν{sub 3} vibrational band of CH{sub 3}F have the same polarization dependence. This result supports the previously proposed cluster model with ortho-H{sub 2} in first and second nearest neighbor sites. The observed polarization dependence function is well described by a simple six-axis void model in which CH{sub 3}F is not aligned along themore » c-axis of the crystal but tilted to 64.9(3)° from it.« less

Dispersion of γ-Alumina Nano-Sized Spherical Particles in a Calamitic Liquid Crystal. Study and Optimization of the Confinement Effects

PubMed Central

Diez-Berart, Sergio; López, David O.; Sebastián, Nerea; de la Fuente, María Rosario; Salud, Josep; Robles-Hernández, Beatriz; Pérez-Jubindo, Miguel Ángel

2014-01-01

We report an experimental study on confined systems formed by butyloxybenzylidene octylaniline liquid crystal (4O.8) + γ-alumina nanoparticles. The effects of the confinement in the thermal and dielectric properties of the liquid crystal under different densities of nanoparticles is analyzed by means of high resolution Modulated Differential Scanning Calorimetry (MDSC) and broadband dielectric spectroscopy. First, a drastic depression of the N-I and SmA-N transition temperatures is observed with confinement, the more concentration of nanoparticles the deeper this depression is, driving the nematic range closer to the room temperature. An interesting experimental law is found for both transition temperatures. Second, the change in shape of the heat capacity peaks is quantified by means of the full width half maximum (FWHM). Third, the confinement does not noticeably affect the molecular dynamics. Finally, the combination of nanoparticles and the external applied electric field tends to favor the alignment of the molecules in metallic cells. All these results indicate that the confinement of liquid crystals by means of γ-alumina nanoparticles could be optimum for liquid crystal-based electrooptic devices. PMID:28788528

Development of a Self Aligned CMOS Process for Flash Lamp Annealed Polycrystalline Silicon TFTs

NASA Astrophysics Data System (ADS)

Bischoff, Paul

The emerging active matrix liquid crystal (AMLCD) display market requires a high performing semiconductor material to meet rising standards of operation. Currently amorphous silicon (a-Si) dominates the market but it does not have the required mobility for it to be used in AMLCD manufacturing. Other materials have been developed including crystallizing a-Si into poly-silicon. A new approach to crystallization through the use of flash lamp annealing (FLA) decreases manufacturing time and greatly improves carrier mobility. Previous work on FLA silicon for the use in CMOS transistors revealed significant lateral dopant diffusion into the channel greatly increasing the minimum channel length required for a working device. This was further confounded by the gate overlap due to misalignment during lithography patterning steps. Through the use of furnace dopant activation instead of FLA dopant activation and a self aligned gate the minimum size transistor can be greatly reduced. A new lithography mask and process flow were developed for the furnace annealing and self aligned gate. Fabrication of the self aligned devices resulted in oxidation of the Molybdenum self aligned gate. Further development is needed to successfully manufacture these devices. Non-self aligned transistors were made simultaneously with self aligned devices and used the furnace activation. These devices showed an increase in sheet resistance from 250 O to 800 O and lower mobility from 380 to 40.2 V/cm2s. The lower mobility can be contributed to an increase in implanted trap density indicating furnace annealing is an inferior activation method over FLA. The minimum transistor size however was reduced from 20 to 5 mum. With improvements in the self aligned process high performing small devices can be manufactured.

Development of microchannel plate x-ray optics

NASA Technical Reports Server (NTRS)

Kaaret, Philip; Chen, Andrew

1994-01-01

The goal of this research program was to develop a novel technique for focusing x-rays based on the optical system of a lobster's eye. A lobster eye employs many closely packed reflecting surfaces arranged within a spherical or cylindrical shell. These optics have two unique properties: they have unlimited fields of view and can be manufactured via replication of identical structures. Because the angular resolution is given by the ratio of the size of the individual optical elements to the focal length, optical elements with sizes on the order of one hundred microns are required to achieve good angular resolution with a compact telescope. We employed anisotropic etching of single crystal silicon wafers for the fabrication of micron-scale optical elements. This technique, commonly referred to as silicon micromachining, is based on silicon fabrication techniques developed by the microelectronics industry. An anisotropic etchant is a chemical which etches certain silicon crystal planes much more rapidly than others. Using wafers in which the slowly etched crystal planes are aligned perpendicularly to the wafer surface, it is possible to etch a pattern completely through a wafer with very little distortion. Our optics consist of rectangular pores etched completely through group of zone axes (110) oriented silicon wafers. The larger surfaces of the pores (the mirror elements) were aligned with the group of zone axes (111) planes of the crystal perpendicular to the wafer surface. We have succeeded in producing silicon lenses with a geometry suitable for 1-d focusing x-ray optics. These lenses have an aspect ratio (40:1) suitable for x-ray reflection and have very good optical surface alignment. We have developed a number of process refinements which improved the quality of the lens geometry and the repeatability of the etch process. A significant progress was made in obtaining good optical surface quality. The RMS roughness was decreased from 110 A for our initial lenses to 30 A in the final lenses. A further factor of three improvement in surface quality is required for the production of efficient x-ray optics. In addition to the silicon fabrication, an x-ray beam line was constructed at Columbia for testing the optics.

Nano-crystallization in ZnO-doped In2O3 thin films via excimer laser annealing for thin-film transistors

NASA Astrophysics Data System (ADS)

Fujii, Mami N.; Ishikawa, Yasuaki; Ishihara, Ryoichi; van der Cingel, Johan; Mofrad, Mohammad R. T.; Bermundo, Juan Paolo Soria; Kawashima, Emi; Tomai, Shigekazu; Yano, Koki; Uraoka, Yukiharu

2016-06-01

In a previous work, we reported the high field effect mobility of ZnO-doped In2O3 (IZO) thin film transistors (TFTs) irradiated by excimer laser annealing (ELA) [M. Fujii et al., Appl. Phys. Lett. 102, 122107 (2013)]. However, a deeper understanding of the effect of ELA on the IZO film characteristics based on crystallinity, carrier concentrations, and optical properties is needed to control localized carrier concentrations for fabricating self-aligned structures in the same oxide film and to adequately explain the physical characteristics. In the case of as-deposited IZO film used as the channel, a high carrier concentration due to a high density of oxygen vacancies was observed; such a film does not show the required TFT characteristics but can act as a conductive film. We achieved a decrease in the carrier concentration of IZO films by crystallization using ELA. This means that ELA can form localized conductive or semi-conductive areas on the IZO film. We confirmed that the reason for the carrier concentration decrease was the decrease of oxygen-deficient regions and film crystallization. The annealed IZO films showed nano-crystalline phase, and the temperature at the substrate was substantially less than the temperature limit for flexible films such as plastic, which is 50°C. This paves the way for the formation of self-aligned structures and separately formed conductive and semi-conductive regions in the same oxide film.

Active and Passive 3D Vector Radiative Transfer with Preferentially-Aligned Ice Particles

NASA Technical Reports Server (NTRS)

Adams, Ian S.; Munchak, Stephen J.; Pelissier, Craig S.; Kuo, Kwo-Sen; Heymsfield, Gerald M.

2017-01-01

For the purposes of interpreting active (radar) and passive (radiometer) microwave and millimeter wave remote sensing data, we have constructed a consistent radiative transfer modeling framework to simulate the responses for arbitrary sensors with differing sensing geometries and hardware configurations. As part of this work, we have implemented a recent method for calculating the electromagnetic properties of individual ice crystals and snow flakes. These calculations will allow us to exploit polarized remote sensing observations to discriminate different particles types and elucidate dynamics of cloud and precipitating systems.

Paintable band-edge liquid crystal lasers.

PubMed

Gardiner, Damian J; Morris, Stephen M; Hands, Philip J W; Mowatt, Carrie; Rutledge, Rupert; Wilkinson, Timothy D; Coles, Harry J

2011-01-31

In this paper we demonstrate photonic band-edge laser emission from emulsion-based polymer dispersed liquid crystals. The lasing medium consists of dye-doped chiral nematic droplets dispersed within a polymer matrix that spontaneously align as the film dries. Such lasers can be easily formed on single substrates with no alignment layers. The system combines the self-organizing periodic structure of chiral nematic liquid crystals with the simplicity of the emulsion procedure so as to produce a material that retains the emission characteristics of band-edge lasers yet can be readily coated. Sequential and stacked layers demonstrate the possibility of achieving simultaneous multi-wavelength laser output from glass, metallic, and flexible substrates.

High Mobility Transport Layer Structures for Rhombohedral Si/Ge/SiGe Devices

NASA Technical Reports Server (NTRS)

Choi, Sang Hyouk (Inventor); Park, Yeonjoon (Inventor); King, Glen C. (Inventor); Kim, Hyun-Jung (Inventor); Lee, Kunik (Inventor)

2017-01-01

An electronic device includes a trigonal crystal substrate defining a (0001) C-plane. The substrate may comprise Sapphire or other suitable material. A plurality of rhombohedrally aligned SiGe (111)-oriented crystals are disposed on the (0001) C-plane of the crystal substrate. A first region of material is disposed on the rhombohedrally aligned SiGe layer. The first region comprises an intrinsic or doped Si, Ge, or SiGe layer. The first region can be layered between two secondary regions comprising n+doped SiGe or n+doped Ge, whereby the first region collects electrons from the two secondary regions.

Thioarsenides: A case for long-range Lewis acid-base-directed van der Waals interactions

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

Gibbs, Gerald V.; Wallace, Adam F.; Downs, R. T.

2011-04-01

Electron density distributions, bond paths, Laplacian and local energy density properties have been calculated for a number of As4Sn (n = 3,4,5) thioarsenide molecular crystals. On the basis of the distributions, the intramolecular As-S and As-As interactions classify as shared bonded interactions and the intermolecular As-S, As-As and S-S interactions classify as closed-shell van der Waals bonded interactions. The bulk of the intermolecular As-S bond paths link regions of locally concentrated electron density (Lewis base regions) with aligned regions of locally depleted electron density (Lewis acid regions) on adjacent molecules. The paths are comparable with intermolecular paths reported for severalmore » other molecular crystals that link aligned Lewis base and acid regions in a key-lock fashion, interactions that classified as long range Lewis acid-base directed van der Waals interactions. As the bulk of the intermolecular As-S bond paths (~70%) link Lewis acid-base regions on adjacent molecules, it appears that molecules adopt an arrangement that maximizes the number of As-S Lewis acid-base intermolecular bonded interactions. The maximization of the number of Lewis acid-base interactions appears to be connected with the close-packed array adopted by molecules: distorted cubic close-packed arrays are adopted for alacránite, pararealgar, uzonite, realgar and β-AsS and the distorted hexagonal close-packed arrays adopted by α- and β-dimorphite. A growth mechanism is proposed for thioarsenide molecular crystals from aqueous species that maximizes the number of long range Lewis acid-base vdW As-S bonded interactions with the resulting directed bond paths structuralizing the molecules as a molecular crystal.« less

Metallic Contact between MoS2 and Ni via Au Nanoglue.

PubMed

Shi, Xinying; Posysaev, Sergei; Huttula, Marko; Pankratov, Vladimir; Hoszowska, Joanna; Dousse, Jean-Claude; Zeeshan, Faisal; Niu, Yuran; Zakharov, Alexei; Li, Taohai; Miroshnichenko, Olga; Zhang, Meng; Wang, Xiao; Huang, Zhongjia; Saukko, Sami; González, Diego López; van Dijken, Sebastiaan; Alatalo, Matti; Cao, Wei

2018-05-01

A critical factor for electronics based on inorganic layered crystals stems from the electrical contact mode between the semiconducting crystals and the metal counterparts in the electric circuit. Here, a materials tailoring strategy via nanocomposite decoration is carried out to reach metallic contact between MoS 2 matrix and transition metal nanoparticles. Nickel nanoparticles (NiNPs) are successfully joined to the sides of a layered MoS 2 crystal through gold nanobuffers, forming semiconducting and magnetic NiNPs@MoS 2 complexes. The intrinsic semiconducting property of MoS 2 remains unchanged, and it can be lowered to only few layers. Chemical bonding of the Ni to the MoS 2 host is verified by synchrotron radiation based photoemission electron microscopy, and further proved by first-principles calculations. Following the system's band alignment, new electron migration channels between metal and the semiconducting side contribute to the metallic contact mechanism, while semiconductor-metal heterojunctions enhance the photocatalytic ability. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A polarization-independent liquid crystal phase modulation using polymer-network liquid crystal with orthogonal alignment layers

NASA Astrophysics Data System (ADS)

Chen, Ming-Syuan; Lin, Wei-Chih; Tsou, Yu-Shih; Lin, Yi-Hsin

2012-10-01

A polarization-independent liquid crystal (LC) phase modulation using polymer-network liquid crystals with orthogonal alignments layers (T-PNLC) is demonstrated. T-PNLC consists of three layers. LC directors in the two layers near glass substrates are orthogonal to each other. In the middle layer, LC directors are perpendicular to the glass substrate. The advantages of such T-PNLC include polarizer-free, larger phase shift (~0.4π rad) than the residual phase type (<0.05π rad), and low operating voltage (< 30Vrms). It does not require bias voltage for avoiding scattering because the refractive index of liquid crystals matches that of polymers. The phase shift of T-PNLC is affected by the cell gap and the curing voltages. The potential applications are laser beam steering, spatial light modulators and electrically tunable micro-lens arrays.

The use of Long-Lived Tracer Observations to Examine Transport Characteristics in the Lower Stratosphere

NASA Astrophysics Data System (ADS)

Lingenfelser, Gretchen Scott

This thesis explores the problem of uniformly aligning Ferroelectric Liquid Crystals (FLCs) over large areas whilst retaining bistability. A novel high tilt alignment (HTA) is presented and its electro-optic performance is compared to the traditional surface stabilised (SS) alignment using three different devices; test cells, displays and all-fibre optic devices. Evidence is presented to show that the SS alignment has a small surface pretilt of the director which reduces the number of zig-zag defects in parallel aligned cells. This is related to the layer structure and a review of the latest proposed structures of SS devices is presented. The HTA device is shown to have many advantages over the SS device; no zig-zag defects, excellent bistability in up to 6 mum thick cells, good mechanical stability and excellent viewing characteristics when multiplexed. These properties are explored and culminate in the production of two FLC displays, one HTA and one SS aligned. The properties of these displays are compared. In order to improve the appearance and frame time of the displays, multiplexing schemes were investigated, including a novel two slot scheme that was successfully used to drive both displays. It was found that the SS display could be driven in a reverse contrast mode by taking advantage of the relaxation process. This decreased the line address time and produced a higher contrast display. A nematic LC all-fibre optic polariser was produced with excellent extinction ratio (45 dB) and low loss (0.2 dB) using evanescent field coupling. A nematic LC modulator was then demonstrated using a novel electrode arrangement. A modulation depth of 28 dB was achieved using low voltages ( 10V) but with 10 kHz but the modulation depth was poor (8.2 dB) because of the unsuitable refractive indices. The potential and uses of LC all-fibre optic devices are discussed.

Crystals for krypton helium-alpha line emission microscopy

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

Koch, Jeffrey A.; Haugh, Michael J.

2018-04-17

A system for reflecting and recording x-ray radiation from an x-ray emitting event to characterize the event. A crystal is aligned to receive radiation along a first path from an x-ray emitting event. Upon striking the crystal, the x-ray reflects from the crystal along a second path due to a reflection plane of the crystal defined by one of the following Miller indices: (9,7,3) or (11,3,3). Exemplary crystalline material is germanium. The x-rays are reflected to a detector aligned to receive reflected x-rays that are reflected from the crystal along the second path and the detector generates a detector signalmore » in response to x-rays impacting the detector. The detector may include a CCD electronic detector, film plates, or any other detector type. A processor receives and processes the detector signal to generate reflection data representing the x-rays emitted from the x-ray emitting event.« less

Homogeneous alignment of nematic liquid crystals by ion beam etched surfaces

NASA Technical Reports Server (NTRS)

Wintucky, E. G.; Mahmood, R.; Johnson, D. L.

1979-01-01

A wide range of ion beam etch parameters capable of producing uniform homogeneous alignment of nematic liquid crystals on SiO2 films are discussed. The alignment surfaces were generated by obliquely incident (angles of 5 to 25 deg) argon ions with energies in the range of 0.5 to 2.0 KeV, ion current densities of 0.1 to 0.6 mA sq cm and etch times of 1 to 9 min. A smaller range of ion beam parameters (2.0 KeV, 0.2 mA sq cm, 5 to 10 deg and 1 to 5 min.) were also investigated with ZrO2 films and found suitable for homogeneous alignment. Extinction ratios were very high (1000), twist angles were small ( or = 3 deg) and tilt-bias angles very small ( or = 1 deg). Preliminary scanning electron microscopy results indicate a parallel oriented surface structure on the ion beam etched surfaces which may determine alignment.

Crystallographic phase induced electro-optic properties of nanorod blend nematic liquid crystal.

PubMed

Kundu, Sudarshan; Hill, Jonathan P; Richards, Gary J; Ariga, Katsuhiko; Khan, Ali Hossain; Thupakula, Umamahesh; Acharya, Somobrata

2011-09-01

Ultrasmall ZnS or PbS nanorods encapsulated in fluid-like soft organic surfactants show excellent miscibility in the nematic liquid crystal (LC ZLI-4792) host resulting in a novel soft matter type blend with enhanced electro-optic properties. The ultranarrow ZnS rods are of wurtzite phase and possess a chemical bipolarity and a net dipole moment. The centrosymmetric ultranarrow PbS rods possess a finite size and shape dependent inherent dipole moment despite their cubic rock-salt structure. When an electric field is applied, the blend aligns along the direction of the field producing a local unidirectional orientation of the rods and LC directors, and defining a unique axis for the system. The local ordering significantly affects the global ordering of the blend allowing a more rapid response of the electro-optic properties. The degree and switching speed of the blends depend upon the magnitude of dipole moments present in the dopant nanorods. We show how a non-mesogenic element designed with preferential crystallographic phase can be introduced within a LC for improvement of the switching properties of the LC blend. These types of unique blends are a model for fundamental conceptual advances in general understanding of interaction behaviour leading consequently to a significant technological advancement for superior device fabrication.

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.

Aligning precisely polarization maintaining photonic crystal fiber and conventional single-mode fiber by online spectrum monitoring

NASA Astrophysics Data System (ADS)

Jiang, Ying; Zeng, Jie; Liang, Dakai; Ni, Xiaoyu; Luo, Wenyong

2013-06-01

The fibers aligning is very important in fusion splicing process. The core of polarization maintaining photonic crystal fiber(PM-PCF) can not be seen in the splicer due to microhole structure of its cross-section. So it is difficult to align precisely PM-PCF and conventional single-mode fiber(SMF).We demonstrate a novel method for aligning precisely PM-PCF and conventional SMF by online spectrum monitoring. Firstly, the light source of halogen lamp is connected to one end face of conventional SMF.Then align roughly one end face of PM-PCF and the other end face of conventional SMF by observing visible light in the other end face of PM-PCF. If there exists visible light, they are believed to align roughly. The other end face of PM-PCF and one end face of the other conventional SMF are aligned precisely in the other splicer by online spectrum monitoring. Now the light source of halogen lamp is changed into a broadband light source with 52nm wavelength range.The other end face of the other conventional SMF is connected to an optical spectrum analyzer.They are translationally and rotationally adjusted in the splicer by monitoring spectrum. When the transmission spectrum power is maximum, the aligning is precise.

Supramolecular Polymer Network-Mediated Self-Assembly of Semicrystalline Polymers with Excellent Crystalline Performance.

PubMed

Cheng, Chih-Chia; Chuang, Wei-Tsung; Lee, Duu-Jong; Xin, Zhong; Chiu, Chih-Wei

2017-03-01

A novel application of supramolecular interactions within semicrystalline polymers, capable of self-assembling into supramolecular polymer networks via self-complementary multiple hydrogen-bonded complexes, is demonstrated for efficient construction of highly controlled self-organizing hierarchical structures to offer a direct, efficient nucleation pathway resulting in superior crystallization performance. Herein, a novel functionalized poly(ε-caprolactone) containing self-complementary sextuple hydrogen-bonded uracil-diamidopyridine (U-DPy) moieties is successfully developed and demonstrated excellent thermal and viscoelastic properties as well as high dynamic structural stability in the bulk state due to physical cross-linking created by reversible sextuple hydrogen bonding between U-DPy units. Due to the ability to vary the extent of the reversible network by tuning the U-DPy content, this newly developed material can be readily adjusted to obtain the desired crystalline products with specific characteristics. Importantly, incorporating only 0.1% U-DPy resulted in a polymer with a high crystallization rate constant, short crystallization half-time, and much more rapid crystallization kinetics than pristine PCL, indicating a low content of U-DPy moieties provides highly efficient nucleation sites that manipulate the nucleation and growth processes of polymer crystals to promote crystallization and chain alignment in bulk. This new system is suggested as a potential new route to substantially improve the performance of polymer crystallization. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The competition between magnetocrystalline and shape anisotropy on the magnetic and magneto-transport properties of crystallographically aligned CuCr2Se4 thin films

NASA Astrophysics Data System (ADS)

Edelman, I.; Esters, M.; Johnson, D. C.; Yurkin, G.; Tarasov, A.; Rautsky, M.; Volochaev, M.; Lyashchenko, S.; Ivantsov, R.; Petrov, D.; Solovyov, L. A.

2017-12-01

Crystallographically aligned nanocrystalline films of the ferromagnetic spinel CuCr2Se4 were successfully synthesized and their structure and alignment were confirmed by X-ray diffraction and high-resolution transmission electron microscopy. The average size of the crystallites is about 200-250 nm, and their (1 1 1) crystal planes are parallel to the film plane. A good match of the film's electronic structure to that of bulk CuCr2Se4 is confirmed by transverse Kerr effect measurements. Four easy 〈1 1 1〉 axes are present in the films. One of these axes is oriented perpendicular and three others are oriented at an angle of 19.5° relative to the film plane. The magnetic properties of the films are determined by a competition between the out-of-plane magnetocrystalline anisotropy and the in-plane shape anisotropy. Magnetic measurements show that the dominating type of anisotropy switches from shape to magnetocrystalline anisotropy near 160 K, which leads to a switch of the effective easy axis from inside the film plane at room temperature to perpendicular to the film plane as the temperature decreases. At last, a moderately large, negative value of the low-temperature magnetoresistance was observed for the first time in CuCr2Se4 films.

Convection in a nematic liquid crystal with homeotropic alignment and heated from below

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

Ahlers, G.

Experimental results for convection in a thin horizontal layer of a homeotropically aligned nematic liquid crystal heated from below and in a vertical magnetic field are presented. A subcritical Hopf bifurcation leads to the convecting state. There is quantitative agreement between the measured and the predicted bifurcation line as a function of magnetic field. The nonlinear state near the bifurcation is one of spatio-temporal chaos which seems to be the result of a zig-zag instability of the straight-roll state.

Crystal preferred orientation of amphibole and implications for seismic anisotropy in the crust

NASA Astrophysics Data System (ADS)

Jung, Haemyeong

2016-04-01

Strong seismic anisotropy is often observed in the middle to lower crust and it has been considered to be originated from the crystal preferred orientation (CPO) of anisotropic minerals such as amphibole. Amphibolite is one of the dominant rocks in the middle to lower crust. In this study, crystal preferred orientations of hornblende in amphibolites at Yeoncheon and Chuncheon areas in South Korea were determined by using the electron backscattered diffraction (EBSD)/SEM with HKL Channel 5 software. In Yeoncheon area, hornblende showed two types of CPOs. Type-I CPO is characterized as (100) poles of hornblende aligned subnormal to foliation and [001] axes aligned subparallel to lineation. Type-II CPO is characterized as (100) poles of hornblende aligned subnormal to foliation and (010) poles aligned subparallel to lineation (refer to Ko and Jung, 2015, Nature Communications). In Chuncheon area, three types of CPOs of hornblende were observed. In addition to the type-I and -II CPOs described above, type-III CPO of hornblende was observed in Chuncheon area and it is characterized as (100) poles of hornblende aligned subnormal to foliation and both [001] axes and (010) poles aligned as a girdle subparallel to foliation. Using the observed CPO and the single crystal elastic constant of hornblende, seismic anisotropy of hornblende was calculated. Seismic anisotropy of P-wave was strong in the range of 10.2 - 13.5 %. Seismic anisotropy of S-wave was also strong in the range of 6.9 - 11.2 %. These results show that hornblende deformed in nature can produce a strong CPO, resulting in a strong seismic anisotropy in the middle to lower crust. Taking into account of the CPO of plagioclase in the rock, seismic anisotropies of whole rock turned out to be maximum P-wave anisotropy (Vp) of 9.8% and maximum S-wave anisotropy (Vs) of 8.2%. Therefore, strong seismic anisotropy found in the middle to lower crust in nature can be attributed to the CPO of hornblende in amphibolite.

Crystalline multiwall carbon nanotubes and their application as a field emission electron source.

PubMed

Liu, Peng; Zhou, Duanliang; Zhang, Chunhai; Wei, Haoming; Yang, Xinhe; Wu, Yang; Li, Qingwei; Liu, Changhong; Du, Bingchu; Liu, Liang; Jiang, Kaili; Fan, Shoushan

2018-05-18

Using super-aligned carbon nanotube (CNT) film, we have fabricated van der Waals crystalline multiwall CNTs (MWCNT) by adopting high pressure and high temperature processing. The CNTs keep parallel to each other and are distributed uniformly. X-ray diffraction characterization shows peaks at the small angle range, which can be assigned to the spacing of the MWCNT crystals. The mechanical, electrical and thermal properties are all greatly improved compared with the original CNT film. The field emission properties of van der Waals crystalline MWCNTs are tested and they show a better surface morphology stability for the large emission current. We have further fabricated a field emission x-ray tube and demonstrated a precise resolution imaging ability.

Structure and blood compatibility of highly oriented PLA/MWNTs composites produced by solid hot drawing.

PubMed

Li, Zhengqiu; Zhao, Xiaowen; Ye, Lin; Coates, Phil; Caton-Rose, Fin; Martyn, Michasel

2014-03-01

Highly oriented poly(lactic acid) (PLA)/multi-walled carbon nanotubes (MWNTs) composites were fabricated through solid hot drawing technology in an effort to improve the mechanical properties and blood biocompatibility of PLA as blood-contacting medical devices. It was found that proper MWNTs content and drawing orientation can improve the tensile strength and modulus of PLA dramatically. With the increase in draw ratio, the cold crystallization peak became smaller, and the glass transition and the melting peak of PLA moved to high temperature, while the crystallinity increased, and the grain size decreased, indicating the stress-induced crystallization of PLA during drawing. MWNTs showed a nucleation effect on PLA, leading to the rise in the melting temperature, increase in crystallinity and reduction of spherulite size for the composites. Moreover, the intensity of (002) diffraction of MWNTs increased with draw ratio, indicating that MWNTs were preferentially aligned and oriented during drawing. Microstructure observation demonstrated that PLA matrix had an ordered fibrillar bundle structure, and MWNTs in the composite tended to align parallel to the drawing direction. In addition, the dispersion of MWNTs in PLA was also improved by orientation. Introduction of MWNTs and drawing orientation could significantly enhance the blood compatibility of PLA by prolonging kinetic clotting time, reducing hemolysis ratio and platelet activation.

Electro-optic characteristics of 4-domain vertical alignment nematic liquid crystal display with interdigital electrode

NASA Astrophysics Data System (ADS)

Hong, S. H.; Jeong, Y. H.; Kim, H. Y.; Cho, H. M.; Lee, W. G.; Lee, S. H.

2000-06-01

We have fabricated a vertically aligned 4-domain nematic liquid crystal display cell with thin film transistor. Unlike the conventional method constructing 4-domain, i.e., protrusion and surrounding electrode which needs additional processes, in this study the pixel design forming 4-domain with interdigital electrodes is suggested. In the device, one pixel is divided into two parts. One part has a horizontal electric field in the vertical direction and the other part has a horizontal one in the horizontal direction. Such fields in the horizontal and vertical direction drive the liquid crystal director to tilt down in four directions. In this article, the electro-optic characteristics of cells with 2 and 4 domain have been studied. The device with 4 domain shows faster response time than normal twisted-nematic and in-plane switching cells, wide viewing angle with optical compensation film, and more stable color characteristics than 2-domain vertical alignment cell with similar structure.

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.

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.

Langmuir Films of Flexible Polymers Transferred to Aqueous/Liquid Crystal Interfaces Induce Uniform Azimuthal Alignment of the Liquid Crystal

PubMed Central

Kinsinger, Michael I.; Buck, Maren E.; Meli, Maria-Victoria; Abbott, Nicholas L.; Lynn, David M.

2009-01-01

We reported recently that amphiphilic polymers can be assembled at interfaces created between aqueous phases and thermotropic liquid crystals (LCs) in ways that (i) couple the organization of the polymer to the order of the LC and (ii) respond to changes in the properties of aqueous phases that can be characterized as changes in the optical appearance of the LC. This investigation sought to characterize the behavior of aqueous-LC interfaces decorated with uniaxially compressed thin films of polymers transferred by Langmuir-Schaefer (LS) transfer. Here, we report physicochemical characterization of interfaces created between aqueous phases and the thermotropic LC 4-cyano-4’-pentylbiphenyl (5CB) decorated with Langmuir films of a novel amphiphilic polymer (polymer 1), synthesized by the addition of hydrophobic and hydrophilic side chains to poly(2-vinyl-4,4’-dimethylazlactone). Initial characterization of this system resulted in the unexpected observation of uniform azimuthal alignment of 5CB after LS transfer of the polymer films to aqueous-5CB interfaces. This paper describes characterization of Langmuir films of polymer 1 hosted at aqueous-5CB interfaces as well as the results of our investigations into the origins of the uniform ordering of the LC observed upon LS transfer. Our results, when combined, support the conclusion that uniform azimuthal alignment of 5CB is the result of long-range ordering of polymer chains in the Langmuir films (in a preferred direction orthogonal to the direction of compression) that is generated during uniaxial compression of the films prior to LS transfer. Although past studies of Langmuir films of polymers at aqueous-air interfaces have demonstrated that in-plane alignment of polymer backbones can be induced by uniaxial compression, these past reports have generally made use of polymers with rigid backbones. One important outcome of this current study is thus the observation of anisotropy and long-range order in Langmuir films of a novel flexible polymer. A second important outcome is the observation that the existence, extent, and dynamics of this order can be identified and characterized optically by transfer of the Langmuir film to a thin film of LC. Additional characterization of Langmuir films of two other flexible polymers [poly(methyl methacrylate) and poly(vinyl stearate)] using this method also resulted in uniform azimuthal alignment of 5CB, suggesting that the generation of long-range order in uniaxially compressed Langmuir films of polymers may also occur more generally over a broader range of polymers with flexible backbones. PMID:19836025

Tunable liquid crystal photonic devices

NASA Astrophysics Data System (ADS)

Fan, Yun-Hsing

2005-07-01

Liquid crystal (LC)-based adaptive optics are important for information processing, optical interconnections, photonics, integrated optics, and optical communications due to their tunable optical properties. In this dissertation, we describe novel liquid crystal photonic devices. In Chap. 3, we demonstrate a novel electrically tunable-efficiency Fresnel lens which is devised for the first time using nanoscale PDLC. The tunable Fresnel lens is very desirable to eliminate the need of external spatial light modulator. The nanoscale LC devices are polarization independent and exhibit a fast response time. Because of the small droplet sizes, the operating voltage is higher than 100 Vrms. To lower the driving voltage, in Chap. 2 and Chap. 3, we have investigated tunable Fresnel lens using polymer-network liquid crystal (PNLC) and phase-separated composite film (PSCOF). The operating voltage is below 12 Vrms. The PNLC and PSCOF devices are polarization dependent. To overcome this shortcoming, stacking two cells with orthogonal alignment directions is a possibility. Using PNLC, we also demonstrated LC blazed grating. The diffraction efficiency of these devices is continuously controlled by the electric field. We also develop a system with continuously tunable focal length. A conventional mechanical zooming system is bulky and power hungry. In Chap. 4, we developed an electrically tunable-focus flat LC spherical lens and microlens array. A huge tunable range from 0.6 m to infinity is achieved by the applied voltage. In Chap. 5, we describe a LC microlens array whose focal length can be switched from positive to negative by the applied voltage. The fast response time feature of our LC microlens array will be very helpful in developing 3-D animated images. In Chap. 6, we demonstrate polymer network liquid crystals for switchable polarizers and optical shutters. The use of dual-frequency liquid crystal and special driving scheme leads to a sub-millisecond response time. In Chap. 7, for the first time, we demonstrate a fast-response and scattering-free homogeneously-aligned PNLC light modulator. The PNLC response time is ˜300x faster than that of a pure LC mixture. The PNLC cell also holds promise for mid and long infrared applications where response time is a critical issue.

Photoaligning and photopatterning technology: applications in displays and photonics

NASA Astrophysics Data System (ADS)

Chigrinov, Vladimir

2016-03-01

The advantages of LC photoalignment technology in comparison with common "rubbing" alignment methods tend to the continuation of the research in this field. Almost all the criteria of perfect LC alignment are met in case of azo-dye layers. Nowadays azo-dye alignment materials can be already used in LCD manufacturing, e.g. for the alignment of monomers in LCP films for new generations of photonics and optics devices. Recently the new application of photoaligned technology for the tunable LC lenses with a variable focal distance was proposed. New optically rewritable (ORW) liquid crystal display and photonics devices with a light controllable structure may include LC E-paper screens, LC lenses with a variable focal distance etc. Fast ferroelectric liquid crystal devices (FLCD) are achieved through the application of nano-scale photo aligning (PA) layers in FLC cells. The novel photoaligned FLC devices may include field sequential color (FSC) FLC with a high resolution, high brightness, low power consumption and extended color gamut to be used for PCs, PDAs, switchable goggles, and new generation of switchable 2D/3D LCD TVs, as well as photonics elements.

Note: A quartz cell with Pt single crystal bead electrode for electrochemical scanning tunneling microscope measurements.

PubMed

Xia, Zhigang; Wang, Jihao; Hou, Yubin; Lu, Qingyou

2014-09-01

In this paper, we provide and demonstrate a design of a unique cell with Pt single crystal bead electrode for electrochemical scanning tunneling microscope (ECSTM) measurements. The active metal Pt electrode can be protected from air contamination during the preparation process. The transparency of the cell allows the tip and bead to be aligned by direct observation. Based on this, a new and effective alignment method is introduced. The high-quality bead preparations through this new cell have been confirmed by the ECSTM images of Pt (111).

Light deflection in gadolinium molybdate ferroelastic crystals

NASA Astrophysics Data System (ADS)

Staniorowski, Piotr; Bornarel, Jean

2000-02-01

The deflection of a He-Ne light beam by polydomain gadolinium molybdate (GMO) crystals has been studied with respect to incidence angle icons/Journals/Common/alpha" ALT="alpha" ALIGN="TOP"/> i on the sample at room temperature. The A and B deflected beams do not cross each other during the icons/Journals/Common/alpha" ALT="alpha" ALIGN="TOP"/> i variation, in contrast to results and calculations previously published. The model using the Fresnel equation confirms this result. The model presented is more accurate for numerical calculation than that using the Huygens construction.

Liquid crystal cells with built-in CdSe nanotubes for chromogenic smart emission devices.

PubMed

Lin, Tsung Ju; Chen, Chin-Chang; Cheng, Soofin; Chen, Yang Fang

2008-01-21

A simple and general approach for controlling optical anisotropy of nanostructured semiconductors is reported. Our design involves the fabrication of liquid crystal devices with built-in semiconductor nanotubes. Quite interestingly, it is found that semiconductor nanotubes can be well aligned along the orientation of liquid crystals molecules automatically, resulting in a very large emission anisotropy with the degree of polarization up to 72%. This intriguing result manifests a way to obtain well aligned semiconductor nanotubes and the emission anisotropy can be easily manipulated by an external bias. The ability to well control the emission anisotropy should open up new opportunities for nanostructured semiconductors, including optical filters, polarized light emitting diodes, flat panel displays, and many other chromogenic smart devices.

Nonlinear Raman spectroscopy of liquid crystals: orientational alignment and switching behaviour in a ferroelectric liquid crystal mixture

NASA Astrophysics Data System (ADS)

Grofcsik, Andras

Picosecond inverse Raman spectroscopy has been employed to probe the alignment behaviour and switching characteristics of a 6 mum thick ferroelectric liquid crystal based on a host mixture of fluorinated phenyl biphenylcarboxylates and a chiral dopant. Optical bistability is observed in the Raman signal on application of dc electric fields of opposite polarity. For particular polarities of the applied field, the Raman signals display a cos4theta dependence on the angle of rotation around the beam direction. Reorientational rate constants of 300 mus and 590 mus are observed for the aromatic core at the high-voltage limit for the rise and decay of the 1600 cm-1 Raman signal on application of a switching ac electric field.

Voltage‐Controlled Switching of Strong Light–Matter Interactions using Liquid Crystals

PubMed Central

Hertzog, Manuel; Rudquist, Per; Hutchison, James A.; George, Jino; Ebbesen, Thomas W.

2017-01-01

Abstract We experimentally demonstrate a fine control over the coupling strength of vibrational light–matter hybrid states by controlling the orientation of a nematic liquid crystal. Through an external voltage, the liquid crystal is seamlessly switched between two orthogonal directions. Using these features, for the first time, we demonstrate electrical switching and increased Rabi splitting through transition dipole moment alignment. The C−Nstr vibration on the liquid crystal molecule is coupled to a cavity mode, and FT‐IR is used to probe the formed vibropolaritonic states. A switching ratio of the Rabi splitting of 1.78 is demonstrated between the parallel and the perpendicular orientation. Furthermore, the orientational order increases the Rabi splitting by 41 % as compared to an isotropic liquid. Finally, by examining the influence of molecular alignment on the Rabi splitting, the scalar product used in theoretical modeling between light and matter in the strong coupling regime is verified. PMID:29155469

Solution-grown small-molecule organic semiconductor with enhanced crystal alignment and areal coverage for organic thin film transistors

DOE PAGES

Bi, Sheng; He, Zhengran; Chen, Jihua; ...

2015-07-24

Drop casting of small-molecule organic semiconductors typically forms crystals with random orientation and poor areal coverage, which leads to significant performance variations of organic thin-film transistors (OTFTs). In this study, we utilize the controlled evaporative self-assembly (CESA) method combined with binary solvent system to control the crystal growth. A small-molecule organic semiconductor,2,5-Di-(2-ethylhexyl)-3,6-bis(5"-n-hexyl-2,2',5',2"]terthiophen-5-yl)-pyrrolo[3,4-c]pyrrole-1,4-dione (SMDPPEH), is used as an example to demonstrate the effectiveness of our approach. By optimizing the double solvent ratios, well-aligned SMDPPEH crystals with significantly improved areal coverage were achieved. As a result, the SMDPPEH based OTFTs exhibit a mobility of 1.6 × 10 -2 cm 2/V s, whichmore » is the highest mobility from SMDPPEH ever reported.« less

Enhanced contrast ratio and viewing angle of polymer-stabilized liquid crystal via refractive index matching between liquid crystal and polymer network.

PubMed

Lee, Ji-Hoon; Lee, Jung Jin; Lim, Young Jin; Kundu, Sudarshan; Kang, Shin-Woong; Lee, Seung Hee

2013-11-04

Long standing electro-optic problems of a polymer-dispersed liquid crystal (PDLC) such as low contrast ratio and transmittances decrease in oblique viewing angle have been challenged with a mixture of dual frequency liquid crystal (DFLC) and reactive mesogen (RM). The DFLC and RM molecules were vertically aligned and then photo-polymerized using a UV light. At scattering state under 50 kHz electric field, DFLC was switched to planar state, giving greater extraordinary refractive index than the normal PDLC cell. Consequently, the scattering intensity and the contrast ratio were increased compared to the conventional PDLC cell. At transparent state under 1 kHz electric field, the extraordinary refractive index of DFLC was simultaneously matched with the refractive index of vertically aligned RM so that the light scattering in oblique viewing angles was minimized, giving rise to high transmittance in all viewing angles.

A Central Positron Source to Perform the Timing Alignment of Detectors in a PET Scanner

NASA Astrophysics Data System (ADS)

Thompson, C. J.; Camborde, M.-L.; Casey, M. E.

2005-10-01

Accurate timing alignment and stability are important to maximize the true counts and minimize the random counts in positron emission tomography. Its importance increases in time-of-flight (TOF) scanners. We propose using a central positron emitting source enclosed in a detector which detects the excess energy of the positron before it annihilates as a timing reference. All crystals can be time-aligned with respect to this central source. We evaluated 10 /spl mu/Ci /sup 22/Na and /sup 68/Ge sources embedded in cylinders of plastic scintillator coupled to a fast PMT. Light flashes produced after the parent isotope emits positrons are detected, and the anode signals from the PMT are the reference time for each positron decay. The time delay before the gamma ray is detected by the scanner's conventional gamma ray detectors is the time offset to be applied to that crystal. Since all detectors are almost the same distance from the central source, TOF errors are minimized. Preliminary results show a mean signal amplitude of >0.5 V from /sup 22/Na at 1000-V PMT bias, a timing FWHM of 850 ps with respect to a small LSO crystal. This suggests it could be useful to align both conventional and TOF PET scanners.

Observations of cavity polaritons in one-dimensional photonic crystals containing a liquid-crystalline semiconductor based on perylene bisimide units

NASA Astrophysics Data System (ADS)

Sakata, T.; Suzuki, M.; Yamamoto, T.; Nakanishi, S.; Funahashi, M.; Tsurumachi, N.

2017-10-01

We investigated the optical transmission properties of one-dimensional photonic crystal (1D-PC) microcavity structures containing the liquid-crystalline (LC) perylene tetracarboxylic bisimide (PTCBI) derivative. We fabricated the microcavity structures for this study by two different methods and observed the cavity polaritons successfully in both samples. For one sample, since the PTCBI molecules were aligned in the cavity layer of the 1D-PC by utilizing a friction transfer method, vacuum Rabi splitting energy was strongly dependent on the polarization of the incident light produced by the peculiar optical features of the LC organic semiconductor. For the other sample, we did not utilize the friction transfer method and did not observe such polarization dependence. However, we did observe a relatively large Rabi splitting energy of 187 meV, probably due to the improvement of optical confinement effect.

Composite germanium monochromators - Results for the TriCS single-crystal diffractometer at SINQ

NASA Astrophysics Data System (ADS)

Schefer, J.; Fischer, S.; Böhm, M.; Keller, L.; Horisberger, M.; Medarde, M.; Fischer, P.

Composite germanium monochromators are foremost in application in neutron diffraction due to their good scattering properties, low absorption values and the diamond structure which avoids second-order contamination when using hhk reflections (all odd). Our slices for the monochromator are built from 24 wafers, each 0.4 mm thick. The alignment of the wafers within the final composite wafer package has been improved by adding tin for the soldering process with a sputtering method instead of foils. Nine slices, each 12.5 mm high, are mounted on separate miniature goniometer heads to the focusing monochromator. The focusing angle is controlled by only one motor/digitizer by using a sophisticated mechanism. Turning the monochromator by 9° around overlineω allow access of the 311 (primary) and 511 (secondary) reflection. We also show the importance of permanent quality control with neutrons. The monochromator will be used on the single-crystal diffractometer TriCS at SINQ.

Bioengineering single crystal growth.

PubMed

Wu, Ching-Hsuan; Park, Alexander; Joester, Derk

2011-02-16

Biomineralization is a "bottom-up" synthesis process that results in the formation of inorganic/organic nanocomposites with unrivaled control over structure, superior mechanical properties, adaptive response, and the capability of self-repair. While de novo design of such highly optimized materials may still be out of reach, engineering of the biosynthetic machinery may offer an alternative route to design advanced materials. Herein, we present an approach using micro-contact-printed lectins for patterning sea urchin embryo primary mesenchyme cells (PMCs) in vitro. We demonstrate not only that PMCs cultured on these substrates show attachment to wheat germ agglutinin and concanavalin A patterns but, more importantly, that the deposition and elongation of calcite spicules occurs cooperatively by multiple cells and in alignment with the printed pattern. This allows us to control the placement and orientation of smooth, cylindrical calcite single crystals where the crystallographic c-direction is parallel to the cylinder axis and the underlying line pattern.

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.

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).

Development of an x-ray prism for analyzer based imaging systems

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

Bewer, Brian; Chapman, Dean

Analyzer crystal based imaging techniques such as diffraction enhanced imaging (DEI) and multiple imaging radiography (MIR) utilize the Bragg peak of perfect crystal diffraction to convert angular changes into intensity changes. These x-ray techniques extend the capability of conventional radiography, which derives image contrast from absorption, by providing large intensity changes for small angle changes introduced from the x-ray beam traversing the sample. Objects that have very little absorption contrast may have considerable refraction and ultrasmall angle x-ray scattering contrast improving visualization and extending the utility of x-ray imaging. To improve on the current DEI technique an x-ray prism (XRP)more » was designed and included in the imaging system. The XRP allows the analyzer crystal to be aligned anywhere on the rocking curve without physically moving the analyzer from the Bragg angle. By using the XRP to set the rocking curve alignment rather than moving the analyzer crystal physically the needed angle sensitivity is changed from submicroradians for direct mechanical movement of the analyzer crystal to tens of milliradians for movement of the XRP angle. However, this improvement in angle positioning comes at the cost of absorption loss in the XRP and depends on the x-ray energy. In addition to using an XRP for crystal alignment it has the potential for scanning quickly through the entire rocking curve. This has the benefit of collecting all the required data for image reconstruction in a single measurement thereby removing some problems with motion artifacts which remain a concern in current DEI/MIR systems especially for living animals.« less

Development of an x-ray prism for analyzer based imaging systems

NASA Astrophysics Data System (ADS)

Bewer, Brian; Chapman, Dean

2010-08-01

Analyzer crystal based imaging techniques such as diffraction enhanced imaging (DEI) and multiple imaging radiography (MIR) utilize the Bragg peak of perfect crystal diffraction to convert angular changes into intensity changes. These x-ray techniques extend the capability of conventional radiography, which derives image contrast from absorption, by providing large intensity changes for small angle changes introduced from the x-ray beam traversing the sample. Objects that have very little absorption contrast may have considerable refraction and ultrasmall angle x-ray scattering contrast improving visualization and extending the utility of x-ray imaging. To improve on the current DEI technique an x-ray prism (XRP) was designed and included in the imaging system. The XRP allows the analyzer crystal to be aligned anywhere on the rocking curve without physically moving the analyzer from the Bragg angle. By using the XRP to set the rocking curve alignment rather than moving the analyzer crystal physically the needed angle sensitivity is changed from submicroradians for direct mechanical movement of the analyzer crystal to tens of milliradians for movement of the XRP angle. However, this improvement in angle positioning comes at the cost of absorption loss in the XRP and depends on the x-ray energy. In addition to using an XRP for crystal alignment it has the potential for scanning quickly through the entire rocking curve. This has the benefit of collecting all the required data for image reconstruction in a single measurement thereby removing some problems with motion artifacts which remain a concern in current DEI/MIR systems especially for living animals.

Development of an x-ray prism for analyzer based imaging systems.

PubMed

Bewer, Brian; Chapman, Dean

2010-08-01

Analyzer crystal based imaging techniques such as diffraction enhanced imaging (DEI) and multiple imaging radiography (MIR) utilize the Bragg peak of perfect crystal diffraction to convert angular changes into intensity changes. These x-ray techniques extend the capability of conventional radiography, which derives image contrast from absorption, by providing large intensity changes for small angle changes introduced from the x-ray beam traversing the sample. Objects that have very little absorption contrast may have considerable refraction and ultrasmall angle x-ray scattering contrast improving visualization and extending the utility of x-ray imaging. To improve on the current DEI technique an x-ray prism (XRP) was designed and included in the imaging system. The XRP allows the analyzer crystal to be aligned anywhere on the rocking curve without physically moving the analyzer from the Bragg angle. By using the XRP to set the rocking curve alignment rather than moving the analyzer crystal physically the needed angle sensitivity is changed from submicroradians for direct mechanical movement of the analyzer crystal to tens of milliradians for movement of the XRP angle. However, this improvement in angle positioning comes at the cost of absorption loss in the XRP and depends on the x-ray energy. In addition to using an XRP for crystal alignment it has the potential for scanning quickly through the entire rocking curve. This has the benefit of collecting all the required data for image reconstruction in a single measurement thereby removing some problems with motion artifacts which remain a concern in current DEI/MIR systems especially for living animals.

Cholesterol-Based Grafted Polymer Brushes as Alignment Coating with Temperature-Tuned Anchoring for Nematic Liquid Crystals.

PubMed

Stetsyshyn, Yurij; Raczkowska, Joanna; Budkowski, Andrzej; Awsiuk, Kamil; Kostruba, Andriy; Nastyshyn, Svyatoslav; Harhay, Khrystyna; Lychkovskyy, Edward; Ohar, Halyna; Nastishin, Yuriy

2016-10-11

Novel alignment coating with temperature-tuned anchoring for nematic liquid crystals (NLCs) was successfully fabricated in three step process, involving polymerization of poly(cholesteryl methacrylate) (PChMa) from oligoproxide grafted to the glass surface premodified with 3-aminopropyltriethoxysilane. Molecular composition, thickness, wettability of the PChMa coating and its alignment action for a NLC were examined with time of flight-secondary ion mass spectrometry, ellipsometry, contact angle measurements, polarization optical microscopy and commercially produced PolScope technique allowing for mapping of the optic axis and optical retardance within the microscope field view. We find that the PChMa coating provides a specific monotonous increase (decrease) in the tilt angle of the NLC director with respect to the substrates normal upon heating (cooling) referred to as anchoring tuning.

Omni-Directional Viewing-Angle Switching through Control of the Beam Divergence Angle in a Liquid Crystal Panel

NASA Astrophysics Data System (ADS)

Baek, Jong-In; Kim, Ki-Han; Kim, Jae Chang; Yoon, Tae-Hoon

2010-01-01

This paper proposes a method of omni-directional viewing-angle switching by controlling the beam diverging angle (BDA) in a liquid crystal (LC) panel. The LCs aligned randomly by in-cell polymer structures diffuse the collimated backlight for the bright state of the wide viewing-angle mode. We align the LCs homogeneously by applying an in-plane field for the narrow viewing-angle mode. By doing this the scattering is significantly reduced so that the small BDA is maintained as it passes through the LC layer. The dark state can be obtained by aligning the LCs homeotropically with a vertical electric field. We demonstrated experimentally the omni-directional switching of the viewing-angle, without an additional panel or backlighting system.

Growth of (Y1-x Ca x )Ba2Cu4O8 in ambient pressure and its tri-axial magnetic alignment

NASA Astrophysics Data System (ADS)

Horii, S.; Yamaki, M.; Shimoyama, J.; Kishio, K.; Doi, T.

2015-10-01

We report the growth of single crystals in ambient pressure and tri-axial orientation under modulated rotation magnetic fields (MRFs) for (Y1-x Ca x )Ba2Cu4O8 [(Y1-x Ca x )124] with x ≤ 0.1. Rectangular (Y1-x Ca x )124 crystals approximately 50 μm in size have been successfully grown for x ≤ 0.1 in a growth temperature region from 650 °C to 750 °C. Their critical temperatures increased with x and exhibited approximately 91 K for x = 0.1. By applying an MRF of 10 T, pulverised powders of (Y1-x Ca x )124 were tri-axially aligned in epoxy resin at room temperature in a whole x region below x = 0.1. The magnitude relationship of the magnetic susceptibilities (χ) along crystallographic directions for (Y1-x Ca x )124 was χ c > χ a > χ b at room temperature and was unchanged with a change in x. From changes in the degrees of the c-axis and the in-plane orientation (Δω) for the (Y1-x Ca x )124 powder samples aligned under three different MRF conditions, it was found that MRFs above at least 1 T were required to achieve almost complete tri-axial alignment with Δω < 5°. Irreversibility lines for H//c were successfully determined even from the powder samples by the introduction of magnetic alignment without using single crystalline samples. The present study indicates that magnetic alignment is a useful process for the fabrication of quasi-single-crystals from the perspective of solid-state physics and the production of cuprate superconducting materials.

Dispersions of Semiconductor Nanoparticles in Thermotropic Liquid Crystal: From Optical Modification to Assisted Self-Assembly

NASA Astrophysics Data System (ADS)

Rodarte, Andrea L.

The interaction of semiconducting quantum dot nanoparticles (QDs) within thermotropic liquid crystalline (LC) materials are studied in this thesis. LC materials are ideal for bottom-up organization of nanoparticles as an active matrix that can be externally manipulated via electric or magnetic fields. In addition, the optical properties of QDs can be modified by the surrounding LC resulting in novel devices such as a quantum dot/liquid crystal laser. The first system studies the dispersion of spherical nanoparticles in the phase. The dispersion is investigated with the use of polarized optical microscopy, fluorescence microscopy and confocal scanning microscopy. Quantum dots well dispersed in the isotropic phase are expelled from ordered domains of LC at the phase transition. Under controlled conditions, the majority of QDs in the system can form ordered three dimensional assemblies that are situated at defect points in the liquid crystal. The internal order of the assemblies is probed utilizing Forster resonance energy transfer (FRET), combined with small angle X-ray scattering (SAXS). Furthermore, the location of these assemblies can be predetermined with the use of beads as defect nucleation points in the cell. The interaction of QDs in a cholesteric liquid crystal (CLC) is also investigated. The reflection band created by the periodic change of index of refraction in a planar aligned CLC acts as a 1-D photonic cavity when the CLC is doped with a low concentration of QDs. A Cano-wedge cell varies the pitch of the CLC leading to the formation of Grandjean steps. This spatially tunes the photonic stop band, changing the resonance condition and continuously altering both the emission wavelength and polarization state of the QD ensemble. Using high resolution spatially and spectrally resolved photoluminescence measurements, the emission is shown to be elliptically polarized and that the tilt of the ellipse, while dependent on the emission wavelength, additionally varies with distance across the Grandjean steps. Using ultrafast spectroscopic techniques the time-resolved emission from QD ensembles in CLC matrices with either planar or homeotropic alignment is observed. In the case of planar alignment and a well-defined spectral stop band the emergence of a second, faster decay time of less than 2 ns is observed. This short recombination pathway is observed only in samples where the QD emission spectrum partially overlaps the CLC stop band by 50% or more. Samples prepared with homeotropic alignment do not have a stop band and, consequently, do not lead to spectral or dynamical modulation of the QD emission. These observations indicate that coupling between the excitonic and the photonic cavity modes results in an enhancement and modulation of spontaneous emission in the liquid crystal medium. This work opens up the possibility of designing new QD based optical devices, such as tunable single photon sources, where spatial control of wavelength and polarization of the embedded QDs would allow great flexibility and added functionalities. For hybrid materials such as soft tunable photonic devices like liquid crystal lasers, stable dispersions of nanoparticles in LC are desired. For the system we investigate functionalizing the nanoparticles with LC like ligands. Isotropic and mesogenic ligands attached to the surface of CdSe (core only) and CdSe/ZnS (core/shell) QDs. The mesogenic ligand's flexible arm structure enhances ligand alignment with the local liquid crystal director, enhancing QD dispersion in the isotropic and nematic phases. To characterize QD dispersion on different length scales, fluorescence microscopy, x-ray scattering and scanning confocal photoluminescent imaging are used. These combined techniques demonstrate that the LC-modified QDs do not aggregate into the dense clusters observed for dots with simple isotropic ligands when dispersed in liquid crystal, but loosely associate in a fluid-like aggregate with an average inter-particle spacing of >10nm. The major goal in this research is to identify the strengths and weaknesses of utilizing liquid crystal materials for hybrid and metamaterials. The techniques developed within this thesis will be useful for the next step of bottom-up metamaterial fabrication.

Effects of flow on the dynamics of a ferromagnetic nematic liquid crystal

NASA Astrophysics Data System (ADS)

Potisk, Tilen; Pleiner, Harald; Svenšek, Daniel; Brand, Helmut R.

2018-04-01

We investigate the effects of flow on the dynamics of ferromagnetic nematic liquid crystals. As a model, we study the coupled dynamics of the magnetization, M , the director field, n , associated with the liquid crystalline orientational order, and the velocity field, v . We evaluate how simple shear flow in a ferromagnetic nematic is modified in the presence of small external magnetic fields, and we make experimentally testable predictions for the resulting effective shear viscosity: an increase by a factor of 2 in a magnetic field of about 20 mT. Flow alignment, a characteristic feature of classical uniaxial nematic liquid crystals, is analyzed for ferromagnetic nematics for the two cases of magnetization in or perpendicular to the shear plane. In the former case, we find that small in-plane magnetic fields are sufficient to suppress tumbling and thus that the boundary between flow alignment and tumbling can be controlled easily. In the latter case, we furthermore find a possibility of flow alignment in a regime for which one obtains tumbling for the pure nematic component. We derive the analogs of the three Miesowicz viscosities well-known from usual nematic liquid crystals, corresponding to nine different configurations. Combinations of these can be used to determine several dynamic coefficients experimentally.

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

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.

Formation of radial aligned and uniform nematic liquid crystal droplets via drop-on-demand inkjet printing into a partially-wet polymer layer

NASA Astrophysics Data System (ADS)

Parry, Ellis; Kim, Dong-Jin; Castrejón-Pita, Alfonso A.; Elston, Steve J.; Morris, Stephen M.

2018-06-01

This paper investigates the drop-on-demand inkjet printing of a nematic liquid crystal (LC) onto a variety of substrates. Achieving both a well-defined droplet boundary and uniformity of the LC director in printed droplets can be challenging when traditional alignment surfaces are employed. Despite the increasing popularity of inkjet printing LCs, the mechanisms that are involved during the deposition process such as drop impact, wetting and spreading have received very little attention, in the way of experiments, as viable routes for promoting alignment of the resultant LC droplets. In this work, radial alignment of the director and uniformity of the droplet boundary are achieved in combination via the use of a partially-wet polymer substrate, which makes use of the forces and flow generated during droplet impact and subsequent wetting process. Our findings could have important consequences for future LC inkjet applications, including the development of smart inks, printable sensors and lasers.

Osteogenesis of human adipose-derived stem cells on hydroxyapatite-mineralized poly(lactic acid) nanofiber sheets.

PubMed

Kung, Fu-Chen; Lin, Chi-Chang; Lai, Wen-Fu T

2014-12-01

Electrospun fiber sheets with various orientations (random, partially aligned, and aligned) and smooth and roughened casted membranes were prepared. Hydroxyapatite (HA) crystals were in situ formed on these material surfaces via immersion in 10× simulated body fluid solution. The size and morphology of the resulting fibers were examined using scanning electron microscopy. The average diameter of the fibers ranged from 225±25 to 1050±150 nm depending on the electrospinning parameters. Biological experiment results show that human adipose-derived stem cells exhibit different adhesion and osteogenic differentiation on the three types of fiber. The cell proliferation and osteogenic differentiation were best on the aligned fibers. Similar results were found for phosphorylated focal adhesion kinase expression. Electrospun poly(lactic acid) aligned fibers mineralized with HA crystals provide a good environment for cell growth and osteogenic differentiation and thus have great potential in the tissue engineering field. Copyright © 2014 Elsevier B.V. All rights reserved.

Strong Effect of Azodye Layer Thickness on RM-Stabilized Photoalignment

DTIC Science & Technology

2017-05-21

to thicker layers (~40 nm). Author Keywords photoalignment; azodye; reactive mesogen 1. Introduction Photoalignment of liquid crystals by azodye...Polymerizable azodyes[3] as well as passivation of the azodye film by spin-coating with a layer of reactive mesogen[4] are currently proposed solutions...thick alignment film rather than a ~40 nm thick alignment film ; cells with thin alignment layers are stable to exposure to polarized light for at

Hydrothermal Growth of Vertically Aligned ZnO Nanorods Using a Biocomposite Seed Layer of ZnO Nanoparticles.

PubMed

Ibupoto, Zafar Hussain; Khun, Kimleang; Eriksson, Martin; AlSalhi, Mohammad; Atif, Muhammad; Ansari, Anees; Willander, Magnus

2013-08-19

Well aligned ZnO nanorods have been prepared by a low temperature aqueous chemical growth method, using a biocomposite seed layer of ZnO nanoparticles prepared in starch and cellulose bio polymers. The effect of different concentrations of biocomposite seed layer on the alignment of ZnO nanorods has been investigated. ZnO nanorods grown on a gold-coated glass substrate have been characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. These techniques have shown that the ZnO nanorods are well aligned and perpendicular to the substrate, and grown with a high density and uniformity on the substrate. Moreover, ZnO nanorods can be grown with an orientation along the c -axis of the substrate and exhibit a wurtzite crystal structure with a dominant (002) peak in an XRD spectrum and possessed a high crystal quality. A photoluminescence (PL) spectroscopy study of the ZnO nanorods has revealed a conventional near band edge ultraviolet emission, along with emission in the visible part of the electromagnetic spectrum due to defect emission. This study provides an alternative method for the fabrication of well aligned ZnO nanorods. This method can be helpful in improving the performance of devices where alignment plays a significant role.

Hydrothermal Growth of Vertically Aligned ZnO Nanorods Using a Biocomposite Seed Layer of ZnO Nanoparticles

PubMed Central

Ibupoto, Zafar Hussain; Khun, Kimleang; Eriksson, Martin; AlSalhi, Mohammad; Atif, Muhammad; Ansari, Anees; Willander, Magnus

2013-01-01

Well aligned ZnO nanorods have been prepared by a low temperature aqueous chemical growth method, using a biocomposite seed layer of ZnO nanoparticles prepared in starch and cellulose bio polymers. The effect of different concentrations of biocomposite seed layer on the alignment of ZnO nanorods has been investigated. ZnO nanorods grown on a gold-coated glass substrate have been characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques. These techniques have shown that the ZnO nanorods are well aligned and perpendicular to the substrate, and grown with a high density and uniformity on the substrate. Moreover, ZnO nanorods can be grown with an orientation along the c-axis of the substrate and exhibit a wurtzite crystal structure with a dominant (002) peak in an XRD spectrum and possessed a high crystal quality. A photoluminescence (PL) spectroscopy study of the ZnO nanorods has revealed a conventional near band edge ultraviolet emission, along with emission in the visible part of the electromagnetic spectrum due to defect emission. This study provides an alternative method for the fabrication of well aligned ZnO nanorods. This method can be helpful in improving the performance of devices where alignment plays a significant role. PMID:28811454

Neutron and X-ray single-crystal diffraction from protein microcrystals via magnetically oriented microcrystal arrays in gels.

PubMed

Tsukui, Shu; Kimura, Fumiko; Kusaka, Katsuhiro; Baba, Seiki; Mizuno, Nobuhiro; Kimura, Tsunehisa

2016-07-01

Protein microcrystals magnetically aligned in D2O hydrogels were subjected to neutron diffraction measurements, and reflections were observed for the first time to a resolution of 3.4 Å from lysozyme microcrystals (∼10 × 10 × 50 µm). This result demonstrated the possibility that magnetically oriented microcrystals consolidated in D2O gels may provide a promising means to obtain single-crystal neutron diffraction from proteins that do not crystallize at the sizes required for neutron diffraction structure determination. In addition, lysozyme microcrystals aligned in H2O hydrogels allowed structure determination at a resolution of 1.76 Å at room temperature by X-ray diffraction. The use of gels has advantages since the microcrystals are measured under hydrated conditions.

Coulomb-like elastic interaction induced by symmetry breaking in nematic liquid crystal colloids.

PubMed

Lee, Beom-Kyu; Kim, Sung-Jo; Kim, Jong-Hyun; Lev, Bohdan

2017-11-21

It is generally thought that colloidal particles in a nematic liquid crystal do not generate the first multipole term called deformation elastic charge as it violates the mechanical equilibrium. Here, we demonstrate theoretically and experimentally that this is not the case, and deformation elastic charges, as well as dipoles and quadrupoles, can be induced through anisotropic boundary conditions. We report the first direct observation of Coulomb-like elastic interactions between colloidal particles in a nematic liquid crystal. The behaviour of two spherical colloidal particles with asymmetric anchoring conditions induced by asymmetric alignment is investigated experimentally; the interaction of two particles located at the boundary of twist and parallel aligned regions is observed. We demonstrate that such particles produce deformation elastic charges and interact by Coulomb-like interactions.

On the colour of wing scales in butterflies: iridescence and preferred orientation of single gyroid photonic crystals

PubMed Central

2017-01-01

Lycaenid butterflies from the genera Callophrys, Cyanophrys and Thecla have evolved remarkable biophotonic gyroid nanostructures within their wing scales that have only recently been replicated by nanoscale additive manufacturing. These nanostructures selectively reflect parts of the visible spectrum to give their characteristic non-iridescent, matte-green appearance, despite a distinct blue–green–yellow iridescence predicted for individual crystals from theory. It has been hypothesized that the organism must achieve its uniform appearance by growing crystals with some restrictions on the possible distribution of orientations, yet preferential orientation observed in Callophrys rubi confirms that this distribution need not be uniform. By analysing scanning electron microscope and optical images of 912 crystals in three wing scales, we find no preference for their rotational alignment in the plane of the scales. However, crystal orientation normal to the scale was highly correlated to their colour at low (conical) angles of view and illumination. This correlation enabled the use of optical images, each containing up to 104–105 crystals, for concluding the preferential alignment seen along the at the level of single scales, appears ubiquitous. By contrast, orientations were found to occur at no greater rate than that expected by chance. Above a critical cone angle, all crystals reflected bright green light indicating the dominant light scattering is due to the predicted band gap along the direction, independent of the domain orientation. Together with the natural variation in scale and wing shapes, we can readily understand the detailed mechanism of uniform colour production and iridescence suppression in these butterflies. It appears that the combination of preferential alignment normal to the wing scale, and uniform distribution within the plane is a near optimal solution for homogenizing the angular distribution of the band gap relative to the wings. Finally, the distributions of orientations, shapes, sizes and degree of order of crystals within single scales provide useful insights for understanding the mechanisms at play in the formation of these biophotonic nanostructures. PMID:28630678

Structural analysis of benzothienobenzothiophene-based soluble organic semiconducting crystals grown by liquid crystal solvent

NASA Astrophysics Data System (ADS)

Shibata, Yosei; Matsuzaki, Tomoya; Ishinabe, Takahiro; Fujikake, Hideo

2018-06-01

In this study, we analyzed organic semiconducting single crystals composed of benzothienobenzothiophene derivatives (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene, C8-BTBT) grown by nematic-phase liquid crystal (LC) solvent. As a result, we clarified that the crystal b-axis direction of the C8-BTBT single crystals was consistent with the LC alignment direction. By optical evaluation and simulation based on density functional theory, we found that the C8-BTBT single crystals in LC solvent exhibited a novel molecular conformation having alkyl chains oriented toward the b-axis.

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

Chao, Tzu-Ling; Yang, Chen-I., E-mail: ciyang@thu.edu.tw

The preparations and properties of three new homochiral three-dimensional (3D) coordination polymers, [M(D-cam)(pyz)(H{sub 2}O){sub 2}]{sub n} (M=Co (1) and Ni (2); D-H{sub 2}cam=(+) D-camphoric acid; pyz=pyrazine) and [Mn{sub 2}(D-cam){sub 2}(H{sub 2}O){sub 2}] (3), under solvothermal conditions is described. Single-crystal X-ray diffraction analyses revealed that all of compounds are homochiral 3D structure. 1 and 2 are isostructural and crystallize in the trigonal space group P3{sub 2}21, while 3 crystallizes in monoclinic space group P2{sub 1}. The structure of 1 and 2 consists of metal-D-cam helical chains which are pillared with pyrazine ligands into a 3D framework structure and 3 features amore » 3D homochiral framework involving one-dimensional manganese-carboxylate chains that are aligned parallel to the b axis. Magnetic susceptibility data of all compounds were collected. The findings indicate that μ{sub 2}-pyrazine dominate weak antiferromagnetic coupling within 1 and 2, while 3 exhibits antiferromagnetic behavior through the carboxylate groups of D-cam ligand. -- Graphical abstract: The preparations and properties of three new homochiral three-dimensional (3D) coordination polymers, [M(D-cam)(pyz)(H{sub 2}O){sub 2}]{sub n} (M=Co (1) and Ni (2); D-H{sub 2}cam=(+) D-camphoric acid; pyz=pyrazine) and [Mn{sub 2}(D-cam){sub 2}(H{sub 2}O){sub 2}] (3), under solvothermal conditions is described. Single-crystal X-ray diffraction analyses revealed that all of compounds are homochiral 3D structure. 1 and 2 are isostructural and crystallize in the trigonal space group P3{sub 2}21, while 3 crystallizes in monoclinic space group P2{sub 1}. The structure of 1 and 2 consists of metal-D-cam helical chains which are pillared with pyrazine ligands into a 3D framework structure and 3 features a 3D homochiral framework involving one-dimensional manganese-carboxylate chains that are aligned parallel to the b axis. Magnetic susceptibility data of all compounds were collected. The findings indicate that μ{sub 2}-pyrazine dominate weak antiferromagnetic coupling within 1 and 2, while 3 exhibits antiferromagnetic behavior through the carboxylate groups of D-cam ligand. Highlights: • Three homochiral 3D coordination polymers were synthesized. • 1 and 2 are 3D structure with metal-D-cam helical chains pillared by pyrazine. • 3 shows a 3D homochiral framework involving 1D manganese-carboxylate chains. • Magnetic data analysis indicates that 1–3 exhibit weak antiferromagnetic coupling.« less

Homeotropic alignment of dendritic columnar liquid crystal induced by hydrogen-bonded triphenylene core bearing fluoroalkyl chains.

PubMed

Ishihara, Shinsuke; Furuki, Yusuke; Hill, Jonathan P; Ariga, Katsuhiko; Takeoka, Shinji

2014-07-01

A 1:3 molar complex of the fluoroalkyl side chain-substituted 2,6,10-tris-carboxymethoxy-3,7,11-tris(4,4,5,5,6,6,7,7,7-nonafluoroheptyloxy)triphenylene (TPF4) with the second generation dendron 3,5-bis(3,4-bis-dodecyloxybenzyloxy)-N-pyridin-4-yl-benzamide (DN) assembled through complementary hydrogen bonding to form a supramolecular columnar liquid crystal, which exhibited homeotropic alignment when sandwiched between octadecyltrichlorosilane (OTS)-coated or indium tin oxide (ITO)-coated glass plates due to specific interactions between the fluoroalkyl side chains and the substrates.

Interfacial chemical reactions between MoS2 lubricants and bearing materials

NASA Technical Reports Server (NTRS)

Zabinski, J. S.; Tatarchuk, B. J.

1989-01-01

XPS and conversion-electron Moessbauer spectroscopy (CEMS) were used to examine iron that was deposited on the basal plane of MoS2 single crystals and subjected to vacuum annealing, oxidizing, and reducing environments. Iron either intercalated into the MoS2 structure or formed oriented iron sulfides, depending on the level of excess S in the MoS2 structure. CEMS data demonstrated that iron sulfide crystal structures preferentially aligned with respect to the MoS2 basal plane, and that alignment (and potentially adhesion) could be varied by appropriate high-temperature annealing procedures.

Can the Kilauea Iki glomerocrysts offer insights into the magmatic processes leading up to the 1959 eruption?

NASA Astrophysics Data System (ADS)

Allison, K. L.; Suckale, J.

2015-12-01

The 1959 eruption at Kilauea Iki, Hawaii, was unusually violent for a near-summit extrusion and the sequence of processes leading up to it remain debated. The eruption might have resulted from the progressive emptying of a stratified magma chamber or from a new magma batch bypassing the base of the magma storage region and mixing with the differentiated magma at shallow depth. In this study, we test if the picritic scoria erupted during the 1959 eruption can shed light on the conditions in the magmatic plumbing system prior to eruption. Scoria from the 1959 eruption contain glomeroporphyritic aggregates of olivine crystals, primarily composed of 2-4 crystals but comprising as many as 16, which vary in composition and three-dimensional texture. The clustering of crystals from different environments and their preferential alignment along crystallographic axes suggest that the glomerocrysts may be the result of synneusis - the drifting together of crystals (Schwindinger and Anderson, 1989). Analogue laboratory experiments of clay crystals in Karo syrup (Schwindinger, 1999), however, show that two crystals settling in a still liquid will not reorient themselves into alignment. Here, we test the hypothesis that a shear-dominated flow field might have facilitated the synneusis of the Kilauea olivines. We investigate the fluid-dynamical conditions under which the glomerocrysts might have formed using direct numerical simulations at the scale of individual crystals. We have implemented an iterative numerical method for simulating the hydrodynamic interactions between olivine crystals and their feedback on the flow field in a magmatic liquid. We solve the Stokes equation in the fluid phase and include rigid, rectangular bodies representing the olivine crystals through distributed Lagrange multipliers. To allow crystals to stick together after collision, the numerical method includes a multibody collision scheme. Additionally, it uses an analytical quadrature scheme instead of discretizing the solid body into material volumes, increasing accuracy and reducing computational expense. Our simulations show that the Kilauea Iki glomerocrysts formed in a magmatic liquid with very low crystallinity (likely less than about 10%) and that shear might have facilitated preferential alignment.

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

Fujii, Mami N., E-mail: f-mami@ms.naist.jp; Ishikawa, Yasuaki; Bermundo, Juan Paolo Soria

In a previous work, we reported the high field effect mobility of ZnO-doped In{sub 2}O{sub 3} (IZO) thin film transistors (TFTs) irradiated by excimer laser annealing (ELA) [M. Fujii et al., Appl. Phys. Lett. 102, 122107 (2013)]. However, a deeper understanding of the effect of ELA on the IZO film characteristics based on crystallinity, carrier concentrations, and optical properties is needed to control localized carrier concentrations for fabricating self-aligned structures in the same oxide film and to adequately explain the physical characteristics. In the case of as-deposited IZO film used as the channel, a high carrier concentration due to amore » high density of oxygen vacancies was observed; such a film does not show the required TFT characteristics but can act as a conductive film. We achieved a decrease in the carrier concentration of IZO films by crystallization using ELA. This means that ELA can form localized conductive or semi-conductive areas on the IZO film. We confirmed that the reason for the carrier concentration decrease was the decrease of oxygen-deficient regions and film crystallization. The annealed IZO films showed nano-crystalline phase, and the temperature at the substrate was substantially less than the temperature limit for flexible films such as plastic, which is 50°C. This paves the way for the formation of self-aligned structures and separately formed conductive and semi-conductive regions in the same oxide film.« less

Materials science: Crystals aligned through graphene

NASA Astrophysics Data System (ADS)

Lee, Minjoo Larry

2017-04-01

Graphene has been used as a 'transparent' layer that allows single crystals of a material to be grown on a substrate, and then lifted off -- in much the same way that baking paper lets cakes be removed easily from tins. See Letter p.340

Centroid stabilization in alignment of FOA corner cube: designing of a matched filter

NASA Astrophysics Data System (ADS)

Awwal, Abdul; Wilhelmsen, Karl; Roberts, Randy; Leach, Richard; Miller Kamm, Victoria; Ngo, Tony; Lowe-Webb, Roger

2015-02-01

The current automation of image-based alignment of NIF high energy laser beams is providing the capability of executing multiple target shots per day. An important aspect of performing multiple shots in a day is to reduce additional time spent aligning specific beams due to perturbations in those beam images. One such alignment is beam centration through the second and third harmonic generating crystals in the final optics assembly (FOA), which employs two retro-reflecting corner cubes to represent the beam center. The FOA houses the frequency conversion crystals for third harmonic generation as the beams enters the target chamber. Beam-to-beam variations and systematic beam changes over time in the FOA corner-cube images can lead to a reduction in accuracy as well as increased convergence durations for the template based centroid detector. This work presents a systematic approach of maintaining FOA corner cube centroid templates so that stable position estimation is applied thereby leading to fast convergence of alignment control loops. In the matched filtering approach, a template is designed based on most recent images taken in the last 60 days. The results show that new filter reduces the divergence of the position estimation of FOA images.

Graphene as transmissive electrodes and aligning layers for liquid-crystal-based electro-optic devices.

PubMed

Basu, Rajratan; Shalov, Samuel A

2017-07-01

In a conventional liquid crystal (LC) cell, polyimide layers are used to align the LC homogeneously in the cell, and transmissive indium tin oxide (ITO) electrodes are used to apply the electric field to reorient the LC along the field. It is experimentally presented here that monolayer graphene films on the two glass substrates can function concurrently as the LC aligning layers and the transparent electrodes to fabricate an LC cell, without using the conventional polyimide and ITO substrates. This replacement can effectively decrease the thickness of all the alignment layers and electrodes from about 100 nm to less than 1 nm. The interaction between LC and graphene through π-π electron stacking imposes a planar alignment on the LC in the graphene-based cell-which is verified using a crossed polarized microscope. The graphene-based LC cell exhibits an excellent nematic director reorientation process from planar to homeotropic configuration through the application of an electric field-which is probed by dielectric and electro-optic measurements. Finally, it is shown that the electro-optic switching is significantly faster in the graphene-based LC cell than in a conventional ITO-polyimide LC cell.

Massive ordering and alignment of cylindrical micro-objects by photovoltaic optoelectronic tweezers.

PubMed

Elvira, Iris; Muñoz-Martínez, Juan F; Barroso, Álvaro; Denz, Cornelia; Ramiro, José B; García-Cabañes, Angel; Agulló-López, Fernando; Carrascosa, Mercedes

2018-01-01

Optical tools for manipulation and trapping of micro- and nano-objects are a fundamental issue for many applications in nano- and biotechnology. This work reports on the use of one such method, known as photovoltaic optoelectronics tweezers, to orientate and organize cylindrical microcrystals, specifically elongated zeolite L, on the surface of Fe-doped LiNbO 3 crystal plates. Patterns of aligned zeolites have been achieved through the forces and torques generated by the bulk photovoltaic effect. The alignment patterns with zeolites parallel or perpendicular to the substrate surface are highly dependent on the features of light distribution and crystal configuration. Moreover, dielectrophoretic chains of zeolites with lengths up to 100 μm have often been observed. The experimental results of zeolite trapping and alignment have been discussed and compared together with theoretical simulations of the evanescent photovoltaic electric field and the dielectrophoretic potential. They demonstrate the remarkable capabilities of the optoelectronic photovoltaic method to orientate and pattern anisotropic microcrystals. The combined action of patterning and alignment offers a unique tool to prepare functional nanostructures with potential applications in a variety of fields such as nonlinear optics or plasmonics.

Controlled Growth of Large-Area Aligned Single-Crystalline Organic Nanoribbon Arrays for Transistors and Light-Emitting Diodes Driving

NASA Astrophysics Data System (ADS)

Wang, Wei; Wang, Liang; Dai, Gaole; Deng, Wei; Zhang, Xiujuan; Jie, Jiansheng; Zhang, Xiaohong

2017-10-01

Organic field-effect transistors (OFETs) based on organic micro-/nanocrystals have been widely reported with charge carrier mobility exceeding 1.0 cm2 V-1 s-1, demonstrating great potential for high-performance, low-cost organic electronic applications. However, fabrication of large-area organic micro-/nanocrystal arrays with consistent crystal growth direction has posed a significant technical challenge. Here, we describe a solution-processed dip-coating technique to grow large-area, aligned 9,10-bis(phenylethynyl) anthracene (BPEA) and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) single-crystalline nanoribbon arrays. The method is scalable to a 5 × 10 cm2 wafer substrate, with around 60% of the wafer surface covered by aligned crystals. The quality of crystals can be easily controlled by tuning the dip-coating speed. Furthermore, OFETs based on well-aligned BPEA and TIPS-PEN single-crystalline nanoribbons were constructed. By optimizing channel lengths and using appropriate metallic electrodes, the BPEA and TIPS-PEN-based OFETs showed hole mobility exceeding 2.0 cm2 V-1 s-1 (average mobility 1.2 cm2 V-1 s-1) and 3.0 cm2 V-1 s-1 (average mobility 2.0 cm2 V-1 s-1), respectively. They both have a high on/off ratio ( I on/ I off) > 109. The performance can well satisfy the requirements for light-emitting diodes driving.

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.

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

Room temperature-synthesized vertically aligned InSb nanowires: electrical transport and field emission characteristics

PubMed Central

2013-01-01

Vertically aligned single-crystal InSb nanowires were synthesized via the electrochemical method at room temperature. The characteristics of Fourier transform infrared spectrum revealed that in the syntheses of InSb nanowires, energy bandgap shifts towards the short wavelength with the occurrence of an electron accumulation layer. The current–voltage curve, based on the metal–semiconductor–metal model, showed a high electron carrier concentration of 2.0 × 1017 cm−3 and a high electron mobility of 446.42 cm2 V−1 s−1. Additionally, the high carrier concentration of the InSb semiconductor with the surface accumulation layer induced a downward band bending effect that reduces the electron tunneling barrier. Consequently, the InSb nanowires exhibit significant field emission properties with an extremely low turn-on field of 1.84 V μm−1 and an estimative threshold field of 3.36 V μm−1. PMID:23399075

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

A bacterial Argonaute with noncanonical guide RNA specificity

PubMed Central

Kaya, Emine; Doxzen, Kevin W.; Knoll, Kilian R.; Wilson, Ross C.; Strutt, Steven C.; Kranzusch, Philip J.; Doudna, Jennifer A.

2016-01-01

Eukaryotic Argonaute proteins induce gene silencing by small RNA-guided recognition and cleavage of mRNA targets. Although structural similarities between human and prokaryotic Argonautes are consistent with shared mechanistic properties, sequence and structure-based alignments suggested that Argonautes encoded within CRISPR-cas [clustered regularly interspaced short palindromic repeats (CRISPR)-associated] bacterial immunity operons have divergent activities. We show here that the CRISPR-associated Marinitoga piezophila Argonaute (MpAgo) protein cleaves single-stranded target sequences using 5′-hydroxylated guide RNAs rather than the 5′-phosphorylated guides used by all known Argonautes. The 2.0-Å resolution crystal structure of an MpAgo–RNA complex reveals a guide strand binding site comprising residues that block 5′ phosphate interactions. Using structure-based sequence alignment, we were able to identify other putative MpAgo-like proteins, all of which are encoded within CRISPR-cas loci. Taken together, our data suggest the evolution of an Argonaute subclass with noncanonical specificity for a 5′-hydroxylated guide. PMID:27035975

Composition and work function relationship in Os–Ru–W ternary alloys

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

Swartzentruber, Phillip D.; Detisch, Michael J.; Balk, T. John, E-mail: john.balk@uky.edu

2015-03-15

Os–Ru thin films with varying concentrations of W were sputter deposited in order to investigate their structure–property relationships. The films were analyzed with x-ray diffraction to investigate their crystal structures, and a Kelvin probe to investigate their work functions. An Os–Ru–W film with ∼30 at. % W yielded a work function maximum of approximately 5.38 eV. These results align well with other studies that found work function minima from thermionic emission data on M-type cathodes with varying amounts of W in the coatings. Furthermore, the results are consistent with other work explaining energy-level alignment and charge transfer of molecules on metalmore » oxides. This may shed light on the mechanism behind the “anomalous effect” first reported by Zalm et al., whereby a high work function coating results in a low work function for emitting cathode surfaces. An important implication of this work is the potential for the Kelvin probe to evaluate the effectiveness of dispenser cathode coatings.« less

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.

Characterization, mechanical behavior and in vitro evaluation of a melt-drawn scaffold for esophageal tissue engineering.

PubMed

Tan, Yu Jun; Yeong, Wai Yee; Tan, Xipeng; An, Jia; Chian, Kerm Sin; Leong, Kah Fai

2016-04-01

Tubular esophageal scaffolds with fiber diameter ranging from 13.9±1.7μm to 65.7±6.2μm were fabricated from the highly elastic poly(l-lactide-co-ε-caprolactone) (PLC) via a melt-drawing method. The morphology, crystallinity, thermal and mechanical properties of the PLC fibers were investigated. They were highly aligned and have a uniform diameter. PLC is found to be semicrystalline consisting of α- and β- lactide (LA) crystals. The crystallinity increases up to 16.8% with increasing melt-drawing speeds due to strain-induced crystallization. Modulus and strength increases while ductility decreases with an increase in crystallinity of the PLC samples. Moisture will not degrade the overall tensile properties but affect its tangent modulus at the low strain. L929 cells are able to attach and proliferate on the scaffolds very well. The cells seeded on the scaffolds show normal morphology with >90% cell viability after 6 days of culture. These results demonstrate that the PLC fibrous scaffold has good potential for use in esophageal tissue engineering application. Copyright © 2015 Elsevier Ltd. All rights reserved.

Van der Waals interaction in uniaxial anisotropic media.

PubMed

Kornilovitch, Pavel E

2013-01-23

Van der Waals interactions between flat surfaces in uniaxial anisotropic media are investigated in the nonretarded limit. The main focus is the effect of nonzero tilt between the optical axis and the surface normal on the strength of the van der Waals attraction. General expressions for the van der Waals free energy are derived using the surface mode method and the transfer-matrix formalism. To facilitate numerical calculations a temperature-dependent three-band parameterization of the dielectric tensor of the liquid crystal 5CB is developed. A solid slab immersed in a liquid crystal experiences a van der Waals torque that aligns the surface normal relative to the optical axis of the medium. The preferred orientation is different for different materials. Two solid slabs in close proximity experience a van der Waals attraction that is strongest for homeotropic alignment of the intervening liquid crystal for all the materials studied. The results have implications for the stability of plate-like colloids in liquid crystal hosts.

Photo-switchable bistable twisted nematic liquid crystal optical switch.

PubMed

Wang, Chun-Ta; Wu, Yueh-Chi; Lin, Tsung-Hsien

2013-02-25

This work demonstrates a photo-switchable bistable optical switch that is based on an azo-chiral doped liquid crystal (ACDLC). The photo-induced isomerization of the azo-chiral dopant can change the chirality of twisted nematic liquid crystal and the gap/pitch ratio of an ACDLC device, enabling switching between 0° and 180° twist states in a homogeneous aligned cell. The bistable 180° and 0° twist states of the azo-chiral doped liquid crystal between crossed polarizers correspond to the ON and OFF states of a light shutter, respectively, and they can be maintained stably for tens of hours. Rapid switching between 180° and 0° twist states can be carried out using 408 and 532 nm addressing light. Such a photo-controllable optical switch requires no specific asymmetric alignment layer or precise control of the cell gap/pitch ratio, so it is easily fabricated and has the potential for use in optical systems.

Manganese oxide nanowires, films, and membranes and methods of making

DOEpatents

Suib, Steven Lawrence [Storrs, CT; Yuan, Jikang [Storrs, CT

2008-10-21

Nanowires, films, and membranes comprising ordered porous manganese oxide-based octahedral molecular sieves, and methods of making, are disclosed. A single crystal ultra-long nanowire includes an ordered porous manganese oxide-based octahedral molecular sieve, and has an average length greater than about 10 micrometers and an average diameter of about 5 nanometers to about 100 nanometers. A film comprises a microporous network comprising a plurality of single crystal nanowires in the form of a layer, wherein a plurality of layers is stacked on a surface of a substrate, wherein the nanowires of each layer are substantially axially aligned. A free standing membrane comprises a microporous network comprising a plurality of single crystal nanowires in the form of a layer, wherein a plurality of layers is aggregately stacked, and wherein the nanowires of each layer are substantially axially aligned.

Effect of orientation on electrically conducting thermoplastic composite properties

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

Genetti, W.B.; Grady, B.P.

1996-10-01

Properties of electrically conducting composites made from low density polyethylene (LDPE), high density polyethylene (HDPE), and polypropylene (PP) filled with nickel flake are being studied as a function of nickel concentration and draw ratio. The effect on electrical conduction, crystallinity, melt temperature, tensile modulus, and elongation at break are being tested. The melt temperature increases with increasing nickel concentration. The electrical conduction increases slowly with increased nickel concentration to the percolation volume fraction, then increases sharply. Orientation by uniaxial stretching of the films should allow conductive pathways to form throughout the polymer more easily by forcing particles closer together, thusmore » reducing the percolation volume fraction. This process could be caused by both alignment of the polymer chains and by stress induced crystallization that forces the particles into smaller amorphous regions.« less

Defects and nanocluster engineering in MgO

NASA Astrophysics Data System (ADS)

Fedorov, A. V.; van Veen, A.; van Huis, M. A.; Schut, H.; Kooi, B. J.; De Hosson, J. Th.; Zimmerman, R. L.

2001-07-01

The optical properties of MgO crystals are known to change after introduction of nanosize metal precipitates. In this work the formation of metallic nanoclusters in the presence of nanosize rectangular shaped cavities was studied. The rectangular cavities were formed by 30 keV He+ implantation followed by 1273 K annealing. The formation of cavities and their location was established by Positron Beam Analysis (PBA). The rectangular shape and their alignment in (100) direction was observed by X-TEM. Subsequently, the samples were implanted with 600 keV Ag and 1000 keV Au in order to introduce the metal ions in the vicinity of the cavities. The samples were then annealed to provide the formation of nanoclusters. The evolution of the implantation induced defects was monitored by PBA. The optical properties were studied by light absorption measurements.

Polymer stabilized liquid crystals: Topology-mediated electro-optical behavior and applications

NASA Astrophysics Data System (ADS)

Weng, Libo

There has been a wide range of liquid crystal polymer composites that vary in polymer concentration from as little as 3 wt.% (polymer stabilized liquid crystal) to as high as 60 wt.% (polymer dispersed liquid crystals). In this dissertation, an approach of surface polymerization based on a low reactive monomer concentration about 1 wt.% is studied in various liquid crystal operation modes. The first part of dissertation describes the development of a vertical alignment (VA) mode with surface polymer stabilization, and the effects of structure-performance relationship of reactive monomers (RMs) and polymerization conditions on the electro-optical behaviors of the liquid crystal device has been explored. The polymer topography plays an important role in modifying and enhancing the electro-optical performance of stabilized liquid crystal alignment. The enabling surface-pinned polymer stabilized vertical alignment (PSVA) approach has led to the development of high-performance and fast-switching displays with controllable pretilt angle, increase in surface anchoring energy, high optical contrast and fast response time. The second part of the dissertation explores a PSVA mode with in-plane switching (IPS) and its application for high-efficiency and fast-switching phase gratings. The diffraction patterns and the electro-optical behaviors including diffraction efficiency and response time are characterized. The diffraction grating mechanism and performance have been validated by computer simulation. Finally, the advantages of surface polymerization approach such as good optical contrast and fast response time have been applied to the fringe-field switching (FFS) system. The concentration of reactive monomer on the electro-optical behavior of the FFS cells is optimized. The outstanding electro-optical results and mechanism of increase in surface anchoring strength are corroborated by the director field simulation. The density and topology of nanoscale polymer protrusions are analyzed and confirmed by morphological study. The developed high-performance polymer-stabilized fringe-field-switching (PS-FFS) could open new types of device applications.

Lipid decorated liquid crystal pressure sensors

NASA Astrophysics Data System (ADS)

Lopatkina, Tetiana; Popov, Piotr; Honaker, Lawrence; Jakli, Antal; Mann, Elizabeth; Mann's Group Collaboration; Jakli's Group Collaboration

Surfactants usually promote the alignment of liquid crystal (LC) director parallel to the surfactant chains, and thus on average normal to the substrate (homeotropic), whereas water promotes tangential (planar) alignment. A water-LC interface is therefore very sensitive to the presence of surfactants, such as lipids: this is the principle of LC-based chemical and biological sensing introduced by Abbott et al.Using a modified configuration, we found that at higher than 10 micro molar lipid concentration, the uniformly dark texture seen for homeotropic alignment between left-, and right-handed circular polarizers becomes unstable and slowly brightens again. This texture shows extreme sensitivity to external air pressure variations offering its use for sensitive pressure sensors. Our analysis indicates an osmotic pressure induced bending of the suspended films explaining both the birefringence and pressure sensitivity. In the talk we will discuss the experimental details of these effects. This work was financially supported by NSF DMR No. DMR-0907055.

Swimming in an anisotropic fluid: How speed depends on alignment angle

NASA Astrophysics Data System (ADS)

Shi, Juan; Powers, Thomas R.

2017-12-01

Orientational order in a fluid affects the swimming behavior of flagellated microorganisms. For example, bacteria tend to swim along the director in lyotropic nematic liquid crystals. To better understand how anisotropy affects propulsion, we study the problem of a sheet supporting small-amplitude traveling waves, also known as the Taylor swimmer, in a nematic liquid crystal. For the case of weak anchoring of the nematic director at the swimmer surface and in the limit of a minimally anisotropic model, we calculate the swimming speed as a function of the angle between the swimmer and the nematic director. The effect of the anisotropy can be to increase or decrease the swimming speed, depending on the angle of alignment. We also show that elastic torque dominates the viscous torque for small-amplitude waves and that the torque tends to align the swimmer along the local director.

Dual-mode switching of a liquid crystal panel for viewing angle control

NASA Astrophysics Data System (ADS)

Baek, Jong-In; Kwon, Yong-Hoan; Kim, Jae Chang; Yoon, Tae-Hoon

2007-03-01

The authors propose a method to control the viewing angle of a liquid crystal (LC) panel using dual-mode switching. To realize both wide viewing angle (WVA) characteristics and narrow viewing angle (NVA) characteristics with a single LC panel, the authors use two different dark states. The LC layer can be aligned homogeneously parallel to the transmission axis of the bottom polarizer for WVA dark state operation, while it can be aligned vertically for NVA dark state operation. The authors demonstrated that viewing angle control can be achieved with a single panel without any loss of contrast at the front.

Optimal configuration of microstructure in ferroelectric materials by stochastic optimization

NASA Astrophysics Data System (ADS)

Jayachandran, K. P.; Guedes, J. M.; Rodrigues, H. C.

2010-07-01

An optimization procedure determining the ideal configuration at the microstructural level of ferroelectric (FE) materials is applied to maximize piezoelectricity. Piezoelectricity in ceramic FEs differs significantly from that of single crystals because of the presence of crystallites (grains) possessing crystallographic axes aligned imperfectly. The piezoelectric properties of a polycrystalline (ceramic) FE is inextricably related to the grain orientation distribution (texture). The set of combination of variables, known as solution space, which dictates the texture of a ceramic is unlimited and hence the choice of the optimal solution which maximizes the piezoelectricity is complicated. Thus, a stochastic global optimization combined with homogenization is employed for the identification of the optimal granular configuration of the FE ceramic microstructure with optimum piezoelectric properties. The macroscopic equilibrium piezoelectric properties of polycrystalline FE is calculated using mathematical homogenization at each iteration step. The configuration of grains characterized by its orientations at each iteration is generated using a randomly selected set of orientation distribution parameters. The optimization procedure applied to the single crystalline phase compares well with the experimental data. Apparent enhancement of piezoelectric coefficient d33 is observed in an optimally oriented BaTiO3 single crystal. Based on the good agreement of results with the published data in single crystals, we proceed to apply the methodology in polycrystals. A configuration of crystallites, simultaneously constraining the orientation distribution of the c-axis (polar axis) while incorporating ab-plane randomness, which would multiply the overall piezoelectricity in ceramic BaTiO3 is also identified. The orientation distribution of the c-axes is found to be a narrow Gaussian distribution centered around 45°. The piezoelectric coefficient in such a ceramic is found to be nearly three times as that of the single crystal. Our optimization model provide designs for materials with enhanced piezoelectric performance, which would stimulate further studies involving materials possessing higher spontaneous polarization.

Effects of alignment layer thickness on the pretilt angle of liquid crystals

NASA Astrophysics Data System (ADS)

Son, Jong-Ho; Zin, Wang-Cheol

2010-12-01

Mixture solutions of vertical- and planar-aligning polyimide precursors were coated on bare glass. The concentrations of the solutions were varied to control the thicknesses of the films. The resulting blend films were baked to induce imidization and then rubbed. The thicknesses (t) of the blend film and of the pure vertical-alignment film affected their surface energies; the pretilt angle can be fully controlled in the range 5.5°≤Θ0≤87° by adjusting t. The surface energy of pure planar-alignment layers was independent of t.

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.)

Structural and Solar Cell Properties of a Ag-Containing Cu2ZnSnS4 Thin Film Derived from Spray Pyrolysis.

PubMed

Nguyen, Thi Hiep; Kawaguchi, Takato; Chantana, Jakapan; Minemoto, Takashi; Harada, Takashi; Nakanishi, Shuji; Ikeda, Shigeru

2018-02-14

A silver (Ag)-incorporated kesterite Cu 2 ZnSnS 4 (CZTS) thin film was fabricated by a facile spray pyrolysis method. Crystallographic analyses indicated successful incorporation of various amounts of Ag up to a Ag/(Ag + Cu) ratio of ca. 0.1 into the crystal lattice of CZTS in a homogeneous manner without formation of other impurity compounds. From the results of morphological investigations, Ag-incorporated films had larger crystal grains than the CZTS film. The sample with a relatively low Ag content (Ag/(Ag + Cu) of ca. 0.02) had a compact morphology without appreciable voids and pinholes. However, an increase in the Ag content in the CZTS film (Ag/(Ag + Cu) ca. 0.10) induced the formation of a large number of pinholes. As can be expected from these morphological properties, the best sunlight conversion efficiency was obtained by the solar cell based on the film with Ag/(Ag + Cu) of ca. 0.02. Electrostructural analyses of the devices suggested that the Ag-incorporated film in the device achieved reduction in the amounts of unfavorable copper on zinc antisite defects compared to the bare CZTS film. Moreover, the use of a Ag-incorporated film improved band alignment at the CdS(buffer)-CZTS interface. These alterations should also contribute to enhancement of device properties.

System and method for forming synthetic protein crystals to determine the conformational structure by crystallography

DOEpatents

Craig, George D.; Glass, Robert; Rupp, Bernhard

1997-01-01

A method for forming synthetic crystals of proteins in a carrier fluid by use of the dipole moments of protein macromolecules that self-align in the Helmholtz layer adjacent to an electrode. The voltage gradients of such layers easily exceed 10.sup.6 V/m. The synthetic protein crystals are subjected to x-ray crystallography to determine the conformational structure of the protein involved.

Crystal and source characterization for the Crystal Backlighter Imager capability at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Krauland, C. M.; Hall, G. N.; Buscho, J. G.; Hibbard, R.; McCarville, T. J.; Lowe-Webb, R.; Ayers, S. L.; Kalantar, D.; Kohut, T.; Kemp, G. E.; Bradley, D. K.; Bell, P.; Landen, O. L.; Brewster, T. N.; Piston, K.

2017-10-01

The Crystal Backlighter Imager (CBI) is a very narrow bandwidth ( 10 eV) x-ray radiography system that uses Bragg reflection from a spherically-curved crystal at near normal incidence. This diagnostic has the capability to image late in an ICF implosion because it only requires the brightness of the backlighter to be larger than the capsule self-emission in that narrow bandwidth. While the limited bandwidth is advantageous for this reason, it also requires that the effective energy of the backlighter atomic line is known to 1 eV accuracy for proper crystal alignment. Any Doppler shift in the line energy must be understood for the imaging system to work. The work presented details characterization experiments done at the Jupiter Laser Facility with a Si (8 6 2) crystal that will be used with a Selenium backlighter in the NIF CBI diagnostic. We used the spherically-bent crystals to image a small ( 200 µm) He α source generated by the Janus laser on a Se foil. Scanning Bragg angles over multiple shots allowed us to map out the spectral line intensity distribution for optimal alignment in NIF. A subsequent Doppler shift measurement using CBI on NIF will also be presented with complementary HYDRA modeling for both experiments. Prepared by LLNL under Contract DE-AC52-07NA27344 and by General Atomics under Contract DE-NA0001808.

Evaluation, development, and characterization of superconducting materials for space applications

NASA Technical Reports Server (NTRS)

Thorpe, Arthur N.

1990-01-01

The anisotropic electromagnetic features of a grain-aligned YBa2Cu3O(x) bulk sample derived from a process of long-time partial melt growth were investigated by the measurements of direct current magnetization (at 77 K) and alternating current susceptibility as a function of temperature, with the fields applied parallel and perpendicular to the c axis, respectively. The extended Bean model was further studied and applied to explain the experimental results. Upon comparison of the grain-aligned sample with pure single crystal materials, it is concluded that because of the existence of more effective pinning sites in the grain-aligned sample, not only its critical current density perpendicular to the c axis is improved, but the one parallel to the c axis is improved even more significantly. The anisotropy in the critical current densities in the grain-aligned sample at 77 K is at least one to two orders of magnitude smaller than in the pure single crystal. The measurement of anisotropy of alternating current susceptibility as a function of temperature, especially its imaginary part, shows that there are still some residues of interlayer weak links in the grain-aligned samples, but they are quite different from and far less serious than the weak links in the sintered sample.

Lattice Boltzmann simulations of liquid crystal particulate flow in a channel with finite anchoring boundary conditions

NASA Astrophysics Data System (ADS)

Zhang, Rui; Roberts, Tyler; de Pablo, Juan; dePablo Team

2014-11-01

Liquid crystals (LC) posses anisotropic viscoelastic properties, and, as such, LC flow can be incredibly complicated. Here we employ a hybrid lattice Boltzmann method (pioneered by Deniston, Yeomans and Cates) to systematically study the hydrodynamics of nematic liquid crystals (LCs) with and without solid particles. This method evolves the velocity field through lattice Boltzmann and the LC-order parameter via a finite-difference solver of the Beris-Edwards equation. The evolution equation of the boundary points with finite anchoring is obtained through Poisson bracket formulation. Our method has been validated by matching the Ericksen-Leslie theory. We demonstrate two applications in the flow alignment regime. We first investigate a hybrid channel flow in which the top and bottom walls have different anchoring directions. By measuring the apparent shear viscosity in terms of Couette flow, we achieve a viscosity inhomogeneous system which may be applicable to nano particle processing. In the other example, we introduce a homeotropic spherical particle to the channel, and focus on the deformations of the defect ring due to anchorings and flow. The results are then compared to the molecular dynamics simulations of a colloid particle in an LC modeled by a Gay-Berne potential.

Liquid Crystal Elastomers—A Path to Biocompatible and Biodegradable 3D-LCE Scaffolds for Tissue Regeneration

PubMed Central

2018-01-01

The development of appropriate materials that can make breakthroughs in tissue engineering has long been pursued by the scientific community. Several types of material have been long tested and re-designed for this purpose. At the same time, liquid crystals (LCs) have captivated the scientific community since their discovery in 1888 and soon after were thought to be, in combination with polymers, artificial muscles. Within the past decade liquid crystal elastomers (LCE) have been attracting increasing interest for their use as smart advanced materials for biological applications. Here, we examine how LCEs can potentially be used as dynamic substrates for culturing cells, moving away from the classical two-dimensional cell-culture nature. We also briefly discuss the integration of a few technologies for the preparation of more sophisticated LCE-composite scaffolds for more dynamic biomaterials. The anisotropic properties of LCEs can be used not only to promote cell attachment and the proliferation of cells, but also to promote cell alignment under LCE-stimulated deformation. 3D LCEs are ideal materials for new insights to simulate and study the development of tissues and the complex interplay between cells. PMID:29510523

Construction, characterization, and environmental testing of a Laue lens prototype using Fe and Al crystals

NASA Astrophysics Data System (ADS)

Wade, C.; Barrière, N. M.; Tomsick, J. A.; Hanlon, L.; Boggs, S. E.; Lowell, A.; von Ballmoos, P.; Massahi, S.

2018-07-01

Laue lenses use Bragg diffraction to concentrate soft γ-rays onto a detector. This decoupling of the collecting area from the detector volume can generate a significant increase in sensitivity for applications in astrophysics and nuclear medicine. A demonstrator lens was constructed at the UC Berkeley's Space Sciences Laboratory in 2014 by gluing 48 Fe and Al diffracting crystals to an aluminium substrate. The goal was to demonstrate a fast and accurate assembly technique that is compatible with the large number of crystals required to fabricate a Laue lens telescope for astronomical observations. We present here the lens design, the assembly technique we used, and the results of measurements of the angular misalignments before and after curing of the glue and during environmental testing (thermal, vacuum, and vibration). We conclude that our alignment technique is fast enough to assemble a full lens made of several thousand crystals. The achieved alignment accuracy had an average of 32.7‧‧ and a standard deviation of 44.1‧‧. The accuracy could be improved by using an alternative glue or by having better control over the asymmetry angle resulting from the crystal cut.

Vertical Alignment of Single-Walled Carbon Nanotubes on Nanostructure Fabricated by Atomic Force Microscope

DTIC Science & Technology

2007-02-16

SWNT films by Langmuir - Blodgett methods,8 and chemical assembly of SWNTs on a large substrate.9 Al- though these methods provide a good way to control... Langmuir - Blodgett to Self-Assembly. Academic: New York, (1991). [10] Moon, J.H., Shin, J.W., Kim, S.Y., Park, J.W. Langmuir , 12, 4621, (1996...aligning CNTs in solu- tion by applying an electric field5 or a magnetic field,6 align- ing SWNTs by blending them with liquid crystal,7 assem- bling

Fabrication of a novel quartz micromachined gyroscope

NASA Astrophysics Data System (ADS)

Xie, Liqiang; Xing, Jianchun; Wang, Haoxu; Wu, Xuezhong

2015-04-01

A novel quartz micromachined gyroscope is proposed in this paper. The novel gyroscope is realized by quartz anisotropic wet etching and 3-dimensional electrodes deposition. In the quartz wet etching process, the quality of Cr/Au mask films affecting the process are studied by experiment. An excellent mask film with 100 Å Cr and 2000 Å Au is achieved by optimization of experimental parameters. Crystal facets after etching seriously affect the following sidewall electrodes deposition process and the structure's mechanical behaviours. Removal of crystal facets is successfully implemented by increasing etching time based on etching rate ratios between facets and crystal planes. In the electrodes deposition process, an aperture mask evaporation method is employed to prepare electrodes on 3-dimensional surfaces of the gyroscope structure. The alignments among the aperture masks are realized by the ABM™ Mask Aligner System. Based on the processes described above, a z-axis quartz gyroscope is fabricated successfully.

Solar radiation control using nematic curvilinear aligned phase (NCAP) liquid crystal technology

NASA Astrophysics Data System (ADS)

vanKonynenburg, Peter; Marsland, Stephen; McCoy, James

1987-11-01

A new, advanced liquid crystal technology has made economical, large area, electrically-controlled windows a commercial reality. The new technology, Nematic Curvilinear Aligned Phase (NCAP), is based on a polymeric material containing small droplets of nematic liquid crystal which is coated and laminated between transparent electrodes and fabricated into large area field effect devices. NCAP windows feature variable solar transmission and reflection through a voltage-controlled scattering mechanism. Laminated window constructions provide the excellent transmission and visibility of glass in the powered condition. In the unpowered condition, the windows are highly translucent, and provide 1) blocked vision for privacy, security, and obscuration of information, and 2) glare control and solar shading. The stability is excellent during accelerated aging tests. Degradation mechanisms which can limit performance and lifetime are discussed. Maximum long term stability is achieved by product designs that incorporate the appropriate window materials to provide environmental protection.

3D Printing of Liquid Crystal Elastomeric Actuators with Spatially Programed Nematic Order.

PubMed

Kotikian, Arda; Truby, Ryan L; Boley, John William; White, Timothy J; Lewis, Jennifer A

2018-03-01

Liquid crystal elastomers (LCEs) are soft materials capable of large, reversible shape changes, which may find potential application as artificial muscles, soft robots, and dynamic functional architectures. Here, the design and additive manufacturing of LCE actuators (LCEAs) with spatially programed nematic order that exhibit large, reversible, and repeatable contraction with high specific work capacity are reported. First, a photopolymerizable, solvent-free, main-chain LCE ink is created via aza-Michael addition with the appropriate viscoelastic properties for 3D printing. Next, high operating temperature direct ink writing of LCE inks is used to align their mesogen domains along the direction of the print path. To demonstrate the power of this additive manufacturing approach, shape-morphing LCEA architectures are fabricated, which undergo reversible planar-to-3D and 3D-to-3D' transformations on demand, that can lift significantly more weight than other LCEAs reported to date. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photoalignment and resulting holographic vector grating formation in composites of low molecular weight liquid crystals and photoreactive liquid crystalline polymers

NASA Astrophysics Data System (ADS)

Sasaki, Tomoyuki; Shoho, Takashi; Goto, Kohei; Noda, Kohei; Kawatsuki, Nobuhiro; Ono, Hiroshi

2015-08-01

Polarization holographic gratings were formed in liquid crystal (LC) cells fabricated from a mixture of low molecular weight nematic LC and a photoreactive liquid crystalline polymer (PLCP) with 4-(4-methoxycinnamoyloxy)biphenyl side groups. The diffraction properties of the gratings were analyzed using theoretical models which were determined based on the polarization patterns of the polarization holography. The results demonstrated that vector gratings comprised of periodic orientation distributions of the LC molecule were induced in the cells based on the axis-selective photoreaction of the PLCP. The vector gratings were erased by applying a sufficiently high voltage to the cells and then were reformed with no hysteresis after the voltage was removed. This phenomenon suggested that the PLCP molecules were stabilized based on the axis-selective photocrosslink reaction and that the LC molecules were aligned by the photocrosslinked PLCP. This LC composite with axis-selective photoreactivity is useful for various optical applications, because of their stability, transparency, and response to applied voltage.

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

On the colour of wing scales in butterflies: iridescence and preferred orientation of single gyroid photonic crystals.

PubMed

Corkery, Robert W; Tyrode, Eric C

2017-08-06

Lycaenid butterflies from the genera Callophrys , Cyanophrys and Thecla have evolved remarkable biophotonic gyroid nanostructures within their wing scales that have only recently been replicated by nanoscale additive manufacturing. These nanostructures selectively reflect parts of the visible spectrum to give their characteristic non-iridescent, matte-green appearance, despite a distinct blue-green-yellow iridescence predicted for individual crystals from theory. It has been hypothesized that the organism must achieve its uniform appearance by growing crystals with some restrictions on the possible distribution of orientations, yet preferential orientation observed in Callophrys rubi confirms that this distribution need not be uniform. By analysing scanning electron microscope and optical images of 912 crystals in three wing scales, we find no preference for their rotational alignment in the plane of the scales. However, crystal orientation normal to the scale was highly correlated to their colour at low (conical) angles of view and illumination. This correlation enabled the use of optical images, each containing up to 10 4 -10 5 crystals, for concluding the preferential alignment seen along the [Formula: see text] at the level of single scales, appears ubiquitous. By contrast, [Formula: see text] orientations were found to occur at no greater rate than that expected by chance. Above a critical cone angle, all crystals reflected bright green light indicating the dominant light scattering is due to the predicted band gap along the [Formula: see text] direction, independent of the domain orientation. Together with the natural variation in scale and wing shapes, we can readily understand the detailed mechanism of uniform colour production and iridescence suppression in these butterflies. It appears that the combination of preferential alignment normal to the wing scale, and uniform distribution within the plane is a near optimal solution for homogenizing the angular distribution of the [Formula: see text] band gap relative to the wings. Finally, the distributions of orientations, shapes, sizes and degree of order of crystals within single scales provide useful insights for understanding the mechanisms at play in the formation of these biophotonic nanostructures.

Scanning electron microscopy analysis of the growth of dental plaque on the surfaces of removable orthodontic aligners after the use of different cleaning methods

PubMed Central

Levrini, Luca; Novara, Francesca; Margherini, Silvia; Tenconi, Camilla; Raspanti, Mario

2015-01-01

Background Advances in orthodontics are leading to the use of minimally invasive technologies, such as transparent removable aligners, and are able to meet high demands in terms of performance and esthetics. However, the most correct method of cleaning these appliances, in order to minimize the effects of microbial colonization, remains to be determined. Purpose The aim of the present study was to identify the most effective method of cleaning removable orthodontic aligners, analyzing the growth of dental plaque as observed under scanning electron microscopy. Methods Twelve subjects were selected for the study. All were free from caries and periodontal disease and were candidates for orthodontic therapy with invisible orthodontic aligners. The trial had a duration of 6 weeks, divided into three 2-week stages, during which three sets of aligners were used. In each stage, the subjects were asked to use a different method of cleaning their aligners: 1) running water (control condition); 2) effervescent tablets containing sodium carbonate and sulfate crystals followed by brushing with a toothbrush; and 3) brushing alone (with a toothbrush and toothpaste). At the end of each 2-week stage, the surfaces of the aligners were analyzed under scanning electron microscopy. Results The best results were obtained with brushing combined with the use of sodium carbonate and sulfate crystals; brushing alone gave slightly inferior results. Conclusion On the basis of previous literature results relating to devices in resin, studies evaluating the reliability of domestic ultrasonic baths for domestic use should be encouraged. At present, pending the availability of experimental evidence, it can be suggested that dental hygienists should strongly advise patients wearing orthodontic aligners to clean them using a combination of brushing and commercially available tablets for cleaning oral appliances. PMID:26719726

Scanning electron microscopy analysis of the growth of dental plaque on the surfaces of removable orthodontic aligners after the use of different cleaning methods.

PubMed

Levrini, Luca; Novara, Francesca; Margherini, Silvia; Tenconi, Camilla; Raspanti, Mario

2015-01-01

Advances in orthodontics are leading to the use of minimally invasive technologies, such as transparent removable aligners, and are able to meet high demands in terms of performance and esthetics. However, the most correct method of cleaning these appliances, in order to minimize the effects of microbial colonization, remains to be determined. The aim of the present study was to identify the most effective method of cleaning removable orthodontic aligners, analyzing the growth of dental plaque as observed under scanning electron microscopy. Twelve subjects were selected for the study. All were free from caries and periodontal disease and were candidates for orthodontic therapy with invisible orthodontic aligners. The trial had a duration of 6 weeks, divided into three 2-week stages, during which three sets of aligners were used. In each stage, the subjects were asked to use a different method of cleaning their aligners: 1) running water (control condition); 2) effervescent tablets containing sodium carbonate and sulfate crystals followed by brushing with a toothbrush; and 3) brushing alone (with a toothbrush and toothpaste). At the end of each 2-week stage, the surfaces of the aligners were analyzed under scanning electron microscopy. The best results were obtained with brushing combined with the use of sodium carbonate and sulfate crystals; brushing alone gave slightly inferior results. On the basis of previous literature results relating to devices in resin, studies evaluating the reliability of domestic ultrasonic baths for domestic use should be encouraged. At present, pending the availability of experimental evidence, it can be suggested that dental hygienists should strongly advise patients wearing orthodontic aligners to clean them using a combination of brushing and commercially available tablets for cleaning oral appliances.

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.

Photoresist thin-film effects on alignment process capability

NASA Astrophysics Data System (ADS)

Flores, Gary E.; Flack, Warren W.

1993-08-01

Two photoresists were selected for alignment characterization based on their dissimilar coating properties and observed differences on alignment capability. The materials are Dynachem OFPR-800 and Shipley System 8. Both photoresists were examined on two challenging alignment levels in a submicron CMOS process, a nitride level and a planarized second level metal. An Ultratech Stepper model 1500 which features a darkfield alignment system with a broadband green light for alignment signal detection was used for this project. Initially, statistically designed linear screening experiments were performed to examine six process factors for each photoresist: viscosity, spin acceleration, spin speed, spin time, softbake time, and softbake temperature. Using the results derived from the screening experiments, a more thorough examination of the statistically significant process factors was performed. A full quadratic experimental design was conducted to examine viscosity, spin speed, and spin time coating properties on alignment. This included a characterization of both intra and inter wafer alignment control and alignment process capability. Insight to the different alignment behavior is analyzed in terms of photoresist material properties and the physical nature of the alignment detection system.

System and method for forming synthetic protein crystals to determine the conformational structure by crystallography

DOEpatents

Craig, G.D.; Glass, R.; Rupp, B.

1997-01-28

A method is disclosed for forming synthetic crystals of proteins in a carrier fluid by use of the dipole moments of protein macromolecules that self-align in the Helmholtz layer adjacent to an electrode. The voltage gradients of such layers easily exceed 10{sup 6}V/m. The synthetic protein crystals are subjected to x-ray crystallography to determine the conformational structure of the protein involved. 2 figs.

The Los Alamos National Laboratory precision double crystal spectrometer

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

Morgan, D.V.; Stevens, C.J.; Liefield, R.J.

1994-03-01

This report discusses the following topics on the LANL precision double crystal X-ray spectrometer: Motivation for construction of the instrument; a brief history of the instrument; mechanical systems; motion control systems; computer control system; vacuum system; alignment program; scan programs; observations of the copper K{alpha} lines; and characteristics and specifications.

Theoretically informed Monte Carlo simulation of liquid crystals by sampling of alignment-tensor fields.

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

Armas-Perez, Julio C.; Londono-Hurtado, Alejandro; Guzman, Orlando

2015-07-27

A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystalmore » droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate.« less

Theoretically informed Monte Carlo simulation of liquid crystals by sampling of alignment-tensor fields

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

Armas-Pérez, Julio C.; Londono-Hurtado, Alejandro; Guzmán, Orlando

2015-07-28

A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystalmore » droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate.« less

Flow-Directed Crystallization for Printed Electronics.

PubMed

Qu, Ge; Kwok, Justin J; Diao, Ying

2016-12-20

The solution printability of organic semiconductors (OSCs) represents a distinct advantage for materials processing, enabling low-cost, high-throughput, and energy-efficient manufacturing with new form factors that are flexible, stretchable, and transparent. While the electronic performance of OSCs is not comparable to that of crystalline silicon, the solution processability of OSCs allows them to complement silicon by tackling challenging aspects for conventional photolithography, such as large-area electronics manufacturing. Despite this, controlling the highly nonequilibrium morphology evolution during OSC printing remains a challenge, hindering the achievement of high electronic device performance and the elucidation of structure-property relationships. Many elegant morphological control methodologies have been developed in recent years including molecular design and novel processing approaches, but few have utilized fluid flow to control morphology in OSC thin films. In this Account, we discuss flow-directed crystallization as an effective strategy for controlling the crystallization kinetics during printing of small molecule and polymer semiconductors. Introducing the concept of flow-directed crystallization to the field of printed electronics is inspired by recent advances in pharmaceutical manufacturing and flow processing of flexible-chain polymers. Although flow-induced crystallization is well studied in these areas, previous findings may not apply directly to the field of printed electronics where the molecular structures (i.e., rigid π-conjugated backbone decorated with flexible side chains) and the intermolecular interactions (i.e., π-π interactions, quadrupole interactions) of OSCs differ substantially from those of pharmaceuticals or flexible-chain polymers. Another critical difference is the important role of solvent evaporation in open systems, which defines the flow characteristics and determines the crystallization kinetics and pathways. In other words, flow-induced crystallization is intimately coupled with the mass transport processes driven by solvent evaporation during printing. In this Account, we will highlight these distinctions of flow-directed crystallization for printed electronics. In the context of solution printing of OSCs, the key issue that flow-directed crystallization addresses is the kinetics mismatch between crystallization and various transport processes during printing. We show that engineering fluid flows can tune the kinetics of OSC crystallization by expediting the nucleation and crystal growth processes, significantly enhancing thin film morphology and device performance. For small molecule semiconductors, nucleation can be enhanced and patterned by directing the evaporative flux via contact line engineering, and defective crystal growth can be alleviated by enhancing mass transport to yield significantly improved coherence length and reduced grain boundaries. For conjugated polymers, extensional and shear flow can expedite nucleation through flow-induced conformation change, facilitating the control of microphase separation, degree of crystallinity, domain alignment, and percolation. Although the nascent concept of flow-directed solution printing has not yet been widely adopted in the field of printed electronics, we anticipate that it can serve as a platform technology in the near future for improving device performance and for systematically tuning thin film morphology to construct structure-property relationships. From a fundamental perspective, it is imperative to develop a better understanding of the effects of fluid flow and mass transport on OSC crystallization as these processes are ubiquitous across all solution processing techniques and can critically impact charge transport properties.

Reflective-emissive liquid-crystal displays constructed from AIE luminogens (Presentation Recording)

NASA Astrophysics Data System (ADS)

Tang, Ben Zhong; Zhao, Dongyu; Qin, Anjun

2015-10-01

The chiral nematic liquid crystal (N*-LC) has plenty of prospective applications in LC display (LCD) owing to the selective reflection and circular dichroism. The molecules in the N*-LC are aligned forming a helically twisted structure and the specific wavelength of incident light is reflected by the periodically varying refractive index in the N*-LC plane without the aid of a polarizer or color filter. However, N*-LC do not emit light which restricts its application in the dark environment. Moreover, the view angle of N*-LC display device was severe limited due to the strong viewing angle dependence of the structure color of the one dimensional photonic crystal of a N*-LC. In order to overcome these weaknesses, we have synthesized a luminescent liquid crystalline compound consisting of a tetraphenylethene (TPE) core, TPE-PPE, as a luminogen with mesogenic moieties. TPE-PPE exhibits both the aggregate-induced emission (AIE) and thermotropic liquid crystalline characteristics. By dissolving a little amount of TPE-PPE into N*-LC host, a circular polarized emission was obtained on the unidirectional orientated LC cell. Utilizing the circular polarized luminescence property of the LC mixture, we fabricated a photoluminescent liquid crystal display (PL-LCD) device which can work under both dark and sunlit conditions. This approach has simplified the device design, lowered the energy consumption and increased brightness and application of the LCD.

Mesomorphism of Newly Synthesized Mesogens and Surface Morphology of Chalcogenide Glass Thin Films

NASA Astrophysics Data System (ADS)

Sharpnack, Lewis Lee

This dissertation research describes three related projects. The first was an investigation of two de Vries smectic liquid crystal phases that exhibit lower thermal dependence of the smectic layer spacing than the corresponding conventional smectic phases and are well suited for use in electrooptical devices. The second project studied newly synthesized mesogens. This included investigations of several liquid crystalline semiconducting mesogens and a multitude of candidate de Vries smectic mesogens. The third was an investigation of a new non-contact alignment layer of Arsenic Sulfide (As2S 3) to anchor the liquid director and use in electrooptical device. In additional to preliminary characterization methodologies such as polarizing optical microscopy and differential scanning calorimetry, two experimental techniques, X-ray diffraction (XRD) and X-ray reflectivity (XRR), were employed. The X-ray studies were conducted using the in-house spectrometers at Kent State University and the synchrotron X-ray source at the Brookhaven National Laboratory. XRR is used to investigate the structure of potential alignment layers. The results provide important insight into the challenges that need to be overcome to develop this alignment material into a viable commercial product. XRD is used to study the structural properties of several members of two new homologous series of liquid crystal compounds. The study of de Vries materials advances our understanding of the role of various molecular moieties on their phase behavior and, most importantly, their relatively temperature independent layer spacing in the Smectic A (SmA) and Smectic C (SmC) phases. This nearly constant layer spacing is critical for developing new fast ferroelectric and electroclinic effect based displays. The Stevenson research group at Queens University synthesized a multitude of new mesogens incorporating a siloxane tail at one end. This moiety is believed to enhance nano-segregation of the molecules and help form de Vries smectic A and C phases. The results indicate that some of the new mesogens exhibit low layer shrinkage that is indicative of the de Vries behavior. The effects of chain lengths and various moieties on the phase behavior is described in detail. These experiments identified several chiral mesogens as viable candidates for use in ferroelectric displays that are currently the subject of further investigations. Many of the non-chiral molecules studied exhibited de Vries or nearly de Vries layer shrinkage, however, these systems would require the addition of a chiral dopant to be used in ferroelectric applications. Three of the chiral siloxane based mesogens displayed ideal de Vries behavior. The smectic layer spacing changed by 1% or less of the total layer thickness for Si3OK11BPO*, Si3OK11BzPO*, and adpc042. These molecules are presently being investigated for device applications and modified with various terminal groups to enhance the miscibility of nano-particle dopants. Structural studies of novel triphenlyene based organic semiconductors mesogens synthesized by the Twieg group were performed. A desirable trait of organic semiconductors is for the pi-electron orbitals to overlap and requires that carbon rings in adjacent molecules be parallel. Results of X-ray studies of a series of triphenylene molecules showed a hexagonal columnar (ColHex) phase. The diffraction patterns revealed that the lateral intermolecular distance was 3.5 A, consistent with the stacking of the triphenelene rings. The high-temperature ColHex phase of these materials at nearly 200 °C may also prove useful for high temperature applications. Films of As2S3 have recently been shown to align liquid crystals. This alignment technique, when fully developed, will eliminate the need for traditional mechanically buffed polymer films deposited on substrates, currently used in liquid crystal displays. Their surface roughness was determined in the two planar directions using x-ray reflectivity profiles to facilitate a comparison with other alignment layers that generate liquid crystal alignment primarily because of their anisotropic surface morphology. Our results reveal that As2S3 films develop anisotropic features under irradiation with polarized blue light that are consistent with the changes that occur in other alignment layers when they are "treated" either with mechanical buffing of polymer films or exposure to linearly polarized UV light. These studies also reveal the development of an extensive oxide layer and the ablation of the film under ambient conditions owing to the absorption of oxygen and moisture. This represents a significant barrier to their commercial applications.

Magnetostructural transition in Fe{sub 5}SiB{sub 2} observed with neutron diffraction

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

Cedervall, Johan, E-mail: johan.cedervall@kemi.uu.se; Kontos, Sofia; Hansen, Thomas C.

2016-03-15

The crystal and magnetic structure of Fe{sub 5}SiB{sub 2} has been studied by a combination of X-ray and neutron diffraction. Also, the magnetocrystalline anisotropy energy constant has been estimated from magnetisation measurements. High quality samples have been prepared using high temperature synthesis and subsequent heat treatment protocols. The crystal structure is tetragonal within the space group I4/mcm and the compound behaves ferromagnetically with a Curie temperature of 760 K. At 172 K a spin reorientation occurs in the compound and the magnetic moments go from aligning along the c-axis (high T) down to the ab-plane (low T). The magnetocrystalline anisotropymore » energy constant has been estimated to 0.3 MJ/m{sup 3} at 300 K. - Highlights: • The crystal and magnetic structure of Fe{sub 5}SiB{sub 2} has been studied by diffraction. • At 172 K a spin reorientation occurs in the compound. • The magnetic moments are aligned along the c-axis at high T. • The magnetic moments are aligned in the ab-plane at low T. • The magnetocrystalline anisotropy energy constant has been estimated to 0.3 MJ/m{sup 3}.« less

Spatiotemporal character of the Bobylev-Pikin flexoelectric instability in a twisted nematic bent-core liquid crystal exposed to very low frequency fields.

PubMed

Krishnamurthy, K S

2014-05-01

The Bobylev-Pikin striped-pattern state induced by a homogeneous electric field is a volume flexoelectric instability, originating in the midregion of a planarly aligned nematic liquid crystal layer. We find that the instability acquires a spatiotemporal character upon excitation by a low frequency (0.5 Hz) square wave field. This is demonstrated using a bent-core liquid crystal, initially in the 90°-twisted planar configuration. The flexoelectric modulation appears close to the cathode at each polarity reversal and, at low voltage amplitudes, decays completely as the field becomes steady. Correspondingly, at successive polarity changes, the stripe direction switches between the alignment directions at the two substrates. For large voltages, the stripes formed nearly along the alignment direction at the cathode gradually reorient toward the midplane director. These observations are generally attributed to inhomogeneous and time-dependent field conditions that come to exist after each polarity reversal. Polarity dependence of the instability is attributed to the formation of intrinsic double layers that bring about an asymmetry in surface fields. Momentary field elevation near the cathode following a voltage sign reversal and concomitant gradient flexoelectric polarization are considered the key factors in accounting for the surfacelike modulation observed at low voltages.

Pinned, optically aligned diagnostic dock for use on the Z facility.

PubMed

Gomez, M R; Rochau, G A; Bailey, J E; Dunham, G S; Kernaghan, M D; Gard, P; Robertson, G K; Owen, A C; Argo, J W; Nielsen, D S; Lake, P W

2012-10-01

The pinned optically aligned diagnostic dock (PODD) is a multi-configuration diagnostic platform designed to measure x-ray emission on the Z facility. The PODD houses two plasma emission acquisition (PEA) systems, which are aligned with a set of precision machined pins. The PEA systems are modular, allowing a single diagnostic housing to support several different diagnostics. The PEA configurations fielded to date include both time-resolved and time-integrated, 1D spatially resolving, elliptical crystal spectrometers, and time-integrated, 1D spatially resolving, convex crystal spectrometers. Additional proposed configurations include time-resolved, monochromatic mirrored pinhole imagers and arrays of filtered x-ray diodes, diamond photo-conducting diode detectors, and bolometers. The versatility of the PODD system will allow the diagnostic configuration of the Z facility to be changed without significantly adding to the turn-around time of the machine. Additionally, the PODD has been designed to allow instrument setup to be completed entirely off-line, leaving only a refined alignment process to be performed just prior to a shot, which is a significant improvement over the instrument the PODD replaces. Example data collected with the PODD are presented.

Energetic basis for the molecular-scale organization of bone

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

Tao, Jinhui; Battle, Keith C.; Pan, Haihua

2014-12-24

The remarkable properties of bone derive from a highly organized arrangement of co-aligned nm-scale apatite platelets within a fibrillar collagen matrix. The origin of this arrangement is poorly understood and the crystal structures of hydroxyapatite (HAP) and the non-mineralized collagen fibrils alone do not provide an explanation. Moreover, little is known about collagen-apatite interaction energies, which should strongly influence both the molecular-scale organization and the resulting mechanical properties of the composite. We investigated collagen-mineral interactions by combining dynamic force spectroscopy (DFS) measurements of binding energies with molecular dynamics (MD) simulations of binding and AFM observations of collagen adsorption on singlemore » crystals of calcium phosphate for four mineral phases of potential importance in bone formation. In all cases, we observe a strong preferential orientation of collagen binding, but comparison between the observed orientations and TEM analyses native tissues shows only calcium-deficient apatite (CDAP) provides an interface with collagen that is consistent with both. MD simulations predict preferred collagen orientations that agree with observations and results from both MD and DFS reveal large values for the binding energy due to multiple binding sites. These findings reconcile apparent contradictions inherent in a hydroxyapatite or carbonated apatite (CAP) model of bone mineral and provide an energetic rationale for the molecular scale organization of bone.« less

Energetic basis for the molecular-scale organization of bone

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

Tao, Jinhui; Battle, Keith C.; Pan, Haihua

The remarkable properties of bone derive from a highly organized arrangement of co-aligned nm-scale apatite platelets within a fibrillar collagen matrix. The origin of this arrangement is poorly understood and the crystal structures of hydroxyapatite (HAP) and the non-mineralized collagen fibrils alone do not provide an explanation. Moreover, little is known about collagen-apatite interaction energies, which should strongly influence both the molecular-scale organization and the resulting mechanical properties of the composite. We investigated collagen-mineral interactions by combining dynamic force spectroscopy (DFS) measurements of binding energies with molecular dynamics (MD) simulations of binding and AFM observations of collagen adsorption on singlemore » crystals of calcium phosphate for four mineral phases of potential importance in bone formation. In all cases, we observe a strong preferential orientation of collagen binding, but comparison between the observed orientations and TEM analyses native tissues shows only calcium-deficient apatite (CDAP) provides an interface with collagen that is consistent with both. MD simulations predict preferred collagen orientations that agree with observations and results from both MD and DFS reveal large values for the binding energy due to multiple binding sites. These findings reconcile apparent contradictions inherent in a hydroxyapatite or carbonated apatite (CAP) model of bone mineral and provide an energetic rationale for the molecular scale organization of bone.« less

NIR-Vis-UV Light-Responsive Actuator Films of Polymer-Dispersed Liquid Crystal/Graphene Oxide Nanocomposites.

PubMed

Cheng, Zhangxiang; Wang, Tianjie; Li, Xiao; Zhang, Yihe; Yu, Haifeng

2015-12-16

To take full advantage of sunlight for photomechanical materials, NIR-vis-UV light-responsive actuator films of polymer-dispersed liquid crystal (PDLC)/graphene oxide (GO) nanocomposites were fabricated. The strategy is based on phase transition of LCs from nematic to isotropic phase induced by combination of photochemical and photothermal processes in the PDLC/GO nanocomposites. Upon mechanical stretching of the film, both topological shape change and mesogenic alignment occurred in the separated LC domains, enabling the film to respond to NIR-vis-UV light. The homodispersed GO flakes act as photoabsorbent and nanoscale heat source to transfer NIR or VIS light into thermal energy, heating the film and photothermally inducing phase transition of LC microdomains. By utilizing photochemical phase transition of LCs upon UV-light irradiation, one azobenzene dye was incorporated into the LC domains, endowing the nanocomposite films with UV-responsive property. Moreover, the light-responsive behaviors can be well-controlled by adjusting the elongation ratio upon mechanical treatment. The NIR-vis-UV light-responsive PDLC/GO nanocomposite films exhibit excellent properties of easy fabrication, low-cost, and good film-forming and mechanical features, promising their numerous applications in the field of soft actuators and optomechanical systems driven directly by sunlight.

Electrically tunable zero dispersion wavelengths in photonic crystal fibers filled with a dual frequency addressable liquid crystal

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

Wahle, Markus, E-mail: markus.wahle@uni-paderborn.de; Kitzerow, Heinz-Siegfried

2015-11-16

We present a liquid crystal (LC) infiltrated photonic crystal fiber, which enables the electrical tuning of the position of zero dispersion wavelengths (ZDWs). A dual frequency addressable liquid crystal is aligned perpendicular on the inclusion walls of a photonic crystal fiber, which results in an escaped radial director field. The orientation of the LC is controlled by applying an external electric field. Due to the high index of the liquid crystal the fiber guides light by the photonic band gap effect. Multiple ZDWs exist in the visible and near infrared. The positions of the ZDWs can be either blue ormore » red shifted depending on the frequency of the applied voltage.« less

A Scalable Fabrication Process for Liquid Crystal Based Uncooled Thermal Imagers

DTIC Science & Technology

2016-02-12

ll.mit.edu). Phillip Bos, Valerie Finnemeyer, Colin McGinty and Douglas Bryant are with the Liquid Crystal Institute at Kent State University, Kent...Crystal-Based Uncooled Thermal Imagers Shaun Berry, Carl Bozler, Robert Reich, Harry Clark Jr., Phillip Bos, Valerie Finnemeyer, Colin McGinty...was aligned to the die features on the wafer with appropriate weight added (Fig. 5b). We used stainless steel bars to apply the weight to the block

Generation of arbitrary vector beams with liquid crystal polarization converters and vector-photoaligned q-plates

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

Chen, Peng; Ji, Wei; Wei, Bing-Yan

Arbitrary vector beams (VBs) are realized by the designed polarization converters and corresponding vector-photoaligned q-plates. The polarization converter is a specific twisted nematic cell with one substrate homogeneously aligned and the other space-variantly aligned. By combining a polarization-sensitive alignment agent with a dynamic micro-lithography system, various categories of liquid crystal polarization converters are demonstrated. Besides, traditional radially/azimuthally polarized light, high-order and multi-ringed VBs, and a VB array with different orders are generated. The obtained converters are further utilized as polarization masks to implement vector-photoaligning. The technique facilitates both the volume duplication of these converters and the generation of another promisingmore » optical element, the q-plate, which is suitable for the generation of VBs for coherent lasers. The combination of proposed polarization converters and correspondingly fabricated q-plates would drastically enhance the capability of polarization control and may bring more possibilities for the design of photonic devices.« less

Flow-aligned, single-shot fiber diffraction using a femtosecond X-ray free-electron laser

DOE PAGES

Popp, David; Loh, N. Duane; Zorgati, Habiba; ...

2017-06-02

A major goal for X-ray free-electron laser (XFEL) based science is to elucidate structures of biological molecules without the need for crystals. Filament systems may provide some of the first single macromolecular structures elucidated by XFEL radiation, since they contain one-dimensional translational symmetry and thereby occupy the diffraction intensity region between the extremes of crystals and single molecules. Here, we demonstrate flow alignment of as few as 100 filaments ( Escherichia coli pili, F-actin, and amyloid fibrils), which when intersected by femtosecond X-ray pulses result in diffraction patterns similar to those obtained from classical fiber diffraction studies. We also determinemore » that F-actin can be flow-aligned to a disorientation of approximately 5 degrees. Using this XFEL-based technique, we determine that gelsolin amyloids are comprised of stacked β-strands running perpendicular to the filament axis, and that a range of order from fibrillar to crystalline is discernable for individual α-synuclein amyloids.« less

Flow-aligned, single-shot fiber diffraction using a femtosecond X-ray free-electron laser

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

Popp, David; Loh, N. Duane; Zorgati, Habiba

A major goal for X-ray free-electron laser (XFEL) based science is to elucidate structures of biological molecules without the need for crystals. Filament systems may provide some of the first single macromolecular structures elucidated by XFEL radiation, since they contain one-dimensional translational symmetry and thereby occupy the diffraction intensity region between the extremes of crystals and single molecules. Here, we demonstrate flow alignment of as few as 100 filaments ( Escherichia coli pili, F-actin, and amyloid fibrils), which when intersected by femtosecond X-ray pulses result in diffraction patterns similar to those obtained from classical fiber diffraction studies. We also determinemore » that F-actin can be flow-aligned to a disorientation of approximately 5 degrees. Using this XFEL-based technique, we determine that gelsolin amyloids are comprised of stacked β-strands running perpendicular to the filament axis, and that a range of order from fibrillar to crystalline is discernable for individual α-synuclein amyloids.« less

Comparison of Friction Characteristics on TN and VA Mode Alignment Films with Friction Force Microscopy

NASA Astrophysics Data System (ADS)

Kwak, Musun; Chung, Hanrok; Kwon, Hyukmin; Kim, Jehyun; Han, Daekyung; Yi, Yoonseon; Lee, Sangmun; Lee, Chulgu; Cha, Sooyoul

Using frictional force microscopy (FFM), the friction surface characteristics were compared between twisted nematic (TN) mode and vertical alignment (VA) mode alignment films (AFs). The friction asymmetry was detected depending on temperature conditions on TN mode AF, but not on VA mode AF. The difference between two modes was explained by leaning intermolecular repulsion caused by the pre-tilt angle uniformity and the density of side chain. No level difference according to temperature conditions appeared when the pre-tilt angle were measured after liquid crystal (LC) injection.

High density protein crystal growth

NASA Technical Reports Server (NTRS)

Rouleau, Robyn (Inventor); Hedden, Douglas Keith (Inventor); Delucas, Lawrence (Inventor)

2004-01-01

A protein crystal growth assembly including a crystal growth cell and further including a cell body having a top side and a bottom side and a first aperture defined therethrough, the cell body having opposing first and second sides and a second aperture defined therethrough. A cell barrel is disposed within the cell body, the cell barrel defining a cavity alignable with the first aperture of the cell body, the cell barrel being rotatable within the second aperture. A reservoir is coupled to the bottom side of the cell body and a cap having a top side is disposed on the top side of the cell body. The protein crystal growth assembly may be employed in methods including vapor diffusion crystallization, liquid to liquid crystallization, batch crystallization, and temperature induction batch mode crystallization.

Electrical tuning of three-dimensional photonic crystals using polymer dispersed liquid crystals

NASA Astrophysics Data System (ADS)

McPhail, Dennis; Straub, Martin; Gu, Min

2005-01-01

Electrically tunable three-dimensional photonic crystals with a tunable wavelength range of over 70nm of stop gaps between 3 and 4μm have been generated in a liquid crystal-polymer composite. The photonic crystals were fabricated by femtosecond-laser direct writing of void channels in an inverse woodpile configuration with 20 layers providing an extinction of infrared light transmission of 70% in the stacking direction. Stable structures could be manufactured up to a liquid crystal concentration of 24%. Applying a direct voltage of several hundred volts in the stacking direction of the photonic crystal changes the alignment of the liquid crystal directors and hence the average refractive index of the structure. This mechanism permits the direct tuning of the photonic stop gap.

Fabric Development in a Late-Hercynian Magmatic Strike-Slip Shear Zone in Southern Corsica: Indications of Melt-Supported Large-Scale Deformation Localization

NASA Astrophysics Data System (ADS)

Kruhl, J. H.; Vernon, R. H.

2009-05-01

The calc-alcaline granitoids of the Hercynian Corsica Batholith show a large-scale magmatic flow pattern, outlined by the alignment of large (mm-cm) euhedral feldspar crystals. The trend of the steep magmatic foliation is generally N-S in the northern part of the island, swings to approximately E-W orientation in the central part of the Batholith and back again to approximately N-S orientation in the southern part. This pattern is intensified by large-scale magmatic layering, mainly kilometer long lenses and layers of mafic and intermediate intrusions into the granitoids. On the macro- to micro-scale, magma mingling and mixing are present, reflecting the complex intrusion history and the compositional variability of the Corsica Batholith on different scales. Around the Golf of Valinco, a steep, sinistral magmatic shear zone is represented by E-W trending magmatic layering in mingled dioritic, tonalitic, and granitic magmas - previously misleadingly interpreted as migmatites - and by a magmatic flow foliation formed by the alignment of platy feldspar crystals, as well as amphibole and biotite. Characteristic magmatic structures include multiple thin layering, boudinage, monoclinic folding, melt-injected micro shear zones, and fragmenting and back- veining of dioritic enclaves. The intensity of grain alignment roughly correlates with the thickness of layers. It is low in thick and short boudins and high in cm-thin and cm-m long layers. The monoclinic folds refold the magmatic layering. Flat faces of amphibole and biotite grains are aligned in the axial planes of the folds. The feldspar crystals are locally recrystallized to a few large polygonal grains (up to 1 mm across), and quartz commonly shows chessboard subgrain patterns. No further indications of solid-state deformation are present. Field observations, as well as pattern quantification on variably oriented rock surfaces, indicate variations of crystal alignment and fabric anisotropy in cm- to more than 100m-wide bands parallel to the E-W oriented layering, and various stages of melt-present fragmentation. These variations are interpreted as variations of flow intensity and possibly strain-rate variation. The observations on the macro- as well as the micro-scale point to repeated injection of mafic to felsic magma and crystallization in the presence of a regional stress field. The resulting km-scale sinistral, sub-horizontal synmagmatic shear zone reflects large-scale movements during late-Hercynian crustal reorganization and represents an excellent example of localization of deformation into magma-enriched parts of the continental crust.

A Fiber Optic Probe for Monitoring Protein Aggregation, Nucleation, and Crystallization

NASA Technical Reports Server (NTRS)

Ansari, Rafat R.; Suh, Kwang I.; Arabshahi, Alireza; Wilson, William W.; Bray, Terry L.; DeLucas, Lawrence J.

1996-01-01

Protein crystals are experimentally grown in hanging drops in microgravity experiments on-board the Space Shuttle orbiter. The technique of dynamic light scattering (DLS) can be used to monitor crystal growth process in hanging droplets (approx. 30 (L)) in microgravity experiments, but elaborate instrumentation and optical alignment problems have made in-situ applications difficult. In this paper we demonstrate that such experiments are now feasible. We apply a newly developed fiber optic probe to various earth and space (micro- gravity) bound protein crystallization system configurations to test its capability. These include conventional batch (cuvette or capillary) systems, hanging drop method in a six-pack hanging drop vapor diffusion apparatus (HDVDA), a modified HDVDA for temperature- induced nucleation and aggregation studies, and a newly envisioned dynamically controlled vapor diffusion system (DCVDS) configuration. Our compact system exploits the principles of DLS and offers a fast (within a few seconds) means of quantitatively and non-invasively monitoring the various growth stages of protein crystallization. In addition to DLS capability, the probe can also be used for performing single-angle static light scattering measurements. It utilizes extremely low levels of laser power (approx. few (W)) without a need of having any optical alignment and vibration isolation. The compact probe is also equipped with a miniaturized microscope for visualization of macroscopic protein crystals. This new optical diagnostic system opens up enormous opportunity for exploring new ways to grow good quality crystals suitable for x-ray crystallographic analysis and may help develop a concrete scientific basis for understanding the process of crystallization.

Analysis of the new polarimeter for the Marshall Space Flight Center vector magnetograph

NASA Technical Reports Server (NTRS)

West, E. A.

1985-01-01

The magnetograph was upgraded in both electronic control of the magnetograph hardware and in the polarization optics. The problems associated with the orignal polarimeter were: (1) field of view errors associated with the natural birefringence of the KD*P crystals; (2.) KD*P electrode failure due to the halfwave dc voltage required in one of the operational sequences; and (3) breakdown of the retardation properties of some KD*Ps when exposed to a zero to halfwave modulation (DC) scheme. The new polarimeter gives up the flexibility provided by two variable waveplates to adjust the retardances of the optics for a particular polarization measurement, but solves the problems associated with the original polarimeter. With the addition of the quartz quarterwave plates, a new optical alignment was developed to allow the remaining KD*P to correct for errors in the waveplates. The new optical alignment of the polarimeter is prescribed. The various sources of error, and how those errors are minimized so that the magnetograph can look at the transverse field in real time are discussed.

Epoxy matrix with triaromatic mesogenic unit in dielectric spectroscopy observation

NASA Astrophysics Data System (ADS)

Włodarska, Magdalena; Mossety-Leszczak, Beata; Bąk, Grzegorz W.; Kisiel, Maciej; Dłużniewski, Maciej; Okrasa, Lidia

2018-04-01

This paper describes the dielectric response of a selected liquid crystal epoxy monomer (plain and in curing systems) in a wide range of frequency and temperature. The dielectric spectroscopy, thanks to its sensitivity, is a very good tool for studying phase transitions, reaction progress, or material properties. This sensitivity is important in the case of liquid crystal epoxy resins, where properties of the final network depend on the choice of monomers, curing agents, curing conditions and post-curing treatment, or applying an external electric or magnetic field during the reaction. In most of the obtained cured products, the collected dielectric data show two relaxation processes. The α-process is related to a structural reorientation; it can usually be linked with the glass transition and the mechanical properties of the material. The β-process can be identified as a molecular motion process, probably associated with the carboxyl groups in the mesogen. A transient Maxwell-Wagner relaxation observed in one of the compositions after the initial curing is removed by post-curing treatment at elevated temperatures. Post-curing is therefore necessary for obtaining uniformly cured products in those cases. In the investigated systems, the choice of a curing agent can change the glass transition temperature by at least 70 °C. The obtained results are in a good agreement with an earlier study employing other techniques. Finally, we assess the influence of the direction of mesogen alignment on the dielectric properties of one selected system, where a global order was induced by applying an external magnetic field in the course of curing.

Standard Reference Material (SRM 1990) for Single Crystal Diffractometer Alignment

USGS Publications Warehouse

Wong-Ng, W.; Siegrist, T.; DeTitta, G.T.; Finger, L.W.; Evans, H.T.; Gabe, E.J.; Enright, G.D.; Armstrong, J.T.; Levenson, M.; Cook, L.P.; Hubbard, C.R.

2001-01-01

An international project was successfully completed which involved two major undertakings: (1) a round-robin to demonstrate the viability of the selected standard and (2) the certification of the lattice parameters of the SRM 1990, a Standard Reference Material?? for single crystal diffractometer alignment. This SRM is a set of ???3500 units of Cr-doped Al2O3, or ruby spheres [(0 420.011 mole fraction % Cr (expanded uncertainty)]. The round-robin consisted of determination of lattice parameters of a pair of crystals' the ruby sphere as a standard, and a zeolite reference to serve as an unknown. Fifty pairs of crystals were dispatched from Hauptman-Woodward Medical Research Institute to volunteers in x-ray laboratories world-wide. A total of 45 sets of data was received from 32 laboratories. The mean unit cell parameters of the ruby spheres was found to be a=4.7608 A?? ?? 0.0062 A??, and c=12.9979 A?? ?? 0.020 A?? (95 % intervals of the laboratory means). The source of errors of outlier data was identified. The SRM project involved the certification of lattice parameters using four well-aligned single crystal diffractometers at (Bell Laboratories) Lucent Technologies and at NRC of Canada (39 ruby spheres), the quantification of the Cr content using a combined microprobe and SEM/EDS technique, and the evaluation of the mosaicity of the ruby spheres using a double-crystal spectrometry method. A confirmation of the lattice parameters was also conducted using a Guinier-Ha??gg camera. Systematic corrections of thermal expansion and refraction corrections were applied. These rubies_ are rhombohedral, with space group R3c. The certified mean unit cell parameters are a=4.76080 ?? 0.00029 A??, and c=12 99568 A?? ?? 0.00087 A?? (expanded uncertainty). These certified lattice parameters fall well within the results of those obtained from the international round-robin study. The Guinier-Ha??gg transmission measurements on five samples of powdered rubies (a=4.7610 A?? ?? 0.0013 A??, and c=12.9954 A?? ?? 0.0034 A??) agreed well with the values obtained from the single crystal spheres.

Standard Reference Material (SRM 1990) For Single Crystal Diffractometer Alignment

PubMed Central

Wong-Ng, W.; Siegrist, T.; DeTitta, G. T.; Finger, L. W.; Evans, H. T.; Gabe, E. J.; Enright, G. D.; Armstrong, J. T.; Levenson, M.; Cook, L. P.; Hubbard, C. R.

2001-01-01

An international project was successfully completed which involved two major undertakings: (1) a round-robin to demonstrate the viability of the selected standard and (2) the certification of the lattice parameters of the SRM 1990, a Standard Reference Material® for single crystal diffractometer alignment. This SRM is a set of ≈3500 units of Cr-doped Al2O3, or ruby spheres [(0.420.011 mole fraction % Cr (expanded uncertainty)]. The round-robin consisted of determination of lattice parameters of a pair of crystals: the ruby sphere as a standard, and a zeolite reference to serve as an unknown. Fifty pairs of crystals were dispatched from Hauptman-Woodward Medical Research Institute to volunteers in x-ray laboratories world-wide. A total of 45 sets of data was received from 32 laboratories. The mean unit cell parameters of the ruby spheres was found to be a=4.7608 ű0.0062 Å, and c=12.9979 ű0.020 Å (95 % intervals of the laboratory means). The source of errors of outlier data was identified. The SRM project involved the certification of lattice parameters using four well-aligned single crystal diffractometers at (Bell Laboratories) Lucent Technologies and at NRC of Canada (39 ruby spheres), the quantification of the Cr content using a combined microprobe and SEM/EDS technique, and the evaluation of the mosaicity of the ruby spheres using a double-crystal spectrometry method. A confirmation of the lattice parameters was also conducted using a Guinier-Hägg camera. Systematic corrections of thermal expansion and refraction corrections were applied. These rubies– are rhombohedral, with space group R3¯c. The certified mean unit cell parameters are a=4.76080±0.00029 Å, and c=12.99568 ű0.00087 Å (expanded uncertainty). These certified lattice parameters fall well within the results of those obtained from the international round-robin study. The Guinier-Hägg transmission measurements on five samples of powdered rubies (a=4.7610 ű0.0013 Å, and c = 12.9954 ű0.0034 Å) agreed well with the values obtained from the single crystal spheres. PMID:27500067

Liquid crystal alignment in electro-responsive nanostructured thermosetting materials based on block copolymer dispersed liquid crystal.

PubMed

Tercjak, A; Garcia, I; Mondragon, I

2008-07-09

Novel well-defined nanostructured thermosetting systems were prepared by modification of a diglicydylether of bisphenol-A epoxy resin (DGEBA) with 10 or 15 wt% amphiphilic poly(styrene-b-ethylene oxide) block copolymer (PSEO) and 30 or 40 wt% low molecular weight liquid crystal 4'-(hexyl)-4-biphenyl-carbonitrile (HBC) using m-xylylenediamine (MXDA) as a curing agent. The competition between well-defined nanostructured materials and the ability for alignment of the liquid crystal phase in the materials obtained has been studied by atomic and electrostatic force microscopy, AFM and EFM, respectively. Based on our knowledge, this is the first time that addition of an adequate amount (10 wt%) of a block copolymer to 40 wt% HBC-(DGEBA/MXDA) leads to a well-organized nanostructured thermosetting system (between a hexagonal and worm-like ordered structure), which is also electro-responsive with high rate contrast. This behavior was confirmed using electrostatic force microscopy (EFM), by means of the response of the HBC liquid crystal phase to the voltage applied to the EFM tip. In contrast, though materials containing 15 wt% PSEO and 30 wt% HBC also form a well-defined nanostructured thermosetting system, they do not show such a high contrast between the uncharged and charged surface.

Investigation of energy band alignments and interfacial properties of rutile NMO2/TiO2 (NM = Ru, Rh, Os, and Ir) by first-principles calculations.

PubMed

Yang, Chen; Zhao, Zong-Yan

2017-11-08

In the field of photocatalysis, constructing hetero-structures is an efficient strategy to improve quantum efficiency. However, a lattice mismatch often induces unfavorable interfacial states that can act as recombination centers for photo-generated electron-hole pairs. If the hetero-structure's components have the same crystal structure, this disadvantage can be easily avoided. Conversely, in the process of loading a noble metal co-catalyst onto the TiO 2 surface, a transition layer of noble metal oxides is often formed between the TiO 2 layer and the noble metal layer. In this article, interfacial properties of hetero-structures composed of a noble metal dioxide and TiO 2 with a rutile crystal structure have been systematically investigated using first-principles calculations. In particular, the Schottky barrier height, band bending, and energy band alignments are studied to provide evidence for practical applications. In all cases, no interfacial states exist in the forbidden band of TiO 2 , and the interfacial formation energy is very small. A strong internal electric field generated by interfacial electron transfer leads to an efficient separation of photo-generated carriers and band bending. Because of the differences in the atomic properties of the components, RuO 2 /TiO 2 and OsO 2 /TiO 2 hetero-structures demonstrate band dividing, while RhO 2 /TiO 2 and IrO 2 /TiO 2 hetero-structures have a pseudo-gap near the Fermi energy level. Furthermore, NMO 2 /TiO 2 hetero-structures show upward band bending. Conversely, RuO 2 /TiO 2 and OsO 2 /TiO 2 hetero-structures present a relatively strong infrared light absorption, while RhO 2 /TiO 2 and IrO 2 /TiO 2 hetero-structures show an obvious absorption edge in the visible light region. Overall, considering all aspects of their properties, RuO 2 /TiO 2 and OsO 2 /TiO 2 hetero-structures are more suitable than others for improving the photocatalytic performance of TiO 2 . These findings will provide useful information for understanding the role and effects of a noble metal dioxide as a transition layer between a noble metal co-catalyst and a TiO 2 photocatalyst.

Magnetically-assembled micro/mesopixels exhibiting light intensity enhancement in the (012) planes of fish guanine crystals

NASA Astrophysics Data System (ADS)

Chikashige, T.; Iwasaka, M.

2018-05-01

In this study, a new method was investigated to form light-reflecting dots at the micrometer scale using the magnetic orientations of biogenic guanine crystals obtained from fish skin and scales. The crystal platelets, possessing average dimensions of 5 μm×20 μm×100 nm, were dispersed in water and observed during exposure to vertical magnetic fields up to 5 T. The magnetic field direction was parallel to Earth's gravity, and allowed the narrowest edges of the crystals to be observed at the micrometer scale for the first time. The magnetic orientation process was initiated under conditions where the crystal platelets in water were laid on a glass substrate or where the platelets had random orientations. In the former case, the crystal platelets followed a two-stage magnetic orientation process where, in the first step, the platelet widths were aligned in the magnetic field direction. The second step required rotation of the ˜20-μm-long plates with respect to the Earth's gravity, where application of a 5 T magnetic field enabled their orientation. Real-time images of the magnetically aligning platelets provided new evidence that the crystal platelets also emitted reflected light from a very narrow window at two crystal planes (i.e., (0 1 ¯ 2 ¯ ) and (0 1 ¯ 2 )). In the latter case with random platelet orientation, spatially-condensed light-reflecting dots appeared while the guanine crystal platelets were floating and maintaining their orientation. The technique developed for controlling light-reflecting microscale objects in an aqueous medium can be applied to produce a type of microfluidic optical tool.

Fracture toughness of materials

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

Burns, S.J.

Crack tip dislocation emission in bulk specimens have been measured in single crystal specimens and the measurements are well below the accepted theoretical values for dislocation emission. The image forces on a dislocation due to the presence of a semi-infinite crack are used to calculate the potential energy of the dislocation around the crack. Expressions for the radial and tangential forces and for slip and climb forces have been found. Crack tip deformation in Mode I and Mode II fractures on both {l brace}100{r brace} and {l brace}110{r brace} planes have been observed in crystals of LiF. The deformation ismore » shown to nearly completely shield {l brace}110{r brace} plane cracks and prevent their propagation while deformation is less effective in shielding {l brace}100{r brace} plane cracks. The fracture toughness of MgO-partially-stabilized ZrO{sub 2} exhibiting transformation toughening been measured. The equations of linear elastic fracture mechanics have been self-consistantly formulated to include the residual displacement from the transformation wake. MgO single crystals were fatigued in plastic strain control at elevated temperatures. At high temperatures, dense bundles of dislocations were observed in transmission electron microscopy aligned perpendicular to the Burgers' vector directions. The thermodynamics of a superconducting second order phase transformation has been related to jumps in physical properties. A simple energy balance, without assuming an equation of state, is used to relate the rate of change of state variables to measurable physical properties. There are no preconceived assumptions about the superconducting mechanism.« less

Aligned Immobilization of Proteins Using AC Electric Fields.

PubMed

Laux, Eva-Maria; Knigge, Xenia; Bier, Frank F; Wenger, Christian; Hölzel, Ralph

2016-03-01

Protein molecules are aligned and immobilized from solution by AC electric fields. In a single-step experiment, the enhanced green fluorescent proteins are immobilized on the surface as well as at the edges of planar nanoelectrodes. Alignment is found to follow the molecules' geometrical shape with their longitudinal axes parallel to the electric field. Simultaneous dielectrophoretic attraction and AC electroosmotic flow are identified as the dominant forces causing protein movement and alignment. Molecular orientation is determined by fluorescence microscopy based on polarized excitation of the proteins' chromophores. The chromophores' orientation with respect to the whole molecule supports X-ray crystal data. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The LPO Iron Pattern beneath the Earth's Inner Core Boundary

NASA Astrophysics Data System (ADS)

Mattesini, Maurizio; Belonoshko, Anatoly; Tkalčić, Hrvoje

2017-04-01

An Earth's inner core surface pattern for the iron Lattice Preferred Orientation (LPO) has been addressed for various iron crystal polymorphs. The geographical distribution of the amount of crystal alienation was achieved by bridging high-quality inner core probing seismic data [PKP(bc-df)] together with ab initio computed elastic constants. We show that the proposed topographic crystal alignment may be used as a boundary condition for dynamo simulations, providing an additional way to discriminate in between different and, often controversial, geodynamical scenarios.

The LPO Iron Pattern beneath the Earth's Inner Core Boundary

NASA Astrophysics Data System (ADS)

Mattesini, M.; Tkalcic, H.; Belonoshko, A. B.; Buforn, E.; Udias, A.

2015-12-01

An Earth's inner core surface pattern for the iron Lattice Preferred Orientation (LPO) has been addressed for various iron crystal polymorphs. The geographical distribution of the amount of crystal alienation was achieved by bridging high-quality inner core probing seismic data [PKP(bc-df)] together with ab initio computed elastic constants. We show that the proposed topographic crystal alignment may be used as a boundary condition for dynamo simulations, providing an additional way to discriminate in between different and, often controversial, geodynamical scenarios.

In-plane pitch control of cholesteric liquid crystals by formation of artificial domains via patterned photopolymerization.

PubMed

Yoshida, Hiroyuki; Miura, Yusuke; Tokuoka, Kazuki; Suzuki, Satoshi; Fujii, Akihiko; Ozaki, Masanori

2008-11-10

A controlled helix pitch modulation in the in-plane direction of a planarly aligned cholesteric liquid crystal cell is demonstrated by using photopolymerizable cholesteric liquid crystals. By fabricating artificial domains with a closed volume via two-photon excitation laser-lithography, the degree of pitch modulation could be controlled by adjusting the surface area to volume ratio of the domain. A pitch modulation of over 60 nm was realized by designing the shape of the artificial domain.

Probing the liquid crystal alignment interface and switching dynamics in a slab waveguide architecture

NASA Astrophysics Data System (ADS)

Gotjen, Henry G.; Kolacz, Jakub; Myers, Jason D.; Frantz, Jesse A.; Bekele, Robel Y.; Naciri, Jawad; Spillmann, Christopher M.

2018-02-01

A non-mechanical refractive laser beam steering device has been developed to provide continuous, two-dimensional steering of infrared beams. The technology implements a dielectric slab waveguide architecture with a liquid crystal (LC) cladding. With voltage control, the birefringence of the LC can be leveraged to tune the effective index of the waveguide under an electrode. With a clever prism electrode design a beam coupled into the waveguide can be deflected continuously in two dimensions as it is coupled out into free space. The optical interaction with LC in this beamsteerer is unique from typical LC applications: only the thin layer of LC (100s of nm) near the alignment interface interacts with the beam's evanescent field. Whereas most LC interactions take place over short path lengths (microns) in the bulk of the material, here we can interrogate the behavior of LC near the alignment interface over long path lengths (centimeters). In this work the beamsteerer is leveraged as a tool to study the behavior of LC near the alignment layer in contrast to the bulk material. We find that scattering is substantially decreased near the alignment interface due to the influence of the surface anchoring energy to suppress thermal fluctuations. By tracking the position of the deflected beam with a high speed camera, we measure response times of the LC near the interface in off-to-on switching ( ms) and on-to-off switching ( 100ms). Combined, this work will provide a path for improved alignment techniques, greater optical throughput, and faster response times in this unique approach to non-mechanical beamsteering.

Fast gray-to-gray switching of a hybrid-aligned liquid crystal cell

NASA Astrophysics Data System (ADS)

Choi, Tae-Hoon; Kim, Jung-Wook; Yoon, Tae-Hoon

2015-03-01

We demonstrate fast gray-to-gray (GTG) switching of a hybrid-aligned liquid crystal cell by applying both vertical and inplane electric fields to liquid crystals (LCs) using a four-terminal electrode structure. The LCs are switched to the bright state through downward tilting and twist deformation initiated by applying an in-plane electric field, whereas they are switched back to the initial dark state through optically hidden relaxation initiated by applying a vertical electric field for a short duration. The top electrode in the proposed device is grounded, which requires a much higher voltage to be applied for in-plane rotation of LCs. Thus, ultrafast turn-on switching of the device is achieved, whereas the turn-off switching of the proposed device is independent of the elastic constants and the viscosity of the LCs so that fast turn-off switching can be achieved. We experimentally obtained a total response time of 0.75 ms. Furthermore, fast GTG response within 3 ms could be achieved.

Optical switch based on the electrically controlled liquid crystal interface.

PubMed

Komar, Andrei A; Tolstik, Alexei L; Melnikova, Elena A; Muravsky, Alexander A

2015-06-01

The peculiarities of the linearly polarized light beam reflection at the interface within the bulk of a nematic liquid crystal (NLC) cell with different orientations of the director are analyzed. Two methods to create the interface are considered. Combination of the planar and homeotropic orientations of the NLC director is realized by means of a spatially structured electrode under the applied voltage. In-plane patterned azimuthal alignment of the NLC director is created by the patterned rubbing alignment technique. All possible orthogonal orientations of the LC director are considered; the configurations for realization of total internal reflection are determined. The revealed relationship between the propagation of optical beams in a liquid crystal material and polarization of laser radiation has enabled realization of the spatial separation for the orthogonally polarized light beams at the interface between two regions of NLC with different director orientations (domains). Owing to variations in the applied voltage and, hence, in the refractive index gradient, the light beam propagation directions may be controlled electrically.

Controlled transition dipole alignment of energy donor and energy acceptor molecules in doped organic crystals, and the effect on intermolecular Förster energy transfer.

PubMed

Wang, Huan; Yue, Bailing; Xie, Zengqi; Gao, Bingrong; Xu, Yuanxiang; Liu, Linlin; Sun, Hongbo; Ma, Yuguang

2013-03-14

The orientation factor κ(2) ranging from 0 to 4, which depends on the relative orientation of the transition dipoles of the energy donor (D) and the energy acceptor (A) in space, is one of the pivotal factors deciding the efficiency and directionality of resonance energy transfer (RET) in a D-A molecular system. In this work, tetracene (Tc) and pentacene (Pc) are successfully doped in a trans-1,4-distyrylbenzene (DSB) crystalline lattice to form definite D-A mutually perpendicular transition dipole orientations. The cross D-A dipole arrangement results in an extremely small orientation factor, which is about two orders smaller than that in the disordered films. The energy transfer properties from the host (DSB) to the guest (Tc/Pc) were investigated in detail by steady-state as well as time-resolved fluorescence spectroscopy. Our experimental research results show that the small value of κ(2) allows less or partial energy transfer from the host (DSB) to the guest (Tc) in a wide range of guest concentration, with the Förster distance of around 1.5 nm. By controlling the doping concentrations in the Tc and Pc doubly doped DSB crystals, we demonstrate, as an example, for the first time the application of the restricted energy transfer by D-A cross transition dipole arrangement for preparation of a large-size, white-emissive organic crystal with the CIE coordinates of (0.36, 0.37) approaching an ideal white light. In contrast, Tc is also doped in an anthracene crystalline lattice to form head-to-tail D-A transition dipole alignment, which is proved to be highly effective to promote the intermolecular energy transfer. In this doped system, the orientation factor is relatively large and the Förster distance is around 7 nm.

Self-assembled ordered structures in thin films of HAT5 discotic liquid crystal.

PubMed

Morales, Piero; Lagerwall, Jan; Vacca, Paolo; Laschat, Sabine; Scalia, Giusy

2010-05-20

Thin films of the discotic liquid crystal hexapentyloxytriphenylene (HAT5), prepared from solution via casting or spin-coating, were investigated by atomic force microscopy and polarizing optical microscopy, revealing large-scale ordered structures substantially different from those typically observed in standard samples of the same material. Thin and very long fibrils of planar-aligned liquid crystal were found, possibly formed as a result of an intermediate lyotropic nematic state arising during the solvent evaporation process. Moreover, in sufficiently thin films the crystallization seems to be suppressed, extending the uniform order of the liquid crystal phase down to room temperature. This should be compared to the bulk situation, where the same material crystallizes into a polymorphic structure at 68 °C.

Tunable growth of TiO2 nanostructures on Ti substrates

NASA Astrophysics Data System (ADS)

Peng, Xinsheng; Wang, Jingpeng; Thomas, Dan F.; Chen, Aicheng

2005-10-01

A simple and facile method is described to directly synthesize TiO2 nanostructures on titanium substrates by oxidizing Ti foil using small organic molecules as the oxygen source. The effect of reaction temperature and oxygen source on the formation of the TiO2 nanostructures has been studied using scanning electron microscopy, x-ray diffraction, transmission electron microscopy, Raman spectroscopy and water contact angle measurement. Polycrystalline grains are formed when pure oxygen and formic acid are used as the oxygen source; elongated micro-crystals are produced when water vapour is used as the oxygen source; oriented and aligned TiO2 nanorod arrays are synthesized when ethanol, acetaldehyde or acetone are used as the oxygen source. The growth mechanism of the TiO2 nanostructures is discussed. The diffusion of Ti atoms to the oxide/gas interface via the network of the grain boundaries of the thin oxide layer is the determining factor for the formation of well-aligned TiO2 nanorod arrays. The wetting properties of the TiO2 nanostructured surfaces formed are dictated by their structure, varying from a hydrophilic surface to a strongly hydrophobic surface as the surface structure changes from polycrystalline grains to well-aligned nanorod arrays. This tunable growth of TiO2 nanostructures is desirable for promising applications of TiO2 nanostructures in the development of optical devices, sensors, photo-catalysts and self-cleaning coatings.

Effects of electric field on thermodynamics and ordering of a dipolar liquid

NASA Astrophysics Data System (ADS)

Johari, G. P.

2016-10-01

We propose that an electric field's role in changing the structural disorder may be investigated by comparing the field-induced entropy decrease, ΔES, against the pressure-induced and cooling-induced entropy decreases, ΔpS and ΔTS, respectively, for the same increase in the dielectric α-relaxation time, Δτα, or in the viscosity. If these three quantities are found to be the same, the change in the number of microstates, Δln Ω = ΔS/R, would be the same whether there is an electric field-induced dipole vector alignment, or not. The available data [S. Samanta and R. Richert, J. Chem. Phys. 142, 044504 (2015)] show that ΔES ≅ ΔpS, and ΔES ≅ ΔTS. We further argue that in the case of conformational disorder without hydrodynamics, as for a flexible molecule's orientationally disordered or plastic crystal, ΔTS would be more negative than ΔES for the same increase in Δτα. For cyclo-octanol plastic crystal, whose octyl-ring would lose some of its dielectrically inactive conformational degrees of freedom on cooling, ΔTS is five-times ΔES. Hence the entropy of such crystals may not be related to their τα, an aspect relevant to certain biopolymer crystals. We also mention other effects of E. The findings are relevant to a number of recent studies on the analysis of the effect of electric field on a liquid's properties. The method can be used to study the role of other entropy-altering variables in liquid crystals and ferromagnetic liquids.

40 CFR Appendix B to Part 80 - Test Methods for Lead in Gasoline

Code of Federal Regulations, 2014 CFR

2014-07-01

... one liter. 4.6 Iodine Solution—Dissolve and dilute 3.0 g iodine crystals with Toluene to 100 ml. 4.7...): Dissolve and dilute 3.0 g iodine crystals (American Chemical Society) with toluene (Burdick & Jackson Lab... and aligned according to Section 7 and the instrument has had substantial time for warm-up. 8.2Auto...

40 CFR Appendix B to Part 80 - Test Methods for Lead in Gasoline

Code of Federal Regulations, 2010 CFR

2010-07-01

... one liter. 4.6 Iodine Solution—Dissolve and dilute 3.0 g iodine crystals with Toluene to 100 ml. 4.7...): Dissolve and dilute 3.0 g iodine crystals (American Chemical Society) with toluene (Burdick & Jackson Lab... and aligned according to Section 7 and the instrument has had substantial time for warm-up. 8.2Auto...

40 CFR Appendix B to Part 80 - Test Methods for Lead in Gasoline

Code of Federal Regulations, 2013 CFR

2013-07-01

... one liter. 4.6 Iodine Solution—Dissolve and dilute 3.0 g iodine crystals with Toluene to 100 ml. 4.7...): Dissolve and dilute 3.0 g iodine crystals (American Chemical Society) with toluene (Burdick & Jackson Lab... and aligned according to Section 7 and the instrument has had substantial time for warm-up. 8.2Auto...

40 CFR Appendix B to Part 80 - Test Methods for Lead in Gasoline

Code of Federal Regulations, 2011 CFR

2011-07-01

... one liter. 4.6 Iodine Solution—Dissolve and dilute 3.0 g iodine crystals with Toluene to 100 ml. 4.7...): Dissolve and dilute 3.0 g iodine crystals (American Chemical Society) with toluene (Burdick & Jackson Lab... and aligned according to Section 7 and the instrument has had substantial time for warm-up. 8.2Auto...

40 CFR Appendix B to Part 80 - Test Methods for Lead in Gasoline

Code of Federal Regulations, 2012 CFR

2012-07-01

... one liter. 4.6 Iodine Solution—Dissolve and dilute 3.0 g iodine crystals with Toluene to 100 ml. 4.7...): Dissolve and dilute 3.0 g iodine crystals (American Chemical Society) with toluene (Burdick & Jackson Lab... and aligned according to Section 7 and the instrument has had substantial time for warm-up. 8.2Auto...

Smectic layer instabilities in liquid crystals.

PubMed

Dierking, Ingo; Mitov, Michel; Osipov, Mikhail A

2015-02-07

Scientists aspire to understand the underlying physics behind the formation of instabilities in soft matter and how to manipulate them for diverse investigations, while engineers aim to design materials that inhibit or impede the nucleation and growth of these instabilities in critical applications. The present paper reviews the field-induced rotational instabilities which may occur in chiral smectic liquid-crystalline layers when subjected to an asymmetric electric field. Such instabilities destroy the so-named bookshelf geometry (in which the smectic layers are normal to the cell surfaces) and have a detrimental effect on all applications of ferroelectric liquid crystals as optical materials. The transformation of the bookshelf geometry into horizontal chevron structures (in which each layer is in a V-shaped structure), and the reorientation dynamics of these chevrons, are discussed in details with respect to the electric field conditions, the material properties and the boundary conditions. Particular attention is given to the polymer-stabilisation of smectic phases as a way to forbid the occurrence of instabilities and the decline of related electro-optical performances. It is also shown which benefit may be gained from layer instabilities to enhance the alignment of the liquid-crystalline geometry in practical devices, such as optical recording by ferroelectric liquid crystals. Finally, the theoretical background of layer instabilities is given and discussed in relation to the experimental data.

Synthesis, crystal structure, and magnetic properties of novel intermetallic compounds R2Co2SiC (R = Pr, Nd).

PubMed

Zhou, Sixuan; Mishra, Trinath; Wang, Man; Shatruk, Michael; Cao, Huibo; Latturner, Susan E

2014-06-16

The intermetallic compounds R2Co2SiC (R = Pr, Nd) were prepared from the reaction of silicon and carbon in either Pr/Co or Nd/Co eutectic flux. These phases crystallize with a new stuffed variant of the W2CoB2 structure type in orthorhombic space group Immm with unit cell parameters a = 3.978(4) Å, b = 6.094(5) Å, c = 8.903(8) Å (Z = 2; R1 = 0.0302) for Nd2Co2SiC. Silicon, cobalt, and carbon atoms form two-dimensional flat sheets, which are separated by puckered layers of rare-earth cations. Magnetic susceptibility measurements indicate that the rare earth cations in both analogues order ferromagnetically at low temperature (TC ≈ 12 K for Nd2Co2SiC and TC ≈ 20 K for Pr2Co2SiC). Single-crystal neutron diffraction data for Nd2Co2SiC indicate that Nd moments initially align ferromagnetically along the c axis around ∼12 K, but below 11 K, they tilt slightly away from the c axis, in the ac plane. Electronic structure calculations confirm the lack of spin polarization for Co 3d moments.

Fiber optic sensor system for detecting movement or position of a rotating wheel bearing

DOEpatents

Veeser, Lynn R.; Rodriguez, Patrick J.; Forman, Peter R.; Monahan, Russell E.; Adler, Jonathan M.

1997-01-01

An improved fiber optic sensor system and integrated sensor bearing assembly for detecting movement or position of a rotating wheel bearing having a multi-pole tone ring which produces an alternating magnetic field indicative of movement and position of the rotating member. A magneto-optical material, such as a bismuth garnet iron (B.I.G.) crystal, having discrete magnetic domains is positioned in the vicinity of the tone ring so that the domains align themselves to the magnetic field generated by the tone ring. A single fiber optic cable, preferably single mode fiber, carries light generated by a source of light to the B.I.G. crystal. The light passes through the B.I.G. crystal and is refracted at domain boundaries in the crystal. The intensity of the refracted light is indicative of the amount of alignment of the domains and therefore the strength of the magnetic field. The refracted light is carried by the fiber optic cable to an optic receiver where the intensity is measured and an electrical signal is generated and sent to a controller indicating the frequency of the changes in light intensity and therefore the rotational speed of the rotating wheel bearing.

Composite Materials with Magnetically Aligned Carbon Nanoparticles Having Enhanced Electrical Properties and Methods of Preparation

NASA Technical Reports Server (NTRS)

Peterson, G.P. (Bud) (Inventor); Hong, Haiping (Inventor); Salem, David R. (Inventor)

2016-01-01

Magnetically aligned carbon nanoparticle composites have enhanced electrical properties. The composites comprise carbon nanoparticles, a host material, magnetically sensitive nanoparticles and a surfactant. In addition to enhanced electrical properties, the composites can have enhanced mechanical and thermal properties.

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

Ishiyama, Takeshi, E-mail: ishiyama@ee.tut.ac.jp; Nakane, Takaya, E-mail: ishiyama@ee.tut.ac.jp; Fujii, Tsutomu, E-mail: ishiyama@ee.tut.ac.jp

Arrays of single-crystal zinc oxide (ZnO) nanowires have been synthesized on silicon substrates by vapor-liquid-solid growth techniques. The effect of growth conditions including substrate temperature and Ar gas flow rate on growth properties of ZnO nanowire arrays were studied. Structural and optical characterization was performed using scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. SEM images of the ZnO nanowire arrays grown at various Ar gas flow rates indicated that the alignment and structural features of ZnO nanowires were affected by the gas flow rate. The PL of the ZnO nanowire arrays exhibited strong ultraviolet (UV) emission at 380 nmmore » and green emission around 510 nm. Moreover, the green emission reduced in Ga-doped sample.« less

Characterization of an in-vacuum PILATUS 1M detector.

PubMed

Wernecke, Jan; Gollwitzer, Christian; Müller, Peter; Krumrey, Michael

2014-05-01

A dedicated in-vacuum X-ray detector based on the hybrid pixel PILATUS 1M detector has been installed at the four-crystal monochromator beamline of the PTB at the electron storage ring BESSY II in Berlin, Germany. Owing to its windowless operation, the detector can be used in the entire photon energy range of the beamline from 10 keV down to 1.75 keV for small-angle X-ray scattering (SAXS) experiments and anomalous SAXS at absorption edges of light elements. The radiometric and geometric properties of the detector such as quantum efficiency, pixel pitch and module alignment have been determined with low uncertainties. The first grazing-incidence SAXS results demonstrate the superior resolution in momentum transfer achievable at low photon energies.

Electrospun bismuth ferrite nanofibers for potential applications in ferroelectric photovoltaic devices.

PubMed

Fei, Linfeng; Hu, Yongming; Li, Xing; Song, Ruobing; Sun, Li; Huang, Haitao; Gu, Haoshuang; Chan, Helen L W; Wang, Yu

2015-02-18

Bismuth ferrite (BFO) nanofibers were synthesized via a sol-gel-based electrospinning process followed by thermal treatment. The influences of processing conditions on the final structure of the samples were investigated. Nanofibers prepared under optimized conditions were found to have a perovskite structure with good quality of crystallization and free of impurity phase. Ferroelectric and piezoelectric responses were obtained from individual nanofiber measured on a piezoelectric force microscope. A prototype photovoltaic device using laterally aligned BFO nanofibers and interdigital electrodes was developed and its performance was examined on a standard photovoltaic system. The BFO nanofibers were found to exhibit an excellent ferroelectric photovoltaic property with the photocurrent several times larger than the literature data obtained on BFO thin films.

Theoretical Studies of Nonuniform Orientational Order in Liquid Crystals and Active Particles

NASA Astrophysics Data System (ADS)

Duzgun, Ayhan

I investigate three systems that exhibit complex patterns in orientational order, which are controlled by geometry interacting with the dynamics of phase transitions, metastability, and activity. 1. Liquid Crystal Elastomers: Liquid-crystal elastomers are remarkable materials that combine the elastic properties of cross-linked polymer networks with the anisotropy of liquid crystals. Any distortion of the polymer network affects the nematic order of the liquid crystal, and, likewise, any change in the magnitude or direction of the nematic order influences the shape of the elastomer. When elastomers are prepared without any alignment, they develop disordered polydomain structures as they are cooled into the nematic phase. To model these polydomain structures, I develop a dynamic theory for the isotropic-nematic transition in elastomers. 2. Active Brownian Particles: Unlike equilibrium systems, active matter is not governed by the conventional laws of thermodynamics. I perform Langevin dynamics simulations and analytic calculations to explore how systems cross over from equilibrium to active behavior as the activity is increased. Based on these results, I calculate how the pressure depends on wall curvature, and hence make analytic predictions for the motion of curved tracers and other effects of confinement in active matter systems. 3. Skyrmions in Liquid Crystals: Skyrmions are localized topological defects in the orientation of an order parameter field, without a singularity in the magnitude of the field. For many years, such defects have been studied in the context of chiral liquid crystals--for example, as bubbles in a confined cholesteric phase or as double-twist tubes in a blue phase. More recently, skyrmions have been investigated extensively in the context of chiral magnets. In this project, I compare skyrmions in chiral liquid crystals with the analogous magnetic defects. Through simulations based on the nematic order tensor, I model both isolated skyrmions and periodic defect lattices.

Mechanical properties and cellular response of novel electrospun nanofibers for ligament tissue engineering: Effects of orientation and geometry.

PubMed

Pauly, Hannah M; Kelly, Daniel J; Popat, Ketul C; Trujillo, Nathan A; Dunne, Nicholas J; McCarthy, Helen O; Haut Donahue, Tammy L

2016-08-01

Electrospun nanofibers are a promising material for ligamentous tissue engineering, however weak mechanical properties of fibers to date have limited their clinical usage. The goal of this work was to modify electrospun nanofibers to create a robust structure that mimics the complex hierarchy of native tendons and ligaments. The scaffolds that were fabricated in this study consisted of either random or aligned nanofibers in flat sheets or rolled nanofiber bundles that mimic the size scale of fascicle units in primarily tensile load bearing soft musculoskeletal tissues. Altering nanofiber orientation and geometry significantly affected mechanical properties; most notably aligned nanofiber sheets had the greatest modulus; 125% higher than that of random nanofiber sheets; and 45% higher than aligned nanofiber bundles. Modifying aligned nanofiber sheets to form aligned nanofiber bundles also resulted in approximately 107% higher yield stresses and 140% higher yield strains. The mechanical properties of aligned nanofiber bundles were in the range of the mechanical properties of the native ACL: modulus=158±32MPa, yield stress=57±23MPa and yield strain=0.38±0.08. Adipose derived stem cells cultured on all surfaces remained viable and proliferated extensively over a 7 day culture period and cells elongated on nanofiber bundles. The results of the study suggest that aligned nanofiber bundles may be useful for ligament and tendon tissue engineering based on their mechanical properties and ability to support cell adhesion, proliferation, and elongation. Copyright © 2016 Elsevier Ltd. All rights reserved.

Liquid crystal devices based on photoalignment and photopatterning materials

NASA Astrophysics Data System (ADS)

Chigrinov, Vladimir

2014-02-01

Liquid crystal (LC) display and photonics devices based on photo-alignment and photo-patterning LC cells are developed. A fast switchable grating based on ferroelectric liquid crystals and orthogonal planar alignment by means of photo alignments. Both 1D and 2D gratings have been constructed. The proposed diffracting element provides fast response time of around 20 μs, contrast of 7000:1 and high diffraction efficiency, at the electric field of 6V/μm. A switchable LC Fresnel zone lens was also developed with the efficiency of ~42% that can be further improved, and the switching time for the 3 μm thick cell is ~6.7 ms which is relatively fast in comparison of existing devices. Thus, because of the photoalignment technology the fabrication of Fresnel lens became considerably simpler than others. A thin high spatial resolution, photo-patterned micropolarizer array for complementary metal-oxide-semiconductor (CMOS) image sensors was implemented for the complete optical visualization of so called "invisible" objects, which are completely transparent (reflective) and colorless. Four Stokes parameters, which fully characterized the reflected light beam can be simultaneously detected using the array of photo-patterned polarizers on CMOS sensor plate. The cheap, high resolution photo-patterned LC matrix sensor was developed to be able successfully compete with the expensive and low reliable wire grid polarizer patterned arrays currently used for the purpose.

Seismic anisotropy in the Earth's innermost inner core: Testing structural models against mineral physics predictions

DOE PAGES

Romanowicz, Barbara; Cao, Aimin; Godwal, Budhiram; ...

2016-01-06

Using an updated data set of ballistic PKIKP travel time data at antipodal distances, we test different models of anisotropy in the Earth's innermost inner core (IMIC) and obtain significantly better fits for a fast axis aligned with Earth's rotation axis, rather than a quasi-equatorial direction, as proposed recently. Reviewing recent results on the single crystal structure and elasticity of iron at core conditions, we find that an hcp structure with the fast c axis parallel to Earth's rotation is more likely but a body-centered cubic structure with the [111] axis aligned in that direction results in very similar predictionsmore » for seismic anisotropy. These models are therefore not distinguishable based on current seismological data. In addition, to match the seismological observations, the inferred strength of anisotropy in the IMIC (6–7%) implies almost perfect alignment of iron crystals, an intriguing, albeit unlikely situation, especially in the presence of heterogeneity, which calls for further studies. Fast axis of anisotropy in the central part of the inner core aligned with Earth's axis of rotation Lastly, the structure of iron in the inner core is most likely hcp, not bcc Not currently possible to distinguish between hcp and bcc structures from seismic observations« less

A mean-field theory for self-propelled particles interacting by velocity alignment mechanisms

NASA Astrophysics Data System (ADS)

Peruani, F.; Deutsch, A.; Bär, M.

2008-04-01

A mean-field approach (MFA) is proposed for the analysis of orientational order in a two-dimensional system of stochastic self-propelled particles interacting by local velocity alignment mechanism. The treatment is applied to the cases of ferromagnetic (F) and liquid-crystal (LC) alignment. In both cases, MFA yields a second order phase transition for a critical noise strength and a scaling exponent of 1/2 for the respective order parameters. We find that the critical noise amplitude ηc at which orientational order emerges in the LC case is smaller than in the F-alignment case, i.e. ηLC C<ηF C. A comparison with simulations of individual-based models with F- resp. LC-alignment shows that the predictions about the critical behavior and the qualitative relation between the respective critical noise amplitudes are correct.

New colored optical security elements using Rolic's LPP/LCP technology: devices for first- to third-level inspection

NASA Astrophysics Data System (ADS)

Moia, Franco

2002-04-01

With linear photo-polymerization (LPP) ROLIC has invented a photo-patternable technology enabling to align not only conventional liquid crystals but also liquid crystals polymers (LCP). ROLIC's optical security device technology derives from its LPP/LCP technology. LPP/LCP security devices are created by structured photo-alignment of an LPP layer through phot-masks, thus generating a high resolution, photo-patterned aligning layer which carries the aligning information of the image to be created. The subsequent LCP layer transforms the aligning information into an optical phase image with low and/or very high information content, such as invisible photographic pictures. The building block capability of the LPP/LCP technology allows the manufacturing of cholesteric and non-cholesteric LPP/LCP devices which cover 1st and/or 2nd level applications. Apart from black/white security devices colored information zones can be integrated. Moreover, we have developed an LPP/LCP security device which covers all three- 1st, 2nd and 3rd- inspection levels in one and the same authentication device: besides a color shift by tilting the device (1st level) and the detection of normally hidden information by use of a simple sheet polarizer (2nd level) the new device contains encrypted hidden information which can be visualized only by superimposing an LPP/LCP inspection tool (key) for decryption (3rd level). This optical key is also based on the LPP/LCP technology and is itself a 3rd level security device.

Current progress and technical challenges of flexible liquid crystal displays

NASA Astrophysics Data System (ADS)

Fujikake, Hideo; Sato, Hiroto

2009-02-01

We focused on several technical approaches to flexible liquid crystal (LC) display in this report. We have been developing flexible displays using plastic film substrates based on polymer-dispersed LC technology with molecular alignment control. In our representative devices, molecular-aligned polymer walls keep plastic-substrate gap constant without LC alignment disorder, and aligned polymer networks create monostable switching of fast-response ferroelectric LC (FLC) for grayscale capability. In the fabrication process, a high-viscosity FLC/monomer solution was printed, sandwiched and pressed between plastic substrates. Then the polymer walls and networks were sequentially formed based on photo-polymerization-induced phase separation in the nematic phase by two exposure processes of patterned and uniform ultraviolet light. The two flexible backlight films of direct illumination and light-guide methods using small three-primary-color light-emitting diodes were fabricated to obtain high-visibility display images. The fabricated flexible FLC panels were driven by external transistor arrays, internal organic thin film transistor (TFT) arrays, and poly-Si TFT arrays. We achieved full-color moving-image displays using the flexible FLC panel and the flexible backlight film based on field-sequential-color driving technique. Otherwise, for backlight-free flexible LC displays, flexible reflective devices of twisted guest-host nematic LC and cholesteric LC were discussed with molecular-aligned polymer walls. Singlesubstrate device structure and fabrication method using self-standing polymer-stabilized nematic LC film and polymer ceiling layer were also proposed for obtaining LC devices with excellent flexibility.

Utilizing Structures of CYP2D6 and BACE1 Complexes To Reduce Risk of Drug–Drug Interactions with a Novel Series of Centrally Efficacious BACE1 Inhibitors

PubMed Central

2016-01-01

In recent years, the first generation of β-secretase (BACE1) inhibitors advanced into clinical development for the treatment of Alzheimer’s disease (AD). However, the alignment of drug-like properties and selectivity remains a major challenge. Herein, we describe the discovery of a novel class of potent, low clearance, CNS penetrant BACE1 inhibitors represented by thioamidine 5. Further profiling suggested that a high fraction of the metabolism (>95%) was due to CYP2D6, increasing the potential risk for victim-based drug–drug interactions (DDI) and variable exposure in the clinic due to the polymorphic nature of this enzyme. To guide future design, we solved crystal structures of CYP2D6 complexes with substrate 5 and its corresponding metabolic product pyrazole 6, which provided insight into the binding mode and movements between substrate/inhibitor complexes. Guided by the BACE1 and CYP2D6 crystal structures, we designed and synthesized analogues with reduced risk for DDI, central efficacy, and improved hERG therapeutic margins. PMID:25781223

Highly Polarized Fluorescent Illumination Using Liquid Crystal Phase.

PubMed

Gim, Min-Jun; Turlapati, Srikanth; Debnath, Somen; Rao, Nandiraju V S; Yoon, Dong Ki

2016-02-10

Liquid crystal (LC) materials are currently the dominant electronic materials in display technology because of the ease of control of molecular orientation using an electric field. However, this technology requires the fabrication of two polarizers to create operational displays, reducing light transmission efficiency below 10%. It is therefore desirable to develop new technologies to enhance the light efficiency while maintaining or improving other properties such as the modulation speed of the molecular orientation. Here we report a uniaxial-oriented B7 smectic liquid crystalline film, using fluorescent bent-core LC molecules, a chemically modified substrate, and an in-plane electric field. A LC droplet under homeotropic boundary conditions of air/LC as well as LC/substrate exhibits large focal conic like optical textures. The in-plane electric field induced uniaxial orientation of the LC molecules, in which molecular polar directors are aligned in the direction of the electric field. This highly oriented LC film exhibits linearly polarized luminescence and microsecond time-scale modulation characteristics. The resultant device is both cheap and easy to fabricate and thus has great potential for electro-optic applications, including LC displays, bioimaging systems, and optical communications.

Confocal Raman microscopy of one dimensional ZnO nanostructures

NASA Astrophysics Data System (ADS)

Singamaneni, Srikanth; Gupta, Maneesh; Yang, Rusen; Wang, Zhong; Tsukruk, Vladimir

2009-03-01

ZnO nanostructures with various shapes (vertically aligned nanorods, nanobelts, nanohelixes, nanorings) have been synthesized using both vapor phase and solution growth methods. In the simplest example of a nanobelt, the fast growth direction can be either (21 1 0) or (011 0) or (0001). Here, we show that confocal Raman microscopy can be employed as a fast and nondestructive analytical technique to identify the crystal planes and reveal the relative orientation of the ZnO nanostructure. Various features of the Raman spectrum of ZnO nanostructures (presence of the A1(TO) mode, width of the E2 mode) were found to be sensitive to relative orientation of the incident source laser and the crystal plane. Furthermore, owing to the optical anisotropy of ZnO, Raman scattering from the substrate is modulated (either enhanced or suppressed with respect to the background) depending on the polarization of the incident light with respect to orientation of the nanobelt. The results presented here describe a novel method to nondestructively identify the growth, relative orientation, and the waveguiding properties of the ZnO nanostructures.

Nematic-like stable glasses without equilibrium liquid crystal phases

DOE Data Explorer

Gomez, Jaritza [Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA; Gujral, Ankit [Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA; Huang, Chengbin [School of Pharmacy, University of Wisconsin-Madison, 777 Highland Avenue, Madison, Wisconsin 53705-2222, USA; Bishop, Camille [Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA; Yu, Lian [School of Pharmacy, University of Wisconsin-Madison, 777 Highland Avenue, Madison, Wisconsin 53705-2222, USA; Ediger, Mark [Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA

2017-02-01

We report the thermal and structural properties of glasses of posaconazole, a rod-like molecule, prepared using physical vapor deposition (PVD). PVD glasses of posaconazole can show substantial molecular orientation depending upon the choice of substrate temperature, Tsubstrate, during deposition.Ellipsometry and IR measurements indicate that glasses prepared at Tsubstrate very near the glass transition temperature (Tg) are highly ordered. For these posaconazole glasses, the orientation order parameter is similar to that observed in macroscopically aligned nematic liquid crystals, indicating that the molecules are mostly parallel to one another and perpendicular to the interface. To our knowledge, these are the most anisotropic glasses ever prepared by PVD from a molecule that does not form equilibrium liquid crystal phases. These results are consistent with a previously proposed mechanism in which molecular orientation in PVD glasses is inherited from the orientation present at the free surface of the equilibrium liquid. This mechanism suggests that molecular orientation at the surface of the equilibrium liquid of posaconazole is nematic-like. Posaconazole glasses can show very high kinetic stability; the isothermal transformation of a 400 nm glass into the supercooled liquid occurs via a propagating front that originates at the free surface and requires ~105 times the structural relaxation time of the liquid (τα). We also studied the kinetic stability of PVD glasses of itraconazole, which is a structurally similar molecule with equilibrium liquid crystal phases. While itraconazole glasses can be even more anisotropic than posaconazole glasses, they exhibit lower kinetic stability.

Neutron diffraction from aligned stacks of lipid bilayers using the WAND instrument

DOE PAGES

Marquardt, Drew; Frontzek, Matthias D.; Zhao, Yu; ...

2018-02-06

Neutron diffraction from aligned stacks of lipid bilayers is examined using the Wide-Angle Neutron Diffractometer (WAND), located at the High Flux Isotope Reactor, Oak Ridge, Tennessee, USA. Data were collected at different levels of hydration and neutron contrast by varying the relative humidity (RH) and H 2O/D 2O ratio from multi-bilayers of dioleoylphosphatidylcholine and sunflower phosphatidylcholine extract aligned on single-crystal silicon substrates. This work highlights the capabilites of a newly fabricated sample hydration cell, which allows the lipid bilayers to be hydrated with varying H/D ratios from the RH generated by saturated salt solutions, and also demonstrates WAND's capability asmore » an instrument suitable for the study of aligned lipid multi-bilayers.« less

Neutron diffraction from aligned stacks of lipid bilayers using the WAND instrument

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

Marquardt, Drew; Frontzek, Matthias D.; Zhao, Yu

Neutron diffraction from aligned stacks of lipid bilayers is examined using the Wide-Angle Neutron Diffractometer (WAND), located at the High Flux Isotope Reactor, Oak Ridge, Tennessee, USA. Data were collected at different levels of hydration and neutron contrast by varying the relative humidity (RH) and H 2O/D 2O ratio from multi-bilayers of dioleoylphosphatidylcholine and sunflower phosphatidylcholine extract aligned on single-crystal silicon substrates. This work highlights the capabilites of a newly fabricated sample hydration cell, which allows the lipid bilayers to be hydrated with varying H/D ratios from the RH generated by saturated salt solutions, and also demonstrates WAND's capability asmore » an instrument suitable for the study of aligned lipid multi-bilayers.« less

Guided growth of large-scale, horizontally aligned arrays of single-walled carbon nanotubes and their use in thin-film transistors.

PubMed

Kocabas, Coskun; Hur, Seung-Hyun; Gaur, Anshu; Meitl, Matthew A; Shim, Moonsub; Rogers, John A

2005-11-01

A convenient process for generating large-scale, horizontally aligned arrays of pristine, single-walled carbon nanotubes (SWNTs) is described. The approach uses guided growth, by chemical vapor deposition (CVD), of SWNTs on miscut single-crystal quartz substrates. Studies of the growth reveal important relationships between the density and alignment of the tubes, the CVD conditions, and the morphology of the quartz. Electrodes and dielectrics patterned on top of these arrays yield thin-film transistors that use the SWNTs as effective thin-film semiconductors. The ability to build high-performance devices of this type suggests significant promise for large-scale aligned arrays of SWNTs in electronics, sensors, and other applications.

12-GHz thin-film transistors on transferrable silicon nanomembranes for high-performance flexible electronics.

PubMed

Sun, Lei; Qin, Guoxuan; Seo, Jung-Hun; Celler, George K; Zhou, Weidong; Ma, Zhenqiang

2010-11-22

Multigigahertz flexible electronics are attractive and have broad applications. A gate-after-source/drain fabrication process using preselectively doped single-crystal silicon nanomembranes (SiNM) is an effective approach to realizing high device speed. However, further downscaling this approach has become difficult in lithography alignment. In this full paper, a local alignment scheme in combination with more accurate SiNM transfer measures for minimizing alignment errors is reported. By realizing 1 μm channel alignment for the SiNMs on a soft plastic substrate, thin-film transistors with a record speed of 12 GHz maximum oscillation frequency are demonstrated. These results indicate the great potential of properly processed SiNMs for high-performance flexible electronics.

Self-assembled structures of Gaussian nematic particles.

PubMed

Nikoubashman, Arash; Likos, Christos N

2010-03-17

We investigate the stable crystalline configurations of a nematic liquid crystal made of soft parallel ellipsoidal particles interacting via a repulsive, anisotropic Gaussian potential. For this purpose, we use genetic algorithms (GA) in order to predict all relevant and possible solid phase candidates into which this fluid can freeze. Subsequently we present and discuss the emerging novel structures and the resulting zero-temperature phase diagram of this system. The latter features a variety of crystalline arrangements, in which the elongated Gaussian particles in general do not align with any one of the high-symmetry crystallographic directions, a compromise arising from the interplay and competition between anisotropic repulsions and crystal ordering. Only at very strong degrees of elongation does a tendency of the Gaussian nematics to align with the longest axis of the elementary unit cell emerge.

Continuous diffraction of molecules and disordered molecular crystals

PubMed Central

Yefanov, Oleksandr M.; Ayyer, Kartik; White, Thomas A.; Barty, Anton; Morgan, Andrew; Mariani, Valerio; Oberthuer, Dominik; Pande, Kanupriya

2017-01-01

The intensities of far-field diffraction patterns of orientationally aligned molecules obey Wilson statistics, whether those molecules are in isolation (giving rise to a continuous diffraction pattern) or arranged in a crystal (giving rise to Bragg peaks). Ensembles of molecules in several orientations, but uncorrelated in position, give rise to the incoherent sum of the diffraction from those objects, modifying the statistics in a similar way as crystal twinning modifies the distribution of Bragg intensities. This situation arises in the continuous diffraction of laser-aligned molecules or translationally disordered molecular crystals. This paper develops the analysis of the intensity statistics of such continuous diffraction to obtain parameters such as scaling, beam coherence and the number of contributing independent object orientations. When measured, continuous molecular diffraction is generally weak and accompanied by a background that far exceeds the strength of the signal. Instead of just relying upon the smallest measured intensities or their mean value to guide the subtraction of the background, it is shown how all measured values can be utilized to estimate the background, noise and signal, by employing a modified ‘noisy Wilson’ distribution that explicitly includes the background. Parameters relating to the background and signal quantities can be estimated from the moments of the measured intensities. The analysis method is demonstrated on previously published continuous diffraction data measured from crystals of photosystem II [Ayyer et al. (2016 ▸), Nature, 530, 202–206]. PMID:28808434

Broadband and polarization reflectors in the lookdown, Selene vomer

PubMed Central

Zhao, Shulei; Brady, Parrish Clawson; Gao, Meng; Etheredge, Robert Ian; Kattawar, George W.; Cummings, Molly E.

2015-01-01

Predator evasion in the open ocean is difficult because there are no objects to hide behind. The silvery surface of fish plays an important role in open water camouflage. Various models have been proposed to account for the broadband reflectance by the fish skin that involve one-dimensional variations in the arrangement of guanine crystal reflectors, yet the three-dimensional organization of these guanine platelets have not been well characterized. Here, we report the three-dimensional organization and the optical properties of integumentary guanine platelets in a silvery marine fish, the lookdown (Selene vomer). Our structural analysis and computational modelling show that stacks of guanine platelets with random yaw angles in the fish skin produce broadband reflectance via colour mixing. Optical axes of the guanine platelets and the collagen layer are aligned closely and provide bulk birefringence properties that influence the polarization reflectance by the skin. These data demonstrate how the lookdown preserves or alters polarization states at different incident polarization angles. These optical properties resulted from the organization of these guanine platelets and the collagen layer may have implications for open ocean camouflage in varying light fields. PMID:25673301

Solution-processed, Self-organized Organic Single Crystal Arrays with Controlled Crystal Orientation

PubMed Central

Kumatani, Akichika; Liu, Chuan; Li, Yun; Darmawan, Peter; Takimiya, Kazuo; Minari, Takeo; Tsukagoshi, Kazuhito

2012-01-01

A facile solution process for the fabrication of organic single crystal semiconductor devices which meets the demand for low-cost and large-area fabrication of high performance electronic devices is demonstrated. In this paper, we develop a bottom-up method which enables direct formation of organic semiconductor single crystals at selected locations with desired orientations. Here oriented growth of one-dimensional organic crystals is achieved by using self-assembly of organic molecules as the driving force to align these crystals in patterned regions. Based upon the self-organized organic single crystals, we fabricate organic field effect transistor arrays which exhibit an average field-effect mobility of 1.1 cm2V−1s−1. This method can be carried out under ambient atmosphere at room temperature, thus particularly promising for production of future plastic electronics. PMID:22563523

Development of Plastic Substrate Technology for Active Matrix Liquid Crystal Displays Final Report CRADA No. TC-761-93

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

Carey, P.; Kamath, H.

Raychem Corporation (RYC) and the Lawrence Livermore National Laboratory (LLNL) conducted a development program with the goal to make rugged, low-cost., high-resolution flat panel displays based on RYC's proprietary Nematic Curvilinear Aligned Phase (NCAP) liquid crystal and LLNL's patented processes for the formation and doping of polycrystalline silicon on low-temperature, flexible, plastic substrates.

Reverse-mode microdroplet liquid crystal display

NASA Astrophysics Data System (ADS)

Ma, Yao-Dong; Wu, Bao Gang; Xu, Gang

1990-04-01

This paper presents the production of the a reverse-mode microdroplet liquid crystal (RMLC) light shutter display. In this unit, the display is formed by a thin polymer film with dispersed liquid crystal microdroplets. The display is light transmissive in the absence of an applied electrical field. The display is converted to a non-transmissive state (i.e. absorbing or scattering) when an electrical field is applied. The "off' and "on" state. of this display are thus exactly opposite to that encountered in "normal-mode" microdroplet liquid crystal display devices such as polymer dispersed liquid crystals (PDLC)15 or Nematic Curvilinear Aligned Phase (NCAP)6. The Reverse Mode Microdroplet Liquid Crystal is obtained by modification of the surface energy of the polymer which encases liquid crystals via reaction of a dopant incorporated inside of the microdroplet during the droplet formation within the inside polymer layer. The liquid crystal used in RMLC is of negative dielectric anisotropy.

Bistable director alignments of nematic liquid crystals confined in frustrated substrates

NASA Astrophysics Data System (ADS)

Araki, Takeaki; Nagura, Jumpei

2017-01-01

We studied in-plane bistable alignments of nematic liquid crystals confined by two frustrated surfaces by means of Monte Carlo simulations of the Lebwohl-Lasher spin model. The surfaces are prepared with orientational checkerboard patterns, on which the director field is locally anchored to be planar yet orthogonal between the neighboring blocks. We found the director field in the bulk tends to be aligned along the diagonal axes of the checkerboard pattern, as reported experimentally [J.-H. Kim et al., Appl. Phys. Lett. 78, 3055 (2001), 10.1063/1.1371246]. The energy barrier between the two stable orientations is increased, when the system is brought to the isotropic-nematic transition temperature. Based on an elastic theory, we found that the bistability is attributed to the spatial modulation of the director field near the frustrated surfaces. As the block size is increased and/or the elastic modulus is reduced, the degree of the director inhomogeneity is increased, enlarging the energy barrier. We also found that the switching rate between the stable states is decreased when the block size is comparable to the cell thickness.

Realization of Multi-Stable Ground States in a Nematic Liquid Crystal by Surface and Electric Field Modification

NASA Astrophysics Data System (ADS)

Gwag, Jin Seog; Kim, Young-Ki; Lee, Chang Hoon; Kim, Jae-Hoon

2015-06-01

Owing to the significant price drop of liquid crystal displays (LCDs) and the efforts to save natural resources, LCDs are even replacing paper to display static images such as price tags and advertising boards. Because of a growing market demand on such devices, the LCD that can be of numerous surface alignments of directors as its ground state, the so-called multi-stable LCD, comes into the limelight due to the great potential for low power consumption. However, the multi-stable LCD with industrial feasibility has not yet been successfully performed. In this paper, we propose a simple and novel configuration for the multi-stable LCD. We demonstrate experimentally and theoretically that a battery of stable surface alignments can be achieved by the field-induced surface dragging effect on an aligning layer with a weak surface anchoring. The simplicity and stability of the proposed system suggest that it is suitable for the multi-stable LCDs to display static images with low power consumption and thus opens applications in various fields.

CAVE: the design of a precision metrology instrument for studying performance of KDP crystals

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

Hibbard, R.L., LLNL

1998-03-30

A device has been developed to measure the frequency conversion performance of large aperture potassium dihydrogen phosphate (KDP) crystals. Third harmonic generation using ICDP is critical to the function of the National Ignition Facility (NIF) laser. The crystals in the converter can be angularly or thermally tuned but are subject to larger aperture inhomogeneities that are functions of growth manufacturing and - mounting. The CAVE (Crystal Alignment Verification Equipment) instrument scans the crystals in a thermally and mechanically controlled environment to determine the local peak tuning angles. The CAVE can then estimate the optimum tuning angle and conversion efficiency overmore » the entire aperture. Coupled with other metrology techniques, the CAVE will help determine which crystal life-cycle components most affect harmonic conversion.« less

Nacre biomineralisation: A review on the mechanisms of crystal nucleation.

PubMed

Nudelman, Fabio

2015-10-01

The wide diversity of biogenic minerals that is found in nature, each with its own morphology, mechanical properties and composition, is remarkable. In order to produce minerals that are optimally adapted for their function, biomineralisation usually occurs under strict cellular control. This control is exerted by specialised proteins and polysaccharides that assemble into a 3-dimensional organic matrix framework, forming a microenvironment where mineral deposition takes place. Molluscs are unique in that they use a striking variety of structural motifs to build their shells, each made of crystals with different morphologies and different calcium carbonate polymorphs. Much of want is known about mollusc shell formation comes from studies on the nacreous layer, or mother-of-pearl. In this review, we discuss two existing models on the nucleation of aragonite crystals during nacre formation: heteroepitaxial nucleation and mineral bridges. The heteroepitaxial nucleation model is based on the identification of chemical functional groups and aragonite-nucleating proteins at the centre of crystal imprints. It proposes that during nacre formation, each aragonite tablet nucleates independently on a nucleation site that is formed by acidic proteins and/or glycoproteins adsorbed on the chitin scaffold. The mineral bridges model is based on the identification of physical connections between the crystals in a stack, which results in a large number of crystals across several layers sharing the same crystallographic orientation. These observations suggest that there is one nucleation event per stack of tablets. Once the first crystal nucleates and reaches the top interlamellar matrix, it continues growing through pores, giving rise to the next layer of nacre, subsequently propagating into a stack. We compare both models and propose that they work in concert to control crystal nucleation in nacre. De novo crystal nucleation has to occur at least once per stack of aligned crystals, and is induced by nucleation sites. We suggest that further growth is controlled both by mineral bridges and nucleation sites. Finally, we discuss the role of amorphous calcium carbonate precursor in nacre formation. Copyright © 2015 Elsevier Ltd. All rights reserved.

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.

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.

Nonlinear Optical Effects in Liquid Crystals.

DTIC Science & Technology

1980-12-10

susceptibilities Lasers , Nematic, Cholesteric, Flexoelectric, Second-harmonic generation 20M AV*--YRAc rR-r, m, revere i It nf le4U7 siad Idsiully byr...samples are irradiated with laser beam at the fundamental frequency. The laser used in a Q-switched Nd-YAG laser . Sample alignment is achieved either...irradiated with laser beam at the fundamental frequency. The laser used is a Q-switched Nd-YAG laser . Sample alignment is achieved either with rubbing

Energetic basis for the molecular-scale organization of bone

DOE PAGES

Tao, Jinhui; Battle, Keith C.; Pan, Haihua; ...

2014-12-24

Here, the remarkable properties of bone derive from a highly organized arrangement of co-aligned nm-scale apatite platelets within a fibrillar collagen matrix. The origin of this arrangement is poorly understood and the crystal structures of hydroxyapatite (HAP) and the non-mineralized collagen fibrils alone do not provide an explanation. Moreover, little is known about collagen-apatite interaction energies, which should strongly influence both the molecular-scale organization and the resulting mechanical properties of the composite. We investigated collagen-mineral interactions by combining dynamic force spectroscopy (DFS) measurements of binding energies with molecular dynamics (MD) simulations of binding and AFM observations of collagen adsorption onmore » single crystals of calcium phosphate for four mineral phases of potential importance in bone formation. In all cases, we observe a strong preferential orientation of collagen binding, but comparison between the observed orientations and TEM analyses native tissues shows only calcium-deficient apatite (CDAP) provides an interface with collagen that is consistent with both. MD simulations predict preferred collagen orientations that agree with observations and results from both MD and DFS reveal large values for the binding energy due to multiple binding sites. These findings reconcile apparent contradictions inherent in a hydroxyapatite or carbonated apatite (CAP) model of bone mineral and provide an energetic rationale for the molecular scale organization of bone.« less

A review on photocatalytic CO2 reduction using perovskite oxide nanomaterials

NASA Astrophysics Data System (ADS)

Zeng, Sheng; Kar, Piyush; Thakur, Ujwal Kumar; Shankar, Karthik

2018-02-01

As the search for efficient catalysts for CO2 photoreduction continues, nanostructured perovskite oxides have emerged as a class of high-performance photocatalytic materials. The perovskite oxide candidates for CO2 photoreduction are primarily nanostructured forms of titanates, niobates, tantalates and cobaltates. These materials form the focus of this review article because they are much sought-after due to their nontoxic nature, adequate chemical stability, and tunable crystal structures, bandgaps and surface energies. As compared to conventional semiconductors and nanomaterial catalysts, nanostructured perovskite oxides also exhibit an extended optical-absorption edge, longer charge carrier lifetimes, and favorable band-alignment with respect to reduction potential of activated CO2 and reduction products of the same. While CO2 reduction product yields of several hundred μmol-1 h-1 are observed with many types of perovskite oxide nanomaterials in stand-alone forms, yield of such quantities are not common with semiconductor nanomaterials of other types. In this review, we present current state-of-the-art synthesis methods to form perovskite oxide nanomaterials, and procedures to engineer their bandgaps. This review also presents a comprehensive summary and discussion on crystal structures, defect distribution, morphologies and electronic properties of the perovskite oxides, and correlation of these properties to CO2 photoreduction performance. This review offers researchers key insights for developing advanced perovskite oxides in order to further improve the yields of CO2 reduction products.

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.

Iron rich low cost superalloys. Ph.D. Thesis. Final Report

NASA Technical Reports Server (NTRS)

Wayne, S. F.

1985-01-01

An iron-rich low-cost superalloy was developed. The alloy, when processed by conventional chill casting, has physical and mechanical properties that compare favorably with existing nickel and cobalt based superalloys while containing significantly lower amounts of strategic elements. Studies were also made on the properties of Cr(20)-Mn(10)-C(3.4)-Fe(bal.), a eutectic alloy processed by chill casting and directional solidification which produced an aligned microstructure consisting of M7C3 fibers in a gamma-Fe matrix. Thermal expansion of the M7C3 (M = Fe, Cr, Mn) carbide lattice was measured up to 800 C and found to be highly anisotropic, with the a-axis being the predominant mode of expansion. Repetitive impact sliding wear experiments performed with the Fe rich eutectic alloy showed that the directionally solidified microstructure greatly improved the alloy's wear resistance as compared to the chill cast microstructure and conventional nickel base superalloys. Studies on the molybdenum cementite phase prove that the crystal structure of the xi phase is not orthorhombic. The crystal structure of the xi phase is made up of octahedra building elements consisting of four Mo and two Fe atoms and trigonal prisms consisting of four Fe and two Mo atoms. The voids are occupied by carbon atoms. The previous chemical formula for the molybdenum cementite MoFe2C is now clearly seen to be Mo12Fe22C10.

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.

The ion capturing effect of 5° SiOx alignment films in liquid crystal devices

NASA Astrophysics Data System (ADS)

Huang, Yi; Bos, Philip J.; Bhowmik, Achintya

2010-09-01

We show that SiOx, deposited at 5° to the interior surface of a liquid crystal cell allows for a surprisingly substantial reduction in the ion concentration of liquid crystal devices. We have investigated this effect and found that this type of film, due to its surface morphology, captures ions from the liquid crystal material. Ion adsorption on 5° SiOx film obeys the Langmuir isotherm. Experimental results shown allow estimation of the ion capturing capacity of these films to be more than an order of 10 000/μm2. These types of materials are useful for new types of very low power liquid crystal devices such as e-books.

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.

Annihilation of photochemical reactivity of photo-alignment layer.

PubMed

Hong, S H; Hwang, Y J; Lee, S G; Shin, D M

2008-09-01

The gas-polymer and liquid-polymer interfacial reactions of photosensitive polyimide can annihilate photo-reactive carbon-carbon double bonds, which remain after photo-alignment process. The annihilation processes dramatically affect voltage holding ratio and reorientation of photo-active functional groups. Photochemical dimerizations were identified using UV-visible and FT-IR spectroscopy. Polyimide films containing cinnamate groups were irradiated by linear polarized ultra violet (LPUV) light. Schadt et al. claims that the photo-alignment results from the anisotropy depletion of the cinnamate side chains as a consequence of the (2+2) cycloaddition reactions. The photo-aligned polyimide induces the orientation of nematic liquid crystals perpendicular to the polarization axis. However, the un-reacted photo-sensitive functional groups generate problems such as image sticking and reduced contrast ratio. Voltage holding ratio and photo-fading observed from photo-alignment layer can be dramatically improved by annihilation process of remnant photoreactive groups.

Design of a self-aligned, wide temperature range (300 mK-300 K) atomic force microscope/magnetic force microscope with 10 nm magnetic force microscope resolution

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

Karcı, Özgür; Department of Nanotechnology and Nanomedicine, Hacettepe University, Beytepe, 06800 Ankara; Dede, Münir

We describe the design of a wide temperature range (300 mK-300 K) atomic force microscope/magnetic force microscope with a self-aligned fibre-cantilever mechanism. An alignment chip with alignment groves and a special mechanical design are used to eliminate tedious and time consuming fibre-cantilever alignment procedure for the entire temperature range. A low noise, Michelson fibre interferometer was integrated into the system for measuring deflection of the cantilever. The spectral noise density of the system was measured to be ~12 fm/√Hz at 4.2 K at 3 mW incident optical power. Abrikosov vortices in BSCCO(2212) single crystal sample and a high density hardmore » disk sample were imaged at 10 nm resolution to demonstrate the performance of the system.« less

Deformation effect in the fast neutron total cross section of aligned /sup 59/Co

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

Fasoli, U.; Pavan, P.; Toniolo, D.

1983-05-01

The variation of the total neutron cross section, ..delta..sigma/sub align/, on /sup 59/Co due to nuclear alignment of the target has been measured over the energy range from 0.8 to 20 MeV employing a cobalt single crystal with a 34% nuclear alignment. The results show that ..delta..sigma/sub align/ oscillates from a minimum of -5% at about 2.5 MeV to a maximum of +1% at about 10 MeV. The data were successfully fitted by optical model coupled-channel calculations. The coupling terms were deduced from a model representing the /sup 59/Co nucleus as a vibrational /sup 60/Ni core coupled to a protonmore » hole in a (1f/sub 7/2/) shell, without free parameters. The optical model parameters were determined by fitting the total cross section, which was independently measured. The theoretical calculations show that, at lower energies, ..delta..sigma/sub align/ depends appreciably on the coupling with the low-lying levels.« less

Dynamical Properties of Transient Spatio-Temporal Patterns in Bacterial Colony of Proteus mirabilis

NASA Astrophysics Data System (ADS)

Watanabe, Kazuhiko; Wakita, Jun-ichi; Itoh, Hiroto; Shimada, Hirotoshi; Kurosu, Sayuri; Ikeda, Takemasa; Yamazaki, Yoshihiro; Matsuyama, Tohey; Matsushita, Mitsugu

2002-02-01

Spatio-temporal patterns emerged inside a colony of bacterial species Proteus mirabilis on the surface of nutrient-rich semisolid agar medium have been investigated. We observed various patterns composed of the following basic types: propagating stripe, propagating stripe with fixed dislocation, expanding and shrinking target, and rotating spiral. The remarkable point is that the pattern changes immediately when we alter the position for observation, but it returns to the original if we restore the observing position within a few minutes. We further investigated mesoscopic and microscopic properties of the spatio-temporal patterns. It turned out that whenever the spatio-temporal patterns are observed in a colony, the areas are composed of two superimposed monolayers of elongated bacterial cells. In each area they are aligned almost parallel with each other like a two-dimensional nematic liquid crystal, and move collectively and independently of another layer. It has been found that the observed spatio-temporal patterns are explained as the moiré effect.

Self-aligned Ni-P ohmic contact scheme for silicon solar cells by electroless deposition

NASA Astrophysics Data System (ADS)

Lee, Eun Kyung; Lim, Dong Chan; Lee, Kyu Hwan; Lim, Jae-Hong

2012-08-01

We report a Ni-P metallization scheme for low resistance ohmic contacts to n-type Si for silicon solar cells. As-deposited Ni-P contacts to n-type Si showed a specific contact resistance of 6.42 × 10-4 Ω·cm2. The specific contact resistance decreased with increasing thermal annealing temperature. When the Ni-P contact was annealed at 600°C for 30 min in ambient air, the specific contact resistance was greatly decreased, to 6.37 × 10-5Ω·cm2. The improved ohmic property was attributed to the decrease in the work function due to the formation of Ni-silicides from Ni in-diffusion during the thermal annealing process. Effects of the annealing process on the electrical and crystal properties of the contacts were investigated by means of various resistivity measurements (circular transmission line method (c-TLM), 4-point probe), glancing angle x-ray diffraction (GAXRD), and x-ray photoelectron spectroscopy (XPS).

Textured silicon nitride: processing and anisotropic properties

PubMed Central

Zhu, Xinwen; Sakka, Yoshio

2008-01-01

Textured silicon nitride (Si3N4) has been intensively studied over the past 15 years because of its use for achieving its superthermal and mechanical properties. In this review we present the fundamental aspects of the processing and anisotropic properties of textured Si3N4, with emphasis on the anisotropic and abnormal grain growth of β-Si3N4, texture structure and texture analysis, processing methods and anisotropic properties. On the basis of the texturing mechanisms, the processing methods described in this article have been classified into two types: hot-working (HW) and templated grain growth (TGG). The HW method includes the hot-pressing, hot-forging and sinter-forging techniques, and the TGG method includes the cold-pressing, extrusion, tape-casting and strong magnetic field alignment techniques for β-Si3N4 seed crystals. Each processing technique is thoroughly discussed in terms of theoretical models and experimental data, including the texturing mechanisms and the factors affecting texture development. Also, methods of synthesizing the rodlike β-Si3N4 single crystals are presented. Various anisotropic properties of textured Si3N4 and their origins are thoroughly described and discussed, such as hardness, elastic modulus, bending strength, fracture toughness, fracture energy, creep behavior, tribological and wear behavior, erosion behavior, contact damage behavior and thermal conductivity. Models are analyzed to determine the thermal anisotropy by considering the intrinsic thermal anisotropy, degree of orientation and various microstructure factors. Textured porous Si3N4 with a unique microstructure composed of oriented elongated β-Si3N4 and anisotropic pores is also described for the first time, with emphasis on its unique mechanical and thermal-mechanical properties. Moreover, as an important related material, textured α-Sialon is also reviewed, because the presence of elongated α-Sialon grains allows the production of textured α-Sialon using the same methods as those used for textured β-Si3N4 and β-Sialon. PMID:27877995

Self-aligned periodic Ni nano dots embedded in nano-oxide layer

NASA Astrophysics Data System (ADS)

Doi, M.; Izumi, M.; Kawasaki, S.; Miyake, K.; Sahashi, M.

The Ni nano constriction dots embedded in the Ta-nano-oxide layer (NOL) was prepared by the ion beam sputtering (IBS) method. After the various conditions of the oxidations, the structural analyses of the NOL were performed by RHEED, AES and in situ STM/AFM observations. From the current image of the conductive AFM for NOL, the periodically aligned metallic dots with the size around 5-10 nm were successfully observed. The mechanism of the formation of the self-organized aligned Ni nano constriction dots is discussed from the standpoint of the grain size, the crystal orientation, the preferred oxidation of Ta at the diffused interface.

A Therapeutic Uricase with Reduced Immunogenicity Risk and Improved Development Properties.

PubMed

Nyborg, Andrew C; Ward, Chris; Zacco, Anna; Chacko, Benoy; Grinberg, Luba; Geoghegan, James C; Bean, Ryan; Wendeler, Michaela; Bartnik, Frank; O'Connor, Ellen; Gruia, Flaviu; Iyer, Vidyashankara; Feng, Hui; Roy, Varnika; Berge, Mark; Miner, Jeffrey N; Wilson, David M; Zhou, Dongmei; Nicholson, Simone; Wilker, Clynn; Wu, Chi Y; Wilson, Susan; Jermutus, Lutz; Wu, Herren; Owen, David A; Osbourn, Jane; Coats, Steven; Baca, Manuel

2016-01-01

Humans and higher primates are unique in that they lack uricase, the enzyme capable of oxidizing uric acid. As a consequence of this enzyme deficiency, humans have high serum uric acid levels. In some people, uric acid levels rise above the solubility limit resulting in crystallization in joints, acute inflammation in response to those crystals causes severe pain; a condition known as gout. Treatment for severe gout includes injection of non-human uricase to reduce serum uric acid levels. Krystexxa® is a hyper-PEGylated pig-baboon chimeric uricase indicated for chronic refractory gout that induces an immunogenic response in 91% of treated patients, including infusion reactions (26%) and anaphylaxis (6.5%). These properties limit its use and effectiveness. An innovative approach has been used to develop a therapeutic uricase with improved properties such as: soluble expression, neutral pH solubility, high E. coli expression level, thermal stability, and excellent activity. More than 200 diverse uricase sequences were aligned to guide protein engineering and reduce putative sequence liabilities. A single uricase lead candidate was identified, which showed low potential for immunogenicity in >200 human donor samples selected to represent diverse HLA haplotypes. Cysteines were engineered into the lead sequence for site specific PEGylation and studies demonstrated >95% PEGylation efficiency. PEGylated uricase retains enzymatic activity in vitro at neutral pH, in human serum and in vivo (rats and canines) and has an extended half-life. In canines, an 85% reduction in serum uric acid levels was observed with a single subcutaneous injection. This PEGylated, non-immunogenic uricase has the potential to provide meaningful benefits to patients with gout.

Production of porous Calcium Phosphate (CaP) ceramics with aligned pores using ceramic/camphene-based co-extrusion.

PubMed

Choi, Won-Young; Kim, Hyoun-Ee; Moon, Young-Wook; Shin, Kwan-Ha; Koh, Young-Hag

2015-01-01

Calcium phosphate (CaP) ceramics are one of the most valuable biomaterials for uses as the bone scaffold owing to their outstanding biocompatability, bioactivity, and biodegradation nature. In particular, these materials with an open porous structure can stimulate bone ingrowth into their 3-dimensionally interconnected pores. However, the creation of pores in bulk materials would inevitably cause a severe reduction in mechanical properties. Thus, it is a challenge to explore new ways of improving the mechanical properties of porous CaP scaffolds without scarifying their high porosity. Porous CaP ceramic scaffolds with aligned pores were successfully produced using ceramic/camphene-based co-extrusion. This aligned porous structure allowed for the achievement of high compressive strength when tested parallel to the direction of aligned pores. In addition, the overall porosity and mechanical properties of the aligned porous CaP ceramic scaffolds could be tailored simply by adjusting the initial CaP content in the CaP/camphene slurry. The porous CaP scaffolds showed excellent in vitro biocompatibility, suggesting their potential as the bone scaffold. Aligned porous CaP ceramic scaffolds with considerably enhanced mechanical properties and tailorable porosity would find very useful applications as the bone scaffold.

Physical vapor deposition as a route to glasses with liquid crystalline order

NASA Astrophysics Data System (ADS)

Gomez, Jaritza

Physical vapor deposition (PVD) is an effective route to prepare glasses with a unique combination of properties. Substrate temperatures near the glass transition (Tg) and slow deposition rates can access enhanced mobility at the surface of the glass allowing molecules at the surface additional time to sample different molecular configurations. The temperature of the substrate can be used to control molecular mobility during deposition and properties in the resulting glasses such as higher density, kinetic stability and preferential molecular orientation. PVD was used to prepare glasses of itraconazole, a smectic A liquid crystal. We characterized molecular orientation using infrared and ellipsometry. Molecular orientation can be controlled by choice of Tsubstrate in a range of temperatures near Tg. Glasses deposited at Tsubstrate = Tg show nearly vertical molecular orientation relative to the substrate; at lower Tsubstrate, molecules are nearly parallel to the substrate. The molecular orientation depends on the temperature of the substrate during preparation and not on the molecular orientation of the underlying layer. This allows preparing samples of layers with differing orientations. We find these glasses are homogeneous solids without evidence of domain boundaries and are molecularly flat. We interpret the combination of properties obtained for vapor-deposited glasses of itraconazole to result from a process where molecular orientation is determined by the structure and dynamics at the free surface of the glass during deposition. We report the thermal and structural properties of glasses prepared using PVD of a rod-like molecule, posaconazole, which does not show equilibrium liquid crystal phases. These glasses show substantial molecular orientation that can be controlled by choice of Tsubstrate during deposition. Ellipsometry and IR indicate that glasses prepared at Tg - 3 K are highly ordered. At these Tsubstrate, molecules show preferential vertical orientation and orientation is similar to that measured in aligned nematic liquid crystal. Our results are consistent with a recently proposed mechanism where molecular orientation in equilibrium liquids can be trapped in PVD glasses and suggest that the orientation at the free surface of posaconazole is nematic-like. In addition, we show posaconazole glasses show high kinetic stability controlled by Tsubstrate.

Rigid Amorphous Fraction in PLA Electrospun Fibers

NASA Astrophysics Data System (ADS)

Cebe, Peggy; Ma, Qian; Simona Cozza, Erika; Pyda, Marek; Mao, Bin; Zhu, Yazhe; Monticelli, Orietta

2013-03-01

Electrospun fibers of poly(lactic acid) (PLA) were formed by adopting a high-speed rotating wheel as the counter-electrode. The molecular orientation, crystallization mechanism, and phase structure and transitions of the aligned ES fibers were investigated. Using thermal analysis and wide angle X-ray scattering (WAXS), we evaluated the confinement that exists in as-spun amorphous, and heat-treated semicrystalline, fibers. Differential scanning calorimetry confirmed the existence of a constrained amorphous phase in as-spun aligned fibers, without the presence of crystals or fillers to serve as fixed physical constraints. Using WAXS, for the first time the mesophase fraction, consisting of oriented amorphous PLA chains, was quantitatively characterized in nanofibers. The authors acknowledge support from the National Science Foundation, Polymers Program under grant DMR-0602473. ESC acknowledges a Ph.D. grant supported by Italian Ministry of Education and Scientific Research.

A novel self-aligned oxygen (SALOX) implanted SOI MOSFET device structure

NASA Astrophysics Data System (ADS)

Tzeng, J. C.; Baerg, W.; Ting, C.; Siu, B.

The morphology of the novel self-aligned oxygen implanted SOI (SALOX SOI) [1] MOSFET was studied. The channel silicon of SALOX SOI was confirmed to be undamaged single crystal silicon and was connected with the substrate. Buried oxide formed by oxygen implantation in this SALOX SOI structure was shown by a cross section transmission electron micrograph (X-TEM) to be amorphous. The source/drain silicon on top of the buried oxide was single crystal, as shown by the transmission electron diffraction (TED) pattern. The source/drain regions were elevated due to the buried oxide volume expansion. A sharp silicon—silicon dioxide interface between the source/drain silicon and buried oxide was observed by Auger electron spectroscopy (AES). Well behaved n-MOS transistor current voltage characteristics were obtained and showed no I-V kink.

Tuning thermal conductivity in molybdenum disulfide by electrochemical intercalation

PubMed Central

Zhu, Gaohua; Liu, Jun; Zheng, Qiye; Zhang, Ruigang; Li, Dongyao; Banerjee, Debasish; Cahill, David G.

2016-01-01

Thermal conductivity of two-dimensional (2D) materials is of interest for energy storage, nanoelectronics and optoelectronics. Here, we report that the thermal conductivity of molybdenum disulfide can be modified by electrochemical intercalation. We observe distinct behaviour for thin films with vertically aligned basal planes and natural bulk crystals with basal planes aligned parallel to the surface. The thermal conductivity is measured as a function of the degree of lithiation, using time-domain thermoreflectance. The change of thermal conductivity correlates with the lithiation-induced structural and compositional disorder. We further show that the ratio of the in-plane to through-plane thermal conductivity of bulk crystal is enhanced by the disorder. These results suggest that stacking disorder and mixture of phases is an effective mechanism to modify the anisotropic thermal conductivity of 2D materials. PMID:27767030

Tunable two-dimensional photonic crystals using liquid crystal infiltration

NASA Astrophysics Data System (ADS)

Leonard, S. W.; Mondia, J. P.; van Driel, H. M.; Toader, O.; John, S.; Busch, K.; Birner, A.; Gösele, U.; Lehmann, V.

2000-01-01

The photonic band gap of a two-dimensional photonic crystal is continuously tuned using the temperature dependent refractive index of a liquid crystal. Liquid crystal E7 was infiltrated into the air pores of a macroporous silicon photonic crystal with a triangular lattice pitch of 1.58 μm and a band gap wavelength range of 3.3-5.7 μm. After infiltration, the band gap for the H polarized field shifted dramatically to 4.4-6.0 μm while that of the E-polarized field collapsed. As the sample was heated to the nematic-isotropic phase transition temperature of the liquid crystal (59 °C), the short-wavelength band edge of the H gap shifted by as much as 70 nm while the long-wavelength edge was constant within experimental error. Band structure calculations incorporating the temperature dependence of the liquid crystal birefringence can account for our results and also point to an escaped-radial alignment of the liquid crystal in the nematic phase.

Experimental characterization of a F/1.5 geometric-phase lens with high-achromatic efficiency and low aberration

NASA Astrophysics Data System (ADS)

Hornburg, Kathryn J.; Kim, Jihwan; Escuti, Michael J.

2017-02-01

We report on the properties of a fast F/1.5 geometric-phase lens with a focal length of 37 mm at 633 nm and a 24.5 mm diameter. This lens employs photo-aligned liquid crystal layers to implement the spatially varying Pancharatnam-Berry phase, leading to the expected polarization- and wavelength-dependent focusing. An achromatic spectrum is achieved using (chiral nematic) multi-twist retarder coatings, with high first-order (>=98%) and low zero-order (<=1%) transmittance across 450-700 nm. We measure traditional optical metrics of the GP lens including focused spot profile and modulation transfer function through knife edge testing and NBS 1963a resolution charts. This work includes a comparison to similar F/# conventional thick and thin lenses.

Positron Interactions with Oriented Polymers and with Chiral Quartz Crystals

NASA Astrophysics Data System (ADS)

Wu, Fei

Positron annihilation in various materials has been applied to characterize microstructure for decades. In this work, PALS was used to study material nanostructure, with a focus on the size and density of free volume and hole relaxation properties in polycarbonate (PC) and polymethylmethacrylate (PMMA); fundamental studies of polarized positron interaction with chiral crystals were also studied. Free volume relaxation in PC and PMMA with different levels of simple shear orientation was studied by PALS. Effects of applied pressure on the free volume recovery were evaluated. Combining the bulk- and pressure-dependent PALS analyses, the removal of applied pressure led to free-volume relaxation in all samples studied. The alignment of the polymer chains and free-volume holes imposes molecular restrictions on the molecular mobility of both PC and PMMA in their glassy states. Results indicated that the relaxation of the free volume holes at temperatures below glass transition is mostly reversible. Longitudinally polarized positron particles were used to reveal asymmetric interactions in chiral quartz crystals. Experimental results showed a significant intensity difference in free positronium annihilation for left handed (LH) and right handed (RH) chiral quartz crystals. Doppler broadening energy spectra (DBES) of z-cut LH or RH quartz disks at different angles were also measured by an "S parameter" to probe the observed difference. It was found that obtained annihilation energy difference of DBES was in agreement with the result of positron annihilation in bulk chiral crystals. PALS was used to compare different orientations and confirm asymmetric interactions in natural versus synthetic quartz LH and RH crystals in z and non-z orientations. Significant lifetime and intensity differences in free positronium annihilation for LH and RH quartz crystals were observed. The trend was found to be same in the related crystallographic orientations of the LH or RH crystals; the direction of incident positrons, z or non-z, did not affect the observed differences in lifetime and intensity trends. The results confirmed the existence of differential interactions of positronium with the asymmetric lattice structures of LH and RH quartz crystals.

Crystal nucleation of colloidal hard dumbbells

NASA Astrophysics Data System (ADS)

Ni, Ran; Dijkstra, Marjolein

2011-01-01

Using computer simulations, we investigate the homogeneous crystal nucleation in suspensions of colloidal hard dumbbells. The free energy barriers are determined by Monte Carlo simulations using the umbrella sampling technique. We calculate the nucleation rates for the plastic crystal and the aperiodic crystal phase using the kinetic prefactor as determined from event driven molecular dynamics simulations. We find good agreement with the nucleation rates determined from spontaneous nucleation events observed in event driven molecular dynamics simulations within error bars of one order of magnitude. We study the effect of aspect ratio of the dumbbells on the nucleation of plastic and aperiodic crystal phases, and we also determine the structure of the critical nuclei. Moreover, we find that the nucleation of the aligned close-packed crystal structure is strongly suppressed by a high free energy barrier at low supersaturations and slow dynamics at high supersaturations.

Growth and transfer of monolithic horizontal nanowire superstructures onto flexible substrates

DOEpatents

Wang, Zhong L; Xu, Sheng

2013-08-27

In a method of making a monolithic elongated nanowire, a mask polymer layer is applied to a selected crystal surface of a seed crystal. A plurality of spaced apart elongated openings is defined through the mask polymer layer, thereby exposing a corresponding plurality of portions of the crystal surface. The openings are disposed so as to be aligned with and parallel to a selected crystal axis of the seed crystal. The portions of the crystal surface are subjected to a chemical nutrient environment that causes crystalline material to grow from the plurality of portions for at least a period of time so that monocrystalline members grow from the elongated openings and until the monocrystalline members laterally expand so that each monocrystalline member grows into and merges with an adjacent one of the monocrystalline members, thereby forming a monolithic elongated nanowire.

Mechanisms of lamellar collagen formation in connective tissues.

PubMed

Ghazanfari, Samaneh; Khademhosseini, Ali; Smit, Theodoor H

2016-08-01

The objective of tissue engineering is to regenerate functional tissues. Engineering functional tissues requires an understanding of the mechanisms that guide the formation and evolution of structure in the extracellular matrix (ECM). In particular, the three-dimensional (3D) collagen fiber arrangement is important as it is the key structural determinant that provides mechanical integrity and biological function. In this review, we survey the current knowledge on collagen organization mechanisms that can be applied to create well-structured functional lamellar tissues and in particular intervertebral disc and cornea. Thus far, the mechanisms behind the formation of cross-aligned collagen fibers in the lamellar structures is not fully understood. We start with cell-induced collagen alignment and strain-stabilization behavior mechanisms which can explain a single anisotropically aligned collagen fiber layer. These mechanisms may explain why there is anisotropy in a single layer in the first place. However, they cannot explain why a consecutive collagen layer is laid down with an alternating alignment. Therefore, we explored another mechanism, called liquid crystal phasing. While dense concentrations of collagen show such behavior, there is little evidence that the conditions for liquid crystal phasing are actually met in vivo. Instead, lysyl aldehyde-derived collagen cross-links have been found essential for correct lamellar matrix deposition. Furthermore, we suggest that supra-cellular (tissue-level) shear stress may be instrumental in the alignment of collagen fibers. Understanding the potential mechanisms behind the lamellar collagen structure in connective tissues will lead to further improvement of the regeneration strategies of functional complex lamellar tissues. Copyright © 2016 Elsevier Ltd. All rights reserved.

Measurement of photoluminescence from a twisted-nematic liquid crystal/dye cell for an application in an energy-harvesting display

NASA Astrophysics Data System (ADS)

Ohta, Masamichi; Itaya, Shunsuke; Ozawa, Shintaro; Binti, M. Azmi; Dianah, Nada; Fujieda, Ichiro

2016-09-01

One can convert a Luminescent Solar Concentrator (LSC) to an energy-harvesting display by scanning a laser beam on it. By incorporating a guest-host system of liquid crystal (LC) and dye materials in an LSC, the power of photoluminescence (PL) utilized for either display or energy-harvesting can be adjusted to the changes in ambient lighting conditions. We have measured basic characteristics of an LC/dye cell with twisted-nematic (TN) alignment. These are absorption of the laser light, PL radiation pattern, contrast of luminance, spreading of the PL generated by a narrow laser beam, and their dependencies on the bias. The results are similar to those of the LC/dye cell with antiparallel (AP) alignment with the following exceptions. First, absorption by the TN cell depends on the bias for both polarization components of the excitation light, while the AP cell exhibits a bias dependency only for the component polarized along the alignment direction. Second, the PL from the TN cell is mostly polarized along the alignment direction on the exit side of the cell while the PL from the AP cell is mostly polarized along its alignment direction. These observations can be attributed to the fact that the polarization plane of a linearly polarized light rotates as it propagated the TN-LC layer. For both AP and TN cells, low-intensity PL is observed from the whole cell surfaces. This can degrade the contrast of a displayed image. Bias application to the cell suppresses this effect.

Fabrication of needle-like ZnO nanorods arrays by a low-temperature seed-layer growth approach in solution

NASA Astrophysics Data System (ADS)

Zhang, Haimin; Quan, Xie; Chen, Shuo; Zhao, Huimin

2007-11-01

Uniform, large-scale, and well-aligned needle-like ZnO nanorods with good photoluminescence and photocatalysis properties on Zn substrates, have been successfully fabricated using a simple low-temperature seed-layer growth approach in solution (50 °C). The formation of ZnO seed-layer by the anodic oxidation technique (AOT) plays an important role in the subsequent growth of highly oriented ZnO nanorods arrays. Temperature also proved to be a significant factor in the growth of ZnO nanorods and had a great effect on their optical properties. X-ray diffraction (XRD) analysis, selected-area electron diffraction (SAED) pattern and high-resolution TEM (HRTEM) indicated that the needle-like ZnO nanorods were single crystal in nature and that they had grown up preferentially along the [0001] direction. The well-aligned ZnO nanorods arrays on Zn substrates exhibited strong UV emission at around 380 nm at room temperature. To investigate their potential as photocatalysts, degradation of pentachlorophenol (PCP) in aqueous solution was carried out using photocatalytic processes, with comparison to direct photolysis. After 1 h, the degradation efficiencies of PCP by direct photolysis and photocatalytic processes achieved 57% and 76% under given experimental conditions, respectively. This improved degradation efficiency of PCP illustrates that ZnO nanorods arrays on Zn substrates have good photocatalytic activity. This simple low-temperature seed-layer growth approach in solution resulted in the development of an effective and low-cost fabrication process for high-quality ZnO nanorods arrays with good optical and photocatalytic properties that can be applicable in many fields such as photocatalysis, photovoltaic cells, luminescent sensors, and photoconductive sensors.

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.

All-optical transistor- and diode-action and logic gates based on anisotropic nonlinear responsive liquid crystal

PubMed Central

Wang, Cheng-Yu; Chen, Chun-Wei; Jau, Hung-Chang; Li, Cheng-Chang; Cheng, Chiao-Yu; Wang, Chun-Ta; Leng, Shi-Ee; Khoo, Iam-Choon; Lin, Tsung-Hsien

2016-01-01

In this paper, we show that anisotropic photosensitive nematic liquid crystals (PNLC) made by incorporating anisotropic absorbing dyes are promising candidates for constructing all-optical elements by virtue of the extraordinarily large optical nonlinearity of the nematic host. In particular, we have demonstrated several room-temperature ‘prototype’ PNLC-based all-optical devices such as optical diode, optical transistor and all primary logic gate operations (OR, AND, NOT) based on such optical transistor. Owing to the anisotropic absorption property and the optical activity of the twist alignment nematic cell, spatially non-reciprocal transmission response can be obtained within a sizeable optical isolation region of ~210 mW. Exploiting the same mechanisms, a tri-terminal configuration as an all-optical analogue of a bipolar junction transistor is fabricated. Its ability to be switched by an optical field enables us to realize an all-optical transistor and demonstrate cascadability, signal fan-out, logic restoration, and various logical gate operations such as OR, AND and NOT. Due to the possibility of synthesizing anisotropic dyes and wide ranging choice of liquid crystals nonlinear optical mechanisms, these all-optical operations can be optimized to have much lower thresholds and faster response speeds. The demonstrated capabilities of these devices have shown great potential in all-optical control system and photonic integrated circuits. PMID:27491391

All-optical transistor- and diode-action and logic gates based on anisotropic nonlinear responsive liquid crystal

NASA Astrophysics Data System (ADS)

Wang, Cheng-Yu; Chen, Chun-Wei; Jau, Hung-Chang; Li, Cheng-Chang; Cheng, Chiao-Yu; Wang, Chun-Ta; Leng, Shi-Ee; Khoo, Iam-Choon; Lin, Tsung-Hsien

2016-08-01

In this paper, we show that anisotropic photosensitive nematic liquid crystals (PNLC) made by incorporating anisotropic absorbing dyes are promising candidates for constructing all-optical elements by virtue of the extraordinarily large optical nonlinearity of the nematic host. In particular, we have demonstrated several room-temperature ‘prototype’ PNLC-based all-optical devices such as optical diode, optical transistor and all primary logic gate operations (OR, AND, NOT) based on such optical transistor. Owing to the anisotropic absorption property and the optical activity of the twist alignment nematic cell, spatially non-reciprocal transmission response can be obtained within a sizeable optical isolation region of ~210 mW. Exploiting the same mechanisms, a tri-terminal configuration as an all-optical analogue of a bipolar junction transistor is fabricated. Its ability to be switched by an optical field enables us to realize an all-optical transistor and demonstrate cascadability, signal fan-out, logic restoration, and various logical gate operations such as OR, AND and NOT. Due to the possibility of synthesizing anisotropic dyes and wide ranging choice of liquid crystals nonlinear optical mechanisms, these all-optical operations can be optimized to have much lower thresholds and faster response speeds. The demonstrated capabilities of these devices have shown great potential in all-optical control system and photonic integrated circuits.

All-optical transistor- and diode-action and logic gates based on anisotropic nonlinear responsive liquid crystal.

PubMed

Wang, Cheng-Yu; Chen, Chun-Wei; Jau, Hung-Chang; Li, Cheng-Chang; Cheng, Chiao-Yu; Wang, Chun-Ta; Leng, Shi-Ee; Khoo, Iam-Choon; Lin, Tsung-Hsien

2016-08-05

In this paper, we show that anisotropic photosensitive nematic liquid crystals (PNLC) made by incorporating anisotropic absorbing dyes are promising candidates for constructing all-optical elements by virtue of the extraordinarily large optical nonlinearity of the nematic host. In particular, we have demonstrated several room-temperature 'prototype' PNLC-based all-optical devices such as optical diode, optical transistor and all primary logic gate operations (OR, AND, NOT) based on such optical transistor. Owing to the anisotropic absorption property and the optical activity of the twist alignment nematic cell, spatially non-reciprocal transmission response can be obtained within a sizeable optical isolation region of ~210 mW. Exploiting the same mechanisms, a tri-terminal configuration as an all-optical analogue of a bipolar junction transistor is fabricated. Its ability to be switched by an optical field enables us to realize an all-optical transistor and demonstrate cascadability, signal fan-out, logic restoration, and various logical gate operations such as OR, AND and NOT. Due to the possibility of synthesizing anisotropic dyes and wide ranging choice of liquid crystals nonlinear optical mechanisms, these all-optical operations can be optimized to have much lower thresholds and faster response speeds. The demonstrated capabilities of these devices have shown great potential in all-optical control system and photonic integrated circuits.

Strongly correlated electron behavior in single crystalline U2Os3Al9

NASA Astrophysics Data System (ADS)

Kumar, Neeraj; Das, Pranab Kumar; Kulkarni, Ruta; Thamizhavel, A.; Dhar, S. K.

2012-12-01

We report the magnetic properties of a single crystal of a new compound U2Os3Al9 which crystallizes in the well known Y2Co3Ga9 type orthorhombic structure with space group Cmcm. The susceptibility of U2Os3Al9 shows a peak at 7 K typical of antiferromagnetic ordering. The susceptibility in the paramagnetic state is anisotropic, the easy axis of magnetization lying in the ab-plane of the orthorhombic crystal lattice. The magnetization at 2 K, measured up to a maximum field of 160 kOe, shows a metamagnetic transition near 118 kOe when the field is aligned along [010] in addition to a small metamagnetic transition near 25 kOe. The bulk antiferromagnetic ordering of the uranium ions at TN = 7 K is confirmed by a peak in the heat capacity with ΔC nearly 7 J/U.mol K. An extrapolation of the heat capacity data from the paramagnetic regime to T = 0 gives an enhanced electronic specific heat coefficient of 120 mJ/U.mol K2. The electrical resistivity of U2Os3Al9 shows a negative temperature coefficient between 300 and TN which is a signature of spin fluctuations in a narrow band or a Kondo type of interaction. The data thus suggest the presence of strong electron correlations in this compound.

Chain Ends and the Ultimate Tensile Strength of Polyethylene Fibers

NASA Astrophysics Data System (ADS)

O'Connor, Thomas C.; Robbins, Mark O.

Determining the tensile yield mechanisms of oriented polymer fibers remains a challenging problem in polymer mechanics. By maximizing the alignment and crystallinity of polyethylene (PE) fibers, tensile strengths σ ~ 6 - 7 GPa have been achieved. While impressive, first-principal calculations predict carbon backbone bonds would allow strengths four times higher (σ ~ 20 GPa) before breaking. The reduction in strength is caused by crystal defects like chain ends, which allow fibers to yield by chain slip in addition to bond breaking. We use large scale molecular dynamics (MD) simulations to determine the tensile yield mechanism of orthorhombic PE crystals with finite chains spanning 102 -104 carbons in length. The yield stress σy saturates for long chains at ~ 6 . 3 GPa, agreeing well with experiments. Chains do not break but always yield by slip, after nucleation of 1D dislocations at chain ends. Dislocations are accurately described by a Frenkel-Kontorova model, parametrized by the mechanical properties of an ideal crystal. We compute a dislocation core size ξ = 25 . 24 Å and determine the high and low strain rate limits of σy. Our results suggest characterizing such 1D dislocations is an efficient method for predicting fiber strength. This research was performed within the Center for Materials in Extreme Dynamic Environments (CMEDE) under the Hopkins Extreme Materials Institute at Johns Hopkins University. Financial support was provided by Grant W911NF-12-2-0022.

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.

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

Lee, Kyung Eun; Oh, Jung Jae; Yun, Taeyeong

Graphene is an emerging graphitic carbon materials, consisting of sp{sup 2} hybridized two dimensinal honeycomb structure. It has been widely studied to incorporate graphene with polymer to utilize unique property of graphene and reinforce electrical, mechanical and thermal property of polymer. In composite materials, orientation control of graphene significantly influences the property of composite. Until now, a few method has been developed for orientation control of graphene within polymer matrix. Here, we demonstrate facile fabrication of high aligned large graphene oxide (LGO) composites in polydimethylsiloxane (PDMS) matrix exploiting liquid crystallinity. Liquid crystalline aqueous dispersion of LGO is parallel oriented withinmore » flat confinement geometry. Freeze-drying of the aligned LGO dispersion and subsequent infiltration with PDMS produce highly aligned LGO/PDMS composites. Owing to the large shape anisotropy of LGO, liquid crystalline alignment occurred at low concentration of 2 mg/ml in aqueous dispersion, which leads to the 0.2 wt% LGO loaded composites. - Graphical abstract: Liquid crystalline LGO aqueous dispersions are spontaneous parallel aligned between geometric confinement for highly aligned LGO/polymer composite fabrication. - Highlights: • A simple fabrication method for highly aligned LGO/PDMS composites is proposed. • LGO aqueous dispersion shows nematic liquid crystalline phase at 0.8 mg/ml. • In nematic phase, LGO flakes are highly aligned by geometric confinement. • Infiltration of PDMS into freeze-dried LGO allows highly aligned LGO/PDMS composites.« less

Terahertz spectroscopic analysis of crystal orientation in polymers

NASA Astrophysics Data System (ADS)

Azeyanagi, Chisato; Kaneko, Takuya; Ohki, Yoshimichi

2018-05-01

Terahertz time-domain spectroscopy (THz-TDS) is attracting keen attention as a new spectroscopic tool for characterizing various materials. In this research, the possibility of analyzing the crystal orientation in a crystalline polymer by THz-TDS is investigated by measuring angle-resolved THz absorption spectra for sheets of poly(ethylene terephthalate), poly(ethylene naphthalate), and poly(phenylene sulfide). The resultant angle dependence of the absorption intensity of each polymer is similar to that of the crystal orientation examined using pole figures of X-ray diffraction. More specifically, THz-TDS can indicate the alignment of molecules in polymers.

Fluid Physics

NASA Image and Video Library

2003-05-10

These images, from David Weitz’s liquid crystal research, show ordered uniform sized droplets (upper left) before they are dried from their solution. After the droplets are dried (upper right), they are viewed with crossed polarizers that show the deformation caused by drying, a process that orients the bipolar structure of the liquid crystal within the droplets. When an electric field is applied to the dried droplets (lower left), and then increased (lower right), the liquid crystal within the droplets switches its alignment, thereby reducing the amount of light that can be scattered by the droplets when a beam is shone through them.

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

Cooperative ordering and kinetics of cellulose nanocrystal alignment in a magnetic field

DOE PAGES

De France, Kevin J.; Yager, Kevin G.; Hoare, Todd; ...

2016-07-13

Cellulose nanocrystals (CNCs) are emerging nanomaterials that form chiral nematic liquid crystals above a critical concentration (C*) and additionally orient within electromagnetic fields. The control over CNC alignment is significant for materials processing and end use; to date, magnetic alignment has been demonstrated using only strong fields over extended or arbitrary time scales. This work investigates the effects of comparatively weak magnetic fields (0–1.2 T) and CNC concentration (1.65–8.25 wt %) on the kinetics and degree of CNC ordering using small-angle X-ray scattering. Interparticle spacing, correlation length, and orientation order parameters (η and S) increased with time and field strengthmore » following a sigmoidal profile. In a 1.2 T magnetic field for CNC suspensions above C*, partial alignment occurred in under 2 min followed by slower cooperative ordering to achieve nearly perfect alignment in under 200 min (S = –0.499 where S = –0.5 indicates perfect antialignment). At 0.56 T, nearly perfect alignment was also achieved, yet the ordering was 36% slower. Outside of a magnetic field, the order parameter plateaued at 52% alignment (S = –0.26) after 5 h, showcasing the drastic effects of relatively weak magnetic fields on CNC alignment. For suspensions below C*, no magnetic alignment was detected.« less

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.

Lattice-Matched Semiconductor Layers on Single Crystalline Sapphire Substrate

NASA Technical Reports Server (NTRS)

Choi, Sang; King, Glen; Park, Yeonjoon

2009-01-01

SiGe is an important semiconductor alloy for high-speed field effect transistors (FETs), high-temperature thermoelectric devices, photovoltaic solar cells, and photon detectors. The growth of SiGe layer is difficult because SiGe alloys have different lattice constants from those of the common Si wafers, which leads to a high density of defects, including dislocations, micro-twins, cracks, and delaminations. This innovation utilizes newly developed rhombohedral epitaxy of cubic semiconductors on trigonal substrates in order to solve the lattice mismatch problem of SiGe by using trigonal single crystals like sapphire (Al2O3) as substrate to give a unique growth-orientation to the SiGe layer, which is automatically controlled at the interface upon sapphire (0001). This technology is different from previous silicon on insulator (SOI) or SGOI (SiGe on insulator) technologies that use amorphous SiO2 as the growth plane. A cubic semiconductor crystal is a special case of a rhombohedron with the inter-planar angle, alpha = 90 deg. With a mathematical transformation, all rhombohedrons can be described by trigonal crystal lattice structures. Therefore, all cubic lattice constants and crystal planes (hkl) s can be transformed into those of trigonal crystal parameters. These unique alignments enable a new opportunity of perfect lattice matching conditions, which can eliminate misfit dislocations. Previously, these atomic alignments were thought to be impossible or very difficult. With the invention of a new x-ray diffraction measurement method here, growth of cubic semiconductors on trigonal crystals became possible. This epitaxy and lattice-matching condition can be applied not only to SiGe (111)/sapphire (0001) substrate relations, but also to other crystal structures and other materials, including similar crystal structures which have pointgroup rotational symmetries by 120 because the cubic (111) direction has 120 rotational symmetry. The use of slightly miscut (less than plus or minus 10 deg.) sapphire (0001) substrate can be used to improve epitaxial relationships better by providing attractive atomic steps in the epitaxial process.

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light.

PubMed

Vantomme, Ghislaine; Gelebart, Anne Helene; Broer, Dirk J; Meijer, E W

2017-09-20

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems. The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

Controlled growth of periodically aligned copper-silicide nanocrystal arrays on silicon directed by laser-induced periodic surface structures (LIPSS)

NASA Astrophysics Data System (ADS)

Nürnberger, Philipp; Reinhardt, Hendrik M.; Rhinow, Daniel; Riedel, René; Werner, Simon; Hampp, Norbert A.

2017-10-01

In this paper we introduce a versatile tool for the controlled growth and alignment of copper-silicide nanocrystals. The method takes advantage of a unique self-organization phenomenon denoted as laser-induced periodic surface structures (LIPSS). Copper films (3 ± 0.2 nm) are sputter-deposited onto single crystal silicon (100) substrates with a thin oxide layer (4 ± 0.2 nm), and subsequently exposed to linearly polarized nanosecond laser pulses (τ ≈ 6 ns) at a central wavelength of 532 nm. The irradiation triggers dewetting of the Cu film and simultaneous formation of periodic Cu nanowires (LIPSS), which partially penetrate the oxide layer to the Si substrate. These LIPSS act as nucleation centers for the growth of Cu-Si crystals during thermal processing at 500 °C under forming gas 95/5 atmosphere. Exemplified by our model system Cu/SiO2/Si, LIPSS are demonstrated to facilitate the diffusion reaction between Cu and underlying Si. Moreover, adjustment of the laser polarization allows us to precisely control the nanocrystal alignment with respect to the LIPSS orientation. Potential applications and conceivable alternatives of this process are discussed.

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

PubMed Central

Broer, Dirk J.; Meijer, E. W.

2017-01-01

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems. The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program. PMID:28994766

Self-aligning and compressed autosophy video databases

NASA Astrophysics Data System (ADS)

Holtz, Klaus E.

1993-04-01

Autosophy, an emerging new science, explains `self-assembling structures,' such as crystals or living trees, in mathematical terms. This research provides a new mathematical theory of `learning' and a new `information theory' which permits the growing of self-assembling data network in a computer memory similar to the growing of `data crystals' or `data trees' without data processing or programming. Autosophy databases are educated very much like a human child to organize their own internal data storage. Input patterns, such as written questions or images, are converted to points in a mathematical omni dimensional hyperspace. The input patterns are then associated with output patterns, such as written answers or images. Omni dimensional information storage will result in enormous data compression because each pattern fragment is only stored once. Pattern recognition in the text or image files is greatly simplified by the peculiar omni dimensional storage method. Video databases will absorb input images from a TV camera and associate them with textual information. The `black box' operations are totally self-aligning where the input data will determine their own hyperspace storage locations. Self-aligning autosophy databases may lead to a new generation of brain-like devices.

Numerical study of slip system activity and crystal lattice rotation under wedge nanoindents in tungsten single crystals

NASA Astrophysics Data System (ADS)

Volz, T.; Schwaiger, R.; Wang, J.; Weygand, S. M.

2018-05-01

Tungsten is a promising material for plasma facing components in future nuclear fusion reactors. In the present work, we numerically investigate the deformation behavior of unirradiated tungsten (a body-centered cubic (bcc) single crystal) underneath nanoindents. A finite element (FE) model is presented to simulate wedge indentation. Crystal plasticity finite element (CPFE) simulations were performed for face-centered and body-centered single crystals accounting for the slip system family {110} <111> in the bcc crystal system and the {111} <110> slip family in the fcc system. The 90° wedge indenter was aligned parallel to the [1 ¯01 ]-direction and indented the crystal in the [0 1 ¯0 ]-direction up to a maximum indentation depth of 2 µm. In both, the fcc and bcc single crystals, the activity of slip systems was investigated and compared. Good agreement with the results from former investigations on fcc single crystals was observed. Furthermore, the in-plane lattice rotation in the material underneath an indent was determined and compared for the fcc and bcc single crystals.

Centroid stabilization for laser alignment to corner cubes: designing a matched filter

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

Awwal, Abdul A. S.; Bliss, Erlan; Brunton, Gordon

2016-11-08

Automation of image-based alignment of National Ignition Facility high energy laser beams is providing the capability of executing multiple target shots per day. One important alignment is beam centration through the second and third harmonic generating crystals in the final optics assembly (FOA), which employs two retroreflecting corner cubes as centering references for each beam. Beam-to-beam variations and systematic beam changes over time in the FOA corner cube images can lead to a reduction in accuracy as well as increased convergence durations for the template-based position detector. A systematic approach is described that maintains FOA corner cube templates and guaranteesmore » stable position estimation.« less

Centroid stabilization for laser alignment to corner cubes: designing a matched filter

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

Awwal, Abdul A. S.; Bliss, Erlan; Brunton, Gordon

2016-11-08

Automation of image-based alignment of NIF high energy laser beams is providing the capability of executing multiple target shots per day. One important alignment is beam centration through the second and third harmonic generating crystals in the final optics assembly (FOA), which employs two retro-reflecting corner cubes as centering references for each beam. Beam-to-beam variations and systematic beam changes over time in the FOA corner cube images can lead to a reduction in accuracy as well as increased convergence durations for the template-based position detector. A systematic approach is described that maintains FOA corner cube templates and guarantees stable positionmore » estimation.« less

Shape memory behavior of single and polycrystalline nickel rich nickel titanium alloys

NASA Astrophysics Data System (ADS)

Kaya, Irfan

NiTi is the most commonly used shape memory alloy (SMA) and has been widely used for bio-medical, electrical and mechanical applications. Nickel rich NiTi shape memory alloys are coming into prominence due to their distinct superelasticity and shape memory properties as compared to near equi-atomic NiTi shape memory alloys. Besides, their lower density and higher work output than steels makes these alloys an excellent candidate for aerospace and automotive industry. Shape memory properties and phase transformation behavior of high Ni-rich Ni54Ti46 (at.%) polycrystals and Ni-rich Ni 51Ti49 (at.%) single-crystals are determined. Their properties are sensitive to heat treatments that affect the phase transformation behavior of these alloys. Phase transformation properties and microstructure were investigated in aged Ni54Ti46 alloys with differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) to reveal the precipitation characteristics and R-phase formation. It was found that Ni54Ti46 has the ability to exhibit perfect superelasticity under high stress levels (~2 GPa) with 4% total strain after 550°C-3h aging. Stress independent R-phase transformation was found to be responsible for the change in shape memory behavior with stress. The shape memory responses of [001], [011] and [111] oriented Ni 51Ti49 single-crystals alloy were reported under compression to reveal the orientation dependence of their shape memory behavior. It has been found that transformation strain, temperatures and hysteresis, Classius-Clapeyron slopes, critical stress for plastic deformation are highly orientation dependent. The effects of precipitation formation and compressive loading at selected temperatures on the two-way shape memory effect (TWSME) properties of a [111]- oriented Ni51Ti49 shape memory alloy were revealed. Additionally, aligned Ni4Ti3 precipitates were formed in a single crystal of Ni51Ti49 alloy by aging under applied compression stress along the [111] direction. Formation of a single family of Ni4Ti3 precipitates were exhibited significant TWSME without any training or deformation. When the homogenized and aged specimens were loaded in martensite, positive TWSME was observed. After loading at high temperature in austenite, the homogenized specimen did not show TWSME while the aged specimen revealed negative TWSME.

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

Coordinative Alignment of Chiral Molecules to Control over the Chirality Transfer in Spontaneous Resolution and Asymmetric Catalysis.

PubMed

Xia, Zhengqiang; Jing, Xu; He, Cheng; Wang, Xiaoge; Duan, Chunying

2017-11-13

The production and availability of enantiomerically pure compounds that spurred the development of chiral technologies and materials are very important to the fine chemicals and pharmaceutical industries. By coordinative alignment of enantiopure guests in the metal‒organic frameworks, we reported an approach to control over the chirality of homochiral crystallization and asymmetric transformation. Synthesized by achiral triphenylamine derivatives, the chirality of silver frameworks was determined by the encapsulated enantiopure azomethine ylides, from which clear interaction patterns were observed to explore the chiral induction principles. With the changing of addition sequence of substrates, the enantioselectivity of asymmetric cycloaddition was controlled to verify the determinant on the chirality of the bulky MOF materials. The economical chirality amplification that merges a series of complicated self-inductions, bulk homochiral crystallization and enantioselective catalysis opens new avenues for enantiopure chemical synthesis and provides a promising path for the directional design and development of homochiral materials.

Alternative generation of well-aligned uniform lying helix texture in a cholesteric liquid crystal cell

NASA Astrophysics Data System (ADS)

Yu, Chia-Hua; Wu, Po-Chang; Lee, Wei

2017-10-01

This work demonstrates a simple approach for obtaining a well-aligned uniform lying helix (ULH) texture and a tri-bistable feature at ambient temperature in a typical 90°-twisted cell filled with a short-pitch cholesteric liquid crystal. This ULH texture is obtained at room temperature from initially field-induced helix-free homeotropic state by gradually decreasing the applied voltage. Depending on the way and rate of reducing the voltage, three stable states (i.e., Grandjean planar, focal conic, and ULH) are generated and switching between any two of them is realized. Moreover, the electrical operation of the cell in the ULH state enables the tunability in phase retardation via the deformation of the ULH. The observations made in this work may be useful for applications such as tunable phase modulators and energy-efficient photonic devices.

Scalable fabrication of coupled NV center - photonic crystal cavity systems by self-aligned N ion implantation

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

Schröder, T.; Walsh, M.; Zheng, J.

2017-04-06

Towards building large-scale integrated photonic systems for quantum information processing, spatial and spectral alignment of single quantum systems to photonic nanocavities is required. In this paper, we demonstrate spatially targeted implantation of nitrogen vacancy (NV) centers into the mode maximum of 2-d diamond photonic crystal cavities with quality factors up to 8000, achieving an average of 1.1 ± 0.2 NVs per cavity. Nearly all NV-cavity systems have significant emission intensity enhancement, reaching a cavity-fed spectrally selective intensity enhancement, F int, of up to 93. Although spatial NV-cavity overlap is nearly guaranteed within about 40 nm, spectral tuning of the NV’smore » zero-phonon-line (ZPL) is still necessary after fabrication. To demonstrate spectral control, we temperature tune a cavity into an NV ZPL, yielding F ZPL int~5 at cryogenic temperatures.« less

Eliminating crystals in non-oxide optical fiber preforms and optical fibers

NASA Technical Reports Server (NTRS)

LaPointe, Michael R. (Inventor); Tucker, Dennis S. (Inventor)

2010-01-01

A method is provided for eliminating crystals in non-oxide optical fiber preforms as well as optical fibers drawn therefrom. The optical-fiber-drawing axis of the preform is aligned with the force of gravity. A magnetic field is applied to the preform as it is heated to at least a melting temperature thereof. The magnetic field is applied in a direction that is parallel to the preform's optical-fiber-drawing axis. The preform is then cooled to a temperature that is less than a glass transition temperature of the preform while the preform is maintained in the magnetic field. When the processed preform is to have an optical fiber drawn therefrom, the preform's optical-fiber-drawing axis is again aligned with the force of gravity and a magnetic field is again applied along the axis as the optical fiber is drawn from the preform.

A novel structure of gel grown strontium cyanurate crystal and its structural, optical, electrical characterization

NASA Astrophysics Data System (ADS)

Divya, R.; Nair, Lekshmi P.; Bijini, B. R.; Nair, C. M. K.; Gopakumar, N.; Babu, K. Rajendra

2017-12-01

Strontium cyanurate crystals with novel structure and unique optical property like mechanoluminescence have been grown by conventional gel method. Transparent crystals were obtained. The single crystal X-ray diffraction analysis reveals the exquisite structure of the grown crystal. The crystal is centrosymmetric and has a three dimensional polymeric structure. The powder X ray diffraction analysis confirms its crystalline nature. The functional groups present in the crystal were identified by Fourier transform infrared spectroscopy. Elemental analysis confirmed the composition of the complex. A study of thermal properties was done by thermo gravimetric analysis and differential thermal analysis. The optical properties like band gap, refractive index and extinction coefficient were evaluated from the UV visible spectral analysis. The etching study was done to reveal the dislocations in the crystal which in turn explains mechanoluminescence emission. The mechanoluminescence property exhibited by the crystal makes it suitable for stress sensing applications. Besides being a centrosymmetric crystal, it also exhibits NLO behavior. Dielectric properties were studied and theoretical calculations of Fermi energy, valence electron plasma energy, penn gap and polarisability have been done.

Magnetic Cellulose Nanocrystal Based Anisotropic Polylactic Acid Nanocomposite Films: Influence on Electrical, Magnetic, Thermal, and Mechanical Properties.

PubMed

Dhar, Prodyut; Kumar, Amit; Katiyar, Vimal

2016-07-20

This paper reports a single-step co-precipitation method for the fabrication of magnetic cellulose nanocrystals (MGCNCs) with high iron oxide nanoparticle content (∼51 wt % loading) adsorbed onto cellulose nanocrystals (CNCs). X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman spectroscopic studies confirmed that the hydroxyl groups on the surface of CNCs (derived from the bamboo pulp) acted as anchor points for the adsorption of Fe3O4 nanoparticles. The fabricated MGCNCs have a high magnetic moment, which is utilized to orient the magnetoresponsive nanofillers in parallel or perpendicular orientations inside the polylactic acid (PLA) matrix. Magnetic-field-assisted directional alignment of MGCNCs led to the incorporation of anisotropic mechanical, thermal, and electrical properties in the fabricated PLA-MGCNC nanocomposites. Thermomechanical studies showed significant improvement in the elastic modulus and glass-transition temperature for the magnetically oriented samples. Differential scanning calorimetry (DSC) and XRD studies confirmed that the alignment of MGCNCs led to the improvement in the percentage crystallinity and, with the absence of the cold-crystallization phenomenon, finds a potential application in polymer processing in the presence of magnetic field. The tensile strength and percentage elongation for the parallel-oriented samples improved by ∼70 and 240%, respectively, and for perpendicular-oriented samples, by ∼58 and 172%, respectively, in comparison to the unoriented samples. Furthermore, its anisotropically induced electrical and magnetic properties are desirable for fabricating self-biased electronics products. We also demonstrate that the fabricated anisotropic PLA-MGCNC nanocomposites could be laminated into films with the incorporation of directionally tunable mechanical properties. Therefore, the current study provides a novel noninvasive approach of orienting nontoxic bioderived CNCs in the presence of low magnetic fields, with potential applications in the manufacturing of three-dimensional composites with microstructural features comparable to biological materials for high-performance engineering applications.

Magnetically induced ferroelectricity in Bi2CuO4

NASA Astrophysics Data System (ADS)

Zhao, L.; Guo, H.; Schmidt, W.; Nemkovski, K.; Mostovoy, M.; Komarek, A. C.

2017-08-01

The tetragonal copper oxide Bi2CuO4 has an unusual crystal structure with a three-dimensional network of well separated CuO4 plaquettes. The spin structure of Bi2CuO4 in the magnetically ordered state below TN˜43 K remains controversial. Here we present the results of detailed studies of specific heat, magnetic, and dielectric properties of Bi2CuO4 single crystals grown by the floating zone technique, combined with the polarized neutron scattering and high-resolution x-ray measurements. Down to 3.5 K our polarized neutron scattering measurements reveal ordered magnetic Cu moments which are aligned within the a b plane. Below the onset of the long range antiferromagnetic ordering we observe an electric polarization induced by an applied magnetic field, which indicates inversion symmetry breaking by the ordered state of Cu spins. For the magnetic field applied perpendicular to the tetragonal axis, the spin-induced ferroelectricity is explained in terms of the linear magnetoelectric effect that occurs in a metastable magnetic state. A relatively small electric polarization induced by the field parallel to the tetragonal axis may indicate a more complex magnetic ordering in Bi2CuO4 .

Controllable preparation of copper phthalocyanine single crystal nano column and its chlorine gas sensing properties

NASA Astrophysics Data System (ADS)

Zhao, Jianhong; Qiao, Zhenfang; Zhang, Yumin; Zou, Taoyu; Yu, Leiming; Luo, Li; Wang, Xiaoyan; Yang, Yiji; Wang, Hai; Tang, Libin

2016-09-01

The unsubstituted copper phthalocyanine (CuPc) single crystal nano columns were fabricated for the first time as chlorine (Cl2) gas sensors in this paper. The nano columns of CuPc have been prepared on different substrates via template-free physical vapor deposition (PVD) approach. The growth mechanism of CuPc nano column on quartz was explored and the same condition used on other substrates including glass, sapphire (C-plane<0001>, M-plane<10 1 ¯ 0 >, R-plane<1 1 ¯ 02 >), Si and SiO2/Si came to a same conclusion, which confirmed that the aligned growth of CuPc nano column is not substrate-dependent. And then the CuPc nano column with special morphology was integrated as in-situ sensor device which exhibits high sensitivity and selectivity towards Cl2 at room temperature with a minimum detection limit as low as 0.08 ppm. The response of sensor was found to increase linearly (26 ˜659 % ) with the increase for Cl2 within concentration range (0.08 ˜4.0 ppm ) . These results clearly demonstrate the great potential of the nano column growth and device integration approach for sensor device.

Ellipsometric study of YBa2Cu3O(7-x) laser ablated and co-evaporated films

NASA Technical Reports Server (NTRS)

Alterovitz, S. A.; Sieg, R. E.; Warner, J. D.; Stan, M. A.; Vitta, S.

1990-01-01

High temperature superconducting films of YBa2Cu3O(7-x) (YBCO were grown on SrTiO3, LaA1O3, and YSZ substrates using two techniques: excimer laser ablation with in situ annealing and co-evaporation of Y, Cu, and BaF2 with ex-situ annealing. Film thicknesses were typically 5000 A, with predominant c-axis alignment perpendicular to the substrate. Critical temperatures up to Tc(R=O)=90 K were achieved by both techniques. Ellipsometric measurements were taken in the range 1.6 to 4.3 eV using a variable angle spectroscopic ellipsometer. The complex dielectric function of the laser ablated films was reproducible from run to run, and was found to be within 10 percent of that previously reported for (001) oriented single crystals. A dielectric overlayer was observed in these films, with an index of refraction of approximately 1.55 and nearly zero absorption. For the laser ablated films the optical properties were essentially independent of substrate material. The magnitude of the dielectric function obtained for the co-evaported films was much lower than the value reported for single crystals, and was sample dependent.

Low-energy transmission electron diffraction and imaging of large-area graphene

PubMed Central

Zhao, Wei; Xia, Bingyu; Lin, Li; Xiao, Xiaoyang; Liu, Peng; Lin, Xiaoyang; Peng, Hailin; Zhu, Yuanmin; Yu, Rong; Lei, Peng; Wang, Jiangtao; Zhang, Lina; Xu, Yong; Zhao, Mingwen; Peng, Lianmao; Li, Qunqing; Duan, Wenhui; Liu, Zhongfan; Fan, Shoushan; Jiang, Kaili

2017-01-01

Two-dimensional (2D) materials have attracted interest because of their excellent properties and potential applications. A key step in realizing industrial applications is to synthesize wafer-scale single-crystal samples. Until now, single-crystal samples, such as graphene domains up to the centimeter scale, have been synthesized. However, a new challenge is to efficiently characterize large-area samples. Currently, the crystalline characterization of these samples still relies on selected-area electron diffraction (SAED) or low-energy electron diffraction (LEED), which is more suitable for characterizing very small local regions. This paper presents a highly efficient characterization technique that adopts a low-energy electrostatically focused electron gun and a super-aligned carbon nanotube (SACNT) film sample support. It allows rapid crystalline characterization of large-area graphene through a single photograph of a transmission-diffracted image at a large beam size. Additionally, the low-energy electron beam enables the observation of a unique diffraction pattern of adsorbates on the suspended graphene at room temperature. This work presents a simple and convenient method for characterizing the macroscopic structures of 2D materials, and the instrument we constructed allows the study of the weak interaction with 2D materials. PMID:28879233

Low-energy transmission electron diffraction and imaging of large-area graphene.

PubMed

Zhao, Wei; Xia, Bingyu; Lin, Li; Xiao, Xiaoyang; Liu, Peng; Lin, Xiaoyang; Peng, Hailin; Zhu, Yuanmin; Yu, Rong; Lei, Peng; Wang, Jiangtao; Zhang, Lina; Xu, Yong; Zhao, Mingwen; Peng, Lianmao; Li, Qunqing; Duan, Wenhui; Liu, Zhongfan; Fan, Shoushan; Jiang, Kaili

2017-09-01

Two-dimensional (2D) materials have attracted interest because of their excellent properties and potential applications. A key step in realizing industrial applications is to synthesize wafer-scale single-crystal samples. Until now, single-crystal samples, such as graphene domains up to the centimeter scale, have been synthesized. However, a new challenge is to efficiently characterize large-area samples. Currently, the crystalline characterization of these samples still relies on selected-area electron diffraction (SAED) or low-energy electron diffraction (LEED), which is more suitable for characterizing very small local regions. This paper presents a highly efficient characterization technique that adopts a low-energy electrostatically focused electron gun and a super-aligned carbon nanotube (SACNT) film sample support. It allows rapid crystalline characterization of large-area graphene through a single photograph of a transmission-diffracted image at a large beam size. Additionally, the low-energy electron beam enables the observation of a unique diffraction pattern of adsorbates on the suspended graphene at room temperature. This work presents a simple and convenient method for characterizing the macroscopic structures of 2D materials, and the instrument we constructed allows the study of the weak interaction with 2D materials.

Sensing the facet orientation in silver nano-plates using scanning Kelvin probe microscopy in air

NASA Astrophysics Data System (ADS)

Abdellatif, M. H.; Salerno, M.; Polovitsyn, Anatolii; Marras, Sergio; De Angelis, Francesco

2017-05-01

The work function of nano-materials is important for a full characterization of their electronic properties. Because the band alignment, band bending and electronic noise are very sensitive to work function fluctuations, the dependence of the work function of nano-scale crystals on facet orientation can be a critical issue in optimizing optoelectronic devices based on these materials. We used scanning Kelvin probe microscopy to assess the local work function on samples of silver nano-plates at sub-micrometric spatial resolution. With the appropriate choice of the substrate and based on statistical analysis, it was possible to distinguish the surface potential of the different facets of silver nano-plates even if the measurements were done in ambient conditions without the use of vacuum. A phenomenological model was used to calculate the differences of facet work function of the silver nano-plates and the corresponding shift in Fermi level. This theoretical prediction and the experimentally observed difference in surface potential on the silver nano-plates were in good agreement. Our results show the possibility to sense the nano-crystal facets by appropriate choice of the substrate in ambient conditions.

Utilizing Structures of CYP2D6 and BACE1 Complexes To Reduce Risk of Drug–Drug Interactions with a Novel Series of Centrally Efficacious BACE1 Inhibitors

DOE PAGES

Brodney, Michael A.; Beck, Elizabeth M.; Butler, Christopher R.; ...

2015-03-17

In recent years, the first generation of β-secretase (BACE1) inhibitors advanced into clinical development for the treatment of Alzheimer’s disease (AD). However, the alignment of drug-like properties and selectivity remains a major challenge. Here in this paper, we describe the discovery of a novel class of potent, low clearance, CNS penetrant BACE1 inhibitors represented by thioamidine 5. Further profiling suggested that a high fraction of the metabolism (>95%) was due to CYP2D6, increasing the potential risk for victim-based drug–drug interactions (DDI) and variable exposure in the clinic due to the polymorphic nature of this enzyme. To guide future design, wemore » solved crystal structures of CYP2D6 complexes with substrate 5 and its corresponding metabolic product pyrazole 6, which provided insight into the binding mode and movements between substrate/inhibitor complexes. Guided by the BACE1 and CYP2D6 crystal structures, we designed and synthesized analogues with reduced risk for DDI, central efficacy, and improved hERG therapeutic margins.« less

Utilizing Structures of CYP2D6 and BACE1 Complexes To Reduce Risk of Drug–Drug Interactions with a Novel Series of Centrally Efficacious BACE1 Inhibitors

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

Brodney, Michael A.; Beck, Elizabeth M.; Butler, Christopher R.

In recent years, the first generation of β-secretase (BACE1) inhibitors advanced into clinical development for the treatment of Alzheimer’s disease (AD). However, the alignment of drug-like properties and selectivity remains a major challenge. Here in this paper, we describe the discovery of a novel class of potent, low clearance, CNS penetrant BACE1 inhibitors represented by thioamidine 5. Further profiling suggested that a high fraction of the metabolism (>95%) was due to CYP2D6, increasing the potential risk for victim-based drug–drug interactions (DDI) and variable exposure in the clinic due to the polymorphic nature of this enzyme. To guide future design, wemore » solved crystal structures of CYP2D6 complexes with substrate 5 and its corresponding metabolic product pyrazole 6, which provided insight into the binding mode and movements between substrate/inhibitor complexes. Guided by the BACE1 and CYP2D6 crystal structures, we designed and synthesized analogues with reduced risk for DDI, central efficacy, and improved hERG therapeutic margins.« less

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

Liquid crystal point diffraction interferometer. Ph.D. Thesis - Arizona Univ., 1995

NASA Technical Reports Server (NTRS)

Mercer, Carolyn R.

1995-01-01

A new instrument, the liquid crystal point diffraction-interferometer (LCPDI), has been developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point diffraction interferometer (PDI) and adds to it phase stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wavefronts with very high data density and with automated data reduction. This dissertation describes the theory of both the PDI and liquid crystal phase control. The design considerations for the LCPDI are presented, including manufacturing considerations. The operation and performance of the LCPDI are discussed, including sections regarding alignment, calibration, and amplitude modulation effects. The LCPDI is then demonstrated using two phase objects: defocus difference wavefront, and a temperature distribution across a heated chamber filled with silicone oil. The measured results are compared to theoretical or independently measured results and show excellent agreement. A computer simulation of the LCPDI was performed to verify the source of observed periodic phase measurement error. The error stems from intensity variations caused by dye molecules rotating within the liquid crystal layer. Methods are discussed for reducing this error. Algorithms are presented which reduce this error; they are also useful for any phase-stepping interferometer that has unwanted intensity fluctuations, such as those caused by unregulated lasers.

Photoconductivity in the chalcohalide semiconductor, SbSeI: a new candidate for hard radiation detection.

PubMed

Wibowo, Arief C; Malliakas, Christos D; Liu, Zhifu; Peters, John A; Sebastian, Maria; Chung, Duck Young; Wessels, Bruce W; Kanatzidis, Mercouri G

2013-06-17

We investigated an antimony chalcohalide compound, SbSeI, as a potential semiconductor material for X-ray and γ-ray detection. SbSeI has a wide band gap of 1.70 eV with a density of 5.80 g/cm(3), and it crystallizes in the orthorhombic Pnma space group with a one-dimensional chain structure comprised of infinite zigzag chains of dimers [Sb2Se4I8]n running along the crystallographic b axis. In this study, we investigate conditions for vertical Bridgman crystal growth using combinations of the peak temperature and temperature gradients as well as translation rate set in a three-zone furnace. SbSeI samples grown at 495 °C peak temperature and 19 °C/cm temperature gradient with 2.5 mm/h translation rate produced a single phase of columnar needlelike crystals aligned along the translational direction of the growth. The ingot sample exhibited an n-type semiconductor with resistivity of ∼10(8) Ω·cm. Photoconductivity measurements on these specimens allowed us to determine mobility-lifetime (μτ) products for electron and hole carriers that were found to be of similar order of magnitude (∼10(-4) cm(2)/V). Further, the SbSeI ingot with well-aligned, one-dimensional columnar needlelike crystals shows an appreciable response of Ag Kα X-ray.

Broadband and polarization reflectors in the lookdown, Selene vomer.

PubMed

Zhao, Shulei; Brady, Parrish Clawson; Gao, Meng; Etheredge, Robert Ian; Kattawar, George W; Cummings, Molly E

2015-03-06

Predator evasion in the open ocean is difficult because there are no objects to hide behind. The silvery surface of fish plays an important role in open water camouflage. Various models have been proposed to account for the broadband reflectance by the fish skin that involve one-dimensional variations in the arrangement of guanine crystal reflectors, yet the three-dimensional organization of these guanine platelets have not been well characterized. Here, we report the three-dimensional organization and the optical properties of integumentary guanine platelets in a silvery marine fish, the lookdown (Selene vomer). Our structural analysis and computational modelling show that stacks of guanine platelets with random yaw angles in the fish skin produce broadband reflectance via colour mixing. Optical axes of the guanine platelets and the collagen layer are aligned closely and provide bulk birefringence properties that influence the polarization reflectance by the skin. These data demonstrate how the lookdown preserves or alters polarization states at different incident polarization angles. These optical properties resulted from the organization of these guanine platelets and the collagen layer may have implications for open ocean camouflage in varying light fields. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Effect of oxygen partial pressure on superconducting properties of Bi-2212/Ag tapes prepared by doctor-blade method

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

Inoue, N.; Okada, M.; Higashiyama, K.

1997-06-01

The authors have investigated the relationship between oxygen partial pressure (P{sub O{sub 2}}) during the partial-melting process and superconducting properties for doctor-blade processed Bi-2212/Ag tapes. Tapes were heat-treated at various P{sub O{sub 2}} value of 0.01-1.00 atm. The DTA results for the doctor-blade tapes showed the melting point of the oxide rose with increasing P{sub O{sub 2}}. Correspondingly, the optimum heat-treatment temperature also increased with increasing P{sub O{sub 2}}. The tapes at P{sub O{sub 2}}=1.00 atm had the highest J{sub c} values of over 10{sup 5} A/cm{sup 2} at conditions of 4.2K, 10T, and their a.c. susceptibility showed a sharpmore » transition indicating improved intergrain coupling. Examination of cross sections for tapes melted above 0.20atm PO{sub 2} showed the good crystal alignment. From these results, it was concluded that processing at high PO{sub 2} was an effective method to obtain good superconducting properties for doctor-blade tapes.« less

Acoustic methods for high-throughput protein crystal mounting at next-generation macromolecular crystallographic beamlines.

PubMed

Roessler, Christian G; Kuczewski, Anthony; Stearns, Richard; Ellson, Richard; Olechno, Joseph; Orville, Allen M; Allaire, Marc; Soares, Alexei S; Héroux, Annie

2013-09-01

To take full advantage of advanced data collection techniques and high beam flux at next-generation macromolecular crystallography beamlines, rapid and reliable methods will be needed to mount and align many samples per second. One approach is to use an acoustic ejector to eject crystal-containing droplets onto a solid X-ray transparent surface, which can then be positioned and rotated for data collection. Proof-of-concept experiments were conducted at the National Synchrotron Light Source on thermolysin crystals acoustically ejected onto a polyimide `conveyor belt'. Small wedges of data were collected on each crystal, and a complete dataset was assembled from a well diffracting subset of these crystals. Future developments and implementation will focus on achieving ejection and translation of single droplets at a rate of over one hundred per second.

Acoustic methods for high-throughput protein crystal mounting at next-generation macromolecular crystallographic beamlines

PubMed Central

Roessler, Christian G.; Kuczewski, Anthony; Stearns, Richard; Ellson, Richard; Olechno, Joseph; Orville, Allen M.; Allaire, Marc; Soares, Alexei S.; Héroux, Annie

2013-01-01

To take full advantage of advanced data collection techniques and high beam flux at next-generation macromolecular crystallography beamlines, rapid and reliable methods will be needed to mount and align many samples per second. One approach is to use an acoustic ejector to eject crystal-containing droplets onto a solid X-ray transparent surface, which can then be positioned and rotated for data collection. Proof-of-concept experiments were conducted at the National Synchrotron Light Source on thermolysin crystals acoustically ejected onto a polyimide ‘conveyor belt’. Small wedges of data were collected on each crystal, and a complete dataset was assembled from a well diffracting subset of these crystals. Future developments and implementation will focus on achieving ejection and translation of single droplets at a rate of over one hundred per second. PMID:23955046

Wetting of cholesteric liquid crystals.

PubMed

Silvestre, Nuno M; Figueirinhas Pereira, Maria Carolina; Bernardino, Nelson R; Telo da Gama, Margarida M

2016-02-01

We investigate theoretically the wetting properties of cholesteric liquid crystals at a planar substrate. If the properties of substrate and of the interface are such that the cholesteric layers are not distorted, the wetting properties are similar to those of a nematic liquid crystal. If, on the other hand, the anchoring conditions force the distortion of the liquid crystal layers the wetting properties are altered, the free cholesteric-isotropic interface is non-planar and there is a layer of topological defects close to the substrate. These deformations can either promote or hinder the wetting of the substrate by a cholesteric, depending on the properties of the cholesteric liquid crystal.

Characterization of the electro-optic effect in styrylpyridinium cyanine dye thin-film crystals by an ac modulation method

NASA Astrophysics Data System (ADS)

Yoshimura, Tetsuzo

1987-09-01

The electro-optic effect in styrylpyridinium cyanine dye (SPCD) thin-film crystals is characterized by a newly developed ac modulation method that is effective in characterizing thin-film materials of small area. SPCD thin-film crystals 3-10 μm thick were grown from a methanol solution of SPCD. The crystal shows strong dichroism and anisotropy of refractive index, indicating that molecular dipole moments align along a definite direction (z axis). When an electric field is applied along the z axis, SPCD thin-film crystals show a large figure of merit of electro-optic phase retardation of 6.5×10-10 m/V, which is 5 times as large as in LiNbO3 crystal, 2 times that in 2-methyl-4-nitroaniline (MNA) crystal, and is the largest ever reported in organic solids. The electro-optic coefficient r33 of SPCD crystals is estimated to be approximately 4.3×10-10 m/V, which is 6 times larger than that of an MNA crystal. This value is consistent with that expected from second-harmonic generation measurements.

Voltage controlled oscillator is easily aligned, has low phase noise

NASA Technical Reports Server (NTRS)

Sydnor, R. L.

1965-01-01

Voltage Controlled Oscillator /VCO/, represented by an equivalent RF circuit, is easily adjusted for optimum performance by varying the circuit parameter. It contains a crystal drive level which is also easily adjusted to obtain minimum phase noise.

Phase transitions of amorphous solid acetone in confined geometry investigated by reflection absorption infrared spectroscopy.

PubMed

Shin, Sunghwan; Kang, Hani; Kim, Jun Soo; Kang, Heon

2014-11-26

We investigated the phase transformations of amorphous solid acetone under confined geometry by preparing acetone films trapped in amorphous solid water (ASW) or CCl4. Reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD) were used to monitor the phase changes of the acetone sample with increasing temperature. An acetone film trapped in ASW shows an abrupt change in the RAIRS features of the acetone vibrational bands during heating from 80 to 100 K, which indicates the transformation of amorphous solid acetone to a molecularly aligned crystalline phase. Further heating of the sample to 140 K produces an isotropic solid phase, and eventually a fluid phase near 157 K, at which the acetone sample is probably trapped in a pressurized, superheated condition inside the ASW matrix. Inside a CCl4 matrix, amorphous solid acetone crystallizes into a different, isotropic structure at ca. 90 K. We propose that the molecularly aligned crystalline phase formed in ASW is created by heterogeneous nucleation at the acetone-water interface, with resultant crystal growth, whereas the isotropic crystalline phase in CCl4 is formed by homogeneous crystal growth starting from the bulk region of the acetone sample.

Fabrication and material properties of fibrous PHBV scaffolds depending on the cross-ply angle for tissue engineering.

PubMed

Kim, Yang-Hee; Min, Young-Ki; Lee, Byong-Taek

2012-11-01

Fibrous PHBV cross-ply scaffolds were fabricated using the electrospinning technique. The electrospun fibers were arranged depending on angles of alignment, which were 180°, 90°, 60°, and 45°. The stress and strain values of the fibrous PHBV cross-ply scaffolds increased as the cross-ply angle increased. At 180°, the strength and strain values of the fibers depended on tensile loading directions. At an alignment of 90°, the PHBV scaffolds had a stress value of 3.5 MPa, which was more than two times higher than the random structure. The cell morphology and proliferation of L-929 cells was strongly dependant on the fiber alignment and the best results were observed when the angle alignment was high. The results of this study showed that the cross-ply structure of the PHBV scaffold affected not only the cell adhesion and spreading properties but also dictated the mechanical properties, which were dependent on the angles of alignment.

Model of coordination melting of crystals and anisotropy of physical and chemical properties of the surface

NASA Astrophysics Data System (ADS)

Bokarev, Valery P.; Krasnikov, Gennady Ya

2018-02-01

Based on the evaluation of the properties of crystals, such as surface energy and its anisotropy, the surface melting temperature, the anisotropy of the work function of the electron, and the anisotropy of adsorption, were shown the advantages of the model of coordination melting (MCM) in calculating the surface properties of crystals. The model of coordination melting makes it possible to calculate with an acceptable accuracy the specific surface energy of the crystals, the anisotropy of the surface energy, the habit of the natural crystals, the temperature of surface melting of the crystal, the anisotropy of the electron work function and the anisotropy of the adhesive properties of single-crystal surfaces. The advantage of our model is the simplicity of evaluating the surface properties of the crystal based on the data given in the reference literature. In this case, there is no need for a complex mathematical tool, which is used in calculations using quantum chemistry or modeling by molecular dynamics.

Mechanochemical Synthesis of Carbon Nanothread Single Crystals.

PubMed

Li, Xiang; Baldini, Maria; Wang, Tao; Chen, Bo; Xu, En-Shi; Vermilyea, Brian; Crespi, Vincent H; Hoffmann, Roald; Molaison, Jamie J; Tulk, Christopher A; Guthrie, Malcolm; Sinogeikin, Stanislav; Badding, John V

2017-11-15

Synthesis of well-ordered reduced dimensional carbon solids with extended bonding remains a challenge. For example, few single-crystal organic monomers react under topochemical control to produce single-crystal extended solids. We report a mechanochemical synthesis in which slow compression at room temperature under uniaxial stress can convert polycrystalline or single-crystal benzene monomer into single-crystalline packings of carbon nanothreads, a one-dimensional sp 3 carbon nanomaterial. The long-range order over hundreds of microns of these crystals allows them to readily exfoliate into fibers. The mechanochemical reaction produces macroscopic single crystals despite large dimensional changes caused by the formation of multiple strong, covalent C-C bonds to each monomer and a lack of reactant single-crystal order. Therefore, it appears not to follow a topochemical pathway, but rather one guided by uniaxial stress, to which the nanothreads consistently align. Slow-compression room-temperature synthesis may allow diverse molecular monomers to form single-crystalline packings of polymers, threads, and higher dimensional carbon networks.

On crystal versus fiber formation in dipeptide hydrogelator systems.

PubMed

Houton, Kelly A; Morris, Kyle L; Chen, Lin; Schmidtmann, Marc; Jones, James T A; Serpell, Louise C; Lloyd, Gareth O; Adams, Dave J

2012-06-26

Naphthalene dipeptides have been shown to be useful low-molecular-weight gelators. Here we have used a library to explore the relationship between the dipeptide sequence and the hydrogelation efficiency. A number of the naphthalene dipeptides are crystallizable from water, enabling us to investigate the comparison between the gel/fiber phase and the crystal phase. We succeeded in crystallizing one example directly from the gel phase. Using X-ray crystallography, molecular modeling, and X-ray fiber diffraction, we show that the molecular packing of this crystal structure differs from the structure of the gel/fiber phase. Although the crystal structures may provide important insights into stabilizing interactions, our analysis indicates a rearrangement of structural packing within the fibers. These observations are consistent with the fibrillar interactions and interatomic separations promoting 1D assembly whereas in the crystals the peptides are aligned along multiple axes, allowing 3D growth. This observation has an impact on the use of crystal structures to determine supramolecular synthons for gelators.

Structural and optical properties of WTe2 single crystals synthesized by DVT technique

NASA Astrophysics Data System (ADS)

Dixit, Vijay; Vyas, Chirag; Pathak, V. M.; Soalanki, G. K.; Patel, K. D.

2018-05-01

Layered transition metal di-chalcogenide (LTMDCs) crystals have attracted much attention due to their potential in optoelectronic device applications recently due to realization of their monolayer based structures. In the present investigation we report growth of WTe2 single crystals by direct vapor transport (DVT) technique. These crystals are then characterized by energy dispersive analysis of x-rays (EDAX) to study stoichiometric composition after growth. The structural properties are studied by x-ray diffraction (XRD) and selected area electron diffraction (SAED) is used to confirm orthorhombic structure of grown WTe2 crystal. Surface morphological properties of the crystals are also studied by scanning electron microscope (SEM). The optical properties of the grown crystals are studied by UV-Visible spectroscopy which gives direct band gap of 1.44 eV for grown WTe2 single crystals.

Architecture of crossed-lamellar bivalve shells: the southern giant clam (Tridacna derasa, Röding, 1798).

PubMed

Agbaje, O B A; Wirth, R; Morales, L F G; Shirai, K; Kosnik, M; Watanabe, T; Jacob, D E

2017-09-01

Tridacna derasa shells show a crossed lamellar microstructure consisting of three hierarchical lamellar structural orders. The mineral part is intimately intergrown with 0.9 wt% organics, namely polysaccharides, glycosylated and unglycosylated proteins and lipids, identified by Fourier transform infrared spectrometry. Transmission electron microscopy shows nanometre-sized grains with irregular grain boundaries and abundant voids. Twinning is observed across all spatial scales and results in a spread of the crystal orientation angles. Electron backscatter diffraction analysis shows a strong fibre texture with the [001] axes of aragonite aligned radially to the shell surface. The aragonitic [100] and [010] axes are oriented randomly around [001]. The random orientation of anisotropic crystallographic directions in this plane reduces anisotropy of the Young's modulus and adds to the optimization of mechanical properties of bivalve shells.

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.

A Therapeutic Uricase with Reduced Immunogenicity Risk and Improved Development Properties

PubMed Central

Nyborg, Andrew C.; Ward, Chris; Zacco, Anna; Grinberg, Luba; Geoghegan, James C.; Bean, Ryan; Wendeler, Michaela; Bartnik, Frank; O’Connor, Ellen; Gruia, Flaviu; Iyer, Vidyashankara; Feng, Hui; Roy, Varnika; Berge, Mark; Miner, Jeffrey N.; Wilson, David M.; Zhou, Dongmei; Nicholson, Simone; Wilker, Clynn; Wu, Chi Y.; Wilson, Susan; Jermutus, Lutz; Wu, Herren; Owen, David A.; Osbourn, Jane; Coats, Steven; Baca, Manuel

2016-01-01

Humans and higher primates are unique in that they lack uricase, the enzyme capable of oxidizing uric acid. As a consequence of this enzyme deficiency, humans have high serum uric acid levels. In some people, uric acid levels rise above the solubility limit resulting in crystallization in joints, acute inflammation in response to those crystals causes severe pain; a condition known as gout. Treatment for severe gout includes injection of non-human uricase to reduce serum uric acid levels. Krystexxa® is a hyper-PEGylated pig-baboon chimeric uricase indicated for chronic refractory gout that induces an immunogenic response in 91% of treated patients, including infusion reactions (26%) and anaphylaxis (6.5%). These properties limit its use and effectiveness. An innovative approach has been used to develop a therapeutic uricase with improved properties such as: soluble expression, neutral pH solubility, high E. coli expression level, thermal stability, and excellent activity. More than 200 diverse uricase sequences were aligned to guide protein engineering and reduce putative sequence liabilities. A single uricase lead candidate was identified, which showed low potential for immunogenicity in >200 human donor samples selected to represent diverse HLA haplotypes. Cysteines were engineered into the lead sequence for site specific PEGylation and studies demonstrated >95% PEGylation efficiency. PEGylated uricase retains enzymatic activity in vitro at neutral pH, in human serum and in vivo (rats and canines) and has an extended half-life. In canines, an 85% reduction in serum uric acid levels was observed with a single subcutaneous injection. This PEGylated, non-immunogenic uricase has the potential to provide meaningful benefits to patients with gout. PMID:28002433

Photonic Sorting of Aligned, Crystalline Carbon Nanotube Textiles.

PubMed

Bulmer, John S; Gspann, Thurid S; Orozco, Francisco; Sparkes, Martin; Koerner, Hilmar; Di Bernardo, A; Niemiec, Arkadiusz; Robinson, J W A; Koziol, Krzysztof K; Elliott, James A; O'Neill, William

2017-10-11

Floating catalyst chemical vapor deposition uniquely generates aligned carbon nanotube (CNT) textiles with individual CNT lengths magnitudes longer than competing processes, though hindered by impurities and intrinsic/extrinsic defects. We present a photonic-based post-process, particularly suited for these textiles, that selectively removes defective CNTs and other carbons not forming a threshold thermal pathway. In this method, a large diameter laser beam rasters across the surface of a partly aligned CNT textile in air, suspended from its ends. This results in brilliant, localized oxidation, where remaining material is an optically transparent film comprised of few-walled CNTs with profound and unique improvement in microstructure alignment and crystallinity. Raman spectroscopy shows substantial D peak suppression while preserving radial breathing modes. This increases the undoped, specific electrical conductivity at least an order of magnitude to beyond that of single-crystal graphite. Cryogenic conductivity measurements indicate intrinsic transport enhancement, opposed to simply removing nonconductive carbons/residual catalyst.

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.

Influence of hot pressing on the microstructure and fracture toughness of two pressable dental glass-ceramics.

PubMed

Albakry, Mohammad; Guazzato, Massimiliano; Swain, Michael Vincent

2004-10-15

Empress 1 and Empress 2 are well-known pressable all-ceramic dental materials that have generated substantial interest for many clinicians and patients. These two materials are reputed to benefit from heat pressing during the laboratory fabrication procedures, leading to better crystal distribution within a glass matrix, and hence an improved strength. The present study aimed to evaluate the effect of heat pressing on fracture toughness, microstructural features, and porosity. Results showed that Empress 1 had similar fracture toughness values before the pressing procedure, after it, and after the repressing procedure. The microstructural features were also similar among these specimens, but a more uniform distribution of leucite crystals was observed following the pressing and repressing procedures. Empress 2 demonstrated two different fracture toughness values. This was associated with the alignment of lithium disilicate crystals that occurred after the pressing and repressing procedures, which led to different indentation induced crack lengths, depending upon whether cracks propagated parallel to or perpendicular to the aligned crystals, the former having lower toughness than those that propagated in the perpendicular direction. Porosity, in terms of both the size and number of pores, was found to decrease after the pressing and repressing procedures for both materials. Repressing resulted in significant growth of the lithium disilicate crystals in Empress 2, but there was no change for the leucite crystals in Empress 1. The change in the lithium disilicate crystals' size did not have a noticeable effect on the fracture toughness of Empress 2. It was concluded that heat pressing did not significantly affect the fracture toughness of Empress 1, but resulted in two different values for Empress 2. It also decreased the size and number of pores for both materials, which could contribute to the strength improvement found after heat pressing, which has been reported in previous studies.

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.

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.

Theory of liquid crystal orientation under action of light wave field and aligning surfaces

NASA Astrophysics Data System (ADS)

Dadivanyan, A. K.; Chausov, D. N.; Belyaev, V. V.; Barabanova, N. N.; Chausova, O. V.; Kuleshova, Yu D.

2018-03-01

Theoretical models developed in the MRSU group under leadership of Professor Artem Dadivanyan in area of the LC orientation and photo-induced effects are presented. Angular distribution functions of the dye and liquid crystal molecules under action of intensive light beam have been derived. The number of molecules in cluster is estimated. A model of dimers formation in the photoalignment dye is suggested that explains influence of the dye molecular structure on both polar and azimuthal anchoring energy.

Method of fabricating low-dislocation-density epitaxially-grown films with textured surfaces

DOEpatents

Li, Qiming; Wang, George T

2015-01-13

A method for forming a surface-textured single-crystal film layer by growing the film atop a layer of microparticles on a substrate and subsequently selectively etching away the microparticles to release the surface-textured single-crystal film layer from the substrate. This method is applicable to a very wide variety of substrates and films. In some embodiments, the film is an epitaxial film that has been grown in crystallographic alignment with respect to a crystalline substrate.

BCM-2.0 - The new version of computer code ;Basic Channeling with Mathematica©;

NASA Astrophysics Data System (ADS)

Abdrashitov, S. V.; Bogdanov, O. V.; Korotchenko, K. B.; Pivovarov, Yu. L.; Rozhkova, E. I.; Tukhfatullin, T. A.; Eikhorn, Yu. L.

2017-07-01

The new symbolic-numerical code devoted to investigation of the channeling phenomena in periodic potential of a crystal has been developed. The code has been written in Wolfram Language taking advantage of analytical programming method. Newly developed different packages were successfully applied to simulate scattering, radiation, electron-positron pair production and other effects connected with channeling of relativistic particles in aligned crystal. The result of the simulation has been validated against data from channeling experiments carried out at SAGA LS.

Electronically tuned optical filters

NASA Technical Reports Server (NTRS)

Castellano, J. A.; Pasierb, E. F.; Oh, C. S.; Mccaffrey, M. T.

1972-01-01

A detailed account is given of efforts to develop a three layer, polychromic filter that can be tuned electronically. The operation of the filter is based on the cooperative alignment of pleochroic dye molecules by nematic liquid crystals activated by electric fields. This orientation produces changes in the optical density of the material and thus changes in the color of light transmitted through the medium. In addition, attempts to improve materials and devices which employ field induced changes of a cholesteric to a nematic liquid crystal are presented.

Growth of highly textured PbTiO3 films on conductive substrate under hydrothermal conditions

NASA Astrophysics Data System (ADS)

Tang, Haixiong; Zhou, Zhi; Bowland, Christopher C.; Sodano, Henry A.

2015-08-01

Perovskite structure (ABO3) thin films have wide applications in electronic devices due to their unique properties, including high dielectric permittivity, ferroelectricity and piezoelectric coupling. Here, we report an approach to grow highly textured thick lead titanate (PbTiO3) films on conductive substrates by a two-step hydrothermal reaction. Initially, vertically aligned TiO2 nanowire arrays are grown on fluorine-doped tin oxide (FTO) coated glass, which act as template crystals for conversion to the perovskite structure. The PbTiO3 films are then converted from TiO2 NW arrays by diffusing Pb2+ ions into the template through a second hydrothermal reaction. The dielectric permittivity and piezoelectric coupling coefficient (d33) of the PbTiO3 films are as high as 795 at 1 kHz and 52 pm V-1, respectively. The reported process can also potentially be expanded for the assembly of other complex perovskite ATiO3 (A = Ba, Ca, Cd, etc) films by using the highly aligned TiO2 NW arrays as templates. Therefore, the approach introduced here opens up a new door to synthesize ferroelectric thin films on conductive substrates for application in sensors, actuators, and ultrasonic transducers that are important in various industrial and scientific areas.

Surface properties of HMX crystal

NASA Technical Reports Server (NTRS)

Yee, R. Y.; Adicoff, A.; Dibble, E. J.

1980-01-01

The surface properties of Beta-HMX crystals were studied. The surface energies of three principal crystal faces were obtained by measuring contact angles with several reference liquids. The surface energies and polarity of the three crystal faces are found to be different.

Substructure based modeling of nickel single crystals cycled at low plastic strain amplitudes

NASA Astrophysics Data System (ADS)

Zhou, Dong

In this dissertation a meso-scale, substructure-based, composite single crystal model is fully developed from the simple uniaxial model to the 3-D finite element method (FEM) model with explicit substructures and further with substructure evolution parameters, to simulate the completely reversed, strain controlled, low plastic strain amplitude cyclic deformation of nickel single crystals. Rate-dependent viscoplasticity and Armstrong-Frederick type kinematic hardening rules are applied to substructures on slip systems in the model to describe the kinematic hardening behavior of crystals. Three explicit substructure components are assumed in the composite single crystal model, namely "loop patches" and "channels" which are aligned in parallel in a "vein matrix," and persistent slip bands (PSBs) connected in series with the vein matrix. A magnetic domain rotation model is presented to describe the reverse magnetostriction of single crystal nickel. Kinematic hardening parameters are obtained by fitting responses to experimental data in the uniaxial model, and the validity of uniaxial assumption is verified in the 3-D FEM model with explicit substructures. With information gathered from experiments, all control parameters in the model including hardening parameters, volume fraction of loop patches and PSBs, and variation of Young's modulus etc. are correlated to cumulative plastic strain and/or plastic strain amplitude; and the whole cyclic deformation history of single crystal nickel at low plastic strain amplitudes is simulated in the uniaxial model. Then these parameters are implanted in the 3-D FEM model to simulate the formation of PSB bands. A resolved shear stress criterion is set to trigger the formation of PSBs, and stress perturbation in the specimen is obtained by several elements assigned with PSB material properties a priori. Displacement increment, plastic strain amplitude control and overall stress-strain monitor and output are carried out in the user subroutine DISP and URDFIL of ABAQUS, respectively, while constitutive formulations of the FEM model are coded and implemented in UMAT. The results of the simulations are compared to experiments. This model verified the validity of Winter's two-phase model and Taylor's uniform stress assumption, explored substructure evolution and "intrinsic" behavior in substructures and successfully simulated the process of PSB band formation and propagation.

Enhanced Structural and Luminescent Properties of Carbon-Assisted ZnO Nanorod Arrays on (100) Si Substrate

NASA Astrophysics Data System (ADS)

Yoon, Im Taek; Cho, Hak Dong; Lee, Sejoon; Roshchupkin, Dmitry V.

2018-02-01

We have fabricated as-grown ZnO nanorods (NRs) and carbon-assisted NR arrays on semi-insulating (100)-oriented Si substrates. We compared the structural and luminescent properties of them. High-resolution transmission microscopy, field emission scanning electron microscopy, x-ray diffraction and energy-dispersive x-ray revealed that the as-grown ZnO NRs and carbon-assisted ZnO NRs were single crystals with a hexagonal wurtzite structure, and grew with a c-axis orientation perpendicular to the Si substrate. These measurements show that the carbon-assisted ZnO NRs were better synthesized vertically on an Si substrate compared to the as-grown ZnO NRs. Photoluminescence measurements showed that luminescence intensity of the carbon-assisted ZnO NRs was enhanced compared to the as-grown ZnO NRs. The enhanced luminescence intensity of the carbon-assisted ZnO demonstrates the possible improvement in the performance of photovoltaic nanodevices based on ZnO-like materials. This method can be applied to the fabrication of well-aligned ZnO NRs used widely in optoelectronic devices.

Thermal annealing effect on structural and thermoelectric properties of hexagonal Bi2Te3 nanoplate thin films by drop-casting technique

NASA Astrophysics Data System (ADS)

Hosokawa, Yuichi; Wada, Kodai; Tanaka, Masaki; Tomita, Koji; Takashiri, Masayuki

2018-02-01

High-purity hexagonal bismuth telluride (Bi2Te3) nanoplates were prepared by a solvothermal synthesis method, followed by the fabrication of nanoplate thin films by the drop-casting technique. The Bi2Te3 nanoplates exhibited a single-crystalline phase with a rhombohedral crystal structure. The nanoplates had a flat surface with edge sizes ranging from 500 to 2000 nm (average size of 1000 nm) and a thickness of less than 50 nm. The resulting Bi2Te3 nanoplate thin films were composed of well-aligned hexagonal nanoplates along the surface direction with an approximate film thickness of 40 µm. To tightly connect the nanoplates together within the thin films, thermal annealing was performed at different temperatures. We found that the thermoelectric properties, especially the Seebeck coefficient, were very sensitive to the annealing temperature. Finally, the optimum annealing temperature was determined to be 250 °C and the Seebeck coefficient and power factor were -300 µV/K and 3.5 µW/(cm·K2), respectively.

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.

Complex Stoichiometry reordering of PTCDA on Ag(111) upon K Intercalation

NASA Astrophysics Data System (ADS)

Brivio, G. P.; Baby, A.; Zwick, C.; Gruenewald, M.; Forker, R.; Fritz, T.; Fratesi, G.; Hofmann, O. T.; Zojer, E.

Alkali metal atoms are a simple yet efficient n-type dopant of organic semiconductors. However, the molecular crystal structures need be controlled and well understood in order to optimize the electronic properties (charge carrier density and mobility) of the target material. Here, we report that potassium intercalation into PTCDA monolayer domains on a Ag(111) substrate induces distinct stoichiometry-dependent structural reordering processes, resulting in highly ordered and large KxPTCDA domains. The emerging structures are analyzed by low temperature scanning tunneling microscopy (STM), scanning tunneling hydrogen microscopy (STHM), and low-energy electron diffraction (LEED) as a function of the stoichiometry and by density functional theory (DFT) calculations. Large stable monolayer domains are found for x=2,4. The epitaxy types for all intercalated stages are determined as point-on-line. The K atoms adsorb in the vicinity of the oxygen atoms of the PTCDA molecules, and their positions are determined with sub-Angstrom precision. This is a crucial prerequisite for the prospective assessment of the electronic properties of such composite films, as they depend on the mutual alignment between donor atoms and acceptor molecules.

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

Jee, S.S.; DiMasi, E.; Kasinath, R.K.

Bone is a hierarchically structured composite which imparts it with unique mechanical properties and bioresorptive potential. These properties are primarily influenced by the underlying nanostructure of bone, which consists of nanocrystals of hydroxyapatite embedded and uniaxially aligned within collagen fibrils. There is also a small fraction of non-collagenous proteins in bone, and these are thought to play an important role in bone's formation. In our in vitro model system of bone formation, polyanionic peptides are used to mimic the role of the non-collagenous proteins. In our prior studies, we have shown that intrafibrillar mineralization can be achieved in synthetic reconstitutedmore » collagen sponges using a polymer-induced liquid-precursor (PILP) mineralization process. This led to a nanostructured arrangement of hydroxyapatite crystals within the individual fibrils which closely mimics that of bone. This report demonstrates that biogenic collagen scaffolds obtained from turkey tendon, which consist of densely packed and oriented collagen fibrils, can also be mineralized by the PILP process. Synchrotron X-ray diffraction studies show that the mineralization process leads to a high degree of crystallographic orientation at the macroscale, thus emulating that found in the biological system of naturally mineralizing turkey tendon.« less

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

Wenger, D. F.; Sinars, D. B.; Rochau, G. A.

An early prototype of a focusing spectrometer with one-dimensional (1D) spatial resolution (FSSR) instrument was previously developed for use in the vacuum chamber of the Sandia Z facility [Sinars et al., J. Quant. Spectrosc. Radiat. Transf. 99, 595 (2006)]. This instrument used a single, spherically bent crystal to measure time-integrated Ar spectra from 0.295-0.378 nm with {lambda}/{delta}{lambda}>2000 and a 1D axial spatial resolution of {approx}50 {mu}m. We present the design of a final version of this instrument that improves the shielding, can be aligned more accurately, and uses three crystals instead of one. The last change enables coverage of multiplemore » spectral ranges if different crystals are used, or multiple times if identical crystals and time-gated detectors are used. We also present results from initial prototyping tests on the Z facility using two crystals in a time-integrated mode.« less

Dark-field transmission electron microscopy of cortical bone reveals details of extrafibrillar crystals.

PubMed

Schwarcz, Henry P; McNally, Elizabeth A; Botton, Gianluigi A

2014-12-01

In a previous study we showed that most of the mineral in bone is present in the form of "mineral structures", 5-6nm-thick, elongated plates which surround and are oriented parallel to collagen fibrils. Using dark-field transmission electron microscopy, we viewed mineral structures in ion-milled sections of cortical human bone cut parallel to the collagen fibrils. Within the mineral structures we observe single crystals of apatite averaging 5.8±2.7nm in width and 28±19nm in length, their long axes oriented parallel to the fibril axis. Some appear to be composite, co-aligned crystals as thin as 2nm. From their similarity to TEM images of crystals liberated from deproteinated bone we infer that we are viewing sections through platy crystals of apatite that are assembled together to form the mineral structures. Copyright © 2014 Elsevier Inc. All rights reserved.

Fracture of single crystals of the nickel-base superalloy PWA 1480E in helium at 22 C

NASA Technical Reports Server (NTRS)

Chen, P. S.; Wilcox, R. C.

1991-01-01

The fracture behavior and deformation of He-charged (at 22 C) single crystals of PWA 1480E Ni-base superalloy were investigated using SEM and TEM techniques to observe the behavior of tensile fractures in notched single crystals with seven different crystal growth orientations: 100-line, 110-line, 111-line, 013-line, 112-line, 123-line, and 223-line. To identify the cleavage plane orientation, a stereoscopic technique, combined with the use of planar gamma-prime morphologies, was applied. It was found that gamma-prime particles were orderly and closely aligned with edges along the 100-line, 010-line, and 001-line-oriented directions of the gamma matrix. Different crystal growth orientations were found not to affect the morphology of gamma-prime particles. The accumulation of dislocations around gamma/gamma-prime interfaces formed strong barriers to subsequent dislocation movement and was the primary strengthening mechanism at room temperature.

Realignment of Nanocrystal Aggregates into Single Crystals as a Result of Inherent Surface Stress

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

Liu, Zhaoming; Pan, Haihua; Zhu, Genxing

2016-07-19

Assembly of nanoparticles building blocks during single crystal growth is widely observed in both natural and synthetic environments. Although this form of non-classical crystallization is generally described by oriented attachment, random aggregation of building blocks leading to single crystal products is also observed, but the mechanism of crystallographic realignment is unknown. We herein reveal that random attachment during aggregation-based growth initially produces a non-oriented growth front. Subsequent evolution of the orientation is driven by the inherent surface stress applied by the disordered surface layer and results in single crystal formation via grain boundary migration. This mechanism is corroborated by measurementsmore » of orientation rate vs external stress, demonstrating a predictive relationship between the two. These findings advance our understanding of aggregation-based growth of natural minerals by nanocrystals, and suggest an approach to material synthesis that takes advantage of stress induced co-alignment.« less

Microstructure and pinning properties of hexagonal-disc shaped single crystalline MgB2

NASA Astrophysics Data System (ADS)

Jung, C. U.; Kim, J. Y.; Chowdhury, P.; Kim, Kijoon H.; Lee, Sung-Ik; Koh, D. S.; Tamura, N.; Caldwell, W. A.; Patel, J. R.

2002-11-01

We synthesized hexagonal-disc-shaped MgB2 single crystals under high-pressure conditions and analyzed the microstructure and pinning properties. The lattice constants and the Laue pattern of the crystals from x-ray micro-diffraction showed the crystal symmetry of MgB2. A thorough crystallographic mapping within a single crystal showed that the edge and c axis of hexagonal-disc shape exactly matched the [101¯0] and the [0001] directions of the MgB2 phase. Thus, these well-shaped single crystals may be the best candidates for studying the direction dependences of the physical properties. The magnetization curve and the magnetic hysteresis curve for these single crystals showed the existence of a wide reversible region and weak pinning properties, which supported our single crystals being very clean.

Nanoparticles Incorporated inside Single-Crystals: Enhanced Fluorescent Properties

DOE PAGES

Liu, Yujing; Zang, Huidong; Wang, Ling; ...

2016-09-25

Incorporation of guest materials inside single-crystalline hosts leads to single-crystal composites that have become more and more frequently seen in both biogenic and synthetic crystals. The unique composite structure together with long-range ordering promises special properties that are, however, less often demonstrated. In this study, we examine the fluorescent properties of quantum dots (QDs) and polymer dots (Pdots) encapsulated inside the hosts of calcite single-crystals. Two CdTe QDs and two Pdots are incorporated into growing calcite crystals, as the QDs and Pdots are dispersed in the crystallization media of agarose gels. As a result, enhanced fluorescent properties are obtained frommore » the QDs and Pdots inside calcite single-crystals with greatly improved photostability and significantly prolonged fluorescence lifetime, compared to those in solutions and gels. Particularly, the fluorescence lifetime increases by 0.5-1.6 times after the QDs or Pdots are incorporated. The enhanced fluorescent properties indicate the advantages of encapsulation by single-crystal hosts that provide dense shells to isolate the fluorescent nanoparticles from atmosphere. As such, this work has implications for advancing the research of single-crystal composites toward their functional design.« less

Morphological changes of gamma prime precipitates in nickel-base superalloy single crystals. Ph.D. Thesis - Case Western Reserve Univ., May 1984

NASA Technical Reports Server (NTRS)

Mackay, R. A.

1984-01-01

Changes in the morphology of the gamma prime precipitate were examined during tensile creep at temperatures between 927 and 1038 C in 001-oriented single crystals of a Ni-Al-Mo-Ta superalloy. In this alloy, which has a large negative misfit of -0.80%, the gamma prime particles link together during creep to form platelets, or rafts, which are aligned with their broad faces perpendicular to the applied tensile axis. The dimensions of the gamma and gamma prime phases were measured as directional coarsening developed in an attempt to trace the changing morphology under various stress levels. In addition, the effects of initial microstructure, as well as slight compositional variations, were related to raft development and creep properties. The results showed that directional coarsening of gamma prime began during primary creep, and under certain conditions, continued to develop after the onset of steady-state creep. The length of the rafts increased linearly with time up to a plateau region. The thickness of the rafts, however, remained equal to the initial gamma prime size at least up through the onset of tertiary creep; this is a clear indication of the stability of the finely-spaced gamma-gamma prime lamellar structure. It was found that the single crystals with the finest gamma prime size exhibited the longest creep lives, because the resultant rafted structure had a larger number of gamma-gamma prime interfaces per unit volume of material.

Van der Waals epitaxial growth of two-dimensional single-crystalline GaSe domains on graphene

DOE PAGES

Li, Xufan; Basile, Leonardo; Huang, Bing; ...

2015-07-22

Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially-structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to stamping, direct epitaxy of vdW heterostructures is ideal for clean interlayer interfaces and scalable device fabrication. Here, we explore the synthesis and preferred orientations of 2D GaSe atomic layers on graphene (Gr) by vdW epitaxy. Guided by the wrinkles on graphene, GaSe nuclei form that share a predominant lattice orientation. Due to vdW epitaxial growth many nuclei grow as perfectly aligned crystals and coalesce to form large (tens of microns), single-crystal flakes. Through theoretical investigationsmore » of interlayer energetics, and measurements of preferred orientations by atomic-resolution STEM and electron diffraction, a 10.9 interlayer rotation of the GaSe lattice with respect to the underlying graphene is found to be the most energetically preferred vdW heterostructure with the largest binding energy and the longest-range ordering. These GaSe/Gr vdW heterostructures exhibit an enhanced Raman E 2 1g band of monolayer GaSe along with highly-quenched photoluminescence due to strong charge transfer. Despite the very large lattice mismatch of GaSe/Gr through vdW epitaxy, the predominant orientation control and convergent formation of large single-crystal flakes demonstrated here is promising for the scalable synthesis of large-area vdW heterostructures for the development of new optical and optoelectronic devices.« less

Van der Waals epitaxial growth of two-dimensional single-crystalline GaSe domains on graphene

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

Li, Xufan; Basile, Leonardo; Huang, Bing

Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially-structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to stamping, direct epitaxy of vdW heterostructures is ideal for clean interlayer interfaces and scalable device fabrication. Here, we explore the synthesis and preferred orientations of 2D GaSe atomic layers on graphene (Gr) by vdW epitaxy. Guided by the wrinkles on graphene, GaSe nuclei form that share a predominant lattice orientation. Due to vdW epitaxial growth many nuclei grow as perfectly aligned crystals and coalesce to form large (tens of microns), single-crystal flakes. Through theoretical investigationsmore » of interlayer energetics, and measurements of preferred orientations by atomic-resolution STEM and electron diffraction, a 10.9 interlayer rotation of the GaSe lattice with respect to the underlying graphene is found to be the most energetically preferred vdW heterostructure with the largest binding energy and the longest-range ordering. These GaSe/Gr vdW heterostructures exhibit an enhanced Raman E 2 1g band of monolayer GaSe along with highly-quenched photoluminescence due to strong charge transfer. Despite the very large lattice mismatch of GaSe/Gr through vdW epitaxy, the predominant orientation control and convergent formation of large single-crystal flakes demonstrated here is promising for the scalable synthesis of large-area vdW heterostructures for the development of new optical and optoelectronic devices.« less

Ferrotoroidial propertiesof Non-Crystallographic Pointgroups

NASA Astrophysics Data System (ADS)

Sireesha, G.; Devi, S. Uma; Yamini Sankar, CH.

2017-08-01

Primary ferroic crystals are the crystals with domain states that are distinguished by properties like spontaneous magnetization, strain, or polarisation. Secondary ferroic crystals are the crystals with domain states that are distinguished by piezoelectric tensor and they are named as Ferromagnetotoroidic (eV2), Ferromagnetoelastic (aeV [V2]) crystals respectively. Here “e” denotes zero rank tensor that changes under spatial inversion, “a” denotes zero rank tensor that changes under time inversion, and “V” denotes a polar vector. Recent observations (Van Aken et al., 2007) identified the fourth type of primary ferroic crystals, a ferrotoroidic crystal with domains distinguished by a toroidial moment. The number of independent constants of quasi crystals is theoretically derived by Wenge Yang et al., (1995). He also formulated the number of independent components of any physical property tensor of quasi crystals using group representation theory. This paper accounts the effect of symmetry on some ferrotoroidial properties of quasi Crystals with 5-fold, 8-fold, 10-fold and 12-fold symmetries using group theoretical methods. Also the number of independent constants is calculated and tabulated that helps in describing the ferrotoroidial properties.

Effect of Shock Waves on Dielectric Properties of KDP Crystal

NASA Astrophysics Data System (ADS)

Sivakumar, A.; Suresh, S.; Pradeep, J. Anto; Balachandar, S.; Martin Britto Dhas, S. A.

2018-05-01

An alternative non-destructive approach is proposed and demonstrated for modifying electrical properties of crystal using shock-waves. The method alters dielectric properties of a potassium dihydrogen phosphate (KDP) crystal by loading shock-waves generated by a table-top shock tube. The experiment involves launching the shock-waves perpendicular to the (100) plane of the crystal using a pressure driven table-top shock tube with Mach number 1.9. Electrical properties of dielectric constant, dielectric loss, permittivity, impedance, AC conductivity, DC conductivity and capacitance as a function of spectrum of frequency from 1 Hz to 1 MHz are reported for both pre- and post-shock wave loaded conditions of the KDP crystal. The experimental results reveal that dielectric constant of KDP crystal is sensitive to the shock waves such that the value decreases for the shock-loaded KDP sample from 158 to 147. The advantage of the proposed approach is that it is an alternative to the conventional doping process for tailoring dielectric properties of this type of crystal.

Tunable organization of cellulose nanocrystals for controlled thermal and optical response

NASA Astrophysics Data System (ADS)

Diaz A., Jairo A.

The biorenewable nature of cellulose nanocrystals (CNCs) has opened up new opportunities for cost-effective, sustainable materials design. By taking advantage of their distinctive structural properties and self-assembly, promising applications have started to nurture the fields of flexible electronics, biomaterials, and nanocomposites. CNCs exhibit two fundamental characteristics: rod-like morphology (5-20 nm wide, 50-500 nm long), and lyotropic behavior (i.e., liquid crystalline mesophases formed in solvents), which offer unique opportunities for structural control and fine tuning of thermal and optical properties based on a proper understanding of their individual behavior and interactions at different length scales. In the present work, we attempt to provide an integral description of the influence of single crystals in the thermal and optical response exhibited by nanostructured films. Our approach involved the connection of experimental evidence with predictions of molecular dynamics (MD) simulations. In order to assess the effect of CNC orientation in the bulk response, we produced cellulose nanostructured films under two different mechanisms, namely, self-organization and shear orientation. Self-organized nanostructured films exhibited the typical iridescent optical reflection generated by chiral nematic organization. Shear oriented films disrupted the cholesteric organization, generating highly aligned structures with high optical transparency. The resultant CNC organization present in all nanostructured films was estimated by a second order statistical orientational distribution based on two- dimensional XRD signals. A new method to determine the coefficient of thermal expansion (CTE) in a contact-free fashion was developed to properly characterize the thermal expansion of thin soft films by excluding other thermally activated phenomena. The method can be readily extended to other soft materials to accurately measure thermal strains in a non-destructive way. By evaluating the magnitude of film CTEs relative to those of individual CNC crystals, we highlighted the significant role played by crystalline interfaces. Likewise, after measuring the thermal conductivity of a single crystal and CNC films having multiple organizations, the interfacial thermal resistance arose as a governing factor for heat transport. We will offer further insights into the intricate connection of thermal and optical properties towards a future efficient manufacture and optimal CNC based-materials design.

Synthesis, crystal structure, and luminescence properties of a new nitride polymorph, β-Sr0.98Eu0.02AlSi4N7

NASA Astrophysics Data System (ADS)

Yoshimura, Fumitaka; Yamane, Hisanori; Nagasako, Makoto

2018-02-01

Prismatic vermilion single crystals 200 μm-2 mm in size, together with a white powder, were obtained by heating a mixture of binary nitrides containing Mg3N2 at 2030 °C under 0.85 MPa of N2. Yellow, thick-platelet single crystals with sizes of 150-500 μm were also found to grow at or near the surface of the product. Single crystal X-ray diffraction demonstrated that the vermilion crystals were orthorhombic Sr0.98Eu0.02AlSi4N7, which has been prepared in previous studies and is termed the α phase of this compound. The yellow crystals were revealed to be a new polymorph of Sr0.98Eu0.02AlSi4N7 (β phase) that crystalized in a monoclinic cell (a = 8.1062(1) Å, b = 9.0953(1) Å, c = 8.9802(2) Å, β = 111.6550(5)°, space group P21) with twins that could be examined by transmission and scanning transmission electron microscopy. β-Sr0.98Eu0.02AlSi4N7 was found to have a three-dimensional network structure formed by the stacking of two types of layers. One is a dreier layer of (Al/Si)N4 tetrahedra that consists of N vertex-sharing double chains of (Al/Si)N4 tetrahedra extending in the c-axis direction with Sr and Eu atoms aligned between the chains, while the other is a layer of (Al/Si)N4 tetrahedra connected by sharing N edges and vertexes. The crystal structure of β-Sr0.98Eu0.02AlSi4N7 is similar to those of certain oxynitrides, such as Sr3Al3+xSi13-xN21-xO2+x:Eu2+ (x ≈ 0) and Sr4.9Eu0.1Al5+xSi21-xN35-xO2+x (x ≈ 0). The peak wavelength and full width at half maximum in the emission spectrum obtained from single crystals of β-Sr0.98Eu0.02AlSi4N7 under excitation at 400 nm were 541 and 66 nm, respectively.

Magnetic order of Nd 5 Pb 3 single crystals

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

Yan, Jiaqiang; Ochi, Masayuki; Cao, Huibo B.

We report millimeter-sized Nd 5Pb 3 single crystals grown out of a Nd–Co flux. We experimentally study the magnetic order of Nd 5Pb 3 single crystals by measuring the anisotropic magnetic properties, electrical resistivity under high pressure up to 8 GPa, specific heat, and neutron single crystal diffraction. Two successive magnetic orders are observed at T N1 = 44 K and T N2 = 8 K. The magnetic cells can be described with a propagation vector $k=(0.5, 0, 0)$ . Cooling below T N1, Nd1 and Nd3 order forming ferromagnetic stripes along the b-axis, and the ferromagnetic stripes are coupledmore » antiferromagnetically along the a-axis for the $k=(0.5, 0, 0)$ magnetic domain. Cooling below T N2, Nd2 orders antiferromagnetically to nearby Nd3 ions. All ordered moments align along the crystallographic c-axis. The magnetic order at T N1 is accompanied by a quick drop of electrical resistivity upon cooling and a lambda-type anomaly in the temperature dependence of specific heat. At T N2, no anomaly was observed in electrical resistivity but there is a weak feature in specific heat. The resistivity measurements under hydrostatic pressures up to 8 GPa suggest a possible phase transition around 6 GPa. Our first-principles band structure calculations show that Nd 5Pb 3 has the same electronic structure as does Y 5Si 3 which has been reported to be a one-dimensional electride with anionic electrons that do not belong to any atom. Our study suggests that R 5Pb 3 (R = rare earth) can be a materials playground for the study of magnetic electrides. To conclude, this deserves further study after experimental confirmation of the presence of anionic electrons.« less

On the molecular anisotropy of liquid crystalline and flexible polymer systems

NASA Astrophysics Data System (ADS)

van Horn, Brett L.

The demand for products of ever increasing quality or for novel applications has required increasing attention to or manipulation of the anisotropy of manufactured parts. Oriented plastics are used everywhere from recording film to automotive body parts to monofilament fishing line. Liquid crystals are also used in a wide array of applications including their dominance in the flat panel display industry, color changing temperature sensors, and woven bullet resistant fabrics. Anisotropy can also be detrimental, for instance sometimes leading to poor fracture resistance or low yield stress along specific directions. Controlling and measuring anisotropy of materials has become increasingly important, but doing so is wrought with challenges. Measuring physical properties of isotropic liquids, such as water or most oils can be done in a straightforward fashion. Their viscosities and densities, for example, have unique values under a given set of conditions. With anisotropic fluids, like liquid crystals, the viscosity, for instance, will not only depend upon temperature, concentration, etc. but also upon the direction of observation, degree of anisotropy, source of anisotropy, and so forth. This added degree of complexity complicates our ability to define the state of the material at which the measurements are made and generally necessitates the use of more sophisticated measurement strategies or techniques. This work presents techniques and tools for investigating anisotropy in liquid crystalline and stretched polymeric systems. Included are the use of conoscopy for the determination of birefringence and orientation of nematic liquid crystals and stretched polymers, the shear response of flow aligning nematic liquid crystal monodomains, and the design of a novel linear rheometer that allows for in situ optical or scattering investigations.

Magnetic order of Nd 5 Pb 3 single crystals

DOE PAGES

Yan, Jiaqiang; Ochi, Masayuki; Cao, Huibo B.; ...

2018-03-02

We report millimeter-sized Nd 5Pb 3 single crystals grown out of a Nd–Co flux. We experimentally study the magnetic order of Nd 5Pb 3 single crystals by measuring the anisotropic magnetic properties, electrical resistivity under high pressure up to 8 GPa, specific heat, and neutron single crystal diffraction. Two successive magnetic orders are observed at T N1 = 44 K and T N2 = 8 K. The magnetic cells can be described with a propagation vector $k=(0.5, 0, 0)$ . Cooling below T N1, Nd1 and Nd3 order forming ferromagnetic stripes along the b-axis, and the ferromagnetic stripes are coupledmore » antiferromagnetically along the a-axis for the $k=(0.5, 0, 0)$ magnetic domain. Cooling below T N2, Nd2 orders antiferromagnetically to nearby Nd3 ions. All ordered moments align along the crystallographic c-axis. The magnetic order at T N1 is accompanied by a quick drop of electrical resistivity upon cooling and a lambda-type anomaly in the temperature dependence of specific heat. At T N2, no anomaly was observed in electrical resistivity but there is a weak feature in specific heat. The resistivity measurements under hydrostatic pressures up to 8 GPa suggest a possible phase transition around 6 GPa. Our first-principles band structure calculations show that Nd 5Pb 3 has the same electronic structure as does Y 5Si 3 which has been reported to be a one-dimensional electride with anionic electrons that do not belong to any atom. Our study suggests that R 5Pb 3 (R = rare earth) can be a materials playground for the study of magnetic electrides. To conclude, this deserves further study after experimental confirmation of the presence of anionic electrons.« less

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).

Smectic C chevrons in nanocylinders

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

Lefort, R., E-mail: ronan.lefort@univ-rennes1.fr; Morineau, D.; Jean, F.

2014-11-17

The structure of an achiral smectic-C liquid crystal confined in nanocylinders with a planar surface anchoring is studied by small angle neutron scattering. We observe an invariant alignment of the nematic director with the pore axis, that promotes an original chevron structure with revolution symmetry.

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

Crystal Graph Convolutional Neural Networks for an Accurate and Interpretable Prediction of Material Properties

NASA Astrophysics Data System (ADS)

Xie, Tian; Grossman, Jeffrey C.

2018-04-01

The use of machine learning methods for accelerating the design of crystalline materials usually requires manually constructed feature vectors or complex transformation of atom coordinates to input the crystal structure, which either constrains the model to certain crystal types or makes it difficult to provide chemical insights. Here, we develop a crystal graph convolutional neural networks framework to directly learn material properties from the connection of atoms in the crystal, providing a universal and interpretable representation of crystalline materials. Our method provides a highly accurate prediction of density functional theory calculated properties for eight different properties of crystals with various structure types and compositions after being trained with 1 04 data points. Further, our framework is interpretable because one can extract the contributions from local chemical environments to global properties. Using an example of perovskites, we show how this information can be utilized to discover empirical rules for materials design.

Investigation of structural and electrical properties of La{sub 0.7}(Ba{sub 1-x}Ca{sub x}){sub 0.3}MnO{sub 3} compounds by sol-gel method

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

Winarsih, Suci; Kurniawan, Budhy, E-mail: bkuru07@gmail.com; Manaf, Azwar

2016-06-17

In this paper, we explored structural and electrical properties of La{sub 0.7}(Ba{sub 1-x}Ca{sub x}){sub 0.3}MnO{sub 3} (x = 0; 0.03; and 0.05) compounds. The general structure of perovskite manganites is AMnO{sub 3} (A= trivalent rare earth with divalent ion-doped). Average A-site cation size, external pressure, and the variance of the cation size σ{sup 2} are one of many factors that affected to magneto-transport properties of manganites as reported by others. In this work we focus only on the electrical properties in La{sub 0.7}Ba{sub 0.3}MnO{sub 3} Ca-doped compound which may influence crystal structure resulting resistivity phenomena under magnetic field influence. Allmore » samples were synthesized by sol-gel method from which fine powders were obtained. The X-ray powder diffraction pattern of powder materials shows that all samples are fully crystalline with a rhombohedral structure. Rietveld refinement shows that the presence of calcium has changed some crystal structural parameters such lattice parameter, Mn–O bond length, and Mn–O–Mn angles. The electrical resistivity of all synthesized materials investigated by four point probe method using Cryogenic Magnet in the temperature range of 50-300 K under influence a magnetic field shows resistivity temperature dependent. In fact presence of calcium has reduced the resistivity. It might occure because it has made an enhancement in the mobility of hopping electrons. The magnetic external field causes the resistivity decreased for all samples because host spin align by delocalizing the charge carries so electron itinerant through the lattice suggested by other authors. Both calcium dopant concentration and the applied external magnetic field shows strong correlation in reduction of resistivity.« less

Crystal growth, structural, optical, mechanical and thermal properties of a new nonlinear optical single crystal: L-Ornithine monohydrochloride.

PubMed

Balakrishnan, T; Ramamurthi, K

2009-03-01

Amino acid family crystals exhibit excellent nonlinear optical and electro optical properties. l-Ornithine monohydrochloride single crystal, belongs to the amino acid group, was grown by the slow evaporation solution growth technique at room temperature. The grown crystals were characterized by single crystal and powder X-ray diffraction analysis, Fourier transform infrared (FTIR) spectroscopy, TGA, DTA and DSC analyses. UV-vis-NIR spectrum shows excellent transmission in the UV, visible and NIR region (300-1600nm). The mechanical properties of grown crystals were studied using Vickers microhardness tester. Its second harmonic generation efficiency was tested using Nd:YAG laser and is 1.25 times that of KDP.

Controllable fabrication of copper phthalocyanine nanostructure crystals.

PubMed

Liu, Fangmei; Sun, Jia; Xiao, Si; Huang, Wenglong; Tao, Shaohua; Zhang, Yi; Gao, Yongli; Yang, Junliang

2015-06-05

Copper phthalocyanine (CuPc) nanostructure crystals, including nanoflower, nanoribbon, and nanowire, were controllably fabricated by temperature gradient physical vapor deposition (TG-PVD) through controlling the growth parameters. In a controllable growth system with carrier gas N2, nanoflower, nanoribbon, and nanowire crystals were formed in a high-temperature zone, medium-temperature zone, and low-temperature zone, respectively. They were proved to be β-phase, coexist of α-phase and β-phase, and α-phase respectively based on x-ray diffraction results. Furthermore, ultralong CuPc nanowires up to several millimeters could be fabricated by TG-PVD without carrier gas, and they were well-aligned to form large-area CuPc nanowire crystal arrays by the Langmuir-Blodgett method. The nanostructure crystals showed unusual optical absorption spectra from the ultraviolet-visible to near-infrared range, which was explained by the diffraction and scattering caused by the wavelength-sized nanostructures. These CuPc nanostructure crystals show potential applications in organic electronic and optoelectronic devices.

Self-Aligned Growth of Organic Semiconductor Single Crystals by Electric Field.

PubMed

Kotsuki, Kenji; Obata, Seiji; Saiki, Koichiro

2016-01-19

We proposed a novel but facile method for growing organic semiconductor single-crystals via solvent vapor annealing (SVA) under electric field. In the conventional SVA growth process, nuclei of crystals appeared anywhere on the substrate and their crystallographic axes were randomly distributed. We applied electric field during the SVA growth of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) on the SiO2/Si substrate on which a pair of electrodes had been deposited beforehand. Real-time observation of the SVA process revealed that rodlike single crystals grew with their long axes parallel to the electric field and bridged the prepatterned electrodes. As a result, C8-BTBT crystals automatically formed a field effect transistor (FET) structure and the mobility reached 1.9 cm(2)/(V s). Electric-field-assisted SVA proved a promising method for constructing high-mobility single-crystal FETs at the desired position by a low-cost solution process.

Membrane crystallization of lysozyme: kinetic aspects

NASA Astrophysics Data System (ADS)

Profio, Gianluca Di; Curcio, Efrem; Cassetta, Alberto; Lamba, Doriano; Drioli, Enrico

2003-10-01

The relevant kinetic aspects related to an innovative method of biological macromolecules crystallization based on microporous hydrophobic membranes, used both as active surfaces to promote heterogeneous nucleation and as a mass-transfer apparatus to concentrate macromolecular solutions by solvent removal in vapour phase, have been evaluated. Polypropylene membranes, supplied in the form of hollow fibres, have been aligned in a versatile system, designed for an on-line spectrophotometric monitoring of hen egg white lysozyme crystallizing solutions (experimental conditions: 0.1 M NaAc/HAc Buffer pH 4.6, 0.5-5.8% wt/vol NaCl, 20°C). The turbidity measurements have been exploited in order to follow: (i) the induction time of crystallization, (ii) the early stage nucleation kinetics based on the Rayleigh scattering theory, and (iii) the crystal growth rate (coupled with data evaluated from image-analysis carried out by optical microscopy) under a model hypothesis of exponential growth of clusters. The crystals have been qualitatively assessed by an X-ray crystallographic analysis carried out at the synchrotron light laboratory ELETTRA.

Advancing flexible volatile compound sensors using liquid crystals encapsulated in polymer fibers

NASA Astrophysics Data System (ADS)

Reyes, Catherine G.; Lagerwall, Jan P. F.

2018-02-01

Until recently, organic vapor sensors using liquid crystals (LCs) have employed rigid glass substrates for confining the LC, and bulky equipment for vapor detection. Previously, we demonstrated that coaxially electrospinning nematic LC within the core of polymer fibers provides an alternative and improved form factor for confinement. This enables ppm level sensitivity to harmful industrial organics, such as toluene, while giving the flexibility of textile-like sheets (imparted by polymer encapsulation). Moreover, toluene vapor responses of the LC-core fiber mats were visible macroscopically with the naked eye depending on the morphology of the fibers produced, and whether they were oriented in specific geometries (aligned, or random). We identified two types of responses: one corresponds to the LC transition from nematic to isotropic, and the other we suggest is due to an anchoring change at the LC-polymer interface that influences the alignment. While we need to study the presence that defects can have in more detail, we noted that fiber mat thickness is crucial in attempting to understand how and why we are able to visualize two responses in aligned LC-fiber mats. Ultimately, we noted that the response of the polymer sheath itself (softening) to organic vapor exposure affects the liquid crystal confinement in the core. From the microscopic point of view, this will influence the threshold concentration that fibers in a mat will overall respond to. In this paper we will discuss three findings the morphologies enabling LC-core fiber mat response to vapor seen both micro- and macroscopically, how thickness of the fiber mat can play a role in the visualization of the responses, and the effect that the polymer structure has in the mat's sensitivity threshold.

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

Controlled Synthesis of Ultralong Carbon Nanotubes with Perfect Structures and Extraordinary Properties.

PubMed

Zhang, Rufan; Zhang, Yingying; Wei, Fei

2017-02-21

Carbon nanotubes (CNTs) have drawn intensive research interest in the past 25 years due to their excellent properties and wide applications. Ultralong CNTs refers to the horizontally aligned CNT arrays which are usually grown on flat substrates, parallel with each other with large intertube distances. They usually have perfect structures, excellent properties, and lengths up to centimeters, even decimeters. Ultralong CNTs are promising candidates as building blocks for transparent displays, nanoelectronics, superstrong tethers, aeronautics and aerospace materials, etc. The controlled synthesis of ultralong CNTs with perfect structures is the key to fully exploit the extraordinary properties of CNTs. CNTs are typical one-dimensional single-crystal nanomaterials. It has always been a great challenge how to grow macroscale single-crystals with no defects. Thus, the synthesis of ultralong CNTs with no defect is of significant importance from both fundamental and industrial aspects. In this Account, we focus on our progress on the controlled synthesis of ultralong CNTs with perfect structures and excellent properties. A deep understanding of the CNT growth mechanism is the first step for the controlled synthesis of ultralong CNTs with high quality. We first introduce the growth mechanism for ultralong CNTs and the main factor affecting their structures. We then discuss the strategies to control the defects in the as-grown ultralong CNTs. With these approaches, ultralong high-quality CNTs with different structures can be obtained. By completely eliminating the factors which may induce defects in the CNT walls, ultralong CNTs with perfect structures can be obtained. Their chiral indices keep unchanged for several centimeters long along the axial direction of the CNTs. The defect-free structures render the ultralong CNTs with excellent electrical, mechanical and thermal properties. The as-grown ultralong CNTs exhibit superhigh mechanical strength (>100 GPa) and their breaking strain (>17.5%) reach the theoretical limits. They also show excellent electrical and thermal properties. In addition, centimeters long CNTs showed macroscale interwall superlubricious properties due to their defect-free structures. Ultralong, defect-free CNTs with controlled structures are highly desirable for many high-end applications. We hope that this Account will shed light on the controlled synthesis of ultralong CNTs with perfect structures and excellent properties. Moreover, the growth mechanism and controlled synthesis of ultralong CNTs with perfect structures also offers a good model for other one-dimensional nanomaterials.

Shear induced alignment of short nanofibers in 3D printed polymer composites.

PubMed

Yunus, Doruk Erdem; Shi, Wentao; Sohrabi, Salman; Liu, Yaling

2016-12-09

3D printing of composite materials offers an opportunity to combine the desired properties of composite materials with the flexibility of additive manufacturing in geometric shape and complexity. In this paper, the shear-induced alignment of aluminum oxide nanowires during stereolithography printing was utilized to fabricate a nanowire reinforced polymer composite. To align the fibers, a lateral oscillation mechanism was implemented and combined with wall pattern printing technique to generate shear flow in both vertical and horizontal directions. A series of specimens were fabricated for testing the composite material's tensile strength. The results showed that mechanical properties of the composite were improved by reinforcement of nanofibers through shear induced alignment. The improvement of tensile strength was approximately ∼28% by aligning the nanowires at 5 wt% (∼1.5% volume fraction) loading of aluminum oxide nanowires.

High Efficient Ultra-Thin Flat Optics Based on Dielectric Metasurfaces

NASA Astrophysics Data System (ADS)

Ozdemir, Aytekin

Metasurfaces which emerged as two-dimensional counterparts of metamaterials, facilitate the realization of arbitrary phase distributions using large arrays with subwavelength and ultra-thin features. Even if metasurfaces are ultra-thin, they still effectively manipulate the phase, amplitude, and polarization of light in transmission or reflection mode. In contrast, conventional optical components are bulky, and they lose their functionality at sub-wavelength scales, which requires conceptually new types of nanoscale optical devices. On the other hand, as the optical systems shrink in size day by day, conventional bulky optical components will have tighter alignment and fabrication tolerances. Since metasurfaces can be fabricated lithographically, alignment can be done during lithographic fabrication, thus eliminating the need for post-fabrication alignments. In this work, various types of metasurface applications are thoroughly investigated for robust wavefront engineering with enhanced characteristics in terms of broad bandwidth, high efficiency and active tunability, while beneficial for application. Plasmonic metasurfaces are not compatible with the CMOS process flow, and, additionally their high absorption and ohmic loss is problematic in transmission based applications. Dielectric metasurfaces, however, offer a strong magnetic response at optical frequencies, and thus they can offer great opportunities for interacting not only with the electric component of a light field, but also with its magnetic component. They show great potential to enable practical device functionalities at optical frequencies, which motivates us to explore them one step further on wavefront engineering and imaging sensor platforms. Therefore, we proposed an efficient ultra-thin flat metalens at near-infrared regime constituted by silicon nanodisks which can support both electric and magnetic dipolar Mie-type resonances. These two dipole resonances can be overlapped at the same frequency by varying the geometric parameters of silicon nanodisks. Having two resonance mechanisms at the same frequency allows us to achieve full (0-2?) phase shift on the transmitted beam. To enable the miniaturization of pixel size for achieving high-resolution, planar, compact-size focal plane arrays (FPAs), we also present and explore the metasurface lens array-based FPAs. The investigated dielectric metasurface lens arrays achieved high focusing efficiency with superior optical crosstalk performance. We see a magnificent application prospect for metasurfaces in enhancing the fill factor and reducing the pixel size of FPAs and CCD, CMOS imaging sensors as well. Moreover, it is of paramount importance to design metasurfaces possessing tunable properties. Thus, we also propose a tunable beam steering device by combining phase manipulating metasurfaces concept and liquid crystals. Tunability feature is implemented by nematic liquid crystals infiltrated into nano holes in SiO2. Using electrically tunable nematic liquid crystals, dynamic beam steering is achieved.