A micromechanical approach for homogenization of elastic metamaterials with dynamic microstructure

NASA Astrophysics Data System (ADS)

Muhlestein, Michael B.; Haberman, Michael R.

2016-08-01

An approximate homogenization technique is presented for generally anisotropic elastic metamaterials consisting of an elastic host material containing randomly distributed heterogeneities displaying frequency-dependent material properties. The dynamic response may arise from relaxation processes such as viscoelasticity or from dynamic microstructure. A Green's function approach is used to model elastic inhomogeneities embedded within a uniform elastic matrix as force sources that are excited by a time-varying, spatially uniform displacement field. Assuming dynamic subwavelength inhomogeneities only interact through their volume-averaged fields implies the macroscopic stress and momentum density fields are functions of both the microscopic strain and velocity fields, and may be related to the macroscopic strain and velocity fields through localization tensors. The macroscopic and microscopic fields are combined to yield a homogenization scheme that predicts the local effective stiffness, density and coupling tensors for an effective Willis-type constitutive equation. It is shown that when internal degrees of freedom of the inhomogeneities are present, Willis-type coupling becomes necessary on the macroscale. To demonstrate the utility of the homogenization technique, the effective properties of an isotropic elastic matrix material containing isotropic and anisotropic spherical inhomogeneities, isotropic spheroidal inhomogeneities and isotropic dynamic spherical inhomogeneities are presented and discussed.

Study on Silicon Microstructure Processing Technology Based on Porous Silicon

NASA Astrophysics Data System (ADS)

Shang, Yingqi; Zhang, Linchao; Qi, Hong; Wu, Yalin; Zhang, Yan; Chen, Jing

2018-03-01

Aiming at the heterogeneity of micro - sealed cavity in silicon microstructure processing technology, the technique of preparing micro - sealed cavity of porous silicon is proposed. The effects of different solutions, different substrate doping concentrations, different current densities, and different etching times on the rate, porosity, thickness and morphology of the prepared porous silicon were studied. The porous silicon was prepared by different process parameters and the prepared porous silicon was tested and analyzed. For the test results, optimize the process parameters and experiments. The experimental results show that the porous silicon can be controlled by optimizing the parameters of the etching solution and the doping concentration of the substrate, and the preparation of porous silicon with different porosity can be realized by different doping concentration, so as to realize the preparation of silicon micro-sealed cavity, to solve the sensor sensitive micro-sealed cavity structure heterogeneous problem, greatly increasing the application of the sensor.

Studies on the reactive melt infiltration of silicon and silicon-molybdenum alloys in porous carbon

NASA Technical Reports Server (NTRS)

Singh, M.; Behrendt, D. R.

1992-01-01

Investigations on the reactive melt infiltration of silicon and silicon-1.7 and 3.2 at percent molybdenum alloys into porous carbon preforms have been carried out by process modeling, differential thermal analysis (DTA) and melt infiltration experiments. These results indicate that the initial pore volume fraction of the porous carbon preform is a critical parameter in determining the final composition of the raction-formed silicon carbide and other residual phases. The pore size of the carbon preform is very detrimental to the exotherm temperatures due to liquid silicon-carbon reactions encountered during the reactive melt infiltration process. A possible mechanism for the liquid silicon-porous (glassy) carbon reaction has been proposed. The composition and microstructure of the reaction-formed silicon carbide has been discussed in terms of carbon preform microstructures, infiltration materials, and temperatures.

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

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

Brannon, R.M.

1996-12-31

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

Composite silicon nanostructure arrays fabricated on optical fibre by chemical etching of multicrystal silicon film.

PubMed

Zuo, Zewen; Zhu, Kai; Ning, Lixin; Cui, Guanglei; Qu, Jun; Huang, Wanxia; Shi, Yi; Liu, Hong

2015-04-17

Integrating nanostructures onto optical fibers presents a promising strategy for developing new-fashioned devices and extending the scope of nanodevices' applications. Here we report the first fabrication of a composite silicon nanostructure on an optical fiber. Through direct chemical etching using an H2O2/HF solution, multicrystal silicon films with columnar microstructures are etched into a vertically aligned, inverted-cone-like nanorod array embedded in a nanocone array. A faster dissolution rate of the silicon at the void-rich boundary regions between the columns is found to be responsible for the separation of the columns, and thus the formation of the nanostructure array. The morphology of the nanorods primarily depends on the microstructure of the columns in the film. Through controlling the microstructure of the as-grown film and the etching parameters, the structural control of the nanostructure is promising. This fabrication method can be extended to a larger length scale, and it even allows roll-to-roll processing.

Sintering and microstructure of silicon carbide ceramic with Y3Al5O12 added by sol-gel method*

PubMed Central

Guo, Xing-zhong; Yang, Hui

2005-01-01

Silicon carbide (SiC) ceramic with YAG (Y3Al5O12) additive added by sol-gel method was liquid-phase sintered at different sintering temperatures, and the sintering mechanism and microstructural characteristics of resulting silicon carbide ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and elemental distribution of surface (EDS). YAG (yttrium aluminum garnet) phase formed before the sintering and its uniform distribution in the SiC/YAG composite powder decreased the sintering temperature and improved the densification of SiC ceramic. The suitable sintering temperature was 1860 °C with the specimen sintered at this temperature having superior sintering and mechanical properties, smaller crystal size and fewer microstructure defects. Three characteristics of improved toughness of SiC ceramic with YAG added by sol-gel method were microstructural densification, main-crack deflection and crystal ‘bridging’. PMID:15682507

Finite element analysis of the upsetting of a 5056 aluminum alloy sample with consideration of its microstructure

NASA Astrophysics Data System (ADS)

Voronin, S. V.; Chaplygin, K. K.

2017-12-01

Computer simulation of upsetting the finite element models (FEMs) of an isotropic 5056 aluminum alloy sample and a 5056 aluminum alloy sample with consideration of microstructure is carried out. The stress and strain distribution patterns at different process stages are obtained. The strain required for the deformation of the FEMs of 5056 alloy samples is determined. The influence of the material microstructure on the stress-strain behavior and technological parameters are demonstrated.

Drilling Holes in Graphite/Epoxy Composites

NASA Technical Reports Server (NTRS)

Daniels, J. G.; Ledbetter, Frank E., III; Penn, B. G.; White, W. L.

1986-01-01

Slurry of silicon carbide powder in water fed onto bit while drilling. Slurry contains about 60 percent silicon carbide by weight. Slurry recirculated by low-power pump. With slurry, dull tools cut as fast as, or faster than, sharp ones. Holes drilled rapidly and efficiently regardless of ply orientation; whether unidirectional, quasi-isotropic symmetrical, or cross-ply.

Metallic coatings on silicon substrates, and methods of forming metallic coatings on silicon substrates

DOEpatents

Branagan, Daniel J [Idaho Falls, ID; Hyde, Timothy A [Idaho Falls, ID; Fincke, James R [Los Alamos, NM

2008-03-11

The invention includes methods of forming a metallic coating on a substrate which contains silicon. A metallic glass layer is formed over a silicon surface of the substrate. The invention includes methods of protecting a silicon substrate. The substrate is provided within a deposition chamber along with a deposition target. Material from the deposition target is deposited over at least a portion of the silicon substrate to form a protective layer or structure which contains metallic glass. The metallic glass comprises iron and one or more of B, Si, P and C. The invention includes structures which have a substrate containing silicon and a metallic layer over the substrate. The metallic layer contains less than or equal to about 2 weight % carbon and has a hardness of at least 9.2 GPa. The metallic layer can have an amorphous microstructure or can be devitrified to have a nanocrystalline microstructure.

Nanocomposite capsules with directional, pulsed nanoparticle release.

PubMed

Udoh, Christiana E; Cabral, João T; Garbin, Valeria

2017-12-01

The precise spatiotemporal delivery of nanoparticles from polymeric capsules is required for applications ranging from medicine to materials science. These capsules derive key performance aspects from their overall shape and dimensions, porosity, and internal microstructure. To this effect, microfluidics provide an exceptional platform for emulsification and subsequent capsule formation. However, facile and robust approaches for nanocomposite capsule fabrication, exhibiting triggered nanoparticle release, remain elusive because of the complex coupling of polymer-nanoparticle phase behavior, diffusion, phase inversion, and directional solidification. We investigate a model system of polyelectrolyte sodium poly(styrene sulfonate) and 22-nm colloidal silica and demonstrate a robust capsule morphology diagram, achieving a range of internal morphologies, including nucleated and bicontinuous microstructures, as well as isotropic and non-isotropic external shapes. Upon dissolution in water, we find that capsules formed with either neat polymers or neat nanoparticles dissolve rapidly and isotropically, whereas bicontinuous, hierarchical, composite capsules dissolve via directional pulses of nanoparticle clusters without disrupting the scaffold, with time scales tunable from seconds to hours. The versatility, facile assembly, and response of these nanocomposite capsules thus show great promise in precision delivery.

SiC (SCS-6) Fiber Reinforced-Reaction Formed SiC Matrix Composites: Microstructure and Interfacial Properties

NASA Technical Reports Server (NTRS)

Singh, M.; Dickerson, R. M.; Olmstead, Forrest A.; Eldridge, J. I.

1997-01-01

Microstructural and interfacial characterization of unidirectional SiC (SCS-6) fiber reinforced-reaction formed SiC (RFSC) composites has been carried out. Silicon-1.7 at.% molybdenum alloy was used as the melt infiltrant, instead of pure silicon, to reduce the activity of silicon in the melt as well as to reduce the amount of free silicon in the matrix. Electron microprobe analysis was used to evaluate the microstructure and phase distribution in these composites. The matrix is SiC with a bi-modal grain-size distribution and small amounts of MoSi2, silicon, and carbon. Fiber push-outs tests on these composites showed that a desirably low interfacial shear strength was achieved. The average debond shear stress at room temperature varied with specimen thickness from 29 to 64 MPa, with higher values observed for thinner specimens. Initial frictional sliding stresses showed little thickness dependence with values generally close to 30 MPa. Push-out test results showed very little change when the test temperature was increased to 800 C from room temperature, indicating an absence of significant residual stresses in the composite.

Microstructure and Mechanical Properties of Reaction-Formed Silicon Carbide (RFSC) Ceramics

NASA Technical Reports Server (NTRS)

Singh, M.; Behrendt, D. R.

1994-01-01

The microstructure and mechanical properties of reaction-formed silicon carbide (RFSC) ceramics fabricated by silicon infiltration of porous carbon preforms are discussed. The morphological characterization of the carbon preforms indicates a very narrow pore size distribution. Measurements of the preform density by physical methods and by mercury porosimetry agree very well and indicate that virtually all of the porosity in the preforms is open to infiltrating liquids. The average room temperature flexural strength of the RFSC material with approximately 8 at.% free silicon is 369 +/- 28 MPa (53.5 +/- 4 ksi). The Weibull strength distribution data give a characteristic strength value of 381 MPa (55 ksi) and a Weibull modulus of 14.3. The residual silicon content is lower and the strengths are superior to those of most commercially available reaction-bonded silicon carbide materials.

Method to fabricate multi-level silicon-based microstructures via use of an etching delay layer

DOEpatents

Manginell, Ronald P.; Schubert, W. Kent; Shul, Randy J.

2005-08-16

New methods for fabrication of silicon microstructures have been developed. In these methods, an etching delay layer is deposited and patterned so as to provide differential control on the depth of features being etched into a substrate material. Structures having features with different depth can be formed thereby in a single etching step.

Metal-assisted etch combined with regularizing etch

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

Yim, Joanne; Miller, Jeff; Jura, Michael

In an aspect of the disclosure, a process for forming nanostructuring on a silicon-containing substrate is provided. The process comprises (a) performing metal-assisted chemical etching on the substrate, (b) performing a clean, including partial or total removal of the metal used to assist the chemical etch, and (c) performing an isotropic or substantially isotropic chemical etch subsequently to the metal-assisted chemical etch of step (a). In an alternative aspect of the disclosure, the process comprises (a) performing metal-assisted chemical etching on the substrate, (b) cleaning the substrate, including removal of some or all of the assisting metal, and (c) performingmore » a chemical etch which results in regularized openings in the silicon substrate.« less

Microstructures of BN/SiC coatings on nicalon fibers

NASA Technical Reports Server (NTRS)

Dickerson, R. M.; Singh, M.

1995-01-01

The microstructures of Nicalon silicon carbide (SiC) fibers and layered coatings of boron nitride (BN) followed by chemical vapor infiltrated silicon carbide (CVI-SiC) were characterized using optical and electron microscopy. Two different precursors and reactions were used to produce the BN layers while the deposition of CVI silicon carbide was nearly identical. Coated tows were examined in cross-section to characterize the chemistry and structures of the constituents and the interfaces. One BN precursor yielded three sublayers while the other gave a relatively homogeneous nanocrystalline layer.

Silicon vertical microstructure fabrication by catalytic etching

NASA Astrophysics Data System (ADS)

Huang, Mao-Jung; Yang, Chii-Rong; Chang, Chun-Ming; Chu, Nien-Nan; Shiao, Ming-Hua

2012-08-01

This study presents an effective, simple and inexpensive process for forming micro-scale vertical structures on a (1 0 0) silicon wafer. Several modified etchants and micro-patterns including rectangular, snake-like, circular and comb patterns were employed to determine the optimum etching process. We found that an etchant solution consisting of 4.6 M hydrofluoric acid, 0.44 M hydrogen peroxide and isopropyl alcohol produces microstructures at an etching rate of 0.47 µm min-1 and surface roughness of 17.4 nm. All the patterns were transferred faithfully to the silicon substrate.

Capacitive pressure-sensitive composites using nickel-silicone rubber: experiments and modeling

NASA Astrophysics Data System (ADS)

Fan, Yuqin; Liao, Changrong; Liao, Ganliang; Tan, Renbing; Xie, Lei

2017-07-01

Capacitive pressure (i.e., piezo-capacitive) sensors have manifested their superiority as a potential electronic skin. The mechanism of the traditional piezo-capacitive sensors is mainly to change the relative permittivity of the flexible composites by compressing the specially fabricated microstructures in the polymer matrix under pressure. Instead, we study the piezo-capacitive effect for a newly reported isotropic flexible composite consisting of silicone rubber (SR) and uniformly dispersed micron-sized conductive nickel particles experimentally and theoretically. The Young’s modulus of the nickel-SR composites (NSRCs) is designed to meet that of human skin. Experimental results show that the NSRCs exhibit remarkable particle concentration dependent capacitance response under uniaxial pressure, and the NSRCs present a good repeatability. We propose a mathematical model at particle level to provide deep insights into the piezo-capacitive mechanism, by considering the adjacent particles in the axial direction as micro capacitors connected in series and in parallel on the horizontal plane. The piezo-capacitive effect is determined by the relative permittivity induced by the particles rearrangement, longitudinal interparticle gap, and deflection angle of micro particle capacitors under pressure. Specifically, the relative capacitance of NSRC capacitor is deduced to be product of two factors: the degree of particle rearrangement, and the relative capacitance of a micro capacitor with the average longitudinal gap. The proposed model well matches and interprets the experimental results.

Silicon etching using only Oxygen at high temperature: An alternative approach to Si micro-machining on 150 mm Si wafers

NASA Astrophysics Data System (ADS)

Chai, Jessica; Walker, Glenn; Wang, Li; Massoubre, David; Tan, Say Hwa; Chaik, Kien; Hold, Leonie; Iacopi, Alan

2015-12-01

Using a combination of low-pressure oxygen and high temperatures, isotropic and anisotropic silicon (Si) etch rates can be controlled up to ten micron per minute. By varying the process conditions, we show that the vertical-to-lateral etch rate ratio can be controlled from 1:1 isotropic etch to 1.8:1 anisotropic. This simple Si etching technique combines the main respective advantages of both wet and dry Si etching techniques such as fast Si etch rate, stiction-free, and high etch rate uniformity across a wafer. In addition, this alternative O2-based Si etching technique has additional advantages not commonly associated with dry etchants such as avoiding the use of halogens and has no toxic by-products, which improves safety and simplifies waste disposal. Furthermore, this process also exhibits very high selectivity (>1000:1) with conventional hard masks such as silicon carbide, silicon dioxide and silicon nitride, enabling deep Si etching. In these initial studies, etch rates as high as 9.2 μm/min could be achieved at 1150 °C. Empirical estimation for the calculation of the etch rate as a function of the feature size and oxygen flow rate are presented and used as proof of concepts.

Distribution of Silicified Microstructures, Regulation of Cinnamyl Alcohol Dehydrogenase and Lodging Resistance in Silicon and Paclobutrazol Mediated Oryza sativa

PubMed Central

Dorairaj, Deivaseeno; Ismail, Mohd Razi

2017-01-01

Lodging is a phenomenon that affects most of the cereal crops including rice, Oryza sativa. This is due to the fragile nature of herbaceous plants whose stems are non-woody, thus affecting its ability to grow upright. Silicon (Si), a beneficial nutrient is often used to toughen and protect plants from biotic and abiotic stresses. Deposition of Si in plant tissues enhances the rigidity and stiffness of the plant as a whole. Silicified cells provide the much needed strength to the culm to resist breaking. Lignin plays important roles in cell wall structural integrity, stem strength, transport, mechanical support, and plant pathogen defense. The aim of this study is to resolve effects of Si on formation of microstructure and regulation of cinnamyl alcohol dehydrogenase (CAD), a key gene responsible for lignin biosynthesis. Besides evaluating silicon, paclobutrazol (PBZ) a plant growth retartdant that reduces internode elongation is also incorporated in this study. Hardness, brittleness and stiffness were improved in presence of silicon thus reducing lodging. Scanning electron micrographs with the aid of energy dispersive x-ray (EDX) was used to map silicon distribution. Presence of trichomes, silica cells, and silica bodies were detected in silicon treated plants. Transcripts of CAD gene was also upregulated in these plants. Besides, phloroglucinol staining showed presence of lignified vascular bundles and sclerenchyma band. In conclusion, silicon treated rice plants showed an increase in lignin content, silicon content, and formation of silicified microstructures. PMID:28747889

Ductile cutting of silicon microstructures with surface inclination measurement and compensation by using a force sensor integrated single point diamond tool

NASA Astrophysics Data System (ADS)

Chen, Yuan-Liu; Cai, Yindi; Shimizu, Yuki; Ito, So; Gao, Wei; Ju, Bing-Feng

2016-02-01

This paper presents a measurement and compensation method of surface inclination for ductile cutting of silicon microstructures by using a diamond tool with a force sensor based on a four-axis ultra-precision lathe. The X- and Y-directional inclinations of a single crystal silicon workpiece with respect to the X- and Y-motion axes of the lathe slides were measured respectively by employing the diamond tool as a touch-trigger probe, in which the tool-workpiece contact is sensitively detected by monitoring the force sensor output. Based on the measurement results, fabrication of silicon microstructures can be thus carried out directly along the tilted silicon workpiece by compensating the cutting motion axis to be parallel to the silicon surface without time-consuming pre-adjustment of the surface inclination or turning of a flat surface. A diamond tool with a negative rake angle was used in the experiment for superior ductile cutting performance. The measurement precision by using the diamond tool as a touch-trigger probe was investigated. Experiments of surface inclination measurement and ultra-precision ductile cutting of a micro-pillar array and a micro-pyramid array with inclination compensation were carried out respectively to demonstrate the feasibility of the proposed method.

Hemispherical cavities on silicon substrates: an overview of micro fabrication techniques

NASA Astrophysics Data System (ADS)

Poncelet, O.; Rasson, J.; Tuyaerts, R.; Coulombier, M.; Kotipalli, R.; Raskin, J.-P.; Francis, L. A.

2018-04-01

Hemispherical photonic crystals found in species like Papilio blumei and Cicendella chinensis have inspired new applications like anti-counterfeiting devices and gas sensors. In this work, we investigate and compare four different ways to micro fabricate such hemispherical cavities: using colloids as template, by wet (HNA) or dry (XeF2) isotropic etching of silicon and by electrochemical etching of silicon. The shape and the roughness of the obtained cavities have been discussed and the pros/cons for each method are highlighted.

Carbon--silicon coating alloys for improved irradiation stability

DOEpatents

Bokros, J.C.

1973-10-01

For ceramic nuclear fuel particles, a fission product-retaining carbon-- silicon alloy coating is described that exhibits low shrinkage after exposure to fast neutron fluences of 1.4 to 4.8 x 10/sup 21/ n/cm/sup 2/ (E = 0.18 MeV) at irradiation temperatures from 950 to 1250 deg C. Isotropic pyrolytic carbon containing from 18 to 34 wt% silicon is co-deposited from a gaseous mixiure of propane, helium, and silane at a temperature of 1350 to 1450 deg C. (Official Gazette)

Evidence for interstellar SiC in the Murray carbonaceous meteorite

NASA Technical Reports Server (NTRS)

Bernatowicz, Thomas; Wopenka, Brigitte; Fraundorf, Gail; Ming, Tang; Anders, Edward

1987-01-01

Silicon carbide has been identified in two separates from the Murray carbonaceous chondrite that are enriched 20,000-fold in isotopically anomalous neon and xenon. The SiC is present in the form of crystalline grains 0.1-1 micron in size. Cubic and 111-plane-twinned cubic are the most common ordered polytypes observed so far. The anomalous isotopic composition of its carbon, nitrogen, and silicon indicates a presolar origin, probably in the atmospheres of red giants. An additional silicon- and oxygen-rich phase shows large isotropic anomalies in nitrogen and silicon, also associated with a presolar origin.

Fabrication of sinterable silicon nitride by injection molding

NASA Technical Reports Server (NTRS)

Quackenbush, C. L.; French, K.; Neil, J. T.

1982-01-01

Transformation of structural ceramics from the laboratory to production requires development of near net shape fabrication techniques which minimize finish grinding. One potential technique for producing large quantities of complex-shaped parts at a low cost, and microstructure of sintered silicon nitride fabricated by injection molding is discussed and compared to data generated from isostatically dry-pressed material. Binder selection methodology, compounding of ceramic and binder components, injection molding techniques, and problems in binder removal are discussed. Strength, oxidation resistance, and microstructure of sintered silicon nitride fabricated by injection molding is discussed and compared to data generated from isostatically dry-pressed material.

Method for providing an arbitrary three-dimensional microstructure in silicon using an anisotropic deep etch

DOEpatents

Morales, Alfredo M.; Gonzales, Marcela

2004-06-15

The present invention describes a method for fabricating an embossing tool or an x-ray mask tool, providing microstructures that smoothly vary in height from point-to-point in etched substrates, i.e., structure which can vary in all three dimensions. The process uses a lithographic technique to transfer an image pattern in the surface of a silicon wafer by exposing and developing the resist and then etching the silicon substrate. Importantly, the photoresist is variably exposed so that when developed some of the resist layer remains. The remaining undeveloped resist acts as an etchant barrier to the reactive plasma used to etch the silicon substrate and therefore provides the ability etch structures of variable depths.

Development of Simultaneous Corrosion Barrier and Optimized Microstructure in FeCrAl Heat-Resistant Alloy for Energy Applications. Part II: The Optimized Creep-Resistant Microstructure

NASA Astrophysics Data System (ADS)

Pimentel, G.; Aranda, M. M.; Chao, J.; González-Carrasco, J. L.; Capdevila, C.

2015-09-01

The first part of this two-part study reported the possibility of simultaneously generating a dense, self-healing α-alumina layer by thermal oxidation and a coarse-grained microstructure with a potential goodness for high-temperature creep resistance in a FeCrAl oxide dispersion-strengthened ferritic alloy that was cold deformed after hot rolling and extrusion. In this second part, the factors affecting the formation of the coarse-grained microstructure such as strain gradients induced during the rolling process are analyzed. It is concluded that larger strain gradients lead to more refined and more isotropic grain structures.

Fabrication of spherical microlens array by combining lapping on silicon wafer and rapid surface molding

NASA Astrophysics Data System (ADS)

Liu, Xiaohua; Zhou, Tianfeng; Zhang, Lin; Zhou, Wenchen; Yu, Jianfeng; Lee, L. James; Yi, Allen Y.

2018-07-01

Silicon is a promising mold material for compression molding because of its properties of hardness and abrasion resistance. Silicon wafers with carbide-bonded graphene coating and micro-patterns were evaluated as molds for the fabrication of microlens arrays. This study presents an efficient but flexible manufacturing method for microlens arrays that combines a lapping method and a rapid molding procedure. Unlike conventional processes for microstructures on silicon wafers, such as diamond machining and photolithography, this research demonstrates a unique approach by employing precision steel balls and diamond slurries to create microlenses with accurate geometry. The feasibility of this method was demonstrated by the fabrication of several microlens arrays with different aperture sizes and pitches on silicon molds. The geometrical accuracy and surface roughness of the microlens arrays were measured using an optical profiler. The measurement results indicated good agreement with the optical profile of the design. The silicon molds were then used to copy the microstructures onto polymer substrates. The uniformity and quality of the samples molded through rapid surface molding were also assessed and statistically quantified. To further evaluate the optical functionality of the molded microlens arrays, the focal lengths of the microlens arrays were measured using a simple optical setup. The measurements showed that the microlens arrays molded in this research were compatible with conventional manufacturing methods. This research demonstrated an alternative low-cost and efficient method for microstructure fabrication on silicon wafers, together with the follow-up optical molding processes.

Synthesis and Microstructure Evolution of Nano-Titania Doped Silicon Coatings

NASA Astrophysics Data System (ADS)

Moroz, N. A.; Umapathy, H.; Mohanty, P.

2010-01-01

The Anatase phase of Titania (TiO2) in nanocrystalline form is a well known photocatalyst. Photocatalysts are commercially used to accelerate photoreactions and increase photovoltaic efficiency such as in solar cells. This study investigates the in-flight synthesis of Titania and its doping into a Silicon matrix resulting in a catalyst-dispersed coating. A liquid precursor of Titanium Isopropoxide and ethanol was coaxially fed into the plasma gun to form Titania nanoparticles, while Silicon powder was externally injected downstream. Coatings of 75-150 μm thick were deposited onto flat coupons. Further, Silicon powder was alloyed with aluminum to promote crystallization and reduce the amorphous phase in the Silicon matrix. Dense coatings containing nano-Titania particles were observed under electron microscope. X-ray diffraction showed that both the Rutile and Anatase phases of the Titania exist. The influence of process parameters and aluminum alloying on the microstructure evolution of the doped coatings is analyzed and presented.

The effect of preparation conditions on the structure and mechanical properties of reaction-sintered silicon nitride

NASA Technical Reports Server (NTRS)

Heinrich, J.

1980-01-01

The microstructure of reaction sintered silicon nitride (RSSN) was changed over a wide range by varying the grain density, grain size of the silicon starting powder, nitriding conditions, and by introducing artificial pores. The influence of single microstructural parameters on mechanical properties like room temperature strength, creep behavior, and resistance to thermal shock was investigated. The essential factors influencing these properties were found to be total porosity, pore size distribution, and the fractions of alpha and beta Si3N4. In view of high temperature engineering applications of RSSN, potentials for optimizing the material's properties by controlled processing are discussed.

Dynamic Behavior and Optimization of Advanced Armor Ceramics: January-December 2012 Annual Report

DTIC Science & Technology

2015-03-01

tasks are reviewed: Nanostructured Armor Ceramics: Focus on Boron Carbide; The Role of Microstructure in the Impact Resistance for Silicon Carbide...Task 2: The Role of Microstructure in the Impact Resistance for Silicon Carbide (SiC), Core Program 22 3.1 Long-Range Goals 22 3.2 Background 22 3.3...from a 2-gr drop test using corn starch as a C source; D(0.9) = 1.27 μm ....................................................................12 Fig

Scaling up the Single Transducer Thickness-Independent Ultrasonic Imaging Method for Accurate Characterization of Microstructural Gradients in Monolithic and Composite Tubular Structures

NASA Technical Reports Server (NTRS)

Roth, Don J.; Carney, Dorothy V.; Baaklini, George Y.; Bodis, James R.; Rauser, Richard W.

1998-01-01

Ultrasonic velocity/time-of-flight imaging that uses back surface reflections to gauge volumetric material quality is highly suited for quantitative characterization of microstructural gradients including those due to pore fraction, density, fiber fraction, and chemical composition variations. However, a weakness of conventional pulse-echo ultrasonic velocity/time-of-flight imaging is that the image shows the effects of thickness as well as microstructural variations unless the part is uniformly thick. This limits this imaging method's usefulness in practical applications. Prior studies have described a pulse-echo time-of-flight-based ultrasonic imaging method that requires using a single transducer in combination with a reflector plate placed behind samples that eliminates the effect of thickness variation in the image. In those studies, this method was successful at isolating ultrasonic variations due to material microstructure in plate-like samples of silicon nitride, metal matrix composite, and polymer matrix composite. In this study, the method is engineered for inspection of more complex-shaped structures-those having (hollow) tubular/curved geometry. The experimental inspection technique and results are described as applied to (1) monolithic mullite ceramic and polymer matrix composite 'proof-of-concept' tubular structures that contain machined patches of various depths and (2) as-manufactured monolithic silicon nitride ceramic and silicon carbide/silicon carbide composite tubular structures that might be used in 'real world' applications.

Method for making circular tubular channels with two silicon wafers

DOEpatents

Yu, Conrad M.; Hui, Wing C.

1996-01-01

A two-wafer microcapillary structure is fabricated by depositing boron nitride (BN) or silicon nitride (Si.sub.3 N.sub.4) on two separate silicon wafers (e.g., crystal-plane silicon with [100] or [110] crystal orientation). Photolithography is used with a photoresist to create exposed areas in the deposition for plasma etching. A slit entry through to the silicon is created along the path desired for the ultimate microcapillary. Acetone is used to remove the photoresist. An isotropic etch, e.g., such as HF/HNO.sub.3 /CH.sub.3 COOH, then erodes away the silicon through the trench opening in the deposition layer. A channel with a half-circular cross section is then formed in the silicon along the line of the trench in the deposition layer. Wet etching is then used to remove the deposition layer. The two silicon wafers are aligned and then bonded together face-to-face to complete the microcapillary.

Imaging subtle microstructural variations in ceramics with precision ultrasonic velocity and attenuation measurements

NASA Technical Reports Server (NTRS)

Generazio, Edward R.; Roth, Don J.; Baaklini, George Y.

1987-01-01

Acoustic images of a silicon carbide ceramic disk were obtained using a precision scanning contact pulse echo technique. Phase and cross-correlation velocity, and attenuation maps were used to form color images of microstructural variations. These acoustic images reveal microstructural variations not observable with X-ray radiography.

Effect of processing parameters on reaction bonding of silicon nitride

NASA Technical Reports Server (NTRS)

Richman, M. H.; Gregory, O. J.; Magida, M. B.

1980-01-01

Reaction bonded silicon nitride was developed. The relationship between the various processing parameters and the resulting microstructures was to design and synthesize reaction bonded materials with improved room temperature mechanical properties.

Subwavelength focusing of terahertz waves in silicon hyperbolic metamaterials.

PubMed

Kannegulla, Akash; Cheng, Li-Jing

2016-08-01

We theoretically demonstrate the subwavelength focusing of terahertz (THz) waves in a hyperbolic metamaterial (HMM) based on a two-dimensional subwavelength silicon pillar array microstructure. The silicon microstructure with a doping concentration of at least 10¹⁷  cm^-3 offers a hyperbolic dispersion at terahertz frequency range and promises the focusing of terahertz Gaussian beams. The results agree with the simulation based on effective medium theory. The focusing effect can be controlled by the doping concentration, which determines the real part of the out-of-plane permittivity and, therefore, the refraction angles in HMM. The focusing property in the HMM structure allows the propagation of terahertz wave through a subwavelength aperture. The silicon-based HMM structure can be realized using microfabrication technologies and has the potential to advance terahertz imaging with subwavelength resolution.

Rapid bio-patterning method based on the fabrication of PEG microstructures and layer-by-layer polymeric thin film

NASA Astrophysics Data System (ADS)

Shim, Hyun-Woo; Lee, Ji-Hye; Choi, Chang-Hyoung; Song, Hwan-Moon; Kim, Bo-Yeol; Kim, Dong-Pyo; Lee, Chang-Soo

2007-12-01

The patterning of biomolecules in well-defined microstructures is critical issue for the development of biosensors and biochips. However, the fabrication of microstructures with well-ordered and spatially discrete forms to provide the patterned surface for the immobilization of biomolecules is difficult because of the lack of distinct physical and chemical barriers separating patterns. This study present rapid biomolecule patterning using micromolding in capillaries (MIMIC), soft-lithographic fabrication of PEG microstructures for prevention of nonspecific binding as a biological barrier, and self assembled polymeric thin film for efficient immobilization of proteins or cells. For the proof of concept, protein (FITC-BSA), bacteria (E.coli BL21-pET23b-GFP) were used for biomolecules patterning on polyelectrolyte coated surface within PEG microstructures. The novel approach of MIMIC combined with LbL coating provides a general platform for patterning a broad range of materials because it can be easily applied to various substrates such as glass, silicon, silicon dioxide, and polymers.

Studies of thin-film growth of sputtered hydrogenated amorphous silicon

NASA Astrophysics Data System (ADS)

Moustakas, T. D.

1982-11-01

The anticipated potential use of hydrogenated amorphous silicon (a-SiHx), or related materials, for large area thin film device applications has stimulated extensive research. Studies conducted by Ross and Messier (1981) have shown that the growth habit of the sputtered a-SiHx films is columnar. It is found that films produced at high argon pressure have columnar microstructure, while those produced at low argon pressure show no noticeable microstructure. The preferred interpretation for the lack of microstructure for the low argon pressure films is bombardment of the films by positive Ar(+) ions due to the substrate negative floating potential. Anderson et al. (1979) attribute the microstructural changes to the bombardment of the film by the neutral sputtered Si species from which the film grows. In connection with the present investigation, data are presented which clearly indicate that charged particle bombardment rather than neutral particle bombardment is the cause of the observed microstructural changes as a function of argon pressure.

Characterization of Adhesives for Attaching Reusable Surface Insulation on Space Shuttle Vehicles

NASA Technical Reports Server (NTRS)

Owen, H. P.; Carroll, M. T.

1973-01-01

An extensive development and testing program on adhesive systems shows that: (1) A closed cell silicone rubber sponge bonded to substrates with thin bond lines of glass filled adhesive exhibits density and modulus values approximately one third that of solid silicone adhesives; (2) utilization of glass or phenolic microballoons as fillers in silicone adhesives reduces density but increases moduli of the vulcanized materials; (3) the silicone elastomer based adhesives appear to be complex systems rather than homogeneous, isotropic materials. Tensile, shear, and compression properties plotted versus temperature verify this conjecture; and (4) constant strain-stress relaxation tests on glass-filled adhesive show that stress relaxation is most pronounced near the glass transition temperature.

Ultrasonic Guided-Wave Scan System Used to Characterize Microstructure and Defects in Ceramic Composites

NASA Technical Reports Server (NTRS)

Roth, Don J.; Cosgriff, Laura M.; Martin, Richard E.; Verrilli, Michael J.; Bhatt, Ramakrishna T.

2004-01-01

Ceramic matrix composites (CMCs) are being developed for advanced aerospace propulsion applications to save weight, improve reuse capability, and increase performance. However, mechanical and environmental loads applied to CMCs can cause discrete flaws and distributed microdamage, significantly reducing desirable physical properties. Such microdamage includes fiber/matrix debonding (interface failure), matrix microcracking, fiber fracture and buckling, oxidation, and second phase formation. A recent study (ref. 1) of the durability of a C/SiC CMC discussed the requirement for improved nondestructive evaluation (NDE) methods for monitoring degradation in these materials. Distributed microdamage in CMCs has proven difficult to characterize nondestructively because of the complex microstructure and macrostructure of these materials. This year, an ultrasonic guided-wave scan system developed at the NASA Glenn Research Center was used to characterize various microstructural and flaw conditions in SiC/SiC (silicon carbide fiber in silicon carbide matrix) and C/SiC (carbon fiber in silicon carbide matrix) CMC samples.

Effect of High Si Content on U3Si2 Fuel Microstructure

NASA Astrophysics Data System (ADS)

Rosales, Jhonathan; van Rooyen, Isabella J.; Meher, Subhashish; Hoggan, Rita; Parga, Clemente; Harp, Jason

2018-02-01

The development of U3Si2 as an accident-tolerant nuclear fuel has gained research interest because of its promising high uranium density and improved thermal properties. In the present study, three samples of U3Si2 fuel with varying silicon content have been fabricated by a conventional powder metallurgical route. Microstructural characterization via scanning and transmission electron microscopy reveals the presence of other stoichiometry of uranium silicide such as USi and UO2 in both samples. The detailed phase analysis by x-ray diffraction shows the presence of secondary phases, such as USi, U3Si, and UO2. The samples with higher concentrations of silicon content of 7.5 wt.% display additional elemental Si. These samples also possess an increased amount of the USi phase as compared to that in the conventional sample with 7.3 wt.% silicon. The optimization of U3Si2 fuel performance through the understanding of the role of Si content on its microstructure has been discussed.

Ultra-Sensitive Magnetoresistive Displacement Sensing Device

NASA Technical Reports Server (NTRS)

Olivas, John D. (Inventor); Lairson, Bruce M. (Inventor); Ramesham, Rajeshuni (Inventor)

2003-01-01

An ultrasensitive displacement sensing device for use in accelerometers, pressure gauges, temperature transducers, and the like, comprises a sputter deposited, multilayer, magnetoresistive field sensor with a variable electrical resistance based on an imposed magnetic field. The device detects displacement by sensing changes in the local magnetic field about the magnetoresistive field sensor caused by the displacement of a hard magnetic film on a movable microstructure. The microstructure, which may be a cantilever, membrane, bridge, or other microelement, moves under the influence of an acceleration a known displacement predicted by the configuration and materials selected, and the resulting change in the electrical resistance of the MR sensor can be used to calculate the displacement. Using a micromachining approach, very thin silicon and silicon nitride membranes are fabricated in one preferred embodiment by means of anisotropic etching of silicon wafers. Other approaches include reactive ion etching of silicon on insulator (SOI), or Low Pressure Chemical Vapor Deposition of silicon nitride films over silicon substrates. The device is found to be improved with the use of giant magnetoresistive elements to detect changes in the local magnetic field.

Laser-induced amorphization of silicon during pulsed-laser irradiation of TiN/Ti/polycrystalline silicon/SiO2/silicon

NASA Astrophysics Data System (ADS)

Chong, Y. F.; Pey, K. L.; Wee, A. T. S.; Thompson, M. O.; Tung, C. H.; See, A.

2002-11-01

In this letter, we report on the complex solidification structures formed during laser irradiation of a titanium nitride/titanium/polycrystalline silicon/silicon dioxide/silicon film stack. Due to enhanced optical coupling, the titanium nitride/titanium capping layer increases the melt depth of polycrystalline silicon by more than a factor of 2. It is found that the titanium atoms diffuse through the entire polycrystalline silicon layer during irradiation. Contrary to the expected polycrystalline silicon growth, distinct regions of polycrystalline and amorphous silicon are formed instead. Possible mechanisms for the formation of these microstructures are proposed.

The microstructure of laterally seeded silicon-on-oxide

NASA Astrophysics Data System (ADS)

Pinizzotto, R. F.; Lam, H. W.; Vaandrager, B. L.

1982-03-01

The production of large scale integrated circuits in thin silicon films on insulating substrates is currently of much interest in the electronics industry. One of the most promising techniques of forming this composite structure is by lateral seeding. We have used optical microscopy and transmission electron microscopy to characterize the microstructure of silicon-on-oxide formed by scanning CW laser induced lateral epitaxy. The primary defects are dislocations. Dislocation rearrangement leads to the formation of both small angle boundaries (stable, regular dislocation arrays) and grain boundaries. The grains were found to be misoriented to the <100> direction perpendicular to the film plane by ≤ 4° and to the <100> directions in the plane of the film by ≤ 2°. Internal reflection twins are a common defect. Microtwinning was found to occur at the vertical step caused by the substrate-oxide interface if the substrate to oxide step height was > 120 nm. The microstructure is continuous across successive scan lines. Microstructural defects are found to initiate at the same topographical location in different oxide pads. We propose that this is due to the meeting of two crystallization growth fronts. The liquid silicon between the fronts causes large stresses in this area because of the 9% volume increase during solidification. The defects observed in the bulk may form by a similar mechanism or by dislocation generation at substrate-oxide interface irregularities. The models predict that slower growth leads to improved material quality. This has been observed experimentally.

Abnormal brain white matter microstructure is associated with both pre-hypertension and hypertension

PubMed Central

Gao, He; Bai, Wenjia; Evangelou, Evangelos; Glocker, Ben; O’Regan, Declan P.; Elliott, Paul; Matthews, Paul M.

2017-01-01

Objectives To characterize effects of chronically elevated blood pressure on the brain, we tested for brain white matter microstructural differences associated with normotension, pre-hypertension and hypertension in recently available brain magnetic resonance imaging data from 4659 participants without known neurological or psychiatric disease (62.3±7.4 yrs, 47.0% male) in UK Biobank. Methods For assessment of white matter microstructure, we used measures derived from neurite orientation dispersion and density imaging (NODDI) including the intracellular volume fraction (an estimate of neurite density) and isotropic volume fraction (an index of the relative extra-cellular water diffusion). To estimate differences associated specifically with blood pressure, we applied propensity score matching based on age, sex, educational level, body mass index, and history of smoking, diabetes mellitus and cardiovascular disease to perform separate contrasts of non-hypertensive (normotensive or pre-hypertensive, N = 2332) and hypertensive (N = 2337) individuals and of normotensive (N = 741) and pre-hypertensive (N = 1581) individuals (p<0.05 after Bonferroni correction). Results The brain white matter intracellular volume fraction was significantly lower, and isotropic volume fraction was higher in hypertensive relative to non-hypertensive individuals (N = 1559, each). The white matter isotropic volume fraction also was higher in pre-hypertensive than in normotensive individuals (N = 694, each) in the right superior longitudinal fasciculus and the right superior thalamic radiation, where the lower intracellular volume fraction was observed in the hypertensives relative to the non-hypertensive group. Significance Pathological processes associated with chronically elevated blood pressure are associated with imaging differences suggesting chronic alterations of white matter axonal structure that may affect cognitive functions even with pre-hypertension. PMID:29145428

One - step nanosecond laser microstructuring, sulfur hyperdoping, and annealing of silicon surfaces in liquid carbondisulfide

NASA Astrophysics Data System (ADS)

Van Luong, Nguyen; Danilov, P. A.; Ionin, A. A.; Khmel'nitskii, P. A.; Kudryashov, S. I.; Mel'nik, N. N.; Saraeva, I. N.; Смirnov, H. A.; Rudenko, A. A.; Zayarny, D. A.

2017-09-01

We perform a single-shot IR nanosecond laser processing of commercial silicon wafers in ambient air and under a 2 mm thick carbon disulfide liquid layer. We characterize the surface spots modified in the liquid ambient and the spots ablated under the same conditions in air in terms of its surface topography, chemical composition, band-structure modification, and crystalline structure by means of SEM and EDX microscopy, as well as of FT-IR and Raman spectroscopy. These studies indicate that single-step microstructuring and deep (up to 2-3% on the surface) hyperdoping of the crystalline silicon in its submicron surface layer, preserving via pulsed laser annealing its crystallinity and providing high (103 - 104 cm-1) spectrally at near- and mid-IR absorption coefficients, can be obtained in this novel approach, which is very promising for thin - film silicon photovoltaic devices

Microstructural evolution of laser-exposed silicon targets in SF6 atmospheres

NASA Astrophysics Data System (ADS)

Fowlkes, J. D.; Pedraza, A. J.; Lowndes, D. H.

2000-09-01

The microstructures formed at the surface of silicon during pulsed-laser irradiation in SF6-rich atmospheres consist of an array of microholes surrounded by microcones. It is shown that there is a dynamic interplay between the formation of microholes and microcones. Fluorine produced by the laser-induced decomposition of SF6 is most likely responsible for the etching/ablation process. It is proposed that silicon-rich molecules and clusters that form in and are ejected from the continually deepening microholes sustain the axial and lateral growth of the microcones. The laser-melted layer at the tip and sides of the cones efficiently collects the silicon-rich products formed upon ablation. The total and partial pressures of SF6 in the chamber play a major role in cone development, a clear indication that it is the laser-generated plasma that controls the growth of these cones.

Patterned microstructures formed with MeV Au implantation in Si(1 0 0)

NASA Astrophysics Data System (ADS)

Rout, Bibhudutta; Greco, Richard R.; Zachry, Daniel P.; Dymnikov, Alexander D.; Glass, Gary A.

2006-09-01

Energetic (MeV) Au implantation in Si(1 0 0) (n-type) through masked micropatterns has been used to create layers resistant to KOH wet etching. Microscale patterns were produced in PMMA and SU(8) resist coatings on the silicon substrates using P-beam writing and developed. The silicon substrates were subsequently exposed using 1.5 MeV Au 3+ ions with fluences as high as 1 × 10 16 ions/cm 2 and additional patterns were exposed using copper scanning electron microscope calibration grids as masks on the silicon substrates. When wet etched with KOH microstructures were created in the silicon due to the resistance to KOH etching cause by the Au implantation. The process of combining the fabrication of masked patterns with P-beam writing with broad beam Au implantation through the masks can be a promising, cost-effective process for nanostructure engineering with Si.

Optical properties of ion beam textured metals. [using copper, silicon, aluminum, titanium and stainless steels

NASA Technical Reports Server (NTRS)

Hudson, W. R.; Weigand, A. J.; Mirtich, M. J.

1977-01-01

Copper, silicon, aluminum, titanium and 316 stainless steel were textured by 1000 eV xenon ions from an 8 cm diameter electron bombardment ion source. Simultaneously sputter-deposited tantalum was used to facilitate the development of the surface microstructure. Scanning electron microscopy of the ion textured surfaces revealed two types of microstructure. Copper, silicon, and aluminum developed a cone structure with an average peak-to-peak distance ranging from 1 micron for silicon to 6 microns for aluminum. Titanium and 316 stainless steel developed a serpentine ridge structure. The average peak-to-peak distance for both of these materials was 0.5 micron. Spectral reflectance was measured using an integrating sphere and a holraum reflectometer. Total reflectance for air mass 0 and 2, solar absorptance and total emittance normalized for a 425 K black body were calculated from the reflectance measurements.

Preparation and mechanical properties of carbon nanotube-silicon nitride nano-ceramic matrix composites

NASA Astrophysics Data System (ADS)

Tian, C. Y.; Jiang, H.

2018-01-01

Carbon nanotube-silicon nitride nano-ceramic matrix composites were fabricated by hot-pressing nano-sized Si3N4 powders and carbon nanotubes. The effect of CNTs on the mechanical properties of silicon nitride was researched. The phase compositions and the microstructure characteristics of the samples as well as the distribution of carbon nanotube in the silicon nitride ceramic were analyzed by X-ray diffraction and scanning electron microscope. The results show that the microstructure of composites consists mainly of α-Si3N4, β-Si3N4, Si2N2O and carbon natubes. The addition of proper amount of carbon nanotubes can improve the fracture toughness and the flexural strength, and the optimal amount of carbon nanotube are both 3wt.%. However the Vickers hardness values decrease with the increase of carbon nanotubes content.

Microstructure Characterization of Weakly Textured and Fine Grained AZ61 Sheet

NASA Astrophysics Data System (ADS)

Berman, T. D.; Donlon, W.; Hung, C. K.; Milligan, P.; Decker, R.; Pollock, T. M.; Jones, J. W.

Formability in magnesium alloy sheet is strongly limited by a strong basal texture in the as-rolled material, which is difficulty to remove by thermal processing. We introduce a new process to the control of texture by combining Thixomolding and Thermomechanical Processing (TTMP). Plates of AZ61L with a divorced β-Mg17Al12 eutectic are produced by Thixomolding, resulting in a non-textured, fine grained (2.8 µm) precursor. Sheet produced from the plate by single pass warm-rolling exhibits a weaker texture, and more isotropic tensile deformation than generally observed in AZ-series alloy sheet. Recrystallization annealing produces a further reduction in texture and average grain size (2.3 µm) and results in nearly isotropic room temperature deformation, a yield strength of 220 MPa, and an elongation of 23%. Particle stimulated nucleation of new grains by the β-phase during both dynamic and static recrystallization, is critical for achieving the low levels of texture. The influence of β-phase distribution in microstructure development is discussed.

Optical phase conjugation (OPC)-assisted isotropic focusing.

PubMed

Jang, Mooseok; Sentenac, Anne; Yang, Changhuei

2013-04-08

Isotropic optical focusing - the focusing of light with axial confinement that matches its lateral confinement, is important for a broad range of applications. Conventionally, such focusing is achieved by overlapping the focused beams from a pair of opposite-facing microscope objective lenses. However the exacting requirements for the alignment of the objective lenses and the method's relative intolerance to sample turbidity have significantly limited its utility. In this paper, we present an optical phase conjugation (OPC)-assisted isotropic focusing method that can address both challenges. We exploit the time-reversal nature of OPC playback to naturally guarantee the overlap of the two focused beams even when the objective lenses are significantly misaligned (up to 140 microns transversely and 80 microns axially demonstrated). The scattering correction capability of OPC also enabled us to accomplish isotropic focusing through thick scattering samples (demonstrated with samples of ~7 scattering mean free paths). This method can potentially improve 4Pi microscopy and 3D microstructure patterning.

Effect of Sr Additive Amount and Holding Time on Microstructure of A390 Aluminum Alloy

NASA Astrophysics Data System (ADS)

Zhang, J. H.; Xing, S. M.; Han, Q. Y.; Guo, Q.; Wang, R. F.

2017-11-01

The microstructure of A390 alloy under different Sr additive amounts and holding times was studied by means of direct reading spectrum analysis, energy spectrum analysis, optical microscope and electron microscope. The results show that Sr has a good modification to eutectic Si, while it has a negative effect on primary silicon. The Sr addition will increase the size of primary silicon. When the addition amount of Al-10Sr alloy is 0.6%, the modification of eutectic silicon is the optimum. The Sr has a short incubation period and a fine modification at 10min, but it is more serious burning rate in small furnace smelting, and the modification effect disappears basically after 100min.

Process for forming a chromium diffusion portion and articles made therefrom

DOEpatents

Helmick, David Andrew; Cavanaugh, Dennis William; Feng, Ganjiang; Bucci, David Vincent

2012-09-11

In one embodiment, a method for forming an article with a diffusion portion comprises: forming a slurry comprising chromium and silicon, applying the slurry to the article, and heating the article to a sufficient temperature and for a sufficient period of time to diffuse chromium and silicon into the article and form a diffusion portion comprising silicon and a microstructure comprising .alpha.-chromium. In one embodiment, a gas turbine component comprises: a superalloy and a diffusion portion having a depth of less than or equal to 60 .mu.m measured from the superalloy surface into the gas turbine component. The diffusion portion has a diffusion surface having a microstructure comprising greater than or equal to 40% by volume .alpha.-chromium.

Copper-silicon-magnesium alloys for latent heat storage

DOE PAGES

Gibbs, P. J.; Withey, E. A.; Coker, E. N.; ...

2016-06-21

The systematic development of microstructure, solidification characteristics, and heat of solidification with composition in copper-silicon-magnesium alloys for thermal energy storage is presented. Differential scanning calorimetry was used to relate the thermal characteristics to microstructural development in the investigated alloys and clarifies the location of one of the terminal three-phase eutectics. Repeated thermal cycling highlights the thermal storage stability of the transformation through multiple melting events. In conclusion, two near-terminal eutectic alloys display high enthalpies of solidification, relatively narrow melting ranges, and stable transformation hysteresis behaviors suited to thermal energy storage.

Controlled Directional Solidification of Aluminum - 7 wt Percent Silicon Alloys: Comparison Between Samples Processed on Earth and in the Microgravity Environment Aboard the International Space Station

NASA Technical Reports Server (NTRS)

Grugel, Richard N.; Tewari, Surendra N.; Erdman, Robert G.; Poirier, David R.

2012-01-01

An overview of the international "MIcrostructure Formation in CASTing of Technical Alloys" (MICAST) program is given. Directional solidification processing of metals and alloys is described, and why experiments conducted in the microgravity environment aboard the International Space Station (ISS) are expected to promote our understanding of this commercially relevant practice. Microstructural differences observed when comparing the aluminum - 7 wt% silicon alloys directionally solidified on Earth to those aboard the ISS are presented and discussed.

Microstructural analysis of W-SiCf/SiC composite

NASA Astrophysics Data System (ADS)

Yoon, Hanki; Oh, Jeongseok; Kim, Gonho; Kim, Hyunsu; Takahashi, Heishichiro; Kohyama, Akira

2015-03-01

Continuous silicon carbide fiber-reinforced silicon carbide (SiCf/SiC) composites are promising structure candidates for future fusion power systems such as gas coolant fast channels, extreme high temperature reactor and fusion reactors, because of their intrinsic properties such as excellent mechanical properties, high thermal conductivity, good thermal-shock resistance as well as excellent physical and chemical stability in various environments under elevated temperature conditions. In this study, bonding of tungsten and SiCf/SiC was produced by hot-press method. Microstructure analyses were performed using SEM and TEM.

Method for making circular tubular channels with two silicon wafers

DOEpatents

Yu, C.M.; Hui, W.C.

1996-11-19

A two-wafer microcapillary structure is fabricated by depositing boron nitride (BN) or silicon nitride (Si{sub 3}N{sub 4}) on two separate silicon wafers (e.g., crystal-plane silicon with [100] or [110] crystal orientation). Photolithography is used with a photoresist to create exposed areas in the deposition for plasma etching. A slit entry through to the silicon is created along the path desired for the ultimate microcapillary. Acetone is used to remove the photoresist. An isotropic etch, e.g., such as HF/HNO{sub 3}/CH{sub 3}COOH, then erodes away the silicon through the trench opening in the deposition layer. A channel with a half-circular cross section is then formed in the silicon along the line of the trench in the deposition layer. Wet etching is then used to remove the deposition layer. The two silicon wafers are aligned and then bonded together face-to-face to complete the microcapillary. 11 figs.

Evolution of Mechanical Properties and Microstructures in the Inner Accretionary Prism of the Nankai Subduction Zone

NASA Astrophysics Data System (ADS)

Kuo, S. T.; Kitamura, M.; Kitajima, H.

2016-12-01

Mechanical properties and microstructural characteristics of accretionary prism sediments can provide detailed deformation history and processes in subduction zones. The IODP Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Expedition 348 has extended the deep riser hole down to 3058.5 meters below sea floor (mbsf) to the inner accretionary wedge at Site C0002 located 35 km landward from the trench. Here, we conducted deformation experiments on the core samples recovered from 2185 msbf at Site C0002 to understand mechanical behaviors and deformation of inner prism sediments. We deformed the siltstone samples with a porosity of 20% at 25°C or 60°C under isotropic loading path (S1=S2=S3) and triaxial compression (S1>S2=S3). In the isotropic loading test, we step-wisely increased confining pressure (Pc) from 11.5 to 194 MPa and kept pore pressure (Pp) at 10 MPa. In a series of triaxial compression loading tests, we first increased Pc to the targeting 42-78 MPa and Pp to 20 MPa, and then applied the differential load at a constant displacement rate of 0.005 μm/s while keeping Pc and Pp constant. We will analyze the microstructures of the experimentally deformed samples to understand deformation mechanism. We define yield points based on slope changes in relationships between volumetric strain and effective mean stress (p') for isotropic loading and those between differential stress (q) and axial strain for triaxial loading. The sample yields at p' of 100 MPa (q = 0 MPa) in isotropic loading test. In triaxial loading, the samples at effective pressure (Pe) of 22, 28, and 58 MPa yield at q = 30 MPa (p' = 32 MPa), q = 30 MPa (p' = 38 MPa) and q = 45 MPa (p' = 73 MPa), respectively. Upon yield, the samples deformed at Pe of 22 MPa and 28 MPa show brittle behavior with a peak q of 50 MPa and 55 MPa followed by strain weakening to reach q of 36 and 46 MPa at steady state. Both samples show single fracture planes with angles of 30° to S1. On the other hand, the sample at Pe of 58 MPa shows strain hardening after the yield and exhibits barreling. In triaxial loading experiments, all samples show an increase in volumetric strain with increasing Pe. Our experiment results at different Pe are consistent with a critical state soil mechanics theory. We will further correlate the microstructural features of the deformed samples with the mechanical data.

Role of the heat accumulation effect in the multipulse modes of the femtosecond laser microstructuring of silicon

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

Guk, I. V., E-mail: corchand@gmail.com; Shandybina, G. D.; Yakovlev, E. B.

2016-05-15

The results of quantitative evaluation of the heat accumulation effect during the femtosecond laser microstructuring of the surface of silicon are presented for discussion. In the calculations, the numerical–analytical method is used, in which the dynamics of electronic processes and lattice heating are simulated by the numerical method, and the cooling stage is described on the basis of an analytical solution. The effect of multipulse irradiation on the surface temperature is studied: in the electronic subsystem, as the dependence of the absorbance on the excited carrier density and the dependence of the absorbance on the electron-gas temperature; in the latticemore » subsystem, as the variation in the absorbance from pulse to pulse. It was shown that, in the low-frequency pulse-repetition mode characteristic of the femtosecond microstructuring of silicon, the heat accumulation effect is controlled not by the residual surface temperature by the time of the next pulse arrival, which corresponds to conventional concepts, but by an increase in the maximum temperature from pulse to pulse, from which cooling begins. The accumulation of the residual temperature of the surface can affect the microstructuring process during irradiation near the evaporation threshold or with increasing pulse-repetition rate.« less

Analytical ultrasonics for structural materials

NASA Technical Reports Server (NTRS)

Kupperman, D. S.

1986-01-01

The application of ultrasonic velocity and attenuation measurements to characterize the microstructure of structural materials is discussed. Velocity measurements in cast stainless steel are correlated with microstructural variations ranging from equiaxed (elastically isotropic) to columnar (elastically anisotropic) grain structure. The effect of the anisotropic grain structure on the deviation of ultrasonic waves in cast stainless steel is also reported. Field-implementable techniques for distinguishing equiaxed from columnar grain structures in cast strainless steel structural members are presented. The application of ultrasonic velocity measurements to characterize structural ceramics in the green state is also discussed.

Dipole oscillator strengths, dipole properties and dispersion energies for SiF4

NASA Astrophysics Data System (ADS)

Kumar, Ashok; Kumar, Mukesh; Meath, William J.

2003-01-01

A recommended isotropic dipole oscillator strength distribution (DOSD) has been constructed for the silicon tetrafluoride (SiF4) molecule through the use of quantum mechanical constraint techniques and experimental dipole oscillator strength data. The constraints are furnished by experimental molar refractivity data and the Thomas-Reiche-Kuhn sum rule. The DOSD is used to evaluate a variety of isotropic dipole oscillator strength sums, logarithmic dipole oscillator strength sums and mean excitation energies for the molecule. A pseudo-DOSD for SiF4 is also presented which is used to obtain reliable results for the isotropic dipole-dipole dispersion energy coefficients C6, for the interaction of SiF4 with itself and with 43 other species and the triple-dipole dispersion energy coefficient C9 for (SiF4)3.

Toward a virtual platform for materials processing

NASA Astrophysics Data System (ADS)

Schmitz, G. J.; Prahl, U.

2009-05-01

Any production is based on materials eventually becoming components of a final product. Material properties being determined by the microstructure of the material thus are of utmost importance both for productivity and reliability of processing during production and for application and reliability of the product components. A sound prediction of materials properties therefore is highly important. Such a prediction requires tracking of microstructure and properties evolution along the entire component life cycle starting from a homogeneous, isotropic and stress-free melt and eventually ending in failure under operational load. This article will outline ongoing activities at the RWTH Aachen University aiming at establishing a virtual platform for materials processing comprising a virtual, integrative numerical description of processes and of the microstructure evolution along the entire production chain and even extending further toward microstructure and properties evolution under operational conditions.

Process for forming a chromium diffusion portion and articles made therefrom

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

Helmick, David Andrew; Cavanaugh, Dennis William; Feng, Ganjiang

In one embodiment, a method for forming an article with a diffusion portion comprises: forming a slurry comprising chromium and silicon, applying the slurry to the article, and heating the article to a sufficient temperature and for a sufficient period of time to diffuse chromium and silicon into the article and form a diffusion portion comprising silicon and a microstructure comprising .alpha.-chromium. In one embodiment, a gas turbine component comprises: a superalloy and a diffusion portion having a depth of less than or equal to 60 .mu.m measured from the superalloy surface into the gas turbine component. The diffusion portionmore » has a diffusion surface having a microstructure comprising greater than or equal to 40% by volume .alpha.-chromium.« less

Lithium concentration dependent structure and mechanics of amorphous silicon

NASA Astrophysics Data System (ADS)

Sitinamaluwa, H. S.; Wang, M. C.; Will, G.; Senadeera, W.; Zhang, S.; Yan, C.

2016-06-01

A better understanding of lithium-silicon alloying mechanisms and associated mechanical behavior is essential for the design of Si-based electrodes for Li-ion batteries. Unfortunately, the relationship between the dynamic mechanical response and microstructure evolution during lithiation and delithiation has not been well understood. We use molecular dynamic simulations to investigate lithiated amorphous silicon with a focus to the evolution of its microstructure, phase composition, and stress generation. The results show that the formation of LixSi alloy phase is via different mechanisms, depending on Li concentration. In these alloy phases, the increase in Li concentration results in reduction of modulus of elasticity and fracture strength but increase in ductility in tension. For a LixSi system with uniform Li distribution, volume change induced stress is well below the fracture strength in tension.

Directed dewetting of amorphous silicon film by a donut-shaped laser pulse.

PubMed

Yoo, Jae-Hyuck; In, Jung Bin; Zheng, Cheng; Sakellari, Ioanna; Raman, Rajesh N; Matthews, Manyalibo J; Elhadj, Selim; Grigoropoulos, Costas P

2015-04-24

Irradiation of a thin film with a beam-shaped laser is proposed to achieve site-selectively controlled dewetting of the film into nanoscale structures. As a proof of concept, the laser-directed dewetting of an amorphous silicon thin film on a glass substrate is demonstrated using a donut-shaped laser beam. Upon irradiation of a single laser pulse, the silicon film melts and dewets on the substrate surface. The irradiation with the donut beam induces an unconventional lateral temperature profile in the film, leading to thermocapillary-induced transport of the molten silicon to the center of the beam spot. Upon solidification, the ultrathin amorphous silicon film is transformed to a crystalline silicon nanodome of increased height. This morphological change enables further dimensional reduction of the nanodome as well as removal of the surrounding film material by isotropic silicon etching. These results suggest that laser-based dewetting of thin films can be an effective way for scalable manufacturing of patterned nanostructures.

High-aspect-ratio microstructures with versatile slanting angles on silicon by uniform metal-assisted chemical etching

NASA Astrophysics Data System (ADS)

Li, Liyi; Zhang, Cheng; Tuan, Chia-Chi; Chen, Yun; Wong, C.-P.

2018-05-01

High-aspect-ratio (HAR) microstructures on silicon (Si) play key roles in photonics and electromechanical devices. However, it has been challenging to fabricate HAR microstructures with slanting profiles. Here we report successful fabrication of uniform HAR microstructures with controllable slanting angles on (1 0 0)-Si by slanted uniform metal-assisted chemical etching (SUMaCE). The trenches have width of 2 µm, aspect ratio greater than 20:1 and high geometric uniformity. The slanting angles can be adjusted between 2-70° with respect to the Si surface normal. The results support a fundamental hypothesis that under the UMaCE condition, the preferred etching direction is along the normal of the thin film catalysts, regardless of the relative orientation of the catalyst to Si substrates or the crystalline orientation of the substrates. The SUMaCE method paves the way to HAR 3D microfabrication with arbitrary slanting profiles inside Si.

Mechanical properties of aluminium fused SiO2 particulate composites cast using metallic and non-metallic chills

NASA Astrophysics Data System (ADS)

Harshith, H. S.; Hemanth, Joel

2018-04-01

This research work aims at developing and mechanical characterization of aluminium (LM13) based metal matrix composite reinforced with varying percentage of fused SiO2 (3%,6%,9%,12%). The mechanical properties are completely dependent on the microstructural parameters of the system. Also the microstructure further depends on the cooling rates during solidification process. Various Chills like Silicon carbide, Mild steel, Copper were used during the casting process to increase the rate of solidification, which enhances the mechanical properties of the composite. The chill casted specimens were subjected to tensile and hardness tests followed by microstructure studies. A casting produced using mild steel chill exhibited higher young's modulus and was found to be maximum at 9% reinforcement. Finer microstructure and better UTS were seen for specimen's casted using copper chills, whereas silicon carbide and mild steel chills gave rise to very coarse structure with reduced UTS values compared to copper chills.

Quantifying microstructural dynamics and electrochemical activity of graphite and silicon-graphite lithium ion battery anodes

NASA Astrophysics Data System (ADS)

Pietsch, Patrick; Westhoff, Daniel; Feinauer, Julian; Eller, Jens; Marone, Federica; Stampanoni, Marco; Schmidt, Volker; Wood, Vanessa

2016-09-01

Despite numerous studies presenting advances in tomographic imaging and analysis of lithium ion batteries, graphite-based anodes have received little attention. Weak X-ray attenuation of graphite and, as a result, poor contrast between graphite and the other carbon-based components in an electrode pore space renders data analysis challenging. Here we demonstrate operando tomography of weakly attenuating electrodes during electrochemical (de)lithiation. We use propagation-based phase contrast tomography to facilitate the differentiation between weakly attenuating materials and apply digital volume correlation to capture the dynamics of the electrodes during operation. After validating that we can quantify the local electrochemical activity and microstructural changes throughout graphite electrodes, we apply our technique to graphite-silicon composite electrodes. We show that microstructural changes that occur during (de)lithiation of a pure graphite electrode are of the same order of magnitude as spatial inhomogeneities within it, while strain in composite electrodes is locally pronounced and introduces significant microstructural changes.

Two-Dimensional Nonlinear Finite Element Analysis of CMC Microstructures

NASA Technical Reports Server (NTRS)

Mital, Subodh K.; Goldberg, Robert K.; Bonacuse, Peter J.

2011-01-01

Detailed two-dimensional finite element analyses of the cross-sections of a model CVI (chemical vapor infiltrated) SiC/SiC (silicon carbide fiber in a silicon carbide matrix) ceramic matrix composites are performed. High resolution images of the cross-section of this composite material are generated using serial sectioning of the test specimens. These images are then used to develop very detailed finite element models of the cross-sections using the public domain software OOF2 (Object Oriented Analysis of Material Microstructures). Examination of these images shows that these microstructures have significant variability and irregularity. How these variabilities manifest themselves in the variability in effective properties as well as the stress distribution, damage initiation and damage progression is the overall objective of this work. Results indicate that even though the macroscopic stress-strain behavior of various sections analyzed is very similar, each section has a very distinct damage pattern when subjected to in-plane tensile loads and this damage pattern seems to follow the unique architectural and microstructural details of the analyzed sections.

A semi-phenomenological model to predict the acoustic behavior of fully and partially reticulated polyurethane foams

NASA Astrophysics Data System (ADS)

Doutres, Olivier; Atalla, Noureddine; Dong, Kevin

2013-02-01

This paper proposes simple semi-phenomenological models to predict the sound absorption efficiency of highly porous polyurethane foams from microstructure characterization. In a previous paper [J. Appl. Phys. 110, 064901 (2011)], the authors presented a 3-parameter semi-phenomenological model linking the microstructure properties of fully and partially reticulated isotropic polyurethane foams (i.e., strut length l, strut thickness t, and reticulation rate Rw) to the macroscopic non-acoustic parameters involved in the classical Johnson-Champoux-Allard model (i.e., porosity ϕ, airflow resistivity σ, tortuosity α∝, viscous Λ, and thermal Λ' characteristic lengths). The model was based on existing scaling laws, validated for fully reticulated polyurethane foams, and improved using both geometrical and empirical approaches to account for the presence of membrane closing the pores. This 3-parameter model is applied to six polyurethane foams in this paper and is found highly sensitive to the microstructure characterization; particularly to strut's dimensions. A simplified micro-/macro model is then presented. It is based on the cell size Cs and reticulation rate Rw only, assuming that the geometric ratio between strut length l and strut thickness t is known. This simplified model, called the 2-parameter model, considerably simplifies the microstructure characterization procedure. A comparison of the two proposed semi-phenomenological models is presented using six polyurethane foams being either fully or partially reticulated, isotropic or anisotropic. It is shown that the 2-parameter model is less sensitive to measurement uncertainties compared to the original model and allows a better estimation of polyurethane foams sound absorption behavior.

The Manufacturing of High Porosity Iron with an Ultra-Fine Microstructure via Free Pressureless Spark Plasma Sintering

PubMed Central

Cui, Guodong; Wei, Xialu; Olevsky, Eugene A.; German, Randall M.; Chen, Junying

2016-01-01

High porosity (>40 vol %) iron specimens with micro- and nanoscale isotropic pores were fabricated by carrying out free pressureless spark plasma sintering (FPSPS) of submicron hollow Fe–N powders at 750 °C. Ultra-fine porous microstructures are obtained by imposing high heating rates during the preparation process. This specially designed approach not only avoids the extra procedures of adding and removing space holders during the formation of porous structures, but also triggers the continued phase transitions of the Fe–N system at relatively lower processing temperatures. The compressive strength and energy absorption characteristics of the FPSPS processed specimens are examined here to be correspondingly improved as a result of the refined microstructure. PMID:28773617

Deep Drawing Simulations With Different Polycrystalline Models

NASA Astrophysics Data System (ADS)

Duchêne, Laurent; de Montleau, Pierre; Bouvier, Salima; Habraken, Anne Marie

2004-06-01

The goal of this research is to study the anisotropic material behavior during forming processes, represented by both complex yield loci and kinematic-isotropic hardening models. A first part of this paper describes the main concepts of the `Stress-strain interpolation' model that has been implemented in the non-linear finite element code Lagamine. This model consists of a local description of the yield locus based on the texture of the material through the full constraints Taylor's model. The texture evolution due to plastic deformations is computed throughout the FEM simulations. This `local yield locus' approach was initially linked to the classical isotropic Swift hardening law. Recently, a more complex hardening model was implemented: the physically-based microstructural model of Teodosiu. It takes into account intergranular heterogeneity due to the evolution of dislocation structures, that affects isotropic and kinematic hardening. The influence of the hardening model is compared to the influence of the texture evolution thanks to deep drawing simulations.

Deposition and micro electrical discharge machining of CVD-diamond layers incorporated with silicon

NASA Astrophysics Data System (ADS)

Kühn, R.; Berger, T.; Prieske, M.; Börner, R.; Hackert-Oschätzchen, M.; Zeidler, H.; Schubert, A.

2017-10-01

In metal forming, lubricants have to be used to prevent corrosion or to reduce friction and tool wear. From an economical and ecological point of view, the aim is to avoid the usage of lubricants. For dry deep drawing of aluminum sheets it is intended to apply locally micro-structured wear-resistant carbon based coatings onto steel tools. One type of these coatings are diamond layers prepared by chemical vapor deposition (CVD). Due to the high strength of diamond, milling processes are unsuitable for micro-structuring of these layers. In contrast to this, micro electrical discharge machining (micro EDM) is a suitable process for micro-structuring CVD-diamond layers. Due to its non-contact nature and its process principle of ablating material by melting and evaporating, it is independent of the hardness, brittleness or toughness of the workpiece material. In this study the deposition and micro electrical discharge machining of silicon incorporated CVD-diamond (Si-CVD-diamond) layers were presented. For this, 10 µm thick layers were deposited on molybdenum plates by a laser-induced plasma CVD process (LaPlas-CVD). For the characterization of the coatings RAMAN- and EDX-analyses were conducted. Experiments in EDM were carried out with a tungsten carbide tool electrode with a diameter of 90 µm to investigate the micro-structuring of Si-CVD-diamond. The impact of voltage, discharge energy and tool polarity on process speed and resulting erosion geometry were analyzed. The results show that micro EDM is a suitable technology for micro-structuring of silicon incorporated CVD-diamond layers.

Microstructured silicon radiation detector

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

Okandan, Murat; Derzon, Mark S.; Draper, Bruce L.

2017-03-14

A radiation detector comprises a silicon body in which are defined vertical pores filled with a converter material and situated within silicon depletion regions. One or more charge-collection electrodes are arranged to collect current generated when secondary particles enter the silicon body through walls of the pores. The pores are disposed in low-density clusters, have a majority pore thickness of 5 .mu.m or less, and have a majority aspect ratio, defined as the ratio of pore depth to pore thickness, of at least 10.

Radiation effects in silicon and gallium arsenide solar cells using isotropic and normally incident radiation

NASA Technical Reports Server (NTRS)

Anspaugh, B. E.; Downing, R. G.

1984-01-01

Several types of silicon and gallium arsenide solar cells were irradiated with protons with energies between 50 keV and 10 MeV at both normal and isotropic incidence. Damage coefficients for maximum power relative to 10 MeV were derived for these cells for both cases of omni-directional and normal incidence. The damage coefficients for the silicon cells were found to be somewhat lower than those quoted in the Solar Cell Radiation Handbook. These values were used to compute omni-directional damage coefficients suitable for solar cells protected by coverglasses of practical thickness, which in turn were used to compute solar cell degradation in two proton-dominated orbits. In spite of the difference in the low energy proton damage coefficients, the difference between the handbook prediction and the prediction using the newly derived values was negligible. Damage coefficients for GaAs solar cells for short circuit current, open circuit voltage, and maximum power were also computed relative to 10 MeV protons. They were used to predict cell degradation in the same two orbits and in a 5600 nmi orbit. Results show the performance of the GaAs solar cells in these orbits to be superior to that of the Si cells.

Contribution of first-principles calculations to multinuclear NMR analysis of borosilicate glasses.

PubMed

Soleilhavoup, Anne; Delaye, Jean-Marc; Angeli, Frédéric; Caurant, Daniel; Charpentier, Thibault

2010-12-01

Boron-11 and silicon-29 NMR spectra of xSiO(2)-(1-x)B(2)O(3) glasses (x=0.40, 0.80 and 0.83) have been calculated using a combination of molecular dynamics (MD) simulations with density functional theory (DFT) calculations of NMR parameters. Structure models of 200 atoms have been generated using classical force fields and subsequently relaxed at the PBE-GGAlevel of DFT theory. The gauge including projector augmented wave (GIPAW) method is then employed for computing the shielding and electric field gradient tensors for each silicon and boron atom. Silicon-29 MAS and boron-11 MQMAS NMR spectra of two glasses (x=0.40 and 0.80) have been acquired and theoretical spectra are found to well agree with the experimental data. For boron-11, the NMR parameter distributions have been analysed using a Kernel density estimation (KDE) approach which is shown to highlight its main features. Accordingly, a new analytical model that incorporates the observed correlations between the NMR parameters is introduced. It significantly improves the fit of the (11)B MQMAS spectra and yields, therefore, more reliable NMR parameter distributions. A new analytical model for a quantitative description of the dependence of the silicon-29 and boron-11 isotropic chemical shift upon the bond angles is proposed, which incorporates possibly the effect of SiO(2)-B(2)O(3) intermixing. Combining all the above procedures, we show how distributions of Si-O-T and B-O-T (T=Si, B) bond angles can be estimated from the distribution of isotropic chemical shift of silicon-29 and boron-11, respectively. Copyright © 2010 John Wiley & Sons, Ltd.

Modulating laser intensity profile ellipticity for microstructural control during metal additive manufacturing

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

Roehling, Tien T.; Wu, Sheldon S. Q.; Khairallah, Saad A.

Additively manufactured (AM) metals are often highly textured, containing large columnar grains that initiate epitaxially under steep temperature gradients and rapid solidification conditions. These unique microstructures partially account for the massive property disparity existing between AM and conventionally processed alloys. Although equiaxed grains are desirable for isotropic mechanical behavior, the columnar-to-equiaxed transition remains difficult to predict for conventional solidification processes, and much more so for AM. In this study, the effects of laser intensity profile ellipticity on melt track macrostructures and microstructures were studied in 316L stainless steel. Experimental results were supported by temperature gradients and melt velocities simulated usingmore » the ALE3D multi-physics code. As a general trend, columnar grains preferentially formed with increasing laser power and scan speed for all beam profiles. However, when conduction mode laser heating occurs, scan parameters that result in coarse columnar microstructures using Gaussian profiles produce equiaxed or mixed equiaxed-columnar microstructures using elliptical profiles. Furthermore, by modulating spatial laser intensity profiles on the fly, site-specific microstructures and properties can be directly engineered into additively manufactured parts.« less

Modulating laser intensity profile ellipticity for microstructural control during metal additive manufacturing

DOE PAGES

Roehling, Tien T.; Wu, Sheldon S. Q.; Khairallah, Saad A.; ...

2017-02-12

Additively manufactured (AM) metals are often highly textured, containing large columnar grains that initiate epitaxially under steep temperature gradients and rapid solidification conditions. These unique microstructures partially account for the massive property disparity existing between AM and conventionally processed alloys. Although equiaxed grains are desirable for isotropic mechanical behavior, the columnar-to-equiaxed transition remains difficult to predict for conventional solidification processes, and much more so for AM. In this study, the effects of laser intensity profile ellipticity on melt track macrostructures and microstructures were studied in 316L stainless steel. Experimental results were supported by temperature gradients and melt velocities simulated usingmore » the ALE3D multi-physics code. As a general trend, columnar grains preferentially formed with increasing laser power and scan speed for all beam profiles. However, when conduction mode laser heating occurs, scan parameters that result in coarse columnar microstructures using Gaussian profiles produce equiaxed or mixed equiaxed-columnar microstructures using elliptical profiles. Furthermore, by modulating spatial laser intensity profiles on the fly, site-specific microstructures and properties can be directly engineered into additively manufactured parts.« less

Effects of white matter microstructure on phase and susceptibility maps.

PubMed

Wharton, Samuel; Bowtell, Richard

2015-03-01

To investigate the effects on quantitative susceptibility mapping (QSM) and susceptibility tensor imaging (STI) of the frequency variation produced by the microstructure of white matter (WM). The frequency offsets in a WM tissue sample that are not explained by the effect of bulk isotropic or anisotropic magnetic susceptibility, but rather result from the local microstructure, were characterized for the first time. QSM and STI were then applied to simulated frequency maps that were calculated using a digitized whole-brain, WM model formed from anatomical and diffusion tensor imaging data acquired from a volunteer. In this model, the magnitudes of the frequency contributions due to anisotropy and microstructure were derived from the results of the tissue experiments. The simulations suggest that the frequency contribution of microstructure is much larger than that due to bulk effects of anisotropic magnetic susceptibility. In QSM, the microstructure contribution introduced artificial WM heterogeneity. For the STI processing, the microstructure contribution caused the susceptibility anisotropy to be significantly overestimated. Microstructure-related phase offsets in WM yield artifacts in the calculated susceptibility maps. If susceptibility mapping is to become a robust MRI technique, further research should be carried out to reduce the confounding effects of microstructure-related frequency contributions. © 2014 Wiley Periodicals, Inc.

Effects of White Matter Microstructure on Phase and Susceptibility Maps

PubMed Central

Wharton, Samuel; Bowtell, Richard

2015-01-01

Purpose To investigate the effects on quantitative susceptibility mapping (QSM) and susceptibility tensor imaging (STI) of the frequency variation produced by the microstructure of white matter (WM). Methods The frequency offsets in a WM tissue sample that are not explained by the effect of bulk isotropic or anisotropic magnetic susceptibility, but rather result from the local microstructure, were characterized for the first time. QSM and STI were then applied to simulated frequency maps that were calculated using a digitized whole-brain, WM model formed from anatomical and diffusion tensor imaging data acquired from a volunteer. In this model, the magnitudes of the frequency contributions due to anisotropy and microstructure were derived from the results of the tissue experiments. Results The simulations suggest that the frequency contribution of microstructure is much larger than that due to bulk effects of anisotropic magnetic susceptibility. In QSM, the microstructure contribution introduced artificial WM heterogeneity. For the STI processing, the microstructure contribution caused the susceptibility anisotropy to be significantly overestimated. Conclusion Microstructure-related phase offsets in WM yield artifacts in the calculated susceptibility maps. If susceptibility mapping is to become a robust MRI technique, further research should be carried out to reduce the confounding effects of microstructure-related frequency contributions. Magn Reson Med 73:1258–1269, 2015. © 2014 Wiley Periodicals, Inc. PMID:24619643

Structure of deformed silicon and implications for low cost solar cells

NASA Technical Reports Server (NTRS)

Mardesich, N.; Leipold, M. H.; Turner, G. B.; Digges, T. G., Jr.

1978-01-01

The microstructure and minority carrier lifetime of silicon were investigated in uniaxially compressed silicon samples. The objective of the investigation was to determine if it is feasible to produce silicon solar cells from sheet formed by high temperature rolling. The initial structure of the silicon samples ranged from single crystal to fine-grained polycrystals. The samples had been deformed at strain rates of 0.1 to 8.5/sec and temperatures of 1270-1380 C with subsequent annealing at 1270-1380 C. The results suggest that high temperature rolling of silicon to produce sheet for cells of high efficiency is not practical.

Concurrent multiscale modeling of microstructural effects on localization behavior in finite deformation solid mechanics

DOE PAGES

Alleman, Coleman N.; Foulk, James W.; Mota, Alejandro; ...

2017-11-06

The heterogeneity in mechanical fields introduced by microstructure plays a critical role in the localization of deformation. In order to resolve this incipient stage of failure, it is therefore necessary to incorporate microstructure with sufficient resolution. On the other hand, computational limitations make it infeasible to represent the microstructure in the entire domain at the component scale. Here, the authors demonstrate the use of concurrent multiscale modeling to incorporate explicit, finely resolved microstructure in a critical region while resolving the smoother mechanical fields outside this region with a coarser discretization to limit computational cost. The microstructural physics is modeled withmore » a high-fidelity model that incorporates anisotropic crystal elasticity and rate-dependent crystal plasticity to simulate the behavior of a stainless steel alloy. The component-scale material behavior is treated with a lower fidelity model incorporating isotropic linear elasticity and rate-independent J 2 plasticity. The microstructural and component scale subdomains are modeled concurrently, with coupling via the Schwarz alternating method, which solves boundary-value problems in each subdomain separately and transfers solution information between subdomains via Dirichlet boundary conditions. In this study, the framework is applied to model incipient localization in tensile specimens during necking.« less

Concurrent multiscale modeling of microstructural effects on localization behavior in finite deformation solid mechanics

NASA Astrophysics Data System (ADS)

Alleman, Coleman N.; Foulk, James W.; Mota, Alejandro; Lim, Hojun; Littlewood, David J.

2018-02-01

The heterogeneity in mechanical fields introduced by microstructure plays a critical role in the localization of deformation. To resolve this incipient stage of failure, it is therefore necessary to incorporate microstructure with sufficient resolution. On the other hand, computational limitations make it infeasible to represent the microstructure in the entire domain at the component scale. In this study, the authors demonstrate the use of concurrent multiscale modeling to incorporate explicit, finely resolved microstructure in a critical region while resolving the smoother mechanical fields outside this region with a coarser discretization to limit computational cost. The microstructural physics is modeled with a high-fidelity model that incorporates anisotropic crystal elasticity and rate-dependent crystal plasticity to simulate the behavior of a stainless steel alloy. The component-scale material behavior is treated with a lower fidelity model incorporating isotropic linear elasticity and rate-independent J2 plasticity. The microstructural and component scale subdomains are modeled concurrently, with coupling via the Schwarz alternating method, which solves boundary-value problems in each subdomain separately and transfers solution information between subdomains via Dirichlet boundary conditions. In this study, the framework is applied to model incipient localization in tensile specimens during necking.

Concurrent multiscale modeling of microstructural effects on localization behavior in finite deformation solid mechanics

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

Alleman, Coleman N.; Foulk, James W.; Mota, Alejandro

The heterogeneity in mechanical fields introduced by microstructure plays a critical role in the localization of deformation. In order to resolve this incipient stage of failure, it is therefore necessary to incorporate microstructure with sufficient resolution. On the other hand, computational limitations make it infeasible to represent the microstructure in the entire domain at the component scale. Here, the authors demonstrate the use of concurrent multiscale modeling to incorporate explicit, finely resolved microstructure in a critical region while resolving the smoother mechanical fields outside this region with a coarser discretization to limit computational cost. The microstructural physics is modeled withmore » a high-fidelity model that incorporates anisotropic crystal elasticity and rate-dependent crystal plasticity to simulate the behavior of a stainless steel alloy. The component-scale material behavior is treated with a lower fidelity model incorporating isotropic linear elasticity and rate-independent J 2 plasticity. The microstructural and component scale subdomains are modeled concurrently, with coupling via the Schwarz alternating method, which solves boundary-value problems in each subdomain separately and transfers solution information between subdomains via Dirichlet boundary conditions. In this study, the framework is applied to model incipient localization in tensile specimens during necking.« less

The Compositional Dependence of the Microstructure and Properties of CMSX-4 Superalloys

NASA Astrophysics Data System (ADS)

Yu, Hao; Xu, Wei; Van Der Zwaag, Sybrand

2018-01-01

The degradation of creep resistance in Ni-based single-crystal superalloys is essentially ascribed to their microstructural evolution. Yet there is a lack of work that manages to predict (even qualitatively) the effect of alloying element concentrations on the rate of microstructural degradation. In this research, a computational model is presented to connect the rafting kinetics of Ni superalloys to their chemical composition by combining thermodynamics calculation and a modified microstructural model. To simulate the evolution of key microstructural parameters during creep, the isotropic coarsening rate and γ/ γ' misfit stress are defined as composition-related parameters, and the effect of service temperature, time, and applied stress are taken into consideration. Two commercial superalloys, for which the kinetics of the rafting process are selected as the reference alloys, and the corresponding microstructural parameters are simulated and compared with experimental observations reported in the literature. The results confirm that our physical model not requiring any fitting parameters manages to predict (semiquantitatively) the microstructural parameters for different service conditions, as well as the effects of alloying element concentrations. The model can contribute to the computational design of new Ni-based superalloys.

Melting of SiC powders preplaced duplex stainless steel using TIG welding

NASA Astrophysics Data System (ADS)

Maleque, M. A.; Afiq, M.

2018-01-01

TIG torch welding technique is a conventional melting technique for the cladding of metallic materials. Duplex stainless steels (DSS) show decrease in performance under aggressive environment which may lead to unanticipated failure due to poor surface properties. In this research, surface modification is done by using TIG torch method where silicon carbide (SiC) particles are fused into DSS substrate in order to form a new intermetallic compound at the surface. The effect of particle size, feed rate of SiC preplacement, energy input and shielding gas flow rate on surface topography, microstructure, microstructure and hardness are investigated. Deepest melt pool (1.237 mm) is produced via TIG torch with highest energy input of 1080 J/mm. Observations of surface topography shows rippling marks which confirms that re-solidification process has taken place. Melt microstructure consist of dendritic and globular carbides precipitate as well as partially melted silicon carbides (SiC) particles. Micro hardness recorded at value ranging from 316 HV0.5 to 1277 HV0.5 which shows increment from base hardness of 260 HV0.5kgf. The analyzed result showed that incorporation of silicon carbide particles via TIG Torch method increase the hardness of DSS.

Reactive Processing of Environment Conscious, Biomorphic Ceramics: A Novel and Eco-friendly Route to Advanced Ceramic

NASA Technical Reports Server (NTRS)

Singh, M.

2002-01-01

Environment-conscious, biomorphic ceramics (Ecoceramics) are a new class of materials that can be produced with renewable resources (wood) and wood wastes (wood sawdust). These materials have tailorable properties with numerous potential applications. Silicon carbide-based ecoceramics have been fabricated by the infiltration of wood-derived carbonaceous preforms with oxide and silicon based materials. The wood-derived carbonaceous preforms have been shown to be quite useful in producing porous or dense materials with different microstructures and compositions. The microstructure and mechanical properties (flexural strength, fracture toughness, elastic modulus, and compressive strength) of a wide variety of Sic-based ecoceramics have been measured. Ecoceramics have tailorable properties and behave like ceramic materials manufactured by conventional approaches. In this presentation the fabrication approach, microstructure, and thermomechanical properties of a wide variety of Sic-based Ecoceramics will be reported.

Improvement in current density of nano- and micro-structured Si solar cells by cost-effective elastomeric stamp process

NASA Astrophysics Data System (ADS)

Jeon, Kiseok; Jee, Hongsub; Lim, Sangwoo; Park, Min Joon; Jeong, Chaehwan

2018-03-01

Effective incident light should be controlled for improving the current density of solar cells by employing nano- and micro-structures on silicon surface. The elastomeric stamp process, which is more cost effective and simpler than conventional photolithography, was proposed for the fabrication of nano- and micro-structures. Polydimethylsiloxane (PDMS) was poured on a mother pattern with a diameter of 6 μm and a spacing of 2 μm; then, curing was performed to create a PDMS mold. The regular micropattern was stamped on a low-viscosity resin-coated silicon surface, followed by the simple reactive ion etching process. Nano-structures were formed using the Ag-based electroless etching process. As etching time was increased to 6 min, reflectance decreased to 4.53% and current density improved from 22.35 to 34.72 mA/cm2.

Three-dimensional conformal graphene microstructure for flexible and highly sensitive electronic skin

NASA Astrophysics Data System (ADS)

Yang, Jun; Ran, Qincui; Wei, Dapeng; Sun, Tai; Yu, Leyong; Song, Xuefen; Pu, Lichun; Shi, Haofei; Du, Chunlei

2017-03-01

We demonstrate a highly stretchable electronic skin (E-skin) based on the facile combination of microstructured graphene nanowalls (GNWs) and a polydimethylsiloxane (PDMS) substrate. The microstructure of the GNWs was endowed by conformally growing them on the unpolished silicon wafer without the aid of nanofabrication technology. Then a stamping transfer method was used to replicate the micropattern of the unpolished silicon wafer. Due to the large contact interface between the 3D graphene network and the PDMS, this type of E-skin worked under a stretching ratio of nearly 100%, and showed excellent mechanical strength and high sensitivity, with a change in relative resistance of up to 6500% and a gauge factor of 65.9 at 99.64% strain. Furthermore, the E-skin exhibited an obvious highly sensitive response to joint movement, eye movement and sound vibration, demonstrating broad potential applications in healthcare, body monitoring and wearable devices.

3D-fabrication of tunable and high-density arrays of crystalline silicon nanostructures

NASA Astrophysics Data System (ADS)

Wilbers, J. G. E.; Berenschot, J. W.; Tiggelaar, R. M.; Dogan, T.; Sugimura, K.; van der Wiel, W. G.; Gardeniers, J. G. E.; Tas, N. R.

2018-04-01

In this report, a procedure for the 3D-nanofabrication of ordered, high-density arrays of crystalline silicon nanostructures is described. Two nanolithography methods were utilized for the fabrication of the nanostructure array, viz. displacement Talbot lithography (DTL) and edge lithography (EL). DTL is employed to perform two (orthogonal) resist-patterning steps to pattern a thin Si3N4 layer. The resulting patterned double layer serves as an etch mask for all further etching steps for the fabrication of ordered arrays of silicon nanostructures. The arrays are made by means of anisotropic wet etching of silicon in combination with an isotropic retraction etch step of the etch mask, i.e. EL. The procedure enables fabrication of nanostructures with dimensions below 15 nm and a potential density of 1010 crystals cm-2.

The Manufacturing of High Porosity Iron with an Ultra-Fine Microstructure via Free Pressureless Spark Plasma Sintering

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

Cui, Guodong; Wei, Xialu; Olevsky, Eugene

2016-06-01

High porosity (>40 vol %) iron specimens with micro- and nanoscale isotropic pores were fabricated by carrying out free pressureless spark plasma sintering (FPSPS) of submicron hollow Fe–N powders at 750 °C. Ultra-fine porous microstructures are obtained by imposing high heating rates during the preparation process. This specially designed approach not only avoids the extra procedures of adding and removing space holders during the formation of porous structures, but also triggers the continued phase transitions of the Fe–N system at relatively lower processing temperatures. In conclusion, the compressive strength and energy absorption characteristics of the FPSPS processed specimens are examinedmore » here to be correspondingly improved as a result of the refined microstructure.« less

Progress on Fabrication of Planar Diffusion Couples with Representative TRISO PyC/SiC Microstructure

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

Hunn, John D.; Jolly, Brian C.; Gerczak, Tyler J.

Release of fission products from tristructural-isotropic (TRISO) coated particle fuel limits the fuel’s operational lifetime and creates potential safety and maintenance concerns. A need for diffusion analysis in representative TRISO layers exists to provide fuel performance models with high fidelity data to improve fuel performance and efficiency. An effort has been initiated to better understand fission product transport in, and release from, quality TRISO fuel by investigating diffusion couples with representative pyrocarbon (PyC) and silicon carbide (SiC). Here planar PyC/SiC diffusion couples are being developed with representative PyC/SiC layers using a fluidized bed chemical vapor deposition (FBCVD) system identical tomore » those used to produce laboratory-scale TRISO fuel for the Advanced Gas Reactor Fuel Qualification and Development Program’s (AGR) first fuel irradiation. The diffusivity of silver, the silver and palladium system, europium, and strontium in the PyC/SiC will be studied at elevated temperatures and under high temperature neutron irradiation. The study also includes a comparative study of PyC/SiC diffusion couples with varying TRISO layer properties to understand the influence of SiC microstructure (grain size) and the PyC/SiC interface on fission product transport. The first step in accomplishing these goals is the development of the planar diffusion couples. The diffusion couple construction consists of multiple steps which includes fabrication of the primary PyC/SiC structures with targeted layer properties, introduction of fission product species and seal coating to create an isolated system. Coating development has shown planar PyC/SiC diffusion couples with similar properties to AGR TRISO fuel can be produced. A summary of the coating development process, characterization methods, and status are presented.« less

Heat transfer studies on the liquid droplet radiator

NASA Technical Reports Server (NTRS)

Mattick, A. T.; Nelson, M.

1987-01-01

This paper examines radiation transfer in the droplet sheet of a liquid droplet radiator including non-isotropic scattering by the droplets. Non-isotropic scattering becomes significant for small droplets (diameter less than 0.1 mm) and for low emissivity liquids. For droplets with an emittance of 0.1 and for a droplet sheet optical depth or 5, the radiated power varies by about 12 percent, depending on whether scattering is predominantly forward or backward. An experimental measurement of the power emitted by a cylindrical cloud of heated droplets of silicone fluid is also reported. The measured cloud emissivity correlates, within experimental error, with the analytical model.

Method to control artifacts of microstructural fabrication

DOEpatents

Shul, Randy J.; Willison, Christi G.; Schubert, W. Kent; Manginell, Ronald P.; Mitchell, Mary-Anne; Galambos, Paul C.

2006-09-12

New methods for fabrication of silicon microstructures have been developed. In these methods, an etching delay layer is deposited and patterned so as to provide differential control on the depth of features being etched into a substrate material. Compensation for etching-related structural artifacts can be accomplished by proper use of such an etching delay layer.

Lithium concentration dependent structure and mechanics of amorphous silicon

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

Sitinamaluwa, H. S.; Wang, M. C.; Will, G.

2016-06-28

A better understanding of lithium-silicon alloying mechanisms and associated mechanical behavior is essential for the design of Si-based electrodes for Li-ion batteries. Unfortunately, the relationship between the dynamic mechanical response and microstructure evolution during lithiation and delithiation has not been well understood. We use molecular dynamic simulations to investigate lithiated amorphous silicon with a focus to the evolution of its microstructure, phase composition, and stress generation. The results show that the formation of Li{sub x}Si alloy phase is via different mechanisms, depending on Li concentration. In these alloy phases, the increase in Li concentration results in reduction of modulus ofmore » elasticity and fracture strength but increase in ductility in tension. For a Li{sub x}Si system with uniform Li distribution, volume change induced stress is well below the fracture strength in tension.« less

CVD of silicon carbide on structural fibers - Microstructure and composition

NASA Technical Reports Server (NTRS)

Veitch, Lisa C.; Terepka, Francis M.; Gokoglu, Suleyman A.

1992-01-01

Structural fibers are currently being considered as reinforcements for intermetallic and ceramic materials. Some of these fibers, however, are easily degraded in a high temperature oxidative environment. Therefore, coatings are needed to protect the fibers from environmental attack. Silicon carbide (SiC) was chemically vapor deposited (CVD) on Textron's SCS6 fibers. Fiber temperatures ranging from 1350 to 1500 C were studied. Silane (SiH4) and propane (C2H8) were used for the source gases and different concentrations of these source gases were studied. Deposition rates were determined for each group of fibers at different temperatures. Less variation in deposition rates were observed for the dilute source gas experiments than the concentrated source gas experiments. A careful analysis was performed on the stoichiometry of the CVD SiC coating using electron microprobe. Microstructures for the different conditions were compared. At 1350 C, the microstructures were similar; however, at higher temperatures, the microstructure for the more concentrated source gas group were porous and columnar in comparison to the cross sections taken from the same area for the dilute source gas group.

CVD of silicon carbide on structural fibers: Microstructure and composition

NASA Technical Reports Server (NTRS)

Veitch, Lisa C.; Terepka, Francis M.; Gokoglu, Suleyman A.

1992-01-01

Structural fibers are currently being considered as reinforcements for intermetallic and ceramic materials. Some of these fibers, however, are easily degraded in a high temperature oxidative environment. Therefore, coatings are needed to protect the fibers from environmental attack. Silicon carbide (SiC) was chemically vapor deposited (CVD) on Textron's SCS6 fibers. Fiber temperatures ranging from 1350 to 1500 C were studied. Silane (SiH4) and propane (C2H8) were used for the source gases and different concentrations of these source gases were studied. Deposition rates were determined for each group of fibers at different temperatures. Less variation in deposition rates were observed for the dilute source gas experiments than the concentrated source gas experiments. A careful analysis was performed on the stoichiometry of the CVD SiC coating using electron microprobe. Microstructures for the different conditions were compared. At 1350 C, the microstructures were similar; however, at higher temperatures, the microstructure for the more concentrated source gas group were porous and columnar in comparison to the cross sections taken from the same area for the dilute source gas group.

Fast and cheap fabrication of molding tools for polymer replication

NASA Astrophysics Data System (ADS)

Richter, Christiane; Kirschner, Nadine; Worgull, Matthias; Rapp, Bastian E.

2017-02-01

Polymer replication is a prerequisite for low-cost microstructure components for consumer and end user market. The production of cost-effective microstructure in polymers requires metal molding tools which are often fabricated by direct structuring methods like milling or laser machining both of which are time-consuming and cost-intensive. We present an alternative fabrication method based on replication processes which allows the cheap ( 50 €) and fast ( 12 h) replication of complex microstructures into metal. The process comprises three steps: 1. Generation of the microstructure in a photoresist via lithography. 2. Casting of the structure into a high-temperature silicone which serves as original mold for creation of the metal molding tool. 3. Melting of an eutectic alloy of Sn, Ag and Cu under light pressure directly inside of the silicone within an oven. After cooling to room temperature the metal molding tool can be used for polymer replication into conventional thermoplastic polymers. As a first example we structured polymethylmethacrylate (PMMA) foils with a thickness of 1 mm via hot embossing and feature sizes of 100 μm could be replicated with high fidelity.

TEM Analysis of Interfaces in Diffusion-Bonded Silicon Carbide Ceramics Joined Using Metallic Interlayers

NASA Technical Reports Server (NTRS)

Ozaki, T.; Tsuda, H.; Halbig, M. C.; Singh, M.; Hasegawa, Y.; Mori, S.; Asthana R.

2016-01-01

Silicon Carbide (SiC) is a promising material for thermo-structural applications due to its excellent high-temperature mechanical properties, oxidation resistance, and thermal stability. However, joining and integration technologies are indispensable for this material in order to fabricate large size and complex shape components with desired functionalities. Although diffusion bonding techniques using metallic interlayers have been commonly utilized to bond various SiC ceramics, detailed microstructural observation by Transmission Electron Microscopy (TEM) of the bonded area has not been carried out due to difficulty in preparing TEM samples. In this study, we tried to prepare TEM samples from joints of diffusion bonded SiC ceramics by Focused Ion Beam (FIB) system and carefully investigated the interfacial microstructure by TEM analysis. The samples used in this study were SiC fiber bonded ceramics (SA-Tyrannohex: SA-THX) diffusion bonded with metallic interlayers such as Ti, TiMo, and Mo-B. In this presentation, the result of microstructural analysis obtained by TEM observations and the influence of metallic interlayers and fiber orientation of SA-THX on the joint microstructure will be discussed.

TEM Analysis of Diffusion-Bonded Silicon Carbide Ceramics Joined Using Metallic Interlayers

NASA Technical Reports Server (NTRS)

Ozaki, T.; Tsuda, H.; Halbig, M. C.; Singh, M.; Hasegawa, Y; Mori, S.; Asthana, R.

2017-01-01

Silicon Carbide (SiC) is a promising material for thermostructural applications due to its excellent high-temperature mechanical properties, oxidation resistance, and thermal stability. However, joining and integration technologies are indispensable for this material in order to fabricate large size and complex shape components with desired functionalities. Although diffusion bonding techniques using metallic interlayers have been commonly utilized to bond various SiC ceramics, detailed microstructural observation by Transmission Electron Microscopy (TEM) of the bonded area has not been carried out due to difficulty in preparing TEM samples. In this study, we tried to prepare TEM samples from joints of diffusion bonded SiC ceramics by Focused Ion Beam (FIB) system and carefully investigated the interfacial microstructure by TEM analysis. The samples used in this study were SiC fiber bonded ceramics (SA-Tyrannohex: SA-THX) diffusion bonded with metallic interlayers such as Ti, TiMo, Mo-B and TiCu. In this presentation, we report the microstructure of diffusion bonded SA-THX mainly with TiCu interlayers obtained by TEM observations, and the influence of metallic interlayers on the joint microstructure and microhardness will be discussed.

Studies on wettability of polypropylene/methyl-silicone composite film and polypropylene monolithic material.

PubMed

Hou, Weixin; Mu, Bo; Wang, Qihua

2008-11-01

A polypropylene/methyl-silicone superhydrophobic surface was prepared using a simple casting method. Varying the ratio of polypropylene and methyl-silicone results in different surface microstructure. The wetting behavior of the as-prepared surface was investigated. A polypropylene monolithic material was also prepared. Its superhydrophobicity still retains when the material was cut or abraded. The as-prepared material can also be used to separate some organic solvents from water.

Crystallization of the glassy grain boundary phase in silicon nitride ceramics

NASA Technical Reports Server (NTRS)

Drummond, Charles H., III

1991-01-01

The role was studied of the intergranular glassy phase in silicon nitride as-processed with yttria as a sintering aid. The microstructure, crystallization, and viscosity of the glassy phase were areas studied. Crystallization of the intergranular glassy phase to more refractory crystalline phases should improve the high temperature mechanical properties of the silicon nitride. The addition of a nucleating agent will increase the rate of crystallization. The measurement of the viscosity of the glassy phase will permit the estimation of the high temperature deformation of the silicon nitride.

Supersaturating Silicon with Titanium by Continuous-Wave Laser Irradiation of Sputtered Titanium Film on Silicon

NASA Astrophysics Data System (ADS)

Bao-Dian, Fan; Yu, Qiu; Rong, Chen; Miao, Pan; Li-Han, Cai; Jiang-Hui, Zheng; Chao, Chen

2016-02-01

Not Available Supported by the National Natural Science Foundation of China under Grant No 61076056, and the Opening Project of State Key Laboratory of High Performance Ceramics and Superfine Microstructure of Shanghai Institute of Ceramics of Chinese Academy of Sciences under Grant No SKL201404SIC.

Decal transfer microfabrication

DOEpatents

Nuzzo, Ralph G.; Childs, William Robert

2004-10-19

A method of making a microstructure includes forming a pattern in a surface of a silicon-containing elastomer, oxidizing the pattern, contacting the pattern with a substrate; and bonding the oxidized pattern and the substrate such that the pattern and the substrate are irreversibly attached. The silicon-containing elastomer may be removably attached to a transfer pad.

In-chip microstructures and photonic devices fabricated by nonlinear laser lithography deep inside silicon

PubMed Central

Makey, Ghaith; Elahi, Parviz; Çolakoğlu, Tahir; Ergeçen, Emre; Yavuz, Özgün; Hübner, René; Borra, Mona Zolfaghari; Pavlov, Ihor; Bek, Alpan; Turan, Raşit; Kesim, Denizhan Koray; Tozburun, Serhat; Ilday, Serim; Ilday, F. Ömer

2017-01-01

Silicon is an excellent material for microelectronics and integrated photonics1–3 with untapped potential for mid-IR optics4. Despite broad recognition of the importance of the third dimension5,6, current lithography methods do not allow fabrication of photonic devices and functional microelements directly inside silicon chips. Even relatively simple curved geometries cannot be realised with techniques like reactive ion etching. Embedded optical elements, like in glass7, electronic devices, and better electronic-photonic integration are lacking8. Here, we demonstrate laser-based fabrication of complex 3D structures deep inside silicon using 1 µm-sized dots and rod-like structures of adjustable length as basic building blocks. The laser-modified Si has a different optical index than unmodified parts, which enables numerous photonic devices. Optionally, these parts are chemically etched to produce desired 3D shapes. We exemplify a plethora of subsurface, i.e., “in-chip” microstructures for microfluidic cooling of chips, vias, MEMS, photovoltaic applications and photonic devices that match or surpass the corresponding state-of-the-art device performances. PMID:28983323

In-chip microstructures and photonic devices fabricated by nonlinear laser lithography deep inside silicon

NASA Astrophysics Data System (ADS)

Tokel, Onur; Turnalı, Ahmet; Makey, Ghaith; Elahi, Parviz; ćolakoǧlu, Tahir; Ergeçen, Emre; Yavuz, Ã.-zgün; Hübner, René; Zolfaghari Borra, Mona; Pavlov, Ihor; Bek, Alpan; Turan, Raşit; Kesim, Denizhan Koray; Tozburun, Serhat; Ilday, Serim; Ilday, F. Ã.-mer

2017-10-01

Silicon is an excellent material for microelectronics and integrated photonics1-3, with untapped potential for mid-infrared optics4. Despite broad recognition of the importance of the third dimension5,6, current lithography methods do not allow the fabrication of photonic devices and functional microelements directly inside silicon chips. Even relatively simple curved geometries cannot be realized with techniques like reactive ion etching. Embedded optical elements7, electronic devices and better electronic-photonic integration are lacking8. Here, we demonstrate laser-based fabrication of complex 3D structures deep inside silicon using 1-µm-sized dots and rod-like structures of adjustable length as basic building blocks. The laser-modified Si has an optical index different to that in unmodified parts, enabling the creation of numerous photonic devices. Optionally, these parts can be chemically etched to produce desired 3D shapes. We exemplify a plethora of subsurface—that is, `in-chip'—microstructures for microfluidic cooling of chips, vias, micro-electro-mechanical systems, photovoltaic applications and photonic devices that match or surpass corresponding state-of-the-art device performances.

Investigation on laser-plasma coupling in intense, ultrashort irradiation of a nanostructured silicon target

NASA Astrophysics Data System (ADS)

Cristoforetti, G.; Anzalone, A.; Baffigi, F.; Bussolino, G.; D'Arrigo, G.; Fulgentini, L.; Giulietti, A.; Koester, P.; Labate, L.; Tudisco, S.; Gizzi, L. A.

2014-09-01

One of the most interesting research fields in laser-matter interaction studies is the investigation of effects and mechanisms produced by nano- or micro-structured targets, mainly devoted to the enhancing of laser-target or laser-plasma coupling. In intense and ultra-intense laser interaction regimes, the observed enhancement of x-ray plasma emission and/or hot electron conversion efficiency is explained by a variety of mechanisms depending on the dimensions and shape of the structures irradiated. In the present work, the attention is mainly focused on the lowering of the plasma formation threshold which is induced by the larger absorptivity. Flat and nanostructured silicon targets were here irradiated with an ultrashort laser pulse, in the range 1 × 1017-2 × 1018 W µm2 cm-2. The effects of structures on laser-plasma coupling were investigated at different laser pulse polarizations, by utilizing x-ray yield and 3/2ω harmonics emission. While the measured enhancement of x-ray emission is negligible at intensities larger than 1018 W µm2 cm-2, due to the destruction of the structures by the amplified spontaneous emission (ASE) pre-pulse, a dramatic enhancement, strongly dependent on pulse polarization, was observed at intensities lower than ˜3.5 × 1017 W µm2 cm-2. Relying on the three-halves harmonic emission and on the non-isotropic character of the x-ray yield, induced by the two-plasmon decay instability, the results are explained by the significant lowering of the plasma threshold produced by the nanostructures. In this view, the strong x-ray enhancement obtained by s-polarized pulses is produced by the interaction of the laser pulse with the preplasma, resulting from the interaction of the ASE pedestal with the nanostructures.

Self-Assembly in Systems Containing Silicone Compounds

NASA Astrophysics Data System (ADS)

Ferreira, Maira Silva; Loh, Watson

2009-01-01

Chemical systems formed by silicone solvents and surfactants have potential applications in a variety of industrial products. In spite of their technological relevance, there are few reports on the scientific literature that focus on characterizing such ternary systems. In this work, we have aimed to develop a general, structural investigation on the phase diagram of one system that typically comprises silicone-based chemicals, by means of the SAXS (small-angle X-ray scattering) technique. Important features such as the presence of diverse aggregation states in the overall system, either on their own or in equilibrium with other structures, have been detected. As a result, optically isotropic chemical systems (direct and/or reversed microemulsions) and liquid crystals with lamellar or hexagonal packing have been identified and characterized.

Phase Transformation Behavior of Medium Manganese Steels with 3 Wt Pct Aluminum and 3 Wt Pct Silicon During Intercritical Annealing

NASA Astrophysics Data System (ADS)

Sun, Binhan; Fazeli, Fateh; Scott, Colin; Yue, Stephen

2016-10-01

Medium manganese steels alloyed with sufficient aluminum and silicon amounts contain high fractions of retained austenite adjustable to various transformation-induced plasticity/twinning-induced plasticity effects, in addition to a reduced density suitable for lightweight vehicle body-in-white assemblies. Two hot rolled medium manganese steels containing 3 wt pct aluminum and 3 wt pct silicon were subjected to different annealing treatments in the present study. The evolution of the microstructure in terms of austenite transformation upon reheating and the subsequent austenite decomposition during quenching was investigated. Manganese content of the steels prevailed the microstructural response. The microstructure of the leaner alloy with 7 wt pct Mn (7Mn) was substantially influenced by the annealing temperature, including the variation of phase constituents, the morphology and composition of intercritical austenite, the Ms temperature and the retained austenite fraction. In contrast, the richer variant 10 wt pct Mn steel (10Mn) exhibited a substantially stable ferrite-austenite duplex phase microstructure containing a fixed amount of retained austenite which was found to be independent of the variations of intercritical annealing temperature. Austenite formation from hot band ferrite-pearlite/bainite mixtures was very rapid during annealing at 1273 K (1000 °C), regardless of Mn contents. Austenite growth was believed to be controlled at early stages by carbon diffusion following pearlite/bainite dissolution. The redistribution of Mn in ferrite and particularly in austenite at later stages was too subtle to result in a measureable change in austenite fraction. Further, the hot band microstructure of both steels contained a large fraction of coarse-grained δ-ferrite, which remained almost unchanged during intercritical annealing. A recently developed thermodynamic database was evaluated using the experimental data. The new database achieved a better agreement with the experimental results for the 7Mn steel compared with the existing commercial TCFE database; however, some discrepancy in the predicted phase fractions and compositions still existed. The phase transformation behavior of the two steels during annealing and its implication on the design of high aluminum-silicon medium manganese steels were discussed in detail.

Development of Matrix Microstructures in UHTC Composites

NASA Technical Reports Server (NTRS)

Johnson, Sylvia; Stackpoole, Margaret; Gusman, Michael

2012-01-01

One of the major issues hindering the use of ultra high temperature ceramics for aerospace applications is low fracture toughness. There is considerable interest in developing fiber-reinforced composites to improve fracture toughness. Considerable knowledge has been gained in controlling and improving the microstructure of monolithic UHTCs, and this paper addresses the question of transferring that knowledge to composites. Some model composites have been made and the microstructures of the matrix developed has been explored and compared to the microstructure of monolithic materials in the hafnium diboride/silicon carbide family. Both 2D and 3D weaves have been impregnated and processed.

Novel polymer composite having diamond particles and boron nitride platelets for thermal management of electric vehicle motors

NASA Astrophysics Data System (ADS)

Nakajima, Anri; Shoji, Atsushi; Yonemori, Kei; Seo, Nobuhide

2016-02-01

Thermal conductivities of silicone matrix polymers including fillers of diamond particles and/or hexagonal boron nitride (h-BN) platelets were systematically investigated in an attempt to find a thermal interface material (TIM) having high isotropic thermal conductivity and high electrical insulating ability to enable efficient heat dissipation from the motor coil ends of electric vehicles. The TIM with mixed fillers of diamond particles and h-BN platelets had a maximum thermal conductivity of 6.1 W m-1 K-1 that was almost isotropic. This is the highest value among the thermal conductivities of TIMs with silicone matrix polymer reported to date. The mechanism behind the thermal conductivity of the TIMs was also examined from the viewpoint of the change in the number of thermally conductive networks and/or a decrease in the thermal resistivity of junctions of neighboring diamond particles through the incorporation of h-BN platelets. The TIMs developed in this study will make it possible to manage the heat of electric motors and will help to popularize electric vehicles.

Microstructure and Mechanical Properties of Reaction-Formed Joints in Reaction Bonded Silicon Carbide Ceramics

NASA Technical Reports Server (NTRS)

Singh, M.

1998-01-01

A reaction-bonded silicon carbide (RB-SiC) ceramic material (Carborundum's Cerastar RB-SIC) has been joined using a reaction forming approach. Microstructure and mechanical properties of three types of reaction-formed joints (350 micron, 50-55 micron, and 20-25 micron thick) have been evaluated. Thick (approximately 350 micron) joints consist mainly of silicon with a small amount of silicon carbide. The flexural strength of thick joints is about 44 plus or minus 2 MPa, and fracture always occurs at the joints. The microscopic examination of fracture surfaces of specimens with thick joints tested at room temperature revealed the failure mode to be typically brittle. Thin joints (<50-55 micron) consist of silicon carbide and silicon phases. The room and high temperature flexural strengths of thin (<50-55 micron) reaction-formed joints have been found to be at least equal to that of the bulk Cerastar RB-SIC materials because the flexure bars fracture away from the joint regions. In this case, the fracture origins appear to be inhomogeneities inside the parent material. This was always found to be the case for thin joints tested at temperatures up to 1350C in air. This observation suggests that the strength of Cerastar RB-SIC material containing a thin joint is not limited by the joint strength but by the strength of the bulk (parent) materials.

Design and application of permanent magnet flux sources for mechanical testing of magnetoactive elastomers at variable field directions.

PubMed

Hiptmair, F; Major, Z; Haßlacher, R; Hild, S

2015-08-01

Magnetoactive elastomers (MAEs) are a class of smart materials whose mechanical properties can be rapidly and reversibly changed by an external magnetic field. Due to this tunability, they are useable for actuators or in active vibration control applications. An extensive magnetomechanical characterization is necessary for MAE material development and requires experiments under cyclic loading in uniform but variable magnetic fields. MAE testing apparatus typically rely on fields of adjustable strength, but fixed (transverse) direction, often provided by electromagnets. In this work, two permanent magnet flux sources were developed as an add-on for a modular test stand, to allow for mechanical testing in uniform fields of variable direction. MAE specimens, based on a silicone matrix with isotropic and anisotropic carbonyl iron particle distributions, were subjected to dynamic mechanical analysis under different field and loading configurations. The magneto-induced increase of stiffness and energy dissipation was determined by the change of the hysteresis loop area and dynamic modulus values. A distinct influence of the composite microstructure and the loading state was observed. Due to the very soft and flexible matrix used for preparing the MAE samples, the material stiffness and damping behavior could be varied over a wide range via the applied field direction and intensity.

Femtosecond laser fabricating black silicon in alkaline solution

NASA Astrophysics Data System (ADS)

Meng, Jiao; Song, Haiying; Li, Xiaoli; Liu, Shibing

2015-03-01

An efficient approach for enhancing the surface antireflection is proposed, in which a black silicon is fabricated by a femtosecond laser in alkaline solution. In the experiment, 2 wt% NaOH solution is formulated at room temperature (22 ± 1 °C). Then, a polished silicon is scanned via femtosecond laser irradiation in 2 wt% NaOH solution. Jungle-like microstructures on the black silicon surface are characterized using an atomic force microscopy. The reflectance of the black silicon is measured at the wavelengths ranging from 400 to 750 nm. Compared to the polished silicon, the black silicon can significantly suppress the optical reflection throughout the visible region (<5 %). Meanwhile, we also investigated the factors of the black silicon, including the femtosecond laser pulse energy and the scanning speed. This method is simple and effective to acquire the black silicon, which probably has a large advantage in fast and cost-effective black silicon fabrication.

Micromechanics of fatigue in woven and stitched composites

NASA Technical Reports Server (NTRS)

Cox, B. N.; Dadkhah, M. S.; Inman, R. V.; Mitchell, M. R.; Morris, W. L.; Schroeder, S.

1991-01-01

The goal is to determine how microstructural factors, especially the architecture of microstructural factors, control fatigue damage in 3D reinforced polymer composites. Test materials were fabricated from various preforms, including stitched quasi-isotropic laminates, and through-the-thickness angle interlock, layer-to-layer angle interlock, and through-the-thickness stitching effect weaves. Preforms were impregnated with a tough resin by a special vacuum infiltration method. Most tests are being performed in uniaxial compression/compression loading. In all cases to date, failure has occurred not by delamination, but by shear failure, which occurs suddenly rather than by gradual macroscopic crack growth. Some theoretical aspects of bridging are also examined.

A Novel Approach for Controlling the Band Formation in Medium Mn Steels

NASA Astrophysics Data System (ADS)

Farahani, H.; Xu, W.; van der Zwaag, S.

2018-06-01

Formation of the microstructural ferrite/pearlite bands in medium Mn steels is an undesirable phenomenon commonly addressed through fast cooling treatments. In this study, a novel approach using the cyclic partial phase transformation concept is applied successfully to prevent microstructural band formation in a micro-chemically banded Fe-C-Mn-Si steel. The effectiveness of the new approach is assessed using the ASTM E1268-01 standard. The cyclic intercritical treatments lead to formation of isotropic microstructures even for cooling rates far below the critical one determined in conventional continuous cooling. In contrast, isothermal intercritical experiments have no effect on the critical cooling rate to suppress microstructural band formation. The origin of the suppression of band formation either by means of fast cooling or a cyclic partial phase transformation is investigated in detail. Theoretical modeling and microstructural observations confirm that band formation is suppressed only if the intercritical annealing treatment leads to partial reversion of the austenite-ferrite interfaces. The resulting interfacial Mn enrichment is responsible for suppression of the band formation upon final cooling at low cooling rates.

Friction behavior of a microstructured polymer surface inspired by snake skin.

PubMed

Baum, Martina J; Heepe, Lars; Gorb, Stanislav N

2014-01-01

The aim of this study was to understand the influence of microstructures found on ventral scales of the biological model, Lampropeltis getula californiae, the California King Snake, on the friction behavior. For this purpose, we compared snake-inspired anisotropic microstructured surfaces to other microstructured surfaces with isotropic and anisotropic geometry. To exclude that the friction measurements were influenced by physico-chemical variations, all friction measurements were performed on the same epoxy polymer. For frictional measurements a microtribometer was used. Original data were processed by fast Fourier transformation (FFT) with a zero frequency related to the average friction and other peaks resulting from periodic stick-slip behavior. The data showed that the specific ventral surface ornamentation of snakes does not only reduce the frictional coefficient and generate anisotropic frictional properties, but also reduces stick-slip vibrations during sliding, which might be an adaptation to reduce wear. Based on this extensive comparative study of different microstructured polymer samples, it was experimentally demonstrated that the friction-induced stick-slip behavior does not solely depend on the frictional coefficient of the contact pair.

A Novel Approach for Controlling the Band Formation in Medium Mn Steels

NASA Astrophysics Data System (ADS)

Farahani, H.; Xu, W.; van der Zwaag, S.

2018-03-01

Formation of the microstructural ferrite/pearlite bands in medium Mn steels is an undesirable phenomenon commonly addressed through fast cooling treatments. In this study, a novel approach using the cyclic partial phase transformation concept is applied successfully to prevent microstructural band formation in a micro-chemically banded Fe-C-Mn-Si steel. The effectiveness of the new approach is assessed using the ASTM E1268-01 standard. The cyclic intercritical treatments lead to formation of isotropic microstructures even for cooling rates far below the critical one determined in conventional continuous cooling. In contrast, isothermal intercritical experiments have no effect on the critical cooling rate to suppress microstructural band formation. The origin of the suppression of band formation either by means of fast cooling or a cyclic partial phase transformation is investigated in detail. Theoretical modeling and microstructural observations confirm that band formation is suppressed only if the intercritical annealing treatment leads to partial reversion of the austenite-ferrite interfaces. The resulting interfacial Mn enrichment is responsible for suppression of the band formation upon final cooling at low cooling rates.

Micromechanical modeling of elastic properties of cortical bone accounting for anisotropy of dense tissue.

PubMed

Salguero, Laura; Saadat, Fatemeh; Sevostianov, Igor

2014-10-17

The paper analyzes the connection between microstructure of the osteonal cortical bone and its overall elastic properties. The existing models either neglect anisotropy of the dense tissue or simplify cortical bone microstructure (accounting for Haversian canals only). These simplifications (related mostly to insufficient mathematical apparatus) complicate quantitative analysis of the effect of microstructural changes - produced by age, microgravity, or some diseases - on the overall mechanical performance of cortical bone. The present analysis fills this gap; it accounts for anisotropy of the dense tissue and uses realistic model of the porous microstructure. The approach is based on recent results of Sevostianov et al. (2005) and Saadat et al. (2012) on inhomogeneities in a transversely-isotropic material. Bone's microstructure is modeled according to books of Martin and Burr (1989), Currey (2002), and Fung (1993) and includes four main families of pores. The calculated elastic constants for porous cortical bone are in agreement with available experimental data. The influence of each of the pore types on the overall moduli is examined. Copyright © 2014 Elsevier Ltd. All rights reserved.

Melt infiltration of silicon carbide compacts. II - Evaluation of solidification microstructures

NASA Technical Reports Server (NTRS)

Asthana, Rajiv; Rohatgi, Pradeep K.

1993-01-01

Microstructural aspects of alloy solidification within the interstices of porous compacts of platelet-shaped single crystals of alpha-SiC, when the latter are infiltrated with a hot metal under pressure, have been described. Microstructural evidence is presented of selective reorientation of platelets and nonhomogeneous solute distribution under shear of pressurized melt, of constrained growth of primary solid within finite width zones, and of the modulation of coring due to microsegregation as a result of variations in the pore size of compacts.

An Array of Layers in Silicon Sulfides: Chain-like and Ground State Structures

NASA Astrophysics Data System (ADS)

Alonso-Lanza, Tomás; Ayuela, Andrés; Aguilera-Granja, Faustino

While much is known about isoelectronic materials related to carbon nanostructures, such as boron nitride layers and nanotubes, rather less is known about equivalent silicon based materials. Following the recent discovery of phosphorene, we here discuss isoelectronic silicon monosulfide monolayers. We describe a set of anisotropic ground state structures that clearly have a high stability with respect to the near isotropic silicon monosulfide monolayers. The source of the layer anisotropy is related to the presence of Si-S double chains linked by some Si-Si covalent bonds, which lie at the core of the increased stability, together with a remarkable spd hybridization on Si. The involvement of d orbitals brings more variety to silicon-sulfide based nanostructures that are isoelectronic to phosphorene, which could be relevant for future applications, adding extra degrees of freedom. Spanish Ministry of Economy and Competitiveness MINECO, Basque Government (ETORTEK Program 2014), University of the Basque Country (GrantGrant No. IT-366-07) and MPC Material Physics Center - San Sebastián.

Fabrication of Cantilever-Bump Type Si Probe Card

NASA Astrophysics Data System (ADS)

Park, Jeong-Yong; Lee, Dong-Seok; Kim, Dong-Kwon; Lee, Jong-Hyun

2000-12-01

Probe card is most important part in the test system which selects the good or bad chip of integrated circuit (IC) chips. Silicon vertical probe card is able to test multiple semiconductor chips simultaneously. We presented cantilever-bump type vertical probe card. It was fabricated by dry etching using RIE(reactive ion etching) technique and porous silicon micromachining using silicon direct bonded (SDB) wafer. Cantilevers and bumps were fabricated by isotropic etching using RIE@. 3-dimensional structures were formed by porous silicon micromachining technique using SDB wafer. Contact resistance of fabricated probe card was less than 2 Ω and its life time was more than 200,000 turns. The process used in this work is very simple and reproducible, which has good controllability in the tip dimension and spacing. It is expected that the fabricated probe card can reduce testing time, can promote productivity and enables burn-in test.

Microstructural Rearrangements and their Rheological Implications in a Model Thixotropic Elastoviscoplastic Fluid

NASA Astrophysics Data System (ADS)

Jamali, Safa; McKinley, Gareth H.; Armstrong, Robert C.

2017-01-01

We identify the sequence of microstructural changes that characterize the evolution of an attractive particulate gel under flow and discuss their implications on macroscopic rheology. Dissipative particle dynamics is used to monitor shear-driven evolution of a fabric tensor constructed from the ensemble spatial configuration of individual attractive constituents within the gel. By decomposing this tensor into isotropic and nonisotropic components we show that the average coordination number correlates directly with the flow curve of the shear stress versus shear rate, consistent with theoretical predictions for attractive systems. We show that the evolution in nonisotropic local particle rearrangements are primarily responsible for stress overshoots (strain-hardening) at the inception of steady shear flow and also lead, at larger times and longer scales, to microstructural localization phenomena such as shear banding flow-induced structure formation in the vorticity direction.

The mechanics of surface expansion anisotropy in Medicago truncatula root hairs.

PubMed

Dumais, Jacques; Long, Sharon R; Shaw, Sidney L

2004-10-01

Wall expansion in tip-growing cells shows variations according to position and direction. In Medicago truncatula root hairs, wall expansion exhibits a strong meridional gradient with a maximum near the pole of the cell. Root hair cells also show a striking expansion anisotropy, i.e. over most of the dome surface the rate of circumferential wall expansion exceeds the rate of meridional expansion. Concomitant measurements of expansion rates and wall stresses reveal that the extensibility of the cell wall must vary abruptly along the meridian of the cell to maintain the gradient of wall expansion. To determine the mechanical basis of expansion anisotropy, we compared measurements of wall expansion with expansion patterns predicted from wall structural models that were either fully isotropic, transversely isotropic, or fully anisotropic. Our results indicate that a model based on a transversely isotropic wall structure can provide a good fit of the data although a fully anisotropic model offers the best fit overall. We discuss how such mechanical properties could be controlled at the microstructural level.

Effects of isotropic and anisotropic slip on droplet impingement on a superhydrophobic surface

NASA Astrophysics Data System (ADS)

Clavijo, Cristian E.; Crockett, Julie; Maynes, Daniel

2015-12-01

The dynamics of single droplet impingement on micro-textured superhydrophobic surfaces with isotropic and anisotropic slip are investigated. While several analytical models exist to predict droplet impact on superhydrophobic surfaces, no previous model has rigorously considered the effect of the shear-free region above the gas cavities resulting in an apparent slip that is inherent for many of these surfaces. This paper presents a model that accounts for slip during spreading and recoiling. A broad range of Weber numbers and slip length values were investigated at low Ohnesorge numbers. The results show that surface slip exerts negligible influence throughout the impingement process for low Weber numbers but can exert significant influence for high Weber numbers (on the order of 102). When anisotropic slip prevails, the droplet exhibits an elliptical shape at the point of maximum spread, with greater eccentricity for increasing slip and increasing Weber number. Experiments were performed on isotropic and anisotropic micro-structured superhydrophobic surfaces and the agreement between the experimental results and the model is very good.

Formation of porous silicon oxide from substrate-bound silicon rich silicon oxide layers by continuous-wave laser irradiation

NASA Astrophysics Data System (ADS)

Wang, Nan; Fricke-Begemann, Th.; Peretzki, P.; Ihlemann, J.; Seibt, M.

2018-03-01

Silicon nanocrystals embedded in silicon oxide that show room temperature photoluminescence (PL) have great potential in silicon light emission applications. Nanocrystalline silicon particle formation by laser irradiation has the unique advantage of spatially controlled heating, which is compatible with modern silicon micro-fabrication technology. In this paper, we employ continuous wave laser irradiation to decompose substrate-bound silicon-rich silicon oxide films into crystalline silicon particles and silicon dioxide. The resulting microstructure is studied using transmission electron microscopy techniques with considerable emphasis on the formation and properties of laser damaged regions which typically quench room temperature PL from the nanoparticles. It is shown that such regions consist of an amorphous matrix with a composition similar to silicon dioxide which contains some nanometric silicon particles in addition to pores. A mechanism referred to as "selective silicon ablation" is proposed which consistently explains the experimental observations. Implications for the damage-free laser decomposition of silicon-rich silicon oxides and also for controlled production of porous silicon dioxide films are discussed.

Evolution of a Native Oxide Layer at the a-Si:H/c-Si Interface and Its Influence on a Silicon Heterojunction Solar Cell.

PubMed

Liu, Wenzhu; Meng, Fanying; Zhang, Xiaoyu; Liu, Zhengxin

2015-12-09

The interface microstructure of a silicon heterojunction (SHJ) solar cell was investigated. We found an ultrathin native oxide layer (NOL) with a thickness of several angstroms was formed on the crystalline silicon (c-Si) surface in a very short time (∼30 s) after being etched by HF solution. Although the NOL had a loose structure with defects that are detrimental for surface passivation, it acted as a barrier to restrain the epitaxial growth of hydrogenated amorphous silicon (a-Si:H) during the plasma-enhanced chemical vapor deposition (PECVD). The microstructure change of the NOL during the PECVD deposition of a-Si:H layers with different conditions and under different H2 plasma treatments were systemically investigated in detail. When a brief H2 plasma was applied to treat the a-Si:H layer after the PECVD deposition, interstitial oxygen and small-size SiO2 precipitates were transformed to hydrogenated amorphous silicon suboxide alloy (a-SiO(x):H, x ∼ 1.5). In the meantime, the interface defect density was reduced by about 50%, and the parameters of the SHJ solar cell were improved due to the post H2 plasma treatment.

Role of an Oxidant Mixture as Surface Modifier of Porous Silicon Microstructures Evaluated by Spectroscopic Ellipsometry

PubMed Central

Montiel-González, Zeuz; Escobar, Salvador; Nava, Rocío; del Río, J. Antonio; Tagüeña-Martínez, Julia

2016-01-01

Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This mixture can chemically modify their microstructure by changing the thickness and surface passivation of the pore walls. In this work, we prepared a series of samples (with and without oxidant mixture) and we evaluated the structural differences through their scanning electron micrographs and their optical properties determined by spectroscopic ellipsometry. The results showed that ellipsometry is sensitive to slight variations in the porous silicon structure, caused by changes in their preparation. The fitting process, based on models constructed from the features observed in the micrographs, allowed us to see that the mayor effect of the oxidant mixture is on samples of high porosity, where the surface oxidation strongly contributes to the skeleton thinning during the electrochemical etching. This suggests the existence of a porosity threshold for the action of the oxidant mixture. These results could have a significant impact on the design of complex porous silicon structures for different optoelectronic applications. PMID:27097767

Role of an Oxidant Mixture as Surface Modifier of Porous Silicon Microstructures Evaluated by Spectroscopic Ellipsometry.

PubMed

Montiel-González, Zeuz; Escobar, Salvador; Nava, Rocío; del Río, J Antonio; Tagüeña-Martínez, Julia

2016-04-21

Current research on porous silicon includes the construction of complex structures with luminescent and/or photonic properties. However, their preparation with both characteristics is still challenging. Recently, our group reported a possible method to achieve that by adding an oxidant mixture to the electrolyte used to produce porous silicon. This mixture can chemically modify their microstructure by changing the thickness and surface passivation of the pore walls. In this work, we prepared a series of samples (with and without oxidant mixture) and we evaluated the structural differences through their scanning electron micrographs and their optical properties determined by spectroscopic ellipsometry. The results showed that ellipsometry is sensitive to slight variations in the porous silicon structure, caused by changes in their preparation. The fitting process, based on models constructed from the features observed in the micrographs, allowed us to see that the mayor effect of the oxidant mixture is on samples of high porosity, where the surface oxidation strongly contributes to the skeleton thinning during the electrochemical etching. This suggests the existence of a porosity threshold for the action of the oxidant mixture. These results could have a significant impact on the design of complex porous silicon structures for different optoelectronic applications.

Role of isostaticity and load-bearing microstructure in the elasticity of yielded colloidal gels.

PubMed

Hsiao, Lilian C; Newman, Richmond S; Glotzer, Sharon C; Solomon, Michael J

2012-10-02

We report a simple correlation between microstructure and strain-dependent elasticity in colloidal gels by visualizing the evolution of cluster structure in high strain-rate flows. We control the initial gel microstructure by inducing different levels of isotropic depletion attraction between particles suspended in refractive index matched solvents. Contrary to previous ideas from mode coupling and micromechanical treatments, our studies show that bond breakage occurs mainly due to the erosion of rigid clusters that persist far beyond the yield strain. This rigidity contributes to gel elasticity even when the sample is fully fluidized; the origin of the elasticity is the slow Brownian relaxation of rigid, hydrodynamically interacting clusters. We find a power-law scaling of the elastic modulus with the stress-bearing volume fraction that is valid over a range of volume fractions and gelation conditions. These results provide a conceptual framework to quantitatively connect the flow-induced microstructure of soft materials to their nonlinear rheology.

Rheological properties of isotropic magnetorheological elastomers featuring an epoxidized natural rubber

NASA Astrophysics Data System (ADS)

Azhani Yunus, Nurul; Amri Mazlan, Saiful; Ubaidillah; Choi, Seung-Bok; Imaduddin, Fitrian; Aziz, Siti Aishah Abdul; Khairi, Muntaz Hana Ahmad

2016-10-01

This study presents principal field-dependent rheological properties of magnetorheological elastomers (MREs) in which an epoxidized natural rubber (ENR) is adopted as a matrix (in short, we call it ENR-based MREs). The isotropic ENR-based MRE samples are fabricated by mixing the ENR compound with carbonyl iron particles (CIPs) with different weight percentages. The morphological properties of the samples are firstly analysed using the microstructure assessment. The influences of the magnetic field on the viscoelastic properties of ENR-based MREs are then examined through the dynamic test under various excitation frequencies. The microstructure of MRE samples exhibits a homogeneous distribution of CIPs in the ENR matrix. The dramatic increment of storage modulus, loss modulus and loss tangent of the ENR-based MREs are also observed from the field-dependent rheological test. This directly demonstrates that the stiffness and damping properties of the samples can be adjusted by the magnetic field. It is also seen that the CIP content, exciting frequency and the magnetic field essentially influence the dynamic properties of the ENR-based MREs. The strong correlation between the magnetization and the magneto-induced storage modulus could be used as a useful guidance in synthesizing the ENR-based MREs for certain applications.

Realistic micromechanical modeling and simulation of two-phase heterogeneous materials

NASA Astrophysics Data System (ADS)

Sreeranganathan, Arun

This dissertation research focuses on micromechanical modeling and simulations of two-phase heterogeneous materials exhibiting anisotropic and non-uniform microstructures with long-range spatial correlations. Completed work involves development of methodologies for realistic micromechanical analyses of materials using a combination of stereological techniques, two- and three-dimensional digital image processing, and finite element based modeling tools. The methodologies are developed via its applications to two technologically important material systems, namely, discontinuously reinforced aluminum composites containing silicon carbide particles as reinforcement, and boron modified titanium alloys containing in situ formed titanium boride whiskers. Microstructural attributes such as the shape, size, volume fraction, and spatial distribution of the reinforcement phase in these materials were incorporated in the models without any simplifying assumptions. Instrumented indentation was used to determine the constitutive properties of individual microstructural phases. Micromechanical analyses were performed using realistic 2D and 3D models and the results were compared with experimental data. Results indicated that 2D models fail to capture the deformation behavior of these materials and 3D analyses are required for realistic simulations. The effect of clustering of silicon carbide particles and associated porosity on the mechanical response of discontinuously reinforced aluminum composites was investigated using 3D models. Parametric studies were carried out using computer simulated microstructures incorporating realistic microstructural attributes. The intrinsic merit of this research is the development and integration of the required enabling techniques and methodologies for representation, modeling, and simulations of complex geometry of microstructures in two- and three-dimensional space facilitating better understanding of the effects of microstructural geometry on the mechanical behavior of materials.

Laser ablation and column formation in silicon under oxygen-rich atmospheres

NASA Astrophysics Data System (ADS)

Pedraza, A. J.; Fowlkes, J. D.; Lowndes, D. H.

2000-11-01

The microstructure formed at the surface of silicon by cumulative pulsed-laser irradiation in oxygen-rich atmospheres consists of an array of microcolumns surrounded by microcanyons and microholes. Formation of SiOx at the exposed surface of silicon is most likely responsible for the occurrence of etching/ablation that causes the continuous deepening of canyons and holes. The growth mechanism of columns that is supported by the experimental evidence presented here is a process in which the columns are fed at their tips by the silicon-rich ablation plasma produced during pulsed-laser irradiation.

Temperature Dependence of Power Reflectivity of the First-Wall Materials in the Synchrotron Radiation Range

NASA Astrophysics Data System (ADS)

Takada, Noriharu; Nagatsu, Masaaki; Shimada, Michiya

1995-07-01

The temperature dependence of power reflectivity in the synchrotron radiation range was measured for candidate first-wall materials of the fusion reactor, such as B4C-coated isotropic graphite, C/C composite material, silicon carbide (SiC), tungsten (W), molybdenum (Mo) and SUS-316. The measurements were carried out using a vacuum vessel with a pressure of about 3 mTorr to avoid oxidation. Distinct temperature dependence of reflectivity was observed only for B4C-coated isotropic graphite. For the other materials, power reflectivities were insensitive to temperature in the range from 300 K to ˜900 K. Theoretical analysis of the results is also presented.

Determination of the Tribological Fundamentals of Solid Lubricated Ceramics. Volume 3. Appendices P through II

DTIC Science & Technology

1991-09-01

9H and tungsten silicides may also be present in the microstructure. The non-SiC eiemental concentrations for NC-203 would not be expected to exceed...lesser amounts of yttrium silicate and tungsten silicide . Trace amounts of a-Si 3N4 , silicon oxynitride, tungsten-iron- silicide , and yttrium silicon...SiC ESK On this sample, we detect Silicon, Carbon, and also Oxygen and Nitrogen, as well as Calcium and Sodium traces. After ionic etching up to about

Preparation and Characterization of Ceramizable Kaolin/VMQ and Kaolin/ZB/VMQ Composites

NASA Astrophysics Data System (ADS)

Zhang, X.; Qin, Y.; Pei, Y.; Huang, Z. X.

Ceramizable silicone-based composite was prepared by using methyl vinyl silicone rubber (VMQ) as matrix, calcined Kaolin and zinc borate (ZB) as additives. This composition can form interpenetrating network structures after crosslinking, and then improve heat-resistant properties by firing in air. The results of different formulations were investigated by FTIR. TG-DTG SEM and XRD. It showed that when the temperature above 600°C. the fillers and silicon rubber started to transform from organic to inorganic and internal microstructure became denser.

Environment Conscious Ceramics (Ecoceramics): An Eco-Friendly Route to Advanced Ceramic Materials

NASA Technical Reports Server (NTRS)

Singh, M.

2001-01-01

Environment conscious ceramics (Ecoceramics) are a new class of materials, which can be produced with renewable natural resources (wood) or wood wastes (wood sawdust). This technology provides an eco-friendly route to advanced ceramic materials. Ecoceramics have tailorable properties and behave like ceramic materials manufactured by conventional approaches. Silicon carbide-based ecoceramics have been fabricated by reactive infiltration of carbonaceous preforms by molten silicon or silicon-refractory metal alloys. The fabrication approach, microstructure, and mechanical properties of SiC-based ecoceramics are presented.

Three-dimensional collimation of in-plane-propagating light using silicon micromachined mirror

NASA Astrophysics Data System (ADS)

Sabry, Yasser M.; Khalil, Diaa; Saadany, Bassam; Bourouina, Tarik

2014-03-01

We demonstrate light collimation of single-mode optical fibers using deeply-etched three-dimensional curved micromirror on silicon chip. The three-dimensional curvature of the mirror is controlled by a process combining deep reactive ion etching and isotropic etching of silicon. The produced surface is astigmatic with out-of-plane radius of curvature that is about one half the in-plane radius of curvature. Having a 300-μm in-plane radius and incident beam inplane inclined with an angle of 45 degrees with respect to the principal axis, the reflected beam is maintained stigmatic with about 4.25 times reduction in the beam expansion angle in free space and about 12-dB reduction in propagation losses, when received by a limited-aperture detector.

Effect of microstructure on transformation-induced plasticity of silicon-containing low-alloy steel

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

Tomita, Yoshiyuki; Morioka, Kojiro

1997-04-01

Fe-0.6C-1.5Si-0.8Mn steel was studied to determine the effect of the microstructure on transformation-induced plasticity (TRIP) of silicon-containing low-alloy steel. A remarkable increase in elongation through TRIP can develop in the steel subjected to the following heat treatments: (1) austemper combined with subcritical annealing (SA Aus-T): subcritical annealing at 993K followed by austempering at 673K and then light tempering (after austenitization at 1173K); (2) austemper coupled with interrupted quenching (IQ Aus-T): interrupted quenching at 533K followed by austempering at 673K and light tempering (after austenization at 1,173K). The SA Aus-T treatment produced the triple structures of carbide-free upper bainite, retained austenitemore » ({gamma}R), and free ferrite. As a result of the IQ Aus-T treatment, the triple structures of carbide-free upper bainite, {gamma}R, and tempered martensite appeared. The results are described and microstructural factors in TRIP are discussed.« less

Failure mechanisms of single-crystal silicon electrodes in lithium-ion batteries

PubMed Central

Shi, Feifei; Song, Zhichao; Ross, Philip N.; Somorjai, Gabor A.; Ritchie, Robert O.; Komvopoulos, Kyriakos

2016-01-01

Long-term durability is a major obstacle limiting the widespread use of lithium-ion batteries in heavy-duty applications and others demanding extended lifetime. As one of the root causes of the degradation of battery performance, the electrode failure mechanisms are still unknown. In this paper, we reveal the fundamental fracture mechanisms of single-crystal silicon electrodes over extended lithiation/delithiation cycles, using electrochemical testing, microstructure characterization, fracture mechanics and finite element analysis. Anisotropic lithium invasion causes crack initiation perpendicular to the electrode surface, followed by growth through the electrode thickness. The low fracture energy of the lithiated/unlithiated silicon interface provides a weak microstructural path for crack deflection, accounting for the crack patterns and delamination observed after repeated cycling. On the basis of this physical understanding, we demonstrate how electrolyte additives can heal electrode cracks and provide strategies to enhance the fracture resistance in future lithium-ion batteries from surface chemical, electrochemical and material science perspectives. PMID:27297565

Failure mechanisms of single-crystal silicon electrodes in lithium-ion batteries

DOE PAGES

Shi, Feifei; Song, Zhichao; Ross, Philip N.; ...

2016-06-14

Long-term durability is a major obstacle limiting the widespread use of lithium-ion batteries in heavy-duty applications and others demanding extended lifetime. As one of the root causes of the degradation of battery performance, the electrode failure mechanisms are still unknown. In this paper, we reveal the fundamental fracture mechanisms of single-crystal silicon electrodes over extended lithiation/delithiation cycles, using electrochemical testing, microstructure characterization, fracture mechanics and finite element analysis. Anisotropic lithium invasion causes crack initiation perpendicular to the electrode surface, followed by growth through the electrode thickness. The low fracture energy of the lithiated/unlithiated silicon interface provides a weak microstructural pathmore » for crack deflection, accounting for the crack patterns and delamination observed after repeated cycling. On the basis of this physical understanding, we demonstrate how electrolyte additives can heal electrode cracks and provide strategies to enhance the fracture resistance in future lithium-ion batteries from surface chemical, electrochemical and material science perspectives.« less

Failure mechanisms of single-crystal silicon electrodes in lithium-ion batteries

NASA Astrophysics Data System (ADS)

Shi, Feifei; Song, Zhichao; Ross, Philip N.; Somorjai, Gabor A.; Ritchie, Robert O.; Komvopoulos, Kyriakos

2016-06-01

Long-term durability is a major obstacle limiting the widespread use of lithium-ion batteries in heavy-duty applications and others demanding extended lifetime. As one of the root causes of the degradation of battery performance, the electrode failure mechanisms are still unknown. In this paper, we reveal the fundamental fracture mechanisms of single-crystal silicon electrodes over extended lithiation/delithiation cycles, using electrochemical testing, microstructure characterization, fracture mechanics and finite element analysis. Anisotropic lithium invasion causes crack initiation perpendicular to the electrode surface, followed by growth through the electrode thickness. The low fracture energy of the lithiated/unlithiated silicon interface provides a weak microstructural path for crack deflection, accounting for the crack patterns and delamination observed after repeated cycling. On the basis of this physical understanding, we demonstrate how electrolyte additives can heal electrode cracks and provide strategies to enhance the fracture resistance in future lithium-ion batteries from surface chemical, electrochemical and material science perspectives.

Effect Of Chromium Underlayer On The Properties Of Nano-Crystalline Diamond Films

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

Garratt, Elias; AlFaify, Salem; Yoshitake, T.

2013-01-11

This paper investigated the effect of chromium underlayer on the structure, microstructure and composition of the nano-crystalline diamond films. Nano-crystalline diamond thin films were deposited at high temperature in microwave-induced plasma diluted with nitrogen, on silicon substrate with a thin film of chromium as an underlayer. The composition, structure and microstructure of the deposited layers were analyzed using non-Rutherford Backscattering Spectrometry, Raman Spectroscopy, Near-Edge X-Ray Absorption Fine Structure, X-ray Diffraction and Atomic Force Microscopy. Nanoindentation studies showed that the films deposited on chromium underlayer have higher hardness values compared to those deposited on silicon without an underlayer. Diamond and graphiticmore » phases of the films evaluated by x-ray and optical spectroscopic analysis determined consistency between sp2 and sp3 phases of carbon in chromium sample to that of diamond grown on silicon. Diffusion of chromium was observed using ion beam analysis which was correlated with the formation of chromium complexes by x-ray diffraction.« less

Tensile Properties and Microstructural Characterization of Hi-Nicalon SiC/RBSN Composites

NASA Technical Reports Server (NTRS)

Bhatt, Ramakrishna T.

1998-01-01

The room temperature physical and mechanical properties of silicon carbide fiber-reinforced reaction-bonded silicon nitride matrix composites (SiC/RBSN) were measured, and the composite microstructure was analyzed. The composites consist of nearly 24 vol% of aligned Hi-Nicalon SiC fiber yarns in a approx. 30 vol% porous silicon nitride matrix. The fiber yarns were coated by chemical vapor deposition with a 0.8 mm layer of boron nitride (BN) followed by a 0.2 mm layer of SiC. In the as-fabricated condition, both 1-D and 2-D composites exhibited high strength and graceful failure, and showed improved properties w en compared with unreinforced matrix of comparable density. No indication of reaction between the SiC fiber and BN coating was noticed, but the outer SiC layer reacted locally with the nitridation enhancing additive in the RBSN matrix. A comparison is made between the predicted and measured values of matrix cracking strength.

Tensile Properties and Microstructural Characterization of Hi-Nicalon SiC/RBSN Composites

NASA Technical Reports Server (NTRS)

Bhatt, Ramakrishna T.

1998-01-01

The room temperature physical and mechanical properties of silicon carbide fiber-reinforced reaction-bonded silicon nitride matrix composites (SiC/RBSN) were measured, and the composite microstructure was analyzed. The composites consist of nearly 24 vol% of aligned Hi-Nicalon SiC fiber yarns in a approx. 30 vo1% porous silicon nitride matrix. The fiber yarns were coated by chemical vapor deposition with a 0.8 micron layer of boron nitride (BN) followed by a 0.2 micron layer of SiC. In the as-fabricated condition, both 1-D and 2-D composites exhibited high strength and graceful failure, and showed improved properties when compared with unreinforced matrix of comparable density. No indication of reaction between the SiC fiber and BN coating was noticed, but the outer SiC layer reacted locally with the nitridation enhancing additive in the RBSN matrix. A comparison is made between the predicted and measured values of matrix cracking strength.

Material parameter computation for multi-layered vocal fold models.

PubMed

Schmidt, Bastian; Stingl, Michael; Leugering, Günter; Berry, David A; Döllinger, Michael

2011-04-01

Today, the prevention and treatment of voice disorders is an ever-increasing health concern. Since many occupations rely on verbal communication, vocal health is necessary just to maintain one's livelihood. Commonly applied models to study vocal fold vibrations and air flow distributions are self sustained physical models of the larynx composed of artificial silicone vocal folds. Choosing appropriate mechanical parameters for these vocal fold models while considering simplifications due to manufacturing restrictions is difficult but crucial for achieving realistic behavior. In the present work, a combination of experimental and numerical approaches to compute material parameters for synthetic vocal fold models is presented. The material parameters are derived from deformation behaviors of excised human larynges. The resulting deformations are used as reference displacements for a tracking functional to be optimized. Material optimization was applied to three-dimensional vocal fold models based on isotropic and transverse-isotropic material laws, considering both a layered model with homogeneous material properties on each layer and an inhomogeneous model. The best results exhibited a transversal-isotropic inhomogeneous (i.e., not producible) model. For the homogeneous model (three layers), the transversal-isotropic material parameters were also computed for each layer yielding deformations similar to the measured human vocal fold deformations.

TOPICAL REVIEW: Ultra-thin film encapsulation processes for micro-electro-mechanical devices and systems

NASA Astrophysics Data System (ADS)

Stoldt, Conrad R.; Bright, Victor M.

2006-05-01

A range of physical properties can be achieved in micro-electro-mechanical systems (MEMS) through their encapsulation with solid-state, ultra-thin coatings. This paper reviews the application of single source chemical vapour deposition and atomic layer deposition (ALD) in the growth of submicron films on polycrystalline silicon microstructures for the improvement of microscale reliability and performance. In particular, microstructure encapsulation with silicon carbide, tungsten, alumina and alumina-zinc oxide alloy ultra-thin films is highlighted, and the mechanical, electrical, tribological and chemical impact of these overlayers is detailed. The potential use of solid-state, ultra-thin coatings in commercial microsystems is explored using radio frequency MEMS as a case study for the ALD alloy alumina-zinc oxide thin film.

Microstructural Effects on the Corrosion Behavior of Alloys and Ceramics

DTIC Science & Technology

2008-06-30

Cr ferritic- martensitic steel HCMI2A, and silicon carbide fabricated by means of chemical vapor deposition (CVD). The study focused on the effect of...12%Cr ferritic- martensitic steel HCM12A, and silicon carbide fabricated by means of chemical vapor deposition (CVD). The study focused on the effect...3 1.4.3. Ferritic/ martensitic steel H CM 12A

Recycling of silicon: from industrial waste to biocompatible nanoparticles for nanomedicine

NASA Astrophysics Data System (ADS)

Kozlov, N. K.; Natashina, U. A.; Tamarov, K. P.; Gongalsky, M. B.; Solovyev, V. V.; Kudryavtsev, A. A.; Sivakov, V.; Osminkina, L. A.

2017-09-01

The formation of photoluminescent porous silicon (PSi) nanoparticles (NPs) is usually based on an expensive semiconductor grade wafers technology. Here, we report a low-cost method of PSi NPs synthesis from the industrial silicon waste remained after the wafer production. The proposed method is based on metal-assisted wet-chemical etching (MACE) of the silicon surface of cm-sized metallurgical grade silicon stones which leads to a nanostructuring of the surface due to an anisotropic etching, with subsequent ultrasound fracturing in water. The obtained PSi NPs exhibit bright red room temperature photoluminescence (PL) and demonstrate similar microstructure and physical characteristics in comparison with the nanoparticles synthesized from semiconductor grade Si wafers. PSi NPs prepared from metallurgical grade silicon stones, similar to silicon NPs synthesized from high purity silicon wafer, show low toxicity to biological objects that open the possibility of using such type of NPs in nanomedicine.

Graphitized silicon carbide microbeams: wafer-level, self-aligned graphene on silicon wafers

NASA Astrophysics Data System (ADS)

Cunning, Benjamin V.; Ahmed, Mohsin; Mishra, Neeraj; Ranjbar Kermany, Atieh; Wood, Barry; Iacopi, Francesca

2014-08-01

Currently proven methods that are used to obtain devices with high-quality graphene on silicon wafers involve the transfer of graphene flakes from a growth substrate, resulting in fundamental limitations for large-scale device fabrication. Moreover, the complex three-dimensional structures of interest for microelectromechanical and nanoelectromechanical systems are hardly compatible with such transfer processes. Here, we introduce a methodology for obtaining thousands of microbeams, made of graphitized silicon carbide on silicon, through a site-selective and wafer-scale approach. A Ni-Cu alloy catalyst mediates a self-aligned graphitization on prepatterned SiC microstructures at a temperature that is compatible with silicon technologies. The graphene nanocoating leads to a dramatically enhanced electrical conductivity, which elevates this approach to an ideal method for the replacement of conductive metal films in silicon carbide-based MEMS and NEMS devices.

Development of refractory armored silicon carbide by infrared transient liquid phase processing

NASA Astrophysics Data System (ADS)

Hinoki, Tatsuya; Snead, Lance L.; Blue, Craig A.

2005-12-01

Tungsten (W) and molybdenum (Mo) were coated on silicon carbide (SiC) for use as a refractory armor using a high power plasma arc lamp at powers up to 23.5 MW/m 2 in an argon flow environment. Both tungsten powder and molybdenum powder melted and formed coating layers on silicon carbide within a few seconds. The effect of substrate pre-treatment (vapor deposition of titanium (Ti) and tungsten, and annealing) and sample heating conditions on microstructure of the coating and coating/substrate interface were investigated. The microstructure was observed by scanning electron microscopy (SEM) and optical microscopy (OM). The mechanical properties of the coated materials were evaluated by four-point flexural tests. A strong tungsten coating was successfully applied to the silicon carbide substrate. Tungsten vapor deposition and pre-heating at 5.2 MW/m 2 made for a refractory layer containing no cracks propagating into the silicon carbide substrate. The tungsten coating was formed without the thick reaction layer. For this study, small tungsten carbide grains were observed adjacent to the interface in all conditions. In addition, relatively large, widely scattered tungsten carbide grains and a eutectic structure of tungsten and silicon were observed through the thickness in the coatings formed at lower powers and longer heating times. The strength of the silicon carbide substrate was somewhat decreased as a result of the processing. Vapor deposition of tungsten prior to powder coating helped prevent this degradation. In contrast, molybdenum coating was more challenging than tungsten coating due to the larger coefficient of thermal expansion (CTE) mismatch as compared to tungsten and silicon carbide. From this work it is concluded that refractory armoring of silicon carbide by Infrared Transient Liquid Phase Processing is possible. The tungsten armored silicon carbide samples proved uniform, strong, and capable of withstanding thermal fatigue testing.

Dynamic mechanical properties of hydroxyapatite/polyethylene oxide nanocomposites: characterizing isotropic and post-processing microstructures

NASA Astrophysics Data System (ADS)

Shofner, Meisha; Lee, Ji Hoon

2012-02-01

Compatible component interfaces in polymer nanocomposites can be used to facilitate a dispersed morphology and improved physical properties as has been shown extensively in experimental results concerning amorphous matrix nanocomposites. In this research, a block copolymer compatibilized interface is employed in a semi-crystalline matrix to prevent large scale nanoparticle clustering and enable microstructure construction with post-processing drawing. The specific materials used are hydroxyapatite nanoparticles coated with a polyethylene oxide-b-polymethacrylic acid block copolymer and a polyethylene oxide matrix. Two particle shapes are used: spherical and needle-shaped. Characterization of the dynamic mechanical properties indicated that the two nanoparticle systems provided similar levels of reinforcement to the matrix. For the needle-shaped nanoparticles, the post-processing step increased matrix crystallinity and changed the thermomechanical reinforcement trends. These results will be used to further refine the post-processing parameters to achieve a nanocomposite microstructure with triangulated arrays of nanoparticles.

Morphology-Dependent Hardness of Cr7C3-Ni-Rich Alloy Composite vs Orientation Independent Hardness of Cr7C3 Primary Phase in a Laser Clad Microstructure

NASA Astrophysics Data System (ADS)

Venkatesh, Lakshmi Narayanan; Suresh Babu, Pitchuka; Gundakaram, Ravi Chandra; Doherty, Roger D.; Joshi, Shrikant V.; Samajdar, Indradev

2017-04-01

Microstructural evolution with superheating was studied in chromium carbide-nickel coatings deposited by laser cladding. At lower superheating, selective growth of <0001> direction from the high density of Cr7C3 grains nucleated resulted in a columnar structure with (0001) texture. Increased superheating lead to the loss of columnar structure as well as the (0001) texture. The hexagonal Cr7C3 showed an unusual isotropic nanoindentation hardness evidently correlated with its low c/ a ratio. However, the rod-like morphology of the carbide dendrites resulted in significant anisotropy in the hardness of the composite.

High strength, high ductility low carbon steel

DOEpatents

Koo, Jayoung; Thomas, Gareth

1978-01-01

A high strength, high ductility low carbon steel consisting essentially of iron, 0.05-0.15 wt% carbon, and 1-3 wt% silicon. Minor amounts of other constituents may be present. The steel is characterized by a duplex ferrite-martensite microstructure in a fibrous morphology. The microstructure is developed by heat treatment consisting of initial austenitizing treatment followed by annealing in the (.alpha. + .gamma.) range with intermediate quenching.

Grain Boundary Conformed Volumetric Mesh Generation from a Three-Dimensional Voxellated Polycrystalline Microstructure

NASA Astrophysics Data System (ADS)

Lee, Myeong-Jin; Jeon, Young-Ju; Son, Ga-Eun; Sung, Sihwa; Kim, Ju-Young; Han, Heung Nam; Cho, Soo Gyeong; Jung, Sang-Hyun; Lee, Sukbin

2018-07-01

We present a new comprehensive scheme for generating grain boundary conformed, volumetric mesh elements from a three-dimensional voxellated polycrystalline microstructure. From the voxellated image of a polycrystalline microstructure obtained from the Monte Carlo Potts model in the context of isotropic normal grain growth simulation, its grain boundary network is approximated as a curvature-maintained conformal triangular surface mesh using a set of in-house codes. In order to improve the surface mesh quality and to adjust mesh resolution, various re-meshing techniques in a commercial software are applied to the approximated grain boundary mesh. It is found that the aspect ratio, the minimum angle and the Jacobian value of the re-meshed surface triangular mesh are successfully improved. Using such an enhanced surface mesh, conformal volumetric tetrahedral elements of the polycrystalline microstructure are created using a commercial software, again. The resultant mesh seamlessly retains the short- and long-range curvature of grain boundaries and junctions as well as the realistic morphology of the grains inside the polycrystal. It is noted that the proposed scheme is the first to successfully generate three-dimensional mesh elements for polycrystals with high enough quality to be used for the microstructure-based finite element analysis, while the realistic characteristics of grain boundaries and grains are maintained from the corresponding voxellated microstructure image.

Grain Boundary Conformed Volumetric Mesh Generation from a Three-Dimensional Voxellated Polycrystalline Microstructure

NASA Astrophysics Data System (ADS)

Lee, Myeong-Jin; Jeon, Young-Ju; Son, Ga-Eun; Sung, Sihwa; Kim, Ju-Young; Han, Heung Nam; Cho, Soo Gyeong; Jung, Sang-Hyun; Lee, Sukbin

2018-03-01

We present a new comprehensive scheme for generating grain boundary conformed, volumetric mesh elements from a three-dimensional voxellated polycrystalline microstructure. From the voxellated image of a polycrystalline microstructure obtained from the Monte Carlo Potts model in the context of isotropic normal grain growth simulation, its grain boundary network is approximated as a curvature-maintained conformal triangular surface mesh using a set of in-house codes. In order to improve the surface mesh quality and to adjust mesh resolution, various re-meshing techniques in a commercial software are applied to the approximated grain boundary mesh. It is found that the aspect ratio, the minimum angle and the Jacobian value of the re-meshed surface triangular mesh are successfully improved. Using such an enhanced surface mesh, conformal volumetric tetrahedral elements of the polycrystalline microstructure are created using a commercial software, again. The resultant mesh seamlessly retains the short- and long-range curvature of grain boundaries and junctions as well as the realistic morphology of the grains inside the polycrystal. It is noted that the proposed scheme is the first to successfully generate three-dimensional mesh elements for polycrystals with high enough quality to be used for the microstructure-based finite element analysis, while the realistic characteristics of grain boundaries and grains are maintained from the corresponding voxellated microstructure image.

Efficient 3D porous microstructure reconstruction via Gaussian random field and hybrid optimization.

PubMed

Jiang, Z; Chen, W; Burkhart, C

2013-11-01

Obtaining an accurate three-dimensional (3D) structure of a porous microstructure is important for assessing the material properties based on finite element analysis. Whereas directly obtaining 3D images of the microstructure is impractical under many circumstances, two sets of methods have been developed in literature to generate (reconstruct) 3D microstructure from its 2D images: one characterizes the microstructure based on certain statistical descriptors, typically two-point correlation function and cluster correlation function, and then performs an optimization process to build a 3D structure that matches those statistical descriptors; the other method models the microstructure using stochastic models like a Gaussian random field and generates a 3D structure directly from the function. The former obtains a relatively accurate 3D microstructure, but computationally the optimization process can be very intensive, especially for problems with large image size; the latter generates a 3D microstructure quickly but sacrifices the accuracy due to issues in numerical implementations. A hybrid optimization approach of modelling the 3D porous microstructure of random isotropic two-phase materials is proposed in this paper, which combines the two sets of methods and hence maintains the accuracy of the correlation-based method with improved efficiency. The proposed technique is verified for 3D reconstructions based on silica polymer composite images with different volume fractions. A comparison of the reconstructed microstructures and the optimization histories for both the original correlation-based method and our hybrid approach demonstrates the improved efficiency of the approach. © 2013 The Authors Journal of Microscopy © 2013 Royal Microscopical Society.

Radiographic and ultrasonic characterization of sintered silicon carbide

NASA Technical Reports Server (NTRS)

Baaklini, G. Y.; Abel, P. B.

1988-01-01

The capabilities were investigated of projection microfocus X-radiography, ultrasonic velocity and attenuation, and reflection scanning acoustic microscopy for characterizing silicon carbide specimens. Silicon carbide batches covered a range of densities and different microstructural characteristics. Room temperature, four point flexural strength tests were conducted. Fractography was used to identify types, sizes, and locations of fracture origins. Fracture toughness values were calculated from fracture strength and flaw characterization data. Detection capabilities of radiography and acoustic microscopy for fracture-causing flaws were evaluated. Applicability of ultrasonics for verifying material strength and toughness was examined.

Flaw imaging and ultrasonic techniques for characterizing sintered silicon carbide

NASA Technical Reports Server (NTRS)

Baaklini, George Y.; Abel, Phillip B.

1987-01-01

The capabilities were investigated of projection microfocus x-radiography, ultrasonic velocity and attenuation, and reflection scanning acoustic microscopy for characterizing silicon carbide specimens. Silicon carbide batches covered a range of densities and different microstructural characteristics. Room temperature, four point flexural strength tests were conducted. Fractography was used to identify types, sizes, and locations of fracture origins. Fracture toughness values were calculated from fracture strength and flaw characterization data. Detection capabilities of radiography and acoustic microscopy for fracture-causing flaws were evaluated. Applicability of ultrasonics for verifying material strength and toughness was examined.

Effective thermo-mechanical properties and shape memory effect of CNT/SMP composites

NASA Astrophysics Data System (ADS)

Yang, Qingsheng; Liu, Xia; Leng, Fangfang

2009-07-01

Shape memory polymer (SMP) has been applied in many fields as intelligent sensors and actuators. In order to improve the mechanical properties and recovery force of SMP, the addition of minor amounts of carbon nanotubes (CNT) into SMP has attracted wide attention. A micromechanical model and thermo-mechanical properties of CNT/SMP composites were studied in this paper. The thermo-mechanical constitutive relation of intellectual composites with isotropic and transversely isotropic CNT was obtained. Moreover, the shape memory effect of CNT/SMP composites and the effect of temperature and the volume fraction of CNT were discussed. The work shows that CNT/SMP composites exhibit excellent macroscopic thermo-mechanical properties and shape memory effect, while both of them can be affected remarkably by temperature and the microstructure parameters.

Electrically induced formation of uncapped, hollow polymeric microstructures

NASA Astrophysics Data System (ADS)

Lee, Sung Hun; Kim, Pilnam; Jeong, Hoon Eui; Suh, Kahp Y.

2006-11-01

Uncapped, hollow polymeric microstructures were fabricated on a silicon substrate using electric field induced stretching and detachment. Initially, square or cylinder microposts were generated using a solvent-assisted capillary molding technique, and a featureless electrode mask was positioned on the top of the microstructure with spacers maintaining an air gap (~20 µm). Upon exposure to an external electric field (1.0-3.0 V µm-1), the hollow microstructures were destabilized and stretched by the well-known electrohydrodynamic instability, resulting in contact of the top polymer surface with the mask. Subsequently, detachment of the capping layer occurred upon removal of the mask due to larger adhesion forces at the polymer/mask interface than cohesion forces of the polymer. These hollow microstructures were tested to capture the budding yeast, Saccharomyces cerevisiae, for shear protection.

Fabrication of poly(ethylene glycol) hydrogel microstructures using photolithography

NASA Technical Reports Server (NTRS)

Revzin, A.; Russell, R. J.; Yadavalli, V. K.; Koh, W. G.; Deister, C.; Hile, D. D.; Mellott, M. B.; Pishko, M. V.

2001-01-01

The fabrication of hydrogel microstructures based upon poly(ethylene glycol) diacrylates, dimethacrylates, and tetraacrylates patterned photolithographically on silicon or glass substrates is described. A silicon/silicon dioxide surface was treated with 3-(trichlorosilyl)propyl methacrylate to form a self-assembled monolayer (SAM) with pendant acrylate groups. The SAM presence on the surface was verified using ellipsometry and time-of-flight secondary ion mass spectrometry. A solution containing an acrylated or methacrylated poly(ethylene glycol) derivative and a photoinitiator (2,2-dimethoxy-2-phenylacetophenone) was spin-coated onto the treated substrate, exposed to 365 nm ultraviolet light through a photomask, and developed with either toluene, water, or supercritical CO2. As a result of this process, three-dimensional, cross-linked PEG hydrogel microstructures were immobilized on the surface. Diameters of cylindrical array members were varied from 600 to 7 micrometers by the use of different photomasks, while height varied from 3 to 12 micrometers, depending on the molecular weight of the PEG macromer. In the case of 7 micrometers diameter elements, as many as 400 elements were reproducibly generated in a 1 mm2 square pattern. The resultant hydrogel patterns were hydrated for as long as 3 weeks without delamination from the substrate. In addition, micropatterning of different molecular weights of PEG was demonstrated. Arrays of hydrogel disks containing an immobilized protein conjugated to a pH sensitive fluorophore were also prepared. The pH sensitivity of the gel-immobilized dye was similar to that in an aqueous buffer, and no leaching of the dye-labeled protein from the hydrogel microstructure was observed over a 1 week period. Changes in fluorescence were also observed for immobilized fluorophore labeled acetylcholine esterase upon the addition of acetyl acholine.

Analysis of composition and microstructures of Ge grown on porous silicon using Raman spectroscopy and transmission electron microscopy

NASA Astrophysics Data System (ADS)

Aouassa, Mansour; Jadli, Imen; Hassayoun, Latifa Slimen; Maaref, Hassen; Panczer, Gerard; Favre, Luc; Ronda, Antoine; Berbezier, Isabelle

2017-12-01

Composition and microstructure of Ge grown on porous silicon (PSi) by Molecular Beam Epitaxy (MBE) at different temperatures are examined using High Resolution Transmission Electron Microscopy (HRTEM) and Raman spectroscopy. Ge grown at 400 °C on PSi buffer produces a planar Ge film with high crystalline quality compared to Ge grown on bulk Si. This result is attributed to the compliant nature of PSi. Increasing growth temperature >600 °C, changes the PSi morphology, increase the Ge/Si intermixing in the pores during Ge growth and lead to obtain a composite SiGe/Si substrate. Ge content in the composite SiGe substrate can controlled via growth temperature. These substrates serve as low cost virtual substrate for high efficiency III-V/Si solar cells.

Morphing Carbon Nanotube Microstructures

DTIC Science & Technology

2015-02-20

most fibrous nanoscale aerogels and foams, having n=2-3, which is attributed to 2 low connectivity between the constituent struts 7. When comparing...CNTs incidentally resembles the Young’s moduli of isotropic CNT foams 30, CNT aerogels 31, and Si aerogels 32 which scale as ~ρ3, and commonly...characteristics of ultrahigh surface area single-walled carbon nanotube aerogels . Adv. Funct. Mater. 23, 377-383 (2013). 8. R. M. German, Sintering

Microstructure and fracture in SiC whisker reinforced 2124 aluminum composite

NASA Technical Reports Server (NTRS)

Nieh, T. G.; Raninen, R. A.; Chellman, D. J.

1985-01-01

The microstructures of extruded and hot-rolled 2124 Al-15 percent (by weight) SiC whisker composites have been investigated, experimentally. Among the specific factors studied were: the strength of the whisker-matrix interfaces; (2) the presence of oxides; (3) the presence of defective whiskers; (4) and the presence of distribution of intermetallic compounds, impurities in the SiC(w) powder, and microstructural inhomogeneities. Modifications in the microstructure of the SiC/AL composites due to hot rolling and extrusion are illustrated in a series of microphotographs. It was found that hot rolling along the axis of extrusion was associated with some types of whisker damage, while the whiskers still retain their original orientation. Hot-rolling perpendicular to the axis of extrusion, however, tended to rotate the whiskers and produced a nearly isotropic material. Whisker free zones were virtually eliminated or reduced in size by hot rolling. In situ Auger fractography of the composite showed that the interfacial bonding between the SiC and the Al matrix was good and that Al2O2 had no significant influence on the fracture mechanics of the composite.

Isotropic microscale mechanical properties of coral skeletons

PubMed Central

Pasquini, Luca; Molinari, Alan; Fantazzini, Paola; Dauphen, Yannicke; Cuif, Jean-Pierre; Levy, Oren; Dubinsky, Zvy; Caroselli, Erik; Prada, Fiorella; Goffredo, Stefano; Di Giosia, Matteo; Reggi, Michela; Falini, Giuseppe

2015-01-01

Scleractinian corals are a major source of biogenic calcium carbonate, yet the relationship between their skeletal microstructure and mechanical properties has been scarcely studied. In this work, the skeletons of two coral species: solitary Balanophyllia europaea and colonial Stylophora pistillata, were investigated by nanoindentation. The hardness HIT and Young's modulus EIT were determined from the analysis of several load–depth data on two perpendicular sections of the skeletons: longitudinal (parallel to the main growth axis) and transverse. Within the experimental and statistical uncertainty, the average values of the mechanical parameters are independent on the section's orientation. The hydration state of the skeletons did not affect the mechanical properties. The measured values, EIT in the 76–77 GPa range, and HIT in the 4.9–5.1 GPa range, are close to the ones expected for polycrystalline pure aragonite. Notably, a small difference in HIT is observed between the species. Different from corals, single-crystal aragonite and the nacreous layer of the seashell Atrina rigida exhibit clearly orientation-dependent mechanical properties. The homogeneous and isotropic mechanical behaviour of the coral skeletons at the microscale is correlated with the microstructure, observed by electron microscopy and atomic force microscopy, and with the X-ray diffraction patterns of the longitudinal and transverse sections. PMID:25977958

Preparation of Nd-Fe-B/α-Fe nano-composite thick-film magnets on various substrates using PLD with high laser energy density above 10 J/cm2

NASA Astrophysics Data System (ADS)

Nakano, M.; Kondo, H.; Yamashita, A.; Yanai, T.; Itakura, M.; Fukunaga, H.

2018-05-01

PLD (Pulsed Laser Deposition) method with high laser energy density (LED) above 10 J/cm2 followed by a flash annealing enabled us to obtain isotropic nano-composite thick-film magnets with (BH)max ≧ 80 kJ/m3 on polycrystalline Ta substrates. We also have demonstrated that a dispersed structure composed of α-Fe together with Nd2Fe14B phases with the average grain diameter of approximately 20 nm could be formed on the Ta substrates. In this study, we tried to enhance the (BH)max value by controlling the microstructure due to the usage of different metal based substrates with each high melting point such as Ti, Nb, and W. Although it was difficult to vary the microstructure and to improve the magnetic properties of the films deposited on the substrates, we confirmed that isotropic thick-film magnets with (BH)max ≧ 80 kJ/m3 based on the nano-dispersed α-Fe and Nd2Fe14B phases could be obtained on various metal substrates with totally different polycrystalline structure. On the other hand, the use of a glass substrate lead to the deterioration of magnetic properties of a film prepared using the same preparation process.

A silicon microwire under a three-dimensional anisotropic tensile stress

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

Ji, Xiaoyu; Poilvert, Nicolas; Liu, Wenjun

Three-dimensional tensile stress, or triaxial tensile stress, is difficult to achieve in a material. We present the investigation of an unusual three-dimensional anisotropic tensile stress field and its influence on the electronic properties of a single crystal silicon microwire. The microwire was created by laser heating an amorphous silicon wire deposited in a 1.7 μm silica glass capillary by high pressure chemical vapor deposition. Tensile strain arises due to the thermal expansion mismatch between silicon and silica. Synchrotron X-ray micro-beam Laue diffraction (μ-Laue) microscopy reveals that the three principal strain components are +0.47% (corresponding to a tensile stress of +0.7more » GPa) along the fiber axis and nearly isotropic +0.02% (corresponding to a tensile stress of +0.3 GPa) in the cross-sectional plane. This effect was accompanied with a reduction of 30 meV in the band gap energy of silicon, as predicted by the density-functional theory calculations and in close agreement with energy-dependent photoconductivity measurements. While silicon has been explored under many stress states, this study explores a stress state where all three principal stress components are tensile. Given the technological importance of silicon, the influence of such an unusual stress state on its electronic properties is of fundamental interest.« less

Mechanically flexible optically transparent silicon fabric with high thermal budget devices from bulk silicon (100)

NASA Astrophysics Data System (ADS)

Hussain, Muhammad M.; Rojas, Jhonathan P.; Torres Sevilla, Galo A.

2013-05-01

Today's information age is driven by silicon based electronics. For nearly four decades semiconductor industry has perfected the fabrication process of continuingly scaled transistor - heart of modern day electronics. In future, silicon industry will be more pervasive, whose application will range from ultra-mobile computation to bio-integrated medical electronics. Emergence of flexible electronics opens up interesting opportunities to expand the horizon of electronics industry. However, silicon - industry's darling material is rigid and brittle. Therefore, we report a generic batch fabrication process to convert nearly any silicon electronics into a flexible one without compromising its (i) performance; (ii) ultra-large-scale-integration complexity to integrate billions of transistors within small areas; (iii) state-of-the-art process compatibility, (iv) advanced materials used in modern semiconductor technology; (v) the most widely used and well-studied low-cost substrate mono-crystalline bulk silicon (100). In our process, we make trenches using anisotropic reactive ion etching (RIE) in the inactive areas (in between the devices) of a silicon substrate (after the devices have been fabricated following the regular CMOS process), followed by a dielectric based spacer formation to protect the sidewall of the trench and then performing an isotropic etch to create caves in silicon. When these caves meet with each other the top portion of the silicon with the devices is ready to be peeled off from the bottom silicon substrate. Release process does not need to use any external support. Released silicon fabric (25 μm thick) is mechanically flexible (5 mm bending radius) and the trenches make it semi-transparent (transparency of 7%).

Low-temperature (120 °C) growth of nanocrystalline silicon films prepared by plasma enhanced chemical vapor deposition from SiCl 4/H 2 gases: Microstructure characterization

NASA Astrophysics Data System (ADS)

Zhang, L.; Gao, J. H.; Xiao, J. Q.; Wen, L. S.; Gong, J.; Sun, C.

2012-01-01

Hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared using diluted tetrachlorosilane (SiCl4) with various hydrogen flow rates (Hf) by plasma enhanced chemical vapor deposition (PECVD) at a constant substrate temperature (Ts) as low as 120 °C. Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), infrared spectra (IR) and spectroscopic ellipsometry (SE) were employed to investigate the microstructure and hydrogen bonding of the nc-Si:H films. Our results showed that the microstructure and hydrogen content of the films could be effectively tailored by the hydrogen flow rates, and a distinct transition from amorphous to nanocrystalline phase was observed with an increase of Hf. At an optimal preparation condition, a deposition rate was as high as 3.7 nm/min and the crystallinity reached up to 64.1%. In addition, the effect of hydrogen on the low-temperature growth of nc-Si:H film was proposed in relation to the surface reaction of radicals and the hydrogen diffusion in the surface growing region.

Pressureless sintered beta prime-Si3N4 solid solution: Fabrication, microstructure, and strength

NASA Technical Reports Server (NTRS)

Dutta, S.

1977-01-01

Si3N4, AlN, and Al2O3 were used as basic constituents in a study of the pressureless sintering of beta prime-Si3N4 solid solution as a function of temperature. Y2O3-SiO2 additions were used to promote liquid-phase sintering. The sintered specimens were characterized with respect to density, microstructure, strength, oxidation, and thermal shock resistance. Density greater than 98 percent of theoretical was achieved by pressureless sintering at 1750 C. The microstructure consisted essentially of fine-grained beta prime-Si3N4 solid solution as the major phase. Modulus of rupture strengths up to 483 MPa were achieved at moderate temperature (1000 C), but decreased to 228 MPa at 1380 C. This substantial strength loss was attributed to a glassy grain boundary phase formed during cooling from the sintering temperature. The best oxidation resistance was exhibited by a composition containing 3 mol % Y2O3-SiO2 additives. Water quench thermal shock resistance was equivalent to that of reaction sintered silicon nitride but lower than hot-pressed silicon nitride.

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

Astrova, E. V., E-mail: east@mail.ioffe.ru; Rumyantsev, A. M.; Li, G. V.

The anisotropy of lithium intercalation into the silicon anodes of Li-ion batteries is studied on microstructures having the form of a grid with 0.5-μm-thick vertical walls and on silicon wafers of varied orientation. Electrochemical lithiation is performed at room temperature in the galvanostatic mode. The charging curves of the microstructure and flat Si anodes are examined. Secondary-ion mass spectroscopy is used to determine the distribution of intercalated Li atoms across the wafer thickness. The experimental data are analyzed in terms of the two-phase model in which the lithiation process is limited by the propagation velocity of the front between themore » amorphous alloy with a high Li content and the crystalline Si substrate. The relationship between the rates of Li intercalation into different crystallographic planes: (110), (111), and (100), is found to be V{sub 110}: V{sub 111}: V{sub 100} = 3.1: 1.1: 1.0. It is demonstrated that microstructure anodes with (110) walls have the highest cycle life and withstand ~600 cycles when charged and discharged at a rate of 0.36 C.« less

Silicon and aluminum doping effects on the microstructure and properties of polymeric amorphous carbon films

NASA Astrophysics Data System (ADS)

Liu, Xiaoqiang; Hao, Junying; Xie, Yuntao

2016-08-01

Polymeric amorphous carbon films were prepared by radio frequency (R.F. 13.56 MHz) magnetron sputtering deposition. The microstructure evolution of the deposited polymeric films induced by silicon (Si) and aluminum(Al) doping were scrutinized through infrared spectroscopy, multi-wavelength Raman spectroscopy, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The comparative results show that Si doping can enhance polymerization and Al doping results in an increase in the ordered carbon clusters. Si and Al co-doping into polymeric films leads to the formation of an unusual dual nanostructure consisting of cross-linked polymer-like hydrocarbon chains and fullerene-like carbon clusters. The super-high elasticity and super-low friction coefficients (<0.002) under a high vacuum were obtained through Si and Al co-doping into the films. Unconventionally, the co-doped polymeric films exhibited a superior wear resistance even though they were very soft. The relationship between the microstructure and properties of the polymeric amorphous carbon films with different elements doping are also discussed in detail.

Fabrication of 20.19% Efficient Single-Crystalline Silicon Solar Cell with Inverted Pyramid Microstructure.

PubMed

Zhang, Chunyang; Chen, Lingzhi; Zhu, Yingjie; Guan, Zisheng

2018-04-03

This paper reports inverted pyramid microstructure-based single-crystalline silicon (sc-Si) solar cell with a conversion efficiency up to 20.19% in standard size of 156.75 × 156.75 mm 2 . The inverted pyramid microstructures were fabricated jointly by metal-assisted chemical etching process (MACE) with ultra-low concentration of silver ions and optimized alkaline anisotropic texturing process. And the inverted pyramid sizes were controlled by changing the parameters in both MACE and alkaline anisotropic texturing. Regarding passivation efficiency, the textured sc-Si with normal reflectivity of 9.2% and inverted pyramid size of 1 μm was used to fabricate solar cells. The best batch of solar cells showed a 0.19% higher of conversion efficiency and a 0.22 mA cm -2 improvement in short-circuit current density, and the excellent photoelectric property surpasses that of the same structure solar cell reported before. This technology shows great potential to be an alternative for large-scale production of high efficient sc-Si solar cells in the future.

Microstructural evolution of neutron-irradiated Ni-Si and Ni-Al alloys

NASA Astrophysics Data System (ADS)

Takahashi, H.; Garner, F. A.

1992-10-01

Additions of silicon and aluminum suppress the neutron-induced swelling of pure nickel but to different degrees. Silicon is much more effective initially when compared to aluminum on a per atom basis but silicon exhibits a nonmonotonic influence on swelling with increasing concentration. Silicon tends to segregate toward grain boundaries while aluminum segregates away from these boundaries. Whereas the formation of the Ni 3Si phase is frequently observed in charged particle irradiation experiments conducted at much higher displacement rates, it did not occur during neutron irradiation in this study. Precipitation also did not occur in Ni-5Al during neutron irradiation, nor has it been reported to occur during ion irradiation.

Femtosecond Laser Microstructuring and Chalcogen Inclusion in Silicon

DTIC Science & Technology

2011-02-12

a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. a ...material a potential candidate for a variety of optoelectronic devices. In this report, we demonstrate the capability of chalcogen (S, Se, Te...the diffusion behavior of dopants in silicon matrix. Our findings contribute to a better understanding of the mechanism of infrared absorption in

Controllable Si (100) micro/nanostructures by chemical-etching-assisted femtosecond laser single-pulse irradiation

NASA Astrophysics Data System (ADS)

Li, Xiaowei; Xie, Qian; Jiang, Lan; Han, Weina; Wang, Qingsong; Wang, Andong; Hu, Jie; Lu, Yongfeng

2017-05-01

In this study, silicon micro/nanostructures of controlled size and shape are fabricated by chemical-etching-assisted femtosecond laser single-pulse irradiation, which is a flexible, high-throughput method. The pulse fluence is altered to create various laser printing patterns for the etching mask, resulting in the sequential evolution of three distinct surface micro/nanostructures, namely, ring-like microstructures, flat-top pillar microstructures, and spike nanostructures. The characterized diameter of micro/nanostructures reveals that they can be flexibly tuned from the micrometer (˜2 μm) to nanometer (˜313 nm) scales by varying the laser pulse fluence in a wide range. Micro-Raman spectroscopy and transmission electron microscopy are utilized to demonstrate that the phase state changes from single-crystalline silicon (c-Si) to amorphous silicon (a-Si) after single-pulse femtosecond laser irradiation. This amorphous layer with a lower etching rate then acts as a mask in the wet etching process. Meanwhile, the on-the-fly punching technique enables the efficient fabrication of large-area patterned surfaces on the centimeter scale. This study presents a highly efficient method of controllably manufacturing silicon micro/nanostructures with different single-pulse patterns, which has promising applications in the photonic, solar cell, and sensors fields.

Dynamic Modulus and Damping of Boron, Silicon Carbide, and Alumina Fibers

NASA Technical Reports Server (NTRS)

Dicarlo, J. A.; Williams, W.

1980-01-01

The dynamic modulus and damping capacity for boron, silicon carbide, and silicon carbide coated boron fibers were measured from-190 to 800 C. The single fiber vibration test also allowed measurement of transverse thermal conductivity for the silicon carbide fibers. Temperature dependent damping capacity data for alumina fibers were calculated from axial damping results for alumina-aluminum composites. The dynamics fiber data indicate essentially elastic behavior for both the silicon carbide and alumina fibers. In contrast, the boron based fibers are strongly anelastic, displaying frequency dependent moduli and very high microstructural damping. Ths single fiber damping results were compared with composite damping data in order to investigate the practical and basic effects of employing the four fiber types as reinforcement for aluminum and titanium matrices.

Angle-adjustable density field formulation for the modeling of crystalline microstructure

NASA Astrophysics Data System (ADS)

Wang, Zi-Le; Liu, Zhirong; Huang, Zhi-Feng

2018-05-01

A continuum density field formulation with particle-scale resolution is constructed to simultaneously incorporate the orientation dependence of interparticle interactions and the rotational invariance of the system, a fundamental but challenging issue in modeling the structure and dynamics of a broad range of material systems across variable scales. This generalized phase field crystal-type approach is based upon the complete expansion of particle direct correlation functions and the concept of isotropic tensors. Through applications to the modeling of various two- and three-dimensional crystalline structures, our study demonstrates the capability of bond-angle control in this continuum field theory and its effects on the emergence of ordered phases, and provides a systematic way of performing tunable angle analyses for crystalline microstructures.

Characterization of deliberately nickel-doped silicon wafers and solar cells. [microstructure, electrical properties, and energy conversion efficiency

NASA Technical Reports Server (NTRS)

Salama, A. M.

1980-01-01

Microstructural and electrical evaluation tests were performed on nickel-doped p-type silicon wafers before and after solar cell fabrication. The concentration levels of nickel in silicon were 5 x 10 to the 14th power, 4 x 10 to the 15th power, and 8 x 10 to the 15th power atoms/cu cm. It was found that nickel precipitated out during the growth process in all three ingots. Clumps of precipitates, some of which exhibited star shape, were present at different depths. If the clumps are distributed at depths approximately 20 micron apart and if they are larger than 10 micron in diameter, degradation occurs in solar cell electrical properties and cell conversion efficiency. The larger the size of the precipitate clump, the greater the degradation in solar cell efficiency. A large grain boundary around the cell effective area acted as a gettering center for the precipitates and impurities and caused improvement in solar cell efficiency. Details of the evaluation test results are given.

Noninteractive macroscopic reliability model for whisker-reinforced ceramic composites

NASA Technical Reports Server (NTRS)

Duffy, Stephen F.; Arnold, Steven M.

1990-01-01

Considerable research is underway in the field of material science focusing on incorporating silicon carbide whiskers into silicon nitride and alumina matrices. These composites show the requisite thermal stability and thermal shock resistance necessary for use as components in advanced gas turbines and heat exchangers. This paper presents a macroscopic noninteractive reliability model for whisker-reinforced ceramic composites. The theory is multiaxial and is applicable to composites that can be characterized as transversely isotropic. Enough processing data exists to suggest this idealization encompasses a significantly large class of fabricated components. A qualitative assessment of the model is made by presenting reliability surfaces in several different stress spaces and for different values of model parameters.

Processing study of injection molding of silicon nitride for engine applications

NASA Technical Reports Server (NTRS)

Rorabaugh, M. E.; Yeh, H. C.

1985-01-01

The high hardness of silicon nitride, which is currently under consideration as a structural material for such hot engine components as turbine blades, renders machining of the material prohibitively costly; the near net shape forming technique of injection molding is accordingly favored as a means for component fabrication. Attention is presently given to the relationships between injection molding processing parameters and the resulting microstructural and mechanical properties of the resulting engine parts. An experimental program has been conducted under NASA sponsorship which tests the quality of injection molded bars of silicon nitride at various stages of processing.

Metal-assisted chemical etching using sputtered gold: a simple route to black silicon

NASA Astrophysics Data System (ADS)

Kurek, Agnieszka; Barry, Seán T.

2011-08-01

We report an accessible and simple method of producing 'black silicon' with aspect ratios as high as 8 using common laboratory equipment. Gold was sputtered to a thickness of 8 nm using a low-vacuum sputter coater. The structures were etched into silicon substrates using an aqueous H2O2/HF solution, and the gold was then removed using aqua regia. Ultrasonication was necessary to produce columnar structures, and an etch time of 24 min gave a velvety, non-reflective surface. The surface features after 24 min etching were uniformly microstructured over an area of square centimetres.

Relationship of microstructure properties to oxygen impurities in nanocrystalline silicon photovoltaic materials

NASA Astrophysics Data System (ADS)

Xu, H.; Wen, C.; Liu, H.; Li, Z. P.; Shen, W. Z.

2013-03-01

We have fully investigated the correlation of microstructure properties and oxygen impurities in hydrogenated nanocrystalline silicon photovoltaic films. The achievement has been realized through a series of different hydrogen dilution ratio treatment by plasma enhanced chemical vapor deposition system. Raman scattering, x-ray diffraction, and ultraviolet-visible transmission techniques have been employed to characterize the physical structural characterization and to elucidate the structure evolution. The bonding configuration of the oxygen impurities was investigated by x-ray photoelectron spectroscopy and the Si-O stretching mode of infrared-transmission, indicating that the films were well oxidized in SiO2 form. Based on the consistence between the proposed structure factor and the oxygen content, we have demonstrated that there are two dominant disordered structure regions closely related to the post-oxidation contamination: plate-like configuration and clustered microvoids.

Microstructure and photovoltaic performance of polycrystalline silicon thin films on temperature-stable ZnO:Al layers

NASA Astrophysics Data System (ADS)

Becker, C.; Ruske, F.; Sontheimer, T.; Gorka, B.; Bloeck, U.; Gall, S.; Rech, B.

2009-10-01

Polycrystalline silicon (poly-Si) thin films have been prepared by electron-beam evaporation and thermal annealing for the development of thin-film solar cells on glass coated with ZnO:Al as a transparent, conductive layer. The poly-Si microstructure and photovoltaic performance were investigated as functions of the deposition temperature by Raman spectroscopy, scanning and transmission electron microscopies including defect analysis, x-ray diffraction, external quantum efficiency, and open circuit measurements. It is found that two temperature regimes can be distinguished: Poly-Si films fabricated by deposition at low temperatures (Tdep<400 °C) and a subsequent thermal solid phase crystallization step exhibit 1-3 μm large, randomly oriented grains, but a quite poor photovoltaic performance. However, silicon films deposited at higher temperatures (Tdep>400 °C) directly in crystalline phase reveal columnar, up to 300 nm big crystals with a strong ⟨110⟩ orientation and much better solar cell parameters. It can be concluded from the results that the electrical quality of the material, reflected by the open circuit voltage of the solar cell, only marginally depends on crystal size and shape but rather on the intragrain properties of the material. The carrier collection, described by the short circuit current of the cell, seems to be positively influenced by preferential ⟨110⟩ orientation of the grains. The correlation between experimental, microstructural, and photovoltaic parameters will be discussed in detail.

Structure disorder degree of polysilicon thin films grown by different processing: Constant C from Raman spectroscopy

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

Wang, Quan, E-mail: wangq@mail.ujs.edu.cn; State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000; Zhang, Yanmin

2013-11-14

Flat, low-stress, boron-doped polysilicon thin films were prepared on single crystalline silicon substrates by low pressure chemical vapor deposition. It was found that the polysilicon films with different deposition processing have different microstructure properties. The confinement effect, tensile stresses, defects, and the Fano effect all have a great influence on the line shape of Raman scattering peak. But the effect results are different. The microstructure and the surface layer are two important mechanisms dominating the internal stress in three types of polysilicon thin films. For low-stress polysilicon thin film, the tensile stresses are mainly due to the change of microstructuremore » after thermal annealing. But the tensile stresses in flat polysilicon thin film are induced by the silicon carbide layer at surface. After the thin film doped with boron atoms, the phenomenon of the tensile stresses increasing can be explained by the change of microstructure and the increase in the content of silicon carbide. We also investigated the disorder degree states for three polysilicon thin films by analyzing a constant C. It was found that the disorder degree of low-stress polysilicon thin film larger than that of flat and boron-doped polysilicon thin films due to the phase transformation after annealing. After the flat polysilicon thin film doped with boron atoms, there is no obvious change in the disorder degree and the disorder degree in some regions even decreases.« less

Influence of the porosity on the dispersion of the phase velocity of longitudinal acoustic waves in isotropic metal-matrix composites

NASA Astrophysics Data System (ADS)

Karabutov, A. A.; Podymova, N. B.

2017-05-01

The influence of the volumetric porosity of isotropic metal-matrix composite materials, which are reinforced with ceramic microparticles, on the dispersion of the phase velocity of longitudinal acoustic waves is investigated. For this purpose, the method of broadband acoustic spectroscopy with a laser source of ultrasound and piezoelectric detection of nanosecond ultrasonic pulses is used. Composite samples based on a silumin matrix with added silicon carbide (SiC) microparticles in different mass concentrations (3.8-15.5%) were investigated. As the concentration of SiC particles in a sample increases, its porosity that is determined using the hydrostatic-weighing method also increases. The simultaneous increase in the filler concentration and porosity leads to the appearance of a dispersion of the phase velocity of longitudinal acoustic waves in the sample within the frequency range of 3-25 MHz. The obtained empirical relationship between the relative change in the phase velocity and the sample porosity can be used to obtain a proximate quantitative estimate of the bulk porosity of the isotropic metal-matrix composite materials.

Decal transfer lithography

DOEpatents

Nuzzo, Ralph G.; Childs, William R.; Motala, Michael J.; Lee, Keon Jae

2010-02-16

A method of making a microstructure includes selectively activating a portion of a surface of a silicon-containing elastomer, contacting the activated portion with a substance, and bonding the activated portion and the substance, such that the activated portion of the surface and the substance in contact with the activated portion are irreversibly attached. The selective activation may be accomplished by positioning a mask on the surface of the silicon-containing elastomer, and irradiating the exposed portion with UV radiation.

Role of oxygen on microstructure and thermoelectric properties of silicon nanocomposites

NASA Astrophysics Data System (ADS)

Schierning, G.; Theissmann, R.; Stein, N.; Petermann, N.; Becker, A.; Engenhorst, M.; Kessler, V.; Geller, M.; Beckel, A.; Wiggers, H.; Schmechel, R.

2011-12-01

Phosphorus-doped silicon nanopowder from a gas phase process was compacted by DC-current sintering in order to obtain thermoelectrically active, nanocrystalline bulk silicon. A density between 95% and 96% compared to the density of single crystalline silicon was achieved, while preserving the nanocrystalline character with an average crystallite size of best 25 nm. As a native surface oxidation of the nanopowder usually occurs during nanopowder handling, a focus of this work is on the role of oxygen on microstructure and transport properties of the nanocomposite. A characterization with transmission electron microscopy (TEM) showed that the original core/shell structure of the nanoparticles was not found within the sintered nanocomposites. Two different types of oxide precipitates could be identified by energy filtered imaging technique. For a detailed analysis, 3-dimensional tomography with reconstruction was done using a needle-shaped sample prepared by focused ion beam (FIB). The 3-dimensional distribution of silicon dioxide precipitates confirmed that the initial core/shell structure breaks down and precipitates are formed. It is further found that residual pores are exclusively located within oxide precipitates. Thermoelectric characterization was done on silicon nanocomposites sintered between 960 °C and 1060 °C with varying oxygen content between room temperature and 950 °C. The higher sintering temperature led to a better electrical activation of the phosphorus dopant. The oxidic precipitates support densification and seem to be able to reduce the thermal conductivity therefore enhancing thermoelectric properties. A peak figure of merit, zT, of 0.5 at 950 °C was measured for a sample sintered at 1060 °C with a mean crystallite size of 46 nm.

Elasto-Capillary Folding Using Stop-Programmable Hinges Fabricated by 3D Micro-Machining

PubMed Central

Legrain, Antoine; Berenschot, Erwin J. W.; Tas, Niels R.; Abelmann, Leon

2015-01-01

We show elasto-capillary folding of silicon nitride objects with accurate folding angles between flaps of (70.6 ± 0.1)° and demonstrate the feasibility of such accurate micro-assembly with a final folding angle of 90°. The folding angle is defined by stop-programmable hinges that are fabricated starting from silicon molds employing accurate three-dimensional corner lithography. This nano-patterning method exploits the conformal deposition and the subsequent timed isotropic etching of a thin film in a 3D shaped silicon template. The technique leaves a residue of the thin film in sharp concave corners which can be used as an inversion mask in subsequent steps. Hinges designed to stop the folding at 70.6° were fabricated batchwise by machining the V-grooves obtained by KOH etching in (110) silicon wafers; 90° stop-programmable hinges were obtained starting from silicon molds obtained by dry etching on (100) wafers. The presented technique has potential to achieve any folding angle and opens a new route towards creating structures with increased complexity, which will ultimately lead to a novel method for device fabrication. PMID:25992886

Optofluidic encapsulation and manipulation of silicon microchips using image processing based optofluidic maskless lithography and railed microfluidics.

PubMed

Chung, Su Eun; Lee, Seung Ah; Kim, Jiyun; Kwon, Sunghoon

2009-10-07

We demonstrate optofluidic encapsulation of silicon microchips using image processing based optofluidic maskless lithography and manipulation using railed microfluidics. Optofluidic maskless lithography is a dynamic photopolymerization technique of free-floating microstructures within a fluidic channel using spatial light modulator. Using optofluidic maskless lithography via computer-vision aided image processing, polymer encapsulants are fabricated for chip protection and guiding-fins for efficient chip conveying within a fluidic channel. Encapsulated silicon chips with guiding-fins are assembled using railed microfluidics, which is an efficient guiding and heterogeneous self-assembly system of microcomponents. With our technology, externally fabricated silicon microchips are encapsulated, fluidically guided and self-assembled potentially enabling low cost fluidic manipulation and assembly of integrated circuits.

Simultaneous Noncontact Precision Imaging of Microstructural and Thickness Variation in Dielectric Materials Using Terahertz Energy

NASA Technical Reports Server (NTRS)

Roth, Don J.; Seebo, Jeffrey P.; Winfree, William P.

2008-01-01

This article describes a noncontact single-sided terahertz electromagnetic measurement and imaging method that simultaneously characterizes microstructural (egs. spatially-lateral density) and thickness variation in dielectric (insulating) materials. The method was demonstrated for two materials-Space Shuttle External Tank sprayed-on foam insulation and a silicon nitride ceramic. It is believed that this method can be used as an inspection method for current and future NASA thermal protection system and other dielectric material inspection applications, where microstructural and thickness variation require precision mapping. Scale-up to more complex shapes such as cylindrical structures and structures with beveled regions would appear to be feasible.

Mechanical properties of low-alloy-steels with bainitic microstructures and varying carbon content

NASA Astrophysics Data System (ADS)

Weber, A.; Klarner, J.; Vogl, T.; Schöngrundner, R.; Sam, G.; Buchmayr, B.

2016-03-01

Materials used in the oilfield industry are subjected to special conditions. These requirements for seamless steel tubes are between the priorities of strength, toughness and sour gas resistance. Steels with bainitic microstructure provide a great opportunity for those harsh environmental conditions. With different morphologies of bainite, like carbide free, upper or lower bainite, the interaction of high tensile strength and elongation is assumed to be better than with tempered martensite. To form carbide free bainite two ways of processing are proposed, isothermal holding with accurate time control or controlled continuous cooling. Both require knowledge of time-temperature transformation behaviour, which can be reached through a detailed alloying concept, focused on the influence of silicon to supress the carbide nucleation and chromium to stabilize the austenite fraction. The present work is based on three alloys with varying silicon and chromium contents. The carbide free microstructure is obtained by a continuous cooling path. Additionally different heat treatments were done to compare the inherent performance of the bainitic morphologies. The bainitic structures were characterized metallographically for their microstructure and the primary phase by means of transmission electron microscopy. The mechanical properties of carbide-free structures were analysed with quasi-static tensile tests and Charpy impact tests. Moreover, investigations about hydrogen embrittlement were done with focus on the effect of retained austenite. The results were ranked and compared qualitatively.

Utilizing Controlled Vibrations in a Microgravity Environment to Understand and Promote Microstructural Homogeneity During Floating-Zone Crystal Growth

NASA Technical Reports Server (NTRS)

Grugel, Richard N.

1999-01-01

It has been demonstrated in floating-zone configurations utilizing silicone oil and nitrate salts that mechanically induced vibration effectively minimizes detrimental, gravity independent, thermocapillary flow. The processing parameters leading to crystal improvement and aspects of the on-going modeling effort are discussed. Plans for applying the crystal growth technique to commercially relevant materials, e.g., silicon, as well as the value of processing in a microgravity environment are presented.

Ultrasonic nondestructive materials characterization

NASA Technical Reports Server (NTRS)

Green, R. E., Jr.

1986-01-01

A brief review of ultrasonic wave propagation in solid materials is presented with consideration of the altered behavior in anisotropic and nonlinear elastic materials in comparison with isotropic and linear elastic materials. Some experimental results are described in which ultrasonic velocity and attenuation measurements give insight into materials microstructure and associated mechanical properties. Recent developments with laser beam non-contact generation and detection of ultrasound are presented. The results of several years of experimental measurements using high-power ultrasound are discussed, which provide substantial evidence of the inability of presently accepted theories to fully explain the interaction of ultrasound with solid materials. Finally, a special synchrotron X-ray topographic system is described which affords the possibility of observing direct interaction of ultrasonic waves with the microstructural features of real crystalline solid materials for the first time.

Challenges and Opportunities in Reactive Processing and Applications of Advanced Ceramic Materials

NASA Technical Reports Server (NTRS)

Singh, Mrityunjay

2003-01-01

Recently, there has been a great deal of interest in the research, development, and commercialization of innovative synthesis and processing technologies for advanced ceramics and composite materials. Reactive processing approaches have been actively considered due to their robustness, flexibility, and affordability. A wide variety of silicon carbide-based advanced ceramics and composites are currently being fabricated using the processing approaches involving reactive infiltration of liquid and gaseous species into engineered fibrous or microporous carbon performs. The microporous carbon performs have been fabricated using the temperature induced phase separation and pyrolysis of two phase organic (resin-pore former) mixtures and fiber reinforcement of carbon and ceramic particulate bodies. In addition, pyrolyzed native plant cellulose tissues also provide unique carbon templates for manufacturing of non-oxide and oxide ceramics. In spite of great interest in this technology due to their affordability and robustness, there is a lack of scientific basis for process understanding and many technical challenges still remain. The influence of perform properties and other parameters on the resulting microstructure and properties of final material is not well understood. In this presentation, mechanism of silicon-carbon reaction in various systems and the effect of perform microstructure on the mechanical properties of advanced silicon carbide based materials will be discussed. Various examples of applications of reactively processed advanced silicon carbide ceramics and composite materials will be presented.

The spatial-temporal characteristics of type I collagen-based extracellular matrix.

PubMed

Jones, Christopher Allen Rucksack; Liang, Long; Lin, Daniel; Jiao, Yang; Sun, Bo

2014-11-28

Type I collagen abounds in mammalian extracellular matrix (ECM) and is crucial to many biophysical processes. While previous studies have mostly focused on bulk averaged properties, here we provide a comprehensive and quantitative spatial-temporal characterization of the microstructure of type I collagen-based ECM as the gelation temperature varies. The structural characteristics including the density and nematic correlation functions are obtained by analyzing confocal images of collagen gels prepared at a wide range of gelation temperatures (from 16 °C to 36 °C). As temperature increases, the gel microstructure varies from a "bundled" network with strong orientational correlation between the fibers to an isotropic homogeneous network with no significant orientational correlation, as manifested by the decaying of length scales in the correlation functions. We develop a kinetic Monte-Carlo collagen growth model to better understand how ECM microstructure depends on various environmental or kinetic factors. We show that the nucleation rate, growth rate, and an effective hydrodynamic alignment of collagen fibers fully determines the spatiotemporal fluctuations of the density and orientational order of collagen gel microstructure. Also the temperature dependence of the growth rate and nucleation rate follow the prediction of classical nucleation theory.

Highly Porous NiTi with Isotropic Pore Morphology Fabricated by Self-Propagated High-Temperature Synthesis

NASA Astrophysics Data System (ADS)

Hosseini, S. A.; Alizadeh, M.; Ghasemi, A.; Meshkot, M. A.

2013-02-01

Highly porous NiTi with isotropic pore morphology has been successfully produced by self-propagating high-temperature synthesis of elemental Ni/Ti metallic powders. The effects of adding urea and NaCl as temporary pore fillers were investigated on pore morphology, microstructure, chemical composition, and the phase transformation temperatures of specimens. These parameters were studied by optical microscopy, scanning electron microscopy, x-ray diffraction, and differential scanning calorimetry (DSC). Highly porous specimens were obtained with up to 83% total porosity and pore sizes between 300 and 500 μm in diameter. Results show pore characteristics were improved from anisotropic to isotropic and pore morphology was changed from channel-like to irregular by adding pore filler powders. Furthermore, the highly porous specimens produced when using urea as a space holder, were of more uniform composition in comparison to NaCl. DSC results showed that a two-step martensitic phase transformation takes place during the cooling cycles and the austenite finish temperature ( A f) is close to human body temperature. Compression test results reveal that the compressive strength of highly porous NiTi is about 155 MPa and recoverable strain about 6% in superelasticity regime.

Observations on infiltration of silicon carbide compacts with an aluminium alloy

NASA Technical Reports Server (NTRS)

Asthana, R.; Rohatgi, P. K.

1992-01-01

The melt infiltration of ceramic particulates permits an opportunity to observe such fundamental materials phenomena as nucleation, dynamic wetting and growth in constrained environments. Experimental observations are presented on the infiltration behavior and matrix microstructures that form when porous compacts of platelet-shaped single crystals of alpha- (hexagonal) silicon carbide are infiltrated with a liquid 2014 Al alloy. The infiltration process involved counter gravity infiltration of suitably tamped and preheated compacts of silicon carbide platelets under an external pressure in a special pressure chamber for a set period, then by solidification of the infiltrant metal in the interstices of the bed at atmospheric pressure.

Role of bismuth on solidification, microstructure and mechanical properties of a near eutectic Al-Si alloys

NASA Astrophysics Data System (ADS)

Farahany, Saeed; Ourdjini, Ali; Bakar, Tuty Asma Abu; Idris, Mohd Hasbullah

2014-09-01

Computer aided thermal analysis and microstructural observation showed that addition of bismuth (Bi) within the range of 0.25 and 2 wt% produced a greater effect on the Al-Si eutectic phase than on primary aluminium and Al2Cu phases. Results showed that with addition of 1 wt% Bi the eutectic silicon structure was refined from flake-like morphology into lamellar. Bi refines rather than modifies the Si structure and increases the Al-Si eutectic fraction solid and more significantly there was no fading even up to 180 min of melt holding. Transmission electron microscopy study showed that the Si twin spacing decreased from 160 to 75 nm which is likely attributed to the refining effect of Bi. It was also found that addition of 1 wt% Bi increased the tensile strength, elongation and the absorbed energy for fracture due to the refined eutectic silicon structure.

Role of Cellulose Nanocrystals on the Microstructure of Maleic Anhydride Plasma Polymer Thin Films.

PubMed

Brioude, Michel M; Roucoules, Vincent; Haidara, Hamidou; Vonna, Laurent; Laborie, Marie-Pierre

2015-07-01

Recently, it was shown that the microstructure of a maleic anhydride plasma polymer (MAPP) could be tailored ab initio by adjusting the plasma process parameters. In this work, we aim to investigate the ability of cellulose nanocrystals (CNCs) to induce topographical structuration. Thus, a new approach was designed based on the deposition of MAPP on CNCs model surfaces. The nanocellulosic surfaces were produced by spin-coating the CNC suspension on a silicon wafer substrate and on a hydrophobic silicon wafer substrate patterned with circular hydrophilic microsized domains (diameter of 86.9 ± 4.9 μm), resulting in different degrees of CNC aggregation. By depositing the MAPP over these surfaces, it was possible to observe that the surface fraction of nanostructures increased from 20% to 35%. This observation suggests that CNCs can act as nucleation points resulting in more structures, although a critical density of the CNCs is required.

Heat Treatment Effects on the Tensile Properties and Microstructures of a SiC/RBSN Composite in Nitrogen

NASA Technical Reports Server (NTRS)

Bhatt, R. T.

1995-01-01

The room-temperature tensile properties and constituent microstructures of a unidirectionally reinforced SiC/reaction bonded silicon nitride (RBSN) composite have been investigated after heat treatments at 1400, 1600, or 1800 C in nitrogen for up to 100 hr. The composite consisted of approximately 24 vol% of aligned 140 micron diameter, continuous length, chemically vapor deposited SiC fibers in an approximately 40% porous silicon nitride matrix. The composites heat treated at 1400 C for up to 100 hr showed elastic modulus, first matrix cracking strength, and ultimate tensile strength values similar to those of the as-fabricated composites, but those heat treated for 1 hr beyond this temperature displayed losses in all three properties. Recrystallization of the SiC fibers, reaction between the carbon-rich interface coating on the fibers and the RBSN matrix, and dissociation of the RBSN matrix are the reasons for the loss of mechanical properties.

High dose neutron irradiations of Hi-Nicalon Type S silicon carbide composites, Part 1: Microstructural evaluations

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

Perez-Bergquist, Alex G.; Nozawa, Takashi; Shih, Chunghao Phillip

Over the past decade, significant progress has been made in the development of silicon carbide (SiC) composites, composed of near-stoichiometric SiC fibers embedded in a crystalline SiC matrix, to the point that such materials can now be considered nuclear grade. Recent neutron irradiation studies of Hi-Nicalon Type S SiC composites showed excellent radiation response at damage levels of 30-40 dpa at temperatures of 300-800 °C. However, more recent studies of these same fiber composites irradiated to damage levels of >70 dpa at similar temperatures showed a marked decrease in ultimate flexural strength, particularly at 300 °C. Here, electron microscopy ismore » used to analyze the microstructural evolution of these irradiated composites in order to investigate the cause of the degradation. While minimal changes were observed in Hi-Nicalon Type S SiC composites irradiated at 800 °C, substantial microstructural evolution is observed in those irradiated at 300° C. Furthermore, carbonaceous particles in the fibers grew by 25% compared to the virgin case, and severe cracking occurred at interphase layers.« less

Plasma etching a ceramic composite. [evaluating microstructure

NASA Technical Reports Server (NTRS)

Hull, David R.; Leonhardt, Todd A.; Sanders, William A.

1992-01-01

Plasma etching is found to be a superior metallographic technique for evaluating the microstructure of a ceramic matrix composite. The ceramic composite studied is composed of silicon carbide whiskers (SiC(sub W)) in a matrix of silicon nitride (Si3N4), glass, and pores. All four constituents are important in evaluating the microstructure of the composite. Conventionally prepared samples, both as-polished or polished and etched with molten salt, do not allow all four constituents to be observed in one specimen. As-polished specimens allow examination of the glass phase and porosity, while molten salt etching reveals the Si3N4 grain size by removing the glass phase. However, the latter obscures the porosity. Neither technique allows the SiC(sub W) to be distinguished from the Si3N4. Plasma etching with CF4 + 4 percent O2 selectively attacks the Si3N4 grains, leaving SiC(sub W) and glass in relief, while not disturbing the pores. An artifact of the plasma etching reaction is the deposition of a thin layer of carbon on Si3N4, allowing Si3N4 grains to be distinguished from SiC(sub W) by back scattered electron imaging.

Effect of substrate bias voltage on tensile properties of single crystal silicon microstructure fully coated with plasma CVD diamond-like carbon film

NASA Astrophysics Data System (ADS)

Zhang, Wenlei; Hirai, Yoshikazu; Tsuchiya, Toshiyuki; Tabata, Osamu

2018-06-01

Tensile strength and strength distribution in a microstructure of single crystal silicon (SCS) were improved significantly by coating the surface with a diamond-like carbon (DLC) film. To explore the influence of coating parameters and the mechanism of film fracture, SCS microstructure surfaces (120 × 4 × 5 μm3) were fully coated by plasma enhanced chemical vapor deposition (PECVD) of a DLC at five different bias voltages. After the depositions, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), thermal desorption spectrometry (TDS), surface profilometry, atomic force microscope (AFM) measurement, and nanoindentation methods were used to study the chemical and mechanical properties of the deposited DLC films. Tensile test indicated that the average strength of coated samples was 13.2-29.6% higher than that of the SCS sample, and samples fabricated with a -400 V bias voltage were strongest. The fracture toughness of the DLC film was the dominant factor in the observed tensile strength. Deviations in strength were reduced with increasingly negative bias voltage. The effect of residual stress on the tensile properties is discussed in detail.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Influence of the total gas flow rate on high rate growth microcrystalline silicon films and solar cells

NASA Astrophysics Data System (ADS)

Han, Xiao-Yan; Hou, Guo-Fu; Zhang, Xiao-Dan; Wei, Chang-Chun; Li, Gui-Jun; Zhang, De-Kun; Chen, Xin-Liang; Sun, Jian; Zhang, Jian-Jun; Zhao, Ying; Geng, Xin-Hua

2009-08-01

This paper reports that high-rate-deposition of microcrystalline silicon solar cells was performed by very-high-frequency plasma-enhanced chemical vapor deposition. These solar cells, whose intrinsic μc-Si:H layers were prepared by using a different total gas flow rate (Ftotal), behave much differently in performance, although their intrinsic layers have similar crystalline volume fraction, opto-electronic properties and a deposition rate of ~ 1.0 nm/s. The influence of Ftotal on the micro-structural properties was analyzed by Raman and Fourier transformed infrared measurements. The results showed that the vertical uniformity and the compact degree of μc-Si:H thin films were improved with increasing Ftotal. The variation of the microstructure was regarded as the main reason for the difference of the J-V parameters. Combined with optical emission spectroscopy, we found that the gas temperature plays an important role in determining the microstructure of thin films. With Ftotal of 300 sccm, a conversion efficiency of 8.11% has been obtained for the intrinsic layer deposited at 8.5 Å/s (1 Å = 0.1 nm).

Durability Enhancement of a Microelectromechanical System-Based Liquid Droplet Lens

NASA Astrophysics Data System (ADS)

Kyoo Lee, June; Park, Kyung-Woo; Kim, Hak-Rin; Kong, Seong Ho

2010-06-01

In this paper, we propose methods to enhance the durability of a microelectromechanical system (MEMS)-based liquid droplet lens driven by electrowetting. The enhanced durability of the lens is achieved through not only improvement in quality of dielectric layer for electrowetting by minimizing concentration of coarse pinholes, but also mitigation of physical and electrostatic stresses by reforming lens cavity. Silicon dioxide layer is deposited using plasma enhanced chemical vapor deposition, splitting the process into several steps to minimize the pinhole concentration in the oxide layer. And the stresses-reduced cavity in a form of overturned tetra-angular truncated pyramid with rounded corners, which is based on simulated results, is proposed and realized using silicon wet etching processes combined into anisotropic and isotropic etching.

SiO(x) nanoparticles synthesized by an evaporation and condensation process using induction melting of silicon and gas injection.

PubMed

Jang, Bo Yun; Lee, Jin Seok; Kim, Joon Soo

2013-05-01

SiO(x) nanoparticles were synthesized using a specially designed induction melting system equipped with a segmented graphite crucible. The graphite crucible with the segmented wall was the key to enhancing the evaporation rate due to the increase of the evaporation area and convection of the silicon melt. Injection of the gas mixture of oxygen (O2) and argon (Ar) on silicon (Si) melt caused the formation of SiO(x) nanoparticles. The evaporated SiO(x) nanoparticles were then cooled and condensed in a process chamber. The effects of the O2/Ar ratio in the injection gas on the microstructures of the SiO(x) nanoparticles were then investigated. Synthesized SiO(x) nanoparticles were proven to be of a homogeneous amorphous phase with average diameters of 30-35 nm. The microstructures were independent from the O2/Ar ratio of the injected gas. However, x increased from 1.36 to 1.84 as the O2/Ar ratio increased. The purity of the synthesized nanoparticles was about 99.9%. SiO(x) nanoparticles could be applied as the active anode material in a lithium (Li) ion secondary battery.

Reactive Infiltration of Silicon Melt Through Microporous Amorphous Carbon Preforms

NASA Technical Reports Server (NTRS)

Sangsuwan, P.; Tewari, S. N.; Gatica, J. E.; Singh, M.; Dickerson, R.

1999-01-01

The kinetics of unidirectional capillary infiltration of silicon melt into microporous carbon preforms have been investigated as a function of the pore morphology and melt temperature. The infiltrated specimens showed alternating bands of dark and bright regions, which corresponded to the unreacted free carbon and free silicon regions, respectively. The decrease in the infiltration front velocity for increasing infiltration distances, is in qualitative agreement with the closed-form solution of capillarity driven fluid flow through constant cross section cylindrical pores. However, drastic changes in the thermal response and infiltration front morphologies were observed for minute differences in the preforms microstructure. This suggests the need for a dynamic percolation model that would account for the exothermic nature of the silicon-carbon chemical reaction and the associated pore closing phenomenon.

Magnetomechanical effect in silicon (Cz-Si) surface layers

NASA Astrophysics Data System (ADS)

Koplak, O. V.; Dmitriev, A. I.; Morgunov, R. B.

2012-07-01

The mechanical properties of near-surface layers of Czochralski-grown silicon crystals Cz- n-Si(111) have been found to undergo changes in response to an external constant magnetic field ( B ˜ 0.1 T). A magnetically induced variation in the microhardness, Young's modulus, and coefficient of plasticity of silicon crystals correlates with the change in the lattice parameter and internal stresses of the sample. The growth of an oxide film under exposure to a magnetic field plays the principal role in the magnetomechanical effect due to a decrease in the concentration of oxygen complexes in the near-surface layers of the sample. In microstructured silicon, where the surface is considerably more developed, the magnetic field induces more profound changes in the internal stresses as compared to single crystals.

Developing strong concurrent multiphysics multiscale coupling to understand the impact of microstructural mechanisms on the structural scale

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

Foulk, James W.; Alleman, Coleman N.; Mota, Alejandro

The heterogeneity in mechanical fields introduced by microstructure plays a critical role in the localization of deformation. To resolve this incipient stage of failure, it is therefore necessary to incorporate microstructure with sufficient resolution. On the other hand, computational limitations make it infeasible to represent the microstructure in the entire domain at the component scale. In this study, the authors demonstrate the use of concurrent multi- scale modeling to incorporate explicit, finely resolved microstructure in a critical region while resolving the smoother mechanical fields outside this region with a coarser discretization to limit computational cost. The microstructural physics is modeledmore » with a high-fidelity model that incorporates anisotropic crystal elasticity and rate-dependent crystal plasticity to simulate the behavior of a stainless steel alloy. The component-scale material behavior is treated with a lower fidelity model incorporating isotropic linear elasticity and rate-independent J 2 plas- ticity. The microstructural and component scale subdomains are modeled concurrently, with coupling via the Schwarz alternating method, which solves boundary-value problems in each subdomain separately and transfers solution information between subdomains via Dirichlet boundary conditions. Beyond cases studies in concurrent multiscale, we explore progress in crystal plastic- ity through modular designs, solution methodologies, model verification, and extensions to Sierra/SM and manycore applications. Advances in conformal microstructures having both hexahedral and tetrahedral workflows in Sculpt and Cubit are highlighted. A structure-property case study in two-phase metallic composites applies the Materials Knowledge System to local metrics for void evolution. Discussion includes lessons learned, future work, and a summary of funded efforts and proposed work. Finally, an appendix illustrates the need for two-way coupling through a single degree of freedom.« less

Low Earth orbit durability evaluation of protected silicone for advanced refractive photovoltaic concentrator arrays

NASA Technical Reports Server (NTRS)

Degroh, Kim K.; Mccollum, Timothy A.

1994-01-01

The need for efficient, cost effective sources of electrical power in space has led to the development of photovoltaic power systems which make use of novel refractive solar concentrators. These concentrators have been conceived in both point-focus and linear-focus designs. Current concentrator lenses are fabricated from flexible silicones with Fresnel facets along their inside surface. To insure the efficient operation of these power systems, the concentrator lenses must be durable and the silicone material must remain specularly transmitting over a reasonable lifetime in low Earth orbit (LEO) and other space environments. Because of the vulnerability of silicones to atomic oxygen and ultraviolet radiation in LEO these lenses have been coated with a multi-layer metal oxide protective coating. The objective of this research was to evaluate the LEO durability of the multilayer coated silicone for advanced refractive photovoltaic concentrator arrays with respect to optical properties and microstructure. Flat metal oxide coated silicone samples were exposed to ground-laboratory and in-space atomic oxyqen for durability evaluation.

A new active solder for joining electronic components

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

SMITH,RONALD W.; VIANCO,PAUL T.; HERNANDEZ,CYNTHIA L.

Electronic components and micro-sensors utilize ceramic substrates, copper and aluminum interconnect and silicon. The joining of these combinations require pre-metallization such that solders with fluxes can wet such combinations of metals and ceramics. The paper will present a new solder alloy that can bond metals, ceramics and composites. The alloy directly wets and bonds in air without the use flux or premetallized layers. The paper will present typical processing steps and joint microstructures in copper, aluminum, aluminum oxide, aluminum nitride, and silicon joints.

Microstructural Influence on Dynamic Properties of Age Hardenable FeMnAl Alloys

DTIC Science & Technology

2011-04-01

precipitated . In alloys without silicon, β-Mn nucleates within the ferrite . In alloys with silicon, a DO3 intermetallic phase precipitates ...Figure 7 compares the 2.24% Si alloy at 950°C and 1000°C. At 950°C the growth of ferrite and the precipitation of an intermetallic phase is apparent...whereas the alloy remains predominately austenite with 2 vol.% ferrite at 1000°C. The intermetallic phase appears as prism-rods precipitated

Porous silicon carbide and aluminum oxide with unidirectional open porosity as model target materials for radioisotope beam production

NASA Astrophysics Data System (ADS)

Czapski, M.; Stora, T.; Tardivat, C.; Deville, S.; Santos Augusto, R.; Leloup, J.; Bouville, F.; Fernandes Luis, R.

2013-12-01

New silicon carbide (SiC) and aluminum oxide (Al2O3) of a tailor-made microstructure were produced using the ice-templating technique, which permits controlled pore formation conditions within the material. These prototypes will serve to verify aging of the new advanced target materials under irradiation with proton beams. Before this, the evaluation of their mechanical integrity was made based on the energy deposition spectra produced by FLUKA codes.

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

Nagata, Kohki, E-mail: nagata.koki@iri-tokyo.jp; School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571; Ogura, Atsushi

The effects of the fabrication process conditions on the microstructure of silicon dioxide thin films of <10 nm thickness are presented. The microstructure was investigated using grazing-incidence wide and small-angle X-ray scattering methods with synchrotron radiation. The combination of a high brilliance light source and grazing incident configuration enabled the observation of very weak diffuse X-ray scattering from SiO{sub 2} thin films. The results revealed different microstructures, which were dependent on oxidizing species or temperature. The micro-level properties differed from bulk properties reported in the previous literature. It was indicated that these differences originate from inner stress. The detailed structure inmore » an amorphous thin film was not revealed owing to detection difficulties.« less

New Oxide Ceramic Developed for Superior High-Temperature Wear Resistance

NASA Technical Reports Server (NTRS)

Sayir, Ali; Miyoshi, Kazuhisa; Farmer, Serene C.

2003-01-01

Ceramics, for the most part, do not have inherently good tribological properties. For example friction coefficients in excess of 0.7 have been reported for silicon nitride sliding on silicon nitride or on bearing steel (ref. 1). High friction is always accompanied by considerable wear. Despite their inherently poor tribological properties, the high strength and high toughness of silicon nitride (Si3N4) ceramics has led to their successful use in tribological applications (refs. 1 to 4). The upper temperature limit for the application of Si3N4 as wear-resistant material is limited by reaction with the tribological environment (ref. 3). Silicon nitride is known to produce a thin silicon dioxide film with easy shear capability that results in low friction and low wear in a moist environment (ref. 5). At elevated temperatures, the removal of the reaction product that acts as lubricant causes the friction coefficient to increase and, consequently, the wear performance to become poor. New materials are sought that will have wear resistance superior to that of Si3N4 at elevated temperatures and in harsh environments. A new class of oxide ceramic materials has been developed with potential for excellent high-temperature wear resistance. The new material consists of a multicomponent oxide with a two-phase microstructure, in which the wear resistance of the mixed oxide is significantly higher than that of the individual constituents. This is attributed to the strong constraining effects provided by the interlocking microstructures at different length scales, to the large aspect ratio of the phases, to the strong interphase bonding, and to the residual stresses. Fretting wear tests were conducted by rubbing the new ceramic material against boron carbide (B4C). The new ceramic material produced a wear track groove on B4C, suggesting significantly higher wear resistance for the oxide ceramic. The new material did not suffer from any microstructural degradation after the wear test. The wear rate of the new ceramic material at 600 C was determined to be on the order of 10-10 mm3/N-m, which is 3 to 5 orders of magnitude lower than that for the current state-of-theart wear-resistant materials (Si3N4and B4C). The friction coefficient of the new ceramic materials is on the order of 0.4, which is significantly lower than that of silicon nitride. This new class of oxide materials has shown considerable potential for applications requiring high wear resistance at high temperatures and in harsh environments. New understanding of the wear behavior of ceramic materials is emerging as a result of the surprisingly high wear resistance of two-phase oxide ceramics. There is excellent potential for further improvements in the wear resistance of oxide ceramics through optimizing the microstructure and altering the crystallographic properties of specific oxide materials as a second phase to reduce the coefficient of friction at elevated temperatures.

Mechanical Properties and Microstructure of Biomorphic Silicon Carbide Ceramics Fabricated from Wood Precursors

NASA Technical Reports Server (NTRS)

Singh, Mrityunjay; Salem, J. A.; Gray, Hugh R. (Technical Monitor)

2002-01-01

Silicon carbide based, environment friendly, biomorphic ceramics have been fabricated by the pyrolysis and infiltration of natural wood (maple and mahogany) precursors. This technology provides an eco-friendly route to advanced ceramic materials. These biomorphic silicon carbide ceramics have tailorable properties and behave like silicon carbide based materials manufactured by conventional approaches. The elastic moduli and fracture toughness of biomorphic ceramics strongly depend on the properties of starting wood preforms and the degree of molten silicon infiltration. Mechanical properties of silicon carbide ceramics fabricated from maple wood precursors indicate the flexural strengths of 3441+/-58 MPa at room temperature and 230136 MPa at 1350C. Room temperature fracture toughness of the maple based material is 2.6 +/- 0.2 MPa(square root of)m while the mahogany precursor derived ceramics show a fracture toughness of 2.0 +/- 0.2 Mpa(square root of)m. The fracture toughness and the strength increase as the density of final material increases. Fractographic characterization indicates the failure origins to be pores and chipped pockets of silicon.

Properties of HIPed stainless steel powder

NASA Astrophysics Data System (ADS)

Dellis, Ch.; Le Marois, G.; Gentzbittel, J. M.; Robert, G.; Moret, F.

1996-10-01

In the current design of ITER primary wall, 316LN stainless steel is the reference structural material. Austenitic stainless steel is used for water-cooling channels and structures. As material data on hot isostatic pressed (HIP) 316LN were not available in open literature and from powder producers, the main properties of unirradiated samples have been measured in CEA/CEREM. Fully dense material without any porosity is obtained when appropriate HIP parameters are applied. Microstructural examination and mechanical properties are confirmed that the HIPed 316LN material is equivalent to a very good fine-grain, isotropic and uniformly forged 316LN. Moreover, ultrasonic inspection showed that this fine and uniform microstructure produced a remarkably low noise, which allow the use of transverse waves at very high frequencies (4 MHz). Defects undetectable in forged material will be easily detected in HIPed material.

Gray scale x-ray mask

DOEpatents

Morales, Alfredo M [Livermore, CA; Gonzales, Marcela [Seattle, WA

2006-03-07

The present invention describes a method for fabricating an embossing tool or an x-ray mask tool, providing microstructures that smoothly vary in height from point-to-point in etched substrates, i.e., structure which can vary in all three dimensions. The process uses a lithographic technique to transfer an image pattern in the surface of a silicon wafer by exposing and developing the resist and then etching the silicon substrate. Importantly, the photoresist is variably exposed so that when developed some of the resist layer remains. The remaining undeveloped resist acts as an etchant barrier to the reactive plasma used to etch the silicon substrate and therefore provides the ability etch structures of variable depths.

Monolithic integration of fine cylindrical glass microcapillaries on silicon for electrophoretic separation of biomolecules

PubMed Central

Cao, Zhen; Ren, Kangning; Wu, Hongkai; Yobas, Levent

2012-01-01

We demonstrate monolithic integration of fine cylindrical glass microcapillaries (diameter ∼1 μm) on silicon and evaluate their performance for electrophoretic separation of biomolecules. Such microcapillaries are achieved through thermal reflow of a glass layer on microstructured silicon whereby slender voids are moulded into cylindrical tubes. The process allows self-enclosed microcapillaries with a uniform profile. A simplified method is also described to integrate the microcapillaries with a sample-injection cross without the requirement of glass etching. The 10-mm-long microcapillaries sustain field intensities up to 90 kV/m and limit the temperature excursions due to Joule heating to a few degrees Celsius only. PMID:23874369

Nucleate boiling performance on nano/microstructures with different wetting surfaces

PubMed Central

2012-01-01

A study of nucleate boiling phenomena on nano/microstructures is a very basic and useful study with a view to the potential application of modified surfaces as heating surfaces in a number of fields. We present a detailed study of boiling experiments on fabricated nano/microstructured surfaces used as heating surfaces under atmospheric conditions, employing identical nanostructures with two different wettabilities (silicon-oxidized and Teflon-coated). Consequently, enhancements of both boiling heat transfer (BHT) and critical heat flux (CHF) are demonstrated in the nano/microstructures, independent of their wettability. However, the increment of BHT and CHF on each of the different wetting surfaces depended on the wetting characteristics of heating surfaces. The effect of water penetration in the surface structures by capillary phenomena is suggested as a plausible mechanism for the enhanced CHF on the nano/microstructures regardless of the wettability of the surfaces in atmospheric condition. This is supported by comparing bubble shapes generated in actual boiling experiments and dynamic contact angles under atmospheric conditions on Teflon-coated nano/microstructured surfaces. PMID:22559173

Design and Fabrication of Submicron Magnetic Bubble Device Technology.

DTIC Science & Technology

1986-10-31

interface LPE bubble film GGG substrate Figure 2: Cross section of a silicon on garnet magnetodiode. I : R R R/ B>O0 B 0 z V............. ... ..AV dummy...Carnegie Mellon University, Pittsburgh, Pa 15213. Section I Introduction The main thrust of our LPE garnet film growth program is to develop> films ...shown in Table I and the best choice for an isotropic magnetostrictive film is shown by an asterik. Section IM LPE Film Growth Technique All garnet

Liquid crystal droplet formation and anchoring dynamics in a microfluidic device

NASA Astrophysics Data System (ADS)

Steinhaus, Ben; Shen, Amy; Feng, James; Link, Darren

2004-11-01

Liquid crystal drops dispersed in a continuous phase of silicon oil are generated with a narrow distribution in droplet size in microfluidic devices both above and below the nematic to isotropic transition temperature. For these two cases, we observe not only the different LC droplet generation and coalescence dynamics, but also distinct droplet morphology. Our experiments show that the nematic liquid crystalline order is important for the LC droplet formation and anchoring dynamics.

A bioactive metallurgical grade porous silicon-polytetrafluoroethylene sheet for guided bone regeneration applications.

PubMed

Chadwick, E G; Clarkin, O M; Raghavendra, R; Tanner, D A

2014-01-01

The properties of porous silicon make it a promising material for a host of applications including drug delivery, molecular and cell-based biosensing, and tissue engineering. Porous silicon has previously shown its potential for the controlled release of pharmacological agents and in assisting bone healing. Hydroxyapatite, the principle constituent of bone, allows osteointegration in vivo, due to its chemical and physical similarities to bone. Synthetic hydroxyapatite is currently applied as a surface coating to medical devices and prosthetics, encouraging bone in-growth at their surface and improving osseointegration. This paper examines the potential for the use of an economically produced porous silicon particulate-polytetrafluoroethylene sheet for use as a guided bone regeneration device in periodontal and orthopaedic applications. The particulate sheet is comprised of a series of microparticles in a polytetrafluoroethylene matrix and is shown to produce a stable hydroxyapatite on its surface under simulated physiological conditions. The microstructure of the material is examined both before and after simulated body fluid experiments for a period of 1, 7, 14 and 30 days using Scanning Electron Microscopy. The composition is examined using a combination of Energy Dispersive X-ray Spectroscopy, Thin film X-ray diffraction, Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy and the uptake/release of constituents at the fluid-solid interface is explored using Inductively Coupled Plasma-Optical Emission Spectroscopy. Microstructural and compositional analysis reveals progressive growth of crystalline, 'bone-like' apatite on the surface of the material, indicating the likelihood of close bony apposition in vivo.

Microstructure of SiC-Si-Al2O3 composites derived from silicone resin - metal aluminum filler compounds by low temperature reduction process

NASA Astrophysics Data System (ADS)

Narisawa, M.; Abe, Y.

2011-06-01

Concentrated slurry of a silicone resin with low carbon content, 3 μm aluminum particles and ethanol were prepared. After casting, addition of cross-linking agent and drying, silicone resin-aluminum composite with thick sheet form was obtained. The prepared sheet was heat-treated at 933 or 1073K with various holding times to characterize formed phases during the heat treatments. XRD patterns and FT-IR spectra revealed free Si formation and existence of Si-O-Si bond at 933K. The Si-O-Si bond, however, disappeared and silicon carbide was formed at 1073K. SEM observation indicated formation of cracks bridged with a number of tiny struts at 933K and conversion to wholly porous structure at 1073K.

Design of novel materials for additive manufacturing - Isotropic microstructure and high defect tolerance.

PubMed

Günther, J; Brenne, F; Droste, M; Wendler, M; Volkova, O; Biermann, H; Niendorf, T

2018-01-22

Electron Beam Melting (EBM) is a powder-bed additive manufacturing technology enabling the production of complex metallic parts with generally good mechanical properties. However, the performance of powder-bed based additively manufactured materials is governed by multiple factors that are difficult to control. Alloys that solidify in cubic crystal structures are usually affected by strong anisotropy due to the formation of columnar grains of preferred orientation. Moreover, processing induced defects and porosity detrimentally influence static and cyclic mechanical properties. The current study presents results on processing of a metastable austenitic CrMnNi steel by EBM. Due to multiple phase transformations induced by intrinsic heat-treatment in the layer-wise EBM process the material develops a fine-grained microstructure almost without a preferred crystallographic grain orientation. The deformation-induced phase transformation yields high damage tolerance and, thus, excellent mechanical properties less sensitive to process-induced inhomogeneities. Various scan strategies were applied to evaluate the width of an appropriate process window in terms of microstructure evolution, porosity and change of chemical composition.

Test of the Peierls-Nabarro model for dislocations in silicon

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

Ren, Q.; Joos, B.; Duesbery, M.S.

1995-11-01

We show, using an atomistic model with a Stillinger-Weber potential (SWP), that in the absence of reconstruction, the basic assumption of the Peierls-Nabarro (PN) model that the dislocation core is spread within the glide plane is verified for silicon. The Peierls stress (PS) obtained from the two models are in quantitative agreement ({approx}0.3{mu}), when restoring forces obtained from first principles generalized stacking-fault energy surfaces are used in the PN model [B. Joos, Q. Ren, and M. S. Duesbery, Phys. Rev. B {bold 50}, 5890 (1994)]. The PS was found to be isotropic in the glide plane. Within the SWP modelmore » no evidence of dissociation in the shuffle dislocations is found but glide sets do separate into two partials.« less

As-received microstructure of a SiC/Ti-15-3 composite

NASA Technical Reports Server (NTRS)

Lerch, Bradley A.; Hull, David R.; Leonhardt, Todd A.

1988-01-01

A silicon carbide fiber reinforced titanium (Ti-15V-3Cr-3Sn-3Al) composite is metallographically examined. Several methods for examining composite materials are investigated and documented. Polishing techniques for this material are described. An interference layering method is developed to reveal the structure of the fiber, the reaction zone, and various phases within the matrix. Microprobe and transmission electron microscope (TEM) analyses are performed on the fiber/matrix interface. A detailed description of the fiber distribution as well as the microstructure of the fiber and matrix are presented.

Effect of starting powder characteristics on density, microstructure and low temperature oxidation behavior of a Si3N48w/o Y2O3 ceramic

NASA Technical Reports Server (NTRS)

Schuon, S.; Dutta, S.

1980-01-01

The densification and oxidation behavior of Si3N4 - 8w/oY2O3 prepared from three commercial starting powders were studied. Bars of SN 402, SN 502, and CP 85/15 were sintered for 3 to 4.5 hours at 1750 C. A second set was hot pressed for 2 hours at 1750 C. The microstructures were studied by transmission electron microscopy and scanning electron microscopy, densities were determined, and the phase compositions were determined by X-ray diffraction. Densification and microstructure were greatly influenced by the starting powder morphology and impurity content. Although SN 402 exhibited the maximum weight lose, the highest sintered and hot pressed densities were obtained with this powder. All powders had both equiaxed and elongated grains. Sintered bars were composed of beta silicon nitride and n-melelite. In contrast, hot pressed bars contained beta silicon nitride, H-phase, and J-phase, but no melelite. Yttria distribution in sintered bars was related to the presence of cation impurities such as Ca, Fe, and Mg. A limited oxidation study at 750 C in air showed no instability in these Si3N4 - 8 w/oY2O3 specimens, regardless of startin powder.

Metastable growth of pure wurtzite InGaAs microstructures.

PubMed

Ng, Kar Wei; Ko, Wai Son; Lu, Fanglu; Chang-Hasnain, Connie J

2014-08-13

III-V compound semiconductors can exist in two major crystal phases, namely, zincblende (ZB) and wurtzite (WZ). While ZB is thermodynamically favorable in conventional III-V epitaxy, the pure WZ phase can be stable in nanowires with diameters smaller than certain critical values. However, thin nanowires are more vulnerable to surface recombination, and this can ultimately limit their performances as practical devices. In this work, we study a metastable growth mechanism that can yield purely WZ-phased InGaAs microstructures on silicon. InGaAs nucleates as sharp nanoneedles and expand along both axial and radial directions simultaneously in a core-shell fashion. While the base can scale from tens of nanometers to over a micron, the tip can remain sharp over the entire growth. The sharpness maintains a high local surface-to-volume ratio, favoring hexagonal lattice to grow axially. These unique features lead to the formation of microsized pure WZ InGaAs structures on silicon. To verify that the WZ microstructures are truly metastable, we demonstrate, for the first time, the in situ transformation from WZ to the energy-favorable ZB phase inside a transmission electron microscope. This unconventional core-shell growth mechanism can potentially be applied to other III-V materials systems, enabling the effective utilization of the extraordinary properties of the metastable wurtzite crystals.

Effect of specific surface microstructures on substrate endothelialisation and thrombogenicity: Importance for stent design.

PubMed

Lutter, Christoph; Nothhaft, Matthias; Rzany, Alexander; Garlichs, Christoph D; Cicha, Iwona

2015-01-01

In coronary artery disease, highly stenosed arteries are frequently treated by stent implantation, which thereafter necessitates a dual-antiplatelet therapy (DAPT) in order to prevent stent-thrombosis. We hypothesized that specific patterns of microstructures on stents can accelerate endothelialisation thereby reducing their thrombogenicity and the DAPT duration. Differently designed, 2-5 μm high elevations or hollows were lithographically etched on silicon plates, subsequently coated with silicon carbide. Smooth silicon plates and bare metal substrates were used as controls. To assess attachment and growth of human umbilical vein endothelial cells under static or flow conditions, actin cytoskeleton was visualised with green phalloidin. Endothelial migration was assessed in a modified barrier assay. To investigate surface thrombogenicity, platelets were incubated on the structured surfaces in static and flow conditions, and visualised with fluorescein-conjugated P-selectin antibody. Images were taken with incident-light fluorescent microscope for non-transparent objects. Compared to smooth surface, flat cubic elevations (5 μm edge length) improved endothelial cell attachment and growth under static and dynamic conditions, whereas smaller, spiky structures (2 μm edge length) had a negative influence on endothelialisation. Endothelial cell migration was fastest on flat cubic elevations, hollows, and smooth surfaces, whereas spiky structures and bare metal had a negative effect on endothelial migration. Thrombogenicity assays under static and flow conditions showed that platelet adhesion was reduced on the flat elevations and the smooth surface, as compared to the spiky structures, the hollow design and the bare metal substrates. Surface microstructures strongly influence endothelialisation of substrates. Designing stents with surface topography which accelerates endothelialisation and reduces thrombogenicity may be of clinical benefit by improving the safety profile of coronary interventions.

Silicon-containing polymer-derived ceramic nanocomposites (PDC-NCs): preparative approaches and properties.

PubMed

Ionescu, Emanuel; Kleebe, Hans-Joachim; Riedel, Ralf

2012-08-07

Composites consist by definition of at least two materials (Gibbsian phases) with rather different properties. They exhibit a heterogeneous microstructure and possess improved properties with respect to their components. Furthermore, the design of their microstructure allows for tailoring their overall properties. In the last decades, intense work was performed on the synthesis of nanocomposites, which have the feature that at least one of their components is nanoscaled. However, the microstructure-property relationship of nanocomposite materials is still a challenging topic. This tutorial review paper deals with a special class of nanocomposites, i.e. polymer-derived ceramic nanocomposites (PDC-NCs), which have been shown to be promising materials for various structural and functional applications. Within this context, different preparative approaches for PDC-NCs as well as some of their properties will be presented and discussed. Furthermore, recent results concerning the relationship between the nano/microstructure of PDC-NCs and their properties will be highlighted.

Novel Micropatterned Cardiac Cell Cultures with Realistic Ventricular Microstructure

PubMed Central

Badie, Nima; Bursac, Nenad

2009-01-01

Systematic studies of cardiac structure-function relationships to date have been hindered by the intrinsic complexity and variability of in vivo and ex vivo model systems. Thus, we set out to develop a reproducible cell culture system that can accurately replicate the realistic microstructure of native cardiac tissues. Using cell micropatterning techniques, we aligned cultured cardiomyocytes at micro- and macroscopic spatial scales to follow local directions of cardiac fibers in murine ventricular cross sections, as measured by high-resolution diffusion tensor magnetic resonance imaging. To elucidate the roles of ventricular tissue microstructure in macroscopic impulse conduction, we optically mapped membrane potentials in micropatterned cardiac cultures with realistic tissue boundaries and natural cell orientation, cardiac cultures with realistic tissue boundaries but random cell orientation, and standard isotropic monolayers. At 2 Hz pacing, both microscopic changes in cell orientation and ventricular tissue boundaries independently and synergistically increased the spatial dispersion of conduction velocity, but not the action potential duration. The realistic variations in intramural microstructure created unique spatial signatures in micro- and macroscopic impulse propagation within ventricular cross-section cultures. This novel in vitro model system is expected to help bridge the existing gap between experimental structure-function studies in standard cardiac monolayers and intact heart tissues. PMID:19413993

Direct numerical simulations in solid mechanics for quantifying the macroscale effects of microstructure and material model-form error

DOE PAGES

Bishop, Joseph E.; Emery, John M.; Battaile, Corbett C.; ...

2016-03-16

Two fundamental approximations in macroscale solid-mechanics modeling are (1) the assumption of scale separation in homogenization theory and (2) the use of a macroscopic plasticity material model that represents, in a mean sense, the multitude of inelastic processes occurring at the microscale. With the goal of quantifying the errors induced by these approximations on engineering quantities of interest, we perform a set of direct numerical simulations (DNS) in which polycrystalline microstructures are embedded throughout a macroscale structure. The largest simulations model over 50,000 grains. The microstructure is idealized using a randomly close-packed Voronoi tessellation in which each polyhedral Voronoi cellmore » represents a grain. An face centered cubic crystal-plasticity model is used to model the mechanical response of each grain. The overall grain structure is equiaxed, and each grain is randomly oriented with no overall texture. The detailed results from the DNS simulations are compared to results obtained from conventional macroscale simulations that use homogeneous isotropic plasticity models. The macroscale plasticity models are calibrated using a representative volume element of the idealized microstructure. Furthermore, we envision that DNS modeling will be used to gain new insights into the mechanics of material deformation and failure.« less

Scaling relations between trabecular bone volume fraction and microstructure at different skeletal sites.

PubMed

Räth, Christoph; Baum, Thomas; Monetti, Roberto; Sidorenko, Irina; Wolf, Petra; Eckstein, Felix; Matsuura, Maiko; Lochmüller, Eva-Maria; Zysset, Philippe K; Rummeny, Ernst J; Link, Thomas M; Bauer, Jan S

2013-12-01

In this study, we investigated the scaling relations between trabecular bone volume fraction (BV/TV) and parameters of the trabecular microstructure at different skeletal sites. Cylindrical bone samples with a diameter of 8mm were harvested from different skeletal sites of 154 human donors in vitro: 87 from the distal radius, 59/69 from the thoracic/lumbar spine, 51 from the femoral neck, and 83 from the greater trochanter. μCT images were obtained with an isotropic spatial resolution of 26μm. BV/TV and trabecular microstructure parameters (TbN, TbTh, TbSp, scaling indices (< > and σ of α and αz), and Minkowski Functionals (Surface, Curvature, Euler)) were computed for each sample. The regression coefficient β was determined for each skeletal site as the slope of a linear fit in the double-logarithmic representations of the correlations of BV/TV versus the respective microstructure parameter. Statistically significant correlation coefficients ranging from r=0.36 to r=0.97 were observed for BV/TV versus microstructure parameters, except for Curvature and Euler. The regression coefficients β were 0.19 to 0.23 (TbN), 0.21 to 0.30 (TbTh), -0.28 to -0.24 (TbSp), 0.58 to 0.71 (Surface) and 0.12 to 0.16 (<α>), 0.07 to 0.11 (<αz>), -0.44 to -0.30 (σ(α)), and -0.39 to -0.14 (σ(αz)) at the different skeletal sites. The 95% confidence intervals of β overlapped for almost all microstructure parameters at the different skeletal sites. The scaling relations were independent of vertebral fracture status and similar for subjects aged 60-69, 70-79, and >79years. In conclusion, the bone volume fraction-microstructure scaling relations showed a rather universal character. © 2013.

Fabrication of CoFe2O4 ferrite nanowire arrays in porous silicon template and their local magnetic properties

NASA Astrophysics Data System (ADS)

Hui, Zheng; Man-Gui, Han; Long-Jiang, Deng

2016-02-01

CoFe2O4 ferrite nanowire arrays are fabricated in porous silicon templates. The porous silicon templates are prepared via metal-assisted chemical etching with gold (Au) nanoparticles as the catalyst. Subsequently, CoFe2O4 ferrite nanowires are successfully synthesized into porous silicon templates by the sol-gel method. The magnetic hysteresis loop of nanowire array shows an isotropic feature of magnetic properties. The coercivity and squareness ratio (Mr/Ms) of ensemble nanowires are found to be 630 Oe (1 Oe, = 79.5775 A·m-1 and 0.4 respectively. However, the first-order reversal curve (FORC) is adopted to reveal the probability density function of local magnetostatic properties (i.e., interwire interaction field and coercivity). The FORC diagram shows an obvious distribution feature for interaction field and coercivity. The local coercivity with a value of about 1000 Oe is found to have the highest probability. Project supported by the National Natural Science Foundation of China (Grant No. 61271039), the Scientific Projects of Sichuan Province, China (Grant No. 2015HH0016), and the Natural Science Foundations of Zhejiang Province, China (Grant Nos. LQ12E02001 and Y107255).

Thin film silicon by a microwave plasma deposition technique: Growth and devices, and, interface effects in amorphous silicon/crystalline silicon solar cells

NASA Astrophysics Data System (ADS)

Jagannathan, Basanth

Thin film silicon (Si) was deposited by a microwave plasma CVD technique, employing double dilution of silane, for the growth of low hydrogen content Si films with a controllable microstructure on amorphous substrates at low temperatures (<400sp°C). The double dilution was achieved by using a Ar (He) carrier for silane and its subsequent dilution by Hsb2. Structural and electrical properties of the films have been investigated over a wide growth space (temperature, power, pressure and dilution). Amorphous Si films deposited by silane diluted in He showed a compact nature and a hydrogen content of ˜8 at.% with a photo/dark conductivity ratio of 10sp4. Thin film transistors (W/L = 500/25) fabricated on these films, showed an on/off ratio of ˜10sp6 and a low threshold voltage of 2.92 volts. Microcrystalline Si films with a high crystalline content (˜80%) were also prepared by this technique. Such films showed a dark conductivity ˜10sp{-6} S/cm, with a conduction activation energy of 0.49 eV. Film growth and properties have been compared for deposition in Ar and He carrier systems and growth models have been proposed. Low temperature junction formation by undoped thin film silicon was examined through a thin film silicon/p-type crystalline silicon heterojunctions. The thin film silicon layers were deposited by rf glow discharge, dc magnetron sputtering and microwave plasma CVD. The hetero-interface was identified by current transport analysis and high frequency capacitance methods as the key parameter controlling the photovoltaic (PV) response. The effect of the interface on the device properties (PV, junction, and carrier transport) was examined with respect to modifications created by chemical treatment, type of plasma species, their energy and film microstructure interacting with the substrate. Thermally stimulated capacitance was used to determine the interfacial trap parameters. Plasma deposition of thin film silicon on chemically clean c-Si created electron trapping sites while hole traps were seen when a thin oxide was present at the interface. Under optimized conditions, a 10.6% efficient cell (11.5% with SiOsb2 A/R) with an open circuit voltage of 0.55 volts and a short circuit current density of 30 mA/cmsp2 was fabricated.

Viscous propulsion in active transversely isotropic media

NASA Astrophysics Data System (ADS)

Cupples, Gemma; Dyson, Rosemary; Smith, David

2017-11-01

Taylor's swimming sheet is a classical model of microscale propulsion and pumping. Many biological fluids and substances are fibrous, having a preferred direction in their microstructure; for example cervical mucus. To understand how these effects modify viscous propulsion, we extend Taylor's classical model of small-amplitude viscous propulsion of a `swimming sheet' via the transversely-isotropic fluid model of Ericksen, which is linear in strain rate and possesses a distinguished direction. The energetic costs of swimming are significantly altered by all rheological parameters and the initial fibre angle. Propulsion in a passive transversely-isotropic fluid enhances mean rate of working, independent of the initial fibre orientation. In this regime the mean swimming velocity is unchanged from the Newtonian case. The effect of fibre tension, or alternatively a stresslet characterising an active fluid, is also considered. This stress introduces an angular dependence and dramatically changes the streamlines and flow field; fibres aligned with the swimming direction increase the energetic demands of the sheet. The constant fibre stress may result in a reversal of the mean swimming velocity and a negative mean rate of working if sufficiently large relative to the other parameters. Funding is provided by a Biotechnology and Biological Sciences Research Council (BBSRC) Industrial CASE Studentship (BB/L015587/1).

Effects of nitrogen impurities on the microstructure and electronic properties of P-doped Si nanocrystals emebedded in silicon-rich SiNx films

NASA Astrophysics Data System (ADS)

Ma, Deng-Hao; Zhang, Wei-Jia; Luo, Rui-Ying; Jiang, Zhao-Yi; Ma, Qiang; Ma, Xiao-Bo; Fan, Zhi-Qiang; Song, Deng-Yuan; Zhang, Lei

2016-05-01

Phosphorus doped Si nanocrystals (SNCs) emebedded in silicon-rich SiNx:H films were prepared using plasma enhanced chemical vapor deposition technique, and the effects of nitrogen incorporation on the microstructure and electronic properties of the thin films have been systematically studied. Transmission electron microscope and Raman observation revealed that nitrogen incorporation prevents the growth of Si nanocrystals, and that their sizes can be adjusted by varying the flow rate of NH3. The reduction of photoluminescence (PL) intensity in the range of 2.1-2.6 eV of photon energy was observed with increasing nitrogen impurity, and a maximal PL intensity in the range 1.6-2.0 eV was obtained when the incorporation flow ratio NH3/(SiH4+H2+PH3) was 0.02. The conductivity of the films is improved by means of proper nitrogen impurity doping, and proper doping causes the interface charge density of the heterojunction (H-J) device to be lower than the nc-Si:H/c-Si H-J device. As a result, the proper incorporation of nitrogen could not only reduce the silicon banding bond density, but also fill some carrier capture centers, and suppress the nonradiative recombination of electrons.

Surface micro-structuring of silicon by excimer-laser irradiation in reactive atmospheres

NASA Astrophysics Data System (ADS)

Pedraza, A. J.; Fowlkes, J. D.; Jesse, S.; Mao, C.; Lowndes, D. H.

2000-12-01

The formation mechanisms of cones and columns by pulsed-laser irradiation in reactive atmospheres were studied using scanning electron microscopy and profilometry. Deep etching takes place in SF6- and O2- rich atmospheres and consequently, silicon-containing molecules and clusters are released. Transport of silicon from the etched/ablated regions to the tip of columns and cones and to the side of the cones is required because both structures, columns and cones, protrude above the initial surface. The laser-induced micro-structure is influenced not only by the nature but also by the partial pressure of the reactive gas in the atmosphere. Irradiation in Ar following cone formation in SF6 produced no additional growth but rather melting and resolidification. Subsequent irradiation using again a SF6 atmosphere lead to cone restructuring and growth resumption. Thus the effects of etching plus re-deposition that produce column/cone formation and growth are clearly separated from the effects of just melting. On the other hand, irradiation continued in air after first performed in SF6 resulted in: (a) an intense etching of the cones and a tendency to transform them into columns; (b) growth of new columns on top of the existing cones and (c) filamentary nano-structures coating the sides of the columns and cones.

Phase-field study of grain boundary tracking behavior in crack-seal microstructures

NASA Astrophysics Data System (ADS)

Ankit, Kumar; Nestler, Britta; Selzer, Michael; Reichardt, Mathias

2013-12-01

In order to address the growth of crystals in veins, a multiphase-field model is used to capture the dynamics of crystals precipitating from a super-saturated solution. To gain a detailed understanding of the polycrystal growth phenomena in veins, we investigate the influence of various boundary conditions on crystal growth. In particular, we analyze the formation of vein microstructures resulting from the free growth of crystals as well as crack-sealing processes. We define the crystal symmetry by considering the anisotropy in surface energy to simulate crystals with flat facets and sharp corners. The resulting growth competition of crystals with different orientations is studied to deduce a consistent orientation selection rule in the free-growth regime. Using crack-sealing simulations, we correlate the grain boundary tracking behavior depending on the relative rate of crack opening, opening trajectory, initial grain size, and wall roughness. Further, we illustrate how these parameters induce the microstructural transition between blocky (crystals growing anisotropically) to fibrous morphology (isotropic) and formation of grain boundaries. The phase-field simulations of crystals in the free-growth regime (in 2D and 3D) indicate that the growth or consumption of a crystal is dependent on the orientation difference with neighboring crystals. The crack-sealing simulation results (in 2D and 3D) reveal that crystals grow isotropically and grain boundaries track the opening trajectory if the wall roughness is high, opening increments are small, and crystals touch the wall before the next crack increment starts. Further, we find that within the complete crack-seal regime, anisotropy in surface energy results in the formation of curved/oscillating grain boundaries (instead of straight) when the crack-opening velocity is increased and wall roughness is not sufficiently high. Additionally, the overall capability of phase-field method to simulate large-scale polycrystal growth in veins (in 3D) is demonstrated enumerating the main advantages of adopting the novel approach.

Reactive Processing of Environmentally Conscious, Biomorphic Ceramics from Natural Wood Precursors

NASA Technical Reports Server (NTRS)

Singh, M.; Yee, Bo-Moon

2003-01-01

Environmentally conscious, biomorphic ceramics (Ecoceramics) are a new class of materials that are manufactured from renewable resources and wastes. In this study, silicon carbide and oxide-based biomorphic ceramics have been fabricated from pine and jelutong wood precursors. A carbonaceous preform is produced through wood pyrolysis and subsequent infiltration with oxides (ZrO2 sols) and liquid silicon to form ceramics. These biomorphic ceramics show a wide variety of microstructures, densities, and hardness behavior that are determined by the type of wood and infiltrants selected.

Challenges and Opportunities in Design, Fabrication, and Testing of High Temperature Joints in Ceramics and Ceramic Composites

NASA Technical Reports Server (NTRS)

Singh, M.; Levine, S. R. (Technical Monitor)

2001-01-01

Ceramic joining has been recognized as an enabling technology for successful utilization of advanced ceramics and composite materials. A number of joint design and testing issues have been discussed for ceramic joints in silicon carbide-based ceramics and fiber-reinforced composites. These joints have been fabricated using an affordable, robust ceramic joining technology (ARCJoinT). The microstructure and good high temperature mechanical capability (compressive and flexural strengths) of ceramic joints in silicon carbide-based ceramics and composite materials are reported.

Influence of etching current density on microstructural, optical and electrical properties of porous silicon (PS):n-Si heterostructure

NASA Astrophysics Data System (ADS)

Das, M.; Nath, P.; Sarkar, D.

2016-02-01

In this article effect of etching current density (J) on the microstructural, optical and electrical properties of photoelectrochemically prepared heterostructure is reported. Prepared samples are characterized by FESEM, XRD, UV-Visible, Raman and photoluminescence (PL) spectra and current-voltage (I-V) characteristics. FESEM shows presence of mixture of randomly distributed meso- and micro-pores. Porous layer thickness determined by cross section view of SEM is proportional to J. XRD shows crystalline nature but gradually extent of crystallinity decreases with increasing J. Raman spectra show large red-shift and asymmetric broadening with respect to crystalline silicon (c-Si). UV-visible reflectance and PL show blue shift in peaks with increasing J. The I-V characteristics are analyzed by the conventional thermionic emission (TE) model and Cheung's model to estimate the barrier height (φb), ideality factor (n) and series resistance (Rs) for comparison between the two models. The latter model is found to fit better.

Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres

PubMed Central

Coucheron, David A.; Fokine, Michael; Patil, Nilesh; Breiby, Dag Werner; Buset, Ole Tore; Healy, Noel; Peacock, Anna C.; Hawkins, Thomas; Jones, Max; Ballato, John; Gibson, Ursula J.

2016-01-01

Glass fibres with silicon cores have emerged as a versatile platform for all-optical processing, sensing and microscale optoelectronic devices. Using SiGe in the core extends the accessible wavelength range and potential optical functionality because the bandgap and optical properties can be tuned by changing the composition. However, silicon and germanium segregate unevenly during non-equilibrium solidification, presenting new fabrication challenges, and requiring detailed studies of the alloy crystallization dynamics in the fibre geometry. We report the fabrication of SiGe-core optical fibres, and the use of CO2 laser irradiation to heat the glass cladding and recrystallize the core, improving optical transmission. We observe the ramifications of the classic models of solidification at the microscale, and demonstrate suppression of constitutional undercooling at high solidification velocities. Tailoring the recrystallization conditions allows formation of long single crystals with uniform composition, as well as fabrication of compositional microstructures, such as gratings, within the fibre core. PMID:27775066

Fabrication and secondary-phase crystallization of rare-earth disilicate-silicon nitride ceramics

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

Cinibulk, M.K.; Thomas, G.; Johnson, S.M.

1992-08-01

In this paper, the fabrication and intergranular-phase devitrification of silicon nitride densified with rare-earth (RE) oxide additives is investigated. The additions of the oxides of Sm, Gd, Dy, Er, and Yb, having high melting points and behaving similarly to Y[sub 2]O[sub 3], were compositionally controlled to tailor a microstructure with a crystalline secondary phase of RE[sub 2]Si[sub 2]O[sub 7]. The lanthanide oxides were found to be ass effective as Y[sub 2]O[sub 3] in densifying Si[sub 3]N[sub 4], resulting in identical microstructures and densities of 98-99% of theoretical density. The crystallization behavior of all six disilicates was similar, characterized by amore » limited nucleation and rapid growth mechanism resulting in large single crystals. Complete crystallization of the intergranular phase was obtained with the exception of a thin residual amorphous film which was observed at interfaces and believed to be rich in impurities, the cause of incomplete devitrification.« less

Bottom–Up Electrodeposition of Large-Scale Nanotwinned Copper within 3D Through Silicon Via

PubMed Central

Sun, Fu-Long; Li, Cai-Fu; Zhu, Qing-Sheng; Zhang, Hao; Suganuma, Katsuaki

2018-01-01

This paper is the first to report a large-scale directcurrent electrodeposition of columnar nanotwinned copper within through silicon via (TSV) with a high aspect ratio (~4). With this newly developed technique, void-free nanotwinned copper array could be fabricated in low current density (30 mA/cm2) and convection conditions (300 rpm), which are the preconditions for copper deposition with a uniform deep-hole microstructure. The microstructure of a whole cross-section of deposited copper array was made up of (111) orientated columnar grains with parallel nanoscale twins that had thicknesses of about 22 nm. The hardness was also uniform along the growth direction, with 2.34 and 2.68 GPa for the top and bottom of the TSV, respectively. The gelatin additive is also first reported hereas a key factor in forming nanoscale twins by adsorbing on the cathode surface, in order to enhance the overpotential for cathodic reaction during the copper deposition process. PMID:29473865

Laser recrystallization and inscription of compositional microstructures in crystalline SiGe-core fibres

NASA Astrophysics Data System (ADS)

Coucheron, David A.; Fokine, Michael; Patil, Nilesh; Breiby, Dag Werner; Buset, Ole Tore; Healy, Noel; Peacock, Anna C.; Hawkins, Thomas; Jones, Max; Ballato, John; Gibson, Ursula J.

2016-10-01

Glass fibres with silicon cores have emerged as a versatile platform for all-optical processing, sensing and microscale optoelectronic devices. Using SiGe in the core extends the accessible wavelength range and potential optical functionality because the bandgap and optical properties can be tuned by changing the composition. However, silicon and germanium segregate unevenly during non-equilibrium solidification, presenting new fabrication challenges, and requiring detailed studies of the alloy crystallization dynamics in the fibre geometry. We report the fabrication of SiGe-core optical fibres, and the use of CO2 laser irradiation to heat the glass cladding and recrystallize the core, improving optical transmission. We observe the ramifications of the classic models of solidification at the microscale, and demonstrate suppression of constitutional undercooling at high solidification velocities. Tailoring the recrystallization conditions allows formation of long single crystals with uniform composition, as well as fabrication of compositional microstructures, such as gratings, within the fibre core.

Bottom-Up Electrodeposition of Large-Scale Nanotwinned Copper within 3D Through Silicon Via.

PubMed

Sun, Fu-Long; Liu, Zhi-Quan; Li, Cai-Fu; Zhu, Qing-Sheng; Zhang, Hao; Suganuma, Katsuaki

2018-02-23

This paper is the first to report a large-scale directcurrent electrodeposition of columnar nanotwinned copper within through silicon via (TSV) with a high aspect ratio (~4). With this newly developed technique, void-free nanotwinned copper array could be fabricated in low current density (30 mA/cm²) and convection conditions (300 rpm), which are the preconditions for copper deposition with a uniform deep-hole microstructure. The microstructure of a whole cross-section of deposited copper array was made up of (111) orientated columnar grains with parallel nanoscale twins that had thicknesses of about 22 nm. The hardness was also uniform along the growth direction, with 2.34 and 2.68 GPa for the top and bottom of the TSV, respectively. The gelatin additive is also first reported hereas a key factor in forming nanoscale twins by adsorbing on the cathode surface, in order to enhance the overpotential for cathodic reaction during the copper deposition process.

Density change and viscous flow during structural relaxation of plasma-enhanced chemical-vapor-deposited silicon oxide films

NASA Astrophysics Data System (ADS)

Cao, Zhiqiang; Zhang, Xin

2004-10-01

The structural relaxation of plasma-enhanced chemical-vapor-deposited (PECVD) silane-based silicon oxide films during thermal cycling and annealing has been studied using wafer curvature measurements. These measurements, which determine stress in the amorphous silicon oxide films, are sensitive to both plastic deformation and density changes. A quantitative case study of such changes has been done based upon the experimental results. A microstructure-based mechanism elucidates seams as a source of density change and voids as a source of plastic deformation, accompanied by a viscous flow. This theory was then used to explain a series of experimental results that are related to thermal cycling as well as annealing of PECVD silicon oxide films including stress hysteresis generation and reduction and coefficient of thermal-expansion changes. In particular, the thickness effect was examined; PECVD silicon oxide films with a thickness varying from 1to40μm were studied, as certain demanding applications in microelectromechanical systems require such thick films serving as heat/electrical insulation layers.

Impurities in silicon solar cells

NASA Technical Reports Server (NTRS)

Hopkins, R. H.

1985-01-01

Metallic impurities, both singly and in combinations, affect the performance of silicon solar cells. Czochralski silicon web crystals were grown with controlled additions of secondary impurities. The primary electrical dopants were boron and phosphorus. The silicon test ingots were grown under controlled and carefully monitored conditions from high-purity charge and dopant material to minimize unintentional contamination. Following growth, each crystal was characterized by chemical, microstructural, electrical, and solar cell tests to provide a detailed and internally consistent description of the relationships between silicon impurity concentration and solar cell performance. Deep-level spectroscopy measurements were used to measure impurity concentrations at levels below the detectability of other techniques and to study thermally-induced changes in impurity activity. For the majority of contaminants, impurity-induced performance loss is due to a reduction of the base diffusion length. From these observations, a semi-empirical model which predicts cell performance as a function of metal impurity concentration was formulated. The model was then used successfully to predict the behavior of solar cells bearing as many as 11 different impurities.

Atomic Scale Understanding of Poly-Si/SiO2/c-Si Passivated Contacts: Passivation Degradation Due to Metallization

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

Aguiar, Jeffery A.; Young, David; Lee, Benjamin

2016-11-21

The key attributes for achieving high efficiency crystalline silicon solar cells include class leading developments in the ability to approach the theoretical limits of silicon solar technology (29.4% efficiency). The push for high efficiency devices is further compounded with the clear need for passivation to reduce recombination at the metal contacts. At the same time there is stringent requirement to retain the same material device quality, surface passivation, and performance characteristics following subsequent processing. The development of passivated silicon cell structures that retain active front and rear surface passivation and overall material cell quality is therefore a relevant and activemore » area of development. To address the potential outcomes of metallization on passivated silicon stack, we report on some common microstructural features of degradation due to metallization for a series of silicon device stacks. A fundamental materials understanding of the metallization process on retaining high-efficiency passivated Si devices is therefore gained over these series of results.« less

Periodic silicon nanostructures for spectroscopic microsensors

NASA Astrophysics Data System (ADS)

Wehrspohn, Ralf B.; Gesemann, Benjamin; Pergande, Daniel; Geppert, Torsten M.; Schweizer, Stefan L.; Moretton, Susanne; Lambrecht, Armin

2011-09-01

Periodic silicon nanostructures can be used for different kinds of gas sensors depending on the analyte concentration. First we present an optical gas sensor based on the classical non-dispersive infrared technique for ppm-concentration using ultra-compact photonic crystal gas cells. It is conceptually based on low group velocities inside a photonic crystal gas cell and anti-reflection layers coupling light into the device. Experimentally, an enhancement of the CO2 infrared absorption by a factor of 2.6 to 3.5 as compared to an empty cell, due to slow light inside a 2D silicon photonic crystal gas cell, was observed; this is in excellent agreement with numerical simulations. In addition we report on silicon nanotip arrays, suitable for gas ionization in ion mobility microspectrometers (micro-IMS) having detection ranges in principle down to the ppt-range. Such instruments allow the detection of explosives, chemical warfare agents, and illicit drugs, e.g., at airports. We describe the fabrication process of large-scale-ordered nanotips with different tip shapes. Both silicon microstructures have been fabricated by photoelectrochemical etching of silicon.

Plastic Deformation of Micromachined Silicon Diaphragms with a Sealed Cavity at High Temperatures

PubMed Central

Ren, Juan; Ward, Michael; Kinnell, Peter; Craddock, Russell; Wei, Xueyong

2016-01-01

Single crystal silicon (SCS) diaphragms are widely used as pressure sensitive elements in micromachined pressure sensors. However, for harsh environments applications, pure silicon diaphragms are hardly used because of the deterioration of SCS in both electrical and mechanical properties. To survive at the elevated temperature, the silicon structures must work in combination with other advanced materials, such as silicon carbide (SiC) or silicon on insulator (SOI), for improved performance and reduced cost. Hence, in order to extend the operating temperatures of existing SCS microstructures, this work investigates the mechanical behavior of pressurized SCS diaphragms at high temperatures. A model was developed to predict the plastic deformation of SCS diaphragms and was verified by the experiments. The evolution of the deformation was obtained by studying the surface profiles at different anneal stages. The slow continuous deformation was considered as creep for the diaphragms with a radius of 2.5 mm at 600 °C. The occurrence of plastic deformation was successfully predicted by the model and was observed at the operating temperature of 800 °C and 900 °C, respectively. PMID:26861332

Silicon nanowire arrays as thermoelectric material for a power microgenerator

NASA Astrophysics Data System (ADS)

Dávila, D.; Tarancón, A.; Fernández-Regúlez, M.; Calaza, C.; Salleras, M.; San Paulo, A.; Fonseca, L.

2011-10-01

A novel design of a silicon-based thermoelectric power microgenerator is presented in this work. Arrays of silicon nanowires, working as thermoelectric material, have been integrated in planar uni-leg thermocouple microstructures to convert waste heat into electrical energy. Homogeneous, uniformly dense, well-oriented and size-controlled arrays of silicon nanowires have been grown by chemical vapor deposition using the vapor-liquid-solid mechanism. Compatibility issues between the nanowire growth method and microfabrication techniques, such as electrical contact patterning, are discussed. Electrical measurements of the nanowire array electrical conductivity and the Seebeck voltage induced by a controlled thermal gradient or under harvesting operation mode have been carried out to demonstrate the feasibility of the microdevice. A resistance of 240 Ω at room temperature was measured for an array of silicon nanowires 10 µm -long, generating a Seebeck voltage of 80 mV under an imposed thermal gradient of 450 °C, whereas only 4.5 mV were generated under a harvesting operation mode. From the results presented, a Seebeck coefficient of about 150-190 µV K-1 was estimated, which corresponds to typical values for bulk silicon.

Micro-architecture embedding ultra-thin interlayer to bond diamond and silicon via direct fusion

NASA Astrophysics Data System (ADS)

Kim, Jong Cheol; Kim, Jongsik; Xin, Yan; Lee, Jinhyung; Kim, Young-Gyun; Subhash, Ghatu; Singh, Rajiv K.; Arjunan, Arul C.; Lee, Haigun

2018-05-01

The continuous demand on miniaturized electronic circuits bearing high power density illuminates the need to modify the silicon-on-insulator-based chip architecture. This is because of the low thermal conductivity of the few hundred nanometer-thick insulator present between the silicon substrate and active layers. The thick insulator is notorious for releasing the heat generated from the active layers during the operation of devices, leading to degradation in their performance and thus reducing their lifetime. To avoid the heat accumulation, we propose a method to fabricate the silicon-on-diamond (SOD) microstructure featured by an exceptionally thin silicon oxycarbide interlayer (˜3 nm). While exploiting the diamond as an insulator, we employ spark plasma sintering to render the silicon directly fused to the diamond. Notably, this process can manufacture the SOD microarchitecture via a simple/rapid way and incorporates the ultra-thin interlayer for minute thermal resistance. The method invented herein expects to minimize the thermal interfacial resistance of the devices and is thus deemed as a breakthrough appealing to the current chip industry.

Electro-Magnetic Actuated Valve for MEMS Fuel Metering System

DTIC Science & Technology

2007-09-01

This model is utilized material properties of Silicon (Si), Copper (Cu), Nickel Iron ( NiFe ), and air. C11 Air NiSe Figure 5. Design of a simplified a... NiFe are defined and shown table 4. It is assumed that the properties of materials are independent of orientation (i.e. isotropic materials). Relative...dry filn resist. This process enables an integrated NiFe armature with a hole-in-the-wall within the main flow channel. UC Berkeley, Pisano - 2007

Bidirectional scattering of light from tree leaves

NASA Technical Reports Server (NTRS)

Brakke, Thomas W.; Smith, James A.; Harnden, Joann M.

1989-01-01

A laboratory goniometer consisting of an He-Ne laser (632.8 nm), vertical leaf holder, and silicon photovoltaic detector was used to measure the bidirectional scattering (both transmittance and reflectance) of red oak and red maple. The illumination angles were 0, 30, and 60 deg, and the scattering was recorded approximately every 10 deg in the principal plane. The scattering profiles obtained show the non-Lambertian characteristics of the scattering, particularly for the off-nadir illumination directions. The transmitted light was more isotropic than the reflected light.

Direct comparison of polymethylmetacrylate (PMMA) and silicone-on-glass (SOG) for Fresnel lenses in concentrating photovoltaics (CPV)

NASA Astrophysics Data System (ADS)

Annen, Hans Philipp; Fu, Ling; Leutz, Ralf; González, Luis; Mbakop, Jehu

2011-09-01

The CPV community is still undecided on one critical issue: what material to use best for Fresnel lens parquets. Reliability and longevity are the most important, but all other properties play roles as well. We have developed and manufactured Fresnel lenses with the two commonly used materials: PMMA (Polymethylmethacrylate) and silicone on glass (SOG). Both lenses are designed for the same optical train for best comparability. This allows for better understanding the pros and cons of the materials and making an informed choice for a specific CPV module. While PMMA lenses are embossed from pre-fab sheets in a hot-cold process, the silicone lenses are cast from a heat-curing silicone rubber at moderate temperatures, reducing the energy consumption. PMMA allows for the inclusion of custom low-profile 3D (2.5D) structures for module assembly and mechanical alignment, a feature not possible in silicone due to its low rigidity. Both lenses suffer from thermal expansion and refractive index change. While PMMA parquets expand isotropically, SOG prisms deform due to the difference of expansion coefficients between the glass and the silicone. SOG lenses are prone to delamination of the silicone film. The adhesive strength of the film to the glass can be measured using a modified blister test that we developed. The results show large difference with different materials and confirm the necessity of controlling this issue closely. While the small thermal expansion of the glass sheets allows for larger parquet sizes, the deformation of the prisms with temperature may cause a performance hit.

A review of molecular beam epitaxy of ferroelectric BaTiO3 films on Si, Ge and GaAs substrates and their applications

PubMed Central

Mazet, Lucie; Yang, Sang Mo; Kalinin, Sergei V; Schamm-Chardon, Sylvie; Dubourdieu, Catherine

2015-01-01

SrTiO3 epitaxial growth by molecular beam epitaxy (MBE) on silicon has opened up the route to the monolithic integration of various complex oxides on the complementary metal-oxide–semiconductor silicon platform. Among functional oxides, ferroelectric perovskite oxides offer promising perspectives to improve or add functionalities on-chip. We review the growth by MBE of the ferroelectric compound BaTiO3 on silicon (Si), germanium (Ge) and gallium arsenide (GaAs) and we discuss the film properties in terms of crystalline structure, microstructure and ferroelectricity. Finally, we review the last developments in two areas of interest for the applications of BaTiO3 films on silicon, namely integrated photonics, which benefits from the large Pockels effect of BaTiO3, and low power logic devices, which may benefit from the negative capacitance of the ferroelectric. PMID:27877816

High Temperature Joining and Characterization of Joint Properties in Silicon Carbide-Based Composite Materials

NASA Technical Reports Server (NTRS)

Halbig, Michael C.; Singh, Mrityunjay

2015-01-01

Advanced silicon carbide-based ceramics and composites are being developed for a wide variety of high temperature extreme environment applications. Robust high temperature joining and integration technologies are enabling for the fabrication and manufacturing of large and complex shaped components. The development of a new joining approach called SET (Single-step Elevated Temperature) joining will be described along with the overview of previously developed joining approaches including high temperature brazing, ARCJoinT (Affordable, Robust Ceramic Joining Technology), diffusion bonding, and REABOND (Refractory Eutectic Assisted Bonding). Unlike other approaches, SET joining does not have any lower temperature phases and will therefore have a use temperature above 1315C. Optimization of the composition for full conversion to silicon carbide will be discussed. The goal is to find a composition with no remaining carbon or free silicon. Green tape interlayers were developed for joining. Microstructural analysis and preliminary mechanical tests of the joints will be presented.

Conductive-probe atomic force microscopy characterization of silicon nanowire

PubMed Central

2011-01-01

The electrical conduction properties of lateral and vertical silicon nanowires (SiNWs) were investigated using a conductive-probe atomic force microscopy (AFM). Horizontal SiNWs, which were synthesized by the in-plane solid-liquid-solid technique, are randomly deployed into an undoped hydrogenated amorphous silicon layer. Local current mapping shows that the wires have internal microstructures. The local current-voltage measurements on these horizontal wires reveal a power law behavior indicating several transport regimes based on space-charge limited conduction which can be assisted by traps in the high-bias regime (> 1 V). Vertical phosphorus-doped SiNWs were grown by chemical vapor deposition using a gold catalyst-driving vapor-liquid-solid process on higly n-type silicon substrates. The effect of phosphorus doping on the local contact resistance between the AFM tip and the SiNW was put in evidence, and the SiNWs resistivity was estimated. PMID:21711623

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

Sajgalik, P.; Sedlacek, J.; Lences, Z.

Densification of silicon carbide without any sintering aids by hot-pressing and rapid hot pressing was investigated. Full density (>99% t.d.) has been reached at 1850 °C, a temperature of at least 150-200 °C lower compared to the up to now known solid state sintered silicon carbide powders. Silicon carbide was freeze granulated and heat treated prior the densification. Furthermore, evolution of microstructure, mechanical properties and creep behavior were evaluated and compared to reference ceramics from as received silicon carbide powder as well as those of commercial one. Novel method results in dense ceramics with Vickers hardness and indentation fracture toughnessmore » of 29.0 GPa and 5.25 MPam 1/2, respectively. Moreover, the creep rate of 3.8 x 10 –9 s –1 at 1450 °C and the load of 100 MPa is comparable to the commercial α-SiC solid state sintered at 2150 °C.« less

Role of the primary silicon particle on the dry sliding wear of hypereutectic aluminium-silicon alloy A390

NASA Astrophysics Data System (ADS)

Lee, Jung-Moo; Kang, Suk-Bong; Yoon, Sang-Chul

1999-07-01

The wear behavior of hypereutectic aluminium-silicon alloy A390 was investigated using a pin-on-disc wear machine under dry sliding conditions. The wear tests were performed within a load range of 10 to 300N at a constant sliding velocity of 0.5 m/sec. The microstructural and compositional changes that took place during wear were characterized by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analysis (EDXA) system. Based on the metallographic observations the role of the primary silicon particles was suggested. In a low pressure region, primary silicon particles supported the applied load and wear occurred mainly in the matrix. Thus the wear loss did not show much variation with the applied load. In the mid-load range, primary silicon particles did not yet fracture and thus supported the applied load in part. Transition from oxidative to metallic wear occurs mainly in the matrix and the increase of wear loss becomes sharper than that in a low pressure region. In the high pressure region, the fractures of primary silicon Particles occurred and wear loss increased sharply.

Direct depiction of bone microstructure using MRI with zero echo time.

PubMed

Weiger, Markus; Stampanoni, Marco; Pruessmann, Klaas P

2013-05-01

This paper reports a proof of principle of direct depiction of trabecular bone microstructure in vitro by means of magnetic resonance imaging (MRI). Such depiction is achieved by (1)H imaging of water embedded in the bone matrix. The fast transverse relaxation of this compartment with T2(⁎) on the order of a few hundreds of microseconds is addressed by a three-dimensional MRI technique with zero echo time (ZTE). ZTE imaging at an isotropic spatial resolution of 56 μm is demonstrated in a trabecular bone specimen extracted from a bovine bone. In the MR images, the trabecular bone structure is clearly depicted and a high level of robustness against off-resonance artefacts is observed. The structural accuracy of the MR data is investigated by comparison with x-ray micro-computed tomography. Copyright © 2013 Elsevier Inc. All rights reserved.

Toward a benchmark material in aerogel development

NASA Astrophysics Data System (ADS)

Sibille, Laurent; Cronise, Raymond J.; Noever, David A.; Hunt, Arlon J.

1996-03-01

Discovered in the thirties, aerogels constitute today the lightest solids known while exhibiting outstanding thermal and noise insulation properties in air and vacuum. In a far-reaching collaboration, the Space Science Laboratory at NASA Marshall Space Flight Center and the Microstructured Materials Group at Lawrence Berkeley National Laboratory are engaged in a two-fold research effort aiming at characterizing the microstructure of silica aerogels and the development of benchmark samples through the use of in-orbit microgravity environment. Absence of density-driven convection flows and sedimentation is sought to produce aerogel samples with narrow distribution of pore sizes, thus largely improving transparency of the material in the visible range. Furthermore, highly isotropic distribution of doping materials are attainable even in large gels grown in microgravity. Aerospace companies (cryogenic tanks insulation and high temperature insulation of space vehicles), insulation manufacturers (household and industrial applications) as well as pharmaceutical companies (biosensors) are potential end-users of this rapidly developing technology.

Nondestructive ultrasonic characterization of armor grade silicon carbide

NASA Astrophysics Data System (ADS)

Portune, Andrew Richard

Ceramic materials have traditionally been chosen for armor applications for their superior mechanical properties and low densities. At high strain rates seen during ballistic events, the behavior of these materials relies upon the total volumetric flaw concentration more so than any single anomalous flaw. In this context flaws can be defined as any microstructural feature which detriments the performance of the material, potentially including secondary phases, pores, or unreacted sintering additives. Predicting the performance of armor grade ceramic materials depends on knowledge of the absolute and relative concentration and size distribution of bulk heterogeneities. Ultrasound was chosen as a nondestructive technique for characterizing the microstructure of dense silicon carbide ceramics. Acoustic waves interact elastically with grains and inclusions in large sample volumes, and were well suited to determine concentration and size distribution variations for solid inclusions. Methodology was developed for rapid acquisition and analysis of attenuation coefficient spectra. Measurements were conducted at individual points and over large sample areas using a novel technique entitled scanning acoustic spectroscopy. Loss spectra were split into absorption and scattering dominant frequency regimes to simplify analysis. The primary absorption mechanism in polycrystalline silicon carbide was identified as thermoelastic in nature. Correlations between microstructural conditions and parameters within the absorption equation were established through study of commercial and custom engineered SiC materials. Nonlinear least squares regression analysis was used to estimate the size distributions of boron carbide and carbon inclusions within commercial SiC materials. This technique was shown to additionally be capable of approximating grain size distributions in engineered SiC materials which did not contain solid inclusions. Comparisons to results from electron microscopy exhibited favorable agreement between predicted and observed distributions. Developed techniques were applied to large sample areas using scanning acoustic spectroscopy to map variations in the size distribution and concentration of grains and solid inclusions within the bulk microstructure. The experiments performed in this thesis form the foundation of a novel characterization technique capable of mapping variations in sample composition which could be extended to a wide range of dense polycrystalline heterogeneous materials.

Effect of metallic coating on the properties of copper-silicon carbide composites

NASA Astrophysics Data System (ADS)

Chmielewski, M.; Pietrzak, K.; Teodorczyk, M.; Nosewicz, S.; Jarząbek, D.; Zybała, R.; Bazarnik, P.; Lewandowska, M.; Strojny-Nędza, A.

2017-11-01

In the presented paper a coating of SiC particles with a metallic layer was used to prepare copper matrix composite materials. The role of the layer was to protect the silicon carbide from decomposition and dissolution of silicon in the copper matrix during the sintering process. The SiC particles were covered by chromium, tungsten and titanium using Plasma Vapour Deposition method. After powder mixing of components, the final densification process via Spark Plasma Sintering (SPS) method at temperature 950 °C was provided. The almost fully dense materials were obtained (>97.5%). The microstructure of obtained composites was studied using scanning electron microscopy as well as transmission electron microscopy. The microstructural analysis of composites confirmed that regardless of the type of deposited material, there is no evidence for decomposition process of silicon carbide in copper. In order to measure the strength of the interface between ceramic particles and the metal matrix, the micro tensile tests have been performed. Furthermore, thermal diffusivity was measured with the use of the laser pulse technique. In the context of performed studies, the tungsten coating seems to be the most promising solution for heat sink application. Compared to pure composites without metallic layer, Cu-SiC with W coating indicate the higher tensile strength and thermal diffusitivy, irrespective of an amount of SiC reinforcement. The improvement of the composite properties is related to advantageous condition of Cu-SiC interface characterized by well homogenity and low porosity, as well as individual properties of the tungsten coating material.

Conformable large-area position-sensitive photodetectors based on luminescence-collecting silicone waveguides

NASA Astrophysics Data System (ADS)

Bartu, Petr; Koeppe, Robert; Arnold, Nikita; Neulinger, Anton; Fallon, Lisa; Bauer, Siegfried

2010-06-01

Position sensitive detection schemes based on the lateral photoeffect rely on inorganic semiconductors. Such position sensitive devices (PSDs) are reliable and robust, but preparation with large active areas is expensive and use on curved substrates is impossible. Here we present a novel route for the fabrication of conformable PSDs which allows easy preparation on large areas, and use on curved surfaces. Our device is based on stretchable silicone waveguides with embedded fluorescent dyes, used in conjunction with small silicon photodiodes. Impinging laser light (e.g., from a laser pointer) is absorbed by the dye in the PSD and re-emitted as fluorescence light at a larger wavelength. Due to the isotropic emission from the fluorescent dye molecules, most of the re-emitted light is coupled into the planar silicone waveguide and directed to the edges of the device. Here the light signals are detected via embedded small silicon photodiodes arranged in a regular pattern. Using a mathematical algorithm derived by extensive using of models from global positioning system (GPS) systems and human activity monitoring, the position of light spots is easily calculated. Additionally, the device shows high durability against mechanical stress, when clamped in an uniaxial stretcher and mechanically loaded up to 15% strain. The ease of fabrication, conformability, and durability of the device suggests its use as interface devices and as sensor skin for future robots.

Electrowetting Lens Employing Hemispherical Cavity Formed by Hydrofluoric Acid, Nitric Acid, and Acetic Acid Etching of Silicon

NASA Astrophysics Data System (ADS)

Lee, June Kyoo; Choi, Ju Chan; Jang, Won Ick; Kim, Hak-Rin; Kong, Seong Ho

2012-06-01

We demonstrate the design of an electrowetting lens employing a high-aspect-ratio hemispherical lens cavity and its micro-electro-mechanical-system (MEMS) fabrication process in this study. Our preliminary simulation results showed that the physical and electrical durability of the lens can be improved by the mitigation of stresses on the insulator at the hemispherical cavity. High-aspect-ratio hemispherical cavities with various diameters and very smooth sidewall surfaces were uniformly fabricated on a silicon wafer by a sophisticated isotropic wet etching technique. Moreover, we experimentally investigated the optical properties of the MEMS-based electrowetting lens with the proposed cavity. Two immiscible liquids in the proposed lens cavity were electrostatically controlled with negligible optical distortion and low focal-length hysteresis due to the fully axis-symmetrical geometry and smooth sidewall of the cavity.

Microstructure and Sn crystal orientation evolution in Sn-3.5Ag lead-free solders in high temperature packaging applications

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

Zhou, Bite; Muralidharan, Govindarajan; Kurumaddali, Nalini Kanth

2014-01-01

Understanding the reliability of eutectic Sn-3.5Ag lead-free solders in high temperature packaging applications is of significant interest in power electronics for the next generation electric grid. Large area (2.5mm 2.5mm) Sn-3.5Ag solder joints between silicon dies and direct bonded copper substrates were thermally cycled between 5 C and 200 C. Sn crystal orientation and microstructure evolution during thermal cycling were characterized by electron backscatter diffraction (EBSD) in scanning electron microscope (SEM). Comparisons are made between observed initial texture and microstructure and its evolution during thermal cycling. Gradual lattice rotation and grain boundary misorientation evolution suggested the continuous recrystallization mechanism. Recrystallizationmore » behavior was correlated with dislocation slip activities.« less

Application of X-ray microcomputed tomography in the characterization of irradiated nuclear fuel and material specimens

DOE PAGES

Silva, Chinthaka M.; Snead, Lance Lewis; Hunn, John D.; ...

2015-08-03

X-ray microcomputed tomography (µCT) was applied in characterizing the internal structures of a number of irradiated materials, including carbon-carbon fibre composites, nuclear-grade graphite and tristructural isotropic-coated fuel particles. Local cracks in carbon-carbon fibre composites associated with their synthesis process were observed with µCT without any destructive sample preparation. Pore analysis of graphite samples was performed quantitatively, and qualitative analysis of pore distribution was accomplished. It was also shown that high-resolution µCT can be used to probe internal layer defects of tristructural isotropic-coated fuel particles to elucidate the resulting high release of radioisotopes. Layer defects of sizes ranging from 1 tomore » 5 µm and up could be isolated by to-mography. As an added advantage, µCT could also be used to identify regions with high densities of radioisotopes to deter-mine the proper plane and orientation of particle mounting for further analytical characterization, such as materialographic sectioning followed by optical and electron microscopy. Lastly, in fully ceramic matrix fuel forms, despite the highly absorbing matrix, characterization of tristructural isotropic-coated particles embedded in a silicon carbide matrix was accomplished usingµCT and related advanced image analysis techniques.« less

Properties of RBSN and RBSN-SiC composites. [Reaction Bonded Silicon Nitride

NASA Technical Reports Server (NTRS)

Lightfoot, A.; Ker, H. L.; Haggerty, J. S.; Ritter, J. E.

1990-01-01

Strengths, fracture toughnesses, hardnesses, and dimensional changes have been measured for RBSN and RBSN/SiC composites. Samples were made from mixtures of Si and either Si- or C-rich SiC powders. For pure, 75 pct dense RBSN dispersed with octanol, strengths up to 858 MPa have been achieved. Improved strengths result from a combination of microstructural perfection and increased fracture toughness. The mechanical properties of the composites were approximately equal to those of methanol processed RBSN but not quite equal to those of the octanol-processed RBSN. Results are discussed in terms of observed microstructural features.

Solidification, growth mechanisms, and associated properties of aluminum-silicon and magnesium lightweight casting alloys

NASA Astrophysics Data System (ADS)

Hosch, Timothy Al

Continually rising energy prices have inspired increased interest in weight reduction in the automotive and aerospace industries, opening the door for the widespread use and development of lightweight structural materials. Chief among these materials are cast Al-Si and magnesium-based alloys. Utilization of Al-Si alloys depends on obtaining a modified fibrous microstructure in lieu of the intrinsic flake structure, a process which is incompletely understood. The local solidification conditions, mechanisms, and tensile properties associated with the flake to fiber growth mode transition in Al-Si eutectic alloys are investigated here using bridgman type gradient-zone directional solidification. Resulting microstructures are examined through quantitative image analysis of two-dimensional sections and observation of deep-etched sections showing three-dimensional microstructural features. The transition was found to occur in two stages: an initial stage dominated by in-plane plate breakup and rod formation within the plane of the plate, and a second stage where the onset of out-of-plane silicon rod growth leads to the formation of an irregular fibrous structure. Several microstructural parameters were investigated in an attempt to quantify this transition, and it was found that the particle aspect ratio is effective in objectively identifying the onset and completion velocity of the flake to fiber transition. The appearance of intricate out-of-plane silicon instability formations was investigated by adapting a perturbed-interface stability analysis to the Al-Si system. Measurements of silicon equilibrium shape particles provided an estimate of the anisotropy of the solid Si/liquid Al-Si system and incorporation of this silicon anisotropy into the model was found to improve prediction of the instability length scale. Magnesium alloys share many of the benefits of Al-Si alloys, with the added benefit of a 1/3 lower density and increased machinability. Magnesium castings often contain additions of heavier elements, such as zinc, zirconium, and rare earth elements, which significantly improve high temperature performance. However, additions of these elements can lead to macrosegregational effects in castings, which are detectable by radiographic scans. The effect of these flow-line indications on alloy mechanical properties is not well quantified. An examination of these flow-line indications and their effects on mechanical properties in three magnesiumbased casting alloys was performed here in order to determine the best practice for dealing with affected castings. Preliminary results suggest the flow-lines do not measurably impact bulk material properties. Three additional methods of characterizing three-dimensional material structures are also presented: a minimum spanning tree analysis is utilized to quantify local structure in Cu-Zr liquid phase simulations obtained from molecular dynamics; the radial distribution function is applied to directionally solidified Al-Si structures in an attempt to extract local spacing data; and the critical diameter measurement is also defined and applied to irregular eutectic Al-Si structures.

Nitrogen doped silicon-carbon multilayer protective coatings on carbon obtained by thermionic vacuum arc (TVA) method

NASA Astrophysics Data System (ADS)

Ciupinǎ, Victor; Vasile, Eugeniu; Porosnicu, Corneliu; Vladoiu, Rodica; Mandes, Aurelia; Dinca, Virginia; Nicolescu, Virginia; Manu, Radu; Dinca, Paul; Zaharia, Agripina

2018-02-01

To obtain protective nitrogen doped Si-C multilayer coatings on carbon, used to improve the oxidation resistance of carbon, was used TVA method. The initial carbon layer has been deposed on a silicon substrate in the absence of nitrogen, and then a 3nm Si thin film to cover carbon layer was deposed. Further, seven Si and C layers were alternatively deposed in the presence of nitrogen ions. In order to form silicon carbide at the interface between silicon and carbon layers, all carbon, silicon and nitrogen ions energy has increased up to 150eV. The characterization of microstructure and electrical properties of as-prepared N-Si-C multilayer structures were done using Transmission Electron Microscopy (TEM, STEM) techniques, Thermal Desorption Spectroscopy (TDS) and electrical measurements. The retention of oxygen in the protective layer of N-Si-C is due to the following phenomena: (a) The reaction between oxygen and silicon carbide resulting in silicon oxide and carbon dioxide; (b) The reaction involving oxygen, nitrogen and silicon resulting silicon oxinitride with a variable composition; (c) Nitrogen acts as a trapping barrier for oxygen. To perform electrical measurements, ohmic contacts were attached on the N-Si-C samples. Electrical conductivity was measured in constant current mode. To explain the temperature behavior of electrical conductivity we assumed a thermally activated electric transport mechanism.

High-speed microprobe for roughness measurements in high-aspect-ratio microstructures

NASA Astrophysics Data System (ADS)

Doering, Lutz; Brand, Uwe; Bütefisch, Sebastian; Ahbe, Thomas; Weimann, Thomas; Peiner, Erwin; Frank, Thomas

2017-03-01

Cantilever-type silicon microprobes with an integrated tip and a piezoresistive signal read out have successfully proven to bridge the gap between scanning force microscopy and stylus profilometry. Roughness measurements in high-aspect-ratio microstructures (HARMS) with depths down to 5 mm and widths down to 50 µm have been demonstrated. To improve the scanning speed up to 15 mm s-1, the wear of the tip has to be reduced. The atomic layer deposition (ALD) technique with alumina (Al2O3) has been tested for this purpose. Repeated wear measurements with coated and uncoated microprobe cantilevers have been carried out on a roughness standard at a speed of 15 mm s-1. The tip shape and the wear have been measured using a new probing tip reference standard containing rectangular silicon grooves with widths from 0.3 µm to 3 µm. The penetration depth of the microprobe allows one to measure the wear of the tip as well as the tip width and the opening angle of the tip. The roughness parameters obtained on the roughness standard during wear experiments agree well with the reference values measured with a calibrated stylus instrument, nevertheless a small amount of wear still is observable. Further research is necessary in order to obtain wear resistant microprobe tips for non-destructive inspection of microstructures in industry and microform measurements, for example in injection nozzles.

Metal/ceramic composites via infiltration of an interconnected wood-derived ceramic

NASA Astrophysics Data System (ADS)

Wilkes, Thomas E.

The use of composites is increasing as they afford scientists and engineers the ability to combine the advantageous properties of each constituent phase, e.g. metal ductility and ceramic stiffness. With respect to materials design, biomimetics is garnering increasing attention due to the complex, yet efficient, natural microstructures. One such biomimetic, or in this case 'bio-derived,' curiosity is wood-derived ceramic, which is made by either replicating or converting wood into a ceramic. The resulting porous and anisotropic material retains the precursor microstructure. The wide variety of precursors can yield materials with a range of pore sizes and distribution of pores. The purpose of this work was to study the processing, microstructure, and properties of aluminum/silicon carbide composites. The composites were made by infiltrating molten aluminum into porous wood-derived SIC, which was produced by the reactive melt-infiltration of silicon into pyrolyzed wood. The composite microstructure consisted of interconnected SiC surrounding Al-alloy 'fibers.' The strength, modulus, and toughness were measured in both longitudinal and transverse orientations. The Al → SiC load transfer was investigated with high-energy X-ray diffraction in combination with in-situ compressive loading. The properties in flexure were found to decrease with increasing temperature. Despite the complex microstructure, predictions of the composite flexural modulus and longitudinal fracture toughness were obtained using simple models: Halpin-Tsai bounds and the Ashby et al. model of the effect of ductile particle-reinforcements on the toughness of brittle materials (Ashby et al. 1989), respectively. In addition, the Al/SiC research inspired the investigation of carbon-reinforced copper composites. The goal was to explore the feasibility of making a high-thermal conductivity composite by infiltrating copper into wood-derived carbon. Results indicated that Cu/C composites could be made with pressurized infiltration, but the predicted thermal conductivity was low due to the amorphous wood-derived carbon.

A Microstructural Analysis of Orientation Variation in Epitaxial AlN on Si, Its Probable Origin, and Effect on Subsequent GaN Growth

NASA Technical Reports Server (NTRS)

Beye, R.; George, T.; Yang, J. W.; Khan, M. A.

1996-01-01

A structural examination of aluminum nitride growth on [111] silicon was carried out using transmission electron microscopy. Electron diffraction indicates that the basal planes of the wurtzitic overlayer mimic the orientation of the close-packed planes of the substrate. However, considerable, random rotation in the basal plane and random out-of-plane tilts were evident. This article examines these issues with a structural examination of AlN and GaN/AlN on silicon and compares the findings to those reported in the literature.

Manufacture of silicon-based devices having disordered sulfur-doped surface layers

DOEpatents

Carey, III; Edward, James [Newton, MA; Mazur, Eric [Concord, MA

2008-04-08

The present invention provides methods of fabricating a radiation-absorbing semiconductor wafer by irradiating at least one surface location of a silicon substrate, e.g., an n-doped crystalline silicon, by a plurality of temporally short laser pulses, e.g., femtosecond pulses, while exposing that location to a substance, e.g., SF.sub.6, having an electron-donating constituent so as to generate a substantially disordered surface layer (i.e., a microstructured layer) that incorporates a concentration of that electron-donating constituent, e.g., sulfur. The substrate is also annealed at an elevated temperature and for a duration selected to enhance the charge carrier density in the surface layer. For example, the substrate can be annealed at a temperature in a range of about 700 K to about 900 K.

Silicon macroporous arrays with high aspect ratio prepared by ICP etching

NASA Astrophysics Data System (ADS)

Wang, Guozheng; Yang, Bingchen; Wang, Ji; Yang, Jikai; Duanmu, Qingduo

2018-02-01

This paper reports on a macroporous silicon arrays with high aspect ratio, the pores of which are of 162, 205, 252, 276μm depths with 6, 10, 15 and 20 μm diameters respectively, prepared by Multiplex Inductively Coupled Plasma (ICP) etching. It was shown that there are very differences in process of high aspect ratio microstructures between the deep pores, a closed structure, and deep trenches, a open structure. The morphology and the aspect ratio dependent etching were analyzed and discussed. The macroporous silicon etched by ICP process yield an uneven, re-entrant, notched and ripples surface within the pores. The main factors effecting on the RIE lag of HARP etching are the passivation cycle time, the pressure of reactive chamber, and the platen power of ICP system.

Microstructural evolution of a model, shear-banding micellar solution during shear startup and cessation.

PubMed

López-Barrón, Carlos R; Gurnon, A Kate; Eberle, Aaron P R; Porcar, Lionel; Wagner, Norman J

2014-04-01

We present direct measurements of the evolution of the segmental-level microstructure of a stable shear-banding polymerlike micelle solution during flow startup and cessation in the plane of flow. These measurements provide a definitive, quantitative microstructural understanding of the stages observed during flow startup: an initial elastic response with limited alignment that yields with a large stress overshoot to a homogeneous flow with associated micellar alignment that persists for approximately three relaxation times. This transient is followed by a shear (kink) band formation with a flow-aligned low-viscosity band that exhibits shear-induced concentration fluctuations and coexists with a nearly isotropic band of homogenous, highly viscoelastic micellar solution. Stable, steady banding flow is achieved only after approximately two reptation times. Flow cessation from this shear-banded state is also found to be nontrivial, exhibiting an initial fast relaxation with only minor structural relaxation, followed by a slower relaxation of the aligned micellar fluid with the equilibrium fluid's characteristic relaxation time. These measurements resolve a controversy in the literature surrounding the mechanism of shear banding in entangled wormlike micelles and, by means of comparison to existing literature, provide further insights into the mechanisms driving shear-banding instabilities in related systems. The methods and instrumentation described should find broad use in exploring complex fluid rheology and testing microstructure-based constitutive equations.

SiC layer microstructure in AGR-1 and AGR-2 TRISO fuel particles and the influence of its variation on the effective diffusion of key fission products

DOE PAGES

Gerczak, Tyler J.; Hunn, John D.; Lowden, Richard A.; ...

2016-08-15

Tristructural isotropic (TRISO) coated particle fuel is a promising fuel form for advanced reactor concepts such as high temperature gas-cooled reactors (HTGR) and is being developed domestically under the US Department of Energy’s Nuclear Reactor Technologies Initiative in support of Advanced Reactor Technologies. The fuel development and qualification plan includes a series of fuel irradiations to demonstrate fuel performance from the laboratory to commercial scale. The first irradiation campaign, AGR-1, included four separate TRISO fuel variants composed of multiple, laboratory-scale coater batches. The second irradiation campaign, AGR-2, included TRISO fuel particles fabricated by BWX Technologies with a larger coater representativemore » of an industrial-scale system. The SiC layers of as-fabricated particles from the AGR-1 and AGR-2 irradiation campaigns have been investigated by electron backscatter diffraction (EBSD) to provide key information about the microstructural features relevant to fuel performance. The results of a comprehensive study of multiple particles from all constituent batches are reported. The observations indicate that there were microstructural differences between variants and among constituent batches in a single variant. Finally, insights on the influence of microstructure on the effective diffusivity of key fission products in the SiC layer are also discussed.« less

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

Bishop, Joseph E.; Emery, John M.; Battaile, Corbett C.

Two fundamental approximations in macroscale solid-mechanics modeling are (1) the assumption of scale separation in homogenization theory and (2) the use of a macroscopic plasticity material model that represents, in a mean sense, the multitude of inelastic processes occurring at the microscale. With the goal of quantifying the errors induced by these approximations on engineering quantities of interest, we perform a set of direct numerical simulations (DNS) in which polycrystalline microstructures are embedded throughout a macroscale structure. The largest simulations model over 50,000 grains. The microstructure is idealized using a randomly close-packed Voronoi tessellation in which each polyhedral Voronoi cellmore » represents a grain. An face centered cubic crystal-plasticity model is used to model the mechanical response of each grain. The overall grain structure is equiaxed, and each grain is randomly oriented with no overall texture. The detailed results from the DNS simulations are compared to results obtained from conventional macroscale simulations that use homogeneous isotropic plasticity models. The macroscale plasticity models are calibrated using a representative volume element of the idealized microstructure. Furthermore, we envision that DNS modeling will be used to gain new insights into the mechanics of material deformation and failure.« less

Effect of heat treatment on the characteristics of tool steel deposited by the directed energy deposition process

NASA Astrophysics Data System (ADS)

Park, Jun Seok; Lee, Min-Gyu; Cho, Yong-Jae; Sung, Ji Hyun; Jeong, Myeong-Sik; Lee, Sang-Kon; Choi, Yong-Jin; Kim, Da Hye

2016-01-01

The directed energy deposition process has been mainly applied to re-work and the restoration of damaged steel. Differences in material properties between the base and the newly deposited materials are unavoidable, which may affect the mechanical properties and durability of the part. We investigated the effect of heat treatment on the characteristics of tool steel deposited by the DED process. We prepared general tool steel materials of H13 and D2 that were deposited onto heat-treated substrates of H13 and D2, respectively, using a direct metal tooling process. The hardness and microstructure of the deposited steel before and after heat treatment were investigated. The hardness of the deposited H13 steel was higher than that of wrought H13 steel substrate, while that of the deposited D2 was lower than that of wrought D2. The evolution of the microstructures by deposition and heat treatment varied depending on the materials. In particular, the microstructure of the deposited D2 steel after heat treatment consisted of fine carbides in tempered martensite and it is expected that the deposited D2 steel will have isotropic properties and high hardness after heat treatment.

Polytype Stability and Microstructural Characterization of Silicon Carbide Epitaxial Films Grown on [ {11}overline{{2}} {0} ]- and [0001]-Oriented Silicon Carbide Substrates

NASA Astrophysics Data System (ADS)

Bishop, S. M.; Reynolds, C. L.; Liliental-Weber, Z.; Uprety, Y.; Zhu, J.; Wang, D.; Park, M.; Molstad, J. C.; Barnhardt, D. E.; Shrivastava, A.; Sudarshan, T. S.; Davis, R. F.

2007-04-01

The polytype and surface and defect microstructure of epitaxial layers grown on 4H( {11}overline{{2}} {0} ), 4H(0001) on-axis, 4H(0001) 8° off-axis, and 6H(0001) on-axis substrates have been investigated. High-resolution x-ray diffraction (XRD) revealed the epitaxial layers on 4H( {11}overline{{2}} {0} ) and 4H(0001) 8° off-axis to have the 4H-SiC (silicon carbide) polytype, while the 3C-SiC polytype was identified for epitaxial layers on 4H(0001) and 6H(0001) on-axis substrates. Cathodoluminescence (CL), Raman spectroscopy, and transmission electron microscopy (TEM) confirmed these results. The epitaxial surface of 4H( {11}overline{{2}} {0} ) films was specular with a roughness of 0.16-nm root-mean-square (RMS), in contrast to the surfaces of the other epitaxial layer-substrate orientations, which contained curvilinear boundaries, growth pits (˜3 × 104 cm-2), triangular defects >100 μm, and significant step bunching. Molten KOH etching revealed large defect densities within 4H( {11}overline{{2}} {0} ) films that decreased with film thickness to ˜106 cm-2 at 2.5 μm, while cross-sectional TEM studies showed areas free of defects and an indistinguishable film-substrate interface for 4H( {11}overline{{2}} {0} ) epitaxial layers.

Multiscale microstructures and improved thermoelectric performance of Mg2(Si0.4Sn0.6)Sbx solid solutions

NASA Astrophysics Data System (ADS)

Zhang, Xin; Liu, Hongliang; Li, Songhao; Zhang, Feipeng; Lu, Qingmei; Li, Jingfeng

2014-03-01

A series of Sb-doped Mg2(Si0.4Sn0.6)Sbx (0 ≤ x ≤ 0.025) solid solutions were prepared by an induction melting, Melt Spinning (MS) and Spark Plasma Sintering (SPS) method, namely the non-equilibrium technique MS-SPS, using bulks of Magnesium, Silicon, Tin, and Antimony as raw materials. The non-equilibrium technique generates the unique multiscale microstructures of samples containing micronscale grains and nanoscale precipitates, the multiscale microstructures remarkably make the lattice thermal conductivities decreased, particularly for samples with the nanoscale precipitates having the size of 10-20 nm. Meanwhile, Sb-doping greatly increased the electrical performance of samples. Consequently, the Sb-doping combined with the multiscale microstructures strategy remarkably improves the overall thermoelectric (TE) performance of Sb doped samples, and a high dimensionless figure of merit (ZT) value of up to 1.25 at 723 K is obtained with Mg2(Si0.4Sn0.6)Sb0.02 sample in a relatively wide temperature range.

Crystal growth patterns in DC and pulsed plated galvanic copper films on (1 1 1), (1 0 0) and (1 1 0) copper surfaces

NASA Astrophysics Data System (ADS)

Brown, Delilah A.; Morgan, Sean; Peldzinski, Vera; Brüning, Ralf

2017-11-01

Copper films for printed circuit board applications have to be fine-grained to achieve even filling of vias. Electroplated Cu films on roll annealed Cu substrates may have unacceptably large epitaxial crystals. Here galvanic films were plated on oriented single-crystal Cu substrates from an additive-free electrolyte, as well as DC plating and pulse reverse (PR) plating with additives. The distribution of crystallite orientations was mapped with XRD and compared with the microstructure determined by SEM. For the additive-free bath on [1 1 1] and [1 0 0] oriented surfaces a gradual transition from epitaxial to polycrystalline is seen, while films on [1 1 0] substrates are persistently epitaxial. Without bath additives, twinning is the main mechanism for the transition to polycrystalline texture. For DC plating, additives (carriers, accelerators and levelers) promote fine-grained films with isotropic grain orientations, with films on [1 1 0] substrates being partially isotropic. Plating with carriers and accelerators (no leveler) yields films with many distinct crystallite orientations. These orientations result from up to five steps of recursive twinning. PR plating produces isotropic films with no or very few twins (〈1 1 1〉 and 〈1 0 0〉 substrates, respectively), while on 〈1 1 0〉 oriented surfaces the deposits are about 20% epitaxial.

Soft network materials with isotropic negative Poisson's ratios over large strains.

PubMed

Liu, Jianxing; Zhang, Yihui

2018-01-31

Auxetic materials with negative Poisson's ratios have important applications across a broad range of engineering areas, such as biomedical devices, aerospace engineering and automotive engineering. A variety of design strategies have been developed to achieve artificial auxetic materials with controllable responses in the Poisson's ratio. The development of designs that can offer isotropic negative Poisson's ratios over large strains can open up new opportunities in emerging biomedical applications, which, however, remains a challenge. Here, we introduce deterministic routes to soft architected materials that can be tailored precisely to yield the values of Poisson's ratio in the range from -1 to 1, in an isotropic manner, with a tunable strain range from 0% to ∼90%. The designs rely on a network construction in a periodic lattice topology, which incorporates zigzag microstructures as building blocks to connect lattice nodes. Combined experimental and theoretical studies on broad classes of network topologies illustrate the wide-ranging utility of these concepts. Quantitative mechanics modeling under both infinitesimal and finite deformations allows the development of a rigorous design algorithm that determines the necessary network geometries to yield target Poisson ratios over desired strain ranges. Demonstrative examples in artificial skin with both the negative Poisson's ratio and the nonlinear stress-strain curve precisely matching those of the cat's skin and in unusual cylindrical structures with engineered Poisson effect and shape memory effect suggest potential applications of these network materials.

Electrochemically deposited cobalt/platinum (Co/Pt) film into porous silicon: Structural investigation and magnetic properties

NASA Astrophysics Data System (ADS)

Harraz, F. A.; Salem, A. M.; Mohamed, B. A.; Kandil, A.; Ibrahim, I. A.

2013-01-01

A nanostructured CoPt magnetic film was deposited from a single electrolyte into porous silicon layer by an electrochemical technique, followed by annealing at 600 °C in Ar atmosphere during which the CoPt alloy was converted to L10 ordered phase. Porous silicon with pore diameter between 5 and 100 nm was firstly fabricated by galvanostatic anodization of n-type silicon wafer in the presence of CrO3 as oxidizing agent and ethanol or sodium lauryl sulfate as surfactants. The role of the surfactant on the produced pore size and morphology was investigated by means of UV-vis spectra. As-formed porous silicon was consequently used as a template for the electrodeposition of magnetic CoPt film. The phase formation, microstructure and the magnetic properties were fully analyzed by XRD, FE-SEM, EDS and VSM measurements. It was found that, upon annealing the coercivity was significantly increased due to the transformation to the L10 ordered structure. The saturation magnetization and remanence ratio were also found to increase, indicating no loss of Co content or oxidation reaction after the annealing. Results of synthesis and characterization of CoPt/porous silicon nanocomposite are addressed and thoroughly discussed.

Thermal degradation study of silicon carbide threads developed for advanced flexible thermal protection systems

NASA Technical Reports Server (NTRS)

Tran, Huy Kim; Sawko, Paul M.

1992-01-01

Silicon carbide (SiC) fiber is a material that may be used in advanced thermal protection systems (TPS) for future aerospace vehicles. SiC fiber's mechanical properties depend greatly on the presence or absence of sizing and its microstructure. In this research, silicon dioxide is found to be present on the surface of the fiber. Electron Spectroscopy for Chemical Analysis (ESCA) and Scanning Electron Microscopy (SEM) show that a thin oxide layer (SiO2) exists on the as-received fibers, and the oxide thickness increases when the fibers are exposed to high temperature. ESCA also reveals no evidence of Si-C bonding on the fiber surface on both as-received and heat treated fibers. The silicon oxide layer is thought to signal the decomposition of SiC bonds and may be partially responsible for the degradation in the breaking strength observed at temperatures above 400 C. The variation in electrical resistivity of the fibers with increasing temperature indicates a transition to a higher band gap material at 350 to 600 C. This is consistent with a decomposition of SiC involving silicon oxide formation.

Performance of biomorphic Silicon Carbide as particulate filter in diesel boilers.

PubMed

Orihuela, M Pilar; Gómez-Martín, Aurora; Becerra, José A; Chacartegui, Ricardo; Ramírez-Rico, Joaquín

2017-12-01

Biomorphic Silicon Carbide (bioSiC) is a novel porous ceramic material with excellent mechanical and thermal properties. Previous studies have demonstrated that it may be a good candidate for its use as particle filter media of exhaust gases at medium or high temperature. In order to determine the filtration efficiency of biomorphic Silicon Carbide, and its adequacy as substrate for diesel particulate filters, different bioSiC-samples have been tested in the flue gases of a diesel boiler. For this purpose, an experimental facility to extract a fraction of the boiler exhaust flow and filter it under controlled conditions has been designed and built. Several filter samples with different microstructures, obtained from different precursors, have been tested in this bench. The experimental campaign was focused on the measurement of the number and size of particles before and after placing the samples. Results show that the initial efficiency of filters made from natural precursors is severely determined by the cutting direction and associated microstructure. In biomorphic Silicon Carbide derived from radially cut wood, the initial efficiency of the filter is higher than 95%. Nevertheless, when the cut of the wood is axial, the efficiency depends on the pore size and the permeability, reaching in some cases values in the range 70-90%. In this case, the presence of macropores in some of the samples reduces their efficiency as particle traps. In continuous operation, the accumulation of particles within the porous media leads to the formation of a soot cake, which improves the efficiency except in the case when extra-large pores exist. For all the samples, after a few operation cycles, capture efficiency was higher than 95%. These experimental results show the potential for developing filters for diesel boilers based on biomorphic Silicon Carbide. Copyright © 2017 Elsevier Ltd. All rights reserved.

Sintered magnetic cores of high Bs Fe84.3Si4B8P3Cu0.7 nano-crystalline alloy with a lamellar microstructure

NASA Astrophysics Data System (ADS)

Zhang, Yan; Sharma, Parmanand; Makino, Akihiro

2014-05-01

Fabrication of bulk cores of nano-crystalline Fe84.3Si4B8P3Cu0.7 alloy with a lamellar type of microstructure is reported. Amorphous ribbon flakes of size ˜1.0-2.0 mm were compacted in the bulk form by spark plasma sintering technique at different sintering temperatures. High density (˜96.4%) cores with a uniform nano-granular structure made from α-Fe (˜31 nm) were obtained. These cores show excellent mechanical and soft magnetic properties. The lamellar micro-structure is shown to be important in achieving significantly lower magnetic core loss than the non-oriented silicon steel sheets, commercial powder cores and even the core made of the same alloy with finer and randomly oriented powder particles.

Microstructure measurements in natural waters: Methodology and applications

NASA Astrophysics Data System (ADS)

Roget, Elena; Lozovatsky, Iossif; Sanchez, Xavier; Figueroa, Manuel

2006-08-01

Modern approaches to microstructure data processing, including wavelet denoising, are discussed. The wavelet procedure is applied to small-scale shear signals before estimating the dissipation rate ε and to the temperature/density profiles used to calculate Thorpe scales. Microstructure data obtained on the Mediterranean shelf of Catalonia are used to illustrate various approaches to the Thorpe displacement calculations. It is suggested that the Weibull probability function is an appropriate model for the Thorpe scale distribution. Microstructure measurements from the upper layer of the Boadella reservoir (Catalonia, Spain) support this finding. A new analytical approximation for the 1D Panchev-Kesich spectrum is deduced and the results of ε computation are compared with spectral fitting by the widely used Nasmyth spectrum. Applying the Kraichnan spectral model to compute ε from temperature spectra in the convective-viscous sub-range is examined as an alternative to the Batchelor spectrum. Microstructure measurements taken in Lake Banyoles (Catalonia, Spain) and in the North Atlantic were used for spectral calculations. Statistical analysis of eddy Kb and thermal Kθ diffusivities measured on a shallow shelf of the Black Sea shows the importance of process-orientated domain averaging of the diffusivities in obtaining good correspondence between Kb and Kθ in active turbulent regions. In weakly turbulent, stratified interior layers, the averaged Kb and Kθ differ significantly, which may point to the inapplicability of isotropic formulae used for ε and temperature dissipation χθ estimates, as well as to a dependence of the mixing efficiency γ on the Richardson number or in some cases on regions of fossil turbulence.

Effect of processing induced particle alignment on the fracture toughness and fracture behavior of multiphase dental ceramics.

PubMed

Gonzaga, Carla C; Okada, Cristina Yuri; Cesar, Paulo F; Miranda, Walter G; Yoshimura, Humberto N

2009-11-01

To investigate the processing induced particle alignment on fracture behavior of four multiphase dental ceramics (one porcelain, two glass-ceramics and a glass-infiltrated-alumina composite). Disks (Ø12 mm x 1.1mm-thick) and bars (3 mm x 4 mm x 20 mm) of each material were processed according to manufacturer instructions, machined and polished. Fracture toughness (K(Ic)) was determined by the indentation strength method using 3-point bending and biaxial flexure fixtures for the fracture of bars and disks, respectively. Microstructural and fractographic analyses were performed with scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The isotropic microstructure of the porcelain and the leucite-based glass-ceramic resulted in similar fracture toughness values regardless of the specimen geometry. On the other hand, materials containing second-phase particles with high aspect ratio (lithium disilicate glass-ceramic and glass-infiltrated-alumina composite) showed lower fracture toughness for disk specimens compared to bars. For the lithium disilicate glass-ceramic disks, it was demonstrated that the occurrence of particle alignment during the heat-pressing procedure resulted in an unfavorable pattern that created weak microstructural paths during the biaxial test. For the glass-infiltrated-alumina composite, the microstructural analysis showed that the large alumina platelets tended to align their large surfaces perpendicularly to the direction of particle deposition during slip casting of green preforms. The fracture toughness of dental ceramics with anisotropic microstructure should be determined by means of biaxial testing, since it results in lower values.

Probing near-normally propagating bulk acoustic waves using pseudo-reflection geometry Brillouin spectroscopy

NASA Astrophysics Data System (ADS)

Parsons, L. C.; Andrews, G. T.

2012-09-01

Pseudo-reflection geometry Brillouin spectroscopy can be used to probe acoustic wave dispersion approximately along the surface normal of a material system while avoiding the difficulties associated with specularly reflected light encountered in an ideal reflection configuration. As an example of its application, we show analytically that it can be used to determine both the refractive index and bulk acoustic mode velocities of optically-isotropic non-metallic materials and confirm the utility of the approach via a series of experiments on fused quartz, gallium phosphide, water, and porous silicon films.

Fabrication Techniques for Unusual Electronic Systems: Silicon Microstructures for Photovoltaic Modules

ERIC Educational Resources Information Center

Baca, Alfred

2009-01-01

Electronics that can cover large areas, often referred to as macroelectronics, has received increasing attention over the past decade mainly due to it use in display systems, but increasingly due to certain forms of macroelectronics that can be integrated with thin plastic sheets or elastomeric substrates to yield mechanically flexible and…

Microstructure Evolution and Protrusion of Electroplated Cu-Filled Through-Silicon Vias Subjected to Thermal Cyclic Loading

NASA Astrophysics Data System (ADS)

Chen, Si; An, Tong; Qin, Fei; Chen, Pei

2017-10-01

Through-silicon vias (TSVs) have become an important technology for three-dimensional integrated circuit (3D IC) packaging. Protrusion of electroplated Cu-filled vias is a critical reliability issue for TSV technology. In this work, thermal cycling tests were carried out to identify how the microstructure affects protrusion during thermal cycling. Cu protrusion occurs when the loading temperature is higher than 149°C. During the first five thermal cycles, the grain size of Cu plays a dominant role in the protrusion behavior. Larger Cu grain size before thermal cycling results in greater Cu protrusion. With increasing thermal cycle number, the effect of the Cu grain size reduces and the microstrain begins to dominate the Cu protrusion behavior. Higher magnitude of microstrain within Cu results in greater protrusion increment during subsequent thermal cycles. When the thermal cycle number reaches 25, the protrusion rate of Cu slows down due to strain hardening. After 30 thermal cycles, the Cu protrusion stabilizes within the range of 1.92 μm to 2.09 μm.

Corrosion Behavior of Heat-Treated AlSi10Mg Manufactured by Laser Powder Bed Fusion.

PubMed

Cabrini, Marina; Calignano, Flaviana; Fino, Paolo; Lorenzi, Sergio; Lorusso, Massimo; Manfredi, Diego; Testa, Cristian; Pastore, Tommaso

2018-06-21

This experimental work is aimed at studying the effect of microstructural modifications induced by post-processing heat treatments on the corrosion behavior of silicon-aluminum alloys produced by means of laser powder bed fusion (LPBF). The manufacturing technique leads to microstructures characterized by the presence of melt pools, which are quite different compared to casting alloys. In this study, the behavior of an AlSi10Mg alloy was evaluated by means of intergranular corrosion tests according to ISO 11846 standard on heat-treated samples ranging from 200 to 500 °C as well as on untreated samples. We found that temperatures above 200 °C reduced microhardness of the alloy, and different corrosion morphologies occurred due to the modification of both size and distribution of silicon precipitates. Selective penetrating attacks occurred at melt pool borders. The intergranular corrosion phenomena were less intense for as-produced specimens without heat treatments compared to the heat-treated specimens at 200 and 300 °C. General corrosion morphologies were noticed for specimens heat treated at temperatures exceeding 400 °C.

Characteristics research of pressure sensor based on nanopolysilicon thin films resistors

NASA Astrophysics Data System (ADS)

Zhao, Xiaofeng; Li, Dandan; Wen, Dianzhong

2017-10-01

To further improve the sensitivity temperature characteristics of pressure sensor, a kind of pressure sensor taking nanopolysilicon thin films as piezoresistors is proposed in this paper. On the basis of the microstructure analysis by X-ray diffraction (XRD) and scanning electron microscope (SEM) tests, the preparing process of nanopolysilicon thin films is optimized. The effects of film thickness and annealing temperature on the micro-structure of nanopolysilicon thin films were studied, respectively. In order to realize the measurement of external pressure, four nanopolysilicon thin films resistors were arranged at the edges of square silicon diaphragm connected to a Wheatstone bridge, and the chip of the sensor was designed and fabricated on a 〈100〉 orientation silicon wafer by microelectromechanical system (MEMS) technology. Experimental result shows that when I = 6.80 mA, the sensitivity of the sensor PS-1 is 0.308 mV/kPa, and the temperature coefficient of sensitivity (TCS) is about -1742 ppm/∘C in the range of -40-140∘C. It is possible to obviously improve the sensitivity temperature characteristics of pressure sensor by the proposed sensors.

Self-organized microstructures induced by MeV ion beam on silicon surface

NASA Astrophysics Data System (ADS)

Ahmad, Muthanna

2017-02-01

Micro patterning of self organized structure on silicon surface is induced by ion implantation of energetic (MeV) copper ions. This work reports for the first time the ability of using energetic ions for producing highly ordered ripples and dots of micro sizes. The experiments are realized at the Tandem ion beam accelerator (3 MV) at the IBA laboratory of the Atomic Energy Commission of Syria. Similarly to nano patterning formed by slow ions, the formation of micro patterned structures dots and ripples is observed to be depending on the angle of ion beam incidence, energy and ion fluence. The observation of such microstructures formation is limited to a range of ion energies (few MeV) at fluence higher than 1.75 × 1017 ion cm-2. The patterned surface layer is completely amorphousized by the ion implantation. Shadowing effect is observed in the formation of microripples and superstructures in the top of ripples. The superstructure develops new morphology that is not observed before. This morphology has butterfly shape with symmetry in its structure.

Joining and Integration of Silicon Carbide-Based Materials for High Temperature Applications

NASA Technical Reports Server (NTRS)

Halbig, Michael C.; Singh, Mrityunjay

2016-01-01

Advanced joining and integration technologies of silicon carbide-based ceramics and ceramic matrix composites are enabling for their implementation into wide scale aerospace and ground-based applications. The robust joining and integration technologies allow for large and complex shapes to be fabricated and integrated with the larger system. Potential aerospace applications include lean-direct fuel injectors, thermal actuators, turbine vanes, blades, shrouds, combustor liners and other hot section components. Ground based applications include components for energy and environmental systems. Performance requirements and processing challenges are identified for the successful implementation different joining technologies. An overview will be provided of several joining approaches which have been developed for high temperature applications. In addition, various characterization approaches were pursued to provide an understanding of the processing-microstructure-property relationships. Microstructural analysis of the joint interfaces was conducted using optical, scanning electron, and transmission electron microscopy to identify phases and evaluate the bond quality. Mechanical testing results will be presented along with the need for new standardized test methods. The critical need for tailoring interlayer compositions for optimum joint properties will also be highlighted.

Observation of rare-earth segregation in silicon nitride ceramics at subnanometre dimensions.

PubMed

Shibata, Naoya; Pennycook, Stephen J; Gosnell, Tim R; Painter, Gayle S; Shelton, William A; Becher, Paul F

2004-04-15

Silicon nitride (Si3N4) ceramics are used in numerous applications because of their superior mechanical properties. Their intrinsically brittle nature is a critical issue, but can be overcome by introducing whisker-like microstructural features. However, the formation of such anisotropic grains is very sensitive to the type of cations used as the sintering additives. Understanding the origin of dopant effects, central to the design of high-performance Si3N4 ceramics, has been sought for many years. Here we show direct images of dopant atoms (La) within the nanometre-scale intergranular amorphous films typically found at grain boundaries, using aberration corrected Z-contrast scanning transmission electron microscopy. It is clearly shown that the La atoms preferentially segregate to the amorphous/crystal interfaces. First-principles calculations confirm the strong preference of La for the crystalline surfaces, which is essential for forming elongated grains and a toughened microstructure. Whereas principles of micrometre-scale structural design are currently used to improve the mechanical properties of ceramics, this work represents a step towards the atomic-level structural engineering required for the next generation of ceramics.

Phonon Scattering and Confinement in Crystalline Films

NASA Astrophysics Data System (ADS)

Parrish, Kevin D.

The operating temperature of energy conversion and electronic devices affects their efficiency and efficacy. In many devices, however, the reference values of the thermal properties of the materials used are no longer applicable due to processing techniques performed. This leads to challenges in thermal management and thermal engineering that demand accurate predictive tools and high fidelity measurements. The thermal conductivity of strained, nanostructured, and ultra-thin dielectrics are predicted computationally using solutions to the Boltzmann transport equation. Experimental measurements of thermal diffusivity are performed using transient grating spectroscopy. The thermal conductivities of argon, modeled using the Lennard-Jones potential, and silicon, modeled using density functional theory, are predicted under compressive and tensile strain from lattice dynamics calculations. The thermal conductivity of silicon is found to be invariant with compression, a result that is in disagreement with previous computational efforts. This difference is attributed to the more accurate force constants calculated from density functional theory. The invariance is found to be a result of competing effects of increased phonon group velocities and decreased phonon lifetimes, demonstrating how the anharmonic contribution of the atomic potential can scale differently than the harmonic contribution. Using three Monte Carlo techniques, the phonon-boundary scattering and the subsequent thermal conductivity reduction are predicted for nanoporous silicon thin films. The Monte Carlo techniques used are free path sampling, isotropic ray-tracing, and a new technique, modal ray-tracing. The thermal conductivity predictions from all three techniques are observed to be comparable to previous experimental measurements on nanoporous silicon films. The phonon mean free paths predicted from isotropic ray-tracing, however, are unphysical as compared to those predicted by free path sampling. Removing the isotropic assumption, leading to the formulation of modal ray-tracing, corrects the mean free path distribution. The effect of phonon line-of-sight is investigated in nanoporous silicon films using free path sampling. When the line-of-sight is cut off there is a distinct change in thermal conductivity versus porosity. By analyzing the free paths of an obstructed phonon mode, it is concluded that the trend change is due to a hard upper limit on the free paths that can exist due to the nanopore geometry in the material. The transient grating technique is an optical contact-less laser based experiment for measuring the in-plane thermal diffusivity of thin films and membranes. The theory of operation and physical setup of a transient grating experiment is detailed. The procedure for extracting the thermal diffusivity from the raw experimental signal is improved upon by removing arbitrary user choice in the fitting parameters used and constructing a parameterless error minimizing procedure. The thermal conductivity of ultra-thin argon films modeled with the Lennard-Jones potential is calculated from both the Monte Carlo free path sampling technique and from explicit reduced dimensionality lattice dynamics calculations. In these ultra-thin films, the phonon properties are altered in more than a perturbative manner, referred to as the confinement regime. The free path sampling technique, which is a perturbative method, is compared to a reduced dimensionality lattice dynamics calculation where the entire film thickness is taken as the unit cell. Divergence in thermal conductivity magnitude and trend is found at few unit cell thick argon films. Although the phonon group velocities and lifetimes are affected, it is found that alterations to the phonon density of states are the primary cause of the deviation in thermal conductivity in the confinement regime.

Preparation of uranium fuel kernels with silicon carbide nanoparticles using the internal gelation process

NASA Astrophysics Data System (ADS)

Hunt, R. D.; Silva, G. W. C. M.; Lindemer, T. B.; Anderson, K. K.; Collins, J. L.

2012-08-01

The US Department of Energy continues to use the internal gelation process in its preparation of tristructural isotropic coated fuel particles. The focus of this work is to develop uranium fuel kernels with adequately dispersed silicon carbide (SiC) nanoparticles, high crush strengths, uniform particle diameter, and good sphericity. During irradiation to high burnup, the SiC in the uranium kernels will serve as getters for excess oxygen and help control the oxygen potential in order to minimize the potential for kernel migration. The hardness of SiC required modifications to the gelation system that was used to make uranium kernels. Suitable processing conditions and potential equipment changes were identified so that the SiC could be homogeneously dispersed in gel spheres. Finally, dilute hydrogen rather than argon should be used to sinter the uranium kernels with SiC.

Tensile Strength and Microstructural Characterization of Uncoated and Coated HPZ Ceramic Fibers

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Wheeler, Donald R.; Dickerson, Robert M.

1996-01-01

Tensile strengths of as-received HPZ fiber and those surface coated with BN, BN/SiC, and BN/Si3N4 have been determined at room temperature using a two-parameter Weibull distribution. Nominally approx. 0.4 micron BN and 0.2 micron SiC or Si3N4 coatings were deposited on the fibers by chemical vapor deposition using a continuous reactor. The average tensile strength of uncoated HPZ fiber was 2.0 +/- 0.56 GPa (290 +/- 81 ksi) with a Weibull modulus of 4.1. For the BN coated fibers, the average strength and the Weibull modulus increased to 2.39 +/- 0.44 GPa (346 +/- 64 ksi) and 6.5, respectively. The HPZ/BN/SiC fibers showed an average strength of 2.0 +/- 0.32 GPa (290 +/- 47 ksi) and Weibull modulus of 7.3. Average strength of the fibers having a dual BN/Si3N4 surface coating degraded to 1.15 +/- 0.26 GPa (166 +/- 38 ksi) with a Weibull modulus of 5.3. The chemical composition and thickness of the fiber coatings were determined using scanning Auger analysis. Microstructural analysis of the fibers and the coatings was carried out by scanning electron microscopy and transmission electron microscopy. A microporous silica-rich layer approx. 200 nm thick is present on the as-received HPZ fiber surface. The BN coatings on the fibers are amorphous to partly turbostratic and contaminated with carbon and oxygen. Silicon carbide coating was crystalline whereas the silicon nitride coating was amorphous. The silicon carbide and silicon nitride coatings are non-stoichiometric, non-uniform, and granular. Within a fiber tow, the fibers on the outside had thicker and more granular coatings than those on the inside.

Self-formed cylindrical microcapillaries through surface migration of silicon and their application to single-cell analysis

NASA Astrophysics Data System (ADS)

Zeng, Fan; Luo, Yuan; Yobas, Levent; Wong, Man

2013-05-01

Surface migration of monocrystalline silicon has been applied to demonstrate self-formed cylindrical microcapillaries with diameters from 0.8 to 2.8 µm based on the microstructured substrate topography. The microcapillaries are entirely enclosed in silicon and can be conveniently etched to create fluidic access ports and microchannels for their subsequent integration into functional microfluidic devices. Moreover, the microcapillaries can be thermally oxidized through their access ports with silica walls remain intact upon release from surrounding silicon in an effort to enhance optical clarity. Straight microcapillaries and microcapillaries with perpendicular turns and crossings (junctions) have all been fabricated and validated for fluidic continuity with a fluorescein solution pumped through. The utility of the microcapillaries has been showcased on particle traps in which biological cells are probed for single-cell impedance spectroscopy. The approach disclosed, given its full compatibility with semiconductor device fabrication, offers great potential towards intelligent cell and molecule-based devices merging microelectronics and microfluidics.

Silicon strain gages bonded on stainless steel using glass frit for strain sensor applications

NASA Astrophysics Data System (ADS)

Zhang, Zongyang; Cheng, Xingguo; Leng, Yi; Cao, Gang; Liu, Sheng

2014-05-01

In this paper, a steel pressure sensor using strain gages bonded on a 17-4 PH stainless steel (SS) diaphragm based on glass frit technology is proposed. The strain gages with uniform resistance are obtained by growing an epi-silicon layer on a single crystal silicon wafer using epitaxial deposition technique. The inorganic glass frits are used as the bonding material between the strain gages and the 17-4 PH SS diaphragm. Our results show that the output performances of sensors at a high temperature of 125 °C are almost equal those at room temperature, which indicates that the glass frit bonding is a good method and may lead to a significant advance in the high temperature applicability of silicon strain gage sensors. Finally, the microstructure of the cured organic adhesive and the fired glass frit are compared. It may be concluded that the defects of the cured organic adhesive deteriorate the hysteresis and repeatability errors of the sensors.

A review of molecular beam epitaxy of ferroelectric BaTiO 3 films on Si, Ge and GaAs substrates and their applications

DOE PAGES

Mazet, Lucie; Yang, Sang Mo; Kalinin, Sergei V.; ...

2015-06-30

SrTiO 3 epitaxial growth by molecular beam epitaxy (MBE) on silicon has opened up the route to the monolithic integration of various complex oxides on the complementary metal-oxide-semiconductor silicon platform. Among functional oxides, ferroelectric perovskite oxides offer promising perspectives to improve or add functionalities on-chip. We review the growth by MBE of the ferroelectric compound BaTiO 3 on silicon (Si), germanium (Ge) and gallium arsenide (GaAs) and we discuss the film properties in terms of crystalline structure, microstructure and ferroelectricity. Lastly, we review the last developments in two areas of interest for the applications of BaTiO 3 films on silicon,more » namely integrated photonics, which benefits from the large Pockels effect of BaTiO 3, and low power logic devices, which may benefit from the negative capacitance of the ferroelectric.« less

Microstructured Surface Arrays for Injection of Zebrafish Larvae

PubMed Central

Irimia, Daniel

2017-01-01

Abstract Microinjection of zebrafish larvae is an essential technique for delivery of treatments, dyes, microbes, and xenotransplantation into various tissues. Although a number of casts are available to orient embryos at the single-cell stage, no device has been specifically designed to position hatching-stage larvae for microinjection of different tissues. In this study, we present a reusable silicone device consisting of arrayed microstructures, designed to immobilize 2 days postfertilization larvae in lateral, ventral, and dorsal orientations, while providing maximal access to target sites for microinjection. Injection of rhodamine dextran was used to demonstrate the utility of this device for precise microinjection of multiple anatomical targets. PMID:28151697

Microstructural and strength stability of CVD SiC fibers in argon environment

NASA Technical Reports Server (NTRS)

Bhatt, Ramakrishna T.; Hull, David R.

1991-01-01

The room temperature tensile strength and microstructure of three types of commercially available chemically vapor deposited silicon carbide fibers were measured after 1, 10, and 100 hour heat treatments under argon pressures of 0.1 to 310 MPa at temperatures to 2100 C. Two types of fiber had carbon-rich surface coatings and the other contained no coating. All three fiber types showed strength degradation beyond 1400 C. Time and temperature of exposure had greater influence on strength degradation than argon pressure. Recrystallization and growth of near stoichiometric SiC grains appears to be the dominant mechanism for the strength degradation.

Microstructural and strength stability of CVD SiC fibers in argon environments

NASA Technical Reports Server (NTRS)

Bhatt, Ramakrishna T.; Hull, David R.

1991-01-01

The room temperature tensile strength and microstructure of three types of commercially available chemically vapor deposited silicon carbide fibers were measured after 1, 10, and 100 hour heat treatments under argon pressures of 0.1 to 310 MPa at temperatures to 2100 C. Two types of fiber had carbon-rich surface coatings and the other contained no coating. All three fiber types showed strength degradation beyond 1400 C. Time and temperature of exposure had greater influence on strength degradation than argon pressure. Recrystallization and growth of near stoichiometric SiC grains appears to be the dominant mechanism for the strength degradation.

Nonlinear Conductive Behaviour of Silver Nanowires/Silicone Rubber Composites

NASA Astrophysics Data System (ADS)

Lu, Pin; Qu, Zhaoming; Wang, Qingguo; Bai, Liyun; Zhao, Shiyang

2018-01-01

Silver nanowires with an average length of 10 μm and diameter of about 90 nm have been synthesized by polyol reduction of silver nitrate in the presence of polyvinylpyrrolidone(PVP). Silver nanowires (AgNWs)/silicone rubber (SR) composites have been made by mixing silver nanowires into silicone rubber. The nonlinear response of AgNWs/SR composites under high electric field is investigated. The nonlinear Conductive behavior of composites is considered as a competitive process of several effects. From the perspective of the microstructure of composites, the conductive path is established by the quantum tunnel effect between silver nanowires. The influence factors on the conductivity of composites are discussed and analyzed. The results show that the AgNWs/SR composites with nonlinear conductive properties are of great potential application in electromagnetic protection of electron device and system.

Micromachined electrical cauterizer

DOEpatents

Lee, Abraham P.; Krulevitch, Peter A.; Northrup, M. Allen

1999-01-01

A micromachined electrical cauterizer. Microstructures are combined with microelectrodes for highly localized electro cauterization. Using boron etch stops and surface micromachining, microneedles with very smooth surfaces are made. Micromachining also allows for precision placement of electrodes by photolithography with micron sized gaps to allow for concentrated electric fields. A microcauterizer is fabricated by bulk etching silicon to form knife edges, then parallelly placed microelectrodes with gaps as small as 5 .mu.m are patterned and aligned adjacent the knife edges to provide homeostasis while cutting tissue. While most of the microelectrode lines are electrically insulated from the atmosphere by depositing and patterning silicon dioxide on the electric feedthrough portions, a window is opened in the silicon dioxide to expose the parallel microelectrode portion. This helps reduce power loss and assist in focusing the power locally for more efficient and safer procedures.

Micromachined electrical cauterizer

DOEpatents

Lee, A.P.; Krulevitch, P.A.; Northrup, M.A.

1999-08-31

A micromachined electrical cauterizer is disclosed. Microstructures are combined with microelectrodes for highly localized electro cauterization. Using boron etch stops and surface micromachining, microneedles with very smooth surfaces are made. Micromachining also allows for precision placement of electrodes by photolithography with micron sized gaps to allow for concentrated electric fields. A microcauterizer is fabricated by bulk etching silicon to form knife edges, then parallelly placed microelectrodes with gaps as small as 5 {mu}m are patterned and aligned adjacent the knife edges to provide homeostasis while cutting tissue. While most of the microelectrode lines are electrically insulated from the atmosphere by depositing and patterning silicon dioxide on the electric feedthrough portions, a window is opened in the silicon dioxide to expose the parallel microelectrode portion. This helps reduce power loss and assist in focusing the power locally for more efficient and safer procedures. 7 figs.

Effect of the carrier gas flow rate on the microstructure evolution and the generation of the charged nanoparticles during silicon chemical vapor deposition.

PubMed

Youn, Woong-Kyu; Kim, Chan-Soo; Hwang, Nong-Moon

2013-10-01

The generation of charged nanoparticles in the gas phase has been continually reported in many chemical vapor deposition processes. Charged silicon nanoparticles in the gas phase were measured using a differential mobility analyzer connected to an atmospheric-pressure chemical vapor deposition reactor at various nitrogen carrier gas flow rates (300-1000 standard cubic centimeter per minute) under typical conditions for silicon deposition at the reactor temperature of 900 degrees C. The carrier gas flow rate affected not only the growth behavior of nanostructures but also the number concentration and size distribution of both negatively and positively charged nanoparticles. As the carrier gas flow rate decreased, the growth behavior changed from films to nanowires, which grew without catalytic metal nanoparticles on a quartz substrate.

Formation of Widmanstätten Austenite in Strip Cast Grain-Oriented Silicon Steel

NASA Astrophysics Data System (ADS)

Song, Hong-Yu; Liu, Hai-Tao; Wang, Guo-Dong; Jonas, John J.

2017-04-01

The formation of Widmanstätten austenite was studied in strip cast grain-oriented silicon steel. The microstructure was investigated by optical microscopy and scanning electron microscopy. The orientations of the ferrite, Widmanstätten austenite, and martensite were determined using electron backscatter diffraction. The Widmanstätten austenite exhibits a lath-like shape and nucleates directly on the ferrite grain boundaries. This differs significantly from earlier work on duplex stainless steels. The orientation relationship between the Widmanstätten austenite and the parent ferrite is closer to Kurdjumov-Sachs than to Nishiyama-Wassermann. The ferrite boundaries migrate so as to accommodate the habit planes of the laths, leading to the presence of zigzag boundaries in the as-cast strip. Carbon partitioning into the Widmanstätten austenite and silicon partitioning into the parent ferrite were observed.

Study of sintering temperature on the structure of silicon carbide membrane

NASA Astrophysics Data System (ADS)

Sadighzadeh, A.; Mashayekhan, Sh.; Nedaie, B.; Ghorashi, A. H.

2014-09-01

Study of the microstructure of silicon carbide (SiC) membrane as a function of sintering temperature and the percentage amount of additive kaolin is the outcome of the experimental fabrications presented in this paper. The SEM micrographs are used to investigate the impact of above parameters on the porosity of membrane. The experimental results show that the rise in the temperature causes more sintering of powder particles, growing granules, augmentation of the number of pores and consequently increasing the total porosity of membrane. Using XRD analyses, it is found that SiC amorphous phase is highly sensitive to the temperature and its crystallization physically grows with temperature increase.

Microstructure and orientation effects on properties of discontinuous silicon carbide/aluminum composites

NASA Technical Reports Server (NTRS)

Mcdanels, D. L.; Hoffman, C. A.

1984-01-01

Composite panels containing up to 40 vol % discontinuous silicon carbide SiC whisker, nodule, or particulate reinforcement in several aluminum matrices are commercially fabricated and the mechanical properties and microstructual characteristics are evaluated. The yield and tensile strengths and the ductility are controlled primarily by the matrix alloy, the temper condition, and the reinforcement content. Particulate and nodule reinforcements are as effective as whisker reinforcement. Increased ductility is attributed to purer, more uniform starting materials and to more mechanical working during fabrication. Comparing mechanical properties with those of other aluminum alloys shows that these low cost, lightweight composites demonstrate very good potential for application to aerospace structures.

The effect of calcination conditions on the graphitizability of novel synthetic and coal-derived cokes

NASA Astrophysics Data System (ADS)

Bennett, Barbara Ellen

The effects of calcination heating rate and ultimate calcination temperature upon calcined coke and subsequent graphitic material microstructures were studied for materials prepared from three different precursors. The pitch precursors used were Mitsubishi AR pitch (a synthetic, 100% mesophase pitch), the NMP-extracted portion of a raw coal, and the NMP-extracted fraction of a coal liquefaction residue obtained from an HTI pilot plant. These materials were all green-coked under identical conditions. Optical microscopy confirmed that the Mitsubishi coke was very anisotropic and the HTI coke was nearly as anisotropic. The coke produced from the direct coal extract was very isotropic. Crystalline development during calcination heating was verified by high-temperature x-ray diffraction. Experiments were performed to ascertain the effects of varying calcination heating rate and ultimate temperature. It was determined that calcined coke crystallite size increased with increasing temperature for all three materials but was found to be independent of heating rate. The graphene interplanar spacing decreased with increasing temperature for the isotropic NMP-extract material but increased with increasing temperature for the anisotropic materials---Mitsubishi and HTI cokes. Graphene interplanar spacing was also found to be independent of heating rate. Calcined coke real densities were, likewise, found to be independent of heating rate. The anisotropic cokes (Mitsubishi and HTI) exhibited increasing real density with increasing calcination temperature. The NMP-extract coke increased in density up to 1050°C and then suffered a dramatic reduction in real density when heated to 1250°C. This is indicative of puffing. Since there was no corresponding disruption in the crystalline structure, the puffing phenomena was determined to be intercrystalline rather than intracrystalline. After the calcined cokes were graphitized (under identical conditions), the microstructures were re-evaluated. The crystalline properties of the graphitic materials appeared to be independent of calcination conditions---both heating rate and final temperature---for all samples prepared from any given precursor. The calcination step did not influence the microstructure or graphitizability of any of the three materials. The crystallinity of a graphitic material appears to be dictated by the properties of the green coke and cannot be altered by manipulating calcination conditions.

Microstructural optimization of solid-state sintered silicon carbide

NASA Astrophysics Data System (ADS)

Vargas-Gonzalez, Lionel R.

Silicon carbide armor, manufactured through solid-state sintering, liquid-phase sintering, and hot-pressing, is being used by the United States Armed Forces for personal and vehicle protection. There is a lack of consensus, however, on which process results in the best-performing ballistic armor. Previous studies have shown that hot-pressed ceramics processed with secondary oxide and/or rare earth oxides, which exhibit high fracture toughness, perform well in handling and under ballistic impact. This high toughness is due to the intergranular nature of the fracture, creating a tortuous path for cracks and facilitating crack deflection and bridging. However, it has also been shown that higher-hardness sintered SiC materials might perform similarly or better to hot-pressed armor, in spite of the large fracture toughness deficit, if the microstructure (density, grain size, purity) of these materials are improved. In this work, the development of theoretically-dense, clean grain boundary, high hardness solid-state sintered silicon carbide (SiC) armor was pursued. Boron carbide and graphite (added as phenolic resin to ensure the carbon is finely dispersed throughout the microstructure) were used as the sintering aids. SiC batches between 0.25--4.00 wt.% carbon were mixed and spray dried. Cylindrical pellets were pressed at 13.7 MPa, cold-isostatically pressed (CIP) at 344 MPa, sintered under varying sintering soaking temperatures and heating rates, and varying post hot-isostatic pressing (HIP) parameters. Carbon additive amounts between 2.0--2.5 wt.% (based on the resin source), a 0.36 wt.% B4C addition, and a 2050°C sintering soak yielded parts with high sintering densities (˜95.5--96.5%) and a fine, equiaxed microstructure (d50 = 2.525 mum). A slow ramp rate (10°C/min) prevented any occurrence of abnormal grain growth. Post-HIPing at 1900°C removed the remaining closed porosity to yield a theoretically-dense part (3.175 g/cm3, according to rule of mixtures). These parts exhibited higher density and finer microstructure than a commercially-available sintered SiC from Saint-Gobain (Hexoloy Enhanced, 3.153 g/cm3 and d50 = 4.837 mum). Due to the optimized microstructure, Verco SiC parts exhibited the highest Vickers (2628.30 +/- 44.13 kg/mm 2) and Knoop (2098.50 +/- 24.8 kg/mm2) hardness values of any SiC ceramic, and values equal to those of the "gold standard" hot-pressed boron carbide (PAD-B4C). While the fracture toughness of hot-pressed SiC materials (˜4.5 MPa m ) are almost double that of Verco SiC (2.4 MPa m ), Verco SiC is a better performing ballistic product, implying that the higher hardness of the theoretically-dense, clean-grain boundary, fine-grained SiC is the defining mechanical property for optimization of ballistic behavior.

Microstructure factor and mechanical and electronic properties of hydrogenated amorphous and nanocrystalline silicon thin-films for microelectromechanical systems applications

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

Mouro, J.; Gualdino, A.; Chu, V.

2013-11-14

Thin-film silicon allows the fabrication of MEMS devices at low processing temperatures, compatible with monolithic integration in advanced electronic circuits, on large-area, low-cost, and flexible substrates. The most relevant thin-film properties for applications as MEMS structural layers are the deposition rate, electrical conductivity, and mechanical stress. In this work, n{sup +}-type doped hydrogenated amorphous and nanocrystalline silicon thin-films were deposited by RF-PECVD, and the influence of the hydrogen dilution in the reactive mixture, the RF-power coupled to the plasma, the substrate temperature, and the deposition pressure on the structural, electrical, and mechanical properties of the films was studied. Three differentmore » types of silicon films were identified, corresponding to three internal structures: (i) porous amorphous silicon, deposited at high rates and presenting tensile mechanical stress and low electrical conductivity, (ii) dense amorphous silicon, deposited at intermediate rates and presenting compressive mechanical stress and higher values of electrical conductivity, and (iii) nanocrystalline silicon, deposited at very low rates and presenting the highest compressive mechanical stress and electrical conductivity. These results show the combinations of electromechanical material properties available in silicon thin-films and thus allow the optimized selection of a thin silicon film for a given MEMS application. Four representative silicon thin-films were chosen to be used as structural material of electrostatically actuated MEMS microresonators fabricated by surface micromachining. The effect of the mechanical stress of the structural layer was observed to have a great impact on the device resonance frequency, quality factor, and actuation force.« less

A design-centered approach in developing Al-Si-based light-weight alloys with enhanced fatigue life and strength

NASA Astrophysics Data System (ADS)

Fan, Jinghong; Hao, Su

2004-01-01

Material heterogeneities and discontinuities such as porosity, second phase particles, and other defects at meso/micro/nano scales, determine fatigue life, strength, and fracture behavior of aluminum castings. In order to achieve better performance of these alloys, a design-centered computer-aided renovative approach is proposed. Here, the term “design-centered” is used to distinguish the new approach from the traditional trial-and-error design approach by formulating a clear objective, offering a scientific foundation, and developing a computer-aided effective tool for the alloy development. A criterion for tailoring “child” microstructure, obtained by “parent” microstructure through statistical correlation, is proposed for the fatigue design at the initial stage. A dislocations pileup model has been developed. This dislocation model, combined with an optimization analysis, provides an analytical-based solution on a small scale for silicon particles and dendrite cells to enhance both fatigue performance and strength for pore-controlled castings. It can also be used to further tailor microstructures. In addition, a conceptual damage sensitivity map for fatigue life design is proposed. In this map there are critical pore sizes, above which fatigue life is controlled by pores; otherwise it is controlled by other mechanisms such as silicon particles and dendrite cells. In the latter case, the proposed criteria and the dislocation model are the foundations of a guideline in the design-centered approach to maximize both the fatigue life and strength of Al-Si-based light-weight alloy.

Influence of Austempering Heat Treatment on Microstructure and Mechanical Properties of Medium Carbon High Silicon Steel

NASA Astrophysics Data System (ADS)

Palaksha, P. A.; Ravishankar, K. S.

2017-08-01

In the present investigation, the influence of austempering heat treatment on the microstructure and mechanical properties of medium carbon high silicon steel was evaluated. The test specimens were machined from the as-received steel and were first austenitised at 900 °C for 45 minutes, followed by austempering heat treatment in salt bath at various temperatures 300 °C, 350 °C and 400 °C for a fixed duration of two hours, after that those specimens were air-cooled to room temperature. The characterization studies were carried out using optical microscope, scanning electron microscope (SEM) and x-ray diffractometer (XRD) and then correlated to the hardness and tensile properties. Results indicate that, the specimens austempered at lower temperature i.e. at 300 °C, which offered high hardness, tensile strength and lower ductility (1857 MPa and 13.3 %) due to the presence of acicular bainite i.e. lower bainite and also some martensite in the microstructure. At 350 °C, reduction in the tensile strength and hardness was observed, but comparatively higher ductility, which was favored by the presence of bainite laths i.e. upper bainitic structure along with higher retained austenite content. Finally at 400 °C, reduction in both ductility and tensile strength was observed, which is due to the precipitation of carbides between the banite laths, however good strain hardening response was observed at austempering temperatures of 350 °C and 400 °C.

Micro-opto-mechanical devices and systems using epitaxial lift off

NASA Technical Reports Server (NTRS)

Camperi-Ginestet, C.; Kim, Young W.; Wilkinson, S.; Allen, M.; Jokerst, N. M.

1993-01-01

The integration of high quality, single crystal thin film gallium arsenide (GaAs) and indium phosphide (InP) based photonic and electronic materials and devices with host microstructures fabricated from materials such as silicon (Si), glass, and polymers will enable the fabrication of the next generation of micro-opto-mechanical systems (MOMS) and optoelectronic integrated circuits. Thin film semiconductor devices deposited onto arbitrary host substrates and structures create hybrid (more than one material) near-monolithic integrated systems which can be interconnected electrically using standard inexpensive microfabrication techniques such as vacuum metallization and photolithography. These integrated systems take advantage of the optical and electronic properties of compound semiconductor devices while still using host substrate materials such as silicon, polysilicon, glass and polymers in the microstructures. This type of materials optimization for specific tasks creates higher performance systems than those systems which must use trade-offs in device performance to integrate all of the function in a single material system. The low weight of these thin film devices also makes them attractive for integration with micromechanical devices which may have difficulty supporting and translating the full weight of a standard device. These thin film devices and integrated systems will be attractive for applications, however, only when the development of low cost, high yield fabrication and integration techniques makes their use economically feasible. In this paper, we discuss methods for alignment, selective deposition, and interconnection of thin film epitaxial GaAs and InP based devices onto host substrates and host microstructures.

Effects of Mn addition on microstructure and hardness of Al-12.6Si alloy

NASA Astrophysics Data System (ADS)

Biswas, Prosanta; Patra, Surajit; Mondal, Manas Kumar

2018-03-01

In this work, eutectic Al-12.6Si alloy with and without manganese (Mn) have been developed through gravity casting route. The effect of Mn concentration (0.0 wt.%, 1 wt%, 2 wt% and 3 wt%) on microstructural morphology and hardness property of the alloy has been investigated. The eutectic Al-12.6 Si alloy exhibits the presence of combine plate, needle and rod-like eutectic silicon phase with very sharp corners and coarser primary silicon particles within the α-Al phase. In addition of 1wt.% of Mn in the eutectic Al-12.6Si alloy, sharp corners of the primary Si and needle-like eutectic Si are became blunt and particles size is reduced. Further, increase in Mn concentration (2.0 wt.%) in the Al-12.6Si alloy, irregular plate shape Al6(Mn,Fe) intermetallics are formed inside the α-Al phase, but the primary and eutectic phase morphology is similar to the eutectic Al-12.6Si alloy. The volume fraction of Al6(Mn,Fe) increases and Al6(Mn,Fe) particles appear as like chain structure in the alloy with 3 wt.% Mn. An increase in Mn concentration in the Al-12.6Si alloys result in the increase in bulk hardness of the alloy as an effects of microstructure modification as well as the presence of harder Al6(Mn,Fe) phase in the developed alloy.

Influence of trimethylsilane flow on the microstructure, mechanical and tribological properties of CrSiCN coatings in water lubrication

NASA Astrophysics Data System (ADS)

Wu, Zhiwei; Zhou, Fei; Wang, Qianzhi; Zhou, Zhifeng; Yan, Jiwang; Li, Lawrence Kwok-Yan

2015-11-01

CrSiCN coatings with different silicon and carbon contents were deposited on silicon wafers and 316L stainless steels using unbalanced magnetron sputtering via adjusting trimethylsilane (TMS) flow, and their microstructure and mechanical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy(SEM), X-ray photoelectrons spectroscopy(XPS) and nano-indenter, respectively. The tribological properties of CrSiCN coatings sliding against SiC balls in water were investigated using ball-on-disk tribometer. The results showed that the CrSiCN coatings had fine composite microstructure consisting of nanocrystallites of Cr(C, N) crystal and amorphous phases such as a-Si3N4 and a-C(a-CNx). The typical columnar structures changed from fine cluster to coarse ones when the Si content was beyond 3.4 at.%. With an increase in the TMS flow, the hardness and Young's modulus of Corsican coatings all first increased, and then rapidly decreased, but the compressive stress in the coatings varied in the range of 2.8-4.8 GPa. When the TMS flow was 10 sccm, the CrSiCN coatings exhibited the highest hardness of 21.3 GPa and the lowest friction coefficient (0.11) and wear rate (8.4 × 10-8 mm3/N m). But when the TMS flow was beyond 15 sccm, the tribological properties of CrSiCN coatings in water became poor.

High Temperature Elastic Properties of Single Crystal Mullite (Approximately 2.5Al2O3.SiO2) by Brillouin Spectroscopy

NASA Technical Reports Server (NTRS)

Palko, James W.; Sayir, Ali; Sinogeikin, Stanislav V.; Kriven, Waltraud M.; Bass, Jay D.; Farmer, Serene C. (Technical Monitor)

2001-01-01

The complete elastic tensor of mullite has been determined by brillouin spectroscopy at room temperature and elevated temperatures up to 1200C. Equivalent, isotropic moduli (bulk, shear, and Young's) have been calculated. The room temperature values obtained using Voigt-Reuss-Hill averaging are: K(sub VRH) = 173.5 + 6.9 GPa, G(sub VRH) = 88.0 + 3.5 GPa, E(sub VRH) = 225.9 + 9.0 GPa. All moduli show relatively gradual decreases with temperature. The temperature derivatives obtained for the equivalent, isotropic moduli are: dK(sub VRH)/dT = - 17.5 + 2.5 MPa/deg. C, dG(sub VRH)/dT = -8.8 + 1.4 MPa/deg. C, dE(sub VRH)/dT = -22.6 + 2.8 MPa/deg C. Substantial differences between bulk properties calculated from the single crystal measurements in this study and the properties reported in the literature for polycrystalline sintered mullite are identified, indicating the importance of factors such as microstructure, intergranular phases, and composition to the elasticity of mullite ceramics.

Stochastic isotropic hyperelastic materials: constitutive calibration and model selection

NASA Astrophysics Data System (ADS)

Mihai, L. Angela; Woolley, Thomas E.; Goriely, Alain

2018-03-01

Biological and synthetic materials often exhibit intrinsic variability in their elastic responses under large strains, owing to microstructural inhomogeneity or when elastic data are extracted from viscoelastic mechanical tests. For these materials, although hyperelastic models calibrated to mean data are useful, stochastic representations accounting also for data dispersion carry extra information about the variability of material properties found in practical applications. We combine finite elasticity and information theories to construct homogeneous isotropic hyperelastic models with random field parameters calibrated to discrete mean values and standard deviations of either the stress-strain function or the nonlinear shear modulus, which is a function of the deformation, estimated from experimental tests. These quantities can take on different values, corresponding to possible outcomes of the experiments. As multiple models can be derived that adequately represent the observed phenomena, we apply Occam's razor by providing an explicit criterion for model selection based on Bayesian statistics. We then employ this criterion to select a model among competing models calibrated to experimental data for rubber and brain tissue under single or multiaxial loads.

Effects of anisotropic surface texture on the performance of ionic polymer-metal composite (IPMC)

NASA Astrophysics Data System (ADS)

He, Qingsong; Yu, Min; Ding, Haitao; Guo, Dongjie; Dai, Zhendong

2010-04-01

Ionic polymer metal composite (IPMC), an electrically activated polymer (EAP), has attracted great attention for the excellent properties such as large deformation, light weight, low noise, flexibility and low driving voltages, which makes the material a possible application as artificial muscle if the output force can be increased. To improve the property, we manufactured the Nafion membrane by casting from liquid solution, modified the surface by sandblasting or polishing, and obtained the isotropic and anisotropic surface texture respectively. The microstructure of the Nafion surface and metal electrode, effects of surface texture on the output force and displacement of IPMC were studied. Results show that the output force of IPMC with the anisotropic surface texture is 2~4 times higher than that with the isotropic surface texture without enormous sacrifice of the displacement. The output force may reach to 6.63gf (Sinusoidal 3.5V and 0.1Hz, length 20mm, width 5mm and thickness 0.66mm), which suggest an effective way to improve the mechanical properties of IPMC.

Entanglements in Conjugated Polymers

NASA Astrophysics Data System (ADS)

Xie, Renxuan; Lee, Youngmin; Aplan, Melissa; Caggiano, Nick; Gomez, Enrique; Colby, Ralph

Conjugated polymers, such as poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly-((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(thiophen-5-yl)-2,1,3-benzothiadiazole]-2',2''-diyl) (PFTBT), are widely used as hole and electron transport materials in a variety of electronic devices. However, fundamental knowledge regarding chain entanglements and nematic-to-isotropic transition is still lacking and are crucial to maximize charge transport properties. A systematic melt rheology study on P3HT with various molecular weights and regio regularities was performed. We find that the entanglement molecular weight Me is 5.0 kg/mol for regiorandom P3HT, but the apparent Me for regioregular P3HT is significantly higher. The difference is postulated to arise from the presence of a nematic phase only in regioregular P3HT. Analogously, PFTBT shows a clear rheological signature of the nematic-to-isotropic transition as a reversible sharp transition at 278 C. Shearing of this nematic phase leads to anisotropic crystalline order in PFTBT. We postulate that aligning the microstructure will impact charge transport and thereby advance the field of conducting polymers. National Science Foundation.

Thermomechanical deformation behavior of a dynamic strain aging alloy, Hastelloy X

NASA Technical Reports Server (NTRS)

Castelli, Michael G.; Miner, Robert V.; Robinson, David N.

1992-01-01

An experimental study was performed to identify the effects of dynamic strain aging (solute drag) and metallurgical instabilities under thermomechanical loading conditions. The study involved a series of closely controlled thermomechanical deformation tests on the solid-solution-strenghened nickel-base superalloy, Hastelloy X. This alloy exhibits a strong isothermal strain aging peak at approximately 600 C, promoted by the effects of solute drag and precipitation hardening. Macroscopic thermomechanical hardening trends are correlated with microstructural characteristics through the use of transmission electron microscopy. These observations are compared and contrasted with isothermal conditions. Thermomechanical behavior unique to the isothermal database is identified and discussed. The microstructural characteristics were shown to be dominated by effects associated with the highest temperature of the thermomechanical cycle. Results indicate that the deformation behavior of Hastelloy X is thermomechanically path dependent. In addition, guidance is given pertaining to deformation modeling in the context of macroscopic unified theory. An internal state variable is formulated to qualitatively reflect the isotropic hardening trends identified in the TMD experiments.

The growth of metastable peritectic compounds

NASA Technical Reports Server (NTRS)

Pirich, R. G.

1984-01-01

The effects of directional solidification processing on the microstructural, compositional, and magnetic properties of high-melting-temperature, commercially important alloys which form from the liquid state via peritectic or eutectic type reactions were determined. Emphasis was placed on ferromagnetic compounds of the commercially important Co-Sm and Al-Mn systems. The primary dendrite spacing for eutectic Sm2Co17/Co scaled with negative square root of V and varied from approximately 50 microns for V 20 cm/h to hundreds of microns for V 10 cm/h. Since the crystal growth mechanism was dendritic rather than cooperative, the assoicated permanent magnet properties were rather poor. Magnetization as a function of sample orientation indicates that the easy axis of magnetization was primarily along the direction of solidification for the eutectic Sm2Co17/Co and peritectic SmCo5/Sm2Co17 compositions. For the Al-Mn case, magnetization and microstructural characterization suggest isotropic, polycrystalling growth for all solidification velocities studied.

Microsystems Research in Japan

DTIC Science & Technology

2003-09-01

microsystems applications, like microfluidic systems, will require more than planar lithography -based fabrication processes. The committee was impressed by the...United States focused on exploiting silicon planar lithography as the core technology for microstructure fabrication, whereas Japan explored a wide...including LIGA and its extensions, micro-stereolithography, and e-beam lithography . The range of materials seen in Japan was broader than in the

Static Strain Aging Behavior of a Manganese-Silicon Steel After Single and Multi-stage Straining

NASA Astrophysics Data System (ADS)

Seraj, P.; Serajzadeh, S.

2016-03-01

In this work, static strain aging behavior of an alloy steel containing high amounts of silicon and manganese was examined while the influences of initial microstructure and pre-strain on the aging kinetics were evaluated as well. The rate of strain aging in a low carbon steel was also determined and compared with that occurred in the alloy steel. The rates of static strain aging in the steels were defined at room temperature and at 95 °C by means of double-hit tensile testing and hardness measurements. In addition, three-stage aging experiments at 80 °C were carried out to estimate aging behavior under multi-pass deformation processing. The results showed that in-solution manganese and silicon atoms could significantly affect the aging behavior of the steel and reduce the kinetics of static strain aging as compared to the low carbon steel. The initial microstructure also played an important role on the aging behavior. The rapidly cooled steel having mean ferrite grain size of 9.7 μm showed the least aging susceptibility index during the aging experiments. Accordingly, the activation energies for static strain aging were calculated as 93.2 and 85.7 kJ/mole for the alloy steel having fine and coarse ferrite-pearlite structures, respectively while it was computed as 79.1 kJ/mole for the low carbon steel with ferrite mean grain size of about 16.2 μm.

Characterization of nuclear graphite elastic properties using laser ultrasonic methods

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

Zeng, Fan W; Han, Karen; Olasov, Lauren R

2015-01-01

Laser ultrasonic methods have been used to characterize the elastic behaviors of commercially-available and legacy nuclear graphites. Since ultrasonic techniques are sensitive to various aspects of graphite microstructure including preferred grain orientation, microcrack orientation and porosity, laser ultrasonics is a candidate technique for monitoring graphite degradation and structural integrity in environments expected in high-temperature, gas-cooled nuclear reactors. Aspects of materials texture can be assessed by studying ultrasonic wavespeeds as a function of propagation direction and polarization. Shear wave birefringence measurements, in particular, can be used to evaluate elastic anisotropy. In this work, laser ultrasonic measurements of graphite moduli have beenmore » made to provide insight into the relationship between the microstructures and the macroscopic stiffnesses of these materials. In particular, laser ultrasonic measurements have been made using laser line sources to produce shear waves with specific polarizations. By varying the line orientation relative to the sample, shear wave birefringence measurements have been recorded. Results from shear wave birefringence measurements show that an isostatically molded graphite, such as PCIB, behaves isotropically, while an extruded graphite, such as H-451, displays significant ultrasonic texture. Graphites have complicated microstructures that depend on the manufacturing processes used, and ultrasonic texture in these materials could originate from grain orientation and preferred microcrack alignment. Effects on material isotropy due to service related microstructural changes are possible and the ultimate aim of this work is to determine the degree to which these changes can be assessed nondestructively using laser ultrasonics measurements« less

Feasibility of fabricating personalized 3D-printed bone grafts guided by high-resolution imaging

NASA Astrophysics Data System (ADS)

Hong, Abigail L.; Newman, Benjamin T.; Khalid, Arbab; Teter, Olivia M.; Kobe, Elizabeth A.; Shukurova, Malika; Shinde, Rohit; Sipzner, Daniel; Pignolo, Robert J.; Udupa, Jayaram K.; Rajapakse, Chamith S.

2017-03-01

Current methods of bone graft treatment for critical size bone defects can give way to several clinical complications such as limited available bone for autografts, non-matching bone structure, lack of strength which can compromise a patient's skeletal system, and sterilization processes that can prevent osteogenesis in the case of allografts. We intend to overcome these disadvantages by generating a patient-specific 3D printed bone graft guided by high-resolution medical imaging. Our synthetic model allows us to customize the graft for the patients' macro- and microstructure and correct any structural deficiencies in the re-meshing process. These 3D-printed models can presumptively serve as the scaffolding for human mesenchymal stem cell (hMSC) engraftment in order to facilitate bone growth. We performed highresolution CT imaging of a cadaveric human proximal femur at 0.030-mm isotropic voxels. We used these images to generate a 3D computer model that mimics bone geometry from micro to macro scale represented by STereoLithography (STL) format. These models were then reformatted to a format that can be interpreted by the 3D printer. To assess how much of the microstructure was replicated, 3D-printed models were re-imaged using micro-CT at 0.025-mm isotropic voxels and compared to original high-resolution CT images used to generate the 3D model in 32 sub-regions. We found a strong correlation between 3D-printed bone volume and volume of bone in the original images used for 3D printing (R2 = 0.97). We expect to further refine our approach with additional testing to create a viable synthetic bone graft with clinical functionality.

Microstructure-sensitive plasticity and fatigue modeling of extruded 6061 aluminum alloys

NASA Astrophysics Data System (ADS)

McCullough, Robert Ross

In this study, the development of fatigue failure and stress anisotropy in light weight ductile metal alloys, specifically Al-Mg-Si aluminum alloys, was investigated. The experiments were carried out on an extruded 6061 aluminum alloy. Reverse loading experiments were performed up to a prestrain of 5% in both tension-followed-by-compression and compression-followed-by-tension. The development of isotropic and kinematic hardening and subsequent anisotropy was indicated by the observation of the Bauschinger effect phenomenon. Experimental results show that 6061 aluminum alloy exhibited a slight increase in the kinematic hardening versus applied prestrain. However, the ratio of kinematic-to-isotropic hardening remained near unity. An internal state variable (ISV) plasticity and damage model was used to capture the evolution of the anisotropy for the as-received T6 and partially annealed conditions. Following the stress anisotropy experiments, the same extruded 6061 aluminum alloy was tested under fully reversing, strain-controlled low cycle fatigue at up to 2.5% strain amplitudes and two heat treatment conditions. Observations were made of the development of striation fields up to the point of nucleation at cracked and clustered precipitants and free surfaces through localized precipitant slip band development. A finite element enabled micro-mechanics study of fatigue damage development of local strain field in the presence of hard phases was conducted. Both the FEA and experimental data sets were utilized in the implementation of a multi-stage fatigue model in order to predict the microstructure response, including fatigue nucleation and propagation contributions on the total fatigue life in AA6061. Good correlation between experimental and predicted results in the number of cycles to final failure was observed. The AA6061 material maintained relatively consistent low cycle fatigue performance despite two different heat treatments.

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

Custer, Jonathan S.; Fleming, James G.; Roherty-Osmun, Elizabeth

Refractory ternary nitride films for diffusion barriers in microelectronics have been grown using chemical vapor deposition. Thin films of titanium-silicon-nitride, tungsten-boron-nitride, and tungsten-silicon-nitride of various compositions have been deposited on 150 mm Si wafers. The microstructure of the films are either fully amorphous for the tungsten based films, or nauocrystalline TiN in an amorphous matrix for titanium-silicon-nitride. All films exhibit step coverages suitable for use in future microelectronics generations. Selected films have been tested as diffusion barriers between copper and silicon, and generally perform extremely weH. These fiIms are promising candidates for advanced diffusion barriers for microelectronics applications. The manufacturingmore » of silicon wafers into integrated circuits uses many different process and materials. The manufacturing process is usually divided into two parts: the front end of line (FEOL) and the back end of line (BEOL). In the FEOL the individual transistors that are the heart of an integrated circuit are made on the silicon wafer. The responsibility of the BEOL is to wire all the transistors together to make a complete circuit. The transistors are fabricated in the silicon itself. The wiring is made out of metal, currently aluminum and tungsten, insulated by silicon dioxide, see Figure 1. Unfortunately, silicon will diffuse into aluminum, causing aluminum spiking of junctions, killing transistors. Similarly, during chemical vapor deposition (CVD) of tungsten from ~fj, the reactivity of the fluorine can cause "worn-holes" in the silicon, also destroying transistors. The solution to these problems is a so-called diffusion barrier, which will allow current to pass from the transistors to the wiring, but will prevent reactions between silicon and the metal.« less

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

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

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

2014-01-01

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

Advanced Micro-Polycrystalline Silicon Films Formed by Blue-Multi-Laser-Diode Annealing

NASA Astrophysics Data System (ADS)

Noguchi, Takashi; Chen, Yi; Miyahira, Tomoyuki; de Dieu Mugiraneza, Jean; Ogino, Yoshiaki; Iida, Yasuhiro; Sahota, Eiji; Terao, Motoyasu

2010-03-01

Semiconductor blue-multi-laser-diode annealing (BLDA) for amorphous Si film was performed to obtain a film containing uniform polycrystalline silicon (poly-Si) grains as a low temperature poly-Si (LTPS) process used for thin-film transistor (TFT). By adopting continuous wave (CW) mode at the 445 nm wavelength of the BLDA system, the light beam is efficiently absorbed into the thin amorphous silicon film of 50 nm thickness and can be crystallized stably. By adjusting simply the laser power below 6 W with controlled beam shape, the isotropic Si grains from uniform micro-grains to arbitral grain size of polycrystalline phase can be obtained with reproducible by fixing the scan speed at 500 mm/s. As a result of analysis using electron microscopy and atomic force microscopy (AFM), uniform distributed micro-poly-Si grains of smooth surface were observed at a power condition below 5 W and the preferred crystal orientation of (111) face was confirmed. As arbitral grain size can be obtained stably and reproducibly merely by controlling the laser power, BLDA is promising as a next-generation LTPS process for AM OLED panel including a system on glass (SoG).

Characterization of Newly Developed Semisolid Stir Joining Method for Cast Cu Base Alloy (Cu-Al-Si-Fe) and Effect of Stirrer Type on Uniformity of Microstructure

NASA Astrophysics Data System (ADS)

Ferasat, Keyvan; Aashuri, Hossein; Kokabi, Amir Hossein; Nikzad, Siamak; Shafizadeh, Mahdi

2015-02-01

In this research, the semisolid stir joining method was used to overcome the problem of hot cracking in welding aluminum and silicon bronzes. Moreover, the effects of grooved and cylindrical tools on the microstructure and mechanical properties of samples were examined. After welding specimens, mechanical tests were carried out to find differences between the cast and welded samples. Optical microscopy and scanning electron microscopy were used to study microstructure. X-ray diffraction was used to investigate compounds formed during casting and welding. The solidus and liquidus temperatures of the alloy were measured by differential scanning calorimetry. In this study, the temperature of the work pieces was raised to 1203 K (930 °C) that is in the semisolid region, and the weld seams were stirred by two different types of tools at the speed of 1600 rpm. Macro and micro-structural analyses show uniformity in the phase distribution for specimens welded by cylindrical tool. Desirable and uniform mechanical properties obtained when the cylindrical tool was used.

Scanning and Transmission Electron Microscopy of High Temperature Materials

NASA Technical Reports Server (NTRS)

1994-01-01

Software and hardware updates to further extend the capability of the electron microscope were carried out. A range of materials such as intermetallics, metal-matrix composites, ceramic-matrix composites, ceramics and intermetallic compounds, based on refractory elements were examined under this research. Crystal structure, size, shape and volume fraction distribution of various phases which constitute the microstructures were examined. Deformed materials were studied to understand the effect of interfacial microstructure on the deformation and fracture behavior of these materials. Specimens tested for a range of mechanical property requirements, such as stress rupture, creep, low cycle fatigue, high cycle fatigue, thermomechanical fatigue, etc. were examined. Microstructural and microchemical stability of these materials exposed to simulated operating environments were investigated. The EOIM Shuttle post-flight samples were also examined to understand the influence of low gravity processing on microstructure. In addition, fractographic analyses of Nb-Zr-W, titanium aluminide, molybdenum silicide and silicon carbide samples were carried out. Extensive characterization of sapphire fibers in the fiber-reinforced composites made by powder cloth processing was made. Finally, pressure infiltration casting of metal-matrix composites was carried out.

Characterizing the microstructural basis of "unidentified bright objects" in neurofibromatosis type 1: A combined in vivo multicomponent T2 relaxation and multi-shell diffusion MRI analysis.

PubMed

Billiet, Thibo; Mädler, Burkhard; D'Arco, Felice; Peeters, Ronald; Deprez, Sabine; Plasschaert, Ellen; Leemans, Alexander; Zhang, Hui; den Bergh, Bea Van; Vandenbulcke, Mathieu; Legius, Eric; Sunaert, Stefan; Emsell, Louise

2014-01-01

The histopathological basis of "unidentified bright objects" (UBOs) (hyperintense regions seen on T2-weighted magnetic resonance (MR) brain scans in neurofibromatosis-1 (NF1)) remains unclear. New in vivo MRI-based techniques (multi-exponential T2 relaxation (MET2) and diffusion MR imaging (dMRI)) provide measures relating to microstructural change. We combined these methods and present previously unreported data on in vivo UBO microstructure in NF1. 3-Tesla dMRI data were acquired on 17 NF1 patients, covering 30 white matter UBOs. Diffusion tensor, kurtosis and neurite orientation and dispersion density imaging parameters were calculated within UBO sites and in contralateral normal appearing white matter (cNAWM). Analysis of MET2 parameters was performed on 24 UBO-cNAWM pairs. No significant alterations in the myelin water fraction and intra- and extracellular (IE) water fraction were found. Mean T2 time of IE water was significantly higher in UBOs. UBOs furthermore showed increased axial, radial and mean diffusivity, and decreased fractional anisotropy, mean kurtosis and neurite density index compared to cNAWM. Neurite orientation dispersion and isotropic fluid fraction were unaltered. Our results suggest that demyelination and axonal degeneration are unlikely to be present in UBOs, which appear to be mainly caused by a shift towards a higher T2-value of the intra- and extracellular water pool. This may arise from altered microstructural compartmentalization, and an increase in 'extracellular-like', intracellular water, possibly due to intramyelinic edema. These findings confirm the added value of combining dMRI and MET2 to characterize the microstructural basis of T2 hyperintensities in vivo.

Evolution of the microstructure during the process of consolidation and bonding in soft granular solids.

PubMed

Yohannes, B; Gonzalez, M; Abebe, A; Sprockel, O; Nikfar, F; Kiang, S; Cuitiño, A M

2016-04-30

The evolution of microstructure during powder compaction process was investigated using a discrete particle modeling, which accounts for particle size distribution and material properties, such as plasticity, elasticity, and inter-particle bonding. The material properties were calibrated based on powder compaction experiments and validated based on tensile strength test experiments for lactose monohydrate and microcrystalline cellulose, which are commonly used excipient in pharmaceutical industry. The probability distribution function and the orientation of contact forces were used to study the evolution of the microstructure during the application of compaction pressure, unloading, and ejection of the compact from the die. The probability distribution function reveals that the compression contact forces increase as the compaction force increases (or the relative density increases), while the maximum value of the tensile contact forces remains the same. During unloading of the compaction pressure, the distribution approaches a normal distribution with a mean value of zero. As the contact forces evolve, the anisotropy of the powder bed also changes. Particularly, during loading, the compression contact forces are aligned along the direction of the compaction pressure, whereas the tensile contact forces are oriented perpendicular to direction of the compaction pressure. After ejection, the contact forces become isotropic. Copyright © 2016 Elsevier B.V. All rights reserved.

Lamb wave extraction of dispersion curves in micro/nano-plates using couple stress theories

NASA Astrophysics Data System (ADS)

Ghodrati, Behnam; Yaghootian, Amin; Ghanbar Zadeh, Afshin; Mohammad-Sedighi, Hamid

2018-01-01

In this paper, Lamb wave propagation in a homogeneous and isotropic non-classical micro/nano-plates is investigated. To consider the effect of material microstructure on the wave propagation, three size-dependent models namely indeterminate-, modified- and consistent couple stress theories are used to extract the dispersion equations. In the mentioned theories, a parameter called 'characteristic length' is used to consider the size of material microstructure in the governing equations. To generalize the parametric studies and examine the effect of thickness, propagation wavelength, and characteristic length on the behavior of miniature plate structures, the governing equations are nondimensionalized by defining appropriate dimensionless parameters. Then the dispersion curves for phase and group velocities are plotted in terms of a wide frequency-thickness range to study the lamb waves propagation considering microstructure effects in very high frequencies. According to the illustrated results, it was observed that the couple stress theories in the Cosserat type material predict more rigidity than the classical theory; so that in a plate with constant thickness, by increasing the thickness to characteristic length ratio, the results approach to the classical theory, and by reducing this ratio, wave propagation speed in the plate is significantly increased. In addition, it is demonstrated that for high-frequency Lamb waves, it converges to dispersive Rayleigh wave velocity.

An approach for characterising cellular polymeric foam structures using computed tomography

NASA Astrophysics Data System (ADS)

Chen, Youming; Das, Raj; Battley, Mark

2018-02-01

Global properties of foams depend on foam base materials and microstructures. Characterisation of foam microstructures is important for developing numerical foam models. In this study, the microstructures of four polymeric structural foams were imaged using a micro-CT scanner. Image processing and analysis methods were proposed to quantify the relative density, cell wall thickness and cell size of these foams from the captured CT images. Overall, the cells in these foams are fairly isotropic, and cell walls are rather straight. The measured average relative densities are in good agreement with the actual values. Relative density, cell size and cell wall thickness in these foams are found to vary along the thickness of foam panel direction. Cell walls in two of these foams are found to be filled with secondary pores. In addition, it is found that the average cell wall thickness measured from 2D images is around 1.4 times of that measured from 3D images, and the average cell size measured from 3D images is 1.16 times of that measured from 2D images. The distributions of cell wall thickness and cell size measured from 2D images exhibit lager dispersion in comparison to those measured from 3D images.

Preparation and evaluation of silicon nitride matrices for silicon nitride-SiC fiber composites. M.S. Thesis Final Technical Report

NASA Technical Reports Server (NTRS)

Axelson, Scott R.

1988-01-01

Continuous silicon carbide (SiC) fiber was added to three types of silicon nitride (Si3N4) matrices. Efforts were aimed at producing a dense Si3N4 matrix from reaction-bonded silicon nitride (RBSN) by hot-isostatic-pressing (HIP) and pressureless sintering, and from Si3N4 powder by hot-pressing. The sintering additives utilized were chosen to allow for densification, while not causing severe degradation of the fiber. The ceramic microstructures were evaluated using scanning optical microscopy. Vickers indentation was used to determine the microhardness and fracture toughness values of the matrices. The RBSN matrices in this study did not reach more than 80 percent of theoretical density after sintering at various temperatures, pressures, and additive levels. Hot-pressing Si3N4 powder produced the highest density matrices; hardness and toughness values were within an order of magnitude of the best literature values. The best sintering aid composition chosen included Y2O3, SiO2, and Al2O3 or AlN. Photomicrographs demonstrate a significant reduction of fiber attack by this additive composition.

Wafer scale formation of monocrystalline silicon-based Mie resonators via silicon-on-insulator dewetting.

PubMed

Abbarchi, Marco; Naffouti, Meher; Vial, Benjamin; Benkouider, Abdelmalek; Lermusiaux, Laurent; Favre, Luc; Ronda, Antoine; Bidault, Sébastien; Berbezier, Isabelle; Bonod, Nicolas

2014-11-25

Subwavelength-sized dielectric Mie resonators have recently emerged as a promising photonic platform, as they combine the advantages of dielectric microstructures and metallic nanoparticles supporting surface plasmon polaritons. Here, we report the capabilities of a dewetting-based process, independent of the sample size, to fabricate Si-based resonators over large scales starting from commercial silicon-on-insulator (SOI) substrates. Spontaneous dewetting is shown to allow the production of monocrystalline Mie-resonators that feature two resonant modes in the visible spectrum, as observed in confocal scattering spectroscopy. Homogeneous scattering responses and improved spatial ordering of the Si-based resonators are observed when dewetting is assisted by electron beam lithography. Finally, exploiting different thermal agglomeration regimes, we highlight the versatility of this technique, which, when assisted by focused ion beam nanopatterning, produces monocrystalline nanocrystals with ad hoc size, position, and organization in complex multimers.

Thermally Stable Ohmic Contacts on Silicon Carbide Developed for High- Temperature Sensors and Electronics

NASA Technical Reports Server (NTRS)

Okojie, Robert S.

2001-01-01

The NASA aerospace program, in particular, requires breakthrough instrumentation inside the combustion chambers of engines for the purpose of, among other things, improving computational fluid dynamics code validation and active engine behavioral control (combustion, flow, stall, and noise). This environment can be as high as 600 degrees Celsius, which is beyond the capability of silicon and gallium arsenide devices. Silicon-carbide- (SiC-) based devices appear to be the most technologically mature among wide-bandgap semiconductors with the proven capability to function at temperatures above 500 degrees Celsius. However, the contact metalization of SiC degrades severely beyond this temperature because of factors such as the interdiffusion between layers, oxidation of the contact, and compositional and microstructural changes at the metal/semiconductor interface. These mechanisms have been proven to be device killers. Very costly and weight-adding packaging schemes that include vacuum sealing are sometimes adopted as a solution.

The Influence of Nano-Scale Silicon Nitride Additions on the Physical and Magnetic Properties of Iron Sheathed Magnesium Boride Wires

NASA Astrophysics Data System (ADS)

Zhu, W.; Cave, J.

2006-03-01

The enhancement of flux line pinning in magnesium boride wires is a critical issue for their future applications in devices and machines. It is well known that small size dopants can significantly influence the current densities of these materials. Here, the influence of nanometric (<30nm) silicon nitride on physical properties and current density is presented. The iron-sheathed powder in tube wires were prepared using pure magnesium and boron powders with silicon nitride additions. The wires were rolled flat and treated at up to 900 degrees C in flowing argon. SEM and XRD were used to identify phases and microstructures. Magnetization critical currents, up to several 100 of thousands A/cm2, at various temperatures and fields (5K - 20K and up to 3 tesla) show that there are competing mechanisms from chemical and flux pinning effects.

Diffusion Bonding of Silicon Carbide for MEMS-LDI Applications

NASA Technical Reports Server (NTRS)

Halbig, Michael C.; Singh, Mrityunjay; Shpargel, Tarah P.; Kiser, J. Douglas

2007-01-01

A robust joining approach is critically needed for a Micro-Electro-Mechanical Systems-Lean Direct Injector (MEMS-LDI) application which requires leak free joints with high temperature mechanical capability. Diffusion bonding is well suited for the MEMS-LDI application. Diffusion bonds were fabricated using titanium interlayers between silicon carbide substrates during hot pressing. The interlayers consisted of either alloyed titanium foil or physically vapor deposited (PVD) titanium coatings. Microscopy shows that well adhered, crack free diffusion bonds are formed under optimal conditions. Under less than optimal conditions, microcracks are present in the bond layer due to the formation of intermetallic phases. Electron microprobe analysis was used to identify the reaction formed phases in the diffusion bond. Various compatibility issues among the phases in the interlayer and substrate are discussed. Also, the effects of temperature, pressure, time, silicon carbide substrate type, and type of titanium interlayer and thickness on the microstructure and composition of joints are discussed.

Scaling effects in sodium zirconium silicate phosphate (Na 1+ xZr 2Si xP 3- xO 12) ion-conducting thin films

DOE PAGES

Ihlefeld, Jon F.; Gurniak, Emily; Jones, Brad H.; ...

2016-05-04

Preparation of sodium zirconium silicate phosphate (NaSICon), Na 1+xZr 2Si xP 3–xO 12 (0.25 ≤ x ≤ 1.0), thin films has been investigated via a chemical solution approach on platinized silicon substrates. Increasing the silicon content resulted in a reduction in the crystallite size and a reduction in the measured ionic conductivity. Processing temperature was also found to affect microstructure and ionic conductivity with higher processing temperatures resulting in larger crystallite sizes and higher ionic conductivities. The highest room temperature sodium ion conductivity was measured for an x = 0.25 composition at 2.3 × 10 –5 S/cm. In conclusion, themore » decreasing ionic conductivity trends with increasing silicon content and decreasing processing temperature are consistent with grain boundary and defect scattering of conducting ions.« less

Wear and Reactivity Studies of Melt infiltrated Ceramic Matrix Composite

NASA Technical Reports Server (NTRS)

Jarmon, David C.; Ojard, Greg; Brewer, David N.

2013-01-01

As interest grows in the use of ceramic matrix composites (CMCs) for critical gas turbine engine components, the effects of the CMCs interaction with the adjoining structure needs to be understood. A series of CMC/material couples were wear tested in a custom elevated temperature test rig and tested as diffusion couples, to identify interactions. Specifically, melt infiltrated silicon carbide/silicon carbide (MI SiC/SiC) CMC was tested in combination with a nickel-based super alloy, Waspaloy, a thermal barrier coating, Yttria Stabilized Zirconia (YSZ), and a monolithic ceramic, silicon nitride (Si3N4). To make the tests more representative of actual hardware, the surface of the CMC was kept in the as-received state (not machined) with the full surface features/roughness present. Test results include: scanning electron microscope characterization of the surfaces, micro-structural characterization, and microprobe analysis.

Short-pulse laser interactions with disordered materials and liquids

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

Phinney, L.M.; Goldman, C.H.; Longtin, J.P.

High-power, short-pulse lasers in the picosecond and subpicosecond range are utilized in an increasing number of technologies, including materials processing and diagnostics, micro-electronics and devices, and medicine. In these applications, the short-pulse radiation interacts with a wide range of media encompassing disordered materials and liquids. Examples of disordered materials include porous media, polymers, organic tissues, and amorphous forms of silicon, silicon nitride, and silicon dioxide. In order to accurately model, efficiently control, and optimize short-pulse, laser-material interactions, a thorough understanding of the energy transport mechanisms is necessary. Thus, fractals and percolation theory are used to analyze the anomalous diffusion regimemore » in random media. In liquids, the thermal aspects of saturable and multiphoton absorption are examined. Finally, a novel application of short-pulse laser radiation to reduce surface adhesion forces in microstructures through short-pulse laser-induced water desorption is presented.« less

The Effect of Postmastectomy Radiation Therapy on Breast Implants: Material Analysis on Silicone and Polyurethane Prosthesis.

PubMed

Lo Torto, Federico; Relucenti, Michela; Familiari, Giuseppe; Vaia, Nicola; Casella, Donato; Matassa, Roberto; Miglietta, Selenia; Marinozzi, Franco; Bini, Fabiano; Fratoddi, Ilaria; Sciubba, Fabio; Cassese, Raffaele; Tombolini, Vincenzo; Ribuffo, Diego

2018-05-17

The pathogenic mechanism underlying capsular contracture is still unknown. It is certainly a multifactorial process, resulting from human body reaction, biofilm activation, bacteremic seeding, or silicone exposure. The scope of the present article is to investigate the effect of hypofractionated radiotherapy protocol (2.66 Gy × 16 sessions) both on silicone and polyurethane breast implants. Silicone implants and polyurethane underwent irradiation according to a hypofractionated radiotherapy protocol for the treatment of breast cancer. After irradiation implant shells underwent mechanical, chemical, and microstructural evaluation by means of tensile testing, infrared spectra in attenuated total reflectance mode, nuclear magnetic resonance, and field emission scanning electron microscopy. At superficial analysis, irradiated silicone samples show several visible secondary and tertiary blebs. Polyurethane implants showed an open cell structure, which closely resembles a sponge. Morphological observation of struts from treated polyurethane sample shows a more compact structure, with significantly shorter and thicker struts compared with untreated sample. The infrared spectra in attenuated total reflectance mode spectra of irradiated and control samples were compared either for silicon and polyurethane samples. In the case of silicone-based membranes, treated and control specimens showed similar bands, with little differences in the treated one. Nuclear magnetic resonance spectra on the fraction soluble in CDCl3 support these observations. Tensile tests on silicone samples showed a softer behavior of the treated ones. Tensile tests on Polyurethane samples showed no significant differences. Polyurethane implants seem to be more resistant to radiotherapy damage, whereas silicone prosthesis showed more structural, mechanical, and chemical modifications.

Properties of nanocrystalline Si layers embedded in structure of solar cell

NASA Astrophysics Data System (ADS)

Jurečka, Stanislav; Imamura, Kentaro; Matsumoto, Taketoshi; Kobayashi, Hikaru

2017-12-01

Suppression of spectral reflectance from the surface of solar cell is necessary for achieving a high energy conversion efficiency. We developed a simple method for forming nanocrystalline layers with ultralow reflectance in a broad range of wavelengths. The method is based on metal assisted etching of the silicon surface. In this work, we prepared Si solar cell structures with embedded nanocrystalline layers. The microstructure of embedded layer depends on the etching conditions. We examined the microstructure of the etched layers by a transmission electron microscope and analysed the experimental images by statistical and Fourier methods. The obtained results provide information on the applied treatment operations and can be used to optimize the solar cell forming procedure.

Substrate-Influenced Thermo-Mechanical Fatigue of Copper Metallizations: Limits of Stoney’s Equation

PubMed Central

Bigl, Stephan; Wurster, Stefan; Cordill, Megan J.

2017-01-01

Rapid progress in the reduction of substrate thickness for silicon-based microelectronics leads to a significant reduction of the device bending stiffness and the need to address its implication for the thermo-mechanical fatigue behavior of metallization layers. Results on 5 µm thick Cu films reveal a strong substrate thickness-dependent microstructural evolution. Substrates with hs = 323 and 220 µm showed that the Cu microstructure exhibits accelerated grain growth and surface roughening. Moreover, curvature-strain data indicates that Stoney’s simplified curvature-stress relation is not valid for thin substrates with regard to the expected strains, but can be addressed using more sophisticated plate bending theories. PMID:29120407

Environment Conscious, Biomorphic Ceramics from Pine and Jelutong Wood Precursors

NASA Technical Reports Server (NTRS)

Singh, Mrityunjay; Yee, Bo-Moon; Gray, Hugh R. (Technical Monitor)

2002-01-01

Environment conscious, biomorphic ceramics have been fabricated from pine and jelutong wood precursors. A carbonaceous preform is produced through wood pyrolysis and subsequent infiltration with oxides (ZrO2 sols) and liquid silicon to form ceramics. These biomorphic ceramics show a wide variety of microstructures, densities, and hardness behavior that are determined by the type of wood and infiltrants selected.

Quantitative Evaluation of the Effect of Porosity on the Local Young's Modulus of Isotropic Composites by Using the Laser Optoacoustic Method

NASA Astrophysics Data System (ADS)

Podymova, N. B.; Karabutov, A. A.; Kobeleva, L. I.; Chernyshova, T. A.

2013-09-01

An impulse acoustic method with a laser source of ultrasound is proposed and realized experimentally for a quantitative evaluation of the joint effect of porosity (the volume fraction of pores) and the concentration of dispersed filler on the local Young's modulus of isotropic metal-matrix composite materials. The determination of Young's modulus is based on the laser thermooptical excitation of ultrasound and measurements of the phase speed of longitudinal and shears acoustic waves in composite specimens. Silumin-matrix composite specimens reinforced with various volume fractions of silicon carbide (SiC) microparticles of the mean size of 14 μm were investigated. It was found that, to provide an effective growth in Young's modulus by increasing the concentration of SiC, the porosity of a ready specimen should not exceed 2%. The technique developed allows one to carry out a nondestructive local testing of the acoustical and mechanical properties of composites in the actual state, which is necessary for a technological development and improvement of the fabrication process of the materials.

Temperature Induced Voltage Offset Drifts in Silicon Carbide Pressure Sensors

NASA Technical Reports Server (NTRS)

Okojie, Robert S.; Lukco, Dorothy; Nguyen, Vu; Savrun, Ender

2012-01-01

We report the reduction of transient drifts in the zero pressure offset voltage in silicon carbide (SiC) pressure sensors when operating at 600 C. The previously observed maximum drift of +/- 10 mV of the reference offset voltage at 600 C was reduced to within +/- 5 mV. The offset voltage drifts and bridge resistance changes over time at test temperature are explained in terms of the microstructure and phase changes occurring within the contact metallization, as analyzed by Auger electron spectroscopy and field emission scanning electron microscopy. The results have helped to identify the upper temperature reliable operational limit of this particular metallization scheme to be 605 C.

Fabrication and Metrology of High-Precision Foil Mirror Mounting Elements

NASA Technical Reports Server (NTRS)

Schattenburg, Mark L.

2002-01-01

During the period of this Cooperative Agreement, MIT (Massachusetts Institute of Technology) developed advanced methods for applying silicon microstructures for the precision assembly of foil x-ray optics in support of the Constellation-X Spectroscopy X-ray Telescope (SXT) development effort at Goddard Space Flight Center (GSFC). MIT developed improved methods for fabricating and characterizing the precision silicon micro-combs. MIT also developed and characterized assembly tools and several types of metrology tools in order to characterize and reduce the errors associated with precision assembly of foil optics. Results of this effort were published and presented to the scientific community and the GSFC SXT team. A bibliography of papers and presentations is offered.

Effect of hydrogen on the strength and microstructure of selected ceramics

NASA Technical Reports Server (NTRS)

Herbell, Thomas P.; Eckel, Andrew J.; Hull, David R.; Misra, Ajay K.

1990-01-01

Ceramics in monolithic form and as composite constituents in the form of fibers, matrices, and coatings are currently being considered for a variety of high-temperature applications in aeronautics and space. Many of these applications involve exposure to a hydrogen-containing environment. The compatibility of selected ceramics in gaseous high-temperature hydrogen is assessed. Environmental stability regimes for the long term use of ceramic materials are defined by the parameters of temperature, pressure, and moisture content. Thermodynamically predicted reactions between hydrogen and several monolithic ceramics are compared with actual performance in a controlled environment. Morphology of hydrogen attack and the corresponding strength degradation is reported for silicon carbide, silicon nitride, alumina, magnesia, and mullite.

Reactions of silicon-based ceramics in mixed oxidation chlorination environments

NASA Technical Reports Server (NTRS)

Marra, John E.; Kreidler, Eric R.; Jacobson, Nathan S.; Fox, Dennis S.

1988-01-01

The reaction of silicon-based ceramics with 2 percent Cl2/Ar and 1 percent Cl2/1 percent to 20 percent O2/Ar at 950 C was studied with thermogravimetric analysis and high-pressure mass spectrometry. Pure Si, SiO2, several types of SiC, and Si3N4 were examined. The primary corrosion products were SiCl4(g) and SiO2(s) with smaller amounts of volatile silicon oxychlorides. The reactions appear to occur by chlorine penetration of the SiO2 layer, and gas-phase diffusion of the silicon chlorides away from the sample appears to be rate limiting. Pure SiO2 shows very little reaction with Cl2, SiC with excess Si is more reactive than the other materials with Cl2, whereas SiC with excess carbon is more reactive than the other materials with Cl2/O2. Si3N4 shows very little reaction with Cl2. These differences are explained on the basis of thermodynamic and microstructural factors.

Exceptional gettering response of epitaxially grown kerfless silicon

DOE PAGES

Powell, D. M.; Markevich, V. P.; Hofstetter, J.; ...

2016-02-08

The bulk minority-carrier lifetime in p- and n-type kerfless epitaxial (epi) crystalline silicon wafers is shown to increase >500 during phosphorus gettering. We employ kinetic defect simulations and microstructural characterization techniques to elucidate the root cause of this exceptional gettering response. Simulations and deep-level transient spectroscopy (DLTS) indicate that a high concentra- tion of point defects (likely Pt) is “locked in” during fast (60 C/min) cooling during epi wafer growth. The fine dispersion of moderately fast-diffusing recombination-active point defects limits as-grown lifetime but can also be removed during gettering, confirmed by DLTS measurements. Synchrotron-based X-ray fluorescence microscopy indicates metal agglomeratesmore » at structural defects, yet the structural defect density is sufficiently low to enable high lifetimes. Consequently, after phosphorus diffusion gettering, epi silicon exhibits a higher lifetime than materials with similar bulk impurity contents but higher densities of structural defects, including multicrystalline ingot and ribbon silicon materials. As a result, device simulations suggest a solar-cell efficiency potential of this material >23%.« less

Microstructural investigation of nickel silicide thin films and the silicide-silicon interface using transmission electron microscopy.

PubMed

Bhaskaran, M; Sriram, S; Mitchell, D R G; Short, K T; Holland, A S; Mitchell, A

2009-01-01

This article discusses the results of transmission electron microscopy (TEM)-based investigation of nickel silicide (NiSi) thin films grown on silicon. Nickel silicide is currently used as the CMOS technology standard for local interconnects and in electrical contacts. Films were characterized with a range of TEM-based techniques along with glancing angle X-ray diffraction. The nickel silicide thin films were formed by vacuum annealing thin films of nickel (50 nm) deposited on (100) silicon. The cross-sectional samples indicated a final silicide thickness of about 110 nm. This investigation studied and reports on three aspects of the thermally formed thin films: the uniformity in composition of the film using jump ratio maps; the nature of the interface using high resolution imaging; and the crystalline orientation of the thin films using selected-area electron diffraction (SAED). The analysis highlighted uniform composition in the thin films, which was also substantiated by spectroscopy techniques; an interface exhibiting the desired abrupt transition from silicide to silicon; and desired and preferential crystalline orientation corresponding to stoichiometric NiSi, supported by glancing angle X-ray diffraction results.

Fabrication and Characterization of CMOS-MEMS Magnetic Microsensors

PubMed Central

Hsieh, Chen-Hsuan; Dai, Ching-Liang; Yang, Ming-Zhi

2013-01-01

This study investigates the design and fabrication of magnetic microsensors using the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process. The magnetic sensor is composed of springs and interdigitated electrodes, and it is actuated by the Lorentz force. The finite element method (FEM) software CoventorWare is adopted to simulate the displacement and capacitance of the magnetic sensor. A post-CMOS process is utilized to release the suspended structure. The post-process uses an anisotropic dry etching to etch the silicon dioxide layer and an isotropic dry etching to remove the silicon substrate. When a magnetic field is applied to the magnetic sensor, it generates a change in capacitance. A sensing circuit is employed to convert the capacitance variation of the sensor into the output voltage. The experimental results show that the output voltage of the magnetic microsensor varies from 0.05 to 1.94 V in the magnetic field range of 5–200 mT. PMID:24172287

Flexible deep brain neural probes based on a parylene tube structure

NASA Astrophysics Data System (ADS)

Zhao, Zhiguo; Kim, Eric; Luo, Hao; Zhang, Jinsheng; Xu, Yong

2018-01-01

Most microfabricated neural probes have limited shank length, which prevents them from reaching many deep brain structures. This paper reports deep brain neural probes with ultra-long penetrating shanks based on a simple but novel parylene tube structure. The mechanical strength of the parylene tube shank is temporarily enhanced during implantation by inserting a metal wire. The metal wire can be removed after implantation, making the implanted probe very flexible and thus minimizing the stress caused by micromotions of brain tissues. Optogenetic stimulation and chemical delivery capabilities can be potentially integrated by taking advantage of the tube structure. Single-shank prototypes with a shank length of 18.2 mm have been developed. The microfabrication process comprises of deep reactive ion etching (DRIE) of silicon, parylene conformal coating/refilling, and XeF2 isotropic silicon etching. In addition to bench-top insertion characterization, the functionality of developed probes has been preliminarily demonstrated by implanting into the amygdala of a rat and recording neural signals.

Developing Barbed Microtip-Based Electrode Arrays for Biopotential Measurement

PubMed Central

Hsu, Li-Sheng; Tung, Shu-Wei; Kuo, Che-Hsi; Yang, Yao-Joe

2014-01-01

This study involved fabricating barbed microtip-based electrode arrays by using silicon wet etching. KOH anisotropic wet etching was employed to form a standard pyramidal microtip array and HF/HNO3 isotropic etching was used to fabricate barbs on these microtips. To improve the electrical conductance between the tip array on the front side of the wafer and the electrical contact on the back side, a through-silicon via was created during the wet etching process. The experimental results show that the forces required to detach the barbed microtip arrays from human skin, a polydimethylsiloxane (PDMS) polymer, and a polyvinylchloride (PVC) film were larger compared with those required to detach microtip arrays that lacked barbs. The impedances of the skin-electrode interface were measured and the performance levels of the proposed dry electrode were characterized. Electrode prototypes that employed the proposed tip arrays were implemented. Electroencephalogram (EEG) and electrocardiography (ECG) recordings using these electrode prototypes were also demonstrated. PMID:25014098

Anisotropy modulations of femtosecond laser pulse induced periodic surface structures on silicon by adjusting double pulse delay.

PubMed

Han, Weina; Jiang, Lan; Li, Xiaowei; Wang, Qingsong; Li, Hao; Lu, YongFeng

2014-06-30

We demonstrate that the polarization-dependent anisotropy of the laser-induced periodic surface structure (LIPSS) on silicon can be adjusted by designing a femtosecond laser pulse train (800 nm, 50 fs, 1 kHz). By varying the pulse delay from 100 to 1600 fs within a double pulse train to reduce the deposited pulse energy, which weakens the directional surface plasmon polarition (SPP)-laser energy coupling based on the initial formed ripple structure, the polarization-dependent geometrical morphology of the LIPSS evolves from a nearly isotropic circular shape to a somewhat elongated elliptical shape. Meanwhile, the controllable anisotropy of the two-dimensional scanned-line widths with different directions is achieved based on a certain pulse delay combined with the scanning speed. This can effectively realize better control over large-area uniform LIPSS formation. As an example, we further show that the large-area LIPSS can be formed with different scanning times under different pulse delays.

Mechanical characterization of collagen-glycosaminoglycan scaffolds.

PubMed

Harley, Brendan A; Leung, Janet H; Silva, Emilio C C M; Gibson, Lorna J

2007-07-01

Tissue engineering scaffolds are used extensively as three-dimensional analogs of the extracellular matrix (ECM). However, less attention has been paid to characterizing the scaffold microstructure and mechanical properties than to the processing and bioactivity of scaffolds. Collagen-glycosaminoglycan (CG) scaffolds have long been utilized as ECM analogs for the regeneration of skin and are currently being considered for the regeneration of nerve and conjunctiva. Recently a series of CG scaffolds with a uniform pore microstructure has been developed with a range of sizes of equiaxed pores. Experimental characterization and theoretical modeling techniques have previously been used to describe the pore microstructure, specific surface area, cell attachment and permeability of these variants. The results of tensile and compressive tests on these CG scaffolds and of bending tests on the individual struts that define the scaffold network are reported here. The CG scaffold variants exhibited stress-strain behavior characteristic of low-density, open-cell foams with distinct linear elastic, collapse plateau and densification regimes. Scaffolds with equiaxed pores were found to be mechanically isotropic. The independent effects of hydration level, pore size, crosslink density and relative density on the mechanical properties was determined. Independent control over scaffold stiffness and pore size was obtained. Good agreement was observed between experimental results of scaffold mechanical characterization and low-density, open-cell foam model predictions for uniform scaffolds. The characterized scaffold variants provide a standardized framework with defined extracellular environments (microstructure, mechanics) for in vitro studies of the mechanical interactions between cells and scaffolds as well as in vivo tissue engineering studies.

New World Vistas: Air and Space Power for the 21st Century, Materials Volume.

DTIC Science & Technology

1996-06-01

derivatives from niche (non-silicon) materials: IR sensors, radars, lasers, and high - temperature , adverse-environment electronics. Investment in these...Develop metastable interstitial composites to create extremely high temperatures for destroying chemical biological warfare agents. " Explosives: 1...synthesize of high temperature materials that will be tailored for specific applications/ components. These materials will tend to have microstructures on

Evanescent-wave bonding between optical waveguides.

PubMed

Povinelli, Michelle L; Loncar, Marko; Ibanescu, Mihai; Smythe, Elizabeth J; Johnson, Steven G; Capasso, Federico; Joannopoulos, John D

2005-11-15

Forces arising from overlap between the guided waves of parallel, microphotonic waveguides are calculated. Both attractive and repulsive forces, determined by the choice of relative input phase, are found. Using realistic parameters for a silicon-on-insulator material system, we estimate that the forces are large enough to cause observable displacements. Our results illustrate the potential for a broader class of optically tunable microphotonic devices and microstructured artificial materials.

Effect of the powder characteristics of Sisub3Nsub4 on the microstructure of sintered bodies

NASA Technical Reports Server (NTRS)

Woetting, G.; Hausner, H.

1981-01-01

Silicon nitride powders sintered with the addition of 2 wt% Mg0 to 95% theoretical density after attrition milling and subsequent purification were evaluated. Preparation of the powders is described. The powder characteristics (specific surfaces, iron concentration, and oxygen content), and density, weight loss, and phase state of the sinter bodies as a function of powder preparation are presented.

Development of Spacecraft Materials and Structures Fundamentals.

DTIC Science & Technology

1985-08-01

900. This is comparable to the dihedral angle observed in uranium dioxide’ ° and silicon carbide ,’ 2 which...necesjary and identify by bigich numberp FIELD GROUP I suB. GR. Boron carbide , sintering, grain growth, microstructure, microcracking, mechanical...Compacts of boron carbide powders with specific surface area >, 8 m2 / were sintered in argon at temperatures near 2200*C. Several of these powders were

Microstructure, Friction and Wear of Aluminum Matrix Composites

NASA Astrophysics Data System (ADS)

Florea, R. M.

2018-06-01

MMCs are made by dispersing a reinforcing material into a metal matrix. They are prepared by casting, although several technical challenges exist with casting technology. Achieving a homogeneous distribution of reinforcement within the matrix is one such challenge, and this affects directly on the properties and quality of composite. The aluminum alloy composite materials consist of high strength, high stiffness, more thermal stability, more corrosion and wear resistance, and more fatigue life. Aluminum alloy materials found to be the best alternative with its unique capacity of designing the materials to give required properties. In this work a composite is developed by adding silicon carbide in Aluminum metal matrix by mass ratio 5%, 10% and 15%. Mechanical tests such as hardness test and microstructure test are conducted.

Microstructure and mechanical properties of thermoelectric nanostructured n-type silicon-germanium alloys synthesized employing spark plasma sintering

NASA Astrophysics Data System (ADS)

Bathula, Sivaiah; Gahtori, Bhasker; Jayasimhadri, M.; Tripathy, S. K.; Tyagi, Kriti; Srivastava, A. K.; Dhar, Ajay

2014-08-01

Owing to their high thermoelectric (TE) figure-of-merit, nanostructured Si80Ge20 alloys are evolving as a potential replacement for their bulk counterparts in designing efficient radio-isotope TE generators. However, as the mechanical properties of these alloys are equally important in order to avoid in-service catastrophic failure of their TE modules, we report the strength, hardness, fracture toughness, and thermal shock resistance of nanostructured n-type Si80Ge20 alloys synthesized employing spark plasma sintering of mechanically alloyed nanopowders of its constituent elements. These mechanical properties show a significant enhancement, which has been correlated with the microstructural features at nano-scale, delineated by transmission electron microscopy.

Studies on microstructure and mechanical behaviour of A7075- Flyash/SiC hybrid metal matrix composites

NASA Astrophysics Data System (ADS)

Venkata Reddy, V.; Gopi Krishna, M.; Praveen Kumar, K.; Naga Kishore, B. S.; Babu Rao, J.; Bhargava, NRMR

2018-02-01

Experiments have been performed under laboratory condition to review the mechanical behaviour of the hybrid composites with aluminium matrix A7075 alloy, reinforced with silicon carbide (SiC) and Flyash. This has been possible by fabricating the samples through usual stir casting technique. Scanning electron microscopy was used for microstructure analysis. Chemical characterization of both matrix and composites was performed by using EDAX. Density, hardness, tensile and deformation studies were conceded out on both the base alloy and composites. Enhanced hardness and deformed properties were observed for all the composites. Interestingly improved tensile results were obtained for the composites than alloy. Dispersion of (SiC) and Flyash particles in aluminium matrix enhances the hardness of the composites.

Effects of silicon on the oxidation, hot-corrosion, and mechanical behavior of two cast nickel-base superalloys

NASA Technical Reports Server (NTRS)

Miner, R. V., Jr.

1977-01-01

Cast specimens of nickel-base superalloys 713C and Mar-M200 with nominal additions of 0, 0.5, and 1 wt% Si were evaluated for oxidation and corrosion resistance, tensile and stress-rupture properties, microstructure, and phase relations. Results are compared with those of an earlier study of the effects of Si in B-1900. Si had similar effects on all three superalloys. It improves oxidation resistance but the improvement in 713C and Mar-M200 was considerably less than in B-1900. Hot-corrosion resistance is also improved somewhat. Si is, however, detrimental to mechanical properties, in particular, rupture strength and tensile ductility. Si has two obvious microstructural effects. It increases the amount of gamma-prime precipitated in eutectic nodules and promotes a Mo(Ni,Si)2 Laves phase in the alloys containing Mo. These microstructural effects do not appear responsible for the degradation of mechanical properties, however.

Effect of gas flow ratio on the microstructure and mechanical properties of boron phosphide films prepared by reactive magnetron sputtering

NASA Astrophysics Data System (ADS)

Jia, Z. C.; Zhu, J. Q.; Jiang, C. Z.; Shen, W. X.; Han, J. C.; Chen, R. R.

2011-10-01

Boron phosphide films were grown on silicon substrate by radio frequency reactive magnetron sputtering using boron target and hydrogen phosphine at different gas flow ratios (PH 3/Ar) at lower temperature. The chemical composition, microstructure and mechanical properties were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectrum, FTIR spectrum, surface profilometer and nano-indenter. The results indicate that the atomic ratio (P/B) rises from 1.06 up to 1.52 with the gas flow ratio increasing from 3/50 to 15/50. Simultaneously, the hardness and Young's modulus decrease from 25.4 GPa to 22.5 GPa, and 250.4 GPa to 238.4 GPa, respectively. Microstructure transforms from microcrystalline state to amorphous state along with the gas flow ratio increasing. Furthermore higher gas flow ratio leads to lower stress. The BP film prepared at the gas flow ratio of 3/50 can be contributed with the best properties.

Microstructure and growth model for rice-hull-derived SiC whiskers

NASA Technical Reports Server (NTRS)

Nutt, Steven R.

1988-01-01

The microstructure of silicon carbide whiskers grown from rice hulls has been studied using methods of high-resolution analytical electron microscopy. Small, partially crystalline inclusions (about 10 nm) containing calcium, manganese, and oxygen are concentrated in whisker core regions, while peripheral regions are generally inclusion free. The distinct microphase distribution is evidence of a two-stage growth process in which the core region grows first, followed by normal growth toward whisker sides. Partial dislocations extend radially from the core region to the surface and tend to be paired in V-shaped configurations. Whisker surfaces exhibit microroughness due to a tendency to develop small facets on close-packed planes. The microstructural data obtained from TEM observations are used as a basis for discussion of the mechanisms involved in whisker growth, and a model of the growth process is proposed. The model includes a two-dimensional growth mechanism involving vapor, liquid, and solid phases, although it is significantly different from the classical vapor-liquid-solid (VLS) process of whisker growth.

Influence of SMAT Parameters on Microstructural and Mechanical Properties of Al-Mg-Si Alloy AA 6061

NASA Astrophysics Data System (ADS)

Anand Kumar, S.; Satish Kumar, P.; Ganesh Sundara Raman, S.; Sankara Narayanan, T. S. N.

2017-04-01

In the present work, the influence of surface mechanical attrition treatment (SMAT) parameters on the microstructural and mechanical properties of an aluminum-magnesium-silicon alloy AA 6061 was studied using design of experiment technique. Balls of three different diameters were used, and SMAT was done for three different durations. The microstructural features of the surface layer fabricated by SMAT were characterized by cross-sectional scanning electron microscopic observations, x-ray diffraction technique and transmission electron microscopy. The microindentation hardness, nanoindentation hardness and surface roughness were determined. Due to SMAT, nanocrystallites formed on the surface and near-surface regions, and hardness and surface roughness increased. The ball diameter was the most influencing SMAT parameter compared to the treatment duration. However, interaction between ball diameter and treatment duration could not be ignored. Regression equations were developed relating the process parameters to the surface properties. The ball diameter and treatment duration could thus be properly selected as per the required values of roughness and/or the hardness.

Shaping thin film growth and microstructure pathways via plasma and deposition energy: a detailed theoretical, computational and experimental analysis.

PubMed

Sahu, Bibhuti Bhusan; Han, Jeon Geon; Kersten, Holger

2017-02-15

Understanding the science and engineering of thin films using plasma assisted deposition methods with controlled growth and microstructure is a key issue in modern nanotechnology, impacting both fundamental research and technological applications. Different plasma parameters like electrons, ions, radical species and neutrals play a critical role in nucleation and growth and the corresponding film microstructure as well as plasma-induced surface chemistry. The film microstructure is also closely associated with deposition energy which is controlled by electrons, ions, radical species and activated neutrals. The integrated studies on the fundamental physical properties that govern the plasmas seek to determine their structure and modification capabilities under specific experimental conditions. There is a requirement for identification, determination, and quantification of the surface activity of the species in the plasma. Here, we report a detailed study of hydrogenated amorphous and crystalline silicon (c-Si:H) processes to investigate the evolution of plasma parameters using a theoretical model. The deposition processes undertaken using a plasma enhanced chemical vapor deposition method are characterized by a reactive mixture of hydrogen and silane. Later, various contributions of energy fluxes on the substrate are considered and modeled to investigate their role in the growth of the microstructure of the deposited film. Numerous plasma diagnostic tools are used to compare the experimental data with the theoretical results. The film growth and microstructure are evaluated in light of deposition energy flux under different operating conditions.

Improved amorphous/crystalline silicon interface passivation for heterojunction solar cells by low-temperature chemical vapor deposition and post-annealing treatment.

PubMed

Wang, Fengyou; Zhang, Xiaodan; Wang, Liguo; Jiang, Yuanjian; Wei, Changchun; Xu, Shengzhi; Zhao, Ying

2014-10-07

In this study, hydrogenated amorphous silicon (a-Si:H) thin films are deposited using a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) system. The Si-H configuration of the a-Si:H/c-Si interface is regulated by optimizing the deposition temperature and post-annealing duration to improve the minority carrier lifetime (τeff) of a commercial Czochralski (Cz) silicon wafer. The mechanism of this improvement involves saturation of the microstructural defects with hydrogen evolved within the a-Si:H films due to the transformation from SiH2 into SiH during the annealing process. The post-annealing temperature is controlled to ∼180 °C so that silicon heterojunction solar cells (SHJ) could be prepared without an additional annealing step. To achieve better performance of the SHJ solar cells, we also optimize the thickness of the a-Si:H passivation layer. Finally, complete SHJ solar cells are fabricated using different temperatures for the a-Si:H film deposition to study the influence of the deposition temperature on the solar cell parameters. For the optimized a-Si:H deposition conditions, an efficiency of 18.41% is achieved on a textured Cz silicon wafer.

Tribological Characteristics of Submicron SiC(p)-GR(p)/Zn-35Al-1Mg Composites in Semisolidification Casting process

NASA Astrophysics Data System (ADS)

Liu, S.; Fang, Z. W.; Li, L. X.

2018-05-01

Uniform SiC(p)-GR(p)/Zn-35Al-1Mg composites were prepared by powder pressing and semisolidification stirring-casting process by adding submicron silicon carbide and graphite reinforcement particles in an aluminum-zinc alloy matrix. Micro Vickers hardness and microstructures of the novel composites were studied, and their wear properties and wear temperature were measured for different load and friction conditions. The results show that silicon carbide and graphite particles homogeneously mix in the matrix, while contained silicon carbide particles improve the matrix hardness to 8.4%, graphite improves the matrix hardness to 16.8%, but two of them, combined, reduce the matrix hardness to 7.6%; the rate of temperature rise of the zinc-aluminum matrix alloy is the highest than the other three composites and is up to 48.5° C/s at 1.69MPa. At 0.56MPa and sliding 26.4km, the graphite composite anti-wear effect is optimal, while at 1.13MPa, the wear resistance of silicon carbide and graphite compound particles is the best; in the other case of only silicon carbide particles, the wear resistance is increased to 35% at 1.69MPa and 26.4km, and its anti-wear effects are excellent.

Preparation of silicon target material by adding Al-B master alloy in directional solidification

NASA Astrophysics Data System (ADS)

Li, Pengting; Wang, Kai; Ren, Shiqiang; Jiang, Dachuan; Tan, Yi

2017-03-01

The silicon target material was prepared by adding Al-6B master alloy in directional solidification. The microstructure was characterized and the resistivity was studied in this work. The results showed that the purity of the silicon target material was more than 99.999% (5N). The resistivity was ranges from 0.002 to 0.030 Ω·cm along the ingot height. It was revealed that the particles of AlB2 in Al-6B master alloy would react spontaneously and generate clusters of [B] and [Al] in molten silicon at 1723 K. After directional solidification, the content of B and Al were increasing gradually with the increase of solidified fraction. The measured values of B were in good agreement with the curve of the Scheil equation below 80% of the ingot height. The mean concentration of B was about 17.20 ppmw and the mean concentration of Al was about 8.07 ppmw after directional solidification. The measured values of Al were fitting well with the curve of values which the effective segregation coefficient was 0.00378. It was observed that B co-doped Al in directional solidification polysilicon could regulate resistivity mutually. This work provides the theoretical basis and technical support for industrial production of the silicon target material.

Fibrillar structure and elasticity of hydrating collagen: a quantitative multiscale approach.

PubMed

Morin, Claire; Hellmich, Christian; Henits, Peter

2013-01-21

It is well known that hydration of collagenous tissues leads to their swelling, as well as to softening of their elastic behavior. However, it is much less clear which microstructural and micromechanical "rules" are involved in this process. Here, we develop a theoretical approach cast in analytical mathematical formulations, which is experimentally validated by a wealth of independent tests on collagenous tissues, such as X-ray diffraction, vacuum drying, mass measurements, and Brillouin light scattering. The overall emerging picture is the following: air-drying leaves water only in the gap zones between the triple-helical collagen molecules; upon re-hydration, the extrafibrillar space is established at volumes directly proportional to the hydration-induced swelling of the (micro) fibrils, until the maximum equatorial distance between the long collagen molecules is reached. Thereafter, the volume of the fibrils stays constant, and only the extrafibrillar volume continues to grow. At all these hydration stages, the elastic behavior is governed by the same, hydration-invariant mechanical interaction pattern of only two, interpenetrating mechanical phases: transversely isotropic molecular collagen and isotropic water (or empty pores in the vacuum-dried case). Copyright © 2012 Elsevier Ltd. All rights reserved.

Microstructure and corrosion resistance of sputter-deposited titanium-chromium alloy coatings

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

Landolt, D.; Robyr, C.; Mettraux, P.

1998-10-01

Titanium, chromium, and titanium-chromium alloy coatings were sputter-deposited to study their corrosion behaviors in relation to microstructure and composition. Silicon substrates were used to study the effect of alloying on intrinsic corrosion resistance of the coating materials, and brass substrates were used to study the effect of alloying on the penetrating porosity of the coatings. Corrosion behavior was characterized using linear sweep voltammetry. The crystal structure of the coatings was examined by x-ray diffraction (XRD) and the microstructure by scanning electron microscopy (SEM). Electrochemical impedance spectroscopy (EIS) was used to estimate the real surface area of the coatings. Results showedmore » alloying of titanium with chromium greatly influenced microstructure of the coatings. Alloying led to deposits of higher apparent density and, in some cases, to an x-ray amorphous structure. Alloy coatings showed significantly lower corrosion currents than the constituting metals. The effect was attributed to a smoother surface topography. When corrected of differences in real surface area, the intrinsic corrosion rate of the alloy coatings did not differ significantly from that of the constituting metals. Alloy coatings deposited on brass exhibited a lower porosity than titanium or chromium metal coatings produced under identical conditions.« less

Ostwald ripening of faceted Si particles in an Al-Si-Cu melt

DOE PAGES

Shahani, A. J.; Xiao, X.; Skinner, K.; ...

2016-07-04

The microstructural evolution of an Al-Si-Cu alloy during Ostwald ripening is imaged via synchrotron-based, four-dimensional (i.e., space and time resolved) X-ray tomography. Samples of composition Al-32 wt%Si-15 wt%Cu were annealed isothermally at 650 °C, in the two-phase solid-liquid regime, while tomographic projections were collected in situ over the course of five hours. Advances in experimental methods and computational approaches enable us to characterize the local interfacial curvatures and velocities during ripening. The sequence of three-dimensional reconstructions and interfacial shape distributions shows highly faceted Si particles in a copper-enriched liquid, that become increasingly isotropic or rounded over time. In addition, wemore » find that the coarsening rate constant is approximately the same in the binary and ternary systems. By coupling these experimental measurements with CALPHAD modeling and ab initio molecular dynamics simulation, we assess the influence of Cu on the coarsening process. Lastly, we find the unusual “pinning” of microstructure at the junction between rough and smooth interfaces and suggest a mechanism for this behavior.« less

Changes of composition and microstructure of joint interface of tungsten coated carbon by high heat flux

NASA Astrophysics Data System (ADS)

Tokunaga, K.; Matsubara, T.; Miyamoto, Y.; Takao, Y.; Yoshida, N.; Noda, N.; Kubota, Y.; Sogabe, T.; Kato, T.; Plöchl, L.

2000-12-01

Tungsten coatings of 0.5 and 1 mm thickness were successfully deposited by the vacuum plasma spraying (VPS) technique on carbon/carbon fiber composite (CFC), CX-2002U and isotropic fine grained graphite, IG-430U. High heat flux experiments by irradiation of electron beam with uniform profile were performed on the coated samples in order to prove the suitability and load limit of such coating materials. The cross-sectional composition and structure of the interface of VPS-W and carbon material samples were investigated. Compositional analyses showed that the Re/W multi-layer acts as diffusion barrier for carbon and suppresses tungsten carbide formation in the VPS-W layer at high temperature about 1300°C. Microstructure of the joint interface of the sample changed in the case of a peak temperature of about 2800°C. The multi-layer structure completely disappeared and compositional distribution was almost uniform in the interface of the sample after melting and resolidification. The diffusion barrier for carbon is not expected to act in this stage.

Characterization by thermoelectric power of a commercial aluminum-iron-silicon alloy (8011) during isothermal precipitation

NASA Astrophysics Data System (ADS)

Luiggi, Ney José A.

1998-11-01

We have characterized a commercial 8011 (Al-Fe-Si) alloy by studying samples under different initial states of strain hardening and iron and silicon supersaturation using thermoelectric power as a measurement technique. Isothermal kinetics of precipitation are obtained in the temperature range between 225 °C and 600 °C. We determine the atom fraction precipitated for each microstructural condition, identifying the dominant alloying additions and evaluating the typical parameters of the precipitated phases, such as, for example, the apparent activation energy. Finally, we determine the time-temperature-transformation (TTT) diagrams. Our results prove that iron is the alloying addition that controls the precipitation kinetics of the 8011 alloy in the temperature range studied.

NDE of structural ceramics

NASA Technical Reports Server (NTRS)

Klima, S. J.; Vary, A.

1986-01-01

Radiographic, ultrasonic, scanning laser acoustic microscopy (SLAM), and thermo-acoustic microscopy techniques were used to characterize silicon nitride and silicon carbide modulus-of-rupture test specimens in various stages of fabrication. Conventional and microfocus X-ray techniques were found capable of detecting minute high density inclusions in as-received powders, green compacts, and fully densified specimens. Significant density gradients in sintered bars were observed by radiography, ultrasonic velocity, and SLAM. Ultrasonic attenuation was found sensitive to microstructural variations due to grain and void morphology and distribution. SLAM was also capable of detecting voids, inclusions and cracks in finished test bars. Consideration is given to the potential for applying thermo-acoustic microscopy techniques to green and densified ceramics. The detection probability statistics and some limitations of radiography and SLAM also are discussed.

Tribology study of reduced graphene oxide sheets on silicon substrate synthesized via covalent assembly.

PubMed

Ou, Junfei; Wang, Jinqing; Liu, Sheng; Mu, Bo; Ren, Junfang; Wang, Honggang; Yang, Shengrong

2010-10-19

Reduced graphene oxide (RGO) sheets were covalently assembled onto silicon wafers via a multistep route based on the chemical adsorption and thermal reduction of graphene oxide (GO). The formation and microstructure of RGO were analyzed by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, Raman spectroscopy, and water contact angle (WCA) measurements. Characterization by atomic force microscopy (AFM) was performed to evaluate the morphology and microtribological behaviors of the samples. Macrotribological performance was tested on a ball-on-plate tribometer. Results show that the assembled RGO possesses good friction reduction and antiwear ability, properties ascribed to its intrinsic structure, that is, the covalent bonding to the substrate and self-lubricating property of RGO.

Formation of porous surface layers in reaction bonded silicon nitride during processing

NASA Technical Reports Server (NTRS)

Shaw, N. J.; Glasgow, T. K.

1979-01-01

Microstructural examination of reaction bonded silicon nitride (RBSN) has shown that there is often a region adjacent to the as-nitrided surfaces that is even more porous than the interior of this already quite porous material. Because this layer of large porosity is considered detrimental to both the strength and oxidation resistance of RBSN, a study was undertaken to determine if its formation could be prevented during processing. All test bars studied were made from a single batch of Si powder which was milled for 4 hours in heptane in a vibratory mill using high density alumina cylinders as the grinding media. After air drying the powder, bars were compacted in a single acting die and hydropressed.

Development of refractive X-ray focusing optics at Diamond Light Source

NASA Astrophysics Data System (ADS)

Alianelli, L.; Sawhney, K. J. S.; Loader, I. M.; Jenkins, D. W. K.; Stevens, R.; Snigirev, A.; Snigireva, I.

2007-09-01

The Diamond Optics & Metrology Group and the collaborators at the STFC Central Microstructure Facility have initiated a program for the design and fabrication of in-line micro- and nano-focusing optics for synchrotron radiation beamlines. The first type of optics fabricated is a kinoform lens in silicon on the same model proposed by K. Evans- Lutterodt et al [Opt. Expr. 11 (2003) 919.]. The fabrication utilised ultra high resolution electron beam lithographic patterning of an electron sensitive SU8 polymer and deep reactive ion etching of silicon. The first test of the focusing properties was performed at the ESRF BM5 optics beamline. In this paper we present details on the design and fabrication, and discuss the test results.

Investigation of the mechanical properties of FeNiCrMnSi high entropy alloy wear resistant

NASA Astrophysics Data System (ADS)

Buluc, G.; Florea, I.; Chelariu, R.; Popescu, G.; Carcea, I.

2016-06-01

In this paper we investigated microstructure, hardness and wear resistance for FeNiCrMnAl, high entropy alloy. The FeNiCrMnSi, high entropy alloy was elaborated in a medium induction furnace, by choosing the silicon, as an alliance element within the equi- atomic high entropy alloy, we managed to obtain a dendritic structure, the formation of intermetallic compounds or separated silicon. The medium hardness value of the investigated alloy was 948.33 HV and the medium value of the friction coefficient was 0.6655 in the first 20 seconds and 0.5425 for 1667 seconds. The volume loss of the high entropy alloy FeNiCrMnSi was 0.0557 mm3.

Dielectric properties of magnetorheological elastomers with different microstructure

NASA Astrophysics Data System (ADS)

Moucka, R.; Sedlacik, M.; Cvek, M.

2018-03-01

Composite materials containing magnetic particles organised within the polymer matrix by the means of an external magnetic field during the curing process were prepared, and their dielectric properties were compared with their isotropic analogues of the same filler concentration but homogeneous spatial distribution. A substantial dielectric response observed for anisotropic systems in a form of relaxation processes was explained as charge transport via the mechanism of variable range hopping. The changes in registered relaxations' critical frequency and shape of dielectric spectra with the filler concentration were discussed in terms of decreasing anisotropy of the system. The knowledge of the dielectric response of studied systems is essential for their practical applications such as piezoresistive sensors or radio-absorbing materials.

The features of self-assembling organic bilayers important to the formation of anisotropic inorganic materials in microgravity conditions

NASA Technical Reports Server (NTRS)

Talham, Daniel R.; Adair, James H.

2005-01-01

Materials with directional properties are opening new horizons in a variety of applications including chemistry, electronics, and optics. Structural, optical, and electrical properties can be greatly augmented by the fabrication of composite materials with anisotropic microstructures or with anisotropic particles uniformly dispersed in an isotropic matrix. Examples include structural composites, magnetic and optical recording media, photographic film, certain metal and ceramic alloys, and display technologies including flat panel displays. The new applications and the need for model particles in scientific investigations are rapidly out-distancing the ability to synthesize anisotropic particles with specific chemistries and narrowly distributed physical characteristics (e.g. size distribution, shape, and aspect ratio).

Pore- and micro-structural characterization of a novel structural binder based on iron carbonation

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

Das, Sumanta, E-mail: Sumanta.Das@asu.edu; Stone, David, E-mail: dajstone@gmail.com; Convey, Diana, E-mail: Diana.Convey@asu.edu

2014-12-15

The pore- and micro-structural features of a novel binding material based on the carbonation of waste metallic iron powder are reported in this paper. The binder contains metallic iron powder as the major ingredient, followed by additives containing silica and alumina to facilitate favorable reaction product formation. Compressive strengths sufficient for a majority of concrete applications are attained. The material pore structure is investigated primarily through mercury intrusion porosimetry whereas electron microscopy is used for microstructural characterization. Reduction in the overall porosity and the average pore size with an increase in carbonation duration from 1 day to 4 days ismore » noticed. The pore structure features are used in predictive models for gas and moisture transport (water vapor diffusivity and moisture permeability) through the porous medium which dictates its long-term durability when used in structural applications. Comparisons of the pore structure with those of a Portland cement paste are also provided. The morphology of the reaction products in the iron-based binder, and the distribution of constituent elements in the microstructure are also reported. - Highlights: • Carbonation of iron produces a dense microstructure. • Pore volume in iron carbonate lower, critical size higher than those in OPC pastes • Reaction product contains iron, carbon, silicon, aluminum and calcium. • Power-law for porosity-moisture permeability relationship was established.« less

Study program to develop and evaluate die and container materials for the growth of silicon ribbons

NASA Technical Reports Server (NTRS)

1978-01-01

Initial sessile drop experiments on SiC, Si3N4 and A1N were conducted. Very promising results were achieved on both SiC and Si3N4 where minimal penetration of these CNTD coatings by molten silicon was observed. More detailed characterization of the CNTD microstructures was accomplished as well as X-ray characterization of the third and fourth candidate materials system sets (i.e. A1N and altered Si3N4). Polished sections of post sessile drop specimens were also prepared and evaluated. The techniques of full scale crucible hot pressing were developed and die grinding development was initiated. The apparatus for measurement of oxygen partial pressure was reconstructed and calibrated. The sessile drop temperature measurement procedure was calibrated for absorption by the pyrex view-port and additional Auger electron analysis was performed at the interface of molten silicon with CNTD Si3N4 and A1N.

Material removal effect of microchannel processing by femtosecond laser

NASA Astrophysics Data System (ADS)

Zhang, Pan; Chen, Lei; Chen, Jianxiong; Tu, Yiliu

2017-11-01

Material processing using ultra-short-pulse laser is widely used in the field of micromachining, especially for the precision processing of hard and brittle materials. This paper reports a theoretical and experimental study of the ablation characteristics of a silicon wafer under micromachining using a femtosecond laser. The ablation morphology of the silicon wafer surface is surveyed by a detection test with an optical microscope. First, according to the relationship between the diameter of the ablation holes and the incident laser power, the ablation threshold of the silicon wafer is found to be 0.227 J/cm2. Second, the influence of various laser parameters on the size of the ablation microstructure is studied and the ablation morphology is analyzed. Furthermore, a mathematical model is proposed that can calculate the ablation depth per time for a given laser fluence and scanning velocity. Finally, a microchannel milling test is carried out on the micromachining center. The effectiveness and accuracy of the proposed models are verified by comparing the estimated depth to the actual measured results.

Thermal Stability of Hi-Nicalon SiC Fiber in Nitrogen and Silicon Environments

NASA Technical Reports Server (NTRS)

Bhatt, R. T.; Garg, A.

1995-01-01

The room temperature tensile strength of uncoated and two types of pyrolytic boron nitride coated (PBN and Si-rich PBN) Hi-Nicalon SiC fibers was determined after 1 to 400 hr heat treatments to 1800 C under N2 pressures of 0.1, 2, and 4 MPa, and under 0.1 Mpa argon and vacuum environments. In addition, strength stability of both uncoated and coated fibers embedded in silicon powder and exposed to 0.1 MPa N2 for 24 hrs at temperatures to 1400 C was investigated. The uncoated and both types of BN coated fibers exposed to N2 for 1 hr showed noticeable strength degradation above 1400 C and 1600 C, respectively. The strength degradation appeared independent of nitrogen pressure, time of heat treatment, and surface coatings. TEM microstructural analysis suggests that flaws created due to SiC grain growth are responsible for the strength degradation. In contact with silicon powder, the uncoated and both types of PBN coated fibers degrade rapidly above 1350 C.

Feasibility of SiC composite structures for 1644 deg gas turbine seal applications

NASA Technical Reports Server (NTRS)

Darolia, R.

1979-01-01

The feasibility of silicon carbide composite structures was evaluated for 1644 K gas turbine seal applications. The silicon carbide composites evaluated consisted of Si/SiC Silcomp (Trademark) - and sintered silicon carbide as substrates, both with attached surface layers containing BN as an additive. A total of twenty-eight candidates with variations in substrate type and density, and layer chemistry, density, microstructure, and thickness were evaluated for abradability, cold particle erosion resistance, static oxidation resistance, ballistic impact resistance, and fabricability. The BN-free layers with variations in density and pore size were later added for evaluation. The most promising candidates were evaluated for Mach 1.0 gas oxidation/erosion resistance from 1477 K to 1644 K. The as-fabricated rub layers did not perform satisfactorily in the gas oxidation/erosion tests. However, preoxidation was found to be beneficial in improving the hot gas erosion resistance. Overall, the laboratory and rig test evaluations show that material properties are suitable for 1477 K gas turbine seal applications.

Effect of chromium underlayer on the properties of nano-crystalline diamond films

NASA Astrophysics Data System (ADS)

Garratt, E.; AlFaify, S.; Yoshitake, T.; Katamune, Y.; Bowden, M.; Nandasiri, M.; Ghantasala, M.; Mancini, D. C.; Thevuthasan, S.; Kayani, A.

2013-01-01

This paper investigated the effect of chromium underlayer on the structure, microstructure, and composition of the nano-crystalline diamond films. Nano-crystalline diamond thin films were deposited at high temperature in microwave-induced plasma diluted with nitrogen, on single crystal silicon substrate with a thin film of chromium as an underlayer. Characterization of the film was implemented using non-Rutherford backscattering spectrometry, Raman spectroscopy, near-edge x-ray absorption fine structure, x-ray diffraction, and atomic force microscopy. Nanoindentation studies showed that the films deposited on chromium underlayer have higher hardness values compared to those deposited on silicon without an underlayer. Diamond and graphitic phases of the films evaluated by x-ray and optical spectroscopic analyses determined consistency between the sp2 and sp3 phases of carbon in chromium sample to that of diamond grown on silicon. Diffusion of chromium was observed using ion beam analysis which was correlated with the formation of chromium complexes by x-ray diffraction.

Cu6Sn5 Whiskers Precipitated in Sn3.0Ag0.5Cu/Cu Interconnection in Concentrator Silicon Solar Cells Solder Layer

PubMed Central

Zhang, Liang; Liu, Zhi-quan; Yang, Fan; Zhong, Su-juan

2017-01-01

Cu6Sn5 whiskers precipitated in Sn3.0Ag0.5Cu/Cu interconnection in concentrator silicon solar cells solder layer were found and investigated after reflow soldering and during aging. Ag3Sn fibers can be observed around Cu6Sn5 whiskers in the matrix microstructure, which can play an active effect on the reliability of interconnection. Different morphologies of Cu6Sn5 whiskers can be observed, and hexagonal rod structure is the main morphology of Cu6Sn5 whiskers. A hollow structure can be observed in hexagonal Cu6Sn5 whiskers, and a screw dislocation mechanism was used to represent the Cu6Sn5 growth. Based on mechanical property testing and finite element simulation, Cu6Sn5 whiskers were regarded as having a negative effect on the durability of Sn3.0Ag0.5Cu/Cu interconnection in concentrator silicon solar cells solder layer. PMID:28772686

Non-destructive evaluation of nano-sized structure of thin film devices by using small angle neutron scattering.

PubMed

Shin, E J; Seong, B S; Choi, Y; Lee, J K

2011-01-01

Nano-sized multi-layers copper-doped SrZrO3, platinum (Pt) and silicon oxide (SiO2) on silicon substrates were prepared by dense plasma focus (DPF) device with the high purity copper anode tip and analyzed by using small angle neutron scattering (SANS) to establish a reliable method for the non-destructive evaluation of the under-layer structure. Thin film was well formed at the time-to-dip of 5 microsec with stable plasma of DPF. Several smooth intensity peaks were periodically observed when neutron beam penetrates the thin film with multi-layers perpendicularly. The platinum layer is dominant to intensity peaks, where the copper-doped SrZnO3 layer next to the platinum layer causes peak broadening. The silicon oxide layer has less effect on the SANS spectra due to its relative thick thickness. The SANS spectra shows thicknesses of platinum and copper-doped SrZnO3 layers as 53 and 25 nm, respectively, which are well agreement with microstructure observation.

Soviet Developments in High Temperature Ceramics No. 1, January-December 1975

DTIC Science & Technology

1976-02-25

in microstructure and granulometric composition of silicon nitride in the process of hot pressing were studied by optical and electron micrographic...and on the laboratory-made a-alumina specimens^have shown that densely- sintered ceramics can be produced by a simplified process using a- Al -O...dusting of the powdered ceramic materials, spinel slurry deposition and subsequent fusion by a plasma jet traveling along the coated surface at

Directional Thermal Emission and Absorption from Surface Microstructures in Metalized Plastics

DTIC Science & Technology

2013-09-01

conductive surfaces for directional emission is presented. First, key accomplishments in exploiting surface plasmons for coherent thermal emission from...than as an absorbing coating . In the 2005 design proposed by Lee et al., thermally excited surface waves at a silicon carbide to photonic crystal stack...sufficiently to significantly effect the film durability and thermal conductivity , the profile of the cavity begins to change shape. Although a case

Effect of micro-structural modifier on the morphology of silicon rich secondary phase and strain hardening behavior of eutectic Al-Si alloy

NASA Astrophysics Data System (ADS)

Mansoor, M.; Salam, I.; Tauqir, A.

2016-08-01

Eutectic Al-Si alloys find their applications in moderate to severe tribological conditions, for example: pistons, casings of high speed pumps and slide sleeves. The higher hardness, so the better tribological properties, are originated by the formation of a silicon rich secondary phase, however, the morphology of the secondary phase drastically influence the toughness of the alloy. Microstructural modifiers are used to control the toughness which modifies the Si rich secondary phase into dispersed spherical structure instead of needle-like network. In the present study, a mixture of chemical fluxes was used to modify the Si phase. The alloy was cast into a sand mold and characterized by scanning electron microscopy, energy dispersive spectroscopy, hardness testing and tensile testing. It was found that the morphology of the Si phase was altered to acicular structure due to the modification process. In comparison, the un-modified alloy contained Si phase in needle-like structure. The effect of modifier was also pronounced on the mechanical properties, where increase of 50% in yield strength, 56% in tensile strength and 200% in elongation occurred. A discernable raise in strain hardening component indicated the improved strain harden ability and formability of the modified alloy.

Joining and Integration of Silicon Nitride Ceramics for Aerospace and Energy Systems

NASA Technical Reports Server (NTRS)

Singh, M.; Asthana, R.

2009-01-01

Light-weight, creep-resistant silicon nitride ceramics possess excellent high-temperature strength and are projected to significantly raise engine efficiency and performance when used as turbine components in the next-generation turbo-shaft engines without the extensive cooling that is needed for metallic parts. One key aspect of Si3N4 utilization in such applications is its joining response to diverse materials. In an ongoing research program, the joining and integration of Si3N4 ceramics with metallic, ceramic, and composite materials using braze interlayers with the liquidus temperature in the range 750-1240C is being explored. In this paper, the self-joining behavior of Kyocera Si3N4 and St. Gobain Si3N4 using a ductile Cu-based active braze (Cu-ABA) containing Ti will be presented. Joint microstructure, composition, hardness, and strength as revealed by optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Knoop microhardness test, and offset compression shear test will be presented. Additionally, microstructure, composition, and joint strength of Si3N4/Inconel 625 joints made using Cu-ABA, will be presented. The results will be discussed with reference to the role of chemical reactions, wetting behavior, and residual stresses in joints.

A multiphysics microstructure-resolved model for silicon anode lithium-ion batteries

NASA Astrophysics Data System (ADS)

Wang, Miao; Xiao, Xinran; Huang, Xiaosong

2017-04-01

Silicon (Si) is one of the most promising next generation anode materials for lithium-ion batteries (LIBs), but the use of Si in LIBs has been rather limited. The main challenge is its large volume change (up to 300%) during battery cycling. This can lead to the fracture of Si, failure at the interfaces between electrode components, and large dimensional change on the cell level. To optimize the Si electrode/battery design, a model that considers the interactions of different cell components is needed. This paper presents the development of a multiphysics microstructure-resolved model (MRM) for LIB cells with a-Si anode. The model considered the electrochemical reactions, Li transports in electrolyte and electrodes, dimensional changes and stresses, property evolution with the structure, and the coupling relationships. Important model parameters, such as the diffusivity, reaction rate constant, and apparent transfer coefficient, were determined by correlating the simulation results to experiments. The model was validated with experimental results in the literature. The use of this model was demonstrated in a parameter study of Si nanowall|Li cells. The specific and volumetric capacities of the cell as a function of the size, length/size ratio, spacing of the nanostructure, and Li+ concentration in electrolyte were investigated.

Microstructure and ferroelectricity of BaTiO3 thin films on Si for integrated photonics

NASA Astrophysics Data System (ADS)

Kormondy, Kristy J.; Popoff, Youri; Sousa, Marilyne; Eltes, Felix; Caimi, Daniele; Rossell, Marta D.; Fiebig, Manfred; Hoffmann, Patrik; Marchiori, Chiara; Reinke, Michael; Trassin, Morgan; Demkov, Alexander A.; Fompeyrine, Jean; Abe, Stefan

2017-02-01

Significant progress has been made in integrating novel materials into silicon photonic structures in order to extend the functionality of photonic circuits. One of these promising optical materials is BaTiO3 or barium titanate (BTO) that exhibits a very large Pockels coefficient as required for high-speed light modulators. However, all previous demonstrations show a noticable reduction of the Pockels effect in BTO thin films deposited on silicon substrates compared to BTO bulk crystals. Here, we report on the strong dependence of the Pockels effect in BTO thin films on their microstructure, and provide guidelines on how to engineer thin films with strong electro-optic response. We employ several deposition methods such as molecular beam epitaxy and chemical vapor deposition to realize BTO thin films with different morphology and crystalline structure. While a linear electro-optic response is present even in porous, polycrystalline BTO thin films with an effective Pockels coefficient r eff = 6 pm V-1, it is maximized for dense, tetragonal, epitaxial BTO films (r eff = 140 pm V-1). By identifying the key structural predictors of electro-optic response in BTO/Si, we provide a roadmap to fully exploit the linear electro-optic effect in novel hybrid oxide/semiconductor nanophotonic devices.

Membrane-on-a-chip: microstructured silicon/silicon-dioxide chips for high-throughput screening of membrane transport and viral membrane fusion.

PubMed

Kusters, Ilja; van Oijen, Antoine M; Driessen, Arnold J M

2014-04-22

Screening of transport processes across biological membranes is hindered by the challenge to establish fragile supported lipid bilayers and the difficulty to determine at which side of the membrane reactants reside. Here, we present a method for the generation of suspended lipid bilayers with physiological relevant lipid compositions on microstructured Si/SiO2 chips that allow for high-throughput screening of both membrane transport and viral membrane fusion. Simultaneous observation of hundreds of single-membrane channels yields statistical information revealing population heterogeneities of the pore assembly and conductance of the bacterial toxin α-hemolysin (αHL). The influence of lipid composition and ionic strength on αHL pore formation was investigated at the single-channel level, resolving features of the pore-assembly pathway. Pore formation is inhibited by a specific antibody, demonstrating the applicability of the platform for drug screening of bacterial toxins and cell-penetrating agents. Furthermore, fusion of H3N2 influenza viruses with suspended lipid bilayers can be observed directly using a specialized chip architecture. The presented micropore arrays are compatible with fluorescence readout from below using an air objective, thus allowing high-throughput screening of membrane transport in multiwell formats in analogy to plate readers.

Boron depth profiles and residual damage following rapid thermal annealing of low-temperature BSi molecular ion implantation in silicon

NASA Astrophysics Data System (ADS)

Liang, J. H.; Wang, S. C.

2007-08-01

The influence of substrate temperature on both the implantation and post-annealing characteristics of molecular-ion-implanted 5 × 1014 cm-2 77 keV BSi in silicon was investigated in terms of boron depth profiles and damage microstructures. The substrate temperatures under investigation consisted of room temperature (RT) and liquid nitrogen temperature (LT). Post-annealing treatments were performed using rapid thermal annealing (RTA) at 1050 °C for 25 s. Boron depth profiles and damage microstructures in both the as-implanted and as-annealed specimens were determined using secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM), respectively. The as-implanted results revealed that, compared to the RT specimen, the LT specimen yields a shallower boron depth profile with a reduced tail into the bulk. An amorphous layer containing a smooth amorphous-to-crystalline (a/c) interface is evident in the LT specimen while just the opposite is true in the as-implanted RT one. The as-annealed results illustrated that the extension of the boron depth profile into the bulk via transient-enhanced diffusion (TED) in the LT specimen is less than it is in the RT one. Only residual defects are visible in the LT specimen while two clear bands of dislocation loops appear in the RT one.

Nitrogen doped silicon-carbon multilayer protective coatings on carbon obtained by TVA method

NASA Astrophysics Data System (ADS)

Ciupina, Victor; Vasile, Eugeniu; Porosnicu, Corneliu; Lungu, Cristian P.; Vladoiu, Rodica; Jepu, Ionut; Mandes, Aurelia; Dinca, Virginia; Caraiane, Aureliana; Nicolescu, Virginia; Cupsa, Ovidiu; Dinca, Paul; Zaharia, Agripina

2017-08-01

Protective nitrogen doped Si-C multilayer coatings on carbon, used to improve the oxidation resistance of carbon, were obtained by Thermionic Vacuum Arc (TVA) method. The initial carbon layer having a thickness of 100nm has been deposed on a silicon substrate in the absence of nitrogen, and then a 3nm Si thin film to cover carbon layer was deposed. Further, seven Si and C layers were alternatively deposed in the presence of nitrogen ions, each having a thickness of 40nm. In order to form silicon carbide at the interface between silicon and carbon layers, all carbon, silicon and nitrogen ions energy has increased up to 150eV . The characterization of microstructure and electrical properties of as-prepared N-Si-C multilayer structures were done using Transmission Electron Microscopy (TEM, STEM) techniques, Thermal Desorption Spectroscopy (TDS) and electrical measurements. Oxidation protection of carbon is based on the reaction between oxygen and silicon carbide, resulting in SiO2, SiO and CO2, and also by reaction involving N, O and Si, resulting in silicon oxynitride (SiNxOy) with a continuously variable composition, and on the other hand, since nitrogen acts as a trapping barrier for oxygen. To perform electrical measurements, 80% silver filled two-component epoxy-based glue ohmic contacts were attached on the N-Si-C samples. Electrical conductivity was measured in constant current mode. The experimental data show the increase of conductivity with the increase of the nitrogen content. To explain the temperature behavior of electrical conductivity we assumed a thermally activated electric transport mechanism.

Microstructure-property relationships of chemically vapor deposited zirconia fiber coating for environmentally durable silicon carbide/silicon carbide composites

NASA Astrophysics Data System (ADS)

Li, Hao

In SiC/SiC ceramic matrix composites, toughness is obtained by adding a fiber coating, which provides a weak interface for crack deflection and debonding between the fiber and the matrix. However, the most commonly used fiber coatings, carbon and boron nitride, are unstable in oxidative environments. In the present study, the feasibility of using a chemically vapor deposited zirconia (CVD-ZrO2) fiber coating as an oxidation-resistant interphase for SiC/SiC composites was investigated. A study of morphological evolution in the CVD-ZrO2 coating suggested that a size-controlled displacive phase transformation from tetragonal ZrO2 ( t-ZrO2) to monoclinic ZrO2 (m-ZrO 2) was the key mechanism responsible for the weak interface behavior exhibited by the ZrO2 coating. It appeared that a low oxygen partial pressure in the CVD reactor chamber was essential for the nucleation of t-ZrO2 and therefore was responsible for the delamination behavior. With this understanding of the weak interface mechanism, minicomposite specimens containing various ZrO2 fiber coating morphologies were fabricated and tested. A fractographic analysis showed that in-situ fiber strength and minicomposite failure loads were strongly dependent on the phase contents and microstructure of the ZrO2 coating. We determined that an optimum microstructure of the ZrO2 coating should contain a predelaminated interface surrounded by a dense outer layer. The outer layer was needed to protect the fiber from degradation during the subsequent SiC matrix infiltration procedure. A preliminary tensile stress-rupture study indicated that the ZrO2 coating exhibited promising performance in terms of providing the weak interface behavior and maintaining the thermal and oxidative stability at elevated temperatures.

Capabilities of ICP-RIE cryogenic dry etching of silicon: review of exemplary microstructures

NASA Astrophysics Data System (ADS)

Sökmen, Ü.; Stranz, A.; Fündling, S.; Wehmann, H.-H.; Bandalo, V.; Bora, A.; Tornow, M.; Waag, A.; Peiner, E.

2009-10-01

Inductively coupled plasma (ICP) cryogenic dry etching was used to etch submicron pores, nano contact lines, submicron diameter pillars, thin and thick cantilevers, membrane structures and anisotropic deep structures with high aspect ratios in silicon for bio-nanoelectronics, optoelectronics and nano-micro electromechanical systems (NMEMS). The ICP cryogenic dry etching gives us the advantage of switching plasmas between etch rates of 13 nm min-1 and 4 µm min-1 for submicron pores and for membrane structures, respectively. A very thin photoresist mask can endure at -75 °C even during etching 70 µm deep for cantilevers and 300 µm deep for membrane structures. Coating the backsides of silicon membrane substrates with a thin photoresist film inhibited the lateral etching of cantilevers during their front release. Between -95 °C and -140 °C, we realized crystallographic-plane-dependent etching that creates facets only at the etch profile bottom. By varying the oxygen content and the process temperature, we achieved good control over the shape of the etched structures. The formation of black silicon during membrane etching down to 300 µm was delayed by reducing the oxygen content.

Auger Electrons as Probes for Composite Micro- and Nano- structured Materials: Application to Solid Electrolyte Interphases in Graphite and Silicon-Graphite Electrodes

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

Kalaga, Kaushik; Shkrob, Ilya A.; Haasch, Richard T.

In this study, Auger electron spectroscopy (AES) combined with ion sputtering profilometry, Xray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) have been used in a complementary fashion to examine chemical and microstructural changes in graphite (Gr) and silicon/graphite (Si/Gr) blends contained in the negative electrodes of lithium-ion cells. We demonstrate how AES can be used to characterize morphology of the solid-electrolyte interphase (SEI) deposits in such heterogeneous media, complementing well-established methods, such as XPS and SEM. In this way we demonstrate that the SEI does not consist of uniformly thick layers on the graphite and silicon; the thickness ofmore » the SEI layers in cycle-life aged electrodes follows an exponential distribution with a mean of ca. 13 nm for the graphite and ca. 20-25 nm for the silicon nanoparticles (with a crystalline core of 50-70 nm in diameter). Furthermore, a “sticky-sphere” model, in which Si nanoparticles are covered with a layer of polymer binder (that is replaced by the SEI during cycling) of variable thickness is introduced to account for the features observed.« less

Auger Electrons as Probes for Composite Micro- and Nano- structured Materials: Application to Solid Electrolyte Interphases in Graphite and Silicon-Graphite Electrodes

DOE PAGES

Kalaga, Kaushik; Shkrob, Ilya A.; Haasch, Richard T.; ...

2017-10-05

In this study, Auger electron spectroscopy (AES) combined with ion sputtering profilometry, Xray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) have been used in a complementary fashion to examine chemical and microstructural changes in graphite (Gr) and silicon/graphite (Si/Gr) blends contained in the negative electrodes of lithium-ion cells. We demonstrate how AES can be used to characterize morphology of the solid-electrolyte interphase (SEI) deposits in such heterogeneous media, complementing well-established methods, such as XPS and SEM. In this way we demonstrate that the SEI does not consist of uniformly thick layers on the graphite and silicon; the thickness ofmore » the SEI layers in cycle-life aged electrodes follows an exponential distribution with a mean of ca. 13 nm for the graphite and ca. 20-25 nm for the silicon nanoparticles (with a crystalline core of 50-70 nm in diameter). Furthermore, a “sticky-sphere” model, in which Si nanoparticles are covered with a layer of polymer binder (that is replaced by the SEI during cycling) of variable thickness is introduced to account for the features observed.« less

Impurity segregation behavior in polycrystalline silicon ingot grown with variation of electron-beam power

NASA Astrophysics Data System (ADS)

Lee, Jun-Kyu; Lee, Jin-Seok; Jang, Bo-Yun; Kim, Joon-Soo; Ahn, Young-Soo; Cho, Churl-Hee

2014-08-01

Electron beam melting (EBM) systems have been used to improve the purity of metallurgical grade silicon feedstock for photovoltaic application. Our advanced EBM system is able to effectively remove volatile impurities using a heat source with high energy from an electron gun and to continuously allow impurities to segregate at the top of an ingot solidified in a directional solidification (DS) zone in a vacuum chamber. Heat in the silicon melt should move toward the ingot bottom for the desired DS. However, heat flux though the ingot is changed as the ingot becomes longer due to low thermal conductivity of silicon. This causes a non-uniform microstructure of the ingot, finally leading to impurity segregation at its middle. In this research, EB power irradiated on the silicon melt was controlled during the ingot growth in order to suppress the change of heat flux. EB power was reduced from 12 to 6.6 kW during the growth period of 45 min with a drop rate of 0.125 kW/min. Also, the silicon ingot was grown under a constant EB power of 12 kW to estimate the effect of the drop rate of EB power. When the EB power was reduced, the grains with columnar shape were much larger at the middle of the ingot compared to the case of constant EB power. Also, the present research reports a possible reason for the improvement of ingot purity by considering heat flux behaviors.

Fabrication Characterization of Solar-Cell Silicon Wafers Using a Circular-Rhombus Tool

NASA Astrophysics Data System (ADS)

Pa, Pai-Shan

2010-01-01

A new recycling fabrication method using a custom-built designed circular-rhombus tool for a process combining of micro-electroetching and electrochemical machining for removal of the surface layers from silicon wafers of solar cells is demonstrated. The low yields of epoxy film and Si3N4 thin-film depositions are important factors in semiconductor production. The aim of the proposed recycling fabrication method is to replace the current approach, which uses strong acid and grinding and may damage the physical structure of silicon wafers and pollute to the environment. A precisely engineered clean production approach for removal of surface microstructure layers from silicon wafers is to develop a mass production system for recycling defective or discarded silicon wafers of solar cells that can reduce pollution and cost. A large diameter cathode of the circular-rhombus tool (with a small gap between the anode and the cathode) corresponds to a high rate of epoxy film removal. A high feed rate of the silicon wafers combined with a high continuous DC electric voltage results in a high removal rate. The high rotational speed of the circular-rhombus tool increases the discharge mobility and improves the removal effect associated with the high feed rate of the workpiece. A small port radius or large end angle of the rhombus anode provides a large discharge space and good removal effect only a short period of time is required to remove the Si3N4 layer and epoxy film easily and cleanly.

Design and Experimentation with Sandwich Microstructure for Catalytic Combustion-Type Gas Sensors

PubMed Central

Gu, Jun-Tao; Zhang, Yong-De; Jiang, Jin-Gang

2014-01-01

The traditional handmade catalytic combustion gas sensor has some problems such as a pairing difficulty, poor consistency, high power consumption, and not being interchangeable. To address these issues, integrated double catalytic combustion of alcohol gas sensor was designed and manufactured using silicon micro-electro-mechanical systems (MEMS) technology. The temperature field of the sensor is analyzed using the ANSYS finite element analysis method. In this work, the silicon oxide-PECVD-oxidation technique is used to manufacture a SiO2-Si3N2-SiO2 microstructure carrier with a sandwich structure, while wet etching silicon is used to form a beam structure to reduce the heat consumption. Thin-film technology is adopted to manufacture the platinum-film sensitive resistance. Nano Al2O3-ZrO-ThO is coated to format the sensor carrier, and the sensitive unit is dipped in a Pt-Pd catalyst solution to form the catalytic sensitive bridge arm. Meanwhile the uncoated catalyst carrier is considered as the reference unit, realizing an integrated chip based on a micro double bridge and forming sensors. The lines of the Pt thin-film resistance have been observed with an electronic microscope. The compensation of the sensitive material carriers and compensation materials have been analyzed using an energy spectrum. The results show that the alcohol sensor can detect a volume fraction between 0 and 4,500 × 10−6 and has good linear output characteristic. The temperature ranges from −20 to +40 °C. The humidity ranges from 30% to 85% RH. The zero output of the sensor is less than ±2.0% FS. The power consumption is ≤0.2 W, and both the response and recovery time are approximately 20 s. PMID:24625742

Design for low-cost gas metal arc weld-based aluminum 3-D printing

NASA Astrophysics Data System (ADS)

Haselhuhn, Amberlee S.

Additive manufacturing, commonly known as 3-D printing, has the potential to change the state of manufacturing across the globe. Parts are made, or printed, layer by layer using only the materials required to form the part, resulting in much less waste than traditional manufacturing methods. Additive manufacturing has been implemented in a wide variety of industries including aerospace, medical, consumer products, and fashion, using metals, ceramics, polymers, composites, and even organic tissues. However, traditional 3-D printing technologies, particularly those used to print metals, can be prohibitively expensive for small enterprises and the average consumer. A low-cost open-source metal 3-D printer has been developed based upon gas metal arc weld (GMAW) technology. Using this technology, substrate release mechanisms have been developed, allowing the user to remove a printed metal part from a metal substrate by hand. The mechanical and microstructural properties of commercially available weld alloys were characterized and used to guide alloy development in 4000 series aluminum-silicon alloys. Wedge casting experiments were performed to screen magnesium, strontium, and titanium boride alloying additions in hypoeutectic aluminum-silicon alloys for their properties and the ease with which they could be printed. Finally, the top performing alloys, which were approximately 11.6% Si modified with strontium and titanium boride were cast, extruded, and drawn into wire. These wires were printed and the mechanical and microstructural properties were compared with those of commercially available alloys. This work resulted in an easier-to-print aluminum-silicon-strontium alloy that exhibited lower porosity, equivalent yield and tensile strengths, yet nearly twice the ductility compared to commercial alloys.

A nonlinear mechanics model of bio-inspired hierarchical lattice materials consisting of horseshoe microstructures

PubMed Central

Ma, Qiang; Cheng, Huanyu; Jang, Kyung-In; Luan, Haiwen; Hwang, Keh-Chih; Rogers, John A.; Huang, Yonggang; Zhang, Yihui

2016-01-01

Development of advanced synthetic materials that can mimic the mechanical properties of non-mineralized soft biological materials has important implications in a wide range of technologies. Hierarchical lattice materials constructed with horseshoe microstructures belong to this class of bio-inspired synthetic materials, where the mechanical responses can be tailored to match the nonlinear J-shaped stress-strain curves of human skins. The underlying relations between the J-shaped stress-strain curves and their microstructure geometry are essential in designing such systems for targeted applications. Here, a theoretical model of this type of hierarchical lattice material is developed by combining a finite deformation constitutive relation of the building block (i.e., horseshoe microstructure), with the analyses of equilibrium and deformation compatibility in the periodical lattices. The nonlinear J-shaped stress-strain curves and Poisson ratios predicted by this model agree very well with results of finite element analyses (FEA) and experiment. Based on this model, analytic solutions were obtained for some key mechanical quantities, e.g., elastic modulus, Poisson ratio, peak modulus, and critical strain around which the tangent modulus increases rapidly. A negative Poisson effect is revealed in the hierarchical lattice with triangular topology, as opposed to a positive Poisson effect in hierarchical lattices with Kagome and honeycomb topologies. The lattice topology is also found to have a strong influence on the stress-strain curve. For the three isotropic lattice topologies (triangular, Kagome and honeycomb), the hierarchical triangular lattice material renders the sharpest transition in the stress-strain curve and relative high stretchability, given the same porosity and arc angle of horseshoe microstructure. Furthermore, a demonstrative example illustrates the utility of the developed model in the rapid optimization of hierarchical lattice materials for reproducing the desired stress-strain curves of human skins. This study provides theoretical guidelines for future designs of soft bio-mimetic materials with hierarchical lattice constructions. PMID:27087704

A nonlinear mechanics model of bio-inspired hierarchical lattice materials consisting of horseshoe microstructures

NASA Astrophysics Data System (ADS)

Ma, Qiang; Cheng, Huanyu; Jang, Kyung-In; Luan, Haiwen; Hwang, Keh-Chih; Rogers, John A.; Huang, Yonggang; Zhang, Yihui

2016-05-01

Development of advanced synthetic materials that can mimic the mechanical properties of non-mineralized soft biological materials has important implications in a wide range of technologies. Hierarchical lattice materials constructed with horseshoe microstructures belong to this class of bio-inspired synthetic materials, where the mechanical responses can be tailored to match the nonlinear J-shaped stress-strain curves of human skins. The underlying relations between the J-shaped stress-strain curves and their microstructure geometry are essential in designing such systems for targeted applications. Here, a theoretical model of this type of hierarchical lattice material is developed by combining a finite deformation constitutive relation of the building block (i.e., horseshoe microstructure), with the analyses of equilibrium and deformation compatibility in the periodical lattices. The nonlinear J-shaped stress-strain curves and Poisson ratios predicted by this model agree very well with results of finite element analyses (FEA) and experiment. Based on this model, analytic solutions were obtained for some key mechanical quantities, e.g., elastic modulus, Poisson ratio, peak modulus, and critical strain around which the tangent modulus increases rapidly. A negative Poisson effect is revealed in the hierarchical lattice with triangular topology, as opposed to a positive Poisson effect in hierarchical lattices with Kagome and honeycomb topologies. The lattice topology is also found to have a strong influence on the stress-strain curve. For the three isotropic lattice topologies (triangular, Kagome and honeycomb), the hierarchical triangular lattice material renders the sharpest transition in the stress-strain curve and relative high stretchability, given the same porosity and arc angle of horseshoe microstructure. Furthermore, a demonstrative example illustrates the utility of the developed model in the rapid optimization of hierarchical lattice materials for reproducing the desired stress-strain curves of human skins. This study provides theoretical guidelines for future designs of soft bio-mimetic materials with hierarchical lattice constructions.

A nonlinear mechanics model of bio-inspired hierarchical lattice materials consisting of horseshoe microstructures.

PubMed

Ma, Qiang; Cheng, Huanyu; Jang, Kyung-In; Luan, Haiwen; Hwang, Keh-Chih; Rogers, John A; Huang, Yonggang; Zhang, Yihui

2016-05-01

Development of advanced synthetic materials that can mimic the mechanical properties of non-mineralized soft biological materials has important implications in a wide range of technologies. Hierarchical lattice materials constructed with horseshoe microstructures belong to this class of bio-inspired synthetic materials, where the mechanical responses can be tailored to match the nonlinear J-shaped stress-strain curves of human skins. The underlying relations between the J-shaped stress-strain curves and their microstructure geometry are essential in designing such systems for targeted applications. Here, a theoretical model of this type of hierarchical lattice material is developed by combining a finite deformation constitutive relation of the building block (i.e., horseshoe microstructure), with the analyses of equilibrium and deformation compatibility in the periodical lattices. The nonlinear J-shaped stress-strain curves and Poisson ratios predicted by this model agree very well with results of finite element analyses (FEA) and experiment. Based on this model, analytic solutions were obtained for some key mechanical quantities, e.g., elastic modulus, Poisson ratio, peak modulus, and critical strain around which the tangent modulus increases rapidly. A negative Poisson effect is revealed in the hierarchical lattice with triangular topology, as opposed to a positive Poisson effect in hierarchical lattices with Kagome and honeycomb topologies. The lattice topology is also found to have a strong influence on the stress-strain curve. For the three isotropic lattice topologies (triangular, Kagome and honeycomb), the hierarchical triangular lattice material renders the sharpest transition in the stress-strain curve and relative high stretchability, given the same porosity and arc angle of horseshoe microstructure. Furthermore, a demonstrative example illustrates the utility of the developed model in the rapid optimization of hierarchical lattice materials for reproducing the desired stress-strain curves of human skins. This study provides theoretical guidelines for future designs of soft bio-mimetic materials with hierarchical lattice constructions.

Evaluation of co-cokes from bituminous coal with vacuum resid or decant oil, and evaluation of anthracites, as precursors to graphite

NASA Astrophysics Data System (ADS)

Nyathi, Mhlwazi S.

2011-12-01

Graphite is utilized as a neutron moderator and structural component in some nuclear reactor designs. During the reactor operaction the structure of graphite is damaged by collision with fast neutrons. Graphite's resistance to this damage determines its lifetime in the reactor. On neutron irradiation, isotropic or near-isotropic graphite experiences less structural damage than anisotropic graphite. The degree of anisotropy in a graphite artifact is dependent on the structure of its precursor coke. Currently, there exist concerns over a short supply of traditional precursor coke, primarily due to a steadily increasing price of petroleum. The main goal of this study was to study the anisotropic and isotropic properties of graphitized co-cokes and anthracites as a way of investigating the possibility of synthesizing isotropic or near-isotropic graphite from co-cokes and anthracites. Demonstrating the ability to form isotropic or near-isotropic graphite would mean that co-cokes and anthracites have a potential use as filler material in the synthesis of nuclear graphite. The approach used to control the co-coke structure was to vary the reaction conditions. Co-cokes were produced by coking 4:1 blends of vacuum resid/coal and decant oil/coal at temperatures of 465 and 500 °C for reaction times of 12 and 18 hours under autogenous pressure. Co-cokes obtained were calcined at 1420 °C and graphitized at 3000 °C for 24 hours. Optical microscopy, X-ray diffraction, temperature-programmed oxidation and Raman spectroscopy were used to characterize the products. It was found that higher reaction temperature (500 °C) or shorter reaction time (12 hours) leads to an increase in co-coke structural disorder and an increase in the amount of mosaic carbon at the expense of textural components that are necessary for the formation of anisotropic structure, namely, domains and flow domains. Characterization of graphitized co-cokes showed that the quality, as expressed by the degree of graphitization and crystallite dimensions, of the final product is dependent on the nature of the precursor co-coke. The methodology for studying anthracites was to select two anthracites on basis of rank, PSOC1515 being semi-anthracite and DECS21 anthracite. The selected anthracites were graphitized, in both native and demineralized states, under the same conditions as co-cokes. Products obtained from DECS21 showed higher degrees of graphitization and larger crystallite dimensions than products obtained from PSOC1515. Demineralization of anthracites served to increase the degree of graphitization, indicating that the minerals contained in these anthracites have no graphitization-enhancing ability. A larger crystallite length for products obtained from native versions, compared to demineralized versions, was attributed to a formation and decomposition of a silicon carbide during graphitization of native versions. In order to examine the anisotropic and isotropic properties, nuclear-grade graphite samples obtained from Oak Ridge National Laboratory (ORNL) and commercial graphite purchased from Fluka were characterized under similar conditions as graphitized co-cokes and anthracites. These samples served as representatives of "two extremes", with ORNL samples being the isotropic end and commercial graphite being the anisotropic end. Through evaluating relationships between structural parameters, it was observed that graphitized co-cokes are situated, structurally, somewhere between the "two extremes", whereas graphitized anthracites are closer to the anisotropic end. Basically, co-cokes have a better potential than anthracites to transform to isotropic or near-isotropic graphite upon graphitization. By co-coking vacuum resid/coal instead of decant oil/coal or using 500 °C instead of 465 °C, a shift away from commercial graphite towards ORNL samples was attained. Graphitizing a semi-anthracite or demineralizing anthracites before graphitization also caused a shift towards ORNL samples.

Effective response of classical, auxetic and chiral magnetoelastic materials by use of a new variational principle

NASA Astrophysics Data System (ADS)

Danas, K.

2017-08-01

This work provides a rigorous analysis of the effective response, i.e., average magnetization and magnetostriction, of magnetoelastic composites that are subjected to overall magnetic and mechanical loads. It clarifies the differences between a coupled magnetomechanical analysis in which one applies a Eulerian (current) magnetic field and an electroactive one where the Lagrangian (reference) electric field is usually applied. For this, we propose an augmented vector potential variational formulation to carry out numerical periodic homogenization studies of magnetoelastic solids at finite strains and magnetic fields. We show that the developed variational principle can be used for bottom-up design of microstructures with desired magnetomechanical coupling by properly canceling out the macro-geometry and specimen shape effects. To achieve that, we properly treat the average Maxwell stresses arising from the medium surrounding the magnetoelastic representative volume element (RVE), while at the same time we impose a uniform average Eulerian and not Lagrangian magnetic field. The developed variational principle is then used to study a large number of ideal as well as more realistic two-dimensional microstructures. We study the effect of particle volume fraction, particle distribution and particle shape and orientation upon the effective magnetoelastic response at finite strains. We consider also unstructured isotropic microstructures based on random adsorption algorithms and we carry out a convergence study of the representativity of the proposed unit cells. Finally, three-phase two-dimensional auxetic microstructures are analyzed. The first consists of a periodic distribution of voids and particle chains in a polymer matrix, while the second takes advantage of particle shape and chirality to produce negative and positive swelling by proper change of the chirality and the applied magnetic field.

Incomplete initial nutation diffusion imaging: An ultrafast, single-scan approach for diffusion mapping.

PubMed

Ianuş, Andrada; Shemesh, Noam

2018-04-01

Diffusion MRI is confounded by the need to acquire at least two images separated by a repetition time, thereby thwarting the detection of rapid dynamic microstructural changes. The issue is exacerbated when diffusivity variations are accompanied by rapid changes in T 2 . The purpose of the present study is to accelerate diffusion MRI acquisitions such that both reference and diffusion-weighted images necessary for quantitative diffusivity mapping are acquired in a single-shot experiment. A general methodology termed incomplete initial nutation diffusion imaging (INDI), capturing two diffusion contrasts in a single shot, is presented. This methodology creates a longitudinal magnetization reservoir that facilitates the successive acquisition of two images separated by only a few milliseconds. The theory behind INDI is presented, followed by proof-of-concept studies in water phantom, ex vivo, and in vivo experiments at 16.4 and 9.4 T. Mean diffusivities extracted from INDI were comparable with diffusion tensor imaging and the two-shot isotropic diffusion encoding in the water phantom. In ex vivo mouse brain tissues, as well as in the in vivo mouse brain, mean diffusivities extracted from conventional isotropic diffusion encoding and INDI were in excellent agreement. Simulations for signal-to-noise considerations identified the regimes in which INDI is most beneficial. The INDI method accelerates diffusion MRI acquisition to single-shot mode, which can be of great importance for mapping dynamic microstructural properties in vivo without T 2 bias. Magn Reson Med 79:2198-2204, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

Effect of wheel speed on magnetic and mechanical properties of melt spun Fe-6.5 wt.% Si high silicon steel

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

Ouyang, Gaoyuan; Jensen, Brandt; Tang, Wei

Here, Fe-Si electric steel is the most widely used soft magnetic material in electric machines and transformers. Increasing the silicon content from 3.2 wt.% to 6.5 wt.% brings about large improvement in the magnetic and electrical properties. However, 6.5 wt.% silicon steel is inherited with brittleness owing to the formation of B2 and D0 3 ordered phase. To obtain ductility in Fe-6.5wt.% silicon steel, the ordered phase has to be bypassed with methods like rapid cooling. In present paper, the effect of cooling rate on magnetic and mechanical properties of Fe-6.5wt.% silicon steel is studied by tuning the wheel speedmore » during melt spinning process. The cooling rate significantly alters the ordering and microstructure, and thus the mechanical and magnetic properties. X-ray diffraction data shows that D0 3 ordering was fully suppressed at high wheel speeds but starts to nucleate at 10m/s and below, which correlates with the increase of Young’s modulus towards low wheel speeds as tested by nanoindentation. The grain sizes of the ribbons on the wheel side decrease with increasing wheel speeds, ranging from ~100 μm at 1m/s to ~8 μm at 30m/s, which lead to changes in coercivity.« less

Effect of wheel speed on magnetic and mechanical properties of melt spun Fe-6.5 wt.% Si high silicon steel

DOE PAGES

Ouyang, Gaoyuan; Jensen, Brandt; Tang, Wei; ...

2017-12-19

Here, Fe-Si electric steel is the most widely used soft magnetic material in electric machines and transformers. Increasing the silicon content from 3.2 wt.% to 6.5 wt.% brings about large improvement in the magnetic and electrical properties. However, 6.5 wt.% silicon steel is inherited with brittleness owing to the formation of B2 and D0 3 ordered phase. To obtain ductility in Fe-6.5wt.% silicon steel, the ordered phase has to be bypassed with methods like rapid cooling. In present paper, the effect of cooling rate on magnetic and mechanical properties of Fe-6.5wt.% silicon steel is studied by tuning the wheel speedmore » during melt spinning process. The cooling rate significantly alters the ordering and microstructure, and thus the mechanical and magnetic properties. X-ray diffraction data shows that D0 3 ordering was fully suppressed at high wheel speeds but starts to nucleate at 10m/s and below, which correlates with the increase of Young’s modulus towards low wheel speeds as tested by nanoindentation. The grain sizes of the ribbons on the wheel side decrease with increasing wheel speeds, ranging from ~100 μm at 1m/s to ~8 μm at 30m/s, which lead to changes in coercivity.« less

Effect of wheel speed on magnetic and mechanical properties of melt spun Fe-6.5 wt.% Si high silicon steel

NASA Astrophysics Data System (ADS)

Ouyang, Gaoyuan; Jensen, Brandt; Tang, Wei; Dennis, Kevin; Macziewski, Chad; Thimmaiah, Srinivasa; Liang, Yongfeng; Cui, Jun

2018-05-01

Fe-Si electric steel is the most widely used soft magnetic material in electric machines and transformers. Increasing the silicon content from 3.2 wt.% to 6.5 wt.% brings about large improvement in the magnetic and electrical properties. However, 6.5 wt.% silicon steel is inherited with brittleness owing to the formation of B2 and D03 ordered phase. To obtain ductility in Fe-6.5wt.% silicon steel, the ordered phase has to be bypassed with methods like rapid cooling. In present paper, the effect of cooling rate on magnetic and mechanical properties of Fe-6.5wt.% silicon steel is studied by tuning the wheel speed during melt spinning process. The cooling rate significantly alters the ordering and microstructure, and thus the mechanical and magnetic properties. X-ray diffraction data shows that D03 ordering was fully suppressed at high wheel speeds but starts to nucleate at 10m/s and below, which correlates with the increase of Young's modulus towards low wheel speeds as tested by nanoindentation. The grain sizes of the ribbons on the wheel side decrease with increasing wheel speeds, ranging from ˜100 μm at 1m/s to ˜8 μm at 30m/s, which lead to changes in coercivity.

State-of-the-art of SiAlON materials. [conferences

NASA Technical Reports Server (NTRS)

Dutta, S.

1979-01-01

Research presented includes work on phase relations, crystal structure, synthesis, fabrication, and properties of various SiAlONs. The essential features of compositions, fabrication methods, and microstructure are reviewed. High temperature flexure strength, creep, fracture toughness, oxidation, and thermal shock resistance are discussed. These data are compared to those for some currently produced silicon nitride ceramics to assess the potential SiAlON materials for use in advanced gas turbine engines.

Molybdenum disilicide composites

DOEpatents

Rodriguez, Robert P.; Petrovic, John J.

2001-01-01

Molybdenum disilicide/.beta.'-Si.sub.6-z Al.sub.z O.sub.z N.sub.8-z, wherein z=a number from greater than 0 to about 5, composites are made by use of in situ reactions among .alpha.-silicon nitride, molybdenum disilicide, and aluminum. Molybdenum disilicide within a molybdenum disilicide/.beta.'-Si.sub.6-z Al.sub.z O.sub.z N.sub.8-z eutectoid matrix is the resulting microstructure when the invention method is employed.

IR femtochemistry on the surface of wide-gap ionic crystals

NASA Astrophysics Data System (ADS)

Laptev, V. B.; Chekalin, S. V.; Dorofeyev, I. A.; Kompanets, V. O.; Pigulsky, S. V.; Ryabov, E. A.

2018-02-01

We have found and studied a phenomenon of the growth of films resulting from decomposition of some organic and silicon-containing molecules adsorbed on the surface of ionic crystals under the action of IR (1.4-5.4 µm) femtosecond radiation of a moderate intensity, ~1011 W cm-2. In the gas phase, these molecules do not decompose. Microstructured films consisting of amorphous carbon, graphite oxide, and silicon dioxide have been obtained. The formation of carbon films was accompanied by the appearance of different hydrocarbons in the gas phase. The extensive films of graphite oxide have been obtained. The decomposition of molecules on the surface is apparently caused by non-resonant ionization and subsequent deep fragmentation. The mechanisms of ionization at relatively low intensities of the femtosecond IR radiation have been discussed.

Evaluation of Primary Dendrite Arm Spacings from Aluminum-7wt% Silicon alloys Directionally Solidified aboard the International Space Station - Comparison with Theory

NASA Technical Reports Server (NTRS)

Angart, Samuel; Lauer, Mark; Poirier, David; Tewari, Surendra; Rajamure, Ravi; Grugel, Richard

2015-01-01

Aluminum – 7wt% silicon alloys were directionally solidified in the microgravity environment aboard the International Space Station as part of the “MIcrostructure Formation in CASTing of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions” (MICAST) European led program. Cross-sections of the sample during periods of steady-state growth were metallographically prepared from which the primary dendrite arm spacing (lambda 1) was measured. These spacings were found to be in reasonable agreement with the Hunt-Lu model which assumes a diffusion-controlled, convectionless, environment during controlled solidification. Deviation from the model was found and is attributed to gravity-independent thermocapillary convection where, over short distances, the liquid appears to have separated from the crucible wall.

The role of silicon, vacancies, and strain in carbon distribution for low temperature bainite

DOE PAGES

Sampath, S.; Rementeria, R.; Huang, X.; ...

2016-02-19

Here, we investigated the phenomenon of carbon supersaturation and carbon clustering in bainitic ferrite with atom probe tomography (APT) and ab-initio density functional theory (DFT) calculations. The experimental results show a homogeneous distribution of silicon in the microstructure, which contains both ferrite and retained austenite. This distribution is mimicked well by the computational approach. In addition, an accumulation of C in certain regions of the bainitic ferrite with C concentrations up to 13 at % is observed. Based on the DFT results, these clusters are explained as strained, tetragonal regions in the ferritic bainite, in which the solution enthalpy ofmore » C can reach large, negative values. It seems that Si itself only has a minor influence on this phenomenon.« less

Validation of calcaneus trabecular microstructure measurements by HR-pQCT.

PubMed

Metcalf, Louis M; Dall'Ara, Enrico; Paggiosi, Margaret A; Rochester, John R; Vilayphiou, Nicolas; Kemp, Graham J; McCloskey, Eugene V

2018-01-01

Assessment of calcaneus microstructure using high-resolution peripheral quantitative computed tomography (HR-pQCT) might be used to improve fracture risk predictions or to assess responses to pharmacological and physical interventions. To develop a standard clinical protocol for the calcaneus, we validated calcaneus trabecular microstructure measured by HR-pQCT against 'gold-standard' micro-CT measurements. Ten human cadaveric feet were scanned in situ using HR-pQCT (isotropic 82μm voxel size) at 100, 150 and 200ms integration times, and at 100ms integration time following removal of the calcaneus from the foot (ex vivo). Dissected portions of these bones were scanned using micro-computed tomography (micro-CT) at an isotropic 17.4μm voxel size. HR-pQCT images were rigidly registered to those obtained with micro-CT and divided into multiple 5mm sided cubes to evaluate and compare morphometric parameters between the modalities. Standard HR-pQCT measurements (derived bone volume fraction (BV/TV d ); trabecular number, Tb.N; derived trabecular thickness, Tb.Th d ; derived trabecular spacing, Tb.Sp d ) and corresponding micro-CT voxel-based measurements (BV/TV, Tb.N, Tb.Th, Tb.Sp) were compared. A total of 108 regions of interest were analysed across the 10 specimens. At all integration times HR-pQCT BV/TV d was strongly correlated with micro-CT BV/TV (r 2 =0.95-0.98, RMSE=1%), but BV/TV d was systematically lower than that measured by micro-CT (mean bias=5%). In contrast, HR-pQCT systematically overestimated Tb.N at all integration times; of the in situ scans, 200ms yielded the lowest mean bias and the strongest correlation with micro-CT (r 2 =0.61, RMSE=0.15mm -1 ). Regional analysis revealed greater accuracy for Tb.N in the superior regions of the calcaneus at all integration times in situ (mean bias=0.44-0.85mm -1 ; r 2 =0.70-0.88, p<0.001 versus mean bias=0.63-1.46mm -1 ; r 2 ≤0.08, p≥0.21 for inferior regions). Tb.Sp d was underestimated by HR-pQCT compared to micro-CT, but showed similar trends with integration time and the region evaluated as Tb.N. HR-pQCT Tb.Th d was also underestimated and moderately correlated (r 2 =0.53-0.59) with micro-CT Tb.Th, independently from the integration time. Stronger correlations, smaller biases and error were found in the scans of the calcaneus ex vivo compared to in situ. Calcaneus trabecular BV/TV d and trabecular microstructure, particularly in the superior region of the calcaneus, can be assessed by HR-pQCT. The highest integration time examined, 200ms, compared best with micro-CT. Weaker correlations for microstructure at inferior regions, and also with lower integration times, might limit the use of the proposed protocol, which warrants further investigation in vivo. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Response of Velocity Anisotropy of Shale Under Isotropic and Anisotropic Stress Fields

NASA Astrophysics Data System (ADS)

Li, Xiaying; Lei, Xinglin; Li, Qi

2018-03-01

We investigated the responses of P-wave velocity and associated anisotropy in terms of Thomsen's parameters to isotropic and anisotropic stress fields on Longmaxi shales cored along different directions. An array of piezoelectric ceramic transducers allows us to measure P-wave velocities along numerous different propagation directions. Anisotropic parameters, including the P-wave velocity α along a symmetry axis, Thomsen's parameters ɛ and δ, and the orientation of the symmetry axis, could then be extracted by fitting Thomsen's weak anisotropy model to the experimental data. The results indicate that Longmaxi shale displays weakly intrinsic velocity anisotropy with Thomsen's parameters ɛ and δ being approximately 0.05 and 0.15, respectively. The isotropic stress field has only a slight effect on velocity and associated anisotropy in terms of Thomsen's parameters. In contrast, both the magnitude and orientation of the anisotropic stress field with respect to the shale fabric are important in controlling the evolution of velocity and associated anisotropy in a changing stress field. For shale with bedding-parallel loading, velocity anisotropy is enhanced because velocities with smaller angles relative to the maximum stress increase significantly during the entire loading process, whereas those with larger angles increase slightly before the yield stress and afterwards decrease with the increasing differential stress. For shale with bedding-normal loading, anisotropy reversal is observed, and the anisotropy is progressively modified by the applied differential stress. Before reaching the yield stress, velocities with smaller angles relative to the maximum stress increase more significantly and even exceed the level of those with larger angles. After reaching the yield stress, velocities with larger angles decrease more significantly. Microstructural features such as the closure and generation of microcracks can explain the modification of the velocity anisotropy due to the applied stress anisotropy.

Integrating histology and MRI in the first digital brain of common squirrel monkey, Saimiri sciureus

NASA Astrophysics Data System (ADS)

Sun, Peizhen; Parvathaneni, Prasanna; Schilling, Kurt G.; Gao, Yurui; Janve, Vaibhav; Anderson, Adam; Landman, Bennett A.

2015-03-01

This effort is a continuation of development of a digital brain atlas of the common squirrel monkey, Saimiri sciureus, a New World monkey with functional and microstructural organization of central nervous system similar to that of humans. Here, we present the integration of histology with multi-modal magnetic resonance imaging (MRI) atlas constructed from the brain of an adult female squirrel monkey. The central concept of this work is to use block face photography to establish an intermediate common space in coordinate system which preserves the high resolution in-plane resolution of histology while enabling 3-D correspondence with MRI. In vivo MRI acquisitions include high resolution T2 structural imaging (300 μm isotropic) and low resolution diffusion tensor imaging (600 um isotropic). Ex vivo MRI acquisitions include high resolution T2 structural imaging and high resolution diffusion tensor imaging (both 300 μm isotropic). Cortical regions were manually annotated on the co-registered volumes based on published histological sections in-plane. We describe mapping of histology and MRI based data of the common squirrel monkey and construction of a viewing tool that enable online viewing of these datasets. The previously descried atlas MRI is used for its deformation to provide accurate conformation to the MRI, thus adding information at the histological level to the MRI volume. This paper presents the mapping of single 2D image slice in block face as a proof of concept and this can be extended to map the atlas space in 3D coordinate system as part of the future work and can be loaded to an XNAT system for further use.

EPR and transient capacitance studies on electron-irradiated silicon solar cells

NASA Technical Reports Server (NTRS)

Lee, Y. H.; Cheng, L. J.; Mooney, P. M.; Corbett, J. W.

1977-01-01

One and two ohm-cm solar cells irradiated with 1 MeV electrons at 30 C were studied using both EPR and transient capacitance techniques. In 2 ohm-cm cells, Si-G6 and Si-G15 EPR spectra and majority carrier trapping levels at (E sub V + 0.23) eV and (E sub V + 0.38) eV were observed, each of which corresponded to the divacancy and the carbon-oxygen-vacancy complex, respectively. In addition, a boron-associated defect with a minority carrier trapping level at (E sub C -0.27) eV was observed. In 1 ohm-cm cells, the G15 spectrum and majority carrier trap at (E sub V + 0.38) eV were absent and an isotropic EPR line appeared at g = 1.9988 (+ or - 0.0003); additionally, a majority carrier trapping center at (E sub V + 0.32) eV, was found which could be associated with impurity lithium. The formation mechanisms of these defects are discussed according to isochronal annealing data in electron-irradiated p-type silicon.

Facile fabrication of a silicon nanowire sensor by two size reduction steps for detection of alpha-fetoprotein biomarker of liver cancer

NASA Astrophysics Data System (ADS)

Binh Pham, Van; ThanhTung Pham, Xuan; Nhat Khoa Phan, Thanh; Thanh Tuyen Le, Thi; Chien Dang, Mau

2015-12-01

We present a facile technique that only uses conventional micro-techniques and two size-reduction steps to fabricate wafer-scale silicon nanowire (SiNW) with widths of 200 nm. Initially, conventional lithography was used to pattern SiNW with 2 μm width. Then the nanowire width was decreased to 200 nm by two size-reduction steps with isotropic wet etching. The fabricated SiNW was further investigated when used with nanowire field-effect sensors. The electrical characteristics of the fabricated SiNW devices were characterized and pH sensitivity was investigated. Then a simple and effective surface modification process was carried out to modify SiNW for subsequent binding of a desired receptor. The complete SiNW-based biosensor was then used to detect alpha-fetoprotein (AFP), one of the medically approved biomarkers for liver cancer diagnosis. Electrical measurements showed that the developed SiNW biosensor could detect AFP with concentrations of about 100 ng mL-1. This concentration is lower than the necessary AFP concentration for liver cancer diagnosis.

Fabrication and Characterization of CMOS-MEMS Thermoelectric Micro Generators

PubMed Central

Kao, Pin-Hsu; Shih, Po-Jen; Dai, Ching-Liang; Liu, Mao-Chen

2010-01-01

This work presents a thermoelectric micro generator fabricated by the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process and the post-CMOS process. The micro generator is composed of 24 thermocouples in series. Each thermocouple is constructed by p-type and n-type polysilicon strips. The output power of the generator depends on the temperature difference between the hot and cold parts in the thermocouples. In order to prevent heat-receiving in the cold part in the thermocouples, the cold part is covered with a silicon dioxide layer with low thermal conductivity to insulate the heat source. The hot part of the thermocouples is suspended and connected to an aluminum plate, to increases the heat-receiving area in the hot part. The generator requires a post-CMOS process to release the suspended structures. The post-CMOS process uses an anisotropic dry etching to remove the oxide sacrificial layer and an isotropic dry etching to etch the silicon substrate. Experimental results show that the micro generator has an output voltage of 67 μV at the temperature difference of 1 K. PMID:22205869

DIFFUSION OF MAGNESIUM AND MICROSTRUCTURES IN Mg+ IMPLANTED SILICON CARBIDE

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

Jiang, Weilin; Edwards, Danny J.; Jung, Hee Joon

2014-08-28

Following our previous reports [ 1- 3], further isochronal annealing (2 hrs.) of the monocrystalline 6H-SiC and polycrystalline CVD 3C-SiC was performed at 1573 and 1673 K in Ar environment. SIMS data indicate that observable Mg diffusion in 6H-SiC starts and a more rapid diffusion in CVD 3C-SiC occurs at 1573 K. The implanted Mg atoms tend to diffuse deeper into the undamaged CVD 3C-SiC. The microstructure with Mg inclusions in the as-implanted SiC has been initially examined using high-resolution STEM. The presence of Mg in the TEM specimen has been confirmed based on EDS mapping. Additional monocrystalline 3C-SiC samplesmore » have been implanted at 673 K to ion fluence 3 times higher than the previous one. RBS/C analysis has been performed before and after thermal annealing at 1573 K for 12 hrs. Isothermal annealing at 1573 K is being carried out and Mg depth profiles being measured. Microstructures in both the as-implanted and annealed samples are also being examined using STEM.« less

Microengineered Conductive Elastomeric Electrodes for Long-Term Electrophysiological Measurements with Consistent Impedance under Stretch

PubMed Central

Hu, Dinglong; Cheng, Tin Kei; Xie, Kai; Lam, Raymond H. W.

2015-01-01

In this research, we develop a micro-engineered conductive elastomeric electrode for measurements of human bio-potentials with the absence of conductive pastes. Mixing the biocompatible polydimethylsiloxane (PDMS) silicone with other biocompatible conductive nano-particles further provides the material with an electrical conductivity. We apply micro-replica mold casting for the micro-structures, which are arrays of micro-pillars embedded between two bulk conductive-PDMS layers. These micro-structures can reduce the micro-structural deformations along the direction of signal transmission; therefore the corresponding electrical impedance under the physical stretch by the movement of the human body can be maintained. Additionally, we conduct experiments to compare the electrical properties between the bulk conductive-PDMS material and the microengineered electrodes under stretch. We also demonstrate the working performance of these micro-engineered electrodes in the acquisition of the 12-lead electrocardiographs (ECG) of a healthy subject. Together, the presented gel-less microengineered electrodes can provide a more convenient and stable bio-potential measurement platform, making tele-medical care more achievable with reduced technical barriers for instrument installation performed by patients/users themselves. PMID:26512662

Fabrication and hydrophobic characteristics of micro / nanostructures on polydimethylsiloxane surface prepared by picosecond laser

NASA Astrophysics Data System (ADS)

Bin, Wang; Dong, Shiyun; Yan, Shixing; Gang, Xiao; Xie, Zhiwei

2018-03-01

Picosecond laser has ultrashort pulse width and ultrastrong peak power, which makes it widely used in the field of micro-nanoscale fabrication. polydimethylsiloxane (PDMS) is a typical silicone elastomer with good hydrophobicity. In order to further improve the hydrophobicity of PDMS, the picosecond laser was used to fabricate a grid-like microstructure on the surface of PDMS, and the relationship between hydrophobicity of PDMS with surface microstructure and laser processing parameters, such as processing times and cell spacing was studied. The results show that: compared with the unprocessed PDMS, the presence of surface microstructure significantly improved the hydrophobicity of PDMS. When the number of processing is constant, the hydrophobicity of PDMS decreases with the increase of cell spacing. However, when the cell spacing is fixed, the hydrophobicity of PDMS first increases and then decreases with the increase of processing times. In particular, when the times of laser processing is 6 and the cell spacing is 50μm, the contact angle of PDMS increased from 113° to 154°, which reached the level of superhydrophobic.

Conformal Nanocoatings with Uniform and Controllable Thickness on Microstructured Surfaces: A General Assembly Route.

PubMed

Hou, Yi; Wang, Zhen; Cai, Chao; Hao, Xi; Li, Dongdong; Zhao, Ning; Zhao, Yiping; Chen, Li; Ma, Hongwei; Xu, Jian

2018-02-01

Assembling nanoparticles (NPs) on various surfaces are intensively investigated for the construction of functional nanocoatings; however, it is still a challenge to fabricate conformal nanocoatings uniformly on surfaces having micro- or nanostructures. Herein, it is demonstrated that the negatively charged SiO 2 NPs and the positively charged silicon coupling agent can be assembled layer-by-layer on the microstructures based on the combination of electrostatic interaction and condensation reaction. Conformal nanocoatings with controllable thickness are formed on the microstructured surfaces with different compositions and morphologies. The formation mechanism is confirmed by using quartz crystal microbalance with dissipation (QCM-D) to study the assembly process in real time. The universality of this method is illustrated by using other reactive building blocks with opposite charge to build up the conformal nanocoatings. Application in the preparation of antireflective nanocoatings on nonplanar optical materials is demonstrated. This simple, versatile, and scalable strategy for the preparation of conformal nanocoatings is promising for practical applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Probing Phase Transformations and Microstructural Evolutions at the Small Scales: Synchrotron X-ray Microdiffraction for Advanced Applications in [Phase 3 Memory,] 3D IC (Integrated Circuits) and Solar PV (Photovoltaic) Devices

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

Radchenko, I.; Tippabhotla, S. K.; Tamura, N.

2016-10-21

Synchrotron x-ray microdiffraction (μXRD) allows characterization of a crystalline material in small, localized volumes. Phase composition, crystal orientation and strain can all be probed in few-second time scales. Crystalline changes over a large areas can be also probed in a reasonable amount of time with submicron spatial resolution. However, despite all the listed capabilities, μXRD is mostly used to study pure materials but its application in actual device characterization is rather limited. This article will explore the recent developments of the μXRD technique illustrated with its advanced applications in microelectronic devices and solar photovoltaic systems. Application of μXRD in microelectronicsmore » will be illustrated by studying stress and microstructure evolution in Cu TSV (through silicon via) during and after annealing. Here, the approach allowing study of the microstructural evolution in the solder joint of crystalline Si solar cells due to thermal cycling will be also demonstrated.« less

A time-efficient acquisition protocol for multipurpose diffusion-weighted microstructural imaging at 7 Tesla.

PubMed

Sepehrband, Farshid; O'Brien, Kieran; Barth, Markus

2017-12-01

Several diffusion-weighted MRI techniques have been developed and validated during the past 2 decades. While offering various neuroanatomical inferences, these techniques differ in their proposed optimal acquisition design, preventing clinicians and researchers benefiting from all potential inference methods, particularly when limited time is available. This study reports an optimal design that enables for a time-efficient diffusion-weighted MRI acquisition scheme at 7 Tesla. The primary audience of this article is the typical end user, interested in diffusion-weighted microstructural imaging at 7 Tesla. We tested b-values in the range of 700 to 3000 s/mm 2 with different number of angular diffusion-encoding samples, against a data-driven "gold standard." The suggested design is a protocol with b-values of 1000 and 2500 s/mm 2 , with 25 and 50 samples, uniformly distributed over two shells. We also report a range of protocols in which the results of fitting microstructural models to the diffusion-weighted data had high correlation with the gold standard. We estimated minimum acquisition requirements that enable diffusion tensor imaging, higher angular resolution diffusion-weighted imaging, neurite orientation dispersion, and density imaging and white matter tract integrity across whole brain with isotropic resolution of 1.8 mm in less than 11 min. Magn Reson Med 78:2170-2184, 2017. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Structure-Property Correlations in Al-Li Alloy Integrally Stiffened Extrusions

NASA Technical Reports Server (NTRS)

Hales, Stephen J.; Hafley, Robert A.

2001-01-01

The objective of this investigation was to establish the relationship between mechanical property anisotropy, microstructure and crystallographic texture in integrally 'T'-stiffened extruded panels fabricated from the Al-Li alloys 2195, 2098 and 2096. In-plane properties were measured as a function of orientation at two locations in the panels, namely mid-way between (Skin), and directly beneath (Base), the integral 'T' stiffeners. The 2195 extrusion exhibited the best combination of strength and toughness, but was the most anisotropic. The 2098 extrusion exhibited lower strength and comparable toughness, but was more isotropic than 2195. The 2096 extrusion exhibited the lowest strength and poor toughness, but was the most isotropic. All three alloys exhibited highly elongated grain structures and similar location-dependent variations in grain morphology. The textural characteristics comprised a beta + <100> fiber texture, similar to rolled product, in the Skin regions and alpha <111> + <100> fiber texture, comparable to axisymmetric extruded product, in the Base regions. In an attempt to quantitatively correlate texture with yield strength anisotropy, the original 'full constraint' Taylor model and a variant of the 'relaxed constraint' model, explored by Wert et al., were applied to the data. A comparison of the results revealed that the Wert model was consistently more accurate than the Taylor model.

Study on Buckling of Stiff Thin Films on Soft Substrates as Functional Materials

NASA Astrophysics Data System (ADS)

Ma, Teng

In engineering, buckling is mechanical instability of walls or columns under compression and usually is a problem that engineers try to prevent. In everyday life buckles (wrinkles) on different substrates are ubiquitous -- from human skin to a rotten apple they are a commonly observed phenomenon. It seems that buckles with macroscopic wavelengths are not technologically useful; over the past decade or so, however, thanks to the widespread availability of soft polymers and silicone materials micro-buckles with wavelengths in submicron to micron scale have received increasing attention because it is useful for generating well-ordered periodic microstructures spontaneously without conventional lithographic techniques. This thesis investigates the buckling behavior of thin stiff films on soft polymeric substrates and explores a variety of applications, ranging from optical gratings, optical masks, energy harvest to energy storage. A laser scanning technique is proposed to detect micro-strain induced by thermomechanical loads and a periodic buckling microstructure is employed as a diffraction grating with broad wavelength tunability, which is spontaneously generated from a metallic thin film on polymer substrates. A mechanical strategy is also presented for quantitatively buckling nanoribbons of piezoelectric material on polymer substrates involving the combined use of lithographically patterning surface adhesion sites and transfer printing technique. The precisely engineered buckling configurations provide a route to energy harvesters with extremely high levels of stretchability. This stiff-thin-film/polymer hybrid structure is further employed into electrochemical field to circumvent the electrochemically-driven stress issue in silicon-anode-based lithium ion batteries. It shows that the initial flat silicon-nanoribbon-anode on a polymer substrate tends to buckle to mitigate the lithiation-induced stress so as to avoid the pulverization of silicon anode. Spontaneously generated submicron buckles of film/polymer are also used as an optical mask to produce submicron periodic patterns with large filling ratio in contrast to generating only ˜100 nm edge submicron patterns in conventional near-field soft contact photolithography. This thesis aims to deepen understanding of buckling behavior of thin films on compliant substrates and, in turn, to harness the fundamental properties of such instability for diverse applications.

Effects of Heat Treatment on SiC-SiC Ceramic Matrix Composites

NASA Astrophysics Data System (ADS)

Knauf, Michael W.

Residual stresses resulting from the manufacturing process found within a silicon carbide/silicon carbide (SiC/SiC) ceramic matrix composite were thoroughly investigated through the use of high-energy X-ray diffraction and Raman microspectroscopy. The material system studied was a Rolls-Royce composite produced with Hi-Nicalon fibers woven into a five harness satin weave, coated with boron nitride and silicon carbide interphases, and subsequently infiltrated with silicon carbide particles and a silicon matrix. Constituent stress states were measured before, during, and after heat treatments ranging from 900 °C to 1300 °C for varying times between one and sixty minutes. Stress determination methods developed through these analyses can be utilized in the development of ceramic matrix composites and other materials employing boron-doped silicon. X-ray diffraction experiments were performed at the Argonne National Laboratory Advanced Photon Source to investigate the evolution of constituent stresses through heat treatment, and determine how stress states are affected at high temperature through in situ measurements during heat treatments up to 1250 °C for 30 minutes. Silicon carbide particles in the as-received condition exhibited a nearly isotropic stress state with average tensile stresses of approximately 300 MPa. The silicon matrix exhibited a complimentary average compressive stress of approximately 300 MPa. Strong X-ray diffraction evidence is presented demonstrating solid state boron diffusion and increased boron solubility found in silicon throughout heat treatment. While the constituent stress states did evolve through the heat treatment cycles, including approaching nearly stress-free conditions at temperatures close to the manufacturing temperature, no permanent relaxation of stress was observed. Raman spectroscopy was utilized to investigate stresses found within silicon carbide particles embedded within the matrix and the silicon matrix as an alternate method of measurement. The stresses determined through Raman spectroscopy were comparable to those determined through X-ray diffraction. Neither silicon carbide particles nor silicon were significantly affected through heat treatment, corroborating the X-ray diffraction results. Silicon present near fibers exhibited less compressive stress than the majority of silicon found throughout the matrix. Measurements were taken in situ and ex situ to determine the temporal evolution of the stress state at various temperatures. Heat treatments up to 1300 °C for one hour failed to produce significant changes in the residual stress state of the composite constituents. A strong trend was identified in the Raman silicon signal manifesting a continuously decreasing wavenumber with increasing heat treatment temperature between 1100 °C and 1300 °C in timeframes of less than one minute. This was found to be due to a continuously increasing electronic activation of boron within the silicon matrix, stemming from an increase of boron atoms occupying substitutional silicon lattice sites while covalently bonded to surrounding silicon. A methodology to determine the residual stress state of silicon exhibiting varying degrees of boron dopant is proposed by accounting for the changes in the Raman profile parameters. This method also allows for observing activated boron segregation in various matrix areas; wavenumber gradients in these areas exist which have been misconstrued in literature as large variations in stress, while in fact the variability is likely relatively benign.

Evaluation of the MICAST #2-12 AI-7wt%Si Sample Directionally Solidified Aboard the International Space Station

NASA Technical Reports Server (NTRS)

Tewari, Surendra N.; Ghods, Masoud; Angart, Samuel G.; Lauer, Mark; Grugel, Richard N.; Poirier, David R.

2016-01-01

The US team of the European led "MIcrostructure Formation in CASTing of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions" (MICAST) program recently received a third Aluminum - 7wt% silicon alloy that was processed in the microgravity environment aboard the International Space Station. The sample, designated MICAST#2-12, was directionally solidified in the Solidification with Quench Furnace (SQF) at a constant rate of 40micometers/s through an imposed temperature gradient of 31K/cm. Procedures taken to evaluate the state of the sample prior to sectioning for metallographic analysis are reviewed and rational for measuring the microstructural constituents, in particular the primary dendrite arm spacing (Lambda (sub1)), is given. The data are presented, put in context with the earlier samples, and evaluated in view of a relevant theoretical model.

TEM Analysis of Diffusion-Bonded Silicon Carbide Ceramics Joined Using Metallic Interlayers

NASA Technical Reports Server (NTRS)

Ozaki, T.; Hasegawa, Y.; Tsuda, H.; Mori, S.; Halbig, M. C.; Asthana, R.; Singh, M.

2017-01-01

SiC fiber-bonded ceramics (SA-Tyrannohex: SA-THX) diffusion-bonded with TiCu metallic interlayers were investigated. Thin samples of the ceramics were prepared with a focused ion beam (FIB) and the interfacial microstructure of the prepared samples was studied by transmission electron microscopy (TEM) and scanning TEM (STEM). In addition to conventional microstructure observation, for detailed analysis of reaction compounds in diffusion-bonded area, we performed STEM-EDS measurements and selected area electron diffraction (SAD) experiments. The TEM and STEM experiments revealed the diffusion-bonded area was composed of only one reaction layer, which was characterized by TiC precipitates in Cu-Si compound matrix. This reaction layer was in good contact with the SA-THX substrates, and it is concluded that the joint structure led to the excellent bonding strength.

Influence of Ni-P Coated SiC and Laser Scan Speed on the Microstructure and Mechanical Properties of IN625 Metal Matrix Composites

NASA Astrophysics Data System (ADS)

Sateesh, N. H.; Kumar, G. C. Mohan; Krishna, Prasad

2015-12-01

Nickel based Inconel-625 (IN625) metal matrix composites (MMCs) were prepared using pre-heated nickel phosphide (Ni-P) coated silicon carbide (SiC) reinforcement particles by Direct Metal Laser Sintering (DMLS) additive manufacturing process under inert nitrogen atmosphere to obtain interface influences on MMCs. The distribution of SiC particles and microstructures were characterized using optical and scanning electron micrographs, and the mechanical behaviours were thoroughly examined. The results clearly reveal that the interface integrity between the SiC particles and the IN625 matrix, the mixed powders flowability, the SiC ceramic particles and laser beam interaction, and the hardness, and tensile characteristics of the DMLS processed MMCs were improved effectively by the use of Ni-P coated SiC particles.

Influence of Composition and Process Selection on Densification of Silicon Nitride.

DTIC Science & Technology

1982-05-01

9 Accession For NTIS -GRA&I DTIC TAB F] Unannounced 0 Justificatio, Distribution/ Availability Codes Avail and/or Dist 1 Spec ial NI ...concerned with microstructural development and its influence on resultant properties of Si3 N4. Since the early observation that high alpha phase starting...pressed Si3N4 . Knoch and Gazza (2) subsequently investigated the influence of Si3 N4 starting powders with different alpha/beta phase content on the

Microstructure and Aging of Powder-Metallurgy Al Alloys

NASA Technical Reports Server (NTRS)

Blackburn, L. B.

1987-01-01

Report describes experimental study of thermal responses and aging behaviors of three new aluminum alloys. Alloys produced from rapidly solidified powders and contain 3.20 to 5.15 percent copper, 0.24 to 1.73 percent magnesium, 0.08 to 0.92 percent iron, and smaller amounts of manganese, nickel, titanium, silicon, and zinc. Peak hardness achieved at lower aging temperatures than with standard ingot-metallurgy alloys. Alloys of interest for automobile, aircraft, and aerospace applications.

Effects of the polarizability and packing density of transparent oxide films on water vapor permeation.

PubMed

Koo, Won Hoe; Jeong, Soon Moon; Choi, Sang Hun; Kim, Woo Jin; Baik, Hong Koo; Lee, Sung Man; Lee, Se Jong

2005-06-09

The tin oxide and silicon oxide films have been deposited on polycarbonate substrates as gas barrier films, using a thermal evaporation and ion beam assisted deposition process. The oxide films deposited by ion beam assisted deposition show a much lower water vapor transmission rate than those by thermal evaporation. The tin oxide films show a similar water vapor transmission rate to the silicon oxide films in thermal evaporation but a lower water vapor transmission rate in IBAD. These results are related to the fact that the permeation of water vapor with a large dipole moment is affected by the chemistry of oxides and the packing density of the oxide films. The permeation mechanism of water vapor through the oxide films is discussed in terms of the chemical interaction with water vapor and the microstructure of the oxide films. The chemical interaction of water vapor with oxide films has been investigated by the refractive index from ellipsometry and the OH group peak from X-ray photoelectron spectroscopy, and the microstructure of the composite oxide films was characterized using atomic force microscopy and a transmission electron microscope. The activation energy for water vapor permeation through the oxide films has also been measured in relation to the permeation mechanism of water vapor. The diffusivity of water vapor for the tin oxide films has been calculated from the time lag plot, and its implications are discussed.

Optical assessment of tissue anisotropy in ex vivo distended rat bladders

NASA Astrophysics Data System (ADS)

Alali, Sanaz; Aitken, Karen J.; Shröder, Annette; Bagli, Darius J.; Alex Vitkin, I.

2012-08-01

Microstructural remodelling in epithelial layers of various hollow organs, including changes in tissue anisotropy, are known to occur under mechanical distension and during disease processes. In this paper, we analyze how bladder distension alters wall anisotropy using polarized light imaging (followed by Mueller matrix decomposition). Optical retardance values of different regions of normal rat bladders under different distension pressures are derived. Then optical coherence tomography is used to measure local bladder wall thicknesses, enabling the calculation of the tissue birefringence maps as a measure of the tissue anisotropy. Selected two-photon microscopy is also performed to better understand the compositional origins of the obtained anisotropy results. The dome region of the bladder shows maximum birefringence when the bladder is distended to high pressures, whereas the ventral remains roughly isotropic during distension. In addition, the average anisotropy direction is longitudinal, along the urethra to dome. The derived wall anisotropy trends are based on birefringence as an intrinsic property of the tissue organization independent of its thickness, to aid in understanding the structure-functions relation in healthy bladders. These new insights into the wall microstructure of ex vivo distending bladders may help improve the functionality of the artificially engineered bladder tissues.

Structures, properties, and energy-storage mechanisms of the semi-lunar process cuticles in locusts.

PubMed

Wan, Chao; Hao, Zhixiu; Feng, Xiqiao

2016-10-17

Locusts have excellent jumping and kicking abilities to survive in nature, which are achieved through the energy storage and release processes occurring in cuticles, especially in the semi-lunar processes (SLP) at the femorotibial joints. As yet, however, the strain energy-storage mechanisms of the SLP cuticles remain unclear. To decode this mystery, we investigated the microstructure, material composition, and mechanical properties of the SLP cuticle and its remarkable strain energy-storage mechanisms for jumping and kicking. It is found that the SLP cuticle of adult Locusta migratoria manilensis consists of five main parts that exhibit different microstructural features, material compositions, mechanical properties, and biological functions in storing strain energy. The mechanical properties of these five components are all transversely isotropic and strongly depend on their water contents. Finite element simulations indicate that the two parts of the core region of the SLP cuticle likely make significant contributions to its outstanding strain energy-storage ability. This work deepens our understanding of the locomotion behaviors and superior energy-storage mechanisms of insects such as locusts and is helpful for the design and fabrication of strain energy-storage devices.

Structures, properties, and energy-storage mechanisms of the semi-lunar process cuticles in locusts

PubMed Central

Wan, Chao; Hao, Zhixiu; Feng, Xiqiao

2016-01-01

Locusts have excellent jumping and kicking abilities to survive in nature, which are achieved through the energy storage and release processes occurring in cuticles, especially in the semi-lunar processes (SLP) at the femorotibial joints. As yet, however, the strain energy-storage mechanisms of the SLP cuticles remain unclear. To decode this mystery, we investigated the microstructure, material composition, and mechanical properties of the SLP cuticle and its remarkable strain energy-storage mechanisms for jumping and kicking. It is found that the SLP cuticle of adult Locusta migratoria manilensis consists of five main parts that exhibit different microstructural features, material compositions, mechanical properties, and biological functions in storing strain energy. The mechanical properties of these five components are all transversely isotropic and strongly depend on their water contents. Finite element simulations indicate that the two parts of the core region of the SLP cuticle likely make significant contributions to its outstanding strain energy-storage ability. This work deepens our understanding of the locomotion behaviors and superior energy-storage mechanisms of insects such as locusts and is helpful for the design and fabrication of strain energy-storage devices. PMID:27748460

Structures, properties, and energy-storage mechanisms of the semi-lunar process cuticles in locusts

NASA Astrophysics Data System (ADS)

Wan, Chao; Hao, Zhixiu; Feng, Xiqiao

2016-10-01

Locusts have excellent jumping and kicking abilities to survive in nature, which are achieved through the energy storage and release processes occurring in cuticles, especially in the semi-lunar processes (SLP) at the femorotibial joints. As yet, however, the strain energy-storage mechanisms of the SLP cuticles remain unclear. To decode this mystery, we investigated the microstructure, material composition, and mechanical properties of the SLP cuticle and its remarkable strain energy-storage mechanisms for jumping and kicking. It is found that the SLP cuticle of adult Locusta migratoria manilensis consists of five main parts that exhibit different microstructural features, material compositions, mechanical properties, and biological functions in storing strain energy. The mechanical properties of these five components are all transversely isotropic and strongly depend on their water contents. Finite element simulations indicate that the two parts of the core region of the SLP cuticle likely make significant contributions to its outstanding strain energy-storage ability. This work deepens our understanding of the locomotion behaviors and superior energy-storage mechanisms of insects such as locusts and is helpful for the design and fabrication of strain energy-storage devices.

Effect of counterface roughness on the friction of bionic wall-shaped microstructures for gecko-like attachments.

PubMed

Kasem, Haytam; Cohen, Yossi

2017-08-04

Hairy adhesive systems involved in gecko locomotion have drawn the interest of many researchers regarding the development of bionic solutions for fast and reversible adhesive technologies. To date, despite extensive efforts to design gecko-inspired adhesive surfaces, adhesion and friction capacities are often evaluated using smooth and rigid counterfaces, in general glass, whereas most natural and artificial surfaces inevitably have a certain level of roughness. For that reason, in this study experiments tested the effects of the substrate roughness on the friction of bionic wale-shaped microstructures for gecko-like attachments. To this end, 12 substrates with different isotropic roughness were prepared using the same Epoxy material. Friction force was measured under various normal loads. It was concluded that classical roughness parameters, considered separately, are not appropriate to explain roughness-related variations in friction force. This has led us to develop a new integrative roughness parameter that combines characteristics of the surface. The parameter is capable of classifying the obtained experimental results in a readable way. An analytical model based on the experimental results has been developed to predict the variation of the friction force as a function of counterface roughness and applied normal load.

Detecting Compartmental non-Gaussian Diffusion with Symmetrized Double-PFG MRI

PubMed Central

Paulsen, Jeffrey L.; Özarslan, Evren; Komlosh, Michal E.; Basser, Peter J.; Song, Yi-Qiao

2015-01-01

Diffusion in tissue and porous media is known to be non-Gaussian and has been used for clinical indications of stroke and other tissue pathologies. However, when conventional NMR techniques are applied to biological tissues and other heterogeneous materials, the presence of multiple compartments (pores) with different Gaussian diffusivities will also contribute to the measurement of non-Gaussian behavior. Here we present Symmetrized Double PFG (sd-PFG), which can separate these two contributions to non-Gaussian signal decay as having distinct angular modulation frequencies. In contrast to prior angular d-PFG methods, sd-PFG can unambiguously extract kurtosis as an oscillation from samples with isotropic or uniformly oriented anisotropic pores, and can generally extract a combination of compartmental anisotropy and kurtosis. The method further fixes its sensitivity with respect to the time-dependence of the apparent diffusion coefficient. We experimentally demonstrate the measurement of the fourth moment (kurtosis) of diffusion and find it consistent with theoretical predictions. By enabling the unambiguous identification of contributions of compartmental kurtosis to the signal, sd-PFG has the potential to help identify the underlying micro-structural changes corresponding to current kurtosis based diagnostics and act as a novel source of contrast to better resolve tissue micro-structure. PMID:26434812

Structural and microstructural description of the glacial state in triphenyl phosphite from powder synchrotron X-ray diffraction data and Raman scattering investigations

NASA Astrophysics Data System (ADS)

Derollez, P.; Hernandez, O.; Hédoux, A.; Guinet, Y.; Masson, O.; Lefebvre, J.; Descamps, M.

2004-06-01

The structure and microstructure (refinement of the isotropic size and microstrain parameters) of the glacial state in triphenyl phosphite (TPP, P(OC 6H 5) 3) transformed at 222K have been determined from powder synchrotron X-ray diffraction data through a Rietveld and a Le Bail refinement, respectively. It is shown that the glacial state is composed of crystallites of the stable crystal phase coexisting with non-transformed supercooled liquid, the apparent size of the crystallites—depending on the aging temperature at which the glacial state is isothermally formed, [Phys. Rev. B 60 (1999) 9390]—being equal to 329.2(2) Å at 222K. The molecular conformation is slightly less mirror-symmetric than the one in the crystal state, and correlatively only one of the two unusual weak intermolecular C-H⋯O hydrogen bonds already observed in the latter state is encountered in the glacial one. Additional Raman scattering investigations confirm the previous result and reveal in addition that no hydrogen bonding interaction is observed neither in the glass nor in the liquid states.

Surface Coatings for Gas Detection via Porous Silicon

NASA Astrophysics Data System (ADS)

Ozdemir, Serdar; Li, Ji-Guang; Gole, James

2009-03-01

Nanopore covered microporous silicon interfaces have been formed via an electrochemical etch for gas sensor applications. Rapid reversible and sensitive gas sensors have been fabricated. The fabricated porous silicon (PS) gas sensors display the advantages of operation at room temperature as well as at a single, readily accessible temperature with an insensitivity to temperature drift; operation in a heat-sunk configuration, ease of coating with gas-selective materials; low cost of fabrication and operation, and the ability to rapidly assess false positives by operating the sensor in a pulsed mode. The PS surface has been modified with unique coatings on the basis of a general theory in order to achieve maximum sensitivity and selectivity. Sensing of NH3, NOx and PH3 at or below the ppm level have been observed. A typical PS nanostructure coated microstructured hybrid configuration when coated with tin oxide (NOx, CO) and gold nanostructures (NH3) provides a greatly increased sensitivity to the indicated gases. Al2O3 coating of the porous silicon using atomic layer deposition and its effect on PH3 sensing has been investigated. 20-100 nm TiO2 nanoparticles have been produced using sol-gel methods to coat PS surfaces and the effects on the selectivity and the sensitivity have been studied.

Joining and Assembly of Silicon Carbide-based Advanced Ceramics and Composites for High Temperature Applications

NASA Technical Reports Server (NTRS)

Singh, M.

2004-01-01

Silicon carbide based advanced ceramics and fiber reinforced composites are under active consideration for use in wide variety of high temperature applications within the aeronautics, space transportation, energy, and nuclear industries. The engineering designs of ceramic and composite component require fabrication and manufacturing of large and complex shaped parts of various thicknesses. In many instances, it is more economical to build up complex shapes by joining simple geometrical shapes. In addition these components have to be joined or assembled with metallic sub-components. Thus, joining and attachment have been recognized as enabling technologies for successful utilization of ceramic components in various demanding applications. In this presentation, various challenges and opportunities in design, fabrication, and testing o high temperature joints in ceramic matrix composites will be presented. Silicon carbide based advanced ceramics (CVD and hot pressed), and C/SiC and SiC/SiC composites, in different shapes and sizes, have been joined using an affordable, robust ceramic joining technology (ARCJoinT). Microstructure and high temperature mechanical properties of joints in silicon carbide ceramics and CVI and melt infiltrated SiC matrix composites will,be reported. Various joint design philosophies and design issues in joining of ceramics and composites well be discussed.

Effects of Fiber Coatings on Tensile Properties of Hi-Nicalon SiC/RBSN Tow Composites

NASA Technical Reports Server (NTRS)

Bhatt, Ramakrishna T.; Hull, David R.

1997-01-01

Uncoated Hi-Nicalon silicon carbide (SiC) fiber tows and those coated with a single surface layer of pyrolytic boron nitride (PBN), double layers of PBN/Si-rich PBN, and boron nitride (BN)/SiC coatings deposited by chemical vapor deposition (CVD) method were infiltrated with silicon slurry and then exposed to N2, for 4 hr at 1200 and 1400 C. Room temperature ultimate tensile fracture loads and microstructural characterization of uncoated and CVD coated Hi-Nicalon SiC fiber reinforced reaction-bonded silicon nitride (RBSN) tow composites were measured to select suitable interface coating(s) stable under RBSN processing conditions. Results indicate that room temperature ultimate fracture loads of the uncoated Hi-Nicalon SiC/RBSN tow composites nitrided at both temperatures were significantly lower than those of the uncoated Hi-Nicalon tows without slurry infiltration. In contrast, all CVD coated Hi-Nicalon SiC/RBSN tow composites retained a greater fraction of the dry tow fracture load after nitridation at 1200 C, but degraded significantly after nitridation at 1400 C. Reaction between metal impurities (Fe and Ni) present in the attrition milled silicon powder and uncoated regions of SiC fibers appears to be the probable cause for fiber degradation.

The microstructure of the surface layer of magnesium laser alloyed with aluminum and silicon

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

Dziadoń, Andrzej

2016-08-15

The surface layer under analysis was formed as a result of diffusion bonding of a thin AlSi20 plate to a magnesium substrate followed by laser melting. Depending on the process parameters, the laser beam melted the AlSi20 plate only or the AlSi20 plate and a layer of the magnesium surface adjacent to it. Two types of microstructure of the remelted layer were thus analyzed. If the melting zone was limited to the AlSi20 plate, the microstructure of the surface layer was typical of a rapidly solidified hypereutectic Al–Si alloy. Since, however, the liquid AlSi20 reacted with the magnesium substrate, themore » following intermetallic phases formed: Al{sub 3}Mg{sub 2}, Mg{sub 17}Al{sub 12} and Mg{sub 2}Si. The microstructure of the modified surface layer of magnesium was examined using optical, scanning electron and transmission electron microscopy. The analysis of the surface properties of the laser modified magnesium revealed that the thin layer has a microstructure of a rapidly solidified Al–Si alloy offering good protection against corrosion. By contrast, the surface layer containing particles of intermetallic phases was more resistant to abrasion but had lower corrosion resistance than the silumin type layer. - Highlights: •A CO{sub 2} laser was used for surface alloying of Mg with AlSi20. •Before alloying, an AlSi20 plate was diffusion bonded with the Mg substrate. •The process parameters affected the alloyed layer microstructure and properties. •With melting limited to AlSi20, the layer had a structure of rapidly solidified AlSi20. •Mg–Al and Mg–Si phases were present when both the substrate and the plate were melted.« less

Effect of silane/hydrogen ratio on microcrystalline silicon thin films by remote inductively coupled plasma

NASA Astrophysics Data System (ADS)

Guo, Y. N.; Wei, D. Y.; Xiao, S. Q.; Huang, S. Y.; Zhou, H. P.; Xu, S.

2013-05-01

Hydrogenated microcrystalline silicon (μc-Si:H) thin films were prepared by remote low frequency inductively coupled plasma (ICP) chemical vapor deposition system, and the effect of silane/hydrogen ratio on the microstructure and electrical properties of μc-Si:H films was systematically investigated. As silane/hydrogen ratio increases, the crystalline volume fraction Fc decreases and the ratio of the intensity of (220) peak to that of (111) peak drops as silane flow rate is increased. The FTIR result indicates that the μc-Si:H films prepared by remote ICP have a high optical response with a low hydrogen content, which is in favor of reducing light-induced degradation effect. Furthermore, the processing window of the phase transition region for remote ICP is much wider than that for typical ICP. The photosensitivity of μc-Si:H films can exceed 100 at the transition region and this ensures the possibility of the fabrication of microcrystalline silicon thin film solar cells with a open-circuit voltage of about 700 mV.

Photon-trapping microstructures enable high-speed high-efficiency silicon photodiodes

NASA Astrophysics Data System (ADS)

Gao, Yang; Cansizoglu, Hilal; Polat, Kazim G.; Ghandiparsi, Soroush; Kaya, Ahmet; Mamtaz, Hasina H.; Mayet, Ahmed S.; Wang, Yinan; Zhang, Xinzhi; Yamada, Toshishige; Devine, Ekaterina Ponizovskaya; Elrefaie, Aly F.; Wang, Shih-Yuan; Islam, M. Saif

2017-04-01

High-speed, high-efficiency photodetectors play an important role in optical communication links that are increasingly being used in data centres to handle higher volumes of data traffic and higher bandwidths, as big data and cloud computing continue to grow exponentially. Monolithic integration of optical components with signal-processing electronics on a single silicon chip is of paramount importance in the drive to reduce cost and improve performance. We report the first demonstration of micro- and nanoscale holes enabling light trapping in a silicon photodiode, which exhibits an ultrafast impulse response (full-width at half-maximum) of 30 ps and a high efficiency of more than 50%, for use in data-centre optical communications. The photodiode uses micro- and nanostructured holes to enhance, by an order of magnitude, the absorption efficiency of a thin intrinsic layer of less than 2 µm thickness and is designed for a data rate of 20 gigabits per second or higher at a wavelength of 850 nm. Further optimization can improve the efficiency to more than 70%.

Electron spin resonance identification di-carbon-related centers in irradiated silicon

NASA Astrophysics Data System (ADS)

Hayashi, S.; Saito, H.; Itoh, K. M.; Vlasenko, M. P.; Vlasenko, L. S.

2018-04-01

A previously unreported electron spin resonance (ESR) spectrum was found in γ-ray irradiated silicon by the detection of the change in microwave photoconductivity arising from spin-dependent recombination (SDR). In the specially prepared silicon crystals doped by 13C isotope, a well resolved hyperfine structure of SDR-ESR lines due to the interaction between electrons and two equivalent carbon atoms having nuclear spin I = 1/2 was observed. The Si-KU4 spectrum is described by spin Hamiltonian for spin S = 1 and of g and D tensors of orthorhombic symmetry with principal values g1 = 2.008, g2 = 2.002, and g3 =2.007; and D1 = ± 103 MHz, D2 = ∓170 MHz, and D3 = ± 67 MHz where axes 1, 2, and 3 are parallel to the [1 1 ¯ 0 ], [110], and [001] crystal axes, respectively. The hyperfine splitting arising from 13C nuclei is about 0.35 mT. A possible microstructure of the detect leading to the Si-KU4 spectrum is discussed.

Fundamentals of Passive Oxidation In SiC and Si3N4

NASA Technical Reports Server (NTRS)

Thomas-Ogbuji, Linus U.

1998-01-01

The very slow oxidation kinetics of silicon carbide and silicon nitride, which derive from their adherent and passivating oxide films, has been explored at length in a broad series of studies utilizing thermogravimetric analysis, electron and optical micrography, energy dispersive spectrometry, x-ray diffractometry, micro-analytical depth profiling, etc. Some interesting microstructural phenomena accompanying the process of oxidation in the two materials will be presented. In Si3N4 the oxide is stratified, with an SiO2 topscale (which is relatively impervious to O2)underlain by a coherent subscale of silicon oxynitride which is even less permeable to O2- Such "defence in depth" endows Si3N4 with what is perhaps the highest oxidation resistance of any material, and results in a unique set of oxidation processes. In SiC the oxidation reactions are much simpler, yet new issues still emerge; for instance, studies involving controlled devitrification of the amorphous silica scale confirmed that the oxidation rate of SiC drops by more than an order of magnitude when the oxide scale fully crystallizes.

Growth of normally-immiscible materials (NIMs), binary alloys, and metallic fibers by hyperbaric laser chemical vapor deposition

NASA Astrophysics Data System (ADS)

Maxwell, J. L.; Black, M. R.; Chavez, C. A.; Maskaly, K. R.; Espinoza, M.; Boman, M.; Landstrom, L.

2008-06-01

This work demonstrates that two or more elements of negligible solubility (and no known phase diagram) can be co-deposited in fiber form by hyperbaric-pressure laser chemical vapor deposition (HP-LCVD). For the first time, Hg-W alloys were grown as fibers from mixtures of tungsten hexafluoride, mercury vapor, and hydrogen. This new class of materials is termed normally-immiscible materials (NIMs), and includes not only immiscible materials, but also those elemental combinations that have liquid states at exclusive temperatures. This work also demonstrates that a wide variety of other binary and ternary alloys, intermetallics, and mixtures can be grown as fibers, e.g. silicon-tungsten, aluminum-silicon, boron-carbon-silicon, and titanium-carbon-nitride. In addition, pure metallic fibers of aluminum, titanium, and tungsten were deposited, demonstrating that materials of high thermal conductivity can indeed be grown in three-dimensions, provided sufficient vapor pressures are employed. A wide variety of fiber properties and microstructures resulted depending on process conditions; for example, single crystals, fine-grained alloys, and glassy metals could be deposited.

Fabrication of porous silicon nitride ceramics using binder jetting technology

NASA Astrophysics Data System (ADS)

Rabinskiy, L.; Ripetsky, A.; Sitnikov, S.; Solyaev, Y.; Kahramanov, R.

2016-07-01

This paper presents the results of the binder jetting technology application for the processing of the Si3N4-based ceramics. The difference of the developed technology from analogues used for additive manufacturing of silicon nitride ceramics is a method of the separate deposition of the mineral powder and binder without direct injection of suspensions/slurries. It is assumed that such approach allows reducing the technology complexity and simplifying the process of the feedstock preparation, including the simplification of the composite materials production. The binders based on methyl ester of acrylic acid with polyurethane and modified starch were studied. At this stage of the investigations, the technology of green body's fabrication is implemented using a standard HP cartridge mounted on the robotic arm. For the coordinated operation of the cartridge and robot the specially developed software was used. Obtained green bodies of silicon powder were used to produce the ceramic samples via reaction sintering. The results of study of ceramics samples microstructure and composition are presented. Sintered ceramics are characterized by fibrous α-Si3N4 structure and porosity up to 70%.

Enhanced densification, strength and molecular mechanisms in shock compressed porous silicon

NASA Astrophysics Data System (ADS)

Lane, J. Matthew D.; Vogler, Tracy J.

2015-06-01

In most porous materials, void collapse during shock compression couples mechanical energy to thermal energy. Increased temperature drives up pressures and lowers densities in the final Hugoniot states as compared to full-density samples. Some materials, however, exhibit an anomalous enhanced densification in their Hugoniot states when porosity is introduced. We have recently shown that silicon is such a material, and demonstrated a molecular mechanism for the effect using molecular simulation. We will review results from large-scale non-equilibrium molecular dynamics (NEMD) and Hugoniotstat simulations of shock compressed porous silicon, highlighting the mechanism by which porosity produces local shear which nucleate partial phase transition and localized melting at shock pressures below typical thresholds in these materials. Further, we will characterize the stress states and strength of the material as a function of porosity from 5 to 50 percent and with various porosity microstructures. Sandia National Laboratories is a multi program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Measurements Of The Effects Of Grain Boundary And Alloy Scattering On Spectral Phonon Mean Free Path Distributions.

NASA Astrophysics Data System (ADS)

Lubner, Sean; Khan, Md. Imran; Dames, Chris

In the electronics and clean energy fields, it is increasingly necessary to reliably model the dissipation of heat from micro and nanostructures or nanostructured materials such as in batteries, computer chips, and thermoelectrics. In these regimes where length scales are comparable to the mean free paths (MFPs) of energy carriers, the diffusion law of heat conduction begins to break down. In this talk, I present our recent results from using a time domain thermoreflectance (TDTR) technique with laser spot 1/e-squared radii less than 2 microns to measure sub-diffusion thermal transport in silicon, nanograined-silicon (ng-Si), and silicon germanium (SiGe) alloys. Our results experimentally demonstrate that alloy scattering skews phonon spectra toward longer MFPs, while nanostructuring skews phonon spectra toward shorter MFPs. As a consequence, we show that a significant fraction of the heat-carrying phonons in SiGe have MFPs greater than 10 microns at room temperature, and that the thermal conductivity of ng-Si overtakes that of SiGe after microstructuring. NSF.

Probing silicon and aluminium chemical environments in silicate and aluminosilicate glasses by solid state NMR spectroscopy and accurate first-principles calculations

NASA Astrophysics Data System (ADS)

Gambuzzi, Elisa; Pedone, Alfonso; Menziani, Maria Cristina; Angeli, Frédéric; Caurant, Daniel; Charpentier, Thibault

2014-01-01

Silicon and aluminium chemical environments in silicate and aluminosilicate glasses with compositions 60SiO2·20Na2O·20CaO (CSN), 60SiO2·20Al2O3·20CaO (CAS), 78SiO2·11Al2O3·11Na2O (NAS) and 60SiO2·10Al2O3·10Na2O·20CaO (CASN) have been investigated by 27Al and 29Si solid state magic angle spinning (MAS) and multiple quantum MAS (MQMAS) nuclear magnetic resonance (NMR) experiments. To interpret the NMR data, first-principles calculations using density functional theory were performed on structural models of these glasses. These models were generated by Shell-model molecular dynamics (MD) simulations. The theoretical NMR parameters and spectra were computed using the gauge including projected augmented wave (GIPAW) method and spin-effective Hamiltonians, respectively. This synergetic computational-experimental approach offers a clear structural characterization of these glasses, particularly in terms of network polymerization, chemical disorder (i.e. Si and Al distribution in second coordination sphere) and modifier cation distributions. The relationships between the local structural environments and the 29Si and 27Al NMR parameters are highlighted, and show that: (i) the isotropic chemical shift of both 29Si and 27Al increases of about +5 ppm for each Al added in the second sphere and (ii) both the 27Al and 29Si isotropic chemical shifts linearly decrease with the reduction of the average Si/Al-O-T bond angle. Conversely, 27Al and 29Si NMR parameters are much less sensitive to the connectivity with triple bridging oxygen atoms, precluding their indirect detection from 27Al and 29Si NMR.

Improved silicon nitride for advanced heat engines

NASA Technical Reports Server (NTRS)

Yeh, Harry C.; Fang, Ho T.

1991-01-01

The results of a four year program to improve the strength and reliability of injection-molded silicon nitride are summarized. Statistically designed processing experiments were performed to identify and optimize critical processing parameters and compositions. Process improvements were monitored by strength testing at room and elevated temperatures, and microstructural characterization by optical, scanning electron microscopes, and scanning transmission electron microscope. Processing modifications resulted in a 20 percent strength and 72 percent Weibull slope improvement of the baseline material. Additional sintering aids screening and optimization experiments succeeded in developing a new composition (GN-10) capable of 581.2 MPa at 1399 C. A SiC whisker toughened composite using this material as a matrix achieved a room temperature toughness of 6.9 MPa m(exp .5) by the Chevron notched bar technique. Exploratory experiments were conducted on injection molding of turbocharger rotors.

Assessments of Fracture Toughness of Monolithic Ceramics-SEPB Versus SEVNB Methods

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.

2006-01-01

Fracture toughness of a total of 13 advanced monolithic ceramics including silicon nitrides, silicon carbide, aluminas, and glass ceramic was determined at ambient temperature by using both single edge precracked beam (SEPB) and single edge v-notched beam (SEVNB) methods. Relatively good agreement in fracture toughness between the two methods was observed for advanced ceramics with flat R-curves; whereas, poor agreement in fracture toughness was seen for materials with rising R-curves. The discrepancy in fracture toughness between the two methods was due to stable crack growth with crack closure forces acting in the wake region of cracks even in SEVNB test specimens. The effect of discrepancy in fracture toughness was analyzed in terms of microstructural feature (grain size and shape), toughening exponent in R-curve, and stable crack growth determined using back-face strain gaging.