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Sample records for polycrystalline gd-activated cubic

  1. Picosecond pulsed laser processing of polycrystalline diamond and cubic boron nitride composite materials

    NASA Astrophysics Data System (ADS)

    Warhanek, Maximilian G.; Pfaff, Josquin; Meier, Linus; Walter, Christian; Wegener, Konrad

    2016-03-01

    Capabilities and advantages of laser ablation processes utilizing ultrashort pulses have been demonstrated in various applications of scientific and industrial nature. Of particular interest are applications that require high geometrical accuracy, excellent surface integrity and thus tolerate only a negligible heat-affected zone in the processed area. In this context, this work presents a detailed study of the ablation characteristics of common ultrahard composite materials utilized in the cutting tool industry, namely polycrystalline diamond (PCD) and polycrystalline cubic boron nitride composite (PCBN). Due to the high hardness of these materials, conventional mechanical processing is time consuming and costly. Herein, laser ablation is an appealing solution, since no process forces and no wear have to be taken into consideration. However, an industrially viable process requires a detailed understanding of the ablation characteristics of each material. Therefore, the influence of various process parameters on material removal and processing quality at 10 ps pulse duration are investigated for several PCD and PCBN grades. The main focus of this study examines the effect of different laser energy input distributions, such as pulse frequency and burst pulses, on the processing conditions in deep cutting kerfs and the resulting processing speed. Based on these results, recommendations for efficient processing of such materials are derived.

  2. Thermo-radiative and optical properties of a cutting tool based on polycrystalline cubic boron nitride (PCBN)

    NASA Astrophysics Data System (ADS)

    González de Arrieta, I.; Echániz, T.; Pérez-Sáez, R. B.; Tello, M. J.

    2016-04-01

    The normal spectral emissivity of a cutting tool based on polycrystalline cubic boron nitride (PCBN) between 400 °C and 1000 °C has been measured. Its shape shows significant differences with respect to that of pure cubic boron nitride (c-BN). Therefore, while the reflectance spectrum of pure c-BN can be fitted to a Lorentz model for linear dielectrics, the reflectance spectrum of the cutting tool (calculated from the emissivity using Kirchhoff’s laws) requires a combination of a four-parameter Kurosawa model with a double-damping Drude one. A detailed study of the dependence of the emissivity spectrum with temperature is also performed. The experimental data of this paper is required for accurate temperature measurements with radiation thermometers in machining processes.

  3. Hybrid CO2 laser/waterjet (CO2-LWJ) cutting of Polycrystalline Cubic Boron Nitride (PCBN) blanks with phase transformation induced fracture

    NASA Astrophysics Data System (ADS)

    Wu, Zhuoru; Melaibari, Ammar A.; Molian, Pal; Shrotriya, Pranav

    2015-07-01

    The present paper investigates a transformation induced fracture mechanism for the cutting of Polycrystalline Cubic Boron Nitride (PCBN) sample by a hybrid CO2 laser/waterjet (CO2-LWJ) manufacturing process. In CO2-LWJ machining, a laser was used for local heating followed by waterjet quenching leading to fracture propagation along the sample surface. Cutting results indicate that as line energy of the laser was increased the sample response transitioned from scribing to through cutting. Raman spectroscopy analysis of the cut surface indicates that laser heated PCBN undergoes chemical phase transformation from sp3-bonded cubic Boron Nitride (cBN) into hexagonal Boron Nitride (hBN) and other sp2-bonded phases. The sp2-bonded structure occupies more volume than sp3-bonded structure such that the transformed material has a tendency to expand the original material and leads to surface deformation around the cutting path. Surface profile of the cut samples was experimentally measured using profilometry and compared with numerical predictions in order to estimate the expansion strain and dimensions of transformation region. Based on the obtained expansion strain and transformation zone, stress fields and crack driving forces were computed for channeling cracks that result in material separation. Comparison of the crack driving forces with fracture toughness of PCBN shows that transformation induced crack propagation is the feasible mechanism for cutting during CO2-LWJ machining.

  4. High-pressure, high-temperature sintering of polycrystalline cubic boron nitride with improved thermostability and mechanical properties for high temperature applications

    NASA Astrophysics Data System (ADS)

    Yao, Xian

    Polycrystalline cubic boron nitride (PCBN) is one of the few materials suitable for friction stir welding (FSW) of hardened steels, which demands tool materials to possess high temperature strength, toughness, abrasion resistance, thermal and chemical stabilities. In FSW process at temperatures higher than 980°C PCBN consisting of AlB2, as one of the major reaction products, underwent a reverse peritectic reaction: AlB2 → Al(l) + AlB 12 and released liquid Al, which was believed to cause inter-cBN granular cracking in the PCBN tool during FSW of hardened steel. In the present research, PCBN starting with decreased Al additive and addition of fine cBN powder, was HP/HT-sintered at higher B:Al ratio and increased available BN surface area for fast in situ reaction with liquid Al in favor of forming AlB12 instead of AlB2. Titanium powder in HP/HT-sintering of PCBN under the same pressure and temperature conditions resulted in cBN, TiN, and TiB2 reaction products but could not achieve the densification comparable to the Al additives. However, using Ti-coated cBN particles with addition of the fine cBN powder led to PCBN with highly packed reaction products of cBN, TiN, and TiB2 and strong mechanical properties. Applying electron backscattered diffraction (EBSD) method, the PCBN with 10vol%Al additive was detected to consist of 0.5vol% and finely dispersed AlB2 in addition to AlB12 as the major borides in addition to cBN and AlN. Such PCBN was shown to possess high thermostability measured at 1000°C and measureable increases in flexural strength at temperatures up to 1100°C, while room temperature fracture toughness value was retained up to 1100° C as well. Combine x-ray diffraction (XRD) and EBSD results revealed the increase in high-temperature strength was resultant of high residual compressive-stress on cBN grains applied by thermal expansion of the AlN-AlB 12 grainboundary phase. The PCBN sintered from cBN with 10vo%Al powder, possessing improved

  5. Deposition Of Cubic BN On Diamond Interlayers

    NASA Technical Reports Server (NTRS)

    Ong, Tiong P.; Shing, Yuh-Han

    1994-01-01

    Thin films of polycrystalline, pure, cubic boron nitride (c-BN) formed on various substrates, according to proposal, by chemical vapor deposition onto interlayers of polycrystalline diamond. Substrate materials include metals, semiconductors, and insulators. Typical substrates include metal-cutting tools: polycrystalline c-BN coats advantageous for cutting ferrous materials and for use in highly oxidizing environments-applications in which diamond coats tend to dissolve in iron or be oxidized, respectively.

  6. Diffusion in polycrystalline microstructures

    SciTech Connect

    Swiler, T.P.; Holm, E.A.

    1995-07-01

    Mass transport properties are important in polycrystalline materials used as protective films. Traditionally, such properties have been studied by examining model polycrystalline structures, such as a regular array of straight grain boundaries. However, these models do not account for a number of features of real grain ensembles, including the grain size distribution and the topological aspects of grain boundaries. In this study, a finite difference scheme is developed to study transient and steady-state mass transport through realistic two-dimensional polycrystalline microstructures. Effects of microstructural parameters such as average grain size and grain boundary topology are examined, as are effects due to limits of the model.

  7. Composite polycrystalline semiconductor neutron detectors

    NASA Astrophysics Data System (ADS)

    Schieber, M.; Zuck, A.; Marom, G.; Khakhan, O.; Roth, M.; Alfassi, Z. B.

    2007-08-01

    Composite polycrystalline semiconductor detectors bound with different binders, both inorganic molten glasses, such as B 2O 3, PbO/B 2O 3, Bi 2O 3/PbO, and organic polymeric binders, such as isotactic polypropylene (iPP), polystyrene or nylon-6, and coated with different metal electrodes were tested at room temperature for α-particles and very weak thermal neutron sources. The detector materials tested were natural occurring hexagonal BN and cubic LiF, where both are not containing enriched isotopes of 10B or 6Li. The radiation sources were 5.5 MeV α's from 241Am, 5.3 MeV from 210Po and also 4.8 MeV from 226Ra. Some of these detectors were also tested with thermal neutrons from very weak 227Ac 9Be, 241Am- 10Be sources and also from a weak 238Pu+ 9Be and somewhat stronger 252Cf sources. The neutrons were thermalized with paraffin. Despite very low signal to noise ratio of only ˜2, the neutrons could be counted by subtracting the noise from the signal.

  8. Development of Novel Polycrystalline Ceramic Scintillators

    SciTech Connect

    Wisniewska, Monika; Boatner, Lynn A; Neal, John S; Jellison Jr, Gerald Earle; Ramey, Joanne Oxendine; North, Andrea L; Wisniewski, Monica; Payzant, E Andrew; Howe, Jane Y; Lempicki, Aleksander; Brecher, Charlie; Glodo, J.

    2008-01-01

    For several decades most of the efforts to develop new scintillator materials have concentrated on high-light-yield inorganic single-crystals while polycrystalline ceramic scintillators, since their inception in the early 1980 s, have received relatively little attention. Nevertheless, transparent ceramics offer a promising approach to the fabrication of relatively inexpensive scintillators via a simple mechanical compaction and annealing process that eliminates single-crystal growth. Until recently, commonly accepted concepts restricted the polycrystalline ceramic approach to materials exhibiting a cubic crystal structure. Here, we report our results on the development of two novel ceramic scintillators based on the non-cubic crystalline materials: Lu SiO:Ce (LSO:Ce) and LaBr:Ce. While no evidence for texturing has been found in their ceramic microstructures, our LSO:Ce ceramics exhibit a surprisingly high level of transparency/ translucency and very good scintillation characteristics. The LSO:Ce ceramic scintillation reaches a light yield level of about 86% of that of a good LSO:Ce single crystal, and its decay time is even faster than in single crystals. Research on LaBr:Ce shows that translucent ceramics of the high-light-yield rare-earth halides can also be synthesized. Our LaBr:Ce ceramics have light yields above 42 000 photons/MeV (i.e., 70%of the single-crystal light yield).

  9. Low pressure growth of cubic boron nitride films

    NASA Technical Reports Server (NTRS)

    Ong, Tiong P. (Inventor); Shing, Yuh-Han (Inventor)

    1997-01-01

    A method for forming thin films of cubic boron nitride on substrates at low pressures and temperatures. A substrate is first coated with polycrystalline diamond to provide a uniform surface upon which cubic boron nitride can be deposited by chemical vapor deposition. The cubic boron nitride film is useful as a substitute for diamond coatings for a variety of applications in which diamond is not suitable. any tetragonal or hexagonal boron nitride. The cubic boron nitride produced in accordance with the preceding example is particularly well-suited for use as a coating for ultra hard tool bits and abrasives, especially those intended to use in cutting or otherwise fabricating iron.

  10. Polycrystalline photovoltaic cell

    SciTech Connect

    Jordan, J.F.; Lampkin, C.M.

    1983-10-25

    A photovoltaic cell is disclosed, having an electrically conductive substrate, which may be glass having a film of conductive tin oxide; a first layer containing a suitable semiconductor, which layer has a first component film with an amorphous structure and a second component film with a polycrystalline structure; a second layer forming a heterojunction with the first layer; and suitable electrodes where the heterojunction is formed from a solution containing copper, the amorphous film component is superposed above an electrically conductive substrate to resist permeation of the copper-containing material to shorting electrical contact with the substrate. The penetration resistant amorphous layer permits a variety of processes to be used in forming the heterojunction with even very thin layers (1-6 /SUB u/ thick) of underlying polycrystalline semiconductor materials. In some embodiments, the amorphous-like structure may be formed by the addition of aluminum or zirconium compounds to a solution of cadmium salts sprayed over a heated substrate.

  11. Polycrystalline thin film photovoltaics

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Ullal, H. S.; Mitchell, R. L.

    Significant progress has recently been made towards improving the efficiencies of polycrystalline thin-film solar cells and modules using CuInSe2 and CdTe. The history of using CuInSe2 and CdTe for solar cells is reviewed. Initial outdoor stability tests of modules are encouraging. Progress in semiconductor deposition techniques has also been substantial. Both CuInSe2 and CdTe are positioned for commercialization during the 1990s. The major participants in developing these materials are described. The US DOE/SERI (Solar Energy Research Institute) program recognizes the rapid progress and important potential of polycrystalline thin films to meet ambitious cost and performance goals. US DOE/SERI is in the process of funding an initiative in this area with the goal of ensuring US leadership in the development of these technologies. The polycrystalline thin-film module development initiative, the modeling and stability of the devices, and health and safety issues are discussed.

  12. Polycrystalline thin-films

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Mitchell, R.

    1986-02-01

    This annual report summarizes the status, accomplishments, and projected future research directions of the Polycrystalline Thin Film Task in the Photovoltaic Program Branch of the Solar Energy Research Institute's Solar Electric Research Division. Major subcontracted work in this area has concentrated on development of CuInSe2 and CdTe technologies. During FY 1985, major progress was achieved by subcontractors in: (1) developing a new, low-cost method of fabricating CuInSe2, and (2) improving the efficiency of CuInSe2 devices by about 10% (relative). The report also lists research planned to meet the Department of Energy's goals in these technologies.

  13. Modeling of Irradiation Hardening of Polycrystalline Materials

    SciTech Connect

    Li, Dongsheng; Zbib, Hussein M.; Garmestani, Hamid; Sun, Xin; Khaleel, Mohammad A.

    2011-09-14

    High energy particle irradiation of structural polycrystalline materials usually produces irradiation hardening and embrittlement. The development of predict capability for the influence of irradiation on mechanical behavior is very important in materials design for next generation reactors. In this work a multiscale approach was implemented to predict irradiation hardening of body centered cubic (bcc) alpha-iron. The effect of defect density, texture and grain boundary was investigated. In the microscale, dislocation dynamics models were used to predict the critical resolved shear stress from the evolution of local dislocation and defects. In the macroscale, a viscoplastic self-consistent model was applied to predict the irradiation hardening in samples with changes in texture and grain boundary. This multiscale modeling can guide performance evaluation of structural materials used in next generation nuclear reactors.

  14. Polycrystalline semiconductor processing

    DOEpatents

    Glaeser, Andreas M.; Haggerty, John S.; Danforth, Stephen C.

    1983-01-01

    A process for forming large-grain polycrystalline films from amorphous films for use as photovoltaic devices. The process operates on the amorphous film and uses the driving force inherent to the transition from the amorphous state to the crystalline state as the force which drives the grain growth process. The resultant polycrystalline film is characterized by a grain size that is greater than the thickness of the film. A thin amorphous film is deposited on a substrate. The formation of a plurality of crystalline embryos is induced in the amorphous film at predetermined spaced apart locations and nucleation is inhibited elsewhere in the film. The crystalline embryos are caused to grow in the amorphous film, without further nucleation occurring in the film, until the growth of the embryos is halted by imgingement on adjacently growing embryos. The process is applicable to both batch and continuous processing techniques. In either type of process, the thin amorphous film is sequentially doped with p and n type dopants. Doping is effected either before or after the formation and growth of the crystalline embryos in the amorphous film, or during a continuously proceeding crystallization step.

  15. Polycrystalline semiconductor processing

    DOEpatents

    Glaeser, A.M.; Haggerty, J.S.; Danforth, S.C.

    1983-04-05

    A process is described for forming large-grain polycrystalline films from amorphous films for use as photovoltaic devices. The process operates on the amorphous film and uses the driving force inherent to the transition from the amorphous state to the crystalline state as the force which drives the grain growth process. The resultant polycrystalline film is characterized by a grain size that is greater than the thickness of the film. A thin amorphous film is deposited on a substrate. The formation of a plurality of crystalline embryos is induced in the amorphous film at predetermined spaced apart locations and nucleation is inhibited elsewhere in the film. The crystalline embryos are caused to grow in the amorphous film, without further nucleation occurring in the film, until the growth of the embryos is halted by impingement on adjacently growing embryos. The process is applicable to both batch and continuous processing techniques. In either type of process, the thin amorphous film is sequentially doped with p and n type dopants. Doping is effected either before or after the formation and growth of the crystalline embryos in the amorphous film, or during a continuously proceeding crystallization step. 10 figs.

  16. Gelcasting Polycrystalline Alumina

    SciTech Connect

    Janney, M.A.; Zuk, K.J.; Wei, G.C.

    2000-01-01

    OSRAM SYLVANIA INC. is a major U.S. manufacturer of high-intensity lighting. Among its products is the Lumalux TM line of high-pressure sodium vapor arc lamps, which are used for industrial, highway, and street lighting. The key to the performance of these lamps is the polycrystalline alumina (PCA) tube that is used to contain the plasma that is formed in the electric arc. That plasma consists of ionized sodium, mercury, and xenon vapors. The key attributes of the PCA tubes are their transparency ({approximately}97% total transmittance in the visible), their refractoriness (inner wall temperature can reach l2OOC), and their chemical resistance (sodium and mercury vapor are extremely corrosive). The current efficiency of the lamps is very high, up to 100 initial lumens per watt. (Compare incandescent lamps 10-20 lumens per watt, fluorescent lamps 25-90 lumens per watt.)

  17. Polycrystalline thin films

    NASA Astrophysics Data System (ADS)

    Zweibel, K.; Mitchell, R.; Ullal, H.

    1987-02-01

    This annual report for fiscal year 1986 summarizes the status, accomplishments, and projected future research directions of the Polycrystalline Thin Film Task in the Photovoltaic Program Branch of the Solar Energy Research Institute's Solar Electric Research Division. Subcontracted work in this area has concentrated on the development of CuInSe2 and CdTe technologies. During FY 1986, major progress was achieved by subcontractors in (1) achieving 10.5% (SERI-verified) efficiency with CdTe, (2) improving the efficiency of selenized CuInSe2 solar cells to nearly 8%, and (3) developing a transparent contact to CdTe cells for potential use in the top cells of tandem structures.

  18. Gelcasting polycrystalline alumina

    SciTech Connect

    Janney, M.A.

    1997-04-01

    This work is being done as part of a CRADA with Osram-Sylvania, Inc. (OSI) OSI is a major U.S. manufacturer of high-intensity lighting. Among its products is the Lumalux{reg_sign} line of high-pressure sodium vapor arc lamps, which are used for industrial, highway, and street lighting. The key to the performance of these lamps is the polycrystalline alumina (PCA) tube that is used to contain the plasma that is formed in the electric arc. That plasma consists of ionized sodium, mercury, and xenon vapors. The key attributes of the PCA tubes are their transparency (95% total transmittance in the visible region), their refractoriness (inner wall temperature can reach 1400{degrees}C), and their chemical resistance (sodium and mercury vapor are extremely corrosive). The current efficiency of the lamps is very high, on the order of several hundred lumens / watt. (Compare - incandescent lamps -13 lumens/watt fluorescent lamps -30 lumens/watt.) Osram-Sylvania would like to explore using gelcasting to form PCA tubes for Lumalux{reg_sign} lamps, and eventually for metal halide lamps (known as quartz-halogen lamps). Osram-Sylvania, Inc. currently manufactures PCA tubes by isostatic pressing. This process works well for the shapes that they presently use. However, there are several types of tubes that are either difficult or impossible to make by isostatic pressing. It is the desire to make these new shapes and sizes of tubes that has prompted Osram-Sylvania`s interest in gelcasting. The purpose of the CRADA is to determine the feasibility of making PCA items having sufficient optical quality that they are useful in lighting applications using gelcasting.

  19. Piecewise Cubic Interpolation Package

    Energy Science and Technology Software Center (ESTSC)

    1982-04-23

    PCHIP (Piecewise Cubic Interpolation Package) is a set of subroutines for piecewise cubic Hermite interpolation of data. It features software to produce a monotone and "visually pleasing" interpolant to monotone data. Such an interpolant may be more reasonable than a cubic spline if the data contain both 'steep' and 'flat' sections. Interpolation of cumulative probability distribution functions is another application. In PCHIP, all piecewise cubic functions are represented in cubic Hermite form; that is, f(x)more » is determined by its values f(i) and derivatives d(i) at the breakpoints x(i), i=1(1)N. PCHIP contains three routines - PCHIM, PCHIC, and PCHSP to determine derivative values, six routines - CHFEV, PCHFE, CHFDV, PCHFD, PCHID, and PCHIA to evaluate, differentiate, or integrate the resulting cubic Hermite function, and one routine to check for monotonicity. A FORTRAN 77 version and SLATEC version of PCHIP are included.« less

  20. Determination of the Magnetic Ground State of a Polycrystalline Compound Based on Susceptibility Measurements

    SciTech Connect

    Fishman, Randy Scott; Miller, Joel S.

    2011-01-01

    The diruthenium compound [Ru2(O2CMe)4]3[Cr(CN)6] contains two interpenetrating sublattices that behave like giant antiferromagnetically-coupled moments with strong anisotropy. The preferred orientations of the total moment of each sublattice are determined from susceptibility measurements on a polycrystalline sample. In agreement with previous mean-field calculations for the magnetic ground state, the fits to the experimental magnetization imply that the sublattice moments are restricted to cubic diagonals rather than the cubic axis or the edge diagonals. The parameterization of the sublattice susceptibility indicates that the sublattice spin states are more distorted when they are aligned antiparallel.

  1. Anisotropic grain noise in eddy current inspection of noncubic polycrystalline metals

    NASA Astrophysics Data System (ADS)

    Blodgett, Mark; Nagy, Peter B.

    1998-03-01

    This letter discusses the role electrical anisotropy plays in the structural integrity assessment of polycrystalline titanium alloys from the standpoint of fatigue crack detection and the related issue of microstructural noise. In eddy current inspection of noncubic crystallographic classes of polycrystalline metals the electric anisotropy of individual grains produces an inherent microstructural variation or noise that is very similar to the well-known acoustic noise produced by the elastic anisotropy of both cubic and noncubic materials in ultrasonic characterization. The presented results demonstrate that although the electrical grain noise is clearly detrimental in eddy current nondestructive testing for small flaws, it can be also exploited for characterization of the microstructure in noncubic polycrystalline materials such as titanium alloys in the same way acoustic grain noise is used for ultrasonic characterization of the microstructure in different materials.

  2. Plastic flow of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Langer, James

    Leo Kadanoff had a long interest in fluid flows, especially fingering instabilities. This interest was one example of his insatiable curiosity about simple, fundamentally important, and often multidisciplinary phenomena. Here is an example of another class of such phenomena that I had hoped to show him this year. The experts in polycrystalline solid mechanics have insisted for decades that their central problem - dislocation-mediated strain hardening - is intrinsically unsolvable. I think they're wrong. My colleagues and I have made progress recently in theories of both amorphous and polycrystalline plasticity by introducing an effective disorder temperature as a dynamical variable in our equations of motion. In this way, we have been able to describe how the densities of flow defects or dislocations evolve in response to external forcing, and thus to develop theories that promise to become as predictive, and full of surprises, as the laws of fluid flow. For Kadanoff session.

  3. Polycrystalline thin film photovoltaic technology

    SciTech Connect

    Ullal, H.S.; Zweibel, K.; Mitchell, R.L.; Noufi, R.

    1991-03-01

    Low-cost, high-efficiency thin-film modules are an exciting photovoltaic technology option for generating cost-effective electricity in 1995 and beyond. In this paper we review the significant technical progress made in the following thin films: copper indium diselenide, cadmium telluride, and polycrystalline thin silicon films. Also, the recent US DOE/SERI initiative to commercialize these emerging technologies is discussed. 6 refs., 9 figs.

  4. A New Polycrystalline Co-Ni Superalloy

    NASA Astrophysics Data System (ADS)

    Knop, M.; Mulvey, P.; Ismail, F.; Radecka, A.; Rahman, K. M.; Lindley, T. C.; Shollock, B. A.; Hardy, M. C.; Moody, M. P.; Martin, T. L.; Bagot, P. A. J.; Dye, D.

    2014-12-01

    In 2006, a new-ordered L12 phase, Co3(Al,W), was discovered that can form coherently in a face-centered cubic (fcc) A1 Co matrix. Since then, a community has developed that is attempting to take these alloys forward into practical applications in gas turbines. A new candidate polycrystalline Co-Ni γ/ γ' superalloy, V208C, is presented that has the nominal composition 36Co-35Ni-15Cr-10Al-3W-1Ta (at.%). The alloy was produced by conventional powder metallurgy superalloy methods. After forging, a γ' fraction of ~56% and a secondary γ' size of 88 nm were obtained, with a grain size of 2.5 μm. The solvus temperature was 1000°C. The density was found to be 8.52 g cm-3, which is similar to existing Ni alloys with this level of γ'. The alloy showed the flow stress anomaly and a yield strength of 920 MPa at room temperature and 820 MPa at 800°C, similar to that of Mar-M247. These values are significantly higher than those found for either conventional solution and carbide-strengthened Co alloys or the γ/ γ' Co superalloys presented in the literature thus far. The oxidation resistance, with a mass gain of 0.08 mg cm-2 in 100 h at 800°C, is also comparable with that of existing high-temperature Ni superalloys. These results suggest that Co-based and Co-Ni superalloys may hold some promise for the future in gas turbine applications.

  5. Losses in polycrystalline silicon waveguides

    NASA Astrophysics Data System (ADS)

    Foresi, J. S.; Black, M. R.; Agarwal, A. M.; Kimerling, L. C.

    1996-04-01

    The losses of polycrystalline silicon (polySi) waveguides clad by SiO2 are measured by the cutback technique. We report losses of 34 dB/cm at a wavelength of 1.55 μm in waveguides fabricated from chemical mechanical polished polySi deposited at 625 °C. These losses are two orders of magnitude lower than reported absorption measurements for polySi. Waveguides fabricated from unpolished polySi deposited at 625 °C exhibit losses of 77 dB/cm. We find good agreement between calculated and measured losses due to surface scattering.

  6. Phosphorus diffusion in polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Losee, D. L.; Lavine, J. P.; Trabka, E. A.; Lee, S.-T.; Jarman, C. M.

    1984-02-01

    The diffusion of phosphorus in crystallized amorphous Si layers was studied with secondary-ion mass spectroscopy. A two-dimensional diffusion model is used to find effective grain (Dg) and grain-boundary (Dgb) diffusion coefficients. This simplified model leads to Dgb ≤ 10Dg, which is significantly lower than what has been deduced from conventional, larger grained polysilicon. Our result is consistent with specific-gravity measurements, which found a significantly lower ``mass defect'' for layers deposited amorphous and subsequently crystallized as compared to initially polycrystalline layers.

  7. Morphological changes in polycrystalline Fe after compression and release

    NASA Astrophysics Data System (ADS)

    Gunkelmann, Nina; Tramontina, Diego R.; Bringa, Eduardo M.; Urbassek, Herbert M.

    2015-02-01

    Despite a number of large-scale molecular dynamics simulations of shock compressed iron, the morphological properties of simulated recovered samples are still unexplored. Key questions remain open in this area, including the role of dislocation motion and deformation twinning in shear stress release. In this study, we present simulations of homogeneous uniaxial compression and recovery of large polycrystalline iron samples. Our results reveal significant recovery of the body-centered cubic grains with some deformation twinning driven by shear stress, in agreement with experimental results by Wang et al. [Sci. Rep. 3, 1086 (2013)]. The twin fraction agrees reasonably well with a semi-analytical model which assumes a critical shear stress for twinning. On reloading, twins disappear and the material reaches a very low strength value.

  8. Development of transparent polycrystalline beta-silicon carbide

    NASA Astrophysics Data System (ADS)

    Bayya, Shyam S.; Villalobos, Guillermo R.; Hunt, Michael P.; Sanghera, Jasbinder S.; Sadowski, Bryan M.; Aggarwal, Ishwar D.; Cinibulk, Michael; Carney, Carmen; Keller, Kristin

    2013-09-01

    Transparent beta-SiC is of great interest because its high strength, low coefficient of thermal expansion, very high thermal conductivity, and cubic crystal structure give it a very high thermal shock resistance. A transparent, polycrystalline beta-SiC window will find applications in armor, hypersonic missiles, and thermal control for thin disc lasers. SiC is currently available as either small transparent vapor grown disks or larger opaque shapes. Neither of which are useful in window applications. We are developing sintering technology to enable transparent SiC ceramics. This involves developing procedures to make high purity powders and studying their densification behavior. We have been successful in demonstrating transparency in thin sections using Field Assisted Sintering Technology (FAST). This paper will discuss the reaction mechanisms in the formation of beta-SiC powder and its sintering behavior in producing transparent ceramics.

  9. Accurate monotone cubic interpolation

    NASA Technical Reports Server (NTRS)

    Huynh, Hung T.

    1991-01-01

    Monotone piecewise cubic interpolants are simple and effective. They are generally third-order accurate, except near strict local extrema where accuracy degenerates to second-order due to the monotonicity constraint. Algorithms for piecewise cubic interpolants, which preserve monotonicity as well as uniform third and fourth-order accuracy are presented. The gain of accuracy is obtained by relaxing the monotonicity constraint in a geometric framework in which the median function plays a crucial role.

  10. Casting larger polycrystalline silicon ingots

    SciTech Connect

    Wohlgemuth, J.; Tomlinson, T.; Cliber, J.; Shea, S.; Narayanan, M.

    1995-08-01

    Solarex has developed and patented a directional solidification casting process specifically designed for photovoltaics. In this process, silicon feedstock is melted in a ceramic crucible and solidified into a large grained semicrystalline silicon ingot. In-house manufacture of low cost, high purity ceramics is a key to the low cost fabrication of Solarex polycrystalline wafers. The casting process is performed in Solarex designed casting stations. The casting operation is computer controlled. There are no moving parts (except for the loading and unloading) so the growth process proceeds with virtually no operator intervention Today Solarex casting stations are used to produce ingots from which 4 bricks, each 11.4 cm by 11.4 cm in cross section, are cut. The stations themselves are physically capable of holding larger ingots, that would yield either: 4 bricks, 15 cm by 15 an; or 9 bricks, 11.4 cm by 11.4 an in cross-section. One of the tasks in the Solarex Cast Polycrystalline Silicon PVMaT Program is to design and modify one of the castings stations to cast these larger ingots. If successful, this effort will increase the production capacity of Solarex`s casting stations by 73% and reduce the labor content for casting by an equivalent percentage.

  11. Process Research on Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.; Wrigley, C. Y.

    1985-01-01

    Results of hydrogen-passivated polycrysalline silicon solar cell research are summarized. The short-circuit current of solar cells fabricated from large-grain cast polycrystalline silicon is nearly equivalent to that of single-crystal cells, which indicates long bulk minority-carrier diffusion length. Treatments with molecular hydrogen showed no effect on large-grain cast polycrystalline silicon solar cells.

  12. Morphology of polycrystalline cassiterite films

    NASA Astrophysics Data System (ADS)

    Tomaev, V. V.; Glazov, A. I.

    2014-09-01

    Polycrystalline cassiterite films have been grown by the hydropyrolytic method from a 10(H2O) + 5(SnCl2 · 2H2O) solution (in weight fractions) on corundum substrates. The crystallization regularities are considered and a comparative analysis of the properties of natural and artificial cassiterite crystals is performed. The surface morphology is investigated and the size of crystalline grains is determined by scanning electron microscopy. X-ray microprobe analysis showed that all films contain tin and oxygen atoms in a ratio corresponding (within the experimental error) to the chemical formula of tin dioxide. It is established that the surface morphology of cassiterite films is characterized by both single crystallites and aggregates of two or more crystals typical of twins. It is suggest that doping can efficiently be used to control the concentration of twins and the stability of their formation.

  13. Saturation magnetization of polycrystalline iron

    NASA Technical Reports Server (NTRS)

    Behrendt, D. R.; Hegland, D. E.

    1972-01-01

    The magnetic moment per gram, sigma (H sub I, T), where H sub I is the internal field and T is the temperature, was measured for a polycrystalline iron sphere with the vibrating-sample magnetometer. The instrument was calibrated by using a method utilizing the high permeability of an iron sphere. The spontaneous moment, sigma(0, T),was obtained from plots of sigma(H sub I, T) as a function of H sub I for temperatures from 4.2 K to room temperature. The value of the spontaneous moment, sigma(0, T), at 298.9 K was 217.5 + or -0.4 emu/g. The extrapolated moment, sigma(0, 0),at absolute zero from a plot of sigma(0, T) as a function of T to 3/2 power was 221.7 + or - 0.4 emu/g.

  14. Polycrystalline Silicon: a Biocompatibility Assay

    SciTech Connect

    Pecheva, E.; Fingarova, D.; Pramatarova, L.; Hikov, T.; Laquerriere, P.; Bouthors, Sylvie; Dimova-Malinovska, D.; Montgomery, P.

    2010-01-21

    Polycrystalline silicon (poly-Si) layers were functionalized through the growth of biomimetic hydroxyapatite (HA) on their surface. HA is the mineral component of bones and teeth and thus possesses excellent bioactivity and biocompatibility. MG-63 osteoblast-like cells were cultured on both HA-coated and un-coated poly-Si surfaces for 1, 3, 5 and 7 days and toxicity, proliferation and cell morphology were investigated. The results revealed that the poly-Si layers were bioactive and compatible with the osteoblast-like cells. Nevertheless, the HA coating improved the cell interactions with the poly-Si surfaces based on the cell affinity to the specific chemical composition of the bone-like HA and/or to the higher HA roughness.

  15. Estimation of Single-Crystal Elastic Constants from Ultrasonic Measurements on Polycrystalline Specimens

    NASA Astrophysics Data System (ADS)

    Haldipur, P.; Margetan, F. J.; Thompson, R. B.

    2004-02-01

    In past work we reported on measurements of ultrasonic velocity, attenuation and backscattering in nickel-alloy materials used in the fabrication of rotating jet-engine components. Attenuation and backscattering were shown to be correlated to the average grain diameter, which varied with position in the billet specimens studied. The ultrasonic measurements and associated metallographic studies found the local microstructures to be approximately equiaxed and free of texture in these cubic-phase metals. In this paper we explore a method for deducing the single-crystal elastic constants of a metal using the combined ultrasonic and metallographic data for a polycrystalline specimen. We specifically consider the case seen in the jet-engine alloys: polycrystalline cubic microstructures having equiaxed, randomly oriented grains. We demonstrate how the three independent elastic constants {C11, C12, C44} can be deduced from the density, the mean grain diameter, the ultrasonic attenuation at one or more frequencies, and the longitudinal and shear wave speeds. The method makes use of the attenuation theory of Stanke and Kino, and the Hill averaging procedure for estimating the sonic velocity through a polycrystalline material. Elastic constant inputs to the velocity and attenuation models are adjusted to optimize the agreement with experiment. The method is demonstrated using several specimens of Inconel 718 and Waspaloy, and further tested using four specimens of pure Nickel.

  16. Estimation of Single-Crystal Elastic Constants from Ultrasonic Measurements on Polycrystalline Specimens

    SciTech Connect

    Haldipur, P.; Margetan, F.J.; Thompson, R.B.

    2004-02-26

    In past work we reported on measurements of ultrasonic velocity, attenuation and backscattering in nickel-alloy materials used in the fabrication of rotating jet-engine components. Attenuation and backscattering were shown to be correlated to the average grain diameter, which varied with position in the billet specimens studied. The ultrasonic measurements and associated metallographic studies found the local microstructures to be approximately equiaxed and free of texture in these cubic-phase metals. In this paper we explore a method for deducing the single-crystal elastic constants of a metal using the combined ultrasonic and metallographic data for a polycrystalline specimen. We specifically consider the case seen in the jet-engine alloys: polycrystalline cubic microstructures having equiaxed, randomly oriented grains. We demonstrate how the three independent elastic constants {l_brace}C11, C12, C44{r_brace} can be deduced from the density, the mean grain diameter, the ultrasonic attenuation at one or more frequencies, and the longitudinal and shear wave speeds. The method makes use of the attenuation theory of Stanke and Kino, and the Hill averaging procedure for estimating the sonic velocity through a polycrystalline material. Elastic constant inputs to the velocity and attenuation models are adjusted to optimize the agreement with experiment. The method is demonstrated using several specimens of Inconel 718 and Waspaloy, and further tested using four specimens of pure Nickel.

  17. Cubic-normal distribution

    NASA Astrophysics Data System (ADS)

    Peng, Gan Chew; Hin, Pooi Ah; Ho, C. K.

    2015-12-01

    The power-normal distribution given in Yeo and Johnson in year 2000 is a unimodal distribution with wide ranges of skewness and kurtosis. A shortcoming of the power-normal distribution is that the negative and positve parts of the underlying random variable have to be specified by two different expressions of the standard normal random variable. In this paper, we construct a new distribution, called the cubic-normal distribution, via a single polynomial expression in cubic root function. Apart from having the properties which are similar to those of the power-normal distribution, this cubic-normal distribution can be developed into a multivariate version which is more attractive from the theoretical and computational points of view.

  18. Polycrystalline Garnet Porphyroblasts, an EBSD Study

    NASA Astrophysics Data System (ADS)

    Seaton, N. C.; Whitney, D. L.; Anderson, C.; Alpert, A.

    2008-12-01

    Polycrystalline garnet porphyroblasts (PGP's) are significant because their formation provides information about metamorphic crystalline mechanisms, in particular during early stages of crystal growth, which may differ from those governing later stages; and because their existence may affect the chemical and structural evolution of metamorphic rocks. For example, the extent of element exchange between the garnet interior and the matrix may be affected by the presence of grain boundaries within PGP's. There have been several previous studies of PGP's but important questions about them remain; e.g. whether early coalescence is a common method by which garnets crystallize, whether grains rotate during growth to attain an energetically favorable grain-grain contact, and whether deformation and/or precursor minerals or other chemical or mechanical heterogeneities influence the formation of PGP's. PGP's have been detected by us in several different localities including; micaschist from SE Vermont (USA), including locality S35j of Rosenfeld (1968); the Solitude Range (British Columbia, Canada); the Southern Menderes Massif (Turkey); and three zones (garnet, staurolite, kyanite) from the Dutchess County Barrovian sequence in NY (USA). We have identified two types of PGP: cryptic and morphologically distinct. Cryptic PGP have no obvious morphological expression of the high angle boundaries within them and appear to be a single crystal. Morphologically distinct PGP have an obvious depression in the outer grain boundary where it is intersected by the internal grain boundary. Most PGP's contain inclusion trails and the high angle grain boundaries crosscut the trend of these as well as the inclusions themselves. PGP also show major element growth zoning that is not influenced by the internal grain boundaries except in rare cases. PGP's comprise ~ 5-35% of the garnet populations analyzed. More than 95% of the PGP's we have analyzed are comprised of 2-3 domains; the rest contain

  19. Cubic nitride templates

    DOEpatents

    Burrell, Anthony K; McCleskey, Thomas Mark; Jia, Quanxi; Mueller, Alexander H; Luo, Hongmei

    2013-04-30

    A polymer-assisted deposition process for deposition of epitaxial cubic metal nitride films and the like is presented. The process includes solutions of one or more metal precursor and soluble polymers having binding properties for the one or more metal precursor. After a coating operation, the resultant coating is heated at high temperatures under a suitable atmosphere to yield metal nitride films and the like. Such films can be used as templates for the development of high quality cubic GaN based electronic devices.

  20. Magnetic anisotropy of polycrystalline magnetoferritin investigated by SQUID and electron magnetic resonance

    NASA Astrophysics Data System (ADS)

    Moro, F.; de Miguel, R.; Jenkins, M.; Gómez-Moreno, C.; Sells, D.; Tuna, F.; McInnes, E. J. L.; Lostao, A.; Luis, F.; van Slageren, J.

    2014-06-01

    Magnetoferritin molecules with an average inorganic core diameter of 5.7±1.6 nm and polycrystalline internal structure were investigated by a combination of transmission electron microscopy, magnetic susceptibility, magnetization, and electron magnetic resonance (EMR) experiments. The temperature and frequency dependence of the magnetic susceptibility allowed for the determination of the magnetic anisotropy on an experimental time scale which spans from seconds to nanoseconds. In addition, angle-dependent EMR experiments were carried out for the determination of the nanoparticle symmetry and internal magnetic field. Due to the large surface to volume ratio, the nanoparticles show larger and uniaxial rather than cubic magnetic anisotropies compared to bulk maghemite and magnetite.

  1. Hydrogen migration in polycrystalline silicon

    SciTech Connect

    Nickel, N.H.; Jackson, W.B.; Walker, J.

    1996-03-01

    Hydrogen migration in solid-state crystallized and low-pressure chemical-vapor-deposited (LPCVD) polycrystalline silicon (poly-Si) was investigated by deuterium diffusion experiments. The concentration profiles of deuterium, introduced into the poly-Si samples either from a remote D plasma or from a deuterated amorphous-silicon layer, were measured as a function of time and temperature. At high deuterium concentrations the diffusion was dispersive depending on exposure time. The dispersion is consistent with multiple trapping within a distribution of hopping barriers. The data can be explained by a two-level model used to explain diffusion in hydrogenated amorphous silicon. The energy difference between the transport level and the deuterium chemical potential was found to be about 1.2{endash}1.3 eV. The shallow levels for hydrogen trapping are about 0.5 eV below the transport level, while the deep levels are about 1.5{endash}1.7 eV below. The hydrogen chemical potential {mu}{sub H} decreases as the temperature increases. At lower concentrations, {mu}{sub H} was found to depend markedly on the method used to prepare the poly-Si, a result due in part to the dependence of crystallite size on the deposition process. Clear evidence for deuterium deep traps was found only in the solid-state crystallized material. The LPCVD-grown poly-Si, with columnar grains extending through the film thickness, displayed little evidence of deep trapping, and exhibited enhanced D diffusion. Many concentration profiles in the columnar LPCVD material indicated complex diffusion behavior, perhaps reflecting spatial variations of trap densities, complex formation, and/or multiple transport paths. Many aspects of the diffusion in poly-Si are consistent with diffusion data obtained in amorphous silicon. {copyright} {ital 1996 The American Physical Society.}

  2. Process Research of Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.

    1984-01-01

    A passivation process (hydrogenation) that will improve the power generation of solar cells fabricated from presently produced, large grain, cast polycrystalline silicon (Semix), a potentially low cost material are developed. The first objective is to verify the operation of a DC plasma hydrogenation system and to investigate the effect of hydrogen on the electrical performance of a variety of polycrystalline silicon solar cells. The second objective is to parameterize and optimize a hydrogenation process for cast polycrystalline silicon, and will include a process sensitivity analysis. The sample preparation for the first phase is outlined. The hydrogenation system is described, and some early results that were obtained using the hydrogenation system without a plasma are summarized. Light beam induced current (LBIC) measurements of minicell samples, and their correlation to dark current voltage characteristics, are discussed.

  3. Orientation imaging microscopy of polycrystalline sodium chloride

    SciTech Connect

    Staiger, M.P.; Kolbeinsson, I.; Newman, J.; Woodfield, T.; Sato, T.

    2010-04-15

    A novel preparation technique is described that makes possible grain size analysis of polycrystalline NaCl using orientation imaging microscopy via electron backscatter diffraction (EBSD). The preparation methodology is specifically developed to overcome difficulties in preparing microporous NaCl for microscopy. The grain size and crystallographic texture of polycrystalline NaCl samples, prepared via solution pressure and sintered in the range of 650-780 deg. C, were able to be measured successfully with EBSD. The limitations of the preparation technique for EBSD analysis of NaCl are also discussed.

  4. Processing of transparent polycrystalline AlON:Ce3+ scintillators

    DOE PAGESBeta

    Chen, Ching -Fong; Yang, Pin; King, Graham; Tegtmeier, Eric L.

    2015-10-23

    A new polycrystalline ceramic scintillator is reported for potential use in radiation detection and medical imaging applications. The goal was to develop cerium-activated aluminum oxynitride (AlON:Ce3+) ceramics, which can be produced using ceramic processes in comparison to the high-cost, low-yield single-crystal growth technique. A phase pure AlON:Ce3+ powder with cubic symmetry was successfully synthesized at high temperature under a reducing atmosphere to convert Ce4+ to Ce3+ in the solid solution. We explored two different activator concentrations (0.5 and 1.0 mol%). Fully dense and transparent AlON:Ce3+ ceramics were produced by a liquid-phase-assisted pressureless sintering. The crystal field splitting around the Ce3+more » activator in the AlON was comparable to the splitting induced by Br₋ and the Cl₋ ligands, which produced an emission spectrum perfectly matching the maximum quantum efficiency range of the photomultiplier tube for radiation detection. Both optical excitation and radiation ionizations in AlON:Ce3+ were demonstrated. Lastly, challenges and mechanisms related to the radioluminescence efficiency are discussed.« less

  5. Size effects and Hall-Petch relation in polycrystalline cobalt

    NASA Astrophysics Data System (ADS)

    Fleurier, Gwendoline; Hug, Eric; Martinez, Mayerling; Dubos, Pierre-Antoine; Keller, Clément

    2015-02-01

    The mechanical behaviour of polycrystalline hexagonal close-packed cobalt was investigated over a large range of grain size d in order to examine the occurrence of size effects. Crystallographic texture and amount of face centred cubic allotropic phase were maintained unchanged thanks to appropriate heat treatment procedures. The Hall-Petch (HP) relation exhibits two distinct behaviours from the very beginning of plastic strain levels. The conventional HP law is fulfilled for a number of grains across the thickness t higher than a critical value (t/d)c = 14. For t/d lower than (t/d)c, a multicrystalline regime is evidenced highlighting a strong reduction in flow stress. The high value of (t/d)c is related to the low-stacking fault energy of cobalt in the basal plane. The size effect is predominant in the first work hardening stage where slip mechanisms and stacking faults predominate. In the second stage, driven by mechanical twinning processes, this effect is less sensitive. Finally, the size effect could also affect the end of the elastic stage, in link with nonlinear elasticity mechanisms.

  6. Simulation to the Cyclic Deformation of Polycrystalline Aluminum Alloy Using Crystal Plasticity Finite Element Method

    NASA Astrophysics Data System (ADS)

    Luo, Juan; Kang, Guozheng; Shi, Mingxing

    2013-01-01

    A crystal plasticity based finite element model (i.e., FE model) is used in this paper to simulate the cyclic deformation of polycrystalline aluminum alloy plates. The Armstrong-Frederick nonlinear kinematic hardening rule is employed in the single crystal constitutive model to capture the Bauschinger effect and ratcheting of aluminum single crystal presented under the cyclic loading conditions. A simple model of latent hardening is used to consider the interaction of dislocations between different slipping systems. The proposed single crystal constitutive model is implemented numerically into a FE code, i.e., ABAQUS. Then, the proposed model is verified by comparing the simulated results of cyclic deformation with the corresponding experimental ones of a face-centered cubic polycrystalline metal, i.e., rolled 5083 aluminum alloy. In the meantime, it is shown that the model is capable of predicting local heterogeneous deformation in single crystal scale, which plays an important role in the macroscopic deformation of polycrystalline aggregates. Under the cyclic loading conditions, the effect of applied strain amplitude on the responded stress amplitude and the dependence of ratcheting strain on the applied stress level are reproduced reasonably.

  7. Process Research On Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Wohlgemuth, J. H.; Culik, J. S.

    1982-01-01

    The mechanisms limiting performance in polycrystalline silicon was determined. The initial set of experiments in this task entails the fabrication of cells of various thicknesses for four different bulk resistivities between 0.1 and 10 omega-cm. The results for the first two lots are presented.

  8. Stochastic multiscale modeling of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Wen, Bin

    Mechanical properties of engineering materials are sensitive to the underlying random microstructure. Quantification of mechanical property variability induced by microstructure variation is essential for the prediction of extreme properties and microstructure-sensitive design of materials. Recent advances in high throughput characterization of polycrystalline microstructures have resulted in huge data sets of microstructural descriptors and image snapshots. To utilize these large scale experimental data for computing the resulting variability of macroscopic properties, appropriate mathematical representation of microstructures is needed. By exploring the space containing all admissible microstructures that are statistically similar to the available data, one can estimate the distribution/envelope of possible properties by employing efficient stochastic simulation methodologies along with robust physics-based deterministic simulators. The focus of this thesis is on the construction of low-dimensional representations of random microstructures and the development of efficient physics-based simulators for polycrystalline materials. By adopting appropriate stochastic methods, such as Monte Carlo and Adaptive Sparse Grid Collocation methods, the variability of microstructure-sensitive properties of polycrystalline materials is investigated. The primary outcomes of this thesis include: (1) Development of data-driven reduced-order representations of microstructure variations to construct the admissible space of random polycrystalline microstructures. (2) Development of accurate and efficient physics-based simulators for the estimation of material properties based on mesoscale microstructures. (3) Investigating property variability of polycrystalline materials using efficient stochastic simulation methods in combination with the above two developments. The uncertainty quantification framework developed in this work integrates information science and materials science, and

  9. Equilibrium shapes of polycrystalline silicon nanodots

    SciTech Connect

    Korzec, M. D. Wagner, B.; Roczen, M.; Schade, M.; Rech, B.

    2014-02-21

    This study is concerned with the topography of nanostructures consisting of arrays of polycrystalline nanodots. Guided by transmission electron microscopy (TEM) measurements of crystalline Si (c-Si) nanodots that evolved from a “dewetting” process of an amorphous Si (a-Si) layer from a SiO{sub 2} coated substrate, we investigate appropriate formulations for the surface energy density and transitions of energy density states at grain boundaries. We introduce a new numerical minimization formulation that allows to account for adhesion energy from an underlying substrate. We demonstrate our approach first for the free standing case, where the solutions can be compared to well-known Wulff constructions, before we treat the general case for interfacial energy settings that support “partial wetting” and grain boundaries for the polycrystalline case. We then use our method to predict the morphologies of silicon nanodots.

  10. Hydrogen migration in phosphorous doped polycrystalline silicon

    SciTech Connect

    Nickel, N.H.; Kaiser, I.

    1998-12-31

    Hydrogen diffusion in phosphorous doped polycrystalline silicon was investigated by deuterium diffusion experiments. The presence of phosphorous enhances hydrogen diffusion. For high hydrogen concentrations the activation energy of the effective diffusion-coefficient amounts to 0.25--0.35 eV. At low hydrogen concentrations diffusion is governed by deep traps that are present in an appreciable concentration of 6 {times} 10{sup 18}--10{sup 19} cm{sup {minus}3}. The hydrogen chemical-potential, {mu}{sub H}, decreases with increasing temperature at a rate of {approx}0.002 eV/K. The data are discussed in terms of a two-level model used to describe hydrogen diffusion in amorphous and undoped polycrystalline silicon.

  11. Polycrystalline thin films FY 1992 project report

    SciTech Connect

    Zweibel, K.

    1993-01-01

    This report summarizes the activities and results of the Polycrystalline Thin Film Project during FY 1992. The purpose of the DOE/NREL PV (photovoltaic) Program is to facilitate the development of PV that can be used on a large enough scale to produce a significant amount of energy in the US and worldwide. The PV technologies under the Polycrystalline Thin Film project are among the most exciting next-generation'' options for achieving this goal. Over the last 15 years, cell-level progress has been steady, with laboratory cell efficiencies reaching levels of 15 to 16%. This progress, combined with potentially inexpensive manufacturing methods, has attracted significant commercial interest from US and international companies. The NREL/DOE program is designed to support the efforts of US companies through cost-shared subcontracts (called government/industry partnerships'') that we manage and fund and through collaborative technology development work among industry, universities, and our laboratory.

  12. Polycrystalline thin films FY 1992 project report

    SciTech Connect

    Zweibel, K.

    1993-01-01

    This report summarizes the activities and results of the Polycrystalline Thin Film Project during FY 1992. The purpose of the DOE/NREL PV (photovoltaic) Program is to facilitate the development of PV that can be used on a large enough scale to produce a significant amount of energy in the US and worldwide. The PV technologies under the Polycrystalline Thin Film project are among the most exciting ``next-generation`` options for achieving this goal. Over the last 15 years, cell-level progress has been steady, with laboratory cell efficiencies reaching levels of 15 to 16%. This progress, combined with potentially inexpensive manufacturing methods, has attracted significant commercial interest from US and international companies. The NREL/DOE program is designed to support the efforts of US companies through cost-shared subcontracts (called ``government/industry partnerships``) that we manage and fund and through collaborative technology development work among industry, universities, and our laboratory.

  13. Process Research on Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.

    1982-01-01

    The investigation of the performance limiting mechanisms in large grain (greater than 1-2 mm in diameter) polycrystalline silicon was continued by fabricating a set of minicell wafers on a selection of 10 cm x 10 cm wafers. A minicell wafer consists of an array of small (approximately 0.2 sq cm in area) photodiodes which are isolated from one another by a mesa structure. The junction capacitance of each minicell was used to obtain the dopant concentration, and therefore the resistivity, as a function of position across each wafer. The results indicate that there is no significant variation in resistivity with position for any of the polycrystalline wafers, whether Semix or Wacker. However, the resistivity of Semix brick 71-01E did decrease slightly from bottom to top.

  14. Grain-boundary resistance in polycrystalline metals

    NASA Astrophysics Data System (ADS)

    Reiss, G.; Vancea, J.; Hoffmann, H.

    1986-05-01

    Grain boundaries are known to reduce significantly the electrical dc conductivity of polycrystalline metallic materials. In this paper, we give a quantum mechanical calculation of the grain-boundary resistance based on the transfer matrix approach. The results show an exponential decrease of the conductivity with respect to the number of grain boundaries per mean free path in accord with an empirical model proposed recently.

  15. Structure and Electronic Properties of Polycrystalline Dielectrics

    SciTech Connect

    Mckenna, Keith P.; Shluger, AL

    2013-07-07

    We present an overview of the theoretical approaches that can be employed to model polycrystalline oxides along with a discussion of their limitations and associated challenges. We then present results for two metal oxide materials, MgO and HfO2, where theory and experiment have come together to provide insight into the structure and electronic properties of grain boundaries. Finally, we conclude with a discussion and outlook.

  16. Status of polycrystalline solar cell technologies

    NASA Astrophysics Data System (ADS)

    Kapur, Vijay K.; Basol, Bulent M.

    Thin-film cadmium telluride (CdTe) and thin-film copper indium diselenide (CIS) solar cells are discussed. The issues these technologies face before commercialization are addressed. High-efficiency (15-18 percent) polycrystalline silicon modules could dominate the market in the near future, and impressive results for thin-film CdTe and CIS solar cells and their outdoor stability can attract increased interest in these solar cells, which will accelerate their development.

  17. Elastic constants of cubic and wurtzite boron nitrides

    NASA Astrophysics Data System (ADS)

    Nagakubo, A.; Ogi, H.; Sumiya, H.; Kusakabe, K.; Hirao, M.

    2013-06-01

    We synthesized pure polycrystalline cubic boron nitride (cBN) and wurtzite boron nitride (wBN) by the direct conversion method from hexagonal boron nitride, and measured their longitudinal-wave elastic constants CL between 20 and 300 K using picosecond ultrasound spectroscopy. Their room-temperature values are 945 ± 3 GPa and 930 ± 18 GPa for cBN and wBN, respectively. The shear modulus G of cBN was also determined by combining resonance ultrasound spectroscopy and micromechanics calculation as G = 410 GPa. We performed ab-initio calculations and confirmed that the generalized gradient approximation potential fails to yield correct elastic constants, which indicated the necessity of a hybrid-functional method.

  18. Application of neutron holography to polycrystalline samples

    NASA Astrophysics Data System (ADS)

    Szakál, A.; Markó, M.; Krexner, G.; Cser, L.

    2015-07-01

    Neutron holography can be an efficient tool to investigate the local real-space structure of crystalline materials around specific probe nuclei serving as radiation source or detector. The positions of atoms in the neighborhood of such nuclei are observable with high (picometry) accuracy. Measurements of this type require orientational order and, therefore, restrict the range of study essentially to single crystals. However, if the information searched for is limited to the distances between the probe and the surrounding nuclei instead of their positions, holographic techniques can be applied to polycrystalline samples as well. In order to prove this statement, the expected multi-wavelength holographic signal of a polycrystalline sample was calculated. The holographic signal can be obtained by applying time-of-flight techniques, and by using a proper mathematical procedure, the distances between the probe nucleus and the surrounding nuclei can be reconstructed. A model calculation taking into account real instrument parameters confirms this expectation. The experimental verification of the predictions can be undertaken at existing pulsed neutron sources being able to provide the required experimental conditions. This new method opens the way to expand the field of investigation towards gaining information about the local atomic structure of polycrystalline materials which are of importance also in various applications.

  19. Effective structural properties in polycrystalline graphene

    NASA Astrophysics Data System (ADS)

    Hossain, Zubaer

    This talk will discuss effective structural properties in polycrystalline graphene under the presence of atomic scale heterogeneity. Polycrystallinity is ubiquitous in solids, but theories describing their effective behavior remain limited, particularly when heterogeneity is present in the form of nonuniform deformation or composition. Over the decades, exploration of the effective transport and strength properties of heterogeneous systems has been carried out mostly with random distribution of grains or regular periodic structures under various approximations, in translating the underlying physics into a single representative volume element. Although heterogeneity can play a critical role in modulating the basic behavior of low-dimensional materials, it is difficult to capture the local characteristics accurately by these approximations. Taking polycrystalline graphene as an example material, we study the effective structural properties (such as Young's Modulus, Poisson's ratio and Toughness) by using a combination of density functional theory and molecular dynamic simulations. We identify the key mechanisms that govern their effective behavior and exploit the understanding to engineer the behavior by doping with a carefully selected choice of chemical elements.

  20. Characterization of electrochemically modified polycrystalline platinum surfaces

    SciTech Connect

    Krebs, L.C.; Ishida, Takanobu.

    1991-12-01

    The characterization of electrochemically modified polycrystalline platinum surfaces has been accomplished through the use of four major electrochemical techniques. These were chronoamperometry, chronopotentiommetry, cyclic voltammetry, and linear sweep voltammetry. A systematic study on the under-potential deposition of several transition metals has been performed. The most interesting of these were: Ag, Cu, Cd, and Pb. It was determined, by subjecting the platinum electrode surface to a single potential scan between {minus}0.24 and +1.25 V{sub SCE} while stirring the solution, that the electrocatalytic activity would be regenerated. As a consequence of this study, a much simpler method for producing ultra high purity water from acidic permanganate has been developed. This method results in water that surpasses the water produced by pyrocatalytic distillation. It has also been seen that the wettability of polycrystalline platinum surfaces is greatly dependent on the quantity of oxide present. Oxide-free platinum is hydrophobic and gives a contact angle in the range of 55 to 62 degrees. We have also modified polycrystalline platinum surface with the electrically conducting polymer poly-{rho}-phenylene. This polymer is very stable in dilute sulfuric acid solutions, even under applied oxidative potentials. It is also highly resistant to electrochemical hydrogenation. The wettability of the polymer modified platinum surface is severely dependent on the choice of supporting electrolyte chosen for the electrochemical polymerization. Tetraethylammonium tetrafluoroborate produces a film that is as hydrophobic as Teflon, whereas tetraethylammonium perchlorate produces a film that is more hydrophilic than oxide-free platinum.

  1. Abnormality in fracture strength of polycrystalline silicene

    NASA Astrophysics Data System (ADS)

    Liu, Ning; Hong, Jiawang; Pidaparti, Ramana; Wang, Xianqiao

    2016-09-01

    Silicene, a silicon-based homologue of graphene, arouses great interest in nano-electronic devices due to its outstanding electronic properties. However, its promising electronic applications are greatly hindered by lack of understanding in the mechanical strength of silicene. Therefore, in order to design mechanically reliable devices with silicene, it is necessary to thoroughly explore the mechanical properties of silicene. Due to current fabrication methods, graphene is commonly produced in a polycrystalline form; the same may hold for silicene. Here we perform molecular dynamics simulations to investigate the mechanical properties of polycrystalline silicene. First, an annealing process is employed to construct a more realistic modeling structure of polycrystalline silicene. Results indicate that a more stable structure is formed due to the breaking and reformation of bonds between atoms on the grain boundaries. Moreover, as the grain size decreases, the efficiency of the annealing process, which is quantified by the energy change, increases. Subsequently, biaxial tensile tests are performed on the annealed samples in order to explore the relation between grain size and mechanical properties, namely in-plane stiffness, fracture strength and fracture strain etc. Results indicate that as the grain size decreases, the fracture strain increases while the fracture strength shows an inverse trend. The decreasing fracture strength may be partly attributed to the weakening effect from the increasing area density of defects which acts as the reservoir of stress-concentrated sites on the grain boundary. The observed crack localization and propagation and fracture strength are well-explained by a defect-pileup model.

  2. Polycrystalline gamma plutonium's elastic moduli versus temperature

    SciTech Connect

    Migliori, Albert; Betts, J; Trugman, A; Mielke, C H; Mitchell, J N; Ramos, M; Stroe, I

    2009-01-01

    Resonant ultrasound spectroscopy was used to measure the elastic properties of pure polycrystalline {sup 239}Pu in the {gamma} phase. Shear and longitudinal elastic moduli were measured simultaneously and the bulk modulus was computed from them. A smooth, linear, and large decrease of all elastic moduli with increasing temperature was observed. They calculated the Poisson ratio and found that it increases from 0.242 at 519 K to 0.252 at 571 K. These measurements on extremely well characterized pure Pu are in agreement with other reported results where overlap occurs.

  3. Photoinduced conductivity changes in polycrystalline diamond films

    NASA Astrophysics Data System (ADS)

    Gonon, P.; Prawer, S.; Jamieson, D.

    1996-02-01

    We report that the dark electrical properties of polycrystalline chemical vapor deposition diamond films are modified after exposure to UV light. UV illumination gives rise to an increase in the dark conductivity and to a change in the I-V characteristic from Iα exp (aV) for the as-grown material to IαV2 following UV irradiation. Thermally stimulated currents corresponding to an activation energy of about 1.9 eV are observed after UV illumination. The effects of UV irradiation can be totally reversed by thermal annealing and partially reversed by exposing the samples to white light.

  4. Poole-Frenkel conduction in polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Gonon, P.; Boiko, Y.; Prawer, S.; Jamieson, D.

    1996-04-01

    High-field electrical conduction has been studied in undoped polycrystalline diamond over a wide temperature range. The current increases exponentially with the electric field with an exponential factor which increases linearly with the inverse of temperature. The activation energy of the conductivity is found to be strongly field dependent and to decrease linearly with the electric field. The experimental data support a Poole-Frenkel conduction with overlapping centers. The centers are found to be located at around 1.1 eV from the band edge with a density of about 2×1017 cm-3.

  5. Process for Polycrystalline film silicon growth

    DOEpatents

    Wang, Tihu; Ciszek, Theodore F.

    2001-01-01

    A process for depositing polycrystalline silicon on substrates, including foreign substrates, occurs in a chamber at about atmospheric pressure, wherein a temperature gradient is formed, and both the atmospheric pressure and the temperature gradient are maintained throughout the process. Formation of a vapor barrier within the chamber that precludes exit of the constituent chemicals, which include silicon, iodine, silicon diiodide, and silicon tetraiodide. The deposition occurs beneath the vapor barrier. One embodiment of the process also includes the use of a blanketing gas that precludes the entrance of oxygen or other impurities. The process is capable of repetition without the need to reset the deposition zone conditions.

  6. Shock-front broadening in polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Barber, J. L.; Kadau, K.

    2008-04-01

    We analyze a model for the evolution of shock fronts in polycrystalline materials. This model is based on the idea of Meyers and Carvalho [Mater. Sci. Eng. 24, 131 (1976)] that the shock velocity anisotropy within the polycrystal is the most important factor in shock front broadening. Our analysis predicts that the shock front width increases as the 1/2 power of the front penetration distance into the crystal. Our theoretical prediction is in plausible agreement with previous experimental results for the elastic precursor rise time, and it should therefore provide a useful shock width estimate. Furthermore, our theoretical framework is also applicable to other problems involving front propagation in heterogeneous media.

  7. Average intragranular misorientation trends in polycrystalline materials predicted by a viscoplastic self-consistent approach

    DOE PAGESBeta

    Lebensohn, Ricardo A.; Zecevic, Miroslav; Knezevic, Marko; McCabe, Rodney J.

    2015-12-15

    Here, this work presents estimations of average intragranular fluctuations of lattice rotation rates in polycrystalline materials, obtained by means of the viscoplastic self-consistent (VPSC) model. These fluctuations give a tensorial measure of the trend of misorientation developing inside each single crystal grain representing a polycrystalline aggregate. We first report details of the algorithm implemented in the VPSC code to estimate these fluctuations, which are then validated by comparison with corresponding full-field calculations. Next, we present predictions of average intragranular fluctuations of lattice rotation rates for cubic aggregates, which are rationalized by comparison with experimental evidence on annealing textures of fccmore » and bcc polycrystals deformed in tension and compression, respectively, as well as with measured intragranular misorientation distributions in a Cu polycrystal deformed in tension. The orientation-dependent and micromechanically-based estimations of intragranular misorientations that can be derived from the present implementation are necessary to formulate sound sub-models for the prediction of quantitatively accurate deformation textures, grain fragmentation, and recrystallization textures using the VPSC approach.« less

  8. Average intragranular misorientation trends in polycrystalline materials predicted by a viscoplastic self-consistent approach

    SciTech Connect

    Lebensohn, Ricardo A.; Zecevic, Miroslav; Knezevic, Marko; McCabe, Rodney J.

    2015-12-15

    Here, this work presents estimations of average intragranular fluctuations of lattice rotation rates in polycrystalline materials, obtained by means of the viscoplastic self-consistent (VPSC) model. These fluctuations give a tensorial measure of the trend of misorientation developing inside each single crystal grain representing a polycrystalline aggregate. We first report details of the algorithm implemented in the VPSC code to estimate these fluctuations, which are then validated by comparison with corresponding full-field calculations. Next, we present predictions of average intragranular fluctuations of lattice rotation rates for cubic aggregates, which are rationalized by comparison with experimental evidence on annealing textures of fcc and bcc polycrystals deformed in tension and compression, respectively, as well as with measured intragranular misorientation distributions in a Cu polycrystal deformed in tension. The orientation-dependent and micromechanically-based estimations of intragranular misorientations that can be derived from the present implementation are necessary to formulate sound sub-models for the prediction of quantitatively accurate deformation textures, grain fragmentation, and recrystallization textures using the VPSC approach.

  9. Process Research on Polycrystalline Silicon Material (PROPSM)

    NASA Technical Reports Server (NTRS)

    Culik, J. S.; Wrigley, C. Y.

    1984-01-01

    Results of hydrogen-passivated polycrystalline silicon solar cells are summarized. Very small grain or short minority-carrier diffusion length silicon was used. Hydrogenated solar cells fabricated from this material appear to have effective minority-carrier diffusion lengths that are still not very long, as shown by the open-circuit voltages of passivated cells that are still significantly less than those of single-crystal solar cells. The short-circuit current of solar cells fabricated from large-grain cast polycrystalline silicon is nearly equivalent to that of single-crystal cells, which indicates long bulk minority-carrier diffusion length. However, the open-circuit voltage, which is sensitive to grain boundary recombination, is sometimes 20 to 40 mV less. The goal was to minimize variations in open-circuit voltage and fill-factor caused by defects by passivating these defects using a hydrogenation process. Treatments with molecular hydrogen showed no effect on large-grain cast polycrystaline silicon solar cells.

  10. Acoustic study of texture in polycrystalline brass

    SciTech Connect

    Foster, K.; Fairburn, S.L.; Leisure, R.G.; Kim, S.; Balzar, D.; Alers, G.; Ledbetter, H.

    1999-05-01

    Resonant ultrasound spectroscopy was used to measure the orthorhombic elastic constants of rolled, polycrystalline plates of Cu, Cu{endash}5{percent} Zn, and Cu{endash}15{percent} Zn. The experimental results were fit to theoretical expressions to determine the orientation-distribution coefficients W{sub 400}, W{sub 420}, and W{sub 440}. These coefficients are related to texture (the nonrandom orientation of crystallites). The experimental results were in good agreement with theory for the Cu and the Cu{endash}15{percent} Zn materials. The agreement was not as good for the more anisotropic Cu{endash}5{percent} Zn material, especially for the in-plane compressional constants C{sub 11} and C{sub 22}. The ultrasonically derived {ital W}{close_quote}s were compared to those obtained from neutron measurements for the Cu{endash}Zn alloys. Pole plots based on the two types of measurements, using W{sub 400}, W{sub 420}, and W{sub 440}, were in excellent agreement for the 15{percent} Zn material, and in qualitative agreement for the 5{percent} Zn material. The results support the idea that acoustic methods can be used to measure the low-order {ital W}{close_quote}s in polycrystalline materials. {copyright} {ital 1999 Acoustical Society of America.}

  11. US polycrystalline thin film solar cells program

    SciTech Connect

    Ullal, H.S.; Zweibel, K.; Mitchell, R.L. )

    1989-11-01

    The Polycrystalline Thin Film Solar Cells Program, part of the United States National Photovoltaic Program, performs R D on copper indium diselenide and cadmium telluride thin films. The objective of the Program is to support research to develop cells and modules that meet the US Department of Energy's long-term goals by achieving high efficiencies (15%-20%), low-cost ($50/m{sup 2}), and long-time reliability (30 years). The importance of work in this area is due to the fact that the polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells and modules have made rapid advances. They have become the leading thin films for PV in terms of efficiency and stability. The US Department of Energy has increased its funding through an initiative through the Solar Energy Research Institute in CuInSe{sub 2} and CdTe with subcontracts to start in Spring 1990. 23 refs., 5 figs.

  12. Patterned polycrystalline diamond microtip vacuum diode arrays

    SciTech Connect

    Kang, W.P.; Davidson, J.L.; Kinser, D.L.

    1995-12-31

    Electron field emission from an array of patterned pyramids of polycrystalline diamond for vacuum diode applications has been investigated. High current emission from the patterned diamond microtip arrays are obtained at low electric fields. A current density from the diamond microtips of 14mA/cm{sup 2} was observed for a field of <10 V/{mu}m. Field emission for these diamond microtips exhibits significant enhancement both in total emission current and stability compared to pure silicon emitters. Moreover, field emission from patterned polycrystalline diamond pyramidal tip arrays is unique in that the applied field is found to be lower (2-3 order of magnitude lower) compared to that required for emission from Si, Ge, GaAs, and metal surfaces. The fabrication process utilizing silicon shaping and micromachining techniques for the fabrication of diamond diaphragms with diamond microtip arrays for vacuum microelectronic applications has been developed. The processing techniques are compatible with IC fabrication technology. The effect of temperature annealing on the current emission characteristics were also investigated.

  13. Electrical properties of polycrystalline methane hydrate

    USGS Publications Warehouse

    Du Frane, W. L.; Stern, L.A.; Weitemeyer, K.A.; Constable, S.; Pinkston, J.C.; Roberts, J.J.

    2011-01-01

    Electromagnetic (EM) remote-sensing techniques are demonstrated to be sensitive to gas hydrate concentration and distribution and complement other resource assessment techniques, particularly seismic methods. To fully utilize EM results requires knowledge of the electrical properties of individual phases and mixing relations, yet little is known about the electrical properties of gas hydrates. We developed a pressure cell to synthesize gas hydrate while simultaneously measuring in situ frequency-dependent electrical conductivity (σ). Synthesis of methane (CH4) hydrate was verified by thermal monitoring and by post run cryogenic scanning electron microscope imaging. Impedance spectra (20 Hz to 2 MHz) were collected before and after synthesis of polycrystalline CH4 hydrate from polycrystalline ice and used to calculate σ. We determined the σ of CH4 hydrate to be 5 × 10−5 S/m at 0°C with activation energy (Ea) of 30.6 kJ/mol (−15 to 15°C). After dissociation back into ice, σ measurements of samples increased by a factor of ~4 and Ea increased by ~50%, similar to the starting ice samples.

  14. Polycrystalline thin film materials and devices

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E. . Inst. of Energy Conversion)

    1992-10-01

    Results of Phase II of a research program on polycrystalline thin film heterojunction solar cells are presented. Relations between processing, materials properties and device performance were studied. The analysis of these solar cells explains how minority carrier recombination at the interface and at grain boundaries can be reduced by doping of windows and absorber layers, such as in high efficiency CdTe and CuInSe{sub 2} based solar cells. The additional geometric dimension introduced by the polycrystallinity must be taken into consideration. The solar cells are limited by the diode current, caused by recombination in the space charge region. J-V characteristics of CuInSe{sub 2}/(CdZn)S cells were analyzed. Current-voltage and spectral response measurements were also made on high efficiency CdTe/CdS thin film solar cells prepared by vacuum evaporation. Cu-In bilayers were reacted with Se and H{sub 2}Se gas to form CuInSe{sub 2} films; the reaction pathways and the precursor were studied. Several approaches to fabrication of these thin film solar cells in a superstrate configuration were explored. A self-consistent picture of the effects of processing on the evolution of CdTe cells was developed.

  15. Reversible piezomagnetoelectric switching in bulk polycrystalline ceramics

    SciTech Connect

    Stevenson, T. Bennett, J.; Brown, A. P.; Wines, T.; Bell, A. J.; Comyn, T. P.; Smith, R. I.

    2014-08-01

    Magnetoelectric (ME) coupling in materials offer tremendous advantages in device functionality enabling technologies including advanced electronic memory, combining electronic speed, and efficiency with magnetic robustness. However, low cost polycrystalline ME materials are excluded from most commercial applications, operating only at cryogenic temperatures, impractically large electric/magnetic fields, or with low ME coefficients (1-100 mV/cm Oe). Despite this, the technological potential of single compound ME coupling has continued to drive research into multiferroics over the last two decades. Here we show that by manipulating the large induced atomic strain within the polycrystalline, room temperature multiferroic compound 0.7BiFeO{sub 3}–0.3PbTiO{sub 3}, we can induce a reversible, piezoelectric strain controlled ME effect. Employing an in situ neutron diffraction experiment, we have demonstrated that this piezomagnetoelectric effect manifests with an applied electric field >8 kV/mm at the onset of piezoelectric strain, engineered in to the compound by crystallographic phase mixing. This produces a remarkable intrinsic ME coefficient of 1276 mV/cm Oe, due to a strain driven modification to the oxygen sub-lattice, inducing an increase in magnetic moment per Fe{sup 3+} ion of +0.142 μ{sub B}. This work provides a framework for investigations into strain engineered nanostructures to realize low-cost ME devices designed from the atoms up, as well as contributing to the deeper understanding of single phase ME coupling mechanisms.

  16. US Polycrystalline Thin Film Solar Cells Program

    NASA Astrophysics Data System (ADS)

    Ullal, Harin S.; Zweibel, Kenneth; Mitchell, Richard L.

    1989-11-01

    The Polycrystalline Thin Film Solar Cells Program, part of the United States National Photovoltaic Program, performs R and D on copper indium diselenide and cadmium telluride thin films. The objective of the program is to support research to develop cells and modules that meet the U.S. Department of Energy's long-term goals by achieving high efficiencies (15 to 20 percent), low-cost ($50/m(sup 2)), and long-time reliability (30 years). The importance of work in this area is due to the fact that the polycrystalline thin-film CuInSe2 and CdTe solar cells and modules have made rapid advances. They have become the leading thin films for PV in terms of efficiency and stability. The U.S. Department of Energy has increased its funding through an initiative through the Solar Energy Research Institute in CuInSe2 and CdTe with subcontracts to start in spring 1990.

  17. Cubic Unit Cell Construction Kit.

    ERIC Educational Resources Information Center

    Mattson, Bruce

    2000-01-01

    Presents instructions for building a simple interactive unit-cell construction kit that allows for the construction of simple, body-centered, and face-centered cubic lattices. The lit is built from inexpensive and readily available materials and can be built in any number of sizes. (WRM)

  18. Cubication of Conservative Nonlinear Oscillators

    ERIC Educational Resources Information Center

    Belendez, Augusto; Alvarez, Mariela L.; Fernandez, Elena; Pascual, Immaculada

    2009-01-01

    A cubication procedure of the nonlinear differential equation for conservative nonlinear oscillators is analysed and discussed. This scheme is based on the Chebyshev series expansion of the restoring force, and this allows us to approximate the original nonlinear differential equation by a Duffing equation in which the coefficients for the linear…

  19. Progress in polycrystalline thin-film solar cells

    SciTech Connect

    Zweibel, K; Hermann, A; Mitchell, R

    1983-07-01

    Photovoltaic devices based on several polycrystalline thin-film materials have reached near and above 10% sunlight-to-electricity conversion efficiencies. This paper examines the various polycrystalline thin-film PV materials including CuInSe/sub 2/ and CdTe in terms of their material properties, fabrication techniques, problems, and potentials.

  20. Polycrystalline Diamond Schottky Diodes and Their Applications.

    NASA Astrophysics Data System (ADS)

    Zhao, Ganming

    In this work, four-hot-filament CVD techniques for in situ boron doped diamond synthesis on silicon substrates were extensively studied. A novel tungsten filament shape and arrangement used to obtain large-area, uniform, boron doped polycrystalline diamond thin films. Both the experimental results and radiative heat transfer analysis showed that this technique improved the uniformity of the substrate temperature. XRD, Raman and SEM studies indicate that large area, uniform, high quality polycrystalline diamond films were obtained. Schottky diodes were fabricated by either sputter deposition of silver or thermal evaporation of aluminum or gold, on boron doped diamond thin films. High forward current density and a high forward-to-reverse current ratio were exhibited by silver on diamond Schottky diodes. Schottky barrier heights and the majority carrier concentrations of both aluminum and gold contacted diodes were determined from the C-V measurements. Furthermore, a novel theoretical C-V-f analysis of deep level boron doped diamond Schottky diodes was performed. The analytical results agree well with the experimental results. Compressive stress was found to have a large effect on the forward biased I-V characteristics of the diamond Schottky diodes, whereas the effect on the reverse biased characteristics was relatively small. The stress effect on the forward biased diamond Schottky diode was attributed to piezojunction and piezoresistance effects. The measured force sensitivity of the diode was as high as 0.75 V/N at 1 mA forward bias. This result shows that CVD diamond device has potential for mechanical transducer applications. The quantitative photoresponse characteristics of the diodes were studied in the spectral range of 300 -1050 nm. Semi-transparent gold contacts were used for better photoresponse. Quantum efficiency as high as 50% was obtained at 500 nm, when a reverse bias of over 1 volt was applied. The Schottky barrier heights between either gold or

  1. Modelling heat conduction in polycrystalline hexagonal boron-nitride films

    NASA Astrophysics Data System (ADS)

    Mortazavi, Bohayra; Pereira, Luiz Felipe C.; Jiang, Jin-Wu; Rabczuk, Timon

    2015-08-01

    We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets.

  2. Modelling heat conduction in polycrystalline hexagonal boron-nitride films.

    PubMed

    Mortazavi, Bohayra; Pereira, Luiz Felipe C; Jiang, Jin-Wu; Rabczuk, Timon

    2015-01-01

    We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets. PMID:26286820

  3. Modelling heat conduction in polycrystalline hexagonal boron-nitride films

    PubMed Central

    Mortazavi, Bohayra; Pereira, Luiz Felipe C.; Jiang, Jin-Wu; Rabczuk, Timon

    2015-01-01

    We conducted extensive molecular dynamics simulations to investigate the thermal conductivity of polycrystalline hexagonal boron-nitride (h-BN) films. To this aim, we constructed large atomistic models of polycrystalline h-BN sheets with random and uniform grain configuration. By performing equilibrium molecular dynamics (EMD) simulations, we investigated the influence of the average grain size on the thermal conductivity of polycrystalline h-BN films at various temperatures. Using the EMD results, we constructed finite element models of polycrystalline h-BN sheets to probe the thermal conductivity of samples with larger grain sizes. Our multiscale investigations not only provide a general viewpoint regarding the heat conduction in h-BN films but also propose that polycrystalline h-BN sheets present high thermal conductivity comparable to monocrystalline sheets. PMID:26286820

  4. Plastic deformation of polycrystalline zirconium carbide

    NASA Technical Reports Server (NTRS)

    Darolia, R.; Archbold, T. F.

    1976-01-01

    The compressive yield strength of arc-melted polycrystalline zirconium carbide has been found to vary from 77 kg per sq mm at 1200 C to 19 kg per sq mm at 1800 C. Yield drops were observed with plastic strain-rates greater than 0.003/sec but not with slower strain rates. Strain-rate change experiments yielded values for the strain-rate sensitivity parameter m which range from 6.5 at 1500 C to 3.8 at 1800 C, and the product dislocation velocity stress exponent times T was found to decrease linearly with increasing temperature. The deformation rate results are consistent with the Kelly-Rowcliffe model in which the diffusion of carbon assists the motion of dislocations.

  5. Helium Migration Mechanisms in Polycrystalline Uranium Dioxide

    SciTech Connect

    Martin, Guillaume; Desgardin, Pierre; Sauvage, Thierry; Barthe, Marie-France; Garcia, Philippe; Carlot, Gaelle

    2007-07-01

    This study aims at identifying the release mechanisms of helium in uranium dioxide. Two sets of polycrystalline UO{sub 2} sintered samples presenting different microstructures were implanted with {sup 3}He ions at concentrations in the region of 0.1 at.%. Changes in helium concentrations were monitored using two Nuclear Reaction Analysis (NRA) techniques based on the {sup 3}He(d,{alpha}){sup 1}H reaction. {sup 3}He release is measured in-situ during sample annealing at temperatures ranging between 700 deg. C and 1000 deg. C. Accurate helium depth profiles are generated after each annealing stage. Results that provide data for further understanding helium release mechanisms are discussed. It is found that helium diffusion appears to be enhanced above 900 deg. C in the vicinity of grain boundaries possibly as a result of the presence of defects. (authors)

  6. High-temperature creep of polycrystalline chromium

    NASA Technical Reports Server (NTRS)

    Stephens, J. R.; Klopp, W. D.

    1972-01-01

    The creep properties of high-purity, polycrystalline chromium were determined over the temperature range 0.51 to 0.78 T sub m, where T sub m is the melting temperature. Creep rates determined from step-load creep tests can be represented by the general creep equation; epsilon/D = k((sigma/E) to the nth power) where epsilon is the minimum creep rate, D is the diffusivity, k is the creep rate constant, sigma is the applied stress, E is the modulus, and n is the stress exponent, equal to 4.3 for chromium. This correlation and metallographic observations suggest a dislocation climb mechanism is operative in the creep of chromium over the temperature range investigated.

  7. Polycrystalline-thin-film thermophotovoltaic cells

    NASA Astrophysics Data System (ADS)

    Dhere, Neelkanth G.

    1996-02-01

    Thermophotovoltaic (TPV) cells convert thermal energy to electricity. Modularity, portability, silent operation, absence of moving parts, reduced air pollution, rapid start-up, high power densities, potentially high conversion efficiencies, choice of a wide range of heat sources employing fossil fuels, biomass, and even solar radiation are key advantages of TPV cells in comparison with fuel cells, thermionic and thermoelectric convertors, and heat engines. The potential applications of TPV systems include: remote electricity supplies, transportation, co-generation, electric-grid independent appliances, and space, aerospace, and military power applications. The range of bandgaps for achieving high conversion efficiencies using low temperature (1000-2000 K) black-body or selective radiators is in the 0.5-0.75 eV range. Present high efficiency convertors are based on single crystalline materials such as In1-xGaxAs, GaSb, and Ga1-xInxSb. Several polycrystalline thin films such as Hg1-xCdxTe, Sn1-xCd2xTe2, and Pb1-xCdxTe, etc., have great potential for economic large-scale applications. A small fraction of the high concentration of charge carriers generated at high fluences effectively saturates the large density of defects in polycrystalline thin films. Photovoltaic conversion efficiencies of polycrystalline thin films and PV solar cells are comparable to single crystalline Si solar cells, e.g., 17.1% for CuIn1-xGaxSe2 and 15.8% for CdTe. The best recombination-state density Nt is in the range of 10-15-10-16 cm-3 acceptable for TPV applications. Higher efficiencies may be achieved because of the higher fluences, possibility of bandgap tailoring, and use of selective emitters such as rare earth oxides (erbia, holmia, yttria) and rare earth-yttrium aluminium garnets. As compared to higher bandgap semiconductors such as CdTe, it is easier to dope the lower bandgap semiconductors. TPV cell development can benefit from the more mature PV solar cell and opto

  8. Polycrystalline silicon ion sensitive field effect transistors

    NASA Astrophysics Data System (ADS)

    Yan, F.; Estrela, P.; Mo, Y.; Migliorato, P.; Maeda, H.; Inoue, S.; Shimoda, T.

    2005-01-01

    We report the operation of polycrystalline silicon ion sensitive field effect transistors. These devices can be fabricated on inexpensive disposable substrates such as glass or plastics and are, therefore, promising candidates for low cost single-use intelligent multisensors. In this work we have developed an extended gate structure with a Si3N4 sensing layer. Nearly ideal pH sensitivity (54mV /pH) and stable operation have been achieved. Temperature effects have been characterized. A penicillin sensor has been fabricated by functionalizing the sensing area with penicillinase. The sensitivity to penicillin G is about 10mV/mM, in solutions with concentration lower than the saturation value, which is about 7 mM.

  9. Residual Stress Predictions in Polycrystalline Alumina

    SciTech Connect

    VEDULA,VENKATA R.; GLASS,S. JILL; SAYLOR,DAVID M.; ROHRER,GREGORY S.; CARTER,W. CRAIG; LANGER,STEPHEN A.

    1999-12-13

    Microstructure-level residual stresses arise in polycrystalline ceramics during processing as a result of thermal expansion anisotropy and crystallographic disorientation across the grain boundaries. Depending upon the grain size, the magnitude of these stresses can be sufficiently high to cause spontaneous microcracking during the processing of these materials. They are also likely to affect where cracks initiate and propagate under macroscopic loading. The magnitudes of residual stresses in untextured and textured alumina samples were predicted using object oriented finite (OOF) element analysis and experimentally determined grain orientations. The crystallographic orientations were obtained by electron-backscattered diffraction (EBSD). The residual stresses were lower and the stress distributions were narrower in the textured samples compared to those in the untextured samples. Crack initiation and propagation were also simulated using the Griffith fracture criterion. The grain boundary to surface energy ratios required for computations were estimated using AFM groove measurements.

  10. Polycrystalline Thin Film Device Degradation Studies

    SciTech Connect

    Albin, D. S.; McMahon, T. J.; Pankow, J. W.; Noufi, R.; Demtsu, S. H.; Davies, A.

    2005-11-01

    Oxygen during vapor CdCl2 (VCC) treatments significantly reduced resistive shunts observed in CdS/CdTe polycrystalline devices using thinner CdS layers during 100 deg C, open-circuit, 1-sun accelerated stress testing. Cu oxidation resulting from the reduction of various trace oxides present in as-grown and VCC treated films is the proposed mechanism by which Cu diffusion, and subsequent shunts are controlled. Graphite paste layers between metallization and CdTe behave like diffusion barriers and similarly benefit device stability. Ni-based contacts form a protective Ni2Te3 intermetallic layer that reduces metal diffusion but degrades performance through increased series resistance.

  11. Shock front broadening in polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Barber, John; Kadau, Kai

    2008-03-01

    We analyze a model for the evolution of weak shock fronts (or elastic precursor waves) in polycrystalline materials. This model is based on the idea of Meyers and Carvalho [Mater. Sci. Eng. 24, 131 (1976)] that the shock velocity anisotropy within the polycrystal is the most important factor in shock front broadening. Our analysis predicts that the shock front width increases as the 1/2 power of the front penetration distance into the crystal. Our theoretical prediction is in plausible agreement with previous experimental results for the elastic precursor rise time, and it should therefore provide a useful shock width estimate. Furthermore, our theoretical framework is also applicable to other problems involving front propagation in heterogeneous media.

  12. Tensile creep behavior of polycrystalline alumina fibers

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; Goldsby, J. C.

    1993-01-01

    Tensile creep studies were conducted on polycrystalline Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Test conditions were temperatures from 800 to 1050 C and stresses from 60 to 1000 MPa. For both fibers, only a small primary creep portion occurred followed by steady-state creep. The stress exponents for steady-state creep of Nextel 610 and Fiber FP were found to be about 3 and 1, respectively. At lower temperatures, below 1000 C, the finer grained Nextel 610 had a much higher 0.2 percent creep strength for 100 hr than the Fiber FP; while at higher temperatures, Nextel 610 had a comparable creep strength to the Fiber FP. The stress and grain size dependencies suggest Nextel 610 and Fiber FP creep rates are due to grain boundary sliding controlled by interface reaction and Nabarro-Herring mechanisms, respectively.

  13. Interaction of metal layers with polycrystalline Si

    NASA Technical Reports Server (NTRS)

    Nakamura, K.; Olowolafe, J. O.; Lau, S. S.; Nicolet, M.-A.; Mayer, J. W.; Shima, R.

    1976-01-01

    Solid-phase reactions of metal films deposited on 0.5-micron-thick polycrystalline layers of Si grown by chemical vapor deposition at 640 C were investigated by MeV He-4 backscattering spectrometry, glancing angle X-ray diffraction, and SEM observations. For the metals Al, Ag, and Au, which form simple eutectics, heat treatment at temperatures below the eutectic results in erosion of the poly-Si layer and growth of Si crystallites in the metal film. Crystallite formation is observed at temperatures exceeding 550 C for Ag, at those exceeding 400 C for Al, and at those exceeding 200 C for Au films. For Pd, Ni, and Cr, heat treatment results in silicide formation. The same initial silicides (Pd2Si, Ni2Si, and CrSi2), are formed at similar temperatures on single-crystal substrates.

  14. Dynamical electrophotoconductivity in polycrystalline thin films

    NASA Technical Reports Server (NTRS)

    Kowel, S. T.; Kornreich, P. G.

    1982-01-01

    Polycrystalline cadmium sulfide (CdS) films were deposited on lithium niobate (LiNbO3) substrates by vacuum evaporation and annealed to obtain high photosensitivity. The change in photoconductivity of these films due to the penetration of electric fields associated with elastic waves propagating on their substrates was demonstrated and studied. The relationship between the acoustic electric field and the induced change in film conductivity was found to be a nonlinear one. The fractional change in conductivity is strongly dependent on the light intensity and the film temperature, showing a prominent maximum as a function of these quantities. The largest recorded fractional change in conductivity was about 25% at electric fields of the order of 1,000 volts per centimeter. A phenomological model was developed based on the interaction between the space charge created by the electric field and the electron trapping states in the photoconductor.

  15. Vacancy Formation Enthalpy in Polycrystalline Depleted Uranium

    NASA Astrophysics Data System (ADS)

    Lund, K. R.; Lynn, K. G.; Weber, M. H.; Okuniewski, M. A.

    2013-06-01

    Positron Annihilation Spectroscopy was performed as a function of temperature and beam energy on polycrystalline depleted uranium (DU) foil. Samples were run with varying heat profiles all starting at room temperature. While collecting Doppler-Broadening data, the temperature of the sample was cycled several times. The first heat cycle shows an increasing S-parameter near temperatures of 400K to 500K much lower than the first phase transition of 941K indicating increasing vacancies possibly due to oxygen diffusion from the bulk to the surface. Vacancy formation enthalpies were calculated fitting a model to the data to be 1.6± 0.16 eV. Results are compared to previous work [3,4].

  16. Cubic Icosahedra? A Problem in Assigning Symmetry

    ERIC Educational Resources Information Center

    Lloyd, D. R.

    2010-01-01

    There is a standard convention that the icosahedral groups are classified separately from the cubic groups, but these two symmetry types have been conflated as "cubic" in some chemistry textbooks. In this note, the connection between cubic and icosahedral symmetries is examined, using a simple pictorial model. It is shown that octahedral and…

  17. Solving Cubic Equations by Polynomial Decomposition

    ERIC Educational Resources Information Center

    Kulkarni, Raghavendra G.

    2011-01-01

    Several mathematicians struggled to solve cubic equations, and in 1515 Scipione del Ferro reportedly solved the cubic while participating in a local mathematical contest, but did not bother to publish his method. Then it was Cardano (1539) who first published the solution to the general cubic equation in his book "The Great Art, or, The Rules of…

  18. Nuclear spin relaxation of polycrystalline 129 xenon

    NASA Astrophysics Data System (ADS)

    Samuelson, Gary Lee, Jr.

    Through spin exchange optical pumping, it is possible to achieve upwards of 30% nuclear spin polarization in 129Xe with an NMR signal enhancement of some 5 orders of magnitude over typical thermal signals. Hyperpolarized 129Xe has thus found application in several leading-edge technologies. At 1 T and 4.2 K, the characteristic relaxation time of enriched polycrystalline 129Xe (86% 129Xe, 0.1% 131Xe) is well over 200 hrs, sufficient for long-term storage and transport. Longitudinal nuclear spin relaxation of 129Xe at more convenient fields from 1 to 200 G is studied in detail. Significant structure in relaxation times vs. magnetic field is seen; the most prominent new finding being a sharp local long-time T 1 maximum of 1000 mins at ≈3 G. Such structure has not been observed in previous measurements of natural Xe. Below temperatures of 10 K, relaxation can be attributed to cross relaxation with 131Xe, mediated by spin diffusion. Measurements of 129Xe relaxation as a function of magnetic field, temperature and Xe isotopic content are reported and compared with expected theoretical behaviors. It is seen that the characteristic nuclear spin relaxation of enriched 129Xe at 4.2 K is nonexponential at these low fields. For fields between 10 G and 200 G, these nonexponential relaxation curves can be fit well with a specific spin diffusion model. Below 10 G no such fit is possible and thus quantum mechanical details of the coupling between 129Xe, 131Xe and the bulk lattice are considered. These findings support the hypothesis that cross relaxation with 131Xe is indeed a dominant actor in the nuclear spin relaxation of polycrystalline 129 Xe at such low fields and low temperatures.

  19. Mechanical Properties and Failure Mechanisms in Polycrystalline Graphene

    NASA Astrophysics Data System (ADS)

    Gonzalez, Joseph; Perriot, Romain; Oleynik, Ivan

    Large-scale growth of graphene using chemical vapor deposition produces polycrystalline material containing grain boundaries. Recent experiments demonstrate that polycrystalline graphene is nearly as strong as pristine. In this work, the mechanical properties of bi-crystal and polycrystalline graphene samples are investigated by simulating nano-indentation of a circular membrane using classical molecular dynamics and a novel Screened Environment Dependent Reactive Bond Order (SED-REBO) potential. The failure mechanisms and crack propagation in graphene samples containing grain boundaries are also discussed.

  20. Synthesis of growth-type polycrystalline diamond compact (PDC) using the solvent Fe55Ni29Co16 alloy under HPHT

    NASA Astrophysics Data System (ADS)

    Jia, HongSheng; Jia, XiaoPeng; Ma, HongAn; Li, HaiBo

    2012-08-01

    A growth-type polycrystalline diamond compact (PDC) was synthesized under high temperature and high pressure (HPHT). The infiltration technique was used with an Fe55Ni29Co16 (KOV) alloy as the sintering solvent. The morphology and weight ratio of the PDC were investigated through scanning electron microscopy (SEM) and electron dispersion spectroscopy (EDS). Note that the KOV alloy evenly infiltrated throughout the polycrystalline diamond (PCD) layer and WC-Co substrate in a short sintering time due to its low viscosity and high soakage capability. A transition layer confirmed the presence of the M x C phase near the interface of the PDC, which can make the diamond layer and WC-Co substrate combine as a complex material. X-ray diffraction (XRD) performed on the PCD layer confirmed the presence of cubic diamond, WC, cubic CoC x , the high temperature cubic phase of α-Co, the alloy phase of FeNi x , and no graphite phase. Besides, a surface residual stress of the PCD layer, measured with reasonable accuracy using micro-Raman spectroscopy, is found to be a homogeneous compressive stress with an average value of 0.16 GPa, much lower than that of the powders-mixing method.

  1. Graphene film growth on polycrystalline metals.

    PubMed

    Edwards, Rebecca S; Coleman, Karl S

    2013-01-15

    Graphene, a true wonder material, is the newest member of the nanocarbon family. The continuous network of hexagonally arranged carbon atoms gives rise to exceptional electronic, mechanical, and thermal properties, which could result in the application of graphene in next generation electronic components, energy-storage materials such as capacitors and batteries, polymer nanocomposites, transparent conducting electrodes, and mechanical resonators. With one particularly attractive application, optically transparent conducting electrodes or films, graphene has the potential to rival indium tin oxide (ITO) and become a material for producing next generation displays, solar cells, and sensors. Typically, graphene has been produced from graphite using a variety of methods, but these techniques are not suitable for growing large-area graphene films. Therefore researchers have focused much effort on the development of methodology to grow graphene films across extended surfaces. This Account describes current progress in the formation and control of graphene films on polycrystalline metal surfaces. Researchers can grow graphene films on a variety of polycrystalline metal substrates using a range of experimental conditions. In particular, group 8 metals (iron and ruthenium), group 9 metals (cobalt, rhodium, and iridium), group 10 metals (nickel and platinum), and group 11 metals (copper and gold) can support the growth of these films. Stainless steel and other commercial copper-nickel alloys can also serve as substrates for graphene film growth. The use of copper and nickel currently predominates, and these metals produce large-area films that have been efficiently transferred and tested in many electronic devices. Researchers have grown graphene sheets more than 30 in. wide and transferred them onto display plastic ready for incorporation into next generation displays. The further development of graphene films in commercial applications will require high

  2. Estimating Geometric Dislocation Densities in Polycrystalline Materialsfrom Orientation Imaging Microscopy

    SciTech Connect

    Man, Chi-Sing; Gao, Xiang; Godefroy, Scott; Kenik, Edward A

    2010-01-01

    Herein we consider polycrystalline materials which can be taken as statistically homogeneous and whose grains can be adequately modeled as rigid-plastic. Our objective is to obtain, from orientation imaging microscopy (OIM), estimates of geometrically necessary dislocation (GND) densities.

  3. Polycrystalline neutron scattering for Geant4: NXSG4

    NASA Astrophysics Data System (ADS)

    Kittelmann, T.; Boin, M.

    2015-04-01

    An extension to Geant4 based on the nxs library is presented. It has been implemented in order to include effects of low-energy neutron scattering in polycrystalline materials, and is made available to the scientific community.

  4. Polycrystalline silicon semiconducting material by nuclear transmutation doping

    DOEpatents

    Cleland, John W.; Westbrook, Russell D.; Wood, Richard F.; Young, Rosa T.

    1978-01-01

    A NTD semiconductor material comprising polycrystalline silicon having a mean grain size less than 1000 microns and containing phosphorus dispersed uniformly throughout the silicon rather than at the grain boundaries.

  5. Polycrystalline Thin-Film Research: Cadmium Telluride (Fact Sheet)

    SciTech Connect

    Not Available

    2013-06-01

    This National Center for Photovoltaics sheet describes the capabilities of its polycrystalline thin-film research in the area of cadmium telluride. The scope and core competencies and capabilities are discussed.

  6. Thermophysical Properties of Sodium (Beta)-Alumina Polycrystalline Ceramic

    NASA Technical Reports Server (NTRS)

    Ryan, M. A.; Williams, R. M.; Allevato, C. E.; Vining, C. B.; Lowe-Ma, C. K.; Robie, S. B.

    1994-01-01

    Teh thermal diffusivity, heat capacity and thermal conductivity of solid samples of new, Li-stabilized, sodium (Beta)-alumina polycrystalline ceramic have been determined in the temperature range 500-1200 K.

  7. Polycrystalline Thin-Film Research: Cadmium Telluride (Fact Sheet)

    SciTech Connect

    Not Available

    2011-06-01

    Capabilities fact sheet that includes scope, core competencies and capabilities, and contact/web information for Polycrystalline Thin-Film Research: Cadmium Telluride at the National Center for Photovoltaics.

  8. Solution-processed polycrystalline silicon on paper

    SciTech Connect

    Trifunovic, M.; Ishihara, R.; Shimoda, T.

    2015-04-20

    Printing electronics has led to application areas which were formerly impossible with conventional electronic processes. Solutions are used as inks on top of large areas at room temperatures, allowing the production of fully flexible circuitry. Commonly, research in these inks have focused on organic and metal-oxide ink materials due to their printability, while these materials lack in the electronic performance when compared to silicon electronics. Silicon electronics, on the other hand, has only recently found their way in solution processes. Printing of cyclopentasilane as the silicon ink has been conducted and devices with far superior electric performance have been made when compared to other ink materials. A thermal annealing step of this material, however, was necessary, which prevented its usage on inexpensive substrates with a limited thermal budget. In this work, we introduce a method that allows polycrystalline silicon (poly-Si) production directly from the same liquid silicon ink using excimer laser irradiation. In this way, poly-Si could be formed directly on top of paper even with a single laser pulse. Using this method, poly-Si transistors were created at a maximum temperature of only 150 °C. This method allows silicon device formation on inexpensive, temperature sensitive substrates such as polyethylene terephthalate, polyethylene naphthalate or paper, which leads to applications that require low-cost but high-speed electronics.

  9. Stability of polycrystalline Nextel 720 fiber

    SciTech Connect

    Das, G.

    1996-12-31

    The microstructure and tensile properties of polycrystalline Nextel 720 fiber (85 wt.% Al{sub 2}O{sub 3} - 15 wt-% SiO{sub 2}), both crystallized and precrystallized, were evaluated following prolonged thermal exposure at 982{degrees}C in air. The room temperature tensile strengths of Nextel 720 fibers did not appear to suffer degradation for exposures up to 3000 h and the microstructure remained unaffected by thermal exposures. The tensile strength of precrystallized Nextel 720 fiber was also determined at room temperature following heat treatments at 1093-1427{degrees}C in air. The precrystallized Nextel 720 fiber started to show a slight loss of strength after heat treatment at 1093{degrees}C/4 h and the strength deterioration was exacerbated for heat treatments at 1204{degrees}C/4 h and above. Microstructural characterization by x-ray and transmission electron microscopy (TEM) revealed the formation of mullite in heat treated precrystallized Nextel 720 fiber at 1204{degrees}C and a coarsening of microstructure above 1204{degrees}C. The degradation of strength in precrystallized Nextel 720 fiber heat treated at 1204{degrees}C/4 h and above may be attributed to phase instability and grain coarsening. Fractographs showed that fracture originated predominantly at the fiber surface.

  10. Texture and Anisotropy of Polycrystalline Piezoelectics

    SciTech Connect

    Jones,J.; Iverson, B.; Bowman, K.

    2007-01-01

    Piezoelectricity is manifested in ferroelectric ceramics by inducing a preferred volume fraction of one ferroelectric domain variant orientation at the expense of degenerate orientations. The piezoelectric effect is therefore largely controlled by the effectiveness of the electrical poling in producing a bias in ferroelectric (180{sup o}) and ferroelastic (non-180{sup o}) domain orientations. Further enhancement of the piezoelectric effect in bulk ceramics can be accomplished by inducing preferred orientation through grain-orientation processes such as hot forging or tape casting that precede the electrical-poling process. Coupled crystal orientation and domain orientation processing yields ceramics with an even greater piezoelectric response. In this paper, preferred orientations of domains and grains in polycrystalline piezoelectric ceramics generated through both domain- and grain-orientation processing are characterized through pole figures and orientation distribution functions obtained using data from a variety of diffraction techniques. The processing methods used to produce these materials and the methods used to evaluate preferred orientation and texture are described and discussed in the context of prior research. Different sample and crystal symmetries are explored across a range of commercial and laboratory-prepared materials. Some of the variables presented in this work include the effects of in situ thermal depoling and the detailed processing parameters used in tape casting of materials with preferred crystallite orientations. Preferred orientation is also correlated with anisotropic properties, demonstrating a clear influence of both grain and domain orientations on piezoelectricity.

  11. Nonlinear alternating current conduction in polycrystalline manganites

    NASA Astrophysics Data System (ADS)

    Ghosh, T. N.; Nandi, U. N.; Jana, D.; Dey, K.; Giri, S.

    2014-06-01

    The real part of ac conductance Σ(T, f) of yttrium-doped mixed-valent polycrystalline manganite systems La1-x -yYyCaxMnO3 with x = 0.33 and 0.05 and y = 0.07 and iron doped LaMn1-xFexO3 with x = 0.15 is measured as a function of frequency f by varying zero-frequency Ohmic conductance Σ0 by T. The former shows a metal-insulator transition, whereas the latter exhibits insulating character throughout the measured temperature range. At a fixed temperature T, Σ(T, f) remains almost constant to the value Σ0 up to a certain frequency, known as the onset frequency fc and increases from Σ0 as frequency is increased from fc. Scaled appropriately, the data for Σ(T, f) at different T fall on the same universal curve, indicating the existence of a general scaling formalism for the ac conductance. fc scales with Σ0 as fc˜Σ0xf, where xf is the nonlinearity exponent characterising the onset. With the help of data for ac conduction, it is shown that xf is very much phase sensitive and can be used to characterize the different phases in a manganite system originated due to change in temperature or disorder. Scaling theories and existing theoretical models are used to analyze the results of ac conduction and the nonlinearity exponent xf.

  12. Amorphous silicon/polycrystalline thin film solar cells

    SciTech Connect

    Ullal, H.S.

    1991-03-13

    An improved photovoltaic solar cell is described including a p-type amorphous silicon layer, intrinsic amorphous silicon, and an n-type polycrystalline semiconductor such as cadmium sulfide, cadmium zinc sulfide, zinc selenide, gallium phosphide, and gallium nitride. The polycrystalline semiconductor has an energy bandgap greater than that of the amorphous silicon. The solar cell can be provided as a single-junction device or a multijunction device.

  13. Photovoltaic Cell Having A P-Type Polycrystalline Layer With Large Crystals

    DOEpatents

    Albright, Scot P.; Chamberlin, Rhodes R.

    1996-03-26

    A photovoltaic cell has an n-type polycrystalline layer and a p-type polycrystalline layer adjoining the n-type polycrystalline layer to form a photovoltaic junction. The p-type polycrystalline layer comprises a substantially planar layer portion having relatively large crystals adjoining the n-type polycrystalline layer. The planar layer portion includes oxidized impurities which contribute to obtainment of p-type electrical properties in the planar layer portion.

  14. Defect behavior of polycrystalline solar cell silicon

    SciTech Connect

    Schroder, D.K.; Park, S.H.; Hwang, I.G.; Mohr, J.B.; Hanly, M.P.

    1993-05-01

    The major objective of this study, conducted from October 1988 to September 1991, was to gain an understanding of the behavior of impurities in polycrystalline silicon and the influence of these impurities on solar cell efficiency. The authors studied edge-defined film-fed growth (EFG) and cast poly-Si materials and solar cells. With EFG Si they concentrated on chromium-doped materials and cells to determine the role of Cr on solar cell performance. Cast poly-Si samples were not deliberately contaminated. Samples were characterized by cell efficiency, current-voltage, deep-level transient spectroscopy (DLTS), surface photovoltage (SPV), open-circuit voltage decay, secondary ion mass spectrometry, and Fourier transform infrared spectroscopy measurements. They find that Cr forms Cr-B pairs with boron at room temperature and these pairs dissociate into Cr{sub i}{sup +} and B{sup {minus}} during anneals at 210{degrees}C for 10 min. Following the anneal, Cr-B pairs reform at room temperature with a time constant of 230 h. Chromium forms CrSi{sub 2} precipitates in heavily contaminated regions and they find evidence of CrSi{sub 2} gettering, but a lack of chromium segregation or precipitation to grain boundaries and dislocations. Cr-B pairs have well defined DLTS peaks. However, DLTS spectra of other defects are not well defined, giving broad peaks indicative of defects with a range of energy levels in the band gap. In some high-stress, low-efficiency cast poly-Si they detect SiC precipitates, but not in low-stress, high-efficiency samples. SPV measurements result in nonlinear SPV curves in some materials that are likely due to varying optical absorption coefficients due to locally varying stress in the material.

  15. Nonlinear alternating current conduction in polycrystalline manganites

    SciTech Connect

    Ghosh, T. N.; Nandi, U. N.; Jana, D.; Dey, K.; Giri, S.

    2014-06-28

    The real part of ac conductance Σ(T, f) of yttrium-doped mixed-valent polycrystalline manganite systems La{sub 1−x−y}Y{sub y}Ca{sub x}MnO{sub 3} with x = 0.33 and 0.05 and y = 0.07 and iron doped LaMn{sub 1−x}Fe{sub x}O{sub 3} with x = 0.15 is measured as a function of frequency f by varying zero-frequency Ohmic conductance Σ{sub 0} by T. The former shows a metal-insulator transition, whereas the latter exhibits insulating character throughout the measured temperature range. At a fixed temperature T, Σ(T, f) remains almost constant to the value Σ{sub 0} up to a certain frequency, known as the onset frequency f{sub c} and increases from Σ{sub 0} as frequency is increased from f{sub c}. Scaled appropriately, the data for Σ(T, f) at different T fall on the same universal curve, indicating the existence of a general scaling formalism for the ac conductance. f{sub c} scales with Σ{sub 0} as f{sub c}∼Σ{sub 0}{sup x{sub f}}, where x{sub f} is the nonlinearity exponent characterising the onset. With the help of data for ac conduction, it is shown that x{sub f} is very much phase sensitive and can be used to characterize the different phases in a manganite system originated due to change in temperature or disorder. Scaling theories and existing theoretical models are used to analyze the results of ac conduction and the nonlinearity exponent x{sub f}.

  16. Magnetization studies of first-order magnetostructural phase transition in polycrystalline FeRh thin films

    NASA Astrophysics Data System (ADS)

    Lu, Wei; Huang, Ping; Chen, Zhe; He, Chenchong; Wang, Yuxin; Yan, Biao

    2012-10-01

    The nucleation and growth of the transformed phase in the matrix of the original phase played an important role in the progress of magnetic transition. In spite of extensive investigations in B2 ordered FeRh alloy systems, until now few studies have been conducted for clarifying the nucleation and growth mechanism of the antiferromagnetic-ferromagnetic phase transition in FeRh alloys. In this work, B2 ordered polycrystalline FeRh thin films were fabricated on glass substrates by a sputtering technique and subsequent heat treatment. The as-deposited film shows a nonmagnetic property because of its face centred cubic structure. After annealing, the polycrystalline FeRh thin films show a clear first-order magnetostructural phase transition. The FeRh thin film shows an overall activation energy of about 228.6 kJ mol-1 for the entire first-order magnetostructural phase transition process. Results suggest that the first-order magnetostructural phase transition in ordered FeRh thin films follows the Johnson-Mehl-Avrami model with characteristic exponent n in the range 1-4, indicating that the phase transition process is a multi-step process characterized by different nucleation and growth mechanisms of the new ferromagnetic phase. The results obtained in this study will shed light on the underlying physics of the first-order magnetostructural phase transition of ordered FeRh alloys. The applicability of the concepts used in this study to the FeRh system shows universality and can be applied to other material systems where there is a first-order magnetostructural phase transition such as in manganites.

  17. Real-time x-ray diffraction measurements of shocked polycrystalline tin and aluminum.

    PubMed

    Morgan, Dane V; Macy, Don; Stevens, Gerald

    2008-11-01

    A new, fast, single-pulse x-ray diffraction (XRD) diagnostic for determining phase transitions in shocked polycrystalline materials has been developed. The diagnostic consists of a 37-stage Marx bank high-voltage pulse generator coupled to a needle-and-washer electron beam diode via coaxial cable, producing line and bremsstrahlung x-ray emission in a 35 ns pulse. The characteristic K(alpha) lines from the selected anodes of silver and molybdenum are used to produce the diffraction patterns, with thin foil filters employed to remove the characteristic K(beta) line emission. The x-ray beam passes through a pinhole collimator and is incident on the sample with an approximately 3 x 6 mm(2) spot and 1 degrees full width half maximum angular divergence in a Bragg-reflecting geometry. For the experiments described in this report, the angle between the incident beam and the sample surface was 8.5 degrees . A Debye-Scherrer diffraction image was produced on a phosphor located 76 mm from the polycrystalline sample surface. The phosphor image was coupled to a charge-coupled device camera through a coherent fiber-optic bundle. Dynamic single-pulse XRD experiments were conducted with thin foil samples of tin, shock loaded with a 1 mm vitreous carbon back window. Detasheet high explosive with a 2-mm-thick aluminum buffer was used to shock the sample. Analysis of the dynamic shock-loaded tin XRD images revealed a phase transformation of the tin beta phase into an amorphous or liquid state. Identical experiments with shock-loaded aluminum indicated compression of the face-centered-cubic aluminum lattice with no phase transformation. PMID:19045900

  18. Real-time X-ray Diffraction Measurements of Shocked Polycrystalline Tin and Aluminum

    SciTech Connect

    Dane V. Morgan, Don Macy, Gerald Stevens

    2008-11-22

    A new, fast, single-pulse x-ray diffraction (XRD) diagnostic for determining phase transitions in shocked polycrystalline materials has been developed. The diagnostic consists of a 37-stage Marx bank high-voltage pulse generator coupled to a needle-and-washer electron beam diode via coaxial cable, producing line and bremsstrahlung x-ray emission in a 35-ns pulse. The characteristic Kα lines from the selected anodes of silver and molybdenum are used to produce the diffraction patterns, with thin foil filters employed to remove the characteristic Kβ line emission. The x-ray beam passes through a pinhole collimator and is incident on the sample with an approximately 3-mm by 6-mm spot and 1° full-width-half-maximum (FWHM) angular divergence in a Bragg-reflecting geometry. For the experiments described in this report, the angle between the incident beam and the sample surface was 8.5°. A Debye-Scherrer diffraction image was produced on a phosphor located 76 mm from the polycrystalline sample surface. The phosphor image was coupled to a charge-coupled device (CCD) camera through a coherent fiberoptic bundle. Dynamic single-pulse XRD experiments were conducted with thin foil samples of tin, shock loaded with a 1-mm vitreous carbon back window. Detasheet high explosive with a 2-mm-thick aluminum buffer was used to shock the sample. Analysis of the dynamic shock-loaded tin XRD images revealed a phase transformation of the tin beta phase into an amorphous or liquid state. Identical experiments with shock-loaded aluminum indicated compression of the face-centered-cubic (fcc) aluminum lattice with no phase transformation.

  19. Polycrystalline thin film materials and devices

    NASA Astrophysics Data System (ADS)

    Baron, B. N.; Birkmire, R. W.; Phillips, J. E.; Shafarman, W. N.; Hegedus, S. S.; McCandless, B. E.

    1991-11-01

    Results and conclusions of Phase 1 of a multi-year research program on polycrystalline thin film solar cells are presented. The research comprised investigation of the relationships among processing, materials properties and device performance of both CuInSe2 and CdTe solar cells. The kinetics of the formation of CuInSe2 by selenization with hydrogen selenide was investigated and a CuInSe2/Cds solar cell was fabricated. An alternative process involving the reaction of deposited copper-indium-selenium layers was used to obtain single phase CuInSe2 films and a cell efficiency of 7 percent. Detailed investigations of the open circuit voltage of CuInSe2 solar cells showed that a simple Shockley-Read-Hall recombination mechanism can not account for the limitations in open circuit voltage. Examination of the influence of CuInSe2 thickness on cell performance indicated that the back contact behavior has a significant effect when the CuInSe2 is less than 1 micron thick. CdTe/CdS solar cells with efficiencies approaching 10 percent can be repeatedly fabricated using physical vapor deposition and serial post deposition processing. The absence of moisture during post deposition was found to be critical. Improvements in short circuit current of CdTe solar cells to levels approaching 25 mA/cm(exp 2) are achievable by making the CdS window layer thinner. Further reductions in the CdS window layer thickness are presently limited by interdiffusion between the CdS and the CdTe. CdTe/CdS cells stored without protection from the atmosphere were found to degrade. The degradation was attributed to the metal contact. CdTe cells with ZnTe:Cu contacts to the CdTe were found to be more stable than cells with metal contacts. Analysis of current-voltage and spectral response of CdTe/CdS cells indicates the cell operates as a p-n heterojunction with the diode current dominated by SRH recombination in the junction region of the CdTe.

  20. Structural and Magnetic Properties of Sputter-Deposited Polycrystalline Ni-Mn-Ga Ferromagnetic Shape-Memory Thin Films

    NASA Astrophysics Data System (ADS)

    Vinodh Kumar, S.; Seenithurai, S.; Manivel Raja, M.; Mahendran, M.

    2015-10-01

    Polycrystalline Ni-Mn-Ga ferromagnetic shape-memory thin films have been deposited on Si (100) substrates using a direct-current magnetron sputtering technique. The microstructure and the temperature dependence of magnetic properties of the films have been investigated by x-ray diffraction, scanning electron microscopy, and thermomagnetic measurements. As-deposited Ni50.2Mn30.6Ga19.2 film showed quasi-amorphous structure with paramagnetic nature at room temperature. When annealed at 873 K, the quasi-amorphous film attained crystallinity and possessed L21 cubic ordering with high magnetic transition temperature. Saturation magnetization and coercivity values for the annealed film were found to be 220 emu/cm3 and 70 Oe, respectively, indicating soft ferromagnetic character with low magnetocrystalline anisotropy. The magnetic transitions of the film deposited at 100 W were above room temperature, making this a potential candidate for use in microelectromechanical system devices.

  1. Supersymmetric cubic Galileons have ghosts

    NASA Astrophysics Data System (ADS)

    Koehn, Michael; Lehners, Jean-Luc; Ovrut, Burt A.

    2013-07-01

    Galileons are higher-derivative theories of a real scalar which nevertheless admit second-order equations of motion. They have interesting applications as dark energy models and in early universe cosmology, and have been conjectured to arise as descriptions of brane dynamics in string theory. In the present paper, we study the bosonic sector of globally N=1 supersymmetric extensions of the cubic Galileon Lagrangian in detail. Supersymmetry requires that the Galileon scalar now becomes paired with a second real scalar field. We prove that the presence of this second scalar causes the equations of motion to become higher than second order, thus leading to the appearance of ghosts. We also analyze the energy scales up to which, in an effective field theory description, the ghosts can be tamed.

  2. Recent developments in polycrystalline oxide fiber laser materials: production of Yb-doped polycrystalline YAG fiber

    NASA Astrophysics Data System (ADS)

    Lee, HeeDong; Keller, Kristin; Sirn, Brian; Parthasarathy, Triplicane; Cheng, Michael; Hopkins, Frank K.

    2011-09-01

    Laser quality, polycrystalline oxide fibers offer significant advantages over state-of-the-art silica fiber for high energy lasers. Advanced ceramic processing technology, along with a novel powder production process, has potential to produce oxide fibers with an outstanding optical quality for use in the fiber laser applications. The production of contaminant-free green fibers with a high packing density, as well as uniform packing distribution, is a key factor in obtaining laserquality fibers. High quality green fibers are dependent on the powder quality combined with the appropriate slurry formulation. These two fundamental technologies were successfully developed at UES, and used to produce Yb-doped yttrium aluminum garnet (YAG) fibers with high optical quality, high chemical purity, and suitable core diameters down to 20-30 microns.

  3. Neutron diffraction study of Bi doped cubic spinel Co{sub 2}MnO{sub 4}

    SciTech Connect

    Rajeevan, N. E.; Kaushik, S. D.; Kumar, Ravi

    2015-06-24

    Polycrystalline Bi doped spinel Bi{sub x}Co{sub 2-x}MnO{sub 4} compounds were prepared by solid state reaction route. Room temperature neutron diffraction study reveals that all the compounds are formed in cubic phase and there is no change in the crystal structure due to Bi doping and the compound has cubic structure with Fd-3m space group. Cell parameter found to increase with respect to Bi doping and ferrimagnetic nature is established through magnetization. Low temperature neutron diffraction is carried out and emphasis the ferrimagnetic ordering in the samples of Bi{sub x}Co{sub 2-x}MnO{sub 4} series.

  4. Deposition of AlN Thin Films with Cubic Crystal Structures on Silicon Substrates at Room Temperature

    NASA Astrophysics Data System (ADS)

    Ren, Zhong-Min; Lu, Yong-Feng; Goh, Yeow-Whatt; Chong, Tow-Chong; Ng, Mei-Ling; Wang, Jian-Ping; Cheong, Boon-Aik; Liew, Yun-Fook

    2000-05-01

    Cubic AlN thin films were deposited at room temperature by nitrogen-ion-assisted pulsed laser ablation of a hexagonal AlN target. The full-width at half maximum (FWHM) of the X-ray diffraction peak in the θ˜ 2θ scan can reach a value of 0.27 degrees. In the Raman spectroscopy measurement, a new peak at 2333 cm-1 originating from cubic AlN polycrystalline was observed. Nitrogen ions not only effectively promote the formation of stable Al-N bonds but also improve the crystal properties of the deposited thin films. A nitrogen ion energy of 400 eV is proposed for the thin-film deposition.

  5. Synthesis of polycrystalline Co{sub 3}O{sub 4} nanowires with excellent ammonium perchlorate catalytic decomposition property

    SciTech Connect

    Zhou, Hai; Lv, Baoliang; Wu, Dong; Xu, Yao

    2014-12-15

    Graphical abstract: Co{sub 3}O{sub 4} nanowires with excellent ammonium perchlorate catalytic decomposition property were synthesized via a methanamide-assisted hydrolysis and subsequent dissolution–recrystallization process in the presence of methanamide. - Abstract: Co{sub 3}O{sub 4} nanowires, with the length of tens of micrometers and the width of several hundred nanometers, were produced by a hydrothermal treatment and a post-anneal process. X-ray diffraction (XRD) result showed that the Co{sub 3}O{sub 4} nanowires belong to cubic crystal system. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) analysis indicated that the Co{sub 3}O{sub 4} nanowires, composed by single crystalline nanoparticles, were of polycrystalline nature. On the basis of time-dependent experiments, methanamide-assisted hydrolysis and subsequent dissolution–recrystallization process were used to explain the precursors' formation process of the polycrystalline Co{sub 3}O{sub 4} nanowires. The TGA experiments showed that the as-obtained Co{sub 3}O{sub 4} nanowires can catalyze the thermal decomposition of ammonium perchlorate (AP) effectively.

  6. Influence of thickness on physical properties of vacuum evaporated polycrystalline CdTe thin films for solar cell applications

    NASA Astrophysics Data System (ADS)

    Chander, Subhash; Dhaka, M. S.

    2016-02-01

    This paper presents the influence of thickness on physical properties of polycrystalline CdTe thin films. The thin films of thickness 450 nm, 650 nm and 850 nm were deposited employing thermal vacuum evaporation technique on glass and indium tin oxide (ITO) coated glass substrates. The physical properties of these as-grown thin films were investigated employing the X-ray diffraction (XRD), source meter, UV-Vis spectrophotometer, scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The structural analysis reveals that the films have zinc-blende cubic structure and polycrystalline in nature with preferred orientation (111). The structural parameters like lattice constant, interplanar spacing, grain size, strain, dislocation density and number of crystallites per unit area are calculated. The average grain size and optical band gap are found in the range 15.16-21.22 nm and 1.44-1.63 eV respectively and observed to decrease with thickness. The current-voltage characteristics show that the electrical conductivity is observed to decrease with thickness. The surface morphology shows that films are free from crystal defects like pin holes and voids as well as homogeneous and uniform. The EDS patterns show the presence of cadmium and tellurium elements in the as grown films. The experimental results reveal that the film thickness plays significant role on the physical properties of as-grown CdTe thin films and higher thickness may be used as absorber layer to solar cells applications.

  7. A dislocation density based crystal plasticity finite element model: Application to a two-phase polycrystalline HCP/BCC composites

    NASA Astrophysics Data System (ADS)

    Ardeljan, Milan; Beyerlein, Irene J.; Knezevic, Marko

    2014-05-01

    We present a multiscale model for anisotropic, elasto-plastic, rate- and temperature-sensitive deformation of polycrystalline aggregates to large plastic strains. The model accounts for a dislocation-based hardening law for multiple slip modes and links a single-crystal to a polycrystalline response using a crystal plasticity finite element based homogenization. It is capable of predicting local stress and strain fields based on evolving microstructure including the explicit evolution of dislocation density and crystallographic grain reorientation. We apply the model to simulate monotonic mechanical response of a hexagonal close-packed metal, zirconium (Zr), and a body-centered cubic metal, niobium (Nb), and study the texture evolution and deformation mechanisms in a two-phase Zr/Nb layered composite under severe plastic deformation. The model predicts well the texture in both co-deforming phases to very large plastic strains. In addition, it offers insights into the active slip systems underlying texture evolution, indicating that the observed textures develop by a combination of prismatic, pyramidal, and anomalous basal slip in Zr and primarily {110}<111> slip and secondly {112}<111> slip in Nb.

  8. Scaling properties of charge transport in polycrystalline graphene.

    PubMed

    Van Tuan, Dinh; Kotakoski, Jani; Louvet, Thibaud; Ortmann, Frank; Meyer, Jannik C; Roche, Stephan

    2013-04-10

    Polycrystalline graphene is a patchwork of coalescing graphene grains of varying lattice orientations and size, resulting from the chemical vapor deposition (CVD) growth at random nucleation sites on metallic substrates. The morphology of grain boundaries has become an important topic given its fundamental role in limiting the mobility of charge carriers in polycrystalline graphene, as compared to mechanically exfoliated samples. Here we report new insights to the current understanding of charge transport in polycrystalline geometries. We created realistic models of large CVD-grown graphene samples and then computed the corresponding charge carrier mobilities as a function of the average grain size and the coalescence quality between the grains. Our results reveal a remarkably simple scaling law for the mean free path and conductivity, correlated to atomic-scale charge density fluctuations along grain boundaries. PMID:23448361

  9. Effect of copper impurity on polycrystalline silicon solar cells

    NASA Technical Reports Server (NTRS)

    Daud, T.; Koliwad, K. M.

    1978-01-01

    The presence of copper impurity, up to 10 to the 15th atoms/cc, in single crystal silicon has been shown to have no deleterious effect on the p-n junction solar cell performance. However, in polycrystalline silicon, copper atoms tend to migrate to the defect sites because of the structural sensitive properties of copper. This study was undertaken to investigate the influence of this behavior of copper impurity on the performance of p-n junction solar cells fabricated from structurally imperfect silicon. Two sets of polycrystalline silicon substrates containing copper were examined. In one set of samples, copper was incorporated during growth, whereas in the other, copper was diffused. Solar cells were fabricated on both the sets of substrates by a standard process. Dark and light I-V and spectral response characteristics of the cells were measured and compared with copper-free polycrystalline silicon solar cells. The results and the model are discussed.

  10. Electronic structure of polycrystalline Cd metal using 241Am radioisotope

    NASA Astrophysics Data System (ADS)

    Dhaka, M. S.; Sharma, G.; Mishra, M. C.; Sharma, B. K.

    2014-04-01

    Electronic structure study of the polycrystalline cadmium metal is reported. The experimental measurement is undertaken on a polycrystalline sheet sample using 59.54 keV radioisotope of 241Am. These results are compared with the ab initio calculations. The theoretical calculations are performed using linear combination of atomic orbitals (LCAO) method employing the density functional theories (DFT) and Hartree-Fock (HF) and augmented plane wave (APW) methods. The spherically averaged APW and LCAO based theoretical Compton profiles are in good agreement with the experimental measurement however the APW based theoretical calculations show best agreement.

  11. Cu Migration in Polycrystalline CdTe Solar Cells

    SciTech Connect

    Guo, Da; Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Vasileska, Dragica; Ringhofer, Christian

    2014-03-12

    An impurity reaction-diffusion model is applied to Cu defects and related intrinsic defects in polycrystalline CdTe for a better understanding of Cu’s role in the cell level reliability of CdTe PV devices. The simulation yields transient Cu distributions in polycrystalline CdTe during solar cell processing and stressing. Preliminary results for Cu migration using available diffusivity and solubility data show that Cu accumulates near the back contact, a phenomena that is commonly observed in devices after back-contact processing or stress conditions.

  12. Software optimization for electrical conductivity imaging in polycrystalline diamond cutters

    SciTech Connect

    Bogdanov, G.; Ludwig, R.; Wiggins, J.; Bertagnolli, K.

    2014-02-18

    We previously reported on an electrical conductivity imaging instrument developed for measurements on polycrystalline diamond cutters. These cylindrical cutters for oil and gas drilling feature a thick polycrystalline diamond layer on a tungsten carbide substrate. The instrument uses electrical impedance tomography to profile the conductivity in the diamond table. Conductivity images must be acquired quickly, on the order of 5 sec per cutter, to be useful in the manufacturing process. This paper reports on successful efforts to optimize the conductivity reconstruction routine, porting major portions of it to NVIDIA GPUs, including a custom CUDA kernel for Jacobian computation.

  13. MIS and SIS solar cells on polycrystalline silicon

    SciTech Connect

    Cheek, G.; Mertens, R.

    1980-02-01

    MIS and SIS structured solar cells are receiving much attention in the photovoltaic community. Seemingly, these cells could be a viable alternative to thermally diffused p-n junctions for use on thin-film polycrystalline silicon substrates. This review describes MIS/SIS structured solar cells and the possible advantages of these structures for use with thin-film polycrystalline silicon. The results of efficiency calculations are presented. Also addressed are lifetime stability and fabrication techniques amenable to large scale production. Finally, the relative advantages and disadvantages of these cells and the results obtained are presented.

  14. Processing of transparent polycrystalline AlON:Ce3+ scintillators

    SciTech Connect

    Chen, Ching -Fong; Yang, Pin; King, Graham; Tegtmeier, Eric L.

    2015-10-23

    A new polycrystalline ceramic scintillator is reported for potential use in radiation detection and medical imaging applications. The goal was to develop cerium-activated aluminum oxynitride (AlON:Ce3+) ceramics, which can be produced using ceramic processes in comparison to the high-cost, low-yield single-crystal growth technique. A phase pure AlON:Ce3+ powder with cubic symmetry was successfully synthesized at high temperature under a reducing atmosphere to convert Ce4+ to Ce3+ in the solid solution. We explored two different activator concentrations (0.5 and 1.0 mol%). Fully dense and transparent AlON:Ce3+ ceramics were produced by a liquid-phase-assisted pressureless sintering. The crystal field splitting around the Ce3+ activator in the AlON was comparable to the splitting induced by Br₋ and the Cl₋ ligands, which produced an emission spectrum perfectly matching the maximum quantum efficiency range of the photomultiplier tube for radiation detection. Both optical excitation and radiation ionizations in AlON:Ce3+ were demonstrated. Lastly, challenges and mechanisms related to the radioluminescence efficiency are discussed.

  15. Preparation and neutron diffraction study of polycrystalline Cu-Zn-Fe materials

    NASA Astrophysics Data System (ADS)

    Darul, J.; Nowicki, W.

    2009-10-01

    Polycrystalline oxides Cu1-xZnxFe2O4 (0.0≤x≤0.05) have been successfully prepared by a simple combustion method using citrate-nitrate precursors. The nature of structural transition in inverse spinels and ferrimagnetic behavior of the materials have been investigated by the neutron diffraction technique. At room temperature neutron diffraction study confirms the presence of a single-phase structure, where tetragonal unit cell with c/a>1 is observed. In these distorted spinel ferrites it is found that tetragonal → cubic transformation is attributed to the decrease of the concentration of Jahn-Teller ions Cu2+ (d9) in the host structure at the octahedral sites as a result of zinc substitution. The introduction of non-magnetic ion in place of Cu2+ in the spinel unit cell results in the reduction of intersublattice contributions, this in turn decreases temperature of the magnetic ordering (Curie point) in these diluted ferrimagnets.

  16. Generalized Vaidya spacetime for cubic gravity

    NASA Astrophysics Data System (ADS)

    Ruan, Shan-Ming

    2016-03-01

    We present a kind of generalized Vaidya solution of a new cubic gravity in five dimensions whose field equations in spherically symmetric spacetime are always second order like the Lovelock gravity. We also study the thermodynamics of its spherically symmetric apparent horizon and get its entropy expression and generalized Misner-Sharp energy. Finally, we present the first law and second law hold in this gravity. Although all the results are analogous to those in Lovelock gravity, we in fact introduce the contribution of a new cubic term in five dimensions where the cubic Lovelock term is just zero.

  17. The synthesis, characterization, and mechanical properties of thick, ultrahard cubic boron nitride films deposited by ion-assisted sputtering

    SciTech Connect

    Mirkarimi, P.B.; Medlin, D.L.; McCarty, K.F.; Dibble, D.C.; Clift, W.M.; Knapp, J.A.; Barbour, J.C.

    1997-08-01

    Significant ion irradiation is needed during growth to synthesize cubic boron nitride (cBN) films. This results in large film stresses, which have limited cBN film thicknesses to only a few hundred nm and represents a significant barrier in the development of cBN film technology. Using a new hybrid deposition technique, we have synthesized cubic BN films up to 700 nm (0.7 {mu}m) thick. A compositional and structural analysis of the films using several standard characterization techniques confirms that relatively thick polycrystalline films with a high cBN content were synthesized. Thicker cBN films enable hardness measurements to be undertaken without major substrate effects. Nanoindentation measurements yield hardness values for the cubic BN films up to 60{endash}70 GPa, which are greater than values measured for bulk cBN. The measured elastic modulus was observed to be lower than the bulk, and this can be accounted for by an elastic deformation of the silicon substrate. The mechanical properties of the cubic BN films are discussed with reference to other ultrahard thin films such as diamond and diamondlike carbon. {copyright} {ital 1997 American Institute of Physics.}

  18. Raman Microscopic Characterization of Proton-Irradiated Polycrystalline Diamond Films

    NASA Technical Reports Server (NTRS)

    Newton, R. L.; Davidson, J. L.; Lance, M. J.

    2004-01-01

    The microstructural effects of irradiating polycrystalline diamond films with proton dosages ranging from 10(exp 15) to 10(exp 17) H(+) per square centimeter was examined. Scanning Electron Microscopy and Raman microscopy were used to examine the changes in the diamond crystalline lattice as a function of depth. Results indicate that the diamond lattice is retained, even at maximum irradiation levels.

  19. Electron transient transport in CdTe polycrystalline films

    NASA Astrophysics Data System (ADS)

    Ramírez-Bon, R.; Sánchez-Sinencio, F.; González de la Cruz, G.; Zelaya, O.

    1991-11-01

    Electron transient currents between coplanar electrodes have been measured in intrinsic polycrystalline films of CdTe, by means of the time of flight technique. The experimental results: electron transient current vs time, transit time vs voltage and the temperature dependence of the electron drift mobility, show features characteristics of dispersive electrical transport similar to that observed in disordered solids.

  20. Research on polycrystalline thin-film materials, cells, and modules

    NASA Astrophysics Data System (ADS)

    Mitchell, R. L.; Zweibel, K.; Ullal, H. S.

    1990-11-01

    DOE supports research activities in polycrystalline thin films through the Polycrystalline Thin Film Program. This program includes includes R and D in both copper indium diselenide and cadmium telluride thin films for photovoltaic applications. The objective is to support R and D of photovoltaic cells and modules that meet the DOE long term goals of high efficiency (15 to 20 percent), low cost ($50/sq cm), and reliability (30-year life time). Research carried out in this area is receiving increased recognition due to important advances in polycrystalline thin film CuInSe2 and CdTe solar cells and modules. These have become the leading thin film materials for photovoltaics in terms of efficiency and stability. DOE has recognized this potential through a competitive initiative for the development of CuInSe(sub 2) and CdTe modules. The recent progress and future directions are studied of the Polycrystalline Thin Film Program and the status of the subcontracted research on these promising photovoltaic materials.

  1. Research on polycrystalline thin-film materials, cells, and modules

    SciTech Connect

    Mitchell, R.L.; Zweibel, K.; Ullal, H.S.

    1990-11-01

    The US Department of Energy (DOE) supports research activities in polycrystalline thin films through the Polycrystalline Thin-Film Program at the Solar Energy Research Institute (SERI). This program includes research and development (R D) in both copper indium diselenide and cadmium telluride thin films for photovoltaic applications. The objective of this program is to support R D of photovoltaic cells and modules that meet the DOE long-term goals of high efficiency (15%--20%), low cost ($50/m{sup 2}), and reliability (30-year life time). Research carried out in this area is receiving increased recognition due to important advances in polycrystalline thin-film CuInSe{sub 2} and CdTe solar cells and modules. These have become the leading thin-film materials for photovoltaics in terms of efficiency and stability. DOE has recognized this potential through a competitive initiative for the development of CuInSe{sub 2} and CdTe modules. This paper focuses on the recent progress and future directions of the Polycrystalline Thin-Film Program and the status of the subcontracted research on these promising photovoltaic materials. 26 refs., 12 figs, 1 tab.

  2. System of polarization correlometry of biological liquids layers polycrystalline structure

    NASA Astrophysics Data System (ADS)

    Ushenko, A. G.; Boychuk, T. M.; Mincer, O. P.; Angelsky, P. O.; Bodnar, N. B.; Oleinichenko, B. P.; Bizer, L. I.

    2013-09-01

    A model of generalized optical anisotropy of human bile is suggested and a method of polarimetric of the module and phase Fourier of the image of the field of laser radiation is analytically substantiated, that is generated by the mechanisms of linear and circular birefringence of polycrystalline networks with a diagnosis and differentiation of cholelithiasis against a background of chronic cholecystitis.

  3. Anomalous photoelectric effect of a polycrystalline topological insulator film.

    PubMed

    Zhang, Hongbin; Yao, Jiandong; Shao, Jianmei; Li, Hai; Li, Shuwei; Bao, Dinghua; Wang, Chengxin; Yang, Guowei

    2014-01-01

    A topological insulator represents a new state of quantum matter that possesses an insulating bulk band gap as well as a spin-momentum-locked Dirac cone on the surface that is protected by time-reversal symmetry. Photon-dressed surface states and light-induced surface photocurrents have been observed in topological insulators. Here, we report experimental observations of an anomalous photoelectric effect in thin films of Bi2Te3, a polycrystalline topological insulator. Under illumination with non-polarised light, transport measurements reveal that the resistance of the topological surface states suddenly increases when the polycrystalline film is illuminated. The resistance variation is positively dependent on the light intensity but has no relation to the applied electric field; this finding can be attributed to the gap opening of the surface Dirac cone. This observation of an anomalous photoelectric effect in polycrystalline topological insulators offers exciting opportunities for the creation of photodetectors with an unusually broad spectral range. Moreover, polycrystalline topological insulator films provide an attractive material platform for exploring the nature and practical application of topological insulators. PMID:25069391

  4. Rotation-limited growth of three-dimensional body-centered-cubic crystals.

    PubMed

    Tarp, Jens M; Mathiesen, Joachim

    2015-07-01

    According to classical grain growth laws, grain growth is driven by the minimization of surface energy and will continue until a single grain prevails. These laws do not take into account the lattice anisotropy and the details of the microscopic rearrangement of mass between grains. Here we consider coarsening of body-centered-cubic polycrystalline materials in three dimensions using the phase field crystal model. We observe, as a function of the quenching depth, a crossover between a state where grain rotation halts and the growth stagnates and a state where grains coarsen rapidly by coalescence through rotation and alignment of the lattices of neighboring grains. We show that the grain rotation per volume change of a grain follows a power law with an exponent of -1.25. The scaling exponent is consistent with theoretical considerations based on the conservation of dislocations. PMID:26274188

  5. Rotation-limited growth of three-dimensional body-centered-cubic crystals

    NASA Astrophysics Data System (ADS)

    Tarp, Jens M.; Mathiesen, Joachim

    2015-07-01

    According to classical grain growth laws, grain growth is driven by the minimization of surface energy and will continue until a single grain prevails. These laws do not take into account the lattice anisotropy and the details of the microscopic rearrangement of mass between grains. Here we consider coarsening of body-centered-cubic polycrystalline materials in three dimensions using the phase field crystal model. We observe, as a function of the quenching depth, a crossover between a state where grain rotation halts and the growth stagnates and a state where grains coarsen rapidly by coalescence through rotation and alignment of the lattices of neighboring grains. We show that the grain rotation per volume change of a grain follows a power law with an exponent of -1.25 . The scaling exponent is consistent with theoretical considerations based on the conservation of dislocations.

  6. Rolling-induced Face Centered Cubic Titanium in Hexagonal Close Packed Titanium at Room Temperature

    NASA Astrophysics Data System (ADS)

    Wu, H. C.; Kumar, A.; Wang, J.; Bi, X. F.; Tomé, C. N.; Zhang, Z.; Mao, S. X.

    2016-04-01

    Combining transmission electron microscopes and density functional theory calculations, we report the nucleation and growth mechanisms of room temperature rolling induced face-centered cubic titanium (fcc-Ti) in polycrystalline hexagonal close packed titanium (hcp-Ti). Fcc-Ti and hcp-Ti take the orientation relation: <0001>hcp||<001>fcc and , different from the conventional one. The nucleation of fcc-Ti is accomplished via pure-shuffle mechanism with a minimum stable thickness of three atomic layers, and the growth via shear-shuffle mechanisms through gliding two-layer disconnections or pure-shuffle mechanisms through gliding four-layer disconnections. Such phase transformation offers an additional plastic deformation mode comparable to twinning.

  7. Rolling-induced Face Centered Cubic Titanium in Hexagonal Close Packed Titanium at Room Temperature

    PubMed Central

    Wu, H. C.; Kumar, A.; Wang, J.; Bi, X. F.; Tomé, C. N.; Zhang, Z.; Mao, S. X.

    2016-01-01

    Combining transmission electron microscopes and density functional theory calculations, we report the nucleation and growth mechanisms of room temperature rolling induced face-centered cubic titanium (fcc-Ti) in polycrystalline hexagonal close packed titanium (hcp-Ti). Fcc-Ti and hcp-Ti take the orientation relation: 〈0001〉hcp||〈001〉fcc and , different from the conventional one. The nucleation of fcc-Ti is accomplished via pure-shuffle mechanism with a minimum stable thickness of three atomic layers, and the growth via shear-shuffle mechanisms through gliding two-layer disconnections or pure-shuffle mechanisms through gliding four-layer disconnections. Such phase transformation offers an additional plastic deformation mode comparable to twinning. PMID:27067515

  8. Homogeneous nanocrystalline cubic silicon carbide films prepared by inductively coupled plasma chemical vapor deposition.

    PubMed

    Cheng, Qijin; Xu, S; Long, Jidong; Huang, Shiyong; Guo, Jun

    2007-11-21

    Silicon carbide films with different carbon concentrations x(C) have been synthesized by inductively coupled plasma chemical vapor deposition from a SiH(4)/CH(4)/H(2) gas mixture at a low substrate temperature of 500 °C. The characteristics of the films were studied by x-ray photoelectron spectroscopy, x-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared absorption spectroscopy, and Raman spectroscopy. Our experimental results show that, at x(C) = 49 at.%, the film is made up of homogeneous nanocrystalline cubic silicon carbide without any phase of silicon, graphite, or diamond crystallites/clusters. The average size of SiC crystallites is approximately 6 nm. At a lower value of x(C), polycrystalline silicon and amorphous silicon carbide coexist in the films. At a higher value of x(C), amorphous carbon and silicon carbide coexist in the films. PMID:21730481

  9. Electrostatic swelling of bicontinuous cubic lipid phases.

    PubMed

    Tyler, Arwen I I; Barriga, Hanna M G; Parsons, Edward S; McCarthy, Nicola L C; Ces, Oscar; Law, Robert V; Seddon, John M; Brooks, Nicholas J

    2015-04-28

    Lipid bicontinuous cubic phases have attracted enormous interest as bio-compatible scaffolds for use in a wide range of applications including membrane protein crystallisation, drug delivery and biosensing. One of the major bottlenecks that has hindered exploitation of these structures is an inability to create targeted highly swollen bicontinuous cubic structures with large and tunable pore sizes. In contrast, cubic structures found in vivo have periodicities approaching the micron scale. We have been able to engineer and control highly swollen bicontinuous cubic phases of spacegroup Im3m containing only lipids by (a) increasing the bilayer stiffness by adding cholesterol and (b) inducing electrostatic repulsion across the water channels by addition of anionic lipids to monoolein. By controlling the composition of the ternary mixtures we have been able to achieve lattice parameters up to 470 Å, which is 5 times that observed in pure monoolein and nearly twice the size of any lipidic cubic phase reported previously. These lattice parameters significantly exceed the predicted maximum swelling for bicontinuous cubic lipid structures, which suggest that thermal fluctuations should destroy such phases for lattice parameters larger than 300 Å. PMID:25790335

  10. Process for utilizing low-cost graphite substrates for polycrystalline solar cells

    NASA Technical Reports Server (NTRS)

    Chu, T. L. (Inventor)

    1978-01-01

    Low cost polycrystalline silicon solar cells supported on substrates were prepared by depositing successive layers of polycrystalline silicon containing appropriate dopants over supporting substrates of a member selected from the group consisting of metallurgical grade polycrystalline silicon, graphite and steel coated with a diffusion barrier of silica, borosilicate, phosphosilicate, or mixtures thereof such that p-n junction devices were formed which effectively convert solar energy to electrical energy. To improve the conversion efficiency of the polycrystalline silicon solar cells, the crystallite size in the silicon was substantially increased by melting and solidifying a base layer of polycrystalline silicon before depositing the layers which form the p-n junction.

  11. Modified electrodes based on lipidic cubic phases.

    PubMed

    Bilewicz, Renata; Rowiński, Paweł; Rogalska, Ewa

    2005-04-01

    The lipidic cubic phase can be characterized as a curved bilayer forming a three-dimensional, crystallographical, well-ordered structure that is interwoven by aqueous channels. It provides a stable, well-organized environment in which diffusion of both water-soluble and lipid-soluble compounds can take place. Cubic phases based on monoacylglycerols form readily and attract our interest due to their ability to incorporate and stabilize proteins. Their lyotropic and thermotropic phase behaviour has been thoroughly investigated. At hydration over 20%, lipidic cubic phases Ia3d and Pn3m are formed. The latter is stable in the presence of excess water, which is important when the cubic phase is considered as an electrode-modifying material. Due to high viscosity, the cubic phases can be simply smeared over solid substrates such as electrodes and used to host enzymes and synthetic catalysts, leading to new types of catalytically active modified electrodes as shown for the determination of cholesterol, CO(2), or oxygen. The efficiency of transport of small hydrophilic molecules within the film can be determined by voltametry using two types of electrodes: a normal-size electrode working in the linear diffusion regime, and an ultramicroelectrode working under spherical diffusion conditions. This allows determining both the concentration and diffusion coefficient of the electrochemically active probe in the cubic phase. The monoolein-based cubic phase matrices are useful for immobilizing enzymes on the electrode surface (e.g., laccases from Trametes sp. and Rhus vernicifera were employed for monitoring dioxygen). The electronic contact between the electrode and the enzyme was maintained using suitable electroactive probes. PMID:15833697

  12. [Study on the micro-infrared spectra and origin of polycrystalline diamonds from Mengyin kimberlite pipes].

    PubMed

    Yang, Zhi-Jun; Liang, Rong; Zeng, Xiang-Qing; Ge, Tie-Yan; Ai, Qun; Zheng, Yun-Long; Peng, Ming-Sheng

    2012-06-01

    The natural polycrystalline diamonds from the Mengyin kimberlite pipes can be classified as the euhedral faceted polycrystalline diamonds and anhedral rounded polycrystalline diamonds. The results of micro-FTIR spectra characterization of the polycrystalline diamonds show that the concentration of nitrogen is low, varying from 16.69 to 72.81 microgram per gram and is different among different diamond grains or position in polycrystalline diamonds. The euhedral faceted polycrystalline diamonds are Ia AB type and have higher concentration of A-center defects than B-center defects. Most of the anhedral rounded polycrystalline diamonds are Ia AB type and have higher content of B-center defects. A minority of the anhedral rounded polycrystalline diamonds have C-center, A-center and B-center defects simultaneously. The polycrystalline diamonds probably originated from the relatively deeper mantle and were not formed in diamond nucleation stage, but in the diamond growth period or some special conditions after the diamond grains were formed already. Furthermore, the euhedral faceted polycrystalline diamonds were formed slightly later and the anhedral rounded polycrystalline diamonds were formed obviously earlier than the diamond single crystals from the Mengyin kimberlite pipes. PMID:22870630

  13. Polycrystalline thin-film solar cells and modules

    SciTech Connect

    Ullal, H.S.; Stone, J.L.; Zweibel, K.; Surek, T.; Mitchell, R.L.

    1991-12-01

    This paper describes the recent technological advances in polycrystalline thin-film solar cells and modules. Three thin film materials, namely, cadmium telluride (CdTe), copper indium diselenide (CuInSe{sub 2}, CIS) and silicon films (Si-films) have made substantial technical progress, both in device and module performance. Early stability results for modules tested outdoors by various groups worldwide are also encouraging. The major global players actively involved in the development of the these technologies are discussed. Technical issues related to these materials are elucidated. Three 20-kW polycrystalline thin-film demonstration photovoltaic (PV) systems are expected to be installed in Davis, CA in 1992 as part of the Photovoltaics for Utility-Scale Applications (PVUSA) project. This is a joint project between the US Department of Energy (DOE), Pacific Gas and Electric (PG&E), Electric Power Research Institute (EPRI), California Energy Commission (CEC), and a utility consortium.

  14. Polycrystalline thin-film solar cells and modules

    SciTech Connect

    Ullal, H.S.; Stone, J.L.; Zweibel, K.; Surek, T.; Mitchell, R.L.

    1991-12-01

    This paper describes the recent technological advances in polycrystalline thin-film solar cells and modules. Three thin film materials, namely, cadmium telluride (CdTe), copper indium diselenide (CuInSe{sub 2}, CIS) and silicon films (Si-films) have made substantial technical progress, both in device and module performance. Early stability results for modules tested outdoors by various groups worldwide are also encouraging. The major global players actively involved in the development of the these technologies are discussed. Technical issues related to these materials are elucidated. Three 20-kW polycrystalline thin-film demonstration photovoltaic (PV) systems are expected to be installed in Davis, CA in 1992 as part of the Photovoltaics for Utility-Scale Applications (PVUSA) project. This is a joint project between the US Department of Energy (DOE), Pacific Gas and Electric (PG E), Electric Power Research Institute (EPRI), California Energy Commission (CEC), and a utility consortium.

  15. Mechanical instability of monocrystalline and polycrystalline methane hydrates.

    PubMed

    Wu, Jianyang; Ning, Fulong; Trinh, Thuat T; Kjelstrup, Signe; Vlugt, Thijs J H; He, Jianying; Skallerud, Bjørn H; Zhang, Zhiliang

    2015-01-01

    Despite observations of massive methane release and geohazards associated with gas hydrate instability in nature, as well as ductile flow accompanying hydrate dissociation in artificial polycrystalline methane hydrates in the laboratory, the destabilising mechanisms of gas hydrates under deformation and their grain-boundary structures have not yet been elucidated at the molecular level. Here we report direct molecular dynamics simulations of the material instability of monocrystalline and polycrystalline methane hydrates under mechanical loading. The results show dislocation-free brittle failure in monocrystalline hydrates and an unexpected crossover from strengthening to weakening in polycrystals. Upon uniaxial depressurisation, strain-induced hydrate dissociation accompanied by grain-boundary decohesion and sliding destabilises the polycrystals. In contrast, upon compression, appreciable solid-state structural transformation dominates the response. These findings provide molecular insight not only into the metastable structures of grain boundaries, but also into unusual ductile flow with hydrate dissociation as observed during macroscopic compression experiments. PMID:26522051

  16. Nucleation and growth of polycrystalline SiC

    NASA Astrophysics Data System (ADS)

    Kaiser, M.; Schimmel, S.; Jokubavicius, V.; Linnarsson, M. K.; Ou, H.; Syväjärvi, M.; Wellmann, P.

    2014-03-01

    The nucleation and bulk growth of polycrystalline SiC in a 2 inch PVT setup using isostatic and pyrolytic graphite as substrates was studied. Textured nucleation occurs under near-thermal equilibrium conditions at the initial growth stage with hexagonal platelet shaped crystallites of 4H, 6H and 15R polytypes. It is found that pyrolytic graphite results in enhanced texturing of the nucleating gas species. Reducing the pressure leads to growth of the crystallites until a closed polycrystalline SiC layer containing voids with a rough surface is developed. Bulk growth was conducted at 35 mbar Ar pressure at 2250°C in diffusion limited mass transport regime generating a convex shaped growth form of the solid-gas interface leading to lateral expansion of virtually [001] oriented crystallites. Growth at 2350°C led to the stabilization of 6H polytypic grains. The micropipe density in the bulk strongly depends on the substrate used.

  17. Mechanical instability of monocrystalline and polycrystalline methane hydrates

    NASA Astrophysics Data System (ADS)

    Wu, Jianyang; Ning, Fulong; Trinh, Thuat T.; Kjelstrup, Signe; Vlugt, Thijs J. H.; He, Jianying; Skallerud, Bjørn H.; Zhang, Zhiliang

    2015-11-01

    Despite observations of massive methane release and geohazards associated with gas hydrate instability in nature, as well as ductile flow accompanying hydrate dissociation in artificial polycrystalline methane hydrates in the laboratory, the destabilising mechanisms of gas hydrates under deformation and their grain-boundary structures have not yet been elucidated at the molecular level. Here we report direct molecular dynamics simulations of the material instability of monocrystalline and polycrystalline methane hydrates under mechanical loading. The results show dislocation-free brittle failure in monocrystalline hydrates and an unexpected crossover from strengthening to weakening in polycrystals. Upon uniaxial depressurisation, strain-induced hydrate dissociation accompanied by grain-boundary decohesion and sliding destabilises the polycrystals. In contrast, upon compression, appreciable solid-state structural transformation dominates the response. These findings provide molecular insight not only into the metastable structures of grain boundaries, but also into unusual ductile flow with hydrate dissociation as observed during macroscopic compression experiments.

  18. Ultrathin polycrystalline 6,13-Bis(triisopropylsilylethynyl)-pentacene films

    SciTech Connect

    Jung, Min-Cherl; Zhang, Dongrong; Nikiforov, Gueorgui O.; Lee, Michael V.; Qi, Yabing; Joo Shin, Tae; Ahn, Docheon; Lee, Han-Koo; Baik, Jaeyoon; Shin, Hyun-Joon

    2015-03-15

    Ultrathin (<6 nm) polycrystalline films of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-P) are deposited with a two-step spin-coating process. The influence of spin-coating conditions on morphology of the resulting film was examined by atomic force microscopy. Film thickness and RMS surface roughness were in the range of 4.0–6.1 and 0.6–1.1 nm, respectively, except for small holes. Polycrystalline structure was confirmed by grazing incidence x-ray diffraction measurements. Near-edge x-ray absorption fine structure measurements suggested that the plane through aromatic rings of TIPS-P molecules was perpendicular to the substrate surface.

  19. Compton profile study of polycrystalline ZnBr{sub 2}

    SciTech Connect

    Dhaka, M. S.; Sharma, G.; Mishra, M. C.; Kothari, R. K.; Sharma, B. K.

    2010-12-01

    The first ever Compton profile study of polycrystalline ZnBr{sub 2} is presented in this paper. The measurement of polycrystalline sample of ZnBr{sub 2} is performed using 59.54 keV gamma-rays emanating from an {sup 241}Am radioisotope. Theoretical calculations are performed following the Ionic model calculations for a number of configurations Zn{sup +x}Br{sub 2}{sup -x/2}(0.0{<=}x{<=}2.0 in step of 0.5) utilizing free atom profiles. The ionic model suggest transfer of 2.0 electrons from 4 s state of Zn to 4 p state of two Br atoms. The autocorrelation function B(z) is also derived from experiment and the most favoured ionic valence Compton profiles.

  20. Orientation-distribution mapping of polycrystalline materials by Raman microspectroscopy

    PubMed Central

    Schmid, T.; Schäfer, N.; Levcenko, S.; Rissom, T.; Abou-Ras, D.

    2015-01-01

    Raman microspectroscopy provides the means to obtain local orientations on polycrystalline materials at the submicrometer level. The present work demonstrates how orientation-distribution maps composed of Raman intensity distributions can be acquired on large areas of several hundreds of square micrometers. A polycrystalline CuInSe2 thin film was used as a model system. The orientation distributions are evidenced by corresponding measurements using electron backscatter diffraction (EBSD) on the same identical specimen positions. The quantitative, local orientation information obtained by means of EBSD was used to calculate the theoretical Raman intensities for specific grain orientations, which agree well with the experimental values. The presented approach establishes new horizons for Raman microspectroscopy as a tool for quantitative, microstructural analysis at submicrometer resolution. PMID:26673970

  1. Further development and application of polycrystalline metal whiskers

    NASA Technical Reports Server (NTRS)

    Schladitz, H. J.

    1979-01-01

    High strength metal whiskers have a larger versatile field of application than monocrystalline whiskers. Although polycrystalline metal whiskers can be used for composites, preferably by extrusion in thermoplastics or by infiltration of resins or metals into whisker networks, the chief application at present may be the production and various use of whisker networks. Such networks can be produced up to high degrees of porosity and besides high mechanical strength, they have high inside surfaces and high electric conductivity. There are for instance, applications concerning construction of electrodes for batteries and fuel cells, catalysts and also new heat-exchanger material, capable of preparing fuel oil and gasoline in order to assist a high-efficiency combustion. The technical application of polycrystalline metal whiskers require their modification as well as the construction of a pilot production unit.

  2. Mechanical instability of monocrystalline and polycrystalline methane hydrates

    PubMed Central

    Wu, Jianyang; Ning, Fulong; Trinh, Thuat T.; Kjelstrup, Signe; Vlugt, Thijs J. H.; He, Jianying; Skallerud, Bjørn H.; Zhang, Zhiliang

    2015-01-01

    Despite observations of massive methane release and geohazards associated with gas hydrate instability in nature, as well as ductile flow accompanying hydrate dissociation in artificial polycrystalline methane hydrates in the laboratory, the destabilising mechanisms of gas hydrates under deformation and their grain-boundary structures have not yet been elucidated at the molecular level. Here we report direct molecular dynamics simulations of the material instability of monocrystalline and polycrystalline methane hydrates under mechanical loading. The results show dislocation-free brittle failure in monocrystalline hydrates and an unexpected crossover from strengthening to weakening in polycrystals. Upon uniaxial depressurisation, strain-induced hydrate dissociation accompanied by grain-boundary decohesion and sliding destabilises the polycrystals. In contrast, upon compression, appreciable solid-state structural transformation dominates the response. These findings provide molecular insight not only into the metastable structures of grain boundaries, but also into unusual ductile flow with hydrate dissociation as observed during macroscopic compression experiments. PMID:26522051

  3. Boron doped polycrystalline diamond films for strain sensing applications

    SciTech Connect

    Wur, D.; Davidson, J.L.; Kang, W.P.

    1995-12-31

    It has been recently established in our work and others that boron-doped polycrystalline diamond films (PDF) have piezoresistivity (PZR). This property opens PDF to the field of sensor applications using strain sensing. Polycrystalline diamond films have been prepared with microwave plasma enhanced chemical vapor deposition (CVD) method and boron-doped to p-type semiconductors. In addition, by combining the piezoresistive effect in doped PDF and the insulating property of undoped PDF, whereby doped diamond resistors reside on a dielectric diamond substrate diaphragm, a monolithic all-diamond microstructure for examining the strain response of patterned p-doped diamond PZRs was fabricated and characterized. This work examines some critical issues of diamond for strain sensing applications such as its rupture stress and edge stress of diamond diaphragm and the high temperature responses of a diamond strain sensor.

  4. Flexible polycrystalline thin-film photovoltaics for space applications

    NASA Technical Reports Server (NTRS)

    Armstrong, J. H.; Lanning, B. R.; Misra, M. S.; Kapur, V. K.; Basol, B. M.

    1993-01-01

    Polycrystalline thin-film photovoltaics (PV), such as CIS and CdTe, have received considerable attention recently with respect to space power applications. Their combination of stability, efficiency, and economy from large-scale monolithic-integration of modules can have significant impact on cost and weight of PV arrays for spacecraft and planetary experiments. An added advantage, due to their minimal thickness (approximately 6 microns sans substrate), is the ability to manufacture lightweight, flexible devices (approximately 2000 W/kg) using large-volume manufacturing techniques. The photovoltaic effort at Martin Marietta and ISET is discussed, including large-area, large-volume thin-film deposition techniques such as electrodeposition and rotating cylindrical magnetron sputtering. Progress in the development of flexible polycrystalline thin-film PV is presented, including evaluation of flexible CIS cells. In addition, progress on flexible CdTe cells is presented. Finally, examples of lightweight, flexible arrays and their potential cost and weight impact is discussed.

  5. Orientation-distribution mapping of polycrystalline materials by Raman microspectroscopy.

    PubMed

    Schmid, T; Schäfer, N; Levcenko, S; Rissom, T; Abou-Ras, D

    2015-01-01

    Raman microspectroscopy provides the means to obtain local orientations on polycrystalline materials at the submicrometer level. The present work demonstrates how orientation-distribution maps composed of Raman intensity distributions can be acquired on large areas of several hundreds of square micrometers. A polycrystalline CuInSe2 thin film was used as a model system. The orientation distributions are evidenced by corresponding measurements using electron backscatter diffraction (EBSD) on the same identical specimen positions. The quantitative, local orientation information obtained by means of EBSD was used to calculate the theoretical Raman intensities for specific grain orientations, which agree well with the experimental values. The presented approach establishes new horizons for Raman microspectroscopy as a tool for quantitative, microstructural analysis at submicrometer resolution. PMID:26673970

  6. Selective and low temperature synthesis of polycrystalline diamond

    NASA Technical Reports Server (NTRS)

    Ramesham, R.; Roppel, T.; Ellis, C.; Baugh, W.; Jaworske, D. A.

    1991-01-01

    Polycrystalline diamond thin films have been deposited on single-crystal silicon substrates at low temperatures (not above 600 C) using a mixture of hydrogen and methane gases by high-pressure microwave plasma-assisted chemical vapor deposition. Low-temperature deposition has been achieved by cooling the substrate holder with nitrogen gas. For deposition at reduced substrate temperature, it has been found that nucleation of diamond will not occur unless the methane/hydrogen ratio is increased significantly from its value at higher substrate temperature. Selective deposition of polycrystalline diamond thin films has been achieved at 600 C. Decrease in the diamond particle size and growth rate and an increase in surface smoothness have been observed with decreasing substrate temperature during the growth of thin films. As-deposited films are identified by Raman spectroscopy, and the morphology is analyzed by scanning electron microscopy.

  7. Polycrystalline thin-film technology: Recent progress in photovoltaics

    SciTech Connect

    Mitchell, R.L.; Zweibel, K.; Ullal, H.S.

    1991-12-01

    Polycrystalline thin films have made significant technical progress in the past year. Three of these materials that have been studied extensively for photovoltaic (PV) power applications are copper indium diselenide (CuInSe{sub 2}), cadmium telluride (CdTe), and thin-film polycrystalline silicon (x-Si) deposited on ceramic substrates. The first of these materials, polycrystalline thin-film CuInSe{sub 2}, has made some rapid advances in terms of high efficiency and long-term reliability. For CuInSe{sub 2} power modules, a world record has been reported on a 0.4-m{sup 2} module with an aperture-area efficiency of 10.4% and a power output of 40.4 W. Additionally, outdoor reliability testing of CuInSe{sub 2} modules, under both loaded and open-circuit conditions, has resulted in only minor changes in module performance after more than 1000 days of continuous exposure to natural sunlight. CdTe module research has also resulted in several recent improvements. Module performance has been increased with device areas reaching nearly 900 cm{sup 2}. Deposition has been demonstrated by several different techniques, including electrodeposition, spraying, and screen printing. Outdoor reliability testing of CdTe modules was also carried out under both loaded and open-circuit conditions, with more than 600 days of continuous exposure to natural sunlight. These tests were also encouraging and indicated that the modules were stable within measurement error. The highest reported aperture-area module efficiency for CdTe modules is 10%; the semiconductor material was deposited by electrodeposition. A thin-film CdTe photovoltaic system with a power output of 54 W has been deployed in Saudi Arabia for water pumping. The Module Development Initiative has made significant progress in support of the Polycrystalline Thin-Film Program in the past year, and results are presented in this paper.

  8. Oscillation of structure characteristics in polycrystalline nickel during plastic deformation

    SciTech Connect

    Dvorovienko, N.A.; Gernov, S.A.; Sirenko, A.F. . Dept. of Solid State Physics); Hamana, D. . Research Unit of Materiale Physic)

    1993-07-01

    The variation of X-ray diffraction characteristics (breadth at half maximum intensity, integrated intensity, dislocation density and residual stresses), as a function of plastic deformation rate, which occurs by uniaxial tensile test, has been studied. At room temperature the observed oscillation of studied characteristics in deformed polycrystalline nickel is due to the deformation mechanism change. The latter can be a translational displacement due to dislocations or a rotational displacement due to disclination.

  9. A characterization study of a hydroxylated polycrystalline tin oxide surface

    NASA Technical Reports Server (NTRS)

    Hoflund, Gar B.; Grogan, Austin L., Jr.; Asbury, Douglas A.; Schryer, David R.

    1989-01-01

    In this study Auger electron spectroscopy, electron spectroscopy for chemical analysis (ESCA) and electron-stimulated desorption (ESD) have been used to examine a polycrystalline tin oxide surface before and after annealing in vacuum at 500 C. Features due to surface hydroxyl groups are present in both the ESCA and ESD spectra, and ESD shows that several chemical states of hydrogen are present. Annealing at 500 C causes a large reduction in the surface hydrogen concentration but not complete removal.

  10. Photoluminescence of polycrystalline ZnO under different annealing conditions

    NASA Astrophysics Data System (ADS)

    Hur, Tae-Bong; Jeen, Gwang Soo; Hwang, Yoon-Hwae; Kim, Hyung-Kook

    2003-11-01

    We investigated polycrystalline zinc oxide (ZnO) with different annealing conditions in air by x-ray photoelectron spectroscopy and photoluminescence. We found that the concentration of antisite oxide (OZn) increases when ZnO ceramics were in an O-rich condition. As the concentration of antisite oxide (OZn) increased, the photoluminescence intensity of the green band emission increased. The crossover temperature of the free and bound excitons was roughly estimated as 100 K.

  11. Polycrystalline thin-film technology: Recent progress in photovoltaics

    NASA Astrophysics Data System (ADS)

    Mitchell, R. L.; Zweibel, K.; Ullal, H. S.

    1991-12-01

    Polycrystalline thin films have made significant technical progress in the past year. Three of these materials that have been studied extensively for photovoltaic (PV) power applications are copper indium diselenide (CuInSe2), cadmium telluride (CdTe), and thin film polycrystalline silicon (x-Si) deposited on ceramic substrates. The first of these materials, polycrystalline thin film CuInSe2, has made some rapid advances in terms of high efficiency and long term reliability. For CuInSe2 power modules, a world record has been reported on a 0.4 sq m module with an aperture-area efficiency of 10.4 pct. and a power output of 40.4 W. Additionally, outdoor reliability testing of CuInSe2 modules, under both loaded and open-circuit conditions, has resulted in only minor changes in module performance after more than 1000 days of continuous exposure to natural sunlight. CdTe module research has also resulted in several recent improvements. Module performance has been increased with device areas reaching nearly 900 sq cm. Deposition has been demonstrated by several different techniques, including electrodeposition, spraying, and screen printing. Outdoor reliability testing of CdTe modules was also carried out under both loaded and open-circuit conditions, with more than 600 days of continuous exposure to natural sunlight. These tests were also encouraging and indicated that the modules were stable within measurement error. The highest reported aperture-area module efficiency for CdTe modules is 10 pct.; the semiconductor material was deposited by electrodeposition. A thin-film CdTe photovoltaic system with a power output of 54 W has been deployed in Saudi Arabia for water pumping. The Module Development Initiative has made significant progress in support of the Polycrystalline Thin-Film Program in the past year, and results are presented in this paper.

  12. Polycrystalline organic thin film transistors for advanced chemical sensing

    NASA Astrophysics Data System (ADS)

    Torsi, Luisa; Tanese, Maria C.; Cioffi, Nicola; Sabbatini, Luigia; Zambonin, Pier G.

    2003-11-01

    Organic thin-film transistors have seen a dramatic improvement of their performance in the last decade. They have been also proposed as gas sensors. This paper deals with the interesting new aspects that polycrystalline based conducting polymer transistors present when operated as chemical sensors. Such devices are capable to deliver multi-parameter responses that are also extremely repeatable and fast at room temperature. Interesting are also the perspectives for their use as chemically selective devices in array type sensing systems.

  13. Tribological properties of sintered polycrystalline and single crystal silicon carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.; Srinivasan, M.

    1982-01-01

    Tribological studies and X-ray photoelectron spectroscopy analyses were conducted with sintered polycrystalline and single crystal silicon carbide surfaces in sliding contact with iron at various temperatures to 1500 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on both the friction properties and the surface chemistry of silicon carbide. The main contaminants on the as received sintered polycrystalline silicon carbide surfaces are adsorbed carbon, oxygen, graphite, and silicon dioxide. The surface revealed a low coefficient of friction. This is due to the presence of the graphite on the surface. At temperatures of 400 to 600 C graphite and copious amount of silicon dioxide were observed on the polycrystalline silicon carbide surface in addition to silicon carbide. At 800 C, the amount of the silicon dioxide decreased rapidly and the silicon carbide type silicon and carbon peaks were at a maximum intensity in the XPS spectra. The coefficients of friction were high in the temperature range 400 to 800 C. Small amounts of carbon and oxygen contaminants were observed on the as received single crystal silicon carbide surface below 250 C. Silicon carbide type silicon and carbon peaks were seen on the silicon carbide in addition to very small amount of graphite and silicon dioxide at temperatures of 450 to 800 C.

  14. Mechanical properties of irradiated multi-phase polycrystalline BCC materials

    NASA Astrophysics Data System (ADS)

    Song, Dingkun; Xiao, Xiazi; Xue, Jianming; Chu, Haijian; Duan, Huiling

    2015-04-01

    Structure materials under severe irradiations in nuclear environments are known to degrade because of irradiation hardening and loss of ductility, resulting from irradiation-induced defects such as vacancies, interstitials and dislocation loops, etc. In this paper, we develop an elastic-viscoplastic model for irradiated multi-phase polycrystalline BCC materials in which the mechanical behaviors of individual grains and polycrystalline aggregates are both explored. At the microscopic grain scale, we use the internal variable model and propose a new tensorial damage descriptor to represent the geometry character of the defect loop, which facilitates the analysis of the defect loop evolutions and dislocation-defect interactions. At the macroscopic polycrystal scale, the self-consistent scheme is extended to consider the multiphase problem and used to bridge the individual grain behavior to polycrystal properties. Based on the proposed model, we found that the work-hardening coefficient decreases with the increase of irradiation-induced defect loops, and the orientation/loading dependence of mechanical properties is mainly attributed to the different Schmid factors. At the polycrystalline scale, numerical results for pure Fe match well with the irradiation experiment data. The model is further extended to predict the hardening effect of dispersoids in oxide-dispersed strengthened steels by the considering the Orowan bowing. The influences of grain size and irradiation are found to compete to dominate the strengthening behaviors of materials.

  15. Physics of grain boundaries in polycrystalline photovoltaic semiconductors

    SciTech Connect

    Yan, Yanfa Yin, Wan-Jian; Wu, Yelong; Shi, Tingting; Paudel, Naba R.; Li, Chen; Poplawsky, Jonathan; Wang, Zhiwei; Moseley, John; Guthrey, Harvey; Moutinho, Helio; Al-Jassim, Mowafak M.; Pennycook, Stephen J.

    2015-03-21

    Thin-film solar cells based on polycrystalline Cu(In,Ga)Se{sub 2} (CIGS) and CdTe photovoltaic semiconductors have reached remarkable laboratory efficiencies. It is surprising that these thin-film polycrystalline solar cells can reach such high efficiencies despite containing a high density of grain boundaries (GBs), which would seem likely to be nonradiative recombination centers for photo-generated carriers. In this paper, we review our atomistic theoretical understanding of the physics of grain boundaries in CIGS and CdTe absorbers. We show that intrinsic GBs with dislocation cores exhibit deep gap states in both CIGS and CdTe. However, in each solar cell device, the GBs can be chemically modified to improve their photovoltaic properties. In CIGS cells, GBs are found to be Cu-rich and contain O impurities. Density-functional theory calculations reveal that such chemical changes within GBs can remove most of the unwanted gap states. In CdTe cells, GBs are found to contain a high concentration of Cl atoms. Cl atoms donate electrons, creating n-type GBs between p-type CdTe grains, forming local p-n-p junctions along GBs. This leads to enhanced current collections. Therefore, chemical modification of GBs allows for high efficiency polycrystalline CIGS and CdTe thin-film solar cells.

  16. 'Age-hardened alloy' based on bulk polycrystalline oxide ceramic

    NASA Astrophysics Data System (ADS)

    Gurnani, Luv; Singh, Mahesh Kumar; Bhargava, Parag; Mukhopadhyay, Amartya

    2015-05-01

    We report here for the first time the development of 'age-hardened/toughened' ceramic alloy based on MgO in the bulk polycrystalline form. This route allows for the facile development of a 'near-ideal' microstructure characterized by the presence of nanosized and uniformly dispersed second-phase particles (MgFe2O4) within the matrix grains, as well as along the matrix grain boundaries, in a controlled manner. Furthermore, the intragranular second-phase particles are rendered coherent with the matrix (MgO). Development of such microstructural features for two-phase bulk polycrystalline ceramics is extremely challenging following the powder metallurgical route usually adopted for the development of bulk ceramic nanocomposites. Furthermore, unlike for the case of ceramic nanocomposites, the route adopted here does not necessitate the usage of nano-powder, pressure/electric field-assisted sintering techniques and inert/reducing atmosphere. The as-developed bulk polycrystalline MgO-MgFe2O4 alloys possess considerably improved hardness (by ~52%) and indentation toughness (by ~35%), as compared to phase pure MgO.

  17. High temperature adsorption of nitrogen on a polycrystalline nickel surface

    NASA Astrophysics Data System (ADS)

    Boughaba, S.; Auvert, G.

    1994-01-01

    Nickel tetracarbonyl [Ni(CO)4] molecules were used as a probe to investigate the coverage of a heated polycrystalline nickel surface with nitrogen adspecies. For this purpose, the deposition kinetics of nickel (Ni) microstructures from the thermal decomposition of nickel tetracarbonyl was investigated as a function of the partial pressure of nitrogen (N2), used as buffer gas. The laser-induced chemical vapor deposition technique was used to produce polycrystalline nickel lines in an atmosphere of pure Ni(CO)4 or a [Ni(CO)4+N2] mixture. The deposition process was performed on polysilicon/silicon dioxide/<100> monosilicon substrates. As a heat source, a cw argon-ion laser was used. The laser-induced surface temperature was varied in the range 500-850 °C. For Ni(CO)4 partial pressures typically below 0.3 mbar, the nickel deposition rate was found to decrease as the N2 partial pressure increases. For higher Ni(CO)4 partial pressures, the deposition rate was found to be independent of the N2 partial pressure. On the basis of these results, the high temperature adsorption of nitrogen on a polycrystalline nickel surface was investigated. A model which accounts for the dependence of the nickel deposition rate and surface coverage with nitrogen adspecies on the N2 partial pressure was elaborated.

  18. Stress-dependent ultrasonic scattering in polycrystalline materials.

    PubMed

    Kube, Christopher M; Turner, Joseph A

    2016-02-01

    Stress-dependent elastic moduli of polycrystalline materials are used in a statistically based model for the scattering of ultrasonic waves from randomly oriented grains that are members of a stressed polycrystal. The stress is assumed to be homogeneous and can be either residual or generated from external loads. The stress-dependent elastic properties are incorporated into the definition of the differential scattering cross-section, which defines how strongly an incident wave is scattered into various directions. Nine stress-dependent differential scattering cross-sections or scattering coefficients are defined to include all possibilities of incident and scattered waves, which can be either longitudinal or (two) transverse wave types. The evaluation of the scattering coefficients considers polycrystalline aluminum that is uniaxially stressed. An analysis of the influence of incident wave propagation direction, scattering direction, frequency, and grain size on the stress-dependency of the scattering coefficients follows. Scattering coefficients for aluminum indicate that ultrasonic scattering is much more sensitive to a uniaxial stress than ultrasonic phase velocities. By developing the stress-dependent scattering properties of polycrystals, the influence of acoustoelasticity on the amplitudes of waves propagating in stressed polycrystalline materials can be better understood. This work supports the ongoing development of a technique for monitoring and measuring stresses in metallic materials. PMID:26936563

  19. Optical Properties of Anisotropic Polycrystalline Ce+3 activated LSO

    PubMed Central

    Roy, Sudesna; Lingertat, Helmut; Brecher, Charles; Sarin, Vinod

    2012-01-01

    Polycrystalline cerium activated lutetium oxyorthosilicate (LSO:Ce) is highly desirable technique to make cost effective and highly reproducible radiation detectors for medical imaging. In this article methods to improve transparency in polycrystalline LSO:Ce were explored. Two commercially available powders of different particulate sizes (average particle size 30 and 1500 nm) were evaluated for producing dense LSO:Ce by pressure assisted densification routes, such as hot pressing and hot isostatic pressing. Consolidation of the powders at optimum conditions produced three polycrystalline ceramics with average grain sizes of 500 nm, 700 and 2000 nm. Microstructural evolution studies showed that for grain sizes larger than 1 µm, anisotropy in thermal expansion coefficient and elastic constants of LSO, resulted in residual stress at grain boundaries and triple points that led to intragranular microcracking. However, reducing the grain size below 1 µm effectively avoids microcracking, leading to more favorable optical properties. The optical scattering profiles generated by a Stover scatterometer, measured by a He-Ne laser of wavelength 633 nm, showed that by reducing the grain size from 2 µm to 500 nm, the in-line transmission increased by a factor of 103. Although these values were encouraging and showed that small changes in grain size could increase transmission by almost 3 orders of magnitude, even smaller grain sizes need to be achieved in order to get truly transparent material with high in-line transmission. PMID:23505329

  20. Grain-boundary-induced melting in quenched polycrystalline monolayers

    NASA Astrophysics Data System (ADS)

    Deutschländer, Sven; Boitard, Charlotte; Maret, Georg; Keim, Peter

    2015-12-01

    Melting in two dimensions can successfully be explained with the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) scenario which describes the formation of the high-symmetry phase with the thermal activation of topological defects within an (ideally) infinite monodomain. With all state variables being well defined, it should hold also as freezing scenario where oppositely charged topological defects annihilate. The Kibble-Zurek mechanism, on the other hand, shows that spontaneous symmetry breaking alongside a continuous phase transition cannot support an infinite monodomain but leads to polycrystallinity. For any nonzero cooling rate, critical fluctuations will be frozen out in the vicinity of the transition temperature. This leads to domains with different director of the broken symmetry, separated by a defect structure, e.g., grain boundaries in crystalline systems. After instantaneously quenching a colloidal monolayer from a polycrystalline to the isotropic fluid state, we show that such grain boundaries increase the probability for the formation of dislocations. In addition, we determine the temporal decay of defect core energies during the first few Brownian times after the quench. Despite the fact that the KTHNY scenario describes a continuous phase transition and phase equilibrium does not exist, melting in polycrystalline samples starts at grain boundaries similar to first-order phase transitions.

  1. Structural forms of cubic BC2N

    SciTech Connect

    Sun, Hong; Jhi, Seung-Hoon; Roundy, David; Cohen, Marvin L.; Louie, Steven G.

    2001-03-01

    Superhard cubic boron-carbonitrides (c-BC2N) are studied with the use of the ab initio pseudopotential density functional method. The total energy, lattice constant, bulk and shear moduli, and electronic band structures as well as the electron density of states are calculated for all the possible c-BC2N structures in an eight-atom zinc-blende-structured cubic unit cell. The results obtained provide a plausible explanation for recent experimental observations as well as a possible path to synthesis of the materials.

  2. Quadratic-Like Dynamics of Cubic Polynomials

    NASA Astrophysics Data System (ADS)

    Blokh, Alexander; Oversteegen, Lex; Ptacek, Ross; Timorin, Vladlen

    2016-02-01

    A small perturbation of a quadratic polynomial f with a non-repelling fixed point gives a polynomial g with an attracting fixed point and a Jordan curve Julia set, on which g acts like angle doubling. However, there are cubic polynomials with a non-repelling fixed point, for which no perturbation results into a polynomial with Jordan curve Julia set. Motivated by the study of the closure of the Cubic Principal Hyperbolic Domain, we describe such polynomials in terms of their quadratic-like restrictions.

  3. Purely cubic action for string field theory

    NASA Technical Reports Server (NTRS)

    Horowitz, G. T.; Lykken, J.; Rohm, R.; Strominger, A.

    1986-01-01

    It is shown that Witten's (1986) open-bosonic-string field-theory action and a closed-string analog can be written as a purely cubic interaction term. The conventional form of the action arises by expansion around particular solutions of the classical equations of motion. The explicit background dependence of the conventional action via the Becchi-Rouet-Stora-Tyutin operator is eliminated in the cubic formulation. A closed-form expression is found for the full nonlinear gauge-transformation law.

  4. Polycrystalline silicon study: Low-cost silicon refining technology prospects and semiconductor-grade polycrystalline silicon availability through 1988

    NASA Technical Reports Server (NTRS)

    Costogue, E. N.; Ferber, R.; Lutwack, R.; Lorenz, J. H.; Pellin, R.

    1984-01-01

    Photovoltaic arrays that convert solar energy into electrical energy can become a cost effective bulk energy generation alternative, provided that an adequate supply of low cost materials is available. One of the key requirements for economic photovoltaic cells is reasonably priced silicon. At present, the photovoltaic industry is dependent upon polycrystalline silicon refined by the Siemens process primarily for integrated circuits, power devices, and discrete semiconductor devices. This dependency is expected to continue until the DOE sponsored low cost silicon refining technology developments have matured to the point where they are in commercial use. The photovoltaic industry can then develop its own source of supply. Silicon material availability and market pricing projections through 1988 are updated based on data collected early in 1984. The silicon refining industry plans to meet the increasing demands of the semiconductor device and photovoltaic product industries are overviewed. In addition, the DOE sponsored technology research for producing low cost polycrystalline silicon, probabilistic cost analysis for the two most promising production processes for achieving the DOE cost goals, and the impacts of the DOE photovoltaics program silicon refining research upon the commercial polycrystalline silicon refining industry are addressed.

  5. A monotonicity conjecture for real cubic maps

    SciTech Connect

    Dawson, S.P.; Galeeva, R.; Milnor, J.; Tresser, C.

    1993-12-01

    This will be an outline of work in progress. We study the conjecture that the topological entropy of a real cubic map depends ``monotonely`` on its parameters, in the sense that each locus of constant entropy in parameter space is a connected set. This material will be presented in more detail in a later paper.

  6. Sound velocity anisotropy in cubic crystals

    NASA Technical Reports Server (NTRS)

    Tsang, T.; Park, H. Y.

    1983-01-01

    Simple analytical expressions may be derived for sound velocities in cubic crystals by using lattice harmonics or functions which are invariant under the crystal symmetry operations. These expressions are in good agreement with the exact results for typical crystals such as metallic iron and potassium fluoride.

  7. Use of Pom Pons to Illustrate Cubic Crystal Structures.

    ERIC Educational Resources Information Center

    Cady, Susan G.

    1997-01-01

    Describes a method that uses olefin pom pons to illustrate cubic crystal structure. Facilitates hands-on examination of different packing arrangements such as hexagonal close-packed and cubic close-packed structures. (JRH)

  8. Cubic Polynomials with Rational Roots and Critical Points

    ERIC Educational Resources Information Center

    Gupta, Shiv K.; Szymanski, Waclaw

    2010-01-01

    If you want your students to graph a cubic polynomial, it is best to give them one with rational roots and critical points. In this paper, we describe completely all such cubics and explain how to generate them.

  9. Ion beam nitriding of single and polycrystalline austenitic stainless steel

    SciTech Connect

    Abrasonis, G.; Riviere, J.P.; Templier, C.; Declemy, A.; Pranevicius, L.; Milhet, X.

    2005-04-15

    Polycrystalline and single crystalline [orientations (001) and (011)] AISI 316L austenitic stainless steel was implanted at 400 deg. C with 1.2 keV nitrogen ions using a high current density of 0.5 mA cm{sup -2}. The nitrogen distribution profiles were determined using nuclear reaction analysis (NRA). The structure of nitrided polycrystalline stainless steel samples was analyzed using glancing incidence and symmetric x-ray diffraction (XRD) while the structure of the nitrided single crystalline stainless steel samples was analyzed using x-ray diffraction mapping of the reciprocal space. For identical treatment conditions, it is observed that the nitrogen penetration depth is larger for the polycrystalline samples than for the single crystalline ones. The nitrogen penetration depth depends on the orientation, the <001> being more preferential for nitrogen diffusion than <011>. In both type of samples, XRD analysis shows the presence of the phase usually called 'expanded' austenite or {gamma}{sub N} phase. The lattice expansion depends on the crystallographic plane family, the (001) planes showing an anomalously large expansion. The reciprocal lattice maps of the nitrided single crystalline stainless steel demonstrate that during nitriding lattice rotation takes place simultaneously with lattice expansion. The analysis of the results based on the presence of stacking faults, residual compressive stress induced by the lattice expansion, and nitrogen concentration gradient indicates that the average lattice parameter increases with the nitrided layer depth. A possible explanation of the anomalous expansion of the (001) planes is presented, which is based on the combination of faster nitriding rate in the (001) oriented grains and the role of stacking faults and compressive stress.

  10. Aluminum additions in polycrystalline iron-gallium (Galfenol) alloys

    NASA Astrophysics Data System (ADS)

    Brooks, M. D.; Summers, E.; Meloy, R.; Mosley, J.

    2008-03-01

    Galfenol alloys show promise as a new magnetically activated smart material based on their unique combination of relatively high magnetostrictive performance and good mechanical robustness. Investigations of aluminum additions to single crystal iron-gallium alloys have been done previously, and the magnetostrictive response seems to follow the rule of mixtures with decreasing saturation magnetostriction with increasing aluminum content. Aluminum is assumed to substitute for Ga directly in the alloy. Directionally solidified polycrystalline Galfenol alloys with aluminum additions were produced to determine the effects on the magnetic properties. Iron-gallium-aluminum alloys were investigated for two primary reasons: (1) Fe-Al alloys are well established and are typically manufactured using conventional thermo-mechanical processing techniques such as rolling; it is anticipated that aluminum additions will aid in the development of Galfenol alloy rolled sheets (2) Gallium prices continue to rise and a cost effective alternative needs to be investigated. Several Fe-Ga-Al alloy compositions were prepared using the Free Stand Zone Melting (FSZM) directional solidification technique. Alloy composition ranges investigated include: Fe 80.5Ga xAl 19.5-x (4.9<=x<=13), Fe 81.6Ga yAl 18.4-y (4.6<=y<=13.8), and Fe 85Ga zAl 15-z (3.75<=z<=11.25). Alloys were studied using EDS (chemistry verification), EBSD (crystallite orientation), and magnetic characterization techniques to determine the effect of aluminum addition on the polycrystalline binary Fe-Ga system. Magnetic properties such as saturation magnetostriction (λ sat), piezomagnetic constant (d 33), and relative magnetic permeability (μ r) of directionally solidified Fe-Ga-Al polycrystalline alloys will be compared to binary Fe-Ga alloys including investigations into the crystal orientation effects on these properties. Results suggest that up to 50% aluminum can be substituted in the alloy while maintaining considerable

  11. Conductive polycrystalline diamond probes for local anodic oxidation lithography

    NASA Astrophysics Data System (ADS)

    Ulrich, A. J.; Radadia, A. D.

    2015-11-01

    This is the first report characterizing local anodic oxidation (LAO) lithography performed using conductive monolithic polycrystalline diamond (MD) and conductive polycrystalline diamond-coated (DC) tips and comparing it to the diamond-like carbon-coated and metal-coated silicon tips. The range and the rate of increase in the lithographic linewidth and height with tip bias (dw/dV and dh/dV) differed based on the tip material. The DC tips resulted in wider and taller lines and a higher dw/dV and dh/dV compared to metal-coated tips with a similar force constant (k Avg). The metal-coated and the DC tips with comparable k Avg showed comparable threshold voltages, whereas the MD tips with similar k Avg showed a higher threshold voltage. The MD tips exhibited less than half the height and nearly half the dw/dV and dh/dV obtained with the metal-coated tips with similar k Avg, thus also resulting in a smaller width at -10 V. The linewidths were found to be proportional to the inverse of the log of write speed (v) for all the tips; however, the proportionality constant varied with tip material; the DC tips had larger values, and the MD and the metal-coated tips had comparable values. When varying the speed, the height was found to be a sigmoidal function of width, with the MD probes achieving lower height compared to the metal-coated and the DC tips with comparable k Avg. This study expands the application of monolithic conductive polycrystalline diamond (PCD) probes with outstanding wear resistance to fine LAO lithography.

  12. Conductive polycrystalline diamond probes for local anodic oxidation lithography.

    PubMed

    Ulrich, A J; Radadia, A D

    2015-11-20

    This is the first report characterizing local anodic oxidation (LAO) lithography performed using conductive monolithic polycrystalline diamond (MD) and conductive polycrystalline diamond-coated (DC) tips and comparing it to the diamond-like carbon-coated and metal-coated silicon tips. The range and the rate of increase in the lithographic linewidth and height with tip bias (dw/dV and dh/dV) differed based on the tip material. The DC tips resulted in wider and taller lines and a higher dw/dV and dh/dV compared to metal-coated tips with a similar force constant (k(Avg)). The metal-coated and the DC tips with comparable k(Avg) showed comparable threshold voltages, whereas the MD tips with similar k(Avg) showed a higher threshold voltage. The MD tips exhibited less than half the height and nearly half the dw/dV and dh/dV obtained with the metal-coated tips with similar k Avg, thus also resulting in a smaller width at -10 V. The linewidths were found to be proportional to the inverse of the log of write speed(v) for all the tips; however, the proportionality constant varied with tip material; the DC tips had larger values, and the MD and the metal-coated tips had comparable values. When varying the speed, the height was found to be a sigmoidal function of width, with the MD probes achieving lower height compared to the metal-coated and the DC tips with comparable k(Avg). This study expands the application of monolithic conductive polycrystalline diamond (PCD) probes with outstanding wear resistance to fine LAO lithography. PMID:26501841

  13. Advances in polycrystalline thin-film photovoltaics for space applications

    SciTech Connect

    Lanning, B.R.; Armstrong, J.H.; Misra, M.S.

    1994-09-01

    Polycrystalline, thin-film photovoltaics represent one of the few (if not the only) renewable power sources which has the potential to satisfy the demanding technical requirements for future space applications. The demand in space is for deployable, flexible arrays with high power-to-weight ratios and long-term stability (15-20 years). In addition, there is also the demand that these arrays be produced by scalable, low-cost, high yield, processes. An approach to significantly reduce costs and increase reliability is to interconnect individual cells series via monolithic integration. Both CIS and CdTe semiconductor films are optimum absorber materials for thin-film n-p heterojunction solar cells, having band gaps between 0.9-1.5 eV and demonstrated small area efficiencies, with cadmium sulfide window layers, above 16.5 percent. Both CIS and CdTe polycrystalline thin-film cells have been produced on a laboratory scale by a variety of physical and chemical deposition methods, including evaporation, sputtering, and electrodeposition. Translating laboratory processes which yield these high efficiency, small area cells into the design of a manufacturing process capable of producing 1-sq ft modules, however, requires a quantitative understanding of each individual step in the process and its effect on overall module performance. With a proper quantification and understanding of material transport and reactivity for each individual step, manufacturing process can be designed that is not `reactor-specific` and can be controlled intelligently with the design parameters of the process. The objective of this paper is to present an overview of the current efforts at MMC to develop large-scale manufacturing processes for both CIS and CdTe thin-film polycrystalline modules. CIS cells/modules are fabricated in a `substrate configuration` by physical vapor deposition techniques and CdTe cells/modules are fabricated in a `superstrate configuration` by wet chemical methods.

  14. Remobilization in the cratonic lithosphere recorded in polycrystalline diamond

    PubMed

    Jacob; Viljoen; Grassineau; Jagoutz

    2000-08-18

    Polycrystalline diamonds (framesites) from the Venetia kimberlite in South Africa contain silicate minerals whose isotopic and trace element characteristics document remobilization of older carbon and silicate components to form the framesites shortly before kimberlite eruption. Chemical variations within the garnets correlate with carbon isotopes in the diamonds, indicating contemporaneous formation. Trace element, radiogenic, and stable isotope variations can be explained by the interaction of eclogites with a carbonatitic melt, derived by remobilization of material that had been stored for a considerable time in the lithosphere. These results indicate more recent formation of diamonds from older materials within the cratonic lithosphere. PMID:10947983

  15. An acoustic emission study of plastic deformation in polycrystalline aluminium

    NASA Technical Reports Server (NTRS)

    Bill, R. C.; Frederick, J. R.; Felbeck, D. K.

    1979-01-01

    Acoustic emission experiments were performed on polycrystalline and single crystal 99.99% aluminum while undergoing tensile deformation. It was found that acoustic emission counts as a function of grain size showed a maximum value at a particular grain size. Furthermore, the slip area associated with this particular grain size corresponded to the threshold level of detectability of single dislocation slip events. The rate of decline in acoustic emission activity as grain size is increased beyond the peak value suggests that grain boundary associated dislocation sources are giving rise to the bulk of the detected acoustic emissions.

  16. Polycrystalline diamond based detector for Z-pinch plasma diagnosis

    SciTech Connect

    Liu Linyue; Zhao Jizhen; Chen Liang; Ouyang Xiaoping; Wang Lan

    2010-08-15

    A detector setup based on polycrystalline chemical-vapor-deposition diamond film is developed with great characteristics: low dark current (lower than 60 pA within 3 V/{mu}m), fast pulsed response time (rise time: 2-3 ns), flat spectral response (3-5 keV), easy acquisition, low cost, and relative large sensitive area. The characterizing data on Qiangguang-I accelerator show that this detector can satisfy the practical requirements in Z-pinch plasma diagnosis very well, which offers a promising prototype for the x-ray detection in Z-pinch diagnosis.

  17. Statistical thermodynamics of strain hardening in polycrystalline solids

    SciTech Connect

    Langer, James S.

    2015-09-18

    This paper starts with a systematic rederivation of the statistical thermodynamic equations of motion for dislocation-mediated plasticity proposed in 2010 by Langer, Bouchbinder, and Lookman. The paper then uses that theory to explain the anomalous rate-hardening behavior reported in 1988 by Follansbee and Kocks and to explore the relation between hardening rate and grain size reported in 1995 by Meyers et al. A central theme is the need for physics-based, nonequilibrium analyses in developing predictive theories of the strength of polycrystalline materials.

  18. Statistical thermodynamics of strain hardening in polycrystalline solids

    SciTech Connect

    Langer, James S.

    2015-01-01

    This paper starts with a systematic rederivation of the statistical thermodynamic equations of motion for dislocation-mediated plasticity proposed in 2010 by Langer, Bouchbinder, and Lookman. The paper then uses that theory to explain the anomalous rate-hardening behavior reported in 1988 by Follansbee and Kocks and to explore the relation between hardening rate and grain size reported in 1995 by Meyers et al. A central theme is the need for physics-based, nonequilibrium analyses in developing predictive theories of the strength of polycrystalline materials.

  19. PDC (polycrystalline diamond compact) bit research at Sandia National Laboratories

    SciTech Connect

    Finger, J.T.; Glowka, D.A.

    1989-06-01

    From the beginning of the geothermal development program, Sandia has performed and supported research into polycrystalline diamond compact (PDC) bits. These bits are attractive because they are intrinsically efficient in their cutting action (shearing, rather than crushing) and they have no moving parts (eliminating the problems of high-temperature lubricants, bearings, and seals.) This report is a summary description of the analytical and experimental work done by Sandia and our contractors. It describes analysis and laboratory tests of individual cutters and complete bits, as well as full-scale field tests of prototype and commercial bits. The report includes a bibliography of documents giving more detailed information on these topics. 26 refs.

  20. Chemically assisted ion beam etching of polycrystalline and (100)tungsten

    NASA Technical Reports Server (NTRS)

    Garner, Charles

    1987-01-01

    A chemically assisted ion-beam etching technique is described which employs an ion beam from an electron-bombardment ion source and a directed flux of ClF3 neutrals. This technique enables the etching of tungsten foils and films in excess of 40 microns thick with good anisotropy and pattern definition over areas of 30 sq mm, and with a high degree of selectivity. (100) tungsten foils etched with this process exhibit preferred-orientation etching, while polycrystalline tungsten films exhibit high etch rates. This technique can be used to pattern the dispenser cathode surfaces serving as electron emitters in traveling-wave tubes to a controlled porosity.

  1. Nucleation and growth studies of polycrystalline covalent materials

    NASA Astrophysics Data System (ADS)

    Yun, Jungheum

    The chemical vapor deposition of different covalent polycrystalline materials---including diamond, silicon carbide, and carbon nitride---in stagnation flow reactors was rigorously simulated to determine the nucleation and growth mechanisms of these materials. Kinetic models were used to predict the rates of gas-phase and surface chemistry, the temperature and velocity profiles, potential gaseous film growth precursors, the time evolution of nucleation and intermediate layer formation, and the morphological evolution of continuous polycrystalline films. Numerical studies were also carried out to determine the dependence of the kinetics of nucleation and subsequent polycrystalline film growth on operating conditions. The calculated results for carbon nitride deposition indicate that the experimentally measured bond types in the carbon nitride films must result from chemical bond rearrangement occurring on the deposition surface or in the bulk phase once gaseous film growth precursors, including C, CH2 , CH3, C2H2, N, NH, NH2, HCN, and H2CN, are adsorbed. Of these precursors, C and CH 3 dominate the carbon contribution to carbon nitride film growth, and atomic nitrogen is the principal nitrogen bearing species. When the evolution rates of a silicon carbide intermediate layer and diamond clusters are calculated by accounting for gas-phase and surface reactions, surface and bulk diffusion, the mechanism for intermediate layer formation, and heterogeneous diamond nucleation kinetics, it is predicted that higher adsorption energies, in the range of 3.7 to 4.5 eV, lead to larger surface adatom densities, lower saturated nucleation densities, and larger silicon carbide intermediate layer thicknesses. The intermediate layer thickness becomes saturated while the growing diamond nuclei still cover a very small fraction of the silicon carbide. Reports of heteroepitaxial diamond nucleation without silicon carbide intermediate layer formation may be readily explained by a

  2. Progress and issues in polycrystalline thin-film PV technologies

    SciTech Connect

    Zweibel, K.; Ullal, H.S.; Roedern, B. von

    1996-05-01

    Substantial progress has occurred in polycrystalline thin-film photovoltaic technologies in the past 18 months. However, the transition to first-time manufacturing is still under way, and technical problems continue. This paper focuses on the promise and the problems of the copper indium diselenide and cadmium telluride technologies, with an emphasis on continued R&D needs for the near-term transition to manufacturing and for next-generation improvements. In addition, it highlights the joint R&D efforts being performed in the U.S. Department of Energy/National Renewable Energy Laboratory Thin-Film Photovoltaic Partnership Program.

  3. Ultrafast carrier dynamics in polycrystalline bismuth telluride nanofilm

    SciTech Connect

    Jia, Lin; Ma, Weigang; Zhang, Xing

    2014-06-16

    In this study, the dynamics of energy carriers in polycrystalline bismuth telluride nanofilm are investigated by the ultrafast pump-probe method. The energy relaxation processes are quantitatively analyzed by using the numerical fitting models. The extracted hot carrier relaxation times of photon excitation, thermalization, and diffusion are around sub-picosecond. The initial reflectivity recovery is found to be dominantly determined by the carrier diffusion, electron-phonon coupling, and photo-generated carriers trapping processes. High-frequency and low-frequency oscillations are both observed and attributed to coherent optical phonons and coherent acoustic phonons, respectively.

  4. Fabrication of polycrystalline thin films by pulsed laser processing

    DOEpatents

    Mitlitsky, Fred; Truher, Joel B.; Kaschmitter, James L.; Colella, Nicholas J.

    1998-02-03

    A method for fabricating polycrystalline thin films on low-temperature (or high-temperature) substrates which uses processing temperatures that are low enough to avoid damage to the substrate, and then transiently heating select layers of the thin films with at least one pulse of a laser or other homogenized beam source. The pulse length is selected so that the layers of interest are transiently heated to a temperature which allows recrystallization and/or dopant activation while maintaining the substrate at a temperature which is sufficiently low to avoid damage to the substrate. This method is particularly applicable in the fabrication of solar cells.

  5. Fabrication of polycrystalline thin films by pulsed laser processing

    DOEpatents

    Mitlitsky, F.; Truher, J.B.; Kaschmitter, J.L.; Colella, N.J.

    1998-02-03

    A method is disclosed for fabricating polycrystalline thin films on low-temperature (or high-temperature) substrates which uses processing temperatures that are low enough to avoid damage to the substrate, and then transiently heating select layers of the thin films with at least one pulse of a laser or other homogenized beam source. The pulse length is selected so that the layers of interest are transiently heated to a temperature which allows recrystallization and/or dopant activation while maintaining the substrate at a temperature which is sufficiently low to avoid damage to the substrate. This method is particularly applicable in the fabrication of solar cells. 1 fig.

  6. Average g-Factors of Anisotropic Polycrystalline Samples

    SciTech Connect

    Fishman, Randy Scott; Miller, Joel S.

    2010-01-01

    Due to the lack of suitable single crystals, the average g-factor of anisotropic polycrystalline samples are commonly estimated from either the Curie-Weiss susceptibility or the saturation magnetization. We show that the average g-factor obtained from the Curie constant is always greater than or equal to the average g-factor obtained from the saturation magnetization. The average g-factors are equal only for a single crystal or an isotropic polycrystal. We review experimental results for several compounds containing the anisotropic cation [Fe(C5Me5)2]+ and propose an experiment to test this inequality using a compound with a spinless anion.

  7. Polycrystalline Superconducting Thin Films: Texture Control and Critical Current Density

    NASA Astrophysics Data System (ADS)

    Yang, Feng

    1995-01-01

    The growth processes of polycrystalline rm YBa_2CU_3O_{7-X} (YBCO) and yttria-stabilized-zirconia (YSZ) thin films have been developed. The effectiveness of YSZ buffer layers on suppression of the reaction between YBCO thin films and metallic substrates was carefully studied. Grown on the chemically inert surfaces of YSZ buffer layers, YBCO thin films possessed good quality of c-axis alignment with the c axis parallel to the substrate normal, but without any preferred in-plane orientations. This leads to the existence of a large percentage of the high-angle grain boundaries in the YBCO films. The critical current densities (rm J_{c}'s) found in these films were much lower than those in single crystal YBCO thin films, which was the consequence of the weak -link effect of the high-angle grain boundaries in these films. It became clear that the in-plane alignment is vital for achieving high rm J_{c }s in polycrystalline YBCO thin films. To induce the in-plane alignment, ion beam-assisted deposition (IBAD) technique was integrated into the conventional pulsed laser deposition process for the growth of the YSZ buffer layers. It was demonstrated that using IBAD the in-plane orientations of the YSZ grains could be controlled within a certain range of a common direction. This ion -bombardment induced in-plane texturing was explained using the anisotropic sputtering yield theory. Our observations and analyses have provided valuable information on the optimization of the IBAD process, and shed light on the texturing mechanism in YSZ. With the in-plane aligned YSZ buffer layers, YBCO thin films grown on metallic substrates showed improved rm J_{c}s. It was found that the in-plane alignment of YSZ and that of YBCO were closely related. A direct correlation was revealed between the rm J_{c} value and the degree of the in-plane alignment for the YBCO thin films. To explain this correlation, a numerical model was applied to multi-grain superconducting paths with different

  8. Compensation for thermally induced birefringence in polycrystalline ceramic active elements

    SciTech Connect

    Kagan, M A; Khazanov, E A

    2003-10-31

    Polycrystalline ceramics differ significantly from single crystals in that the crystallographic axes (and hence of the axes of thermally induced birefringence) are oriented randomly in each granule of the ceramic. The quaternion formalism is employed to calculate the depolarisation in the ceramics and the efficiency of its compensation. The obtained analytic expressions are in good agreement with the numerical relations. It is shown that the larger the ratio of the sample length to the granule size, the closer the properties of the ceramics to those of a single crystal with the [111] orientation (in particular, the uncompensated depolarisation is inversely proportional to this ratio). (active media)

  9. Near field scanning optical microscopy of polycrystalline semiconductors

    NASA Astrophysics Data System (ADS)

    Herndon, Mary Kay

    1999-09-01

    Photovoltaic devices are commonly used for space applications and remote terrestrial power requirements. Polycrystalline solar cell devices often have much lower efficiencies than their crystalline counterparts, but because they can be fabricated much more cheaply, they can still be cost-effective when compared to single crystal devices. The long term goal of this work is to provide information that will lead to higher quality devices with improved cost efficiency. In order to do this, a better understanding of the mechanisms that take place in these materials is needed. The goal of this thesis was to improve our understanding of these devices by adapting a novel characterization technique, Near Field Scanning Optical Microscopy (NSOM), to the study of polycrystalline films. Visible light NSOM is a relatively new technique that allows for optical characterization of materials with resolution beyond the far-field diffraction limit. By using NSOM to study the physical and electrical properties of polycrystalline solar cells, individual grains can be studied and more insight can be gained as to how various properties of the thin films affect the device efficiency. For this research, an NSOM was designed and built to be versatile enough to handle the sorts of samples and measurements required for studying a variety of photovoltaic devices. As a first step, the NSOM was used to characterize single crystal GaAs solar cell devices. Measurements of topography and NSOM-induced photocurrent were obtained simultaneously on cross sections of the material, allowing the p-n junction to be probed. Because the NSOM data could be compared to an expected result, this allowed verification of the new microscope's imaging capabilities and ensured accurate data interpretation. Effects of surface recombination were detected on the cleaved edges. The NSOM was used to characterize surface quality and study the effects of surface passivation treatments. Of the polycrystalline materials

  10. Low temperature production of large-grain polycrystalline semiconductors

    DOEpatents

    Naseem, Hameed A.; Albarghouti, Marwan

    2007-04-10

    An oxide or nitride layer is provided on an amorphous semiconductor layer prior to performing metal-induced crystallization of the semiconductor layer. The oxide or nitride layer facilitates conversion of the amorphous material into large grain polycrystalline material. Hence, a native silicon dioxide layer provided on hydrogenated amorphous silicon (a-Si:H), followed by deposited Al permits induced crystallization at temperatures far below the solid phase crystallization temperature of a-Si. Solar cells and thin film transistors can be prepared using this method.

  11. Statistical thermodynamics of strain hardening in polycrystalline solids

    NASA Astrophysics Data System (ADS)

    Langer, J. S.

    2015-09-01

    This paper starts with a systematic rederivation of the statistical thermodynamic equations of motion for dislocation-mediated plasticity proposed in 2010 by Langer, Bouchbinder, and Lookman [Acta Mat. 58, 3718 (2010), 10.1016/j.actamat.2010.03.009]. It then uses that theory to explain the anomalous rate-hardening behavior reported in 1988 by Follansbee and Kocks and to explore the relation between hardening rate and grain size reported in 1995 by Meyers et al. A central theme is the need for physics-based, nonequilibrium analyses in developing predictive theories of the strength of polycrystalline materials.

  12. Screen-Cage Ion Plating Of Silver On Polycrystalline Alumina

    NASA Technical Reports Server (NTRS)

    Spalvins, Talivaldis; Sliney, Harold E.; Deadmore, Daniel L.

    1995-01-01

    Screen-cage ion plating (SCIP) cost-effective technique offering high throwing power for deposition of adherent metal films on ceramic substrates. Applies silver films to complexly shaped substrates of polycrystalline alumina. Silver adheres tenaciously and reduces friction. SCIP holds promise for applying lubricating soft metallic films to high-temperature ceramic components of advanced combustion engines. Other potential uses include coating substrates with metal for protection against corrosion, depositing electrical conductors on dielectric substrates, making optically reflective or electrically or thermally conductive surface layers, and applying decorative metal coats to ceramic trophies or sculptures.

  13. Thermophotovoltaic Converters Based on Poly-crystalline GaSb

    NASA Astrophysics Data System (ADS)

    Corregidor, V.; Vincent, J.; Algora, C.; Diéguez, E.

    2007-02-01

    In this work we present the development obtained on GaSb converters manufactured from GaSb polycrystals substrates since the last TPV Conference. As one of the main problem of these GaSb converters was the surface preparation, we present new surface treatments, besides higher structural quality of the ingots. The substrates were selected from polycrystalline ingots grown by vertical Bridgman technique. The electrical measurements show the n-type mobility values up to 1000 cm2ṡV-1ṡs-1. On these substrates, 4 mm2 thermophotovoltaic cells were manufactured and characterized by illuminated J-V curves and quantum efficiency techniques.

  14. Advances in polycrystalline thin-film photovoltaics for space applications

    NASA Technical Reports Server (NTRS)

    Lanning, Bruce R.; Armstrong, Joseph H.; Misra, Mohan S.

    1994-01-01

    Polycrystalline, thin-film photovoltaics represent one of the few (if not the only) renewable power sources which has the potential to satisfy the demanding technical requirements for future space applications. The demand in space is for deployable, flexible arrays with high power-to-weight ratios and long-term stability (15-20 years). In addition, there is also the demand that these arrays be produced by scalable, low-cost, high yield, processes. An approach to significantly reduce costs and increase reliability is to interconnect individual cells series via monolithic integration. Both CIS and CdTe semiconductor films are optimum absorber materials for thin-film n-p heterojunction solar cells, having band gaps between 0.9-1.5 ev and demonstrated small area efficiencies, with cadmium sulfide window layers, above 16.5 percent. Both CIS and CdTe polycrystalline thin-film cells have been produced on a laboratory scale by a variety of physical and chemical deposition methods, including evaporation, sputtering, and electrodeposition. Translating laboratory processes which yield these high efficiency, small area cells into the design of a manufacturing process capable of producing 1-sq ft modules, however, requires a quantitative understanding of each individual step in the process and its (each step) effect on overall module performance. With a proper quantification and understanding of material transport and reactivity for each individual step, manufacturing process can be designed that is not 'reactor-specific' and can be controlled intelligently with the design parameters of the process. The objective of this paper is to present an overview of the current efforts at MMC to develop large-scale manufacturing processes for both CIS and CdTe thin-film polycrystalline modules. CIS cells/modules are fabricated in a 'substrate configuration' by physical vapor deposition techniques and CdTe cells/modules are fabricated in a 'superstrate configuration' by wet chemical

  15. Reactive sticking coefficients for silane and disilane on polycrystalline silicon

    SciTech Connect

    Buss, R.J.; Ho, P.; Breiland, W.G.; Coltrin, M.E.

    1988-04-15

    Reactive sticking coefficients (RSCs) were measured for silane and disilane on polycrystalline silicon for a wide range of temperature and flux (pressure) conditions. The data were obtained from deposition-rate measurements using molecular beam scattering and a very low-pressure cold-wall reactor. The RSCs have nonlinear Arrhenius temperature dependencies and decrease with increasing flux at low (710 /sup 0/C) temperatures. Several simple models are proposed to explain these observations. The results are compared with previous studies of the SiH/sub 4//Si(s) reaction and low-pressure chemical vapor deposition-rate measurements.

  16. [Spectral analyzing effects of atmosphere states on the structure and characteristics of CdTe polycrystalline thin films made by close-spaced sublimation].

    PubMed

    Zheng, Hua-jing; Zheng, Jia-gui; Feng, Liang-huan; Zhang, Jing-quan; Xie, Er-qing

    2005-07-01

    The structure and characteristics of CdTe thin films are dependent on the working atmosphere states in close-spaced sublimation. In the present paper, CdTe polycrystalline thin films were deposited by CSS in mixture atmosphere of argon and oxygen. The physical mechanism of CSS was analyzed, and the temperature distribution in CSS system was measured. The dependence of preliminary nucleus creation on the atmosphere states (involving component and pressure) was studied. Transparencies were measured and optic energy gaps were calculated. The results show that: (1) The CdTe films deposited in different atmospheres are cubic structure. With increasing oxygen concentration, a increases and reaches the maximum at 6% oxygen concentration, then reduces, and increases again after passing the point at 12% oxygen concentration. Among them, the sample depositing at 9% oxygen concentration is the best. The optic energy gaps are 1.50-1.51 eV for all CdTe films. (2) The samples depositing at different pressures at 9% oxygen concentration are all cubical structure of CdTe, and the diffraction peaks of CdS and SnO2:F still appear. With the gas pressure increasing, the crystal size of CdTe minishes, the transparency of the thin film goes down, and the absorption side shifts to the short-wave direction. (3) The polycrystalline thin films with high quality deposit in 4 minutes under the depositing condition that the substrate temperature is 550 degrees C, and source temperature is 620 degrees C at 9% oxygen concentration. PMID:16241058

  17. Lattice thermal transport in large-area polycrystalline graphene

    NASA Astrophysics Data System (ADS)

    Aksamija, Z.; Knezevic, I.

    2014-07-01

    We study lattice thermal transport in large-area polycrystalline graphene, such as the samples grown by chemical vapor deposition (CVD) of carbon on Cu. These systems are composed of single-crystalline grains with a broad range of sizes and crystal orientations, separated by atomically rough grain boundaries. We solve the phonon Boltzmann transport equation and calculate the thermal conductivity in each grain, including scattering from the grain boundary roughness. Thermal transport in the large-area sample is considered in the Corbino-membrane geometry, with heat flowing through a network of thermal resistors and away from a pointlike heat source. The thermal transport in polycrystalline graphene is shown to be highly anisotropic, depending on the individual properties of the grains (their size and boundary roughness), as well as on grain connectivity. Strongest heat conduction occurs along large-grain filaments, while the heat flow is blocked through regions containing predominantly small grains. We discuss how thermal transport in CVD graphene can be tailored by controlling grain disorder.

  18. High velocity sliding at polycrystalline ductile metal interfaces

    NASA Astrophysics Data System (ADS)

    Hammerberg, J. E.; Milhans, J. L.; Ravelo, R.; Germann, T. C.

    2014-03-01

    We present the results of large scale 3-dimensional NonEquilibrium Molecular Dynamics (NEMD) simulations for Al-Al and Al-Ta interfaces for sliding velocities in the range 20-4000 m/s at pressures of 15 GPa. System sizes include 8 M, 26 M and 138 M atoms for times to 40 ns. We discuss polycrystalline samples with initial grain sizes of 13 nm and 20 nm. For velocities above a size dependent critical velocity, vc, the frictional force per unit area agrees with single crystal simulations. For velocities below vc, the polycrystalline interfaces evolve to a new steady state grain size distribution characterized by very large plastic deformation with larger grain sizes, time dependent coarsening and refinement, a graded size distribution in the direction normal to the sliding interface, and significantly larger frictional forces per unit area compared to similar single crystal sliding interfaces. We also find that for the Al-Ta interface the frictional properties are determined by the weaker Al material. This work was performed under the auspices of the U.S. Dept. of Energy under contract DE-AC52-06NA25396. The support of the LANL ASC-PEM program is gratefully acknowledged.

  19. Observations of Dynamic Strain Aging in Polycrystalline NiAl

    NASA Technical Reports Server (NTRS)

    Weaver, M. L.; Noebe, R. D.; Kaufman, M. J.

    1996-01-01

    Dynamic strain aging has been investigated at temperatures between 77 and 1100 K in eight polycrystalline NiAl alloys. The 0.2% offset yield stress and work hardening rates for these alloys generally decreased with increasing temperature. However, local plateaus or maxima were observed in conventional purity and carbon doped alloys at intermediate temperatures (600-900 K). This anomalous behavior was not observed in low interstitial high-purity, nitrogen doped, or in titanium doped materials. Low or negative strain rate sensitivities (SRS) were also observed in all eight alloys in this intermediate temperature range. Coincident with the occurrence of negative SRS was the occurrence of serrated flow in conventional purity alloys containing high concentrations of Si in addition to C. These phenomena have been attributed to dynamic strain aging (DSA). Chemical analysis of the alloys used in this study suggests that the main species causing strain aging in polycrystalline NiAl is C but indicate that residual Si impurities can enhance the strain aging effect.

  20. Collective dynamics underpins Rayleigh behavior in disordered polycrystalline ferroelectrics.

    PubMed

    Bintachitt, P; Jesse, S; Damjanovic, D; Han, Y; Reaney, I M; Trolier-McKinstry, S; Kalinin, S V

    2010-04-20

    Nanoscale and mesoscopic disorder and associated local hysteretic responses underpin the unique properties of spin and cluster glasses, phase-separated oxides, polycrystalline ferroelectrics, and ferromagnets alike. Despite the rich history of the field, the relationship between the statistical descriptors of hysteresis behavior such as Preisach density, and micro and nanostructure has remained elusive. By using polycrystalline ferroelectric capacitors as a model system, we now report quantitative nonlinearity measurements in 0.025-1 microm(3) volumes, approximately 10(6) times smaller than previously possible. We discover that the onset of nonlinear behavior with thickness proceeds through formation and increase of areal density of micron-scale regions with large nonlinear response embedded in a more weakly nonlinear matrix. This observation indicates that large-scale collective domain wall dynamics, as opposed to motion of noninteracting walls, underpins Rayleigh behavior in disordered ferroelectrics. The measurements provide evidence for the existence and extent of the domain avalanches in ferroelectric materials, forcing us to rethink 100-year old paradigms. PMID:20368462

  1. Breakdown of avalanche critical behaviour in polycrystalline plasticity.

    PubMed

    Richeton, Thiebaud; Weiss, Jérôme; Louchet, François

    2005-06-01

    Acoustic emission experiments on creeping ice as well as numerical simulations argue for a self-organization of collective dislocation dynamics during plastic deformation of single crystals into a scale-free pattern of dislocation avalanches characterized by intermittency, power-law distributions of avalanche sizes, complex space-time correlations and aftershock triggering. Here, we address the question of whether such scale-free, close-to-critical dislocation dynamics will still apply to polycrystals. We show that polycrystalline plasticity is also characterized by intermittency and dislocation avalanches. However, grain boundaries hinder the propagation of avalanches, as revealed by a finite (grain)-size effect on avalanche size distributions. We propose that the restraint of large avalanches builds up internal stresses that push temporally the dynamical system into a supercritical state, off the scale-invariant critical regime, and trigger secondary avalanches in neighbouring grains. This modifies the statistical properties of the avalanche population. The results might also bring into question the classical ways of modelling plasticity in polycrystalline materials, based on homogenization procedures. PMID:15880114

  2. GaAs Photovoltaics on Polycrystalline Ge Substrates

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Pal, AnnaMaria T.; McNatt, Jeremiah S.; Wolford, David S.; Landis, Geoffrey A.; Smith, Mark A.; Scheiman, David; Jenkins, Phillip P.; McElroy Bruce

    2007-01-01

    High efficiency III-V multijunction solar cells deposited on metal foil or even polymer substrates can provide tremendous advantages in mass and stowage, particularly for planetary missions. As a first step towards that goal, poly-crystalline p/i/n GaAs solar cells are under development on polycrystalline Ge substrates. Organo Metallic Vapor Phase Epitaxy (OMVPE) parameters for pre-growth bake, nucleation and deposition have been examined. Single junction p/i/n GaAs photovoltaic devices, incorporating InGaP front and back window layers, have been grown and processed. Device performance has shown a dependence upon the thickness of a GaAs buffer layer deposited between the Ge substrate and the active device structure. A thick (2 m) GaAs buffer provides for both increased average device performance as well as reduced sensitivity to variations in grain size and orientation. Illumination under IR light (lambda > 1 micron), the cells showed a Voc, demonstrating the presence of an unintended photoactive junction at the GaAs/Ge interface. The presence of this junction limited the efficiency to approx.13% (estimated with an anti-refection coating) due to the current mismatch and lack of tunnel junction interconnect.

  3. Quantum Hall effect in polycrystalline CVD graphene: grain boundaries impact

    NASA Astrophysics Data System (ADS)

    Ribeiro-Palau, Rebeca; Lafont, Fabien; Schopfer, Felicien; Poirier, Wilfrid; Bouchiat, Vincent; Han, Zhen; Cresti, Alessandro; Cummings, Aron; Roche, Stephan

    2014-03-01

    It was demonstrated by Janssen et al. (New J. Phys. 2011) that graphene could surpass GaAs for quantum Hall resistance standards with an accuracy better than 10-10. Graphene should render possible the realization of a standard operating at T > 4 K and B < 4 T, easing its dissemination towards industry. To materialize this goal scalable graphene with outstanding electronic transport properties is required. We present measurements performed in large area Hall bars made of polycrystalline CVD graphene on Si/SiO2, with a carrier mobility of 0.6 T-1. Even at 20.2 T and 300 mK, the Hall resistance plateaus are insufficiently quantized at ν = +/- 2 and +/- 6 . This is due to a high dissipation manifested by a longitudinal resistance which does not drop to zero. We pointed out unusual power-law temperature dependencies of Rxx and an exponential magnetic field dependence. We do not observe the common thermally activated or VRH behaviors. This can be attributed to the grain boundaries in the sample that short-circuit the edge states, as supported by our numerical simulations. This reveals new and peculiar aspects of the quantum Hall effect in polycrystalline systems. Another unexpected feature is the observation of the ν = 0 and 1 states in such low mobility systems.

  4. Limiting mechanisms in large-grain polycrystalline silicon Spatial homogeneity

    NASA Technical Reports Server (NTRS)

    Culik, J.; Grimes, K.

    1984-01-01

    An experiment to investigate the spatial homogeneity of large-grain polycrystalline silicon shows a number of performance-loss mechanisms. Arrays of up to 400 small (about 0.2 sq cm in area) photodiodes were fabricated on a selection of 10 cm x 10 cm polycrystalline silicon wafers. Measurements of the illuminated current-voltage (J-V) characteristics were used to generate maps of Voc, Jsc, and FF as a function of position; and dark J-V and LBIC analysis were used to determine the cause of low performance in areas with significantly degraded J-V characteristics. In addition to the presence of inclusions, which act as resistive shunts, the performance of many of the cells is limited by quasineutral recombination current, which may vary by up to an order of magnitude across a wafer. The increase is the result of either electrically-active grain boundaries or numerous subgrain boundaries within the grain bulk. In other isolated instances, the open-circuit voltage is reduced by excess space-charge recombination current that is not correlated with either grain or subgrain boundary activity.

  5. Field theory and diffusion creep predictions in polycrystalline aggregates

    NASA Astrophysics Data System (ADS)

    Villani, A.; Busso, E. P.; Forest, S.

    2015-07-01

    In polycrystals, stress-driven vacancy diffusion at high homologous temperatures leads to inelastic deformation. In this work, a novel continuum mechanics framework is proposed to describe the strain fields resulting from such a diffusion-driven process in a polycrystalline aggregate where grains and grain boundaries are explicitly considered. The choice of an anisotropic eigenstrain in the grain boundary region provides the driving force for the diffusive creep processes. The corresponding inelastic strain rate is shown to be related to the gradient of the vacancy flux. Dislocation driven deformation is then introduced as an additional mechanism, through standard crystal plasticity constitutive equations. The fully coupled diffusion-mechanical model is implemented into the finite element method and then used to describe the biaxial creep behaviour of FCC polycrystalline aggregates. The corresponding results revealed for the first time that such a coupled diffusion-stress approach, involving the gradient of the vacancy flux, can accurately predict the well-known macroscopic strain rate dependency on stress and grain size in the diffusion creep regime. They also predict strongly heterogeneous viscoplastic strain fields, especially close to grain boundaries triple junctions. Finally, a smooth transition from Herring and Coble to dislocation creep behaviour is predicted and compared to experimental results for copper.

  6. Origins of Folding Instabilities on Polycrystalline Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Beckmann, N.; Romero, P. A.; Linsler, D.; Dienwiebel, M.; Stolz, U.; Moseler, M.; Gumbsch, P.

    2014-12-01

    Wear and removal of material from polycrystalline metal surfaces is inherently connected to plastic flow. Here, plowing-induced unconstrained surface plastic flow on a nanocrystalline copper surface has been studied by massive molecular dynamics simulations and atomic force microscopy scratch experiments. In agreement with experimental findings, bulges in front of a model asperity develop into vortexlike fold patterns that mark the disruption of laminar flow. We identify dislocation-mediated plastic flow in grains with suitably oriented slip systems as the basic mechanism of bulging and fold formation. The observed folding can be fundamentally explained by the inhomogeneity of plasticity on polycrystalline surfaces which favors bulge formation on grains with suitably oriented slip system. This process is clearly distinct from Kelvin-Helmholtz instabilities in fluids, which have been previously suggested to resemble the formed surface fold patterns. The generated prow grows into a rough chip with stratified lamellae that are identified as the precursors of wear debris. Our findings demonstrate the importance of surface texture and grain structure engineering to achieve ultralow wear in metals.

  7. Creep and stress relaxation modeling of polycrystalline ceramic fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, James A.; Morscher, Gregory N.

    1994-01-01

    A variety of high performance polycrystalline ceramic fibers are currently being considered as reinforcement for high temperature ceramic matrix composites. However, under mechanical loading about 800 C, these fibers display creep related instabilities which can result in detrimental changes in composite dimensions, strength, and internal stress distributions. As a first step toward understanding these effects, this study examines the validity of a mechanism-based empirical model which describes primary stage tensile creep and stress relaxation of polycrystalline ceramic fibers as independent functions of time, temperature, and applied stress or strain. To verify these functional dependencies, a simple bend test is used to measure stress relaxation for four types of commercial ceramic fibers for which direct tensile creep data are available. These fibers include both nonoxide (SCS-6, Nicalon) and oxide (PRD-166, FP) compositions. The results of the Bend Stress Relaxation (BSR) test not only confirm the stress, time, and temperature dependencies predicted by the model, but also allow measurement of model empirical parameters for the four fiber types. In addition, comparison of model tensile creep predictions based on the BSR test results with the literature data show good agreement, supporting both the predictive capability of the model and the use of the BSR text as a simple method for parameter determination for other fibers.

  8. Creep and stress relaxation modeling of polycrystalline ceramic fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, James A.; Morscher, Gregory N.

    1991-01-01

    A variety of high performance polycrystalline ceramic fibers are currently being considered as reinforcement for high temperature ceramic matrix composites. However, under mechanical loading above 800 C, these fibers display creep-related instabilities which can result in detrimental changes in composite dimensions, strength, and internal stress distributions. As a first step toward understanding these effects, this study examines the validity of mechanistic-based empirical model which describes primary stage tensile creep and stress relaxation of polycrystalline ceramic fibers as independent functions of time, temperature, and applied stress or strain. To verify these functional dependencies, a simple bend test is used to measure stress relaxation for four types of commercial ceramic fibers for which direct tensile creep data are available. These fibers include both nonoxide (SCS-6, Nicalon) and oxide (PRD-166, FP) compositions. The results of the bend stress relaxation (BSR) test not only confirm the stress, time, and temperature dependencies predicted by the model but also allow measurement of model empirical parameters for the four fiber types. In addition, comparison of model predictions and BSR test results with the literature tensile creep data show good agreement, supporting both the predictive capability of the model and the use of the BSR test as a simple method for parameter determination for other fibers.

  9. Collective dynamics underpins Rayleigh behavior in disordered polycrystalline ferroelectrics

    PubMed Central

    Bintachitt, P.; Jesse, S.; Damjanovic, D.; Han, Y.; Reaney, I. M.; Trolier-McKinstry, S.; Kalinin, S. V.

    2010-01-01

    Nanoscale and mesoscopic disorder and associated local hysteretic responses underpin the unique properties of spin and cluster glasses, phase-separated oxides, polycrystalline ferroelectrics, and ferromagnets alike. Despite the rich history of the field, the relationship between the statistical descriptors of hysteresis behavior such as Preisach density, and micro and nanostructure has remained elusive. By using polycrystalline ferroelectric capacitors as a model system, we now report quantitative nonlinearity measurements in 0.025–1 μm3 volumes, approximately 106 times smaller than previously possible. We discover that the onset of nonlinear behavior with thickness proceeds through formation and increase of areal density of micron-scale regions with large nonlinear response embedded in a more weakly nonlinear matrix. This observation indicates that large-scale collective domain wall dynamics, as opposed to motion of noninteracting walls, underpins Rayleigh behavior in disordered ferroelectrics. The measurements provide evidence for the existence and extent of the domain avalanches in ferroelectric materials, forcing us to rethink 100-year old paradigms. PMID:20368462

  10. Dielectric and conducting behaviour of polycrystalline holmium octa-molybdate

    NASA Astrophysics Data System (ADS)

    Want, Basharat; Zahoor Ahmad, Bhat; Bhat, Bilal Hamid

    2014-09-01

    Polycrystalline holmium octa-molybdate spherulites have been obtained by using gel diffusion technique and characterized by different physio-chemical techniques. The surfaces of these spherulites are composed of nano-rod with an average diameter of about 80 nm. At room temperature the initial crystal structure is triclinic, space group P1. Thermal studies suggested a phase transition occurring in holmium octa-molybdate crystals at about 793 K. The electrical properties of the system have been studied as a function of frequency and temperature in the ranges of 20 Hz-3 MHz and 290-570 K, respectively. A giant dielectric constant and two loss peaks have been observed in the permittivity formalism. The conducting behaviour of the material is also discussed. The conductivity was found to be 1572 μ Ω-1 m-1 at room temperature and 3 MHz frequency. The conductivity of the polycrystalline material was attributed to the fact that it arises due to the migration of defects on the oxygen sub-lattice. Impedance studies were also performed in the frequency domain to infer the bulk and grain boundary contributions to the overall electric response of the material. The electrical responses have been attributed to the grain, grain-boundary, and interfacial effects.

  11. Wavelets based on Hermite cubic splines

    NASA Astrophysics Data System (ADS)

    Cvejnová, Daniela; Černá, Dana; Finěk, Václav

    2016-06-01

    In 2000, W. Dahmen et al. designed biorthogonal multi-wavelets adapted to the interval [0,1] on the basis of Hermite cubic splines. In recent years, several more simple constructions of wavelet bases based on Hermite cubic splines were proposed. We focus here on wavelet bases with respect to which both the mass and stiffness matrices are sparse in the sense that the number of nonzero elements in any column is bounded by a constant. Then, a matrix-vector multiplication in adaptive wavelet methods can be performed exactly with linear complexity for any second order differential equation with constant coefficients. In this contribution, we shortly review these constructions and propose a new wavelet which leads to improved Riesz constants. Wavelets have four vanishing wavelet moments.

  12. Face-Centered-Cubic Nanostructured Polymer Foams

    NASA Astrophysics Data System (ADS)

    Cui, C.; Baughman, R. H.; Liu, L. M.; Zakhidov, A. A.; Khayrullin, I. I.

    1998-03-01

    Beautifully iridescent polymer foams having Fm-3m cubic symmetry and periodicities on the scale of the wavelength of light have been synthesized by the templating of porous synthetic opals. These fabrication processes involve the filling of porous SiO2 opals (with typical cubic lattice parameters of 250 nm) with either polymers or polymer precursors, polymerization of the precursors if necessary, and removal of the fcc array of SiO2 balls to provide an all-polymer structure. The structures of these foams are similar to periodic minimal surfaces, although the Gaussian curvature can have both positive and negative values. Depending upon whether the internal surfaces of the opal are polymer filled or polymer coated, the polymer replica has either one or two sets of independent channels. We fill these channels with semiconductors, metals, or superconductors to provide electronic and optical materials with novel properties dependent on the nanoscale periodicity.

  13. Method of synthesizing cubic system boron nitride

    SciTech Connect

    Yuzu, S.; Sumiya, H.; Degawa, J.

    1987-10-13

    A method is described for synthetically growing cubic system boron nitride crystals by using boron nitride sources, solvents for dissolving the boron nitride sources, and seed crystals under conditions of ultra-high pressure and high temperature for maintaining the cubic system boron nitride stable. The method comprises the following steps: preparing a synthesizing vessel having at least two chambers, arrayed in order in the synthesizing vessel so as to be heated according to a temperature gradient; placing the solvents having different eutectic temperatures in each chamber with respect to the boron nitride sources according to the temperature gradient; placing the boron nitride source in contact with a portion of each of the solvents heated at a relatively higher temperature and placing at least a seed crystal in a portion of each of the solvents heated at a relatively lower temperature; and growing at least one cubic system boron nitride crystal in each of the solvents in the chambers by heating the synthesizing vessel for establishing the temperature gradient while maintaining conditions of ultra-high pressure and high temperature.

  14. Growth and characterization of cubic and non-cubic Ge nanocrystals

    NASA Astrophysics Data System (ADS)

    Mukherjee, S.; Pradhan, A.; Mukherjee, S.; Maitra, T.; Nayak, A.; Bhunia, S.

    2016-05-01

    Germanium nanocrystals with tetragonal (ST-12) and diamond like cubic (Ge-I) phases have been selectively grown by controlling the ionization and electrostatic potential of Ge clusters in an ion cluster beam deposition system. Predominantly tetragonal nanocrystals were obtained when grown using neutral clusters. The percentage of cubic phase increased when grown by ionizing the clusters and accelerating them towards substrates by applying electrostatic bias in the range of 1.5 -2.5 kV. Raman spectroscopic measurement showed strong peak at 275 cm-1 and 300 cm-1 for tetragonal and cubic Ge nanocrystals, respectively. TEM measurements showed crystalline lattice fringes of both type of the nanocrystals. The selected area electron diffraction patterns showed (111) and (210) as the dominating lattice planes for tetragonal nanocrystals while the cubic phases had (111), (311) and (331) as the prominent lattice planes. The optical absorption edge redshifted from 1.75 to 1.55 eV as the percentage of the cubic phases increased in the NC composition in the composite film.

  15. Impact of thermal annealing on physical properties of vacuum evaporated polycrystalline CdTe thin films for solar cell applications

    NASA Astrophysics Data System (ADS)

    Chander, Subhash; Dhaka, M. S.

    2016-06-01

    A study on impact of post-deposition thermal annealing on the physical properties of CdTe thin films is undertaken in this paper. The thin films of thickness 500 nm were grown on ITO and glass substrates employing thermal vacuum evaporation followed by post-deposition thermal annealing in air atmosphere within low temperature range 150-350 °C. These films were subjected to the XRD, UV-Vis NIR spectrophotometer, source meter, SEM coupled with EDS and AFM for structural, optical, electrical and surface topographical analysis respectively. The diffraction patterns reveal that the films are having zinc-blende cubic structure with preferred orientation along (111) and polycrystalline in nature. The crystallographic parameters are calculated and discussed in detail. The optical band gap is found in the range 1.48-1.64 eV and observed to decrease with thermal annealing. The current-voltage characteristics show that the CdTe films exhibit linear ohmic behavior. The SEM studies show that the as-grown films are homogeneous, uniform and free from defects. The AFM studies reveal that the surface roughness of films is observed to increase with annealing. The experimental results reveal that the thermal annealing has significant impact on the physical properties of CdTe thin films and may be used as absorber layer to the CdTe/CdS thin films solar cells.

  16. Deformation and Phase Transformation Processes in Polycrystalline NiTi and NiTiHf High Temperature Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Benafan, Othmane

    2012-01-01

    The deformation and transformation mechanisms of polycrystalline Ni49.9Ti50.1 and Ni50.3Ti29.7Hf20 (in at.%) shape memory alloys were investigated by combined experimental and modeling efforts aided by an in situ neutron diffraction technique at stress and temperature. The thermomechanical response of the low temperature martensite, the high temperature austenite phases, and changes between these two states during thermomechanical cycling were probed and reported. In the cubic austenite phase, stress-induced martensite, deformation twinning and slip processes were observed which helped in constructing a deformation map that contained the limits over which each of the identified mechanisms was dominant. Deformation of the monoclinic martensitic phase was also investigated where the microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were compared to the bulk macroscopic response. When cycling between these two phases, the evolution of inelastic strains, along with the shape setting procedures were examined and used for the optimization of the transformation properties as a function of deformation levels and temperatures. Finally, this work was extended to the development of multiaxial capabilities at elevated temperatures for the in situ neutron diffraction measurements of shape memory alloys on the VULCAN Diffractometer at Oak Ridge National Laboratory.

  17. Electric-field-induced paraelectric to ferroelectric phase transformation in prototypical polycrystalline BaTiO{sub 3}

    SciTech Connect

    Wang, Zhiyang; Hinterstein, Manuel; Daniels, John E.; Webber, Kyle G.; Hudspeth, Jessica M.

    2014-10-20

    An electric-field-induced paraelectric cubic to ferroelectric tetragonal phase transformation has been directly observed in prototypical polycrystalline BaTiO{sub 3} at temperatures above the Curie point (T{sub C}) using in situ high-energy synchrotron X-ray diffraction. The transformation persisted to a maximum temperature of 4 °C above T{sub C}. The nature of the observed field-induced transformation and the resulting development of domain texture within the induced phase were dependent on the proximity to the transition temperature, corresponding well to previous macroscopic measurements. The transition electric field increased with increasing temperature above T{sub C}, while the magnitude of the resultant tetragonal domain texture at the maximum electric field (4 kV mm{sup −1}) decreased at higher temperatures. These results provide insights into the phase transformation behavior of a prototypical ferroelectric and have important implications for the development of future large-strain phase-change actuator materials.

  18. Growth of poly-crystalline Cu films on Y substrates by picosecond pulsed laser deposition for photocathode applications

    NASA Astrophysics Data System (ADS)

    Gontad, F.; Lorusso, A.; Klini, A.; Manousaki, A.; Perrone, A.; Fotakis, C.

    2015-11-01

    In this work, the deposition of Cu thin films on Y substrates for photocathode applications by pulsed laser deposition employing picosecond laser pulses is reported and compared with the use of nanosecond pulses. The influence of power density (6-50 GW/cm2) on the ablation of the target material, as well as on the properties of the resulting film, is discussed. The material transfer from the target to the substrate surface was found to be rather efficient, in comparison to nanosecond ablation, leading to the growth of films with high thickness. Scanning electron microscope analysis indicated a quasi-continuous film morphology, at low power density values, becoming granular with increasing power density. The structural investigation, through X-ray diffraction, revealed the poly-crystalline nature of the films, with a preferential growth along the (111) crystallographic orientation of Cu cubic network. Finally, energy-dispersive X-ray spectroscopy showed a low contamination level of the grown films, demonstrating the potential of a PLD technique for the fabrication of Cu/Y patterned structures, with applications in radiofrequency electron gun technology.

  19. Polycrystalline ferroelectric or multiferroic oxide articles on biaxially textured substrates and methods for making same

    SciTech Connect

    Goyal, Amit; Shin, Junsoo

    2015-03-31

    A polycrystalline ferroelectric and/or multiferroic oxide article includes a substrate having a biaxially textured surface; at least one biaxially textured buffer layer supported by the substrate; and a biaxially textured ferroelectric or multiferroic oxide layer supported by the buffer layer. Methods for making polycrystalline ferroelectric and/or multiferroic oxide articles are also disclosed.

  20. Combined single-crystalline and polycrystalline CVD diamond substrates for diamond electronics

    SciTech Connect

    Vikharev, A. L. Gorbachev, A. M.; Dukhnovsky, M. P.; Muchnikov, A. B.; Ratnikova, A. K.; Fedorov, Yu. Yu.

    2012-02-15

    The fabrication of diamond substrates in which single-crystalline and polycrystalline CVD diamond form a single wafer, and the epitaxial growth of diamond films on such combined substrates containing polycrystalline and (100) single-crystalline CVD diamond regions are studied.

  1. Micromechanical modelling of partially molten and sand reinforced polycrystalline ice

    NASA Astrophysics Data System (ADS)

    Castelnau, O.; Duval, P.

    2009-12-01

    The viscoplastic behaviour of polycrystalline ice is strongly affected by the very strong anisotropy of ice crystals. Indeed, in the dislocations creep regime relevant for ice sheet flow, dislocation glide on the basal plane of ice single crystals leads to strain-rates ~6 order of magnitude larger than strain-rates that might be obtain if only non-basal glide is activated. At the polycrystal scale, this behaviour is responsible for a strong mechanical interaction between grains in the secondary (stationary) creep regime, and strain-rate is essentially partitioned between soft grains well-oriented for basal glide and hard grains exhibiting an unfavourable orientation for basal slip. As a consequence, the macroscopic flow stress at the polycrystal scale essentially depends on the resistance of the hardest slip systems or on the associated accommodation processes such as climb of basal dislocation on non-basal planes. Creep experiments performed on polycrystalline ices containing a small amount (less than 10% volume fraction) of liquid water show a dramatic increase of strain-rate, by more than one order of magnitude, compared to solid ice when deformed under similar thermo-mechanical conditions. Similarly, a strong hardening is observed when polycrystalline ice is reinforced by sand (which can be considered as a rigid phase here). This behaviour can be explained by micromechanical models, which aims at estimating the mechanical interactions between grains. For example, the presence of water releases stress concentrations at grain boundaries and therefore favours the inactivation of non-basal systems. To estimate such effect and to reach quantitative comparison with experimental data, we make use of the recent Second-Order homogenization mean-field approach of Ponte-Castaneda, based on self-consistent scheme. The advantage of this approach, which has been shown to provide excellent results when applied to many different non-linear composite materials, comes from the

  2. A continuum dislocation dynamics framework for plasticity of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Askari, Hesam Aldin

    The objective of this research is to investigate the mechanical response of polycrystals in different settings to identify the mechanisms that give rise to specific response observed in the deformation process. Particularly the large deformation of magnesium alloys and yield properties of copper in small scales are investigated. We develop a continuum dislocation dynamics framework based on dislocation mechanisms and interaction laws and implement this formulation in a viscoplastic self-consistent scheme to obtain the mechanical response in a polycrystalline system. The versatility of this method allows various applications in the study of problems involving large deformation, study of microstructure and its evolution, superplasticity, study of size effect in polycrystals and stochastic plasticity. The findings from the numerical solution are compared to the experimental results to validate the simulation results. We apply this framework to study the deformation mechanisms in magnesium alloys at moderate to fast strain rates and room temperature to 450 °C. Experiments for the same range of strain rates and temperatures were carried out to obtain the mechanical and material properties, and to compare with the numerical results. The numerical approach for magnesium is divided into four main steps; 1) room temperature unidirectional loading 2) high temperature deformation without grain boundary sliding 3) high temperature with grain boundary sliding mechanism 4) room temperature cyclic loading. We demonstrate the capability of our modeling approach in prediction of mechanical properties and texture evolution and discuss the improvement obtained by using the continuum dislocation dynamics method. The framework was also applied to nano-sized copper polycrystals to study the yield properties at small scales and address the observed yield scatter. By combining our developed method with a Monte Carlo simulation approach, the stochastic plasticity at small length scales

  3. High-pressure deformation and failure of polycrystalline ceramics

    NASA Astrophysics Data System (ADS)

    Zhang, Dongmei

    2005-11-01

    High-strength polycrystalline ceramics are increasingly being used for armor applications because of their light weight and superior ballistic performance over conventional armor steels. However, accurate material modeling needed in ceramic armor design remains a challenge because of their complex behavior under impact loading. A ceramic may display extremely high strength during rapid compression but lose tensile strength when the load reverses from compression to tension. A good understanding of the mechanisms governing the deformation and failure of ceramics under high-stress impact and a capability to accurately predict the resulting effective strengths of both intact and damaged ceramics are critically needed. To this end, a computational methodology for micromechanical analysis of polycrystalline materials has been developed. It combines finite element analysis with microstructural modeling based on the Voronoi polycrystals, and material modeling that considers nonlinear elasticity, crystal plasticity, intergranular shear damage during compression and intergranular Mode-I cracking during tension. Using this method, simulations have been carried out on polycrystalline alpha-6H silicon carbide and alpha-phase aluminum oxide to determine if microplasticity is a viable mechanism of inelastic deformation in ceramics undergoing high-pressure uniaxial-strain compression. Further, the competing roles of in-grain microplasticity and intergranular microdamage during a sequence of dynamic compression and tension have been studied. The results show that microplasticity is a more plausible mechanism than microcracking under uniaxial-strain compression. The deformation by limited slip systems can be highly heterogeneous so that a significant amount of grains may remain elastic and thus result in high macroscopic compressive strength. On the other hand, the failure evolution during dynamic load reversal from compression to tension can be well predicted by intergranular Mode

  4. Electron microscopy of gallium nitride growth on polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Webster, R. F.; Cherns, D.; Kuball, M.; Jiang, Q.; Allsopp, D.

    2015-11-01

    Transmission and scanning electron microscopy were used to examine the growth of gallium nitride (GaN) on polycrystalline diamond substrates grown by metalorganic vapour phase epitaxy with a low-temperature aluminium nitride (AlN) nucleation layer. Growth on unmasked substrates was in the (0001) orientation with threading dislocation densities ≈7 × 109 cm-2. An epitaxial layer overgrowth technique was used to reduce the dislocation densities further, by depositing silicon nitride stripes on the surface and etching the unmasked regions down to the diamond substrate. A re-growth was then performed on the exposed side walls of the original GaN growth, reducing the threading dislocation density in the overgrown regions by two orders of magnitude. The resulting microstructures and the mechanisms of dislocation reduction are discussed.

  5. Creep behavior for advanced polycrystalline SiC fibers

    SciTech Connect

    Youngblood, G.E.; Jones, R.H.; Kohyama, Akira

    1997-04-01

    A bend stress relaxation (BSR) test has been utilized to examine irradiation enhanced creep in polycrystalline SiC fibers which are under development for use as fiber reinforcement in SiC/SiC composite. Qualitative, S-shaped 1hr BSR curves were compared for three selected advanced SiC fiber types and standard Nicalon CG fiber. The temperature corresponding to the middle of the S-curve (where the BSR parameter m = 0.5) is a measure of a fiber`s thermal stability as well as it creep resistance. In order of decreasing thermal creep resistance, the measured transition temperatures were Nicalon S (1450{degrees}C), Sylramic (1420{degrees}C), Hi-Nicalon (1230{degrees}C) and Nicalon CG (1110{degrees}C).

  6. Ultrasonic Backscattering in Polycrystalline Materials of Pwr Components

    NASA Astrophysics Data System (ADS)

    Chassignole, B.; Dupond, O.; Fouquet, T.; Rupin, F.

    2011-06-01

    The ultrasonic examination of metallic components of Pressurized Water Reactors (PWR) is an important challenge for the nuclear industry. During the past decades, EDF R&D has undertaken numerous studies in order to improve the NDT process on these applications and to help to their qualification. The present paper deals with the problem of the structural noise which can potentially disturbs the ultrasonic inspection. In particular, this study proposes a modeling approach to simulate the ultrasonic scattering due to coarse grain structures of polycrystalline materials. The methodology is based on the mixing of a grain scale description of the material and a 2D finite element code (ATHENA) developed by EDF to simulate the ultrasonic propagation in isotropic and anisotropic elastic media. The modeling results are compared to experimental acquisitions on mock-ups containing artificial defects.

  7. Ultrafast dynamics of exciton fission in polycrystalline pentacene.

    PubMed

    Wilson, Mark W B; Rao, Akshay; Clark, Jenny; Kumar, R Sai Santosh; Brida, Daniele; Cerullo, Giulio; Friend, Richard H

    2011-08-10

    We use ultrafast transient absorption spectroscopy with sub-20 fs time resolution and broad spectral coverage to directly probe the process of exciton fission in polycrystalline thin films of pentacene. We observe that the overwhelming majority of initially photogenerated singlet excitons evolve into triplet excitons on an ∼80 fs time scale independent of the excitation wavelength. This implies that exciton fission occurs at a rate comparable to phonon-mediated exciton localization processes and may proceed directly from the initial, delocalized, state. The singlet population is identified due to the brief presence of stimulated emission, which is emitted at wavelengths which vary with the photon energy of the excitation pulse, a violation of Kasha's Rule that confirms that the lowest-lying singlet state is extremely short-lived. This direct demonstration that triplet generation is both rapid and efficient establishes multiple exciton generation by exciton fission as an attractive route to increased efficiency in organic solar cells. PMID:21755937

  8. Fabricating micro-instruments in surface-micromachined polycrystalline silicon

    SciTech Connect

    Comtois, J.H.; Michalicek, M.A.; Barron, C.C.

    1997-04-01

    Smaller, lighter instruments can be fabricated as Micro-Electro-Mechanical Systems (MEMS), having micron scale moving parts packaged together with associated control and measurement electronics. Batch fabrication of these devices will make economical applications such as condition-based machine maintenance and remote sensing. The choice of instrumentation is limited only by the designer`s imagination. This paper presents one genre of MEMS fabrication, surface-micromachined polycrystalline silicon (polysilicon). Two currently available but slightly different polysilicon processes are presented. One is the ARPA-sponsored ``Multi-User MEMS ProcesS`` (MUMPS), available commercially through MCNC; the other is the Sandia National Laboratories ``Sandia Ultra-planar Multilevel MEMS Technology`` (SUMMiT). Example components created in both processes will be presented, with an emphasis on actuators, actuator force testing instruments, and incorporating actuators into larger instruments.

  9. Radiation hardness of three-dimensional polycrystalline diamond detectors

    SciTech Connect

    Lagomarsino, Stefano Sciortino, Silvio; Bellini, Marco; Corsi, Chiara; Cindro, Vladimir; Kanxheri, Keida; Servoli, Leonello; Morozzi, Arianna; Passeri, Daniele; Schmidt, Christian J.

    2015-05-11

    The three-dimensional concept in particle detection is based on the fabrication of columnar electrodes perpendicular to the surface of a solid state radiation sensor. It permits to improve the radiation resistance characteristics of a material by lowering the necessary bias voltage and shortening the charge carrier path inside the material. If applied to a long-recognized exceptionally radiation-hard material like diamond, this concept promises to pave the way to the realization of detectors of unprecedented performances. We fabricated conventional and three-dimensional polycrystalline diamond detectors, and tested them before and after neutron damage up to 1.2 ×10{sup 16 }cm{sup −2}, 1 MeV-equivalent neutron fluence. We found that the signal collected by the three-dimensional detectors is up to three times higher than that of the conventional planar ones, at the highest neutron damage ever experimented.

  10. Structural templating of multiple polycrystalline layers in organic photovoltaic cells

    SciTech Connect

    Lassiter, Brian E; Lunt, Richard R; Renshaw, Kyle; Forrest, Stephen R.

    2010-09-01

    We demonstrate that organic photovoltaic cell performance is influenced by changes in the crystalline orientation of composite layer structures. A 1.5 nm thick self-organized, polycrystalline template layer of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) orients subsequently deposited layers of a diindenoperylene exciton blocking layer, and the donor, copper phthalocyanine (CuPc). Control over the crystalline orientation of the CuPc leads to changes in its frontier energy levels, absorption coefficient, and surface morphology, resulting in an increase of power conversion efficiency at 1 sun from 1.42 ± 0.04% to 2.19 ± 0.05% for a planar heterojunction and from 1.89 ± 0.05% to 2.49 ± 0.03% for a planar-mixed heterojunction.

  11. Modeling Crack Propagation in Polycrystalline Microstructure Using Variational Multiscale Method

    DOE PAGESBeta

    Sun, S.; Sundararaghavan, V.

    2016-01-01

    Crack propagation in a polycrystalline microstructure is analyzed using a novel multiscale model. The model includes an explicit microstructural representation at critical regions (stress concentrators such as notches and cracks) and a reduced order model that statistically captures the microstructure at regions far away from stress concentrations. Crack propagation is modeled in these critical regions using the variational multiscale method. In this approach, a discontinuous displacement field is added to elements that exceed the critical values of normal or tangential tractions during loading. Compared to traditional cohesive zone modeling approaches, the method does not require the use of any specialmore » interface elements in the microstructure and thus can model arbitrary crack paths. The capability of the method in predicting both intergranular and transgranular failure modes in an elastoplastic polycrystal is demonstrated under tensile and three-point bending loads.« less

  12. Electronic properties of polycrystalline graphene under large local strain

    SciTech Connect

    He, Xin; Tang, Ning E-mail: geweikun@mail.tsinghua.edu.cn Duan, Junxi; Mei, Fuhong; Meng, Hu; Lu, Fangchao; Xu, Fujun; Yang, Xuelin; Gao, Li; Wang, Xinqiang; Shen, Bo E-mail: geweikun@mail.tsinghua.edu.cn; Ge, Weikun E-mail: geweikun@mail.tsinghua.edu.cn

    2014-06-16

    To explore the transport properties of polycrystalline graphene under large tensile strain, a strain device has been fabricated using piezocrystal to load local strain onto graphene, up to 22.5%. Ionic liquid gate whose capability of tuning carrier density being much higher than that of a solid gate is used to survey the transfer characteristics of the deformed graphene. The conductance of the Dirac point and field effect mobility of electrons and holes is found to decrease with increasing strain, which is attributed to the scattering of the graphene grain boundaries, the strain induced change of band structure, and defects. However, the transport gap is still not opened. Our study is helpful to evaluate the application of graphene in stretchable electronics.

  13. Anisotropic thermal conductivity of thin polycrystalline oxide samples

    SciTech Connect

    Tiwari, A.; Boussois, K.; Nait-Ali, B.; Smith, D. S.; Blanchart, P.

    2013-11-15

    This paper reports about the development of a modified laser-flash technique and relation to measure the in-plane thermal diffusivity of thin polycrystalline oxide samples. Thermal conductivity is then calculated with the product of diffusivity, specific heat and density. Design and operating features for evaluating in-plane thermal conductivities are described. The technique is advantageous as thin samples are not glued together to measure in-plane thermal conductivities like earlier methods reported in literature. The approach was employed to study anisotropic thermal conductivity in alumina sheet, textured kaolin ceramics and montmorillonite. Since it is rare to find in-plane thermal conductivity values for such anisotropic thin samples in literature, this technique offers a useful variant to existing techniques.

  14. Predicting fracture in micron-scale polycrystalline silicon MEMS structures.

    SciTech Connect

    Hazra, Siddharth S.; de Boer, Maarten Pieter; Boyce, Brad Lee; Ohlhausen, James Anthony; Foulk, James W., III; Reedy, Earl David, Jr.

    2010-09-01

    Designing reliable MEMS structures presents numerous challenges. Polycrystalline silicon fractures in a brittle manner with considerable variability in measured strength. Furthermore, it is not clear how to use a measured tensile strength distribution to predict the strength of a complex MEMS structure. To address such issues, two recently developed high throughput MEMS tensile test techniques have been used to measure strength distribution tails. The measured tensile strength distributions enable the definition of a threshold strength as well as an inferred maximum flaw size. The nature of strength-controlling flaws has been identified and sources of the observed variation in strength investigated. A double edge-notched specimen geometry was also tested to study the effect of a severe, micron-scale stress concentration on the measured strength distribution. Strength-based, Weibull-based, and fracture mechanics-based failure analyses were performed and compared with the experimental results.

  15. Extracting Cu Diffusion Parameters in Polycrystalline CdTe

    SciTech Connect

    Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Guo, Da; Dragica, Vasileska; Ringhofer, Christian

    2014-06-13

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystal-line, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately.

  16. Attosecond dynamical Franz-Keldysh effect in polycrystalline diamond.

    PubMed

    Lucchini, M; Sato, S A; Ludwig, A; Herrmann, J; Volkov, M; Kasmi, L; Shinohara, Y; Yabana, K; Gallmann, L; Keller, U

    2016-08-26

    Short, intense laser pulses can be used to access the transition regime between classical and quantum optical responses in dielectrics. In this regime, the relative roles of inter- and intraband light-driven electronic transitions remain uncertain. We applied attosecond transient absorption spectroscopy to investigate the interaction between polycrystalline diamond and a few-femtosecond infrared pulse with intensity below the critical intensity of optical breakdown. Ab initio time-dependent density functional theory calculations, in tandem with a two-band parabolic model, accounted for the experimental results in the framework of the dynamical Franz-Keldysh effect and identified infrared induction of intraband currents as the main physical mechanism responsible for the observations. PMID:27563093

  17. Single crystal and polycrystalline CVD diamond for demanding optical applications

    NASA Astrophysics Data System (ADS)

    Dodson, J. M.; Brandon, J. R.; Dhillon, H. K.; Friel, I.; Geoghegan, S. L.; Mollart, T. P.; Santini, P.; Scarsbrook, G. A.; Twitchen, D. J.; Whitehead, A. J.; Wilman, J. J.; de Wit, H.

    2011-06-01

    Diamond's extremely wide transparency, combined with its other exceptional properties including hardness, strength and thermal conductivity make it a desirable material for optical windows. Polycrystalline diamond grown by chemical vapour deposition (CVD) has become the preferred window material for high power CO2 laser systems since its development in the 1990s. The range and availability of diamond materials is expanding, and in recent years has been extended to include CVD single crystal diamond. This paper reviews the quality of these materials, looking at optical scatter and absorption around 1 and 10 microns, along with their thermal and mechanical properties. We also discuss selection of appropriate grades and how they may best be integrated into demanding optical applications.

  18. Dependence of resistivity on the doping level of polycrystalline silicon

    NASA Technical Reports Server (NTRS)

    Fripp, A. L.

    1975-01-01

    The electrical resistivity of polycrystalline silicon films has been studied as a function of doping concentration and heat treatment. The films were grown by the chemical vapor decomposition of silane on oxidized silicon wafers. The resistivity of the as-deposited films was widely scattered but independent of dopant atom concentration at the lightly doped levels and was strong function of dopant level in the more heavily doped regions. Postdeposition heat treatments in an oxidizing atmosphere remove scatter in the data. The resultant resistivity for dopant levels less than 10 to the 16th atoms/per cu cm was approximately equal to that of intrinsic silicon. In the next 2 orders of magnitude increase in dopant level, the resistivity dropped 6 orders of magnitude. A model, based on high dopant atom segregation in the grain boundaries, is proposed to explain the results.

  19. Fabrication of translucent boron nitride dispersed polycrystalline silicon nitride ceramics

    NASA Astrophysics Data System (ADS)

    Joshi, B.; Fu, Z.; Niihara, K.; Lee, S. W.

    2011-03-01

    Optical transparency was achieved at infrared region and overall translucent silicon nitride was fabricated using hot press sintering (HPS). The increase in h-BN content decreased the optical transparency. Microstructral observations shows that the optical, mechanical and tribological properties of BN dispersed polycrystalline Si3N4 ceramics were affected by the density, α:β-phase ratio and content of h-BN in sintered ceramics. The hot pressed samples were prepared from the mixture of α-Si3N4, AlN, MgO and h-BN at 1850°C. The composite contained from 0.25 to 2 mass % BN powder with sintering aids (9% AlN + 3% MgO). Maximum transmittance of 57% was achieved for 0.25 mass % BN doped Si3N4 ceramics. Fracture toughness was increased and wear volume and friction coefficient were decreased with increase in BN content.

  20. A new directional solidification technique for polycrystalline solar grade silicon

    NASA Astrophysics Data System (ADS)

    Saito, T.; Shimura, A.; Ichikawa, S.

    A new directional solidification (casting) technique using powder mold releasing agent is described for producing polycrystalline solar grade silicon. Crack-free and stress-free growth of silicon was attainable with fused quartz crucibles coated with nitride powder, such as silicon nitride Si3 N4, on the inner crucible walls. The degree of nitrogen contamination was negligible because of the low nitrogen solubility in solid silicon. Other impurities contents were less than the ppm level. The average grain diameter was close to 0.1 cm. Diffused junction solar cells (n+/p structure) were fabricated by using this boron doped 1 ohm-cm material. An AM1 conversion efficiency of 12.4% on the cells of 20 cm sq area was obtained. The minority carrier diffusion length of this material was estimated to be greater than 80 microns.

  1. Resistive switching in polycrystalline YMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Bogusz, A.; Müller, A. D.; Blaschke, D.; Skorupa, I.; Bürger, D.; Scholz, A.; Schmidt, O. G.; Schmidt, H.

    2014-10-01

    We report a unipolar, nonvolatile resistive switching in polycrystalline YMnO3 thin films grown by pulsed laser deposition and sandwiched between Au top and Ti/Pt bottom electrodes. The ratio of the resistance in the OFF and ON state is larger than 103. The observed phenomena can be attributed to the formation and rupture of conductive filaments within the multiferroic YMnO3 film. The generation of conductive paths under applied electric field is discussed in terms of the presence of grain boundaries and charged domain walls inherently formed in hexagonal YMnO3. Our findings suggest that engineering of the ferroelectric domains might be a promising route for designing and fabrication of novel resistive switching devices.

  2. Structural templating of multiple polycrystalline layers in organic photovoltaic cells.

    PubMed

    Lassiter, Brian E; Lunt, Richard R; Renshaw, C Kyle; Forrest, Stephen R

    2010-09-13

    We demonstrate that organic photovoltaic cell performance is influenced by changes in the crystalline orientation of composite layer structures. A 1.5 nm thick self-organized, polycrystalline template layer of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) orients subsequently deposited layers of a diindenoperylene exciton blocking layer, and the donor, copper phthalocyanine (CuPc). Control over the crystalline orientation of the CuPc leads to changes in its frontier energy levels, absorption coefficient, and surface morphology, resulting in an increase of power conversion efficiency at 1 sun from 1.42 ± 0.04% to 2.19 ± 0.05% for a planar heterojunction and from 1.89 ± 0.05% to 2.49 ± 0.03% for a planar-mixed heterojunction. PMID:21165074

  3. Monitoring of deformation induced microcracking in polycrystalline NiAl

    SciTech Connect

    Wanner, A.; Schietinger, B.; Bidlingmaier, T.; Zalkind, H.; Arzt, E.

    1995-08-01

    Microcracking in polycrystalline near-stoichiometric NiAl produced by room temperature plastic deformation under uniaxial compression was investigated by means of optical microscopy, velocity of sound measurements, and acoustic emission monitoring. Results show that strains greater than 2% are required to produce microcrack populations which can be evaluated by microscopical investigation or velocity of sound measurements. However, acoustic emission monitoring during compression testing indicates that microcracking starts at about 0.7% compressive plastic strain which is identical with the typical tensile fracture strain for NiAl. Thus it is concluded that there is little or no stable microcracking prior to failure in tension. Acoustic emission results show also that the process of microcracking does not primarily occur during the applied compressive deformation. A considerable fraction of the microcracking takes place during the quasi-elastic unloading following deformation.

  4. Analysis of loss mechanisms in polycrystalline thin film solar cells

    NASA Astrophysics Data System (ADS)

    Sites, J. R.

    1990-08-01

    Our goal for thin-film polycrystalline solar cell analysis was to increase the useful information extracted from relatively straightforward electrical measurements. The strategy was to (1) systematize measurements and reporting, (2) organize results in terms of quantitative values for individual sources of current and voltage loss, and (3) evaluate possible analytical techniques to enhance precision and avoid pitfalls, and (4) insist on a viable physical explanation of each loss mechanism. Current-voltage, quantum efficiency, and capacitance measurements on CuInSe2 and CdTe solar cells from a variety of sources have been analyzed. In many cases losses were identified that may be lessened relatively easily. However, the operating voltage loss due to excessive forward recombination current throughout the depletion region remains the primary obstacle to efficiencies competitive with single crystal cells.

  5. Fatigue effect on polarization switching dynamics in polycrystalline bulk ferroelectrics

    NASA Astrophysics Data System (ADS)

    Zhukov, S.; Glaum, J.; Kungl, H.; Sapper, E.; Dittmer, R.; Genenko, Y. A.; von Seggern, H.

    2016-08-01

    Statistical distribution of switching times is a key information necessary to describe the dynamic response of a polycrystalline bulk ferroelectric to an applied electric field. The Inhomogeneous Field Mechanism (IFM) model offers a useful tool which allows extraction of this information from polarization switching measurements over a large time window. In this paper, the model was further developed to account for the presence of non-switchable regions in fatigued materials. Application of the IFM-analysis to bipolar electric cycling induced fatigue process of various lead-based and lead-free ferroelectric ceramics reveals different scenarios of property degradation. Insight is gained into different underlying fatigue mechanisms inherent to the investigated systems.

  6. Spherical silicon photonic microcavities: From amorphous to polycrystalline

    NASA Astrophysics Data System (ADS)

    Fenollosa, R.; Garín, M.; Meseguer, F.

    2016-06-01

    Shaping silicon as a spherical object is not an obvious task, especially when the object size is in the micrometer range. This has the important consequence of transforming bare silicon material in a microcavity, so it is able to confine light efficiently. Here, we have explored the inside volume of such microcavities, both in their amorphous and in their polycrystalline versions. The synthesis method, which is based on chemical vapor deposition, causes amorphous microspheres to have a high content of hydrogen that produces an onionlike distributed porous core when the microspheres are crystallized by a fast annealing regime. This substantially influences the resonant modes. However, a slow crystallization regime does not yield pores, and produces higher-quality-factor resonances that could be fitted to the Mie theory. This allows the establishment of a procedure for obtaining size calibration standards with relative errors of the order of 0.1%.

  7. Leakage current measurements of a pixelated polycrystalline CVD diamond detector

    NASA Astrophysics Data System (ADS)

    Zain, R. M.; Maneuski, D.; O'Shea, V.; Bates, R.; Blue, A.; Cunnigham, L.; Stehl, C.; Berderman, E.; Rahim, R. A.

    2013-01-01

    Diamond has several desirable features when used as a material for radiation detection. With the invention of synthetic growth techniques, it has become feasible to look at developing diamond radiation detectors with reasonable surface areas. Polycrystalline diamond has been grown using a chemical vapour deposition (CVD) technique by the University of Augsburg and detector structures fabricated at the James Watt Nanofabrication Centre (JWNC) in the University of Glasgow in order to produce pixelated detector arrays. The anode and cathode contacts are realised by depositing gold to produce ohmic contacts. Measurements of I-V characteristics were performed to study the material uniformity. The bias voltage is stepped from -1000V to 1000V to investigate the variation of leakage current from pixel to pixel. Bulk leakage current is measured to be less than 1nA.

  8. Ion implantation of erbium into polycrystalline cadmium telluride

    SciTech Connect

    Ushakov, V. V. Klevkov, Yu. V.; Dravin, V. A.

    2015-05-15

    The specific features of the ion implantation of polycrystalline cadmium telluride with grains 20–1000 μm in dimensions are studied. The choice of erbium is motivated by the possibility of using rare-earth elements as luminescent “probes” in studies of the defect and impurity composition of materials and modification of the composition by various technological treatments. From the microphotoluminescence data, it is found that, with decreasing crystal-grain dimensions, the degree of radiation stability of the material is increased. Microphotoluminescence topography of the samples shows the efficiency of the rare-earth probe in detecting regions with higher impurity and defect concentrations, including regions of intergrain boundaries.

  9. Polycrystalline metasurface perfect absorbers fabricated using microsphere photolithography.

    PubMed

    Qu, Chuang; Kinzel, Edward C

    2016-08-01

    Microsphere photolithography (MPL) is a practical, cost-effective nanofabrication technique. It uses self-assembled microspheres in contact with the photoresist as microlenses. The microspheres focus incident light to a sub-diffraction limited array of photonic jets in the photoresist. This Letter explores the MPL technique to pattern metal-insulator-metal metasurfaces with near-perfect absorption at mid-wave infrared (MWIR) frequencies. Experimental results are compared to electromagnetic simulations of both the exposure process and the metasurface response. The microsphere self-assembly technique results in a polycrystalline metasurface; however, the metal-insulator-metal structure is shown to be defect tolerant. While the MPL approach imposes geometric constraints on the metasurface design, once understood, the technique can be used to create functional devices. In particular, the ability to tune the resonant wavelength with the exposure dose raises the potential of hierarchical structures. PMID:27472578

  10. Stress enhanced diffusion of krypton ions in polycrystalline titanium

    SciTech Connect

    Nsengiyumva, S.; Raji, A. T.; Rivière, J. P.; Britton, D. T.; Härting, M.

    2014-07-14

    An experimental investigation on the mutual influence of pre-existing residual stress and point defect following ion implantation is presented. The study has been carried out using polycrystalline titanium samples energetically implanted with krypton ions at different fluences. Ion beam analysis was used to determine the concentration profile of the injected krypton ions, while synchrotron X-ray diffraction has been used for stress determination. Ion beam analysis and synchrotron X-ray diffraction stress profile measurements of the implanted titanium samples show a clear evidence of stress-enhanced diffusion of krypton ions in titanium. It is further observed that for the titanium samples implanted at low fluence, ion implantation modifies the pre-existing residual stress through the introduction of point and open volume defects. The stress fields resulting from the ion implantation act to drift the krypton inclusions towards the surface of titanium.

  11. Phosphorus Doping of Polycrystalline CdTe by Diffusion

    SciTech Connect

    Colegrove, Eric; Albin, David S.; Guthrey, Harvey; Harvey, Steve; Burst, James; Moutinho, Helio; Farrell, Stuart; Al-Jassim, Mowafak; Metzger, Wyatt K.

    2015-06-14

    Phosphorus diffusion in single crystal and polycrystalline CdTe material is explored using various methods. Dynamic secondary ion mass spectroscopy (SIMS) is used to determine 1D P diffusion profiles. A 2D diffusion model is used to determine the expected cross-sectional distribution of P in CdTe after diffusion anneals. Time of flight SIMS and cross-sectional cathodoluminescence corroborates expected P distributions. Devices fabricated with diffused P exhibit hole concentrations up to low 1015 cm-3, however a subsequent activation anneal enabled hole concentrations greater than 1016 cm-3. CdCl2 treatments and Cu based contacts were also explored in conjunction with the P doping process.

  12. Modeling Copper Diffusion in Polycrystalline CdTe Solar Cells

    SciTech Connect

    Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Guo, Da; Vasileska, Dragica; Ringhofer, Christain

    2014-06-06

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystalline, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately

  13. Growth of polycrystalline Heusler alloys for spintronic devices

    NASA Astrophysics Data System (ADS)

    Sagar, J.; Yu, C. N. T.; Lari, L.; Hirohata, A.

    2014-07-01

    We have prepared polycrystalline Co2FeSi thin films on a number of seed layers to optimize their structural and magnetic properties. Using a Cr/Ag combined seed layer, films have been produced with extremely low interfacial roughness (<1 nm) and controllable coercivities in the range 12-27 Oe. Such a structure would be suitable for the free layer in a spintronic device. Using a NiCr seed layer and IrMn as an antiferromagnetic layer a small exchange bias of ˜30 Oe has been achieved. However the use of a 0.5 nm Mn layer at the IrMn/Co2FeSi interface increases the exchange bias (Hex) to 375 Oe after annealing. This structure would be suitable for the pinned layer in a spintronic device.

  14. Defect engineering by ultrasound treatment in polycrystalline silicon

    SciTech Connect

    Ostapenko, S.; Jastrzebski, L.

    1995-08-01

    By applying ultrasound treatment (UST) to bulk and thin film polycrystalline Si (poly-Si) we have found a dramatic improvement of recombination and transport properties. The increasing of minority carrier lifetime by as much as one order of magnitude was found in short diffusion length regions, while exhibiting a strong dispersion for entire solar-grade poly-Si wafer. Relevant mechanisms are attributed to ultrasound processing on crystallographic defects, as well as UST stimulated dissociation of Fe-B pairs followed by Fe{sub i} gettering. A spectacular improvement of hydrogenation efficiency in poly-Si thin-films on glass substrate is demonstrated by resistivity study and confirmed using spatially resolved photoluminescence and nanoscale contact potential difference mapping. By applying UST to commercial solar cells we found the increasing of cell efficiency at low light excitation.

  15. Analytical and computational modeling of the mechanical response of polycrystalline and nanocrystalline metals

    NASA Astrophysics Data System (ADS)

    Fu, Hsueh-Hung

    Metallic materials with different grain sizes exhibit vasty differences in their mechanical behavior. For example, the mechanical strength of nanocrystalline materials is superior to those with coarse grain materials. In recent decades, many analytical and experimental efforts have been contributed to this new materials field. In this research, a computational and analytical study of the grain size effect on the behavior of polycrystalline and nanocrystalline copper. A phenomenological constitutive description of this scaling response is discussed and adopted to build the numerical model. Both elastic and plastic anisotropy are included in this investigation. The material is envisaged as a composite, comprised of the grain interior, with flow stress sigmafG, and grain boundary layer, with flow stress sigmafGB. The hardening rates in the grain interior and grain boundary are different as a result of differences in dislocation source densities and interactions. The material is modeled as a monocrystalline core surrounded by a mantle grain boundary with a higher work hardening rate response. The computational predictions of plastic flow as a function of grain size are made incorporating differences of dislocation accumulation rate in grain-boundary regions and grain interiors. To depict the deformation response of face-centered cubic copper, three material models are implemented into an Eulerian finite element hydrocode. In model I, three sets of crystals with hard, medium and soft orientations are randomly embedded in the computational domain; the flow stress is developed for isotropic von Mises plasticity from the experimental data of C23, C26 and C30. In model II, rate dependent crystal plasticity with planar double slip is implemented in the grain interiors to study the nonuniform deformation and localized plastic flow while the mechanical behavior of grain boundaries is defined as in model I. In model III, both the grain interior and grain boundary are modeled

  16. Cherenkov and Scintillation Properties of Cubic Zirconium

    NASA Technical Reports Server (NTRS)

    Christl, M.J.; Adams, J.H.; Parnell, T.A.; Kuznetsov, E.N.

    2008-01-01

    Cubic zirconium (CZ) is a high index of refraction (n =2.17) material that we have investigated for Cherenkov counter applications. Laboratory and proton accelerator tests of an 18cc sample of CZ show that the expected fast Cherenkov response is accompanied by a longer scintillation component that can be separated by pulse shaping. This presents the possibility of novel particle spectrometers which exploits both properties of CZ. Other high index materials being examined for Cherenkov applications will be discussed. Results from laboratory tests and an accelerator exposure will be presented and a potential application in solar energetic particle instruments will be discussed

  17. Craniofacial reconstruction using rational cubic ball curves.

    PubMed

    Majeed, Abdul; Mt Piah, Abd Rahni; Gobithaasan, R U; Yahya, Zainor Ridzuan

    2015-01-01

    This paper proposes the reconstruction of craniofacial fracture using rational cubic Ball curve. The idea of choosing Ball curve is based on its robustness of computing efficiency over Bezier curve. The main steps are conversion of Digital Imaging and Communications in Medicine (Dicom) images to binary images, boundary extraction and corner point detection, Ball curve fitting with genetic algorithm and final solution conversion to Dicom format. The last section illustrates a real case of craniofacial reconstruction using the proposed method which clearly indicates the applicability of this method. A Graphical User Interface (GUI) has also been developed for practical application. PMID:25880632

  18. Craniofacial Reconstruction Using Rational Cubic Ball Curves

    PubMed Central

    Majeed, Abdul; Mt Piah, Abd Rahni; Gobithaasan, R. U.; Yahya, Zainor Ridzuan

    2015-01-01

    This paper proposes the reconstruction of craniofacial fracture using rational cubic Ball curve. The idea of choosing Ball curve is based on its robustness of computing efficiency over Bezier curve. The main steps are conversion of Digital Imaging and Communications in Medicine (Dicom) images to binary images, boundary extraction and corner point detection, Ball curve fitting with genetic algorithm and final solution conversion to Dicom format. The last section illustrates a real case of craniofacial reconstruction using the proposed method which clearly indicates the applicability of this method. A Graphical User Interface (GUI) has also been developed for practical application. PMID:25880632

  19. Macroscopic elastic properties of textured ZrN-AlN polycrystalline aggregates: From ab initio calculations to grain-scale interactions

    NASA Astrophysics Data System (ADS)

    Holec, D.; Tasnádi, F.; Wagner, P.; Friák, M.; Neugebauer, J.; Mayrhofer, P. H.; Keckes, J.

    2014-11-01

    Despite the fast development of computational material modeling, the theoretical description of macroscopic elastic properties of textured polycrystalline aggregates starting from basic principles remains a challenging task. In this study we use a supercell-based approach to obtain the elastic properties of a random solid solution cubic Zr1 -xAlxN system as a function of the metallic sublattice composition and texture descriptors. The employed special quasirandom structures are optimized not only with respect to short-range-order parameters, but also to make the three cubic directions [1 0 0 ] , [0 1 0 ] , and [0 0 1 ] as similar as possible. In this way, only a small spread of elastic constant tensor components is achieved and an optimum trade-off between modeling of chemical disorder and computational limits regarding the supercell size and calculational time is proposed. The single-crystal elastic constants are shown to vary smoothly with composition, yielding x ≈0.5 an alloy constitution with an almost isotropic response. Consequently, polycrystals with this composition are suggested to have Young's modulus independent of the actual microstructure. This is indeed confirmed by explicit calculations of polycrystal elastic properties, both within the isotropic aggregate limit and with fiber textures with various orientations and sharpness. It turns out that for low AlN mole fractions, the spread of the possible Young's modulus data caused by the texture variation can be larger than 100 GPa. Consequently, our discussion of Young's modulus data of cubic Zr1 -xAlxN contains also the evaluation of the texture typical for thin films.

  20. Design of cubic-phase optical elements using subwavelength microstructures.

    PubMed

    Mirotznik, Mark S; van der Gracht, Joseph; Pustai, David; Mathews, Scott

    2008-01-21

    We describe a design methodology for synthesizing cubic-phase optical elements using two-dimensional subwavelength microstructures. We combined a numerical and experimental approach to demonstrate that by spatially varying the geometric properties of binary subwavelength gratings it is possible to produce a diffractive element with a cubic-phase profile. A test element was designed and fabricated for operation in the LWIR, approximately lambda=10.6 microm. Experimental results verify the cubic-phase nature of the element. PMID:18542199

  1. Surface properties of atomically flat poly-crystalline SrTiO3

    PubMed Central

    Woo, Sungmin; Jeong, Hoidong; Lee, Sang A.; Seo, Hosung; Lacotte, Morgane; David, Adrian; Kim, Hyun You; Prellier, Wilfrid; Kim, Yunseok; Choi, Woo Seok

    2015-01-01

    Comparison between single- and the poly-crystalline structures provides essential information on the role of long-range translational symmetry and grain boundaries. In particular, by comparing single- and poly-crystalline transition metal oxides (TMOs), one can study intriguing physical phenomena such as electronic and ionic conduction at the grain boundaries, phonon propagation, and various domain properties. In order to make an accurate comparison, however, both single- and poly-crystalline samples should have the same quality, e.g., stoichiometry, crystallinity, thickness, etc. Here, by studying the surface properties of atomically flat poly-crystalline SrTiO3 (STO), we propose an approach to simultaneously fabricate both single- and poly-crystalline epitaxial TMO thin films on STO substrates. In order to grow TMOs epitaxially with atomic precision, an atomically flat, single-terminated surface of the substrate is a prerequisite. We first examined (100), (110), and (111) oriented single-crystalline STO surfaces, which required different annealing conditions to achieve atomically flat surfaces, depending on the surface energy. A poly-crystalline STO surface was then prepared at the optimum condition for which all the domains with different crystallographic orientations could be successfully flattened. Based on our atomically flat poly-crystalline STO substrates, we envision expansion of the studies regarding the TMO domains and grain boundaries. PMID:25744275

  2. Multiply charged monopoles in cubic dimer model

    NASA Astrophysics Data System (ADS)

    Ganesh Jaya, Sreejith; Powell, Stephen

    2015-03-01

    The classical cubic dimer model is a 3D statistical mechanical system whose degrees of freedom are dimers that occupy the edges between nearest neighbour vertices of a cubic lattice. Dimer occupancies are subject to the local constraint that every vertex is associated with exactly one dimer. In the presence of an aligning interaction, it is known that the system exhibits an unconventional continuous thermal phase transition from a symmetry broken columnar phase to a Coulomb-phase. The transition is in the NCCP1 universality class, which also describes the Neel-VBS transition in the JQ model and the S =1/2 Heisenberg model with suppression of hedgehog defects. Using Monte-Carlo simulations of a pair of defects in a background of fluctuating dimers, we calculate the scaling exponents for fugacities of monopole defects of charge Q = 2 and 3 at this critical point. Our estimates suggest that Q = 3 monopoles are relevant and could therefore drive the JQ model away from the NCCP1 critical point on a hexagonal lattice.

  3. Polycrystalline GeSn thin films on Si formed by alloy evaporation

    NASA Astrophysics Data System (ADS)

    Kim, Munho; Fan, Wenjuan; Seo, Jung-Hun; Cho, Namki; Liu, Shih-Chia; Geng, Dalong; Liu, Yonghao; Gong, Shaoqin; Wang, Xudong; Zhou, Weidong; Ma, Zhenqiang

    2015-06-01

    Polycrystalline GeSn thin films on Si substrates with a Sn composition up to 4.5% have been fabricated and characterized. The crystalline structure, surface morphology, and infrared (IR) absorption coefficient of the annealed GeSn thin films were carefully investigated. It was found that the GeSn thin films with a Sn composition of 4.5% annealed at 450 °C possessed a desirable polycrystalline structure according to X-ray diffraction (XRD) analyses and Raman spectroscopy analyses. In addition, the absorption coefficient of the polycrystalline GeSn thin films in the IR region was significantly better than that of the single crystalline bulk Ge.

  4. Impact of graphene polycrystallinity on the performance of graphene field-effect transistors

    SciTech Connect

    Jiménez, David; Chaves, Ferney; Cummings, Aron W.; Van Tuan, Dinh; Kotakoski, Jani; Roche, Stephan

    2014-01-27

    We have used a multi-scale physics-based model to predict how the grain size and different grain boundary morphologies of polycrystalline graphene will impact the performance metrics of graphene field-effect transistors. We show that polycrystallinity has a negative impact on the transconductance, which translates to a severe degradation of the maximum and cutoff frequencies. On the other hand, polycrystallinity has a positive impact on current saturation, and a negligible effect on the intrinsic gain. These results reveal the complex role played by graphene grain boundaries and can be used to guide the further development and optimization of graphene-based electronic devices.

  5. Molecular Dynamics Simulations of Displacement Cascades in Single and Polycrystalline Zirconia

    SciTech Connect

    Du Jincheng

    2009-03-10

    Displacement cascades in zirconia have been studied using classical molecular dynamics simulations. Polycrystalline zirconia with nano-meter grains were created using Voronoi polyhedra construction and studied in comparison with single crystalline zirconia. The results show that displacement cascades with similar kinetic energy generated larger number of displaced atoms in polycrystalline than in the single crystal structure. The fraction of atoms with coordination number change was also higher in polycrystalline zirconia that was explained to be due to the diffusion of oxygen and relaxation at grain boundaries.

  6. Synthesis and optical properties of polycrystalline Li2Al2B2O7 (LABO)

    NASA Astrophysics Data System (ADS)

    Dagdale, S. R.; Muley, G. G.

    2016-05-01

    A polycrystalline lithium aluminum borate (Li2Al2B2O7, LABO) has been synthesized by using simple solid-state technique. The obtained LABO polycrystalline was characterized by powder X-ray diffraction; Fourier transform infrared (FT-IR) spectroscopy and second harmonic generation (SHG) efficiency measurement. The functional groups were identified using the FT-IR spectroscopic data. The SHG efficiency of the polycrystalline material was obtained by the classic Kurtz powder technique using a fundamental wavelength 1064 nm of Nd:YAG laser and it is found to be 1.4 times that of potassium dihydrogen phosphate (KDP).

  7. Epitaxial and polycrystalline GaAs solar cells using OM-CVD techniques

    NASA Technical Reports Server (NTRS)

    Yeh, Y. C. M.; Wang, K. L.; Shin, B. K.; Stirn, R. J.

    1980-01-01

    GaAs epitaxial films were grown by chemical vapor deposition using organo-metallic sources (OM-CVD) on single crystal and polycrystalline bulk GaAs, as well as on bulk polycrystalline and recrystallized thin-film Ge substrates. Details of Antireflecting Metal-Oxide-Semiconductor (AMOS) solar cells fabricated on GaAs films grown on bulk polycrystalline Ge and recrystallized Ge thin-film substrates will be discussed, as well as preliminary photovoltaic results obtained for n(+)/p homojunction structures.

  8. Preparation of cubic boron nitride thin film by the helicon wave plasma enhanced chemical vapor deposition

    SciTech Connect

    Kim, S.; Kim, I.; Kim, K.

    1996-12-01

    Cubic boron nitride ({ital c}-BN) film was deposited on Si(100) substrate using the chemical vapor deposition process assisted by high density plasma of Helicon wave with Borazine (B{sub 3}N{sub 3}H{sub 6}) precursor. It was found that the bombardment of ions with high flux and energy onto the film was necessarily required for synthesizing a {ital c}-BN film. Increasing a negative rf bias on the substrate increased the formation fraction of {ital c}-BN in the film. A nearly pure {ital c}-BN phase was synthesized at the conditions of plasma density in the reactor and rf substrate bias, above 10{sup 11} cm{sup {minus}3} and {minus}350 V, respectively. The phase identification of BN film was carried out by the transmission electron microscopy as well as Fourier transformed infrared spectroscopy. The infrared spectra for {ital c}-BN film synthesized at the rf bias of {minus}350 V appeared at 1093 cm{sup {minus}1} with a strong single peak, which is close to a value for the characteristic vibration mode of bulk {ital c}-BN (1065 cm{sup {minus}1}). The {ital c}-BN in the film was also confirmed and found to be a fine poly-crystalline with the grain sizes ranging from 200 to 400 A. {copyright} {ital 1996 American Institute of Physics.}

  9. Characterization of deformation near grain boundaries in polycrystalline metals

    NASA Astrophysics Data System (ADS)

    Seal, James Robert

    Understanding and describing plastic deformation in polycrystalline materials is fundamentally challenging due to the complex atomic rearrangements that must occur at grain boundaries. These atomic rearrangements can have long-range and substantial impacts on a material's bulk behavior and material properties. Thus, there is a significant need to develop new techniques to study, correlate, and describe deformation accommodation at grain boundaries. Understanding how grain boundaries accommodate plastic deformation at the microscale will provide new insight into the evolution of heterogeneous deformation, stress concentration, and damage nucleation. A series of comprehensive experiments have been conducted in order to develop a quantitative and crystallographically based understanding of the relationships between deformation behavior, material microstructure, and slip transfer mechanisms across grain boundaries in polycrystalline materials. Slip transfer events in polycrystalline metals were investigated using novel analysis techniques in scanning electron microscopy (SEM). The objective of these experiments was to correlate observations of slip transfer with a geometric parameter m', which can be used to identify and predict crystallographic arrangements that are better suited for slip transfer. An emphasis was placed on understanding how the parameter m' can be correlated with heterogeneities in local lattice orientations and local stresses near grain boundaries. A large population of slip transfer reactions across α/beta phase boundaries in Ti-5Al-2.5Sn were imaged by SEM and slip system activity was characterized using electron backscattered diffraction (EBSD) and slip trace analysis. Statistical correlations identified that slip transfer across the α/beta phase boundary was strongly influenced by slip plane alignment across the interface. Slip direction alignment was not strongly correlated to observations of slip transfer and the parameter m' was not useful

  10. Singlet exciton fission in polycrystalline pentacene: from photophysics toward devices.

    PubMed

    Wilson, Mark W B; Rao, Akshay; Ehrler, Bruno; Friend, Richard H

    2013-06-18

    Singlet exciton fission is the process in conjugated organic molecules bywhich a photogenerated singlet exciton couples to a nearby chromophore in the ground state, creating a pair of triplet excitons. Researchers first reported this phenomenon in the 1960s, an event that sparked further studies in the following decade. These investigations used fluorescence spectroscopy to establish that exciton fission occurred in single crystals of several acenes. However, research interest has been recently rekindled by the possibility that singlet fission could be used as a carrier multiplication technique to enhance the efficiency of photovoltaic cells. The most successful architecture to-date involves sensitizing a red-absorbing photoactive layer with a blue-absorbing material that undergoes fission, thereby generating additional photocurrent from higher-energy photons. The quest for improved solar cells has spurred a drive to better understand the fission process, which has received timely aid from modern techniques for time-resolved spectroscopy, quantum chemistry, and small-molecule device fabrication. However, the consensus interpretation of the initial studies using ultrafast transient absorption spectroscopy was that exciton fission was suppressed in polycrystalline thin films of pentacene, a material that would be otherwise expected to be an ideal model system, as well as a viable candidate for fission-sensitized photovoltaic devices. In this Account, we review the results of our recent transient absorption and device-based studies of polycrystalline pentacene. We address the controversy surrounding the assignment of spectroscopic features in transient absorption data, and illustrate how a consistent interpretation is possible. This work underpins our conclusion that singlet fission in pentacene is extraordinarily rapid (∼80 fs) and is thus the dominant decay channel for the photoexcited singlet exciton. Further, we discuss our demonstration that triplet excitons

  11. Multiple Diamond Anvil (MDA) apparatus using nano-polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Irifune, T.; Kunimoto, T.; Tange, Y.; Shinmei, T.; Isobe, F.; Kurio, A.; Funakoshi, K.

    2011-12-01

    Thanks to the great efforts by Dave Mao, Bill Bassett, Taro Takahashi, and their colleagues at the University of Rochester through 1960s-70s, diamond anvil cell (DAC) became a major tool to investigate the deep Earth after its invention by scientists at NBS in 1958. DAC can now cover almost the entire pressure and temperature regimes of the Earth's interior, which seems to have solved the longstanding debate on the crystal structure of iron under the P-T conditions of the Earth's inner core. In contrast, various types of static large-volume presses (LVP) have been invented, where tungsten carbide has conventionally been used as anvils. Kawai-type multianvil apparatus (MA), which utilize 6 first-stage harden steel and 8 tungsten carbide anvils, is the most successful LVP, and has been used for accurate measurements of phase transitions, physical properties, element partitioning, etc. at high pressure and temperature. However, pressures using tungsten carbide as the second-stage anvils have been limited to about 30 GPa due to significant plastic deformation of the anvils. Efforts have been made to expand this pressure limit by replacing tungsten carbide anvils with harder sintered diamond (SD) anvils over the last two decades, but the pressures available in KMA with SD anvils have still been limited to below 100 GPa. We succeeded to produce nano-polycrystalline diamond (NPD or HIME-Diamond) in 2003, which is known to have ultrahigh hardness, very high toughness and elastic stiffness, high transmittance of light, relatively low thermal conductivity. These properties are feasible for its use as anvils, and some preliminary experiments of application of NPD anvils to laser heated DAC have successfully made in the last few years. We are now able to synthesize NPD rods with about 1cm in both diameter and length using a newly constructed 6000-ton KMA at Geodynamics Research Center, Ehime University, and have just started to apply this new polycrystalline diamond as anvils

  12. Phase field modeling of grain growth in porous polycrystalline solids

    NASA Astrophysics Data System (ADS)

    Ahmed, Karim E.

    The concurrent evolution of grain size and porosity in porous polycrystalline solids is a technically important problem. All the physical properties of such materials depend strongly on pore fraction and pore and grain sizes and distributions. Theoretical models for the pore-grain boundary interactions during grain growth usually employ restrictive, unrealistic assumptions on the pore and grain shapes and motions to render the problem tractable. However, these assumptions limit the models to be only of qualitative nature and hence cannot be used for predictions. This has motivated us to develop a novel phase field model to investigate the process of grain growth in porous polycrystalline solids. Based on a dynamical system of coupled Cahn-Hilliard and All en-Cahn equations, the model couples the curvature-driven grain boundary motion and the migration of pores via surface diffusion. As such, the model accounts for all possible interactions between the pore and grain boundary, which highly influence the grain growth kinetics. Through a formal asymptotic analysis, the current work demonstrates that the phase field model recovers the corresponding sharp-interface dynamics of the co-evolution of grain boundaries and pores; this analysis also fixes the model kinetic parameters in terms of real materials properties. The model was used to investigate the effect of porosity on the kinetics of grain growth in UO2 and CeO2 in 2D and 3D. It is shown that the model captures the phenomenon of pore breakaway often observed in experiments. Pores on three- and four- grain junctions were found to transform to edge pores (pores on two-grain junction) before complete separation. The simulations demonstrated that inhomogeneous distribution of pores and pore breakaway lead to abnormal grain growth. The simulations also showed that grain growth kinetics in these materials changes from boundary-controlled to pore-controlled as the amount of porosity increases. The kinetic growth

  13. New method for fast morphological characterization of organic polycrystalline films by polarized optical microscopy

    NASA Astrophysics Data System (ADS)

    He, Xiao-Chuan; Yang, Jian-Bing; Yan, Dong-Hang; Weng, Yu-Xiang

    2015-07-01

    A new method to visualize the large-scale crystal grain morphology of organic polycrystalline films is proposed. First, optical anisotropic transmittance images of polycrystalline zinc phthalocyanine (ZnPc) films vacuum deposited by weak epitaxial growth (WEG) method were acquired with polarized optical microscopy (POM). Then morphology properties including crystal grain size, distribution, relative orientation, and crystallinity were derived from these images by fitting with a transition dipole model. At last, atomic force microscopy (AFM) imaging was carried out to confirm the fitting and serve as absolute references. This method can be readily generalized to other organic polycrystalline films, thus providing an efficient way to access the large-scale morphologic properties of organic polycrystalline films, which may prove to be useful in industry as a film quality monitoring method. Project supported by the National Natural Science Foundation of China (Grant No. 20933010) and the National Basic Research Program of China (Grant No. 2013CB834800).

  14. Computational characterizations on the grain-size-dependent properties of polycrystalline nanomaterials

    NASA Astrophysics Data System (ADS)

    Hyun, Sangil; Park, Youngho; Kim, Hyo-tae

    2015-12-01

    The microstructures of real nanomaterials can be quite complex with variety of grain sizes aligned in different crystal orientations and structural defects possibly created in a fabrication process. Material properties of these polycrystalline materials are generally known strongly dependent on the nanoscale morphology. First principle calculations based on the density functional theory need to be employed in these atomic characterizations; however, it may not be suitable for the polycrystalline nanomaterials for which large number of atoms is required in the simulation model. Instead, a mesoscale computer simulation scheme is employed to investigate these morphology-dependent mechanical properties of polycrystalline materials. We demonstrated the Voronoi construction of various polycrystalline atomic models such as two-dimensional graphene and three-dimensional silicon carbide. General behavior of the mechanical characteristics of the bulk nanostructured silicon carbide (SiC) was addressed, particularly the contribution of grain sizes. From this study, the optimal grain size was determined near 10 nm under tensile and compressive deformations.

  15. Polycrystalline Thin-Film Research: Copper Indium Gallium Diselenide (Fact Sheet)

    SciTech Connect

    Not Available

    2011-06-01

    Capabilities fact sheet for the National Center for Photovoltaics: Polycrystalline Thin-Film Research: Copper Indium Gallium Diselenide that includes scope, core competencies and capabilities, and contact/web information.

  16. Platinum-induced structural collapse in layered oxide polycrystalline films

    SciTech Connect

    Wang, Jianlin; Liu, Changhui; Huang, Haoliang; Fu, Zhengping; Peng, Ranran E-mail: yllu@ustc.edu.cn; Zhai, Xiaofang; Lu, Yalin E-mail: yllu@ustc.edu.cn

    2015-03-30

    Effect of a platinum bottom electrode on the SrBi{sub 5}Fe{sub 1−x}Co{sub x}Ti{sub 4}O{sub 18} layered oxide polycrystalline films was systematically studied. The doped cobalt ions react with the platinum to form a secondary phase of PtCoO{sub 2}, which has a typical Delafossite structure with a weak antiferromagnetism and an exceptionally high in-plane electrical conductivity. Formation of PtCoO{sub 2} at the interface partially consumes the cobalt dopant and leads to the structural collapsing from 5 to 4 layers, which was confirmed by X-ray diffraction and high resolution transmission electron microscopy measurements. Considering the weak magnetic contribution from PtCoO{sub 2}, the observed ferromagnetism should be intrinsic of the Aurivillius compounds. Ferroelectric properties were also indicated by the piezoresponse force microscopy. In this work, the platinum induced secondary phase at the interface was observed, which has a strong impact on Aurivillius structural configuration and thus the ferromagnetic and ferroelectric properties.

  17. Photoluminescence of silicon after deposition of polycrystalline diamond films

    SciTech Connect

    Aminev, D. F.; Bagaev, V. S.; Galkina, T. I.; Klokov, A. Yu. Krivobok, V. S.; Ralchenko, V. G.; Savel'ev, A. V.

    2009-09-15

    Low-temperature (5K) photoluminescence of silicon substrates in the range 0.8-1.2 eV is studied before and after deposition of polycrystalline diamond films. The diamond films were deposited in the microwave plasma onto high-purity dislocation-free silicon (with the resitivity {rho} {approx} 3 k{Omega} cm) subjected to mechanical polishing or more delicate chemical and mechanical polishing. The deposition temperature was 750-850 deg. C. In the photoluminescence spectra of the samples with the substrates polished chemically and mechanically, two lines, D{sub 1} and D{sub 2}, corresponding to the dislocation-related emission are recorded. Generation of dislocations in the substrates is caused by efficient adhesion of the diamond film and, as a result, by internal stresses that relax with the formation of dislocations. The experimental spectra are practically identical to the photoluminescence spectra observed in silicon ({rho} {approx} 100 {Omega} cm) with the density of dislocations {approx}10{sup 4} cm{sup -2}.

  18. High-Efficiency Polycrystalline Thin Film Tandem Solar Cells.

    PubMed

    Kranz, Lukas; Abate, Antonio; Feurer, Thomas; Fu, Fan; Avancini, Enrico; Löckinger, Johannes; Reinhard, Patrick; Zakeeruddin, Shaik M; Grätzel, Michael; Buecheler, Stephan; Tiwari, Ayodhya N

    2015-07-16

    A promising way to enhance the efficiency of CIGS solar cells is by combining them with perovskite solar cells in tandem devices. However, so far, such tandem devices had limited efficiency due to challenges in developing NIR-transparent perovskite top cells, which allow photons with energy below the perovskite band gap to be transmitted to the bottom cell. Here, a process for the fabrication of NIR-transparent perovskite solar cells is presented, which enables power conversion efficiencies up to 12.1% combined with an average sub-band gap transmission of 71% for photons with wavelength between 800 and 1000 nm. The combination of a NIR-transparent perovskite top cell with a CIGS bottom cell enabled a tandem device with 19.5% efficiency, which is the highest reported efficiency for a polycrystalline thin film tandem solar cell. Future developments of perovskite/CIGS tandem devices are discussed and prospects for devices with efficiency toward and above 27% are given. PMID:26266847

  19. An anisotropic flow law for incompressible polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Placidi, Luca; Hutter, Kolumban

    2005-11-01

    New and explicit anisotropic constitutive equations between the stretching and deviatoric stress tensors for the two- and three-dimensional cases of incompressible polycrystalline materials are presented. The anisotropy is assumed to be driven by an Orientation Distribution Function (ODF). The polycrystal is composed of transversally isotropic crystallites, the lattice orientation of which can be characterized by a single unit vector. The proposed constitutive equations are valid for any frame of reference and for every state of deformation. The basic assumption of this method is that the principle directions of the stretching and of the stress deviator are the same in the isotropic as well as in the anisotropic case. This means that the proposed constitutive laws are able to model the effects of anisotropy only via a change of the fluidity due to a change of the ODF. Such an assumption is justified to guarantee that, besides knowledge of the parameters involved in the isotropic constitutive equation, the anisotropic material response is completely characterized by only one additional parameter, a type of enhancement factor. Explicit comparisons with experimental data are conducted for Ih ice.

  20. Intergranular stress distributions in polycrystalline aggregates of irradiated stainless steel

    NASA Astrophysics Data System (ADS)

    Hure, J.; El Shawish, S.; Cizelj, L.; Tanguy, B.

    2016-08-01

    In order to predict InterGranular Stress Corrosion Cracking (IGSCC) of post-irradiated austenitic stainless steel in Light Water Reactor (LWR) environment, reliable predictions of intergranular stresses are required. Finite elements simulations have been performed on realistic polycrystalline aggregate with recently proposed physically-based crystal plasticity constitutive equations validated for neutron-irradiated austenitic stainless steel. Intergranular normal stress probability density functions are found with respect to plastic strain and irradiation level, for uniaxial loading conditions. In addition, plastic slip activity jumps at grain boundaries are also presented. Intergranular normal stress distributions describe, from a statistical point of view, the potential increase of intergranular stress with respect to the macroscopic stress due to grain-grain interactions. The distributions are shown to be well described by a master curve once rescaled by the macroscopic stress, in the range of irradiation level and strain considered in this study. The upper tail of this master curve is shown to be insensitive to free surface effect, which is relevant for IGSCC predictions, and also relatively insensitive to small perturbations in crystallographic texture, but sensitive to grain shapes.

  1. Properties of boron-doped thin films of polycrystalline silicon

    SciTech Connect

    Merabet, Souad

    2013-12-16

    The properties of polycrystalline-silicon films deposited by low pressure chemical vapor deposition and doped heavily in situ boron-doped with concentration level of around 2×10{sup 20}cm{sup −3} has been studied. Their properties are analyzed using electrical and structural characterization means by four points probe resistivity measurements and X-ray diffraction spectra. The thermal-oxidation process are performed on sub-micron layers of 200nm/c-Si and 200nm/SiO{sub 2} deposited at temperatures T{sub d} ranged between 520°C and 605°C and thermally-oxidized in dry oxygen ambient at 945°C. Compared to the as-grown resistivity with silicon wafers is known to be in the following sequence <ρ{sub 200nm/c−Si}> < <ρ{sub 200nm/SiO2}> and <ρ{sub 520}> < <ρ{sub 605}>. The measure X-ray spectra is shown, that the Bragg peaks are marked according to the crystal orientation in the film deposited on bare substrates (poly/c-Si), for the second series of films deposited on bare oxidized substrates (poly/SiO{sub 2}) are clearly different.

  2. Memristive Phenomena in Polycrystalline Single Layer MoS2

    NASA Astrophysics Data System (ADS)

    Sangwan, Vinod; Jariwala, Deep; Kim, In-Soo; Chen, Kan-Sheng; Marks, Tobin; Lauhon, Lincoln; Hersam, Mark; Hersam Laboratory Team

    Recently, a new class of layered two-dimensional semiconductors has shown promise for various electronic applications. In particular, ultrathin transition metal dichalcogenides (e.g. MoS2) present a host of attractive features such as high carrier mobility and tunable band-gap. However, available growth methods produce polycrystalline films with grain-boundaries and point defects that can be detrimental in conventional electronic devices. In contrast, we have developed unconventional device structures that exploit these defects for useful electronic functions. In particular, we observe grain-boundary mediated memristive phenomena in single layer MoS2 transistors. Memristor current-voltage characteristics depend strongly on the topology of grain-boundaries in MoS2. A grain boundary directly connecting metal electrodes produces thermally assisted switching with dynamic negative differential resistance, whereas a grain boundary bisecting the channel shows non-filamentary soft-switching. In addition, devices with intersecting grain boundaries in the channel show bipolar resistive switching with high on/off ratios up to ~103. Furthermore, the gate electrode in the field-effect geometry can be used to control the absolute resistance of the on and off states. Correlated electrostatic force microscopy, photoluminescence, and Raman microscopy reveal the role of sulfur vacancies in the switching mechanism. This abstract is replacing MAR16-2015-004166 that had exceeded the character limit.

  3. Memristive Phenomena in Polycrystalline Single Layer MoS2

    NASA Astrophysics Data System (ADS)

    Sangwan, Vinod; Jariwala, Deep; Kim, In-Soo; Chen, Kan-Sheng; Marks, Tobin; Lauhon, Lincoln; Hersam, Mark; Hersam Laboratory Team

    Recently, a new class of layered two-dimensional semiconductors has shown promise for various electronic applications. In particular, single layer transition metal dichalcogenides (e.g. MoS2) present a host of attractive features such as high electrical conductivity, tunable band-gap, and strong light-matter interaction. However, available growth methods produce large-area polycrystalline films with grain-boundaries and point defects that can be detrimental in conventional electronic devices. In contrast, we have developed unconventional device structures that exploit these defects for useful electronic functions. In particular, we observe grain-boundary mediated memristive phenomena in single layer MoS2 transistors. Memristor current-voltage characteristics depend strongly on the topology of grain-boundaries in MoS2. A grain boundary directly connecting metal electrodes produces thermally assisted switching with dynamic negative differential resistance, whereas a grain boundary bisecting the channel shows non-filamentary soft-switching. In addition, devices with intersecting grain boundaries in the channel show bipolar resistive switching with high on/off ratios up to ~103. Furthermore, the gate electrode in the field-effect geometry can be used to control the absolute resistance of the on and off states. Complementary electrostatic force microscopy, photoluminescence, and Raman microscopy reveal the role of sulfur vacancies in the switching mechanism.

  4. Rapid epitaxy-free graphene synthesis on silicidated polycrystalline platinum

    PubMed Central

    Babenko, Vitaliy; Murdock, Adrian T.; Koós, Antal A.; Britton, Jude; Crossley, Alison; Holdway, Philip; Moffat, Jonathan; Huang, Jian; Alexander-Webber, Jack A.; Nicholas, Robin J.; Grobert, Nicole

    2015-01-01

    Large-area synthesis of high-quality graphene by chemical vapour deposition on metallic substrates requires polishing or substrate grain enlargement followed by a lengthy growth period. Here we demonstrate a novel substrate processing method for facile synthesis of mm-sized, single-crystal graphene by coating polycrystalline platinum foils with a silicon-containing film. The film reacts with platinum on heating, resulting in the formation of a liquid platinum silicide layer that screens the platinum lattice and fills topographic defects. This reduces the dependence on the surface properties of the catalytic substrate, improving the crystallinity, uniformity and size of graphene domains. At elevated temperatures growth rates of more than an order of magnitude higher (120 μm min−1) than typically reported are achieved, allowing savings in costs for consumable materials, energy and time. This generic technique paves the way for using a whole new range of eutectic substrates for the large-area synthesis of 2D materials. PMID:26175062

  5. HighP–TNano-Mechanics of Polycrystalline Nickel

    PubMed Central

    2007-01-01

    We have conducted highP–Tsynchrotron X-ray and time-of-flight neutron diffraction experiments as well as indentation measurements to study equation of state, constitutive properties, and hardness of nanocrystalline and bulk nickel. Our lattice volume–pressure data present a clear evidence of elastic softening in nanocrystalline Ni as compared with the bulk nickel. We show that the enhanced overall compressibility of nanocrystalline Ni is a consequence of the higher compressibility of the surface shell of Ni nanocrystals, which supports the results of molecular dynamics simulation and a generalized model of a nanocrystal with expanded surface layer. The analytical methods we developed based on the peak-profile of diffraction data allow us to identify “micro/local” yield due to high stress concentration at the grain-to-grain contacts and “macro/bulk” yield due to deviatoric stress over the entire sample. The graphic approach of our strain/stress analyses can also reveal the corresponding yield strength, grain crushing/growth, work hardening/softening, and thermal relaxation under highP–Tconditions, as well as the intrinsic residual/surface strains in the polycrystalline bulks. From micro-indentation measurements, we found that a low-temperature annealing (T < 0.4 Tm) hardens nanocrystalline Ni, leading to an inverse Hall–Petch relationship. We explain this abnormal Hall–Petch effect in terms of impurity segregation to the grain boundaries of the nanocrystalline Ni. PMID:21794186

  6. Electrical conductivity of the polycrystalline films of p-terphenyl

    NASA Astrophysics Data System (ADS)

    Tkaczyk, S. W.

    1999-04-01

    Some results of p-terphenyl thin films investigations are presented. The mechanism of DC conductivity within unordered polycrystalline structures of p-terphenyl was investigated. The measurements were carried out for p-terphenyl films' thickness varying from 2 micrometers up to 15 micrometers . During the experiment the polarization voltage and temperature were changed from 0 to 200 V and 15 to 325 K, respectively. The p-terphenyl films were supplied with gold and aluminum electrodes. The obtained results and their analysis indicate that the injection of charge from the electrodes into the area of the investigated material proceeds by field- and thermoemission. The charge transport through the material's bulk is controlled by traps (hopping mechanism and Poole- Frenkel phenomenon). The determined values of the activation energy are in the range of kT (for the hopping area at low temperatures) through 0.06 eV in the range of 100 - 200 K to about 0.6 eV in the metallic conductivity area (220 - 320 K).

  7. Polycrystalline Mercuric Iodide Films on CMOS Readout Arrays

    PubMed Central

    Hartsough, Neal E.; Iwanczyk, Jan S.; Nygard, Einar; Malakhov, Nail; Barber, William C.; Gandhi, Thulasidharan

    2009-01-01

    We have created high-resolution x-ray imaging devices using polycrystalline mercuric iodide (HgI2) films grown directly onto CMOS readout chips using a thermal vapor transport process. Images from prototype 400×400 pixel HgI2-coated CMOS readout chips are presented, where the pixel grid is 30 μm × 30 μm. The devices exhibited sensitivity of 6.2 μC/Rcm2 with corresponding dark current of ∼2.7 nA/cm2, and a 80 μm FWHM planar image response to a 50 μm slit aperture. X-ray CT images demonstrate a point spread function sufficient to obtain a 50 μm spatial resolution in reconstructed CT images at a substantially reduced dose compared to phosphor-coated readouts. The use of CMOS technology allows for small pixels (30 μm), fast readout speeds (8 fps for a 3200×3200 pixel array), and future design flexibility due to the use of well-developed fabrication processes. PMID:20161098

  8. Electrical measurements on ion-implanted LPCVD polycrystalline silicon films

    NASA Astrophysics Data System (ADS)

    Huang, Ruey-Shing; Cheng, Chin-Hsiung; Liu, J. C.; Lee, M. K.; Chen, C. T.

    1983-07-01

    The electrical conduction properties of ion implanted polycrystalline silicon films have been studied. The polysilicon films were deposited by pyrolysis of silane at 647°C in LPCVD system onto oxide-coated silicon wafers to a thickness of 0.6 μm. Dopants were itroducd by implanting with boron or phosphorus ions, accelerated to 145 keV; doses ranged from 1 × 10 12 cm -2 to 1 × 10 15 cm -2. Film resistivities spanning 8 orders of magnitude were obtained using this doping range. Current-voltage characteristics of polysilicon resistors were measured at temperatures ranging from 24 to 140°C. The associated barrier heights and activation energies were derived. The grain-boundary trapping states density was estimated to be 5 × 10 12 cm -2. We found that both dopant atom segregation and carrier trapping at the grain boundaries play important roles in polysilicon electrical conduction properties. However, within the dose range studies, the dopant atom segragation is most detrimental to the film conductivity for doses < 1 × 10 13 cm -2; as the dose is increased, carrier trapping effects become more pronounced for doses up to 5 × 10 14 cm -2. For doses ⩾ 5 × 10 14 cm -2, conduction due to carriers tunneling through the potential barriers at grain boundaries has to be considered.

  9. Nanophotoactivity of Porphyrin Functionalized Polycrystalline ZnO Films.

    PubMed

    Rogero, Celia; Pickup, David F; Colchero, Jaime; Azaceta, Eneko; Tena-Zaera, Ramón; Palacios-Lidón, Elisa

    2016-07-01

    Kelvin probe force microscopy in darkness and under illumination is reported to provide nanoscale-resolved surface photovoltage maps of hybrid materials. In particular, nanoscale charge injection and charge recombination mechanisms occurring in ZnO polycrystalline surfaces functionalized with Protoporphyrin IX (H2PPIX) are analyzed. Local surface potential and surface photovoltage maps not only reveal that upon molecular adsorption the bare ZnO work function increases, but also they allow study of its local dependence. Nanometer-sized regions not correlated with apparent topographic features were identified, presenting values significantly different from the average work function. Depending on the region, the response to the light excitation is different, distinguishing two relaxation processes, one faster than the other. This behavior can be explained in terms of electrons trapped closed to the molecule-semiconductor interface or electrons pushed into the ZnO bulk, respectively. Moreover, the origin of these differences is correlated with the H2PPIX-ZnO bonding and molecules configuration and aggregation. The chenodeoxycholic acid (CDCA) coadsorption leads to a more homogeneous surface potential distribution, confirming the antiaggregate effect of this additive, while the surface photovoltage is mostly dominated by the slow relaxation component. This work reveals the complexity of real device architectures with ill-defined surfaces even in a relatively simple system with only one type of dye molecule and hightlights the importance of nanoscale characterization with appropriate tools. PMID:27303943

  10. Magnetization reversal in individual micrometer-sized polycrystalline Permalloy rings

    NASA Astrophysics Data System (ADS)

    Moore, T. A.; Hayward, T. J.; Tse, D. H. Y.; Bland, J. A. C.; Castaño, F. J.; Ross, C. A.

    2005-03-01

    The magnetization reversal of individual 2 μm and 5 μm diameter polycrystalline Permalloy rings, with respective widths 0.75 μm and 1 μm, thickness 45 nm, has been investigated by focused magneto-optic Kerr effect (MOKE) magnetometry. Micromagnetic simulation of the reversal in the 2 μm diameter ring reveals that the onion-to-vortex state switching occurs by nucleation and subsequent annihilation of vortex walls that span the width of the ring, and that the vortex-to-reverse-onion state switching occurs by expansion of a reverse domain. The hysteresis loop shows good agreement with the experimental MOKE loop. Measurements of the switching through one-half of a 5 μm diameter ring enable the determination of the circulation of the vortex states accessed during one applied field cycle. The rings switch via one vortex state (either clockwise or anticlockwise) on both downward and upward applied field sweeps. The number of applied field cycles spent switching via one vortex state before changing to switch via the opposite vortex state is random, likely to be due to the history of the spin configuration and thermal fluctuations.

  11. Electrical conduction and deep levels in polycrystalline diamond films

    NASA Astrophysics Data System (ADS)

    Gonon, P.; Deneuville, A.; Fontaine, F.; Gheeraert, E.

    1995-12-01

    We have studied the dark conductivity (field, temperature, and frequency dependence), and the photoconductivity in undoped polycrystalline diamond films. Detailed analysis reveals that either of two alternative models can be invoked to explain all the observed features of the dark conductivity. The first model is a Hill-type hopping conduction involving the presence of discrete acceptor states located at 0.91 eV above the valence band with a density around 1017 cm-3. The second model involves the presence of a band-tail of acceptor states extending about 1 eV above the valence band. In this case, variable range hopping conduction dominates at low fields with a density of states at the Fermi level around 5×1015 cm-3 eV-1, while space charge limited currents dominate at high fields. The states controlling the dark conductivity give rise to photoconduction with a threshold around 0.85 eV and a peak at 1.1 eV. The shape of the photoconductivity spectrum suggests that lattice relaxation (with a Franck-Condon shift around 0.08 eV) occurs at these states. Peaks in the photoconductivity at 1.4 eV and at 1.9 eV give evidence for the presence of deeper states in these films.

  12. Creep behavior for advanced polycrystalline SiC fibers

    SciTech Connect

    Youngblood, G.E.; Jones, R.H.; Kohyama, Akira

    1997-08-01

    A bend stress relaxation (BSR) test is planned to examine irradiation enhanced creep in polycrystalline SiC fibers which are under development for use as fiber reinforcement in SiC/SiC composite. Baseline 1 hr and 100 hr BSR thermal creep {open_quotes}m{close_quotes} curves have been obtained for five selected advanced SiC fiber types and for standard Nicalon CG fiber. The transition temperature, that temperature where the S-shaped m-curve has a value 0.5, is a measure of fiber creep resistance. In order of decreasing thermal creep resistance, with the 100 hr BSR transition temperature given in parenthesis, the fibers ranked: Sylramic (1261{degrees}C), Nicalon S (1256{degrees}C), annealed Hi Nicalon (1215{degrees}C), Hi Nicalon (1078{degrees}C), Nicalon CG (1003{degrees}C) and Tyranno E (932{degrees}C). The thermal creep for Sylramic, Nicalon S, Hi Nicalon and Nicalon CG fibers in a 5000 hr irradiation creep BSR test is projected from the temperature dependence of the m-curves determined during 1 and 100 hr BSR control tests.

  13. Platinum-induced structural collapse in layered oxide polycrystalline films

    NASA Astrophysics Data System (ADS)

    Wang, Jianlin; Huang, Haoliang; Liu, Changhui; Fu, Zhengping; Zhai, Xiaofang; Peng, Ranran; Lu, Yalin

    2015-03-01

    Effect of a platinum bottom electrode on the SrBi5Fe1-xCoxTi4O18 layered oxide polycrystalline films was systematically studied. The doped cobalt ions react with the platinum to form a secondary phase of PtCoO2, which has a typical Delafossite structure with a weak antiferromagnetism and an exceptionally high in-plane electrical conductivity. Formation of PtCoO2 at the interface partially consumes the cobalt dopant and leads to the structural collapsing from 5 to 4 layers, which was confirmed by X-ray diffraction and high resolution transmission electron microscopy measurements. Considering the weak magnetic contribution from PtCoO2, the observed ferromagnetism should be intrinsic of the Aurivillius compounds. Ferroelectric properties were also indicated by the piezoresponse force microscopy. In this work, the platinum induced secondary phase at the interface was observed, which has a strong impact on Aurivillius structural configuration and thus the ferromagnetic and ferroelectric properties.

  14. Polycrystalline-Diamond MEMS Biosensors Including Neural Microelectrode-Arrays.

    PubMed

    Varney, Michael W; Aslam, Dean M; Janoudi, Abed; Chan, Ho-Yin; Wang, Donna H

    2011-01-01

    Diamond is a material of interest due to its unique combination of properties, including its chemical inertness and biocompatibility. Polycrystalline diamond (poly-C) has been used in experimental biosensors that utilize electrochemical methods and antigen-antibody binding for the detection of biological molecules. Boron-doped poly-C electrodes have been found to be very advantageous for electrochemical applications due to their large potential window, low background current and noise, and low detection limits (as low as 500 fM). The biocompatibility of poly-C is found to be comparable, or superior to, other materials commonly used for implants, such as titanium and 316 stainless steel. We have developed a diamond-based, neural microelectrode-array (MEA), due to the desirability of poly-C as a biosensor. These diamond probes have been used for in vivo electrical recording and in vitro electrochemical detection. Poly-C electrodes have been used for electrical recording of neural activity. In vitro studies indicate that the diamond probe can detect norepinephrine at a 5 nM level. We propose a combination of diamond micro-machining and surface functionalization for manufacturing diamond pathogen-microsensors. PMID:25586924

  15. Polycrystalline-Diamond MEMS Biosensors Including Neural Microelectrode-Arrays

    PubMed Central

    Varney, Michael W.; Aslam, Dean M.; Janoudi, Abed; Chan, Ho-Yin; Wang, Donna H.

    2011-01-01

    Diamond is a material of interest due to its unique combination of properties, including its chemical inertness and biocompatibility. Polycrystalline diamond (poly-C) has been used in experimental biosensors that utilize electrochemical methods and antigen-antibody binding for the detection of biological molecules. Boron-doped poly-C electrodes have been found to be very advantageous for electrochemical applications due to their large potential window, low background current and noise, and low detection limits (as low as 500 fM). The biocompatibility of poly-C is found to be comparable, or superior to, other materials commonly used for implants, such as titanium and 316 stainless steel. We have developed a diamond-based, neural microelectrode-array (MEA), due to the desirability of poly-C as a biosensor. These diamond probes have been used for in vivo electrical recording and in vitro electrochemical detection. Poly-C electrodes have been used for electrical recording of neural activity. In vitro studies indicate that the diamond probe can detect norepinephrine at a 5 nM level. We propose a combination of diamond micro-machining and surface functionalization for manufacturing diamond pathogen-microsensors. PMID:25586924

  16. Improvements in cast polycrystalline silicon PV manufacturing technology

    NASA Astrophysics Data System (ADS)

    Wohlgemuth, John H.

    1997-02-01

    The objectives of this NREL sponsored Photovoltaic Manufacturing Technology (PVMaT) Program are to advance Solarex's cast polycrystalline silicon manufacturing technology, reduce module production cost in half, increase module performance and expand Solarex's commercial production capacity by a factor of three. To meet these objectives Solarex has: 1) Modified the casting process and stations and is now casting larger ingots in production; 2) Developed wire saw technology to cut wafers with less kerf loss and has transferred this technology to production; 3) Developed a laboratory process to increase cell efficiencies using back surface fields, mechanical texturing and gettering; 4) Modified the casting, wires saw and cell processes in order to fabricate larger (15.2 cm by 15.2 cm) wafers and cells; 5) Improved the automated assembly of modules, reducing labor requirements and increasing throughput; and 6) Developed a frameless module with a lower cost backsheet and a simple, low cost electrical termination system. Solarex is now in the process of developing the equipment necessary for automated handling of thin 15.2 cm by 15.2 cm wafers and cells. This paper will discuss the efforts during the first two and a half years of the program.

  17. Distributions of methyl group rotational barriers in polycrystalline organic solids

    SciTech Connect

    Beckmann, Peter A. E-mail: wangxianlong@uestc.edu.cn; Conn, Kathleen G.; Mallory, Clelia W.; Mallory, Frank B.; Rheingold, Arnold L.; Rotkina, Lolita; Wang, Xianlong E-mail: wangxianlong@uestc.edu.cn

    2013-11-28

    We bring together solid state {sup 1}H spin-lattice relaxation rate measurements, scanning electron microscopy, single crystal X-ray diffraction, and electronic structure calculations for two methyl substituted organic compounds to investigate methyl group (CH{sub 3}) rotational dynamics in the solid state. Methyl group rotational barrier heights are computed using electronic structure calculations, both in isolated molecules and in molecular clusters mimicking a perfect single crystal environment. The calculations are performed on suitable clusters built from the X-ray diffraction studies. These calculations allow for an estimate of the intramolecular and the intermolecular contributions to the barrier heights. The {sup 1}H relaxation measurements, on the other hand, are performed with polycrystalline samples which have been investigated with scanning electron microscopy. The {sup 1}H relaxation measurements are best fitted with a distribution of activation energies for methyl group rotation and we propose, based on the scanning electron microscopy images, that this distribution arises from molecules near crystallite surfaces or near other crystal imperfections (vacancies, dislocations, etc.). An activation energy characterizing this distribution is compared with a barrier height determined from the electronic structure calculations and a consistent model for methyl group rotation is developed. The compounds are 1,6-dimethylphenanthrene and 1,8-dimethylphenanthrene and the methyl group barriers being discussed and compared are in the 2–12 kJ mol{sup −1} range.

  18. Stress-rupture behavior of small diameter polycrystalline alumina fibers

    NASA Technical Reports Server (NTRS)

    Yun, Hee Mann; Goldsby, Jon C.; Dicarlo, James A.

    1993-01-01

    Continuous length polycrystalline alumina fibers are candidates as reinforcement in high temperature composite materials. Interest therefore exists in characterizing the thermomechanical behavior of these materials, obtaining possible insights into underlying mechanisms, and understanding fiber performance under long term use. Results are reported on the time-temperature dependent strength behavior of Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Below 1000 C and 100 hours, Nextel 610 with the smaller grain size had a greater fast fracture and rupture strength than Fiber FP. The time exponents for stress-rupture of these fibers were found to decrease from approximately 13 at 900 C to below 3 near 1050 C, suggesting a transition from slow crack growth to creep rupture as the controlling fracture mechanism. For both fiber types, an effective activation energy of 690 kJ/mol was measured for rupture. This allowed stress-rupture predictions to be made for extended times at use temperatures below 1000 C.

  19. Finite elastic-plastic deformation of polycrystalline metals

    NASA Technical Reports Server (NTRS)

    Iwakuma, T.; Nemat-Nasser, S.

    1984-01-01

    Applying Hill's self-consistent method to finite elastic-plastic deformations, the overall moduli of polycrystalline solids are estimated. The model predicts a Bauschinger effect, hardening, and formation of vertex or corner on the yield surface for both microscopically non-hardening and hardening crystals. The changes in the instantaneous moduli with deformation are examined, and their asymptotic behavior, especially in relation to possible localization of deformations, is discussed. An interesting conclusion is that small second-order quantities, such as shape changes of grains and residual stresses (measured relative to the crystal elastic moduli), have a first-order effect on the overall response, as they lead to a loss of the overall stability by localized deformation. The predicted incipience of localization for a uniaxial deformation in two dimensions depends on the initial yield strain, but the orientation of localization is slightly less than 45 deg with respect to the tensile direction, although the numerical instability makes it very difficult to estimate this direction accurately.

  20. Conformal window manufacturing process development and demonstration for polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Smith, Nathan E.; Gould, Alan R.; Hordin, Tom; Medicus, Kate; Walters, Mark; Brophy, Matthew; DeGroote Nelson, Jessica

    2013-09-01

    Conformal windows pose new and unique challenges to manufacturing due to the shape, measurement of, and requested hard polycrystalline materials. Their non-rotationally symmetric shape and high departure surfaces do not lend themselves to traditional optical fabrication processes. The hard crystalline materials are another challenge due to increased processing time and possibility of grain decoration. We have developed and demonstrated a process for manufacturing various conformal windows out of fused silica, glass, zinc-sulfide multispectral, and spinel. The current process involves CNC generation/grinding, VIBE polishing, and sub-aperture figure correction. The CNC generation step incorporates an ultrasonic assisted grinding machine; the machine settings and tool are being continuously optimized for minimal sub-surface damage and surface form error. In VIBE, polishing to less than 5 nm rms surface roughness while maintaining overall form error is accomplished with a full aperture conformal polishing tool and with rapid removal rates. The final sub-aperture polishing step corrects the overall form error. Currently we utilize our CMM for surface form measurement and have shown that we can produce spinel conformal windows with form error within +/-10 micrometers of the nominal shape, without grain decoration. This conformal window manufacturing process is continuously optimized for cost reduction and precision of the final optic.

  1. Surface Analysis of 4-Aminothiophenol Adsorption at Polycrystalline Platinum Electrodes

    NASA Technical Reports Server (NTRS)

    Rosario-Castro, Belinda I.; Fachini, Estevao R.; Contes, Enid J.; Perez-Davis, Marla E.; Cabrera, Carlos R.

    2008-01-01

    Formation of self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) on polycrystalline platinum electrodes has been studied by surface analysis and electrochemistry techniques. The 4-ATP monolayer was characterized by cyclic voltammetry (CV), Raman spectroscopy, reflection absorption infrared (RAIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) experiments give an idea about the packing quality of the monolayer. RAIR and Raman spectra for 4-ATP modified platinum electrodes showed the characteristic adsorption bands for neat 4-ATP indicating the adsorption of 4-ATP molecules on platinum surface. The adsorption on platinum was also evidenced by the presence of sulfur and nitrogen peaks by XPS survey spectra of the modified platinum electrodes. High resolution XPS studies and RAIR spectrum for platinum electrodes modified with 4-ATP indicate that molecules are sulfur-bonded to the platinum surface. The formation of S-Pt bond suggests that ATP adsorption gives up an amino terminated SAM. Thickness of the monolayer was evaluated via angle-resolved XPS (AR-XPS) analyses. Derivatization of 4-ATP SAM was performed using 16-Br hexadecanoic acid.

  2. The interpretation of polycrystalline coherent inelastic neutron scattering from aluminium

    PubMed Central

    Roach, Daniel L.; Ross, D. Keith; Gale, Julian D.; Taylor, Jon W.

    2013-01-01

    A new approach to the interpretation and analysis of coherent inelastic neutron scattering from polycrystals (poly-CINS) is presented. This article describes a simulation of the one-phonon coherent inelastic scattering from a lattice model of an arbitrary crystal system. The one-phonon component is characterized by sharp features, determined, for example, by boundaries of the (Q, ω) regions where one-phonon scattering is allowed. These features may be identified with the same features apparent in the measured total coherent inelastic cross section, the other components of which (multiphonon or multiple scattering) show no sharp features. The parameters of the model can then be relaxed to improve the fit between model and experiment. This method is of particular interest where no single crystals are available. To test the approach, the poly-CINS has been measured for polycrystalline aluminium using the MARI spectrometer (ISIS), because both lattice dynamical models and measured dispersion curves are available for this material. The models used include a simple Lennard-Jones model fitted to the elastic constants of this material plus a number of embedded atom method force fields. The agreement obtained suggests that the method demonstrated should be effective in developing models for other materials where single-crystal dispersion curves are not available. PMID:24282332

  3. Polycrystalline CVD diamond pixel array detector for nuclear particles monitoring

    NASA Astrophysics Data System (ADS)

    Pacilli, M.; Allegrini, P.; Girolami, M.; Conte, G.; Spiriti, E.; Ralchenko, V. G.; Komlenok, M. S.; Khomic, A. A.; Konov, V. I.

    2013-02-01

    We report the 90Sr beta response of a polycrystalline diamond pixel detector fabricated using metal-less graphitic ohmic contacts. Laser induced graphitization was used to realize multiple squared conductive contacts with 1mm × 1mm area, 0.2 mm apart, on one detector side while on the other side, for biasing, a 9mm × 9mm large graphite contact was realized. A proximity board was used to wire bonding nine pixels at a time and evaluate the charge collection homogeneity among the 36 detector pixels. Different configurations of biasing were experimented to test the charge collection and noise performance: connecting the pixel at the ground potential of the charge amplifier led to best results and minimum noise pedestal. The expected exponential trend typical of beta particles has been observed. Reversing the bias polarity the pulse height distribution (PHD) does not changes and signal saturation of any pixel was observed around ±200V (0.4 V/μm). Reasonable pixels response uniformity has been evidenced even if smaller pitch 50÷100 μm structures need to be tested.

  4. Deformation twinning in a polycrystalline magnesium alloy during dynamic compression

    NASA Astrophysics Data System (ADS)

    Hustedt, Caleb; Lloyd, Jeffrey; Lambert, Paul; Kannan, Vignesh; Casem, Daniel; Ramesh, K. T.; Sinclair, Nicholas; Becker, Richard; Hufnagel, Todd

    We report the results of combined in situ x-ray diffraction studies and crystal plasticity modeling of deformation twinning in polycrystalline magnesium during dynamic compression. Diffraction experiments were conducted at the Dynamic Compression Sector (DCS) of the Advanced Photon Source, on magnesium alloy (AZ31B) specimens (with various crystallographic textures) loaded at strain rates of ~1000 s-1 in a compression Kolsky bar. The diffraction patterns, recorded with temporal resolution of 5-10 microseconds, provide information about the evolution of crystallographic texture during deformation, which we interpret in terms of the twinning mechanism (so-called ``extension'' or ``tensile'' twinning). We compare our observations quantitatively with predictions of the evolution of crystallographic texture from an efficient reduced crystal plasticity model. This model explicitly accounts for basal slip and extension twinning on a rate-independent basis, but treats other mechanisms (pyramidal and prismatic slip) as isotropic, rate-dependent functions. This combination yields substantial improvements in efficiency over full crystal-plasticity models while retaining key aspects of the most important deformation mechanisms.

  5. A smoothing algorithm using cubic spline functions

    NASA Technical Reports Server (NTRS)

    Smith, R. E., Jr.; Price, J. M.; Howser, L. M.

    1974-01-01

    Two algorithms are presented for smoothing arbitrary sets of data. They are the explicit variable algorithm and the parametric variable algorithm. The former would be used where large gradients are not encountered because of the smaller amount of calculation required. The latter would be used if the data being smoothed were double valued or experienced large gradients. Both algorithms use a least-squares technique to obtain a cubic spline fit to the data. The advantage of the spline fit is that the first and second derivatives are continuous. This method is best used in an interactive graphics environment so that the junction values for the spline curve can be manipulated to improve the fit.

  6. Black holes in a cubic Galileon universe

    NASA Astrophysics Data System (ADS)

    Babichev, E.; Charmousis, C.; Lehébel, A.; Moskalets, T.

    2016-09-01

    We find and study the properties of black hole solutions for a subclass of Horndeski theory including the cubic Galileon term. The theory under study has shift symmetry but not reflection symmetry for the scalar field. The Galileon is assumed to have linear time dependence characterized by a velocity parameter. We give analytic 3-dimensional solutions that are akin to the BTZ solutions but with a non-trivial scalar field that modifies the effective cosmological constant. We then study the 4-dimensional asymptotically flat and de Sitter solutions. The latter present three different branches according to their effective cosmological constant. For two of these branches, we find families of black hole solutions, parametrized by the velocity of the scalar field. These spherically symmetric solutions, obtained numerically, are different from GR solutions close to the black hole event horizon, while they have the same de-Sitter asymptotic behavior. The velocity parameter represents black hole primary hair.

  7. Experimental study of grain interactions on rolling texture development in face-centered cubic metals

    NASA Astrophysics Data System (ADS)

    Kumar Ray, Atish

    There exists considerable debate in the texture community about whether grain interactions are a necessary factor to explain the development of deformation textures in polycrystalline metals. Computer simulations indicate that grain interactions play a significant role, while experimental evidence shows that the material type and starting orientation are more important in the development of texture and microstructure. A balanced review of the literature on face-centered cubic metals shows that the opposing viewpoints have developed due to the lack of any complete experimental study which considers both the intrinsic (material type and starting orientation) and extrinsic (grain interaction) factors. In this study, a novel method was developed to assemble ideally orientated crystalline aggregates in 99.99% aluminum (Al) or copper (Cu) to experimentally evaluate the effect of grain interactions on room temperature deformation texture. Ideal orientations relevant to face-centered cubic rolling textures, Cube {100} <001>, Goss {110} <001>, Brass {110} <11¯2> and Copper {112} <111¯> were paired in different combinations and deformed by plane strain compression to moderate strain levels of 1.0 to 1.5. Orientation dependent mechanical behavior was distinguishable from that of the neighbor-influenced behavior. In interacting crystals the constraint on the rolling direction shear strains (gammaXY , gammaXZ) was found to be most critical to show the effect of interactions via the evolution of local microstructure and microtexture. Interacting crystals with increasing deformations were observed to gradually rotate towards the S-component, {123} <634>. Apart from the average lattice reorientations, the interacting crystals also developed strong long-range orientation gradients inside the bulk of the crystal, which were identified as accumulating misorientations across the deformation boundaries. Based on a statistical procedure using quaternions, the orientation and

  8. Ellipsometric study of cubic SiC

    NASA Technical Reports Server (NTRS)

    Alterovitz, Samuel A.; Shoemaker, Neil S.; Powell, J. A.

    1990-01-01

    Variable angle spectroscopic ellipsometry (VASE) was applied to cubic SiC. This technique gives absolute values of the refractive index (n) and the extinction coefficient (k) of a substrate and/or a thin film of unknown material. The samples were grown by chemical vapor deposition (CVD) on p-type silicon. The substrate was aligned either on the (001) axis or 1 degree of (001). Several growth temperatures and growth durations were used. The samples were divided into two groups: (1) thick films of order 10 microns grown near optimal conditions of temperature, flow, and gas ratio; and (2) thin films of order 100 A grown at various temperatures. The ellipsometric results for samples in group 1 were analyzed using a two-phase model (substrate and ambient). Results show that for wavelengths in the visible, the refractive index of these CVD samples is equal to that reported for single crystal cubic SiC, within the experimental error, which is on the order of 1 percent. However, the extinction coefficient has a relatively large value, even above the band gap. The absorption is sample dependent and has a broad peak in the visible. The results for samples in group 2 were analyzed using a three-phase model (substrate, film, and ambient). The dielectric functions of the film, deducted from the measured n and k, were further analyzed using the effective medium approximation. The results show that the films contain 30 to 40 vol. percent amorphous silicon, i.e., silicon with only short-range order.

  9. Polarization-phase images of liquor polycrystalline films in determining time of death.

    PubMed

    Garazdyuk, M S; Bachinskyi, V T; Vanchulyak, O Ya; Ushenko, A G; Dubolazov, O V; Gorsky, M P

    2016-04-20

    An optical model for generalized optical anisotropy of polycrystalline networks of albumin and globulin liquor of the human brain has been suggested. The polarization-phase method for spatial and frequency differentiation of linear and circular birefringence coordinate distributions has been analytically substantiated. A set of criteria documenting the dynamics of polarization-phase images of liquor polycrystalline films has been identified in determining time of death. PMID:27140134

  10. Charge carrier transport in polycrystalline organic thin film based field effect transistors

    NASA Astrophysics Data System (ADS)

    Rani, Varsha; Sharma, Akanksha; Ghosh, Subhasis

    2016-05-01

    The charge carrier transport mechanism in polycrystalline thin film based organic field effect transistors (OFETs) has been explained using two competing models, multiple trapping and releases (MTR) model and percolation model. It has been shown that MTR model is most suitable for explaining charge carrier transport in grainy polycrystalline organic thin films. The energetic distribution of traps determined independently using Mayer-Neldel rule (MNR) is in excellent agreement with the values obtained by MTR model for copper phthalocyanine and pentacene based OFETs.

  11. The effect of heat treatment on the resistivity of polycrystalline silicon films

    NASA Technical Reports Server (NTRS)

    Fripp, A. L., Jr.

    1975-01-01

    The resistivity of doped polycrystalline silicon films has been studied as a function of post deposition heat treatments in an oxidizing atmosphere. It was found that a short oxidation cycle may produce a resistivity increase as large as three orders of magnitude in the polycrystalline films. The extent of change was dependent on the initial resistivity and the films' doping level and was independent of the total oxidation time.

  12. Method for production of free-standing polycrystalline boron phosphide film

    DOEpatents

    Baughman, Richard J.; Ginley, David S.

    1985-01-01

    A process for producing a free-standing polycrystalline boron phosphide film comprises growing a film of boron phosphide in a vertical growth apparatus on a metal substrate. The metal substrate has a coefficient of thermal expansion sufficiently different from that of boron phosphide that the film separates cleanly from the substrate upon cooling thereof, and the substrate is preferably titanium. The invention also comprises a free-standing polycrystalline boron phosphide film for use in electronic device fabrication.

  13. Free-standing polycrystalline boron phosphide film and method for production thereof

    DOEpatents

    Baughman, R.J.; Ginley, D.S.

    1982-09-09

    A process for producing a free-standing polycrystalline boron phosphide film comprises growing a film of boron phosphide in a vertical growth apparatus on a metal substrate. The metal substrate has a coefficient of thermal expansion sufficiently different from that of boron phosphide that the film separates cleanly from the substrate upon cooling thereof, and the substrate is preferably titanium. The invention also comprises a free-standing polycrystalline boron phosphide film for use in electronic device fabrication.

  14. Experimental study on anelasticty of polycrystalline material for seismological application

    NASA Astrophysics Data System (ADS)

    Takei, Y.; Karasawa, F.

    2012-12-01

    Due to the recent progress in seismology, we can obtain highly-resolved seismic velocity structures in the upper mantle. In order to interpret the velocity structures in terms of temperature heterogeneity, chemical heterogeneity, and fluid/melt distribution, it is important to assess the quantitative effects of temperature, chemical composition, and fluid/melt on Vp and Vs. Although these effects at the ultrasonic frequencies (anharmonic effect, poroelastic effect) have been measured and assessed quantitatively, these effects at the seismic frequencies are subject to large uncertainty due to the uncertainty in rock anelasticity, which additionally causes modulus relaxation at lower frequencies (anelastic effect). Previous studies have shown that anelasticity of polycrystalline materials follows the similarity rule in which frequency normalized to the Maxwell frequency, f/fM, can be used as a master variable (Morris & Jackson, 2009a; McCarthy et al, 2012). The general applicability of this Maxwell frequency scaling shows that the anelastic relaxation in those experiments is caused by diffusionally accommodated grain boundary sliding (GBS) (Gribb & Cooper, 1998; McCarthy et al, 2012). However, normalized frequency of the existing experimental data is usually considerably lower than the seismic frequencies normalized to the Maxwell frequency of the upper mantle (f/fM=106-1010). Therefore, in order to clarify the mechanism and scaling law applicable to the seismic waves, we have to measure anelasticity at higher normalized frequencies. Theoretical models (e.g., Raj, 1975; Morris & Jackson, 2009b) predict that at higher normalized frequencies, dominant GBS mechanism changes from diffusionally accommodated GBS to elastically accommodated GBS. However, the transition frequency and total relaxation strength associated with the elastically accommodated GBS, which are important in the application to seismology, have so far been difficult to constrain theoretically

  15. Low- cycle fatigue behavior of polycrystalline nial at 1000 k

    NASA Astrophysics Data System (ADS)

    Lerch, B. A.; Noebe, R. D.

    1994-02-01

    The low-cycle fatigue behavior of polycrystalline NiAl was determined at 1000 K, a temperature above the monotonic brittle-to-ductile transition temperature (BDTT). Fully reversed, plastic strain-controlled fatigue tests were conducted on B2 intermetallic samples prepared by two fab-rication techniques: hot isostatic pressing (HIP) of prealloyed powders and extrusion of vacuum induction-melted [cast plus extruded (C+E)] castings. At 1000 K, in an air environment both the hot-isostatically pressed (“hipped”) and C + E samples cyclically softened throughout most of their fatigue lives, though the absolute change in stress was no greater than about 35 MPa. At this temperature, samples were insensitive to processing defects, which were a source of failure initiation in room-temperature tests. The processing method had a small effect on fatigue life; the lives of the hipped samples were about a factor of 3 shorter than the fatigue lives of the C+E NiAl. The C+E material also underwent dynamic grain growth during testing, while the hipped NiAl maintained a constant grain size. Stable fatigue-crack growth in both materials was intergranular in nature, while final fracture by tensile overload occurred by transgranular cleavage. However, at plastic strain ranges below 0.3 pct, the fatigue lives of the hipped NiAl were controlled by intergranular cavitation and creep processes such that the fatigue lives were shorter than anticipated. Finally, hipped samples tested in vacuum had a factor of 3 longer life than specimens tested in air. A comparison of NiAl to typical superalloys (which it may replace) showed that NiAl exhibited a superior fatigue life on a plastic strain basis but was inferior to most superalloys on a stress basis.

  16. Deposited silicon photonics: Optical interconnect devices in polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Preston, Kyle Jonathan

    Silicon photonics has tremendous potential to provide high-bandwidth and low-power data communication for applications such as computing and telecommunication, over length scales ranging from 100 kilometers over fiber to centimeter-length on-chip waveguides. Many silicon photonic building blocks have been demonstrated to date, but critical work remains to determine the best approaches for integrating together silicon photonics with microelectronics. In this thesis, I explore a novel method for integration of silicon photonics on the CMOS platform by using a deposited material: polycrystalline silicon. I will show the first demonstrations of electrically-active optical filters, modulators, and photodetectors in this material. In principle, this material platform would allow for the integration of silicon photonic devices and systems on top of any substrate, including complex CMOS and memory chips or even glass and plastic substrates. In Chapter 1, I introduce the state-of-the-art in silicon photonics, describe several integration schemes under development, and introduce the idea of using deposited materials. In Chapter 2, I demonstrate the use of polysilicon to make integrated microring resonators, and show the integration of different silicon materials together. Chapter 3 discusses the use of polysilicon as both an optical waveguiding layer and an electrode material in slot waveguides for the application of light emitters. Chapter 4 demonstrates the use of a pump-probe experiment to measure the free carrier lifetime in the material and demonstrate all-optical modulation. In Chapter 5, I demonstrate the first high-speed integrated electro-optic modulator in polysilicon, a necessary device for optical transmitters. In Chapter 6, I show how defects inside the same material enable integrated photodetectors at near-infrared telecommunication wavelengths. Chapter 7 shows initial results in adapting the material processing for lower temperatures, necessary for integration

  17. Fundamentals of polycrystalline thin film materials and devices

    NASA Astrophysics Data System (ADS)

    Baron, Bill N.; Birkmire, Robert W.; Phillips, James E.; Shafarman, William N.; Hegedus, Steven S.; McCandless, Brian E.

    1991-01-01

    This report presents the results of a one-year research program on polycrystalline thin-film solar cells. The research was conducted to better understand the limitations and potential of solar cells using CuInSe2 and CdTe by systematically investigating the fundamental relationships linking material processing, material properties, and device behavior. By selenizing Cu and In layers, we fabricated device-quality CuInSe2 thin films and demonstrated a CuInSe2 solar cell with 7 percent efficiency. We added Ga, to increase the band gap of CuInSe2 devices to increase the open-circuit voltage to 0.55 V. We fabricated and analyzed CuInGaSe2/CuInSe2 devices to demonstrate the potential for combining the benefits of higher V(sub oc) while retaining the current-generating capacity of CuInSe2. We fabricated an innovative superstrate device design with more than 5 percent efficiency, as well as a bifacial spectral-response technique for determining the electron diffusion length and optical absorption coefficient of CuInSe2 in an operational cell. The diffusion length was found to be greater than 1 micron. We qualitatively modeled the effect of reducing heat treatments in hydrogen and oxidizing treatments in air on the I-V behavior of CuInSe2 devices. We also investigated post-deposition heat treatments and chemical processing and used them to fabricate a 9.6 percent-efficient CdTe/CdS solar cell using physical vapor deposition.

  18. Fundamentals of polycrystalline thin film materials and devices

    SciTech Connect

    Baron, B.N.; Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E. . Inst. of Energy Conversion)

    1991-01-01

    This report presents the results of a one-year research program on polycrystalline thin-film solar cells. The research was conducted to better understand the limitations and potential of solar cells using CuInSe{sub 2} and CdTe by systematically investigating the fundamental relationships linking material processing, material properties, and device behavior. By selenizing Cu and In layers, we fabricated device-quality CuInSe{sub 2} thin films and demonstrated a CuInSe{sub 2} solar cell with 7% efficiency. We added Ga, to increase the band gap of CuInSe{sub 2} devices to increase the open-circuit voltage to 0.55 V. We fabricated and analyzed Cu(InGa)Se{sub 2}/CuInSe{sub 2} devices to demonstrate the potential for combining the benefits of higher V{sub oc} while retaining the current-generating capacity of CuInSe{sub 2}. We fabricated an innovative superstrate device design with more than 5% efficiency, as well as a bifacial spectral-response technique for determining the electron diffusion length and optical absorption coefficient of CuInSe{sub 2} in an operational cell. The diffusion length was found to be greater than 1 {mu}m. We qualitatively modeled the effect of reducing heat treatments in hydrogen and oxidizing treatments in air on the I-V behavior of CuInSe{sub 2} devices. We also investigated post-deposition heat treatments and chemical processing and used them to fabricate a 9.6%-efficient CdTe/CdS solar cell using physical vapor deposition.

  19. Intergranular Strain Evolution near Fatigue Crack Tips in Polycrystalline Metals

    SciTech Connect

    Zheng, Lili; Gao, Yanfei; Lee, Sooyeol; Barabash, Rozaliya; Lee, Jinhaeng; Liaw, Peter K

    2011-01-01

    The deformation field near a steady fatigue crack includes a plastic zone in front of the crack tip and a plastic wake behind it, and the magnitude, distribution, and history of the residual strain along the crack path depend on the stress multiaxiality, material properties, and history of stress intensity factor and crack growth rate. An in situ, full-field, non-destructive measurement of lattice strain (which relies on the intergranular interactions of the inhomogeneous deformation fields in neighboring grains) by neutron diffraction techniques has been performed for the fatigue test of a Ni-based superalloy compact tension specimen. These microscopic grain level measurements provided unprecedented information on the fatigue growth mechanisms. A two-scale model is developed to predict the lattice strain evolution near fatigue crack tips in polycrystalline materials. An irreversible, hysteretic cohesive interface model is adopted to simulate a steady fatigue crack, which allows us to generate the stress/strain distribution and history near the fatigue crack tip. The continuum deformation history is used as inputs for the micromechanical analysis of lattice strain evolution using the slip-based crystal plasticity model, thus making a mechanistic connection between macro- and micro-strains. Predictions from perfect grain-boundary simulations exhibit the same lattice strain distributions as in neutron diffraction measurements, except for discrepancies near the crack tip within about one-tenth of the plastic zone size. By considering the intergranular damage, which leads to vanishing intergranular strains as damage proceeds, we find a significantly improved agreement between predicted and measured lattice strains inside the fatigue process zone. Consequently, the intergranular damage near fatigue crack tip is concluded to be responsible for fatigue crack growth.

  20. Chemical vapor deposition (CVD) of cubic silicon carbide. Patent Application

    SciTech Connect

    Addamiano, A.

    1985-07-02

    This invention relates to the growth of cubic silicon carbide crystals. More specifically, this invention relates to the growth of cubic silicon carbide by Chemical Vapor Deposition (CVD). One object of the present invention is to provide a novel method for the production of cubic SiC for high temperature electronic devices. Another object of the present invention is to provide a novel method for the production of highly pure, single crystal cubic SiC that is duplicable. Another object of the present invention is to provide a novel method for the production of large-area single-crystal wafers of cubic SiC. These and other objects of the present invention can be achieved by a method for chemical vapor deposition (CVD) of cubic Silicon Carbide (SiC) comprising the steps of etching silicon substrated having one mechanically polished face; depositing a thin buffer layer of cubic SiC formed by reaction between a heated Si substrate and a H2-C3H8 gas mixuture; and depositing SiC on the buffer layer at high temperature using H2+C3HY+SiH4 mixture.

  1. Highly Doped Polycrystalline Silicon Microelectrodes Reduce Noise in Neuronal Recordings In Vivo

    PubMed Central

    Saha, Rajarshi; Jackson, Nathan; Patel, Chetan; Muthuswamy, Jit

    2013-01-01

    The aims of this study are to 1) experimentally validate for the first time the nonlinear current-potential characteristics of bulk doped polycrystalline silicon in the small amplitude voltage regimes (0–200 μV) and 2) test if noise amplitudes (0–15 μV) from single neuronal electrical recordings get selectively attenuated in doped polycrystalline silicon microelectrodes due to the above property. In highly doped polycrystalline silicon, bulk resistances of several hundred kilo-ohms were experimentally measured for voltages typical of noise amplitudes and 9–10 kΩ for voltages typical of neural signal amplitudes (>150–200 μV). Acute multiunit measurements and noise measurements were made in n = 6 and n = 8 anesthetized adult rats, respectively, using polycrystalline silicon and tungsten microelectrodes. There was no significant difference in the peak-to-peak amplitudes of action potentials recorded from either microelectrode (p > 0.10). However, noise power in the recordings from tungsten microelectrodes (26.36 ± 10.13 pW) was significantly higher (p < 0.001) than the corresponding value in polycrystalline silicon microelectrodes (7.49 ± 2.66 pW). We conclude that polycrystalline silicon microelectrodes result in selective attenuation of noise power in electrical recordings compared to tungsten microelectrodes. This reduction in noise compared to tungsten microelectrodes is likely due to the exponentially higher bulk resistances offered by highly doped bulk polycrystalline silicon in the range of voltages corresponding to noise in multiunit measurements. PMID:20667815

  2. Radiation damage in cubic-stabilized zirconia

    SciTech Connect

    Costantini, Jean-Marc; Beuneu, Francois; Weber, William J

    2013-01-01

    Cubic yttria-stabilized zirconia (YSZ) can be used for nuclear applications as an inert matrix for actinide immobilization or transmutation. Indeed, the large amount of native oxygen vacancies leads to a high radiation tolerance of this material owing to defect recombination occurring in the atomic displacements cascades induced by fast neutron irradiation or ion implantations, as showed by Molecular dynamics (MD) simulations. Amorphization cannot be obtained in YSZ either by nuclear-collision or electronic-excitation damage, just like in urania. A kind of polygonization structure with slightly disoriented crystalline domains is obtained in both cases. In the first steps of damage, specific isolated point defects (like F+-type color centers) and point-defect clusters are produced by nuclear collisions with charged particles or neutrons. Further increase of damage leads to dislocation-loop formation, then to collapse of the dislocation network into a polygonization structure. For swift heavy ion irradiations, a similar polygonization structure is obtained above a threshold stopping power value of about 20-30 keV nm-1.

  3. Topological Oxide Insulator in Cubic Perovskite Structure

    PubMed Central

    Jin, Hosub; Rhim, Sonny H.; Im, Jino; Freeman, Arthur J.

    2013-01-01

    The emergence of topologically protected conducting states with the chiral spin texture is the most prominent feature at the surface of topological insulators. On the application side, large band gap and high resistivity to distinguish surface from bulk degrees of freedom should be guaranteed for the full usage of the surface states. Here, we suggest that the oxide cubic perovskite YBiO3, more than just an oxide, defines itself as a new three-dimensional topological insulator exhibiting both a large bulk band gap and a high resistivity. Based on first-principles calculations varying the spin-orbit coupling strength, the non-trivial band topology of YBiO3 is investigated, where the spin-orbit coupling of the Bi 6p orbital plays a crucial role. Taking the exquisite synthesis techniques in oxide electronics into account, YBiO3 can also be used to provide various interface configurations hosting exotic topological phenomena combined with other quantum phases. PMID:23575973

  4. Topological Oxide Insulator in Cubic Perovskite Structure

    NASA Astrophysics Data System (ADS)

    Jin, Hosub; Rhim, Sonny H.; Im, Jino; Freeman, Arthur J.

    2013-04-01

    The emergence of topologically protected conducting states with the chiral spin texture is the most prominent feature at the surface of topological insulators. On the application side, large band gap and high resistivity to distinguish surface from bulk degrees of freedom should be guaranteed for the full usage of the surface states. Here, we suggest that the oxide cubic perovskite YBiO3, more than just an oxide, defines itself as a new three-dimensional topological insulator exhibiting both a large bulk band gap and a high resistivity. Based on first-principles calculations varying the spin-orbit coupling strength, the non-trivial band topology of YBiO3 is investigated, where the spin-orbit coupling of the Bi 6p orbital plays a crucial role. Taking the exquisite synthesis techniques in oxide electronics into account, YBiO3 can also be used to provide various interface configurations hosting exotic topological phenomena combined with other quantum phases.

  5. Smooth cubic commensurate oxides on gallium nitride

    SciTech Connect

    Paisley, Elizabeth A.; Gaddy, Benjamin E.; LeBeau, James M.; Shelton, Christopher T.; Losego, Mark D.; Mita, Seiji; Collazo, Ramón; Sitar, Zlatko; Irving, Douglas L.; Maria, Jon-Paul; Biegalski, Michael D.; Christen, Hans M.

    2014-02-14

    Smooth, commensurate alloys of 〈111〉-oriented Mg{sub 0.52}Ca{sub 0.48}O (MCO) thin films are demonstrated on Ga-polar, c+ [0001]-oriented GaN by surfactant-assisted molecular beam epitaxy and pulsed laser deposition. These are unique examples of coherent cubic oxide|nitride interfaces with structural and morphological perfection. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100× reduction in leakage current density for the surfactant-assisted samples. HAADF-STEM images of the MCO|GaN interface show commensurate alignment of atomic planes with minimal defects due to lattice mismatch. STEM and DFT calculations show that GaN c/2 steps create incoherent boundaries in MCO over layers which manifest as two in-plane rotations and determine consequently the density of structural defects in otherwise coherent MCO. This new understanding of interfacial steps between HCP and FCC crystals identifies the steps needed to create globally defect-free heterostructures.

  6. Triangulation of cubic panorama for view synthesis.

    PubMed

    Zhang, Chunxiao; Zhao, Yan; Wu, Falin

    2011-08-01

    An unstructured triangulation approach, new to our knowledge, is proposed to apply triangular meshes for representing and rendering a scene on a cubic panorama (CP). It sophisticatedly converts a complicated three-dimensional triangulation into a simple three-step triangulation. First, a two-dimensional Delaunay triangulation is individually carried out on each face. Second, an improved polygonal triangulation is implemented in the intermediate regions of each of two faces. Third, a cobweblike triangulation is designed for the remaining intermediate regions after unfolding four faces to the top/bottom face. Since the last two steps well solve the boundary problem arising from cube edges, the triangulation with irregular-distribution feature points is implemented in a CP as a whole. The triangular meshes can be warped from multiple reference CPs onto an arbitrary viewpoint by face-to-face homography transformations. The experiments indicate that the proposed triangulation approach provides a good modeling for the scene with photorealistic rendered CPs. PMID:21833101

  7. Amorphous and polycrystalline water ices in space environments

    NASA Astrophysics Data System (ADS)

    Andrade, Diana; Pilling, Sergio; Da Silveira, Enio; Barros, Ana

    2016-07-01

    Ices are an important reservoir of more complex molecular species in several space environments, containing information about the composition and formation of these regions. Water ice is the dominant constituent of interstellar ices in most lines of sight and is about 70 % of the composition in comets, being a key molecule in astrochemical models. It is believed that one of the reactive species possibly evaporated from the water ices is the hydronium ion, H_{3}O^{+}, which plays an important role in the oxygen chemistry network. This ion has been detected in the lunar surface of Enceladus and Titan, and toward the Sagittarius B2 molecular Clouds, where H_{2}O and OH were also identified. In this work, the ion desorption due to radiolysis in ices constituted by water at three different temperatures (40, 70 and 125 K) is studied, to investigate the different allotropic water ices. A discussion on the rate of H_{3}O^{+} and water delivered to gas phase, as well as the half-life of water ice grains, inside dense molecular clouds considering a constants cosmic ray flux is given. The ions desorbed from water ice have been mass/charge analyzed by a time-of-flight spectrometer. Among the results, it is seen that in the positive ion spectrum of high density amorphous water ice at 40 K the highest desorption yields (ejected ions/impact) correspond to H^{+}, H_{3}O^{+} and clusters formed by (H_{2}O)_{n}R^{+}, where R^{+} is H_{3}O^{+} and 1 ≤ n ≤ 25. At T = 125 K, the ice is in its low density polycrystalline form and new clusters are present, such as (H_{2}O)_{n}R^{+}, where R^{+} is H_{2}^{+} and H_{3}^{+} (for low n), beyond H_{3}O^{+}. Therefore, it is seen that (H_{2}O)_{n}H_{3}O^{+} series (with n between 1 and 25) is dominant in all cases. The H_{3}O^{+} desorption yield at 40 K is about 5times10^{-3} ions/impact. This value is 4-5 times higher than the one obtained at T > 125 K. This behavior is also seen to all series member and consequently to the sum (Yn).

  8. The latent fingerprint in mass transport of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Thirunavukarasu, Gopinath; Kundu, Sukumar; Chatterjee, Subrata

    2016-02-01

    Herein, a systematic investigation was carried out to reach a rational understanding and to provide information concerning the possible causes for a significant influence of pressure variation in the underlying processes of mass transport in polycrystalline materials. The authors focused their research in solid-state diffusion, a part of the subject "Mass Transport in Solids". Theories on diffusion are the subject by itself which exists as a latent fingerprint in every text of higher learning in interdisciplinary science. In this research, authors prepared sandwich samples of titanium alloy and stainless steel using nickel as an intermediate metal. The samples were processed at three different levels of bonding pressure (3, 4 and 5 MPa) while bonding temperature and bonding time was maintained at 750 °C and 1 h, respectively, throughout the experiments. It was observed that the net flux of atomic diffusion of nickel atoms into Ti-alloy at TiA/Ni interface increased by ~63 % with the rise in the bonding pressure from 3 to 4 MPa, but decreased by ~40 % with the rise in the bonding pressure from 4 to 5 MPa. At the same time, the net flux of atomic diffusion of nickel atoms into stainless steel at Ni/SS interface increased by ~19 % with the rise in the bonding pressure from 3 to 4 MPa, but increased by ~17 % with the rise in the bonding pressure from 4 to 5 MPa. Here authors showed that the pressure variations have different effects at the TiA/Ni interface and Ni/SS interface, and tried to explain the explicit mechanisms operating behind them. In general for sandwich samples processed irrespective of bonding pressure chosen, the net flux of Ni-atoms diffused into SS is greater than that of the net flux of Ni-atoms diffused in Ti-alloy matrix by four orders of magnitude. The calculated diffusivity of Ni-atoms into Ti-alloy reaches its highest value of ~5.083 × 10-19 m2/s for the sandwich sample processed using 4-MPa bonding-pressure, whereas the diffusivity of Ni

  9. Diffusion of fluorine atoms in cubic Ca/sub 0. 25/La/sub 0. 75/F/sub 2. 75/

    SciTech Connect

    Livshits, A.I.; Buznik, V.M.; Bendeliani, N.A.

    1987-07-01

    The authors use the continuous NMR method to study /sup 19/F in a Ca/sub 0.25/La/sub 0.75/F/sub 2.75/ polycrystalline solid solution of cubic structure Fm3m. The spectral behavior was analyzed during change in temperature by comparison with the results of NMR studies on Ca/sub 1-x/La/sub x/F/sub 2+x/ solid solutions. The maximum anion mobility in such solid solutions occurs in samples with 0.35 is less than x is less than 0.75. It was established that the structure of tysonite as a solid solution of the same composition is more favorable from the standpoint of better ionic conductivity at temperature below 400K.

  10. Nitrogen-free sol-gel synthesis of Al-substituted cubic garnet Li7La3Zr2O12 (LLZO)

    NASA Astrophysics Data System (ADS)

    Rosenkiewitz, N.; Schuhmacher, J.; Bockmeyer, M.; Deubener, J.

    2015-03-01

    A nitrogen-free sol-gel synthesis of Al-substituted cubic lithium lanthanum zirconium garnet (c-LLZO) was developed. Polycrystalline powders of c-LLZO of the composition Li6.42Al0.32La3Zr1.91O12.02 were prepared from the molecular mixtures of lithium acetate, lanthanum acetate, zirconium propoxide and aluminum chloride and subsequent annealing of the dried precursor sol at 1000 °C for 7 h free of nitrogen oxide gas emissions. The obtained powders had traces of lithium zirconate (<4 wt%), an ionic conductivity of the order of 10-5 S cm-1 and showed a heterogeneous microstructure, which was assumed to result from early melt formation.

  11. The electrical conduction properties of poly-crystalline indium-zinc-oxide film

    SciTech Connect

    Tomai, S.; Terai, K.; Junke, T.; Tsuruma, Y.; Ebata, K.; Yano, K.; Uraoka, Y.

    2014-02-28

    We have developed a high-mobility and high-uniform oxide semiconductor using poly-crystalline semiconductor material composed of indium and zinc (p-IZO). A typical conduction mechanism of p-IZO film was demonstrated by the grain boundary scattering model as in polycrystalline silicon. The grain boundary potential of the 2-h-annealed IZO film was calculated to be 100 meV, which was comparable to that of the polycrystalline silicon. However, the p-IZO thin film transistor (TFT) measurement shows rather uniform characteristics. It denotes that the mobility deterioration around the grain boundaries is lower than the case for low-temperature polycrystalline silicon. This assertion was made based on the difference of the mobility between the polycrystalline and amorphous IZO film being much smaller than is the case for silicon transistors. Therefore, we conclude that the p-IZO is a promising material for a TFT channel, which realizes high drift mobility and uniformity simultaneously.

  12. Process Research On Polycrystalline Silicon Material (PROPSM). [flat plate solar array project

    NASA Technical Reports Server (NTRS)

    Culik, J. S.

    1983-01-01

    The performance-limiting mechanisms in large-grain (greater than 1 to 2 mm in diameter) polycrystalline silicon solar cells were investigated by fabricating a matrix of 4 sq cm solar cells of various thickness from 10 cm x 10 cm polycrystalline silicon wafers of several bulk resistivities. Analysis of the illuminated I-V characteristics of these cells suggests that bulk recombination is the dominant factor limiting the short-circuit current. The average open-circuit voltage of the polycrystalline solar cells is 30 to 70 mV lower than that of co-processed single-crystal cells; the fill-factor is comparable. Both open-circuit voltage and fill-factor of the polycrystalline cells have substantial scatter that is not related to either thickness or resistivity. This implies that these characteristics are sensitive to an additional mechanism that is probably spatial in nature. A damage-gettering heat-treatment improved the minority-carrier diffusion length in low lifetime polycrystalline silicon, however, extended high temperature heat-treatment degraded the lifetime.

  13. March 20, 2012 Space Station Briefing: Cubic Satellite Deploy (Narrated)

    NASA Video Gallery

    This animation, presented by Expedition 32 Lead Flight Director Dina Contella during the March 20, 2012 ISS Program and Science Overview Briefing, shows the deploy of small cubic satellites (often ...

  14. Monotonicity preserving splines using rational Ball cubic interpolation

    NASA Astrophysics Data System (ADS)

    Zakaria, Wan Zafira Ezza Wan; Jamal, Ena; Ali, Jamaludin Md.

    2015-10-01

    In scientific application and Computer Aided Design (CAD), users usually need to generate a spline passing through a given set of data which preserves certain shape properties of the data such as positivity, monotonicity or convexity [1]. The required curves have to be a smooth shape-preserving interpolation. In this paper a rational cubic spline in Ball representation is developed to generate an interpolant that preserves monotonicity. In this paper to control the shape of the interpolant three shape parameters are introduced. The shape parameters in the description of the rational cubic interpolation are subjected to monotonicity constrained. The necessary and sufficient conditions of the rational cubic interpolation are derived and visually the proposed rational cubic interpolant gives a very pleasing result.

  15. March 20, 2012 Space Station Briefing: Cubic Satellite Deploy

    NASA Video Gallery

    This animation, presented by Expedition 32 Lead Flight Director Dina Contella during the March 20, 2012 ISS Program and Science Overview Briefing, shows the deploy of small cubic satellites (often ...

  16. Late-time attractor for the cubic nonlinear wave equation

    SciTech Connect

    Szpak, Nikodem

    2010-08-15

    We apply our recently developed scaling technique for obtaining late-time asymptotics to the cubic nonlinear wave equation and explain the appearance and approach to the two-parameter attractor found recently by Bizon and Zenginoglu.

  17. The Coulombic Lattice Potential of Ionic Compounds: The Cubic Perovskites.

    ERIC Educational Resources Information Center

    Francisco, E.; And Others

    1988-01-01

    Presents coulombic models representing the particles of a system by point charges interacting through Coulomb's law to explain coulombic lattice potential. Uses rubidium manganese trifluoride as an example of cubic perovskite structure. Discusses the effects on cluster properties. (CW)

  18. A highly ordered cubic mesoporous silica/graphene nanocomposite.

    PubMed

    Lee, Chang-Wook; Roh, Kwang Chul; Kim, Kwang-Bum

    2013-10-21

    A highly ordered cubic mesoporous silica (KIT-6)/graphene nanocomposite and 2D KIT-6 nanoflakes were synthesized using a novel synthesis methodology. The non-ionic triblock copolymer, P123, played a dual role as a structure-directing agent in the formation of the cubic mesoporous structure and as a cross-linking agent between mesoporous silica and graphene. The prepared (KIT-6)/graphene nanocomposite could act as a template for the preparation of mesoporous material/graphene nanocomposites. PMID:24057016

  19. Observational Opportunities with the CUBIC Experiment on SAC-B

    NASA Astrophysics Data System (ADS)

    Nousek, J. A.; Burrows, D. N.; Moskalenko, E. I.

    1996-12-01

    The CUBIC experiment on the SAC-B satellite is now collecting data on the Diffuse X-Ray Background and bright point sources over an energy range of 0.2 - 10 keV with energy resolution ranging from 40 - 160 eV over this bandpass. CUBIC observations, several of which are discussed in other posters at this session, provide 2 - 4 high quality spectra per week. CUBIC was built as a PI-class instrument, and at present data rights are divided between Penn State (90%) and Leicester University (10%). We present the observing plan for the first six months of CUBIC operations. We are currently collaborating with several astronomers who are not on the CUBIC team but have expressed interest in one or more of these targets. We invite additional collaborations on targets which are not currently assigned to a specific observer. In order to make these data more accessible to the astronomical community, we are proposing to institute a modest Guest Investigator program. If supported by ADP funding, this would permit observing requests from outside astronomers and would place a large fraction of the CUBIC data in a public archive at the HEASARC.

  20. The compressibility of cubic white and orthorhombic, rhombohedral, and simple cubic black phosphorus

    SciTech Connect

    Clark, Simon M; Zaug, Joseph

    2010-03-10

    The effect of pressure on the crystal structure of white phosphorus has been studied up to 22.4 GPa. The ?alpha phase was found to transform into the alpha' phase at 0.87 +- 0.04 GPa with a volume change of 0.1 +- 0.3 cc/mol. A fit of a second order Birch- Murnaghan equation to the data gave Vo = 16.94 ? 0.08 cc/mol and Ko = 6.7 +- 0.5 GPa for the alpha phase and Vo = 16.4 +- 0.1 cc/mol and Ko = 9.1 +- 0.3 GPa for the alpha' phase. The alpha' phase was found to transform to the A17 phase of black phosphorus at 2.68 +- 0.34 GPa and then with increasing pressure to the A7 and then simple cubic phase of black phosphorus. A fit of a second order Birch-Murnaghan equation to our data combined with previous measurements gave Vo = 11.43 +- 0.05 cc/mol and Ko = 34.7 +- 0.5 GPa for the A17 phase, Vo = 9.62 +- 0.01 cc/mol and Ko = 65.0 +- 0.6 GPa for the A7 phase and , Vo = 9.23 +- 0.01 cc/mol and Ko = 72.5 +- 0.3 GPa for the simple cubic phase.

  1. On the shock response of cubic metals

    NASA Astrophysics Data System (ADS)

    Bourne, N. K.; Gray, G. T.; Millett, J. C. F.

    2009-11-01

    The response of four cubic metals to shock loading is reviewed in order to understand the effects of microstructure on continuum response. Experiments are described that link defect generation and storage mechanisms at the mesoscale to observations in the bulk. Four materials were reviewed; these were fcc nickel, the ordered fcc intermetallic Ni3Al, the bcc metal tantalum, and two alloys based on the intermetallic phase TiAl; Ti-46.5Al-2Cr-2Nb and Ti-48Al-2Cr-2Nb-1B. The experiments described are in two groups: first, equation of state and shear strength measurements using Manganin stress gauges and, second, postshock microstructural examinations and measurement of changes in mechanical properties. The behaviors described are linked through the description of time dependent plasticity mechanisms to the final states achieved. Recovered targets displayed dislocation microstructures illustrating processes active during the shock-loading process. Reloading of previously shock-prestrained samples illustrated shock strengthening for the fcc metals Ni and Ni3Al while showing no such effect for bcc Ta and for the intermetallic TiAl. This difference in effective shock hardening has been related, on the one hand, to the fact that bcc metals have fewer available slip systems that can operate than fcc crystals and to the observation that the lower symmetry materials (Ta and TiAl) both possess high Peierls stress and thus have higher resistances to defect motion in the lattice under shock-loading conditions. These behaviors, compared between these four materials, illustrate the role of defect generation, transport, storage, and interaction in determining the response of materials to shock prestraining.

  2. Polyimide nanocomposites based on cubic zirconium tungstate

    NASA Astrophysics Data System (ADS)

    Ramasubramanian Sharma, Gayathri

    2009-12-01

    In this research, cubic zirconium tungstate (ZrW2O8) was used as a filler to reduce the CTE of polyimides (PI), and the effect of ZrW2O8 nanoparticles on the bulk polymer properties was studied. Polyimides are high performance polymers with exceptional thermal stability, and there is a need for PIs with low CTEs for high temperature applications. The nanofiller, cubic ZrW2O8, is well known for its isotropic negative thermal expansion (NTE) over a wide temperature range from -272.7 to 777°C. The preparation of nanocomposites involved the synthesis of ZrW 2O8 nanofiller, engineering the polymer-filler interface using linker groups and optimization of processing strategies to prepare free-standing PI nanocomposite films. A hydrothermal method was used to synthesize ZrW 2O8 nanoparticles. Polyimide-ZrW2O8 interface interaction was enhanced by covalently bonding linker moieties to the surface of ZrW2O8 nanoparticles. Specifically, ZrW 2O8 nanoparticles were functionalized with two different linker groups: (1) a short aliphatic silane, and (2) low molecular weight PI. The surface functionalization was confirmed using X-ray photoelectron spectroscopy and thermal gravimetric analysis (TGA). Reprecipitation blending was used to prepare the freestanding PI-ZrW2O8 nanocomposite films with up to 15 volume% filler loading. SEM images showed the improvements in polymer-filler wetting behavior achieved using interface engineering. SEM images indicated that there was better filler dispersion in the PI matrix using reprecipitation blending, compared to the filler dispersion achieved in the nanocomposites prepared using conventional blending technique. The structure-property relationships in PI-ZrW2O8 nanocomposites were investigated by studying the thermal degradation, glass transition, tensile and thermal expansion properties of the nanocomposites. The properties were studied as a function of filler loading and interface linker groups. Addition of ZrW2O8 nanoparticles did not

  3. Measuring long-range carrier diffusion across multiple grains in polycrystalline semiconductors by photoluminescence imaging

    PubMed Central

    Alberi, K.; Fluegel, B.; Moutinho, H.; Dhere, R. G.; Li, J. V.; Mascarenhas, A.

    2013-01-01

    Thin-film polycrystalline semiconductors are currently at the forefront of inexpensive large-area solar cell and integrated circuit technologies because of their reduced processing and substrate selection constraints. Understanding the extent to which structural and electronic defects influence carrier transport in these materials is critical to controlling the optoelectronic properties, yet many measurement techniques are only capable of indirectly probing their effects. Here we apply a novel photoluminescence imaging technique to directly observe the low temperature diffusion of photocarriers through and across defect states in polycrystalline CdTe thin films. Our measurements show that an inhomogeneous distribution of localized defect states mediates long-range hole transport across multiple grain boundaries to locations exceeding 10 μm from the point of photogeneration. These results provide new insight into the key role deep trap states have in low temperature carrier transport in polycrystalline CdTe by revealing their propensity to act as networks for hopping conduction. PMID:24158163

  4. The effects of intragrain defects on the local photoresponse of polycrystalline silicon solar cells

    NASA Astrophysics Data System (ADS)

    Inoue, N.; Wilmsen, C. W.; Jones, K. A.

    1981-02-01

    Intragrain defects in Wacker cast and Monsanto zone-refined polycrystalline silicon materials were investigated using the electron-beam-induced current (EBIC) technique. The EBIC response maps were compared with etch pit, local diffusion length and local photoresponse measurements. It was determined that the Wacker polycrystalline silicon has a much lower density of defects than does the Monsanto polycrystalline silicon and that most of the defects in the Wacker material are not active recombination sites. A correlation was found between the recombination site density, as determined by EBIC, and the local diffusion length. It is shown that a large density of intragrain recombination sites greatly reduces the minority carrier diffusion length and thus can significantly reduce the photoresponse of solar cells.

  5. The importance of stress percolation patterns in rocks and other polycrystalline materials

    PubMed Central

    Burnley, P.C.

    2013-01-01

    A new framework for thinking about the deformation behavior of rocks and other heterogeneous polycrystalline materials is proposed, based on understanding the patterns of stress transmission through these materials. Here, using finite element models, I show that stress percolates through polycrystalline materials that have heterogeneous elastic and plastic properties of the same order as those found in rocks. The pattern of stress percolation is related to the degree of heterogeneity in and statistical distribution of the elastic and plastic properties of the constituent grains in the aggregate. The development of these stress patterns leads directly to shear localization, and their existence provides insight into the formation of rhythmic features such as compositional banding and foliation in rocks that are reacting or dissolving while being deformed. In addition, this framework provides a foundation for understanding and predicting the macroscopic rheology of polycrystalline materials based on single-crystal elastic and plastic mechanical properties. PMID:23823992

  6. Refractive index and extinction coefficient of doped polycrystalline silicon films in infrared spectrum

    NASA Astrophysics Data System (ADS)

    Zhang, Xia; Zhang, Dacheng

    2016-03-01

    The refractive index and extinction coefficient in infrared spectrum of the polycrystalline silicon films with different doped dosages, base on the inverse calculation, are obtained by means of utilizing the measured reflectance and transmittance of a layer of material and multilayer films, and the equations derived from photonics and electromagnetic theory. The calculation results demonstrate that the refractive index of the doped polycrystalline silicon films decreases with the doped dosages increasing and the extinction coefficient increases with the doped dosages increasing for a given wavelength. This method used for determining the refractive index and extinction coefficient of the polycrystalline silicon films is effective and has the advantage of that the measured samples are fabricated simply.

  7. Corrosion/Electrochemistry of Monocrystalline and Polycrystalline Beryllium in Aqueous Chloride Environment

    SciTech Connect

    Friedman, J.; Hanafee, J.E.

    2000-01-01

    Corrosion characteristics of high-purity polycrystalline beryllium as a function of pH and NaCl concentration were studied at 25 C, using cyclic polarization tests. Single crystal beryllium specimens oriented close to the (0001), (1010), and (1120) planes using Laue back reflection techniques were studied using cyclic polarization tests in 0.01M NaCl with a nominal pH of 7. Pit morphology of the polycrystalline and single crystals was studied using conventional scanning electron microscopy. On the polycrystalline specimens, passivity appears to be more a function of solution pH than of chloride concentration. Single crystal studies show dramatic differences in cyclic polarization plots and SEM micrographs. The two prism planes (1010) and (1120) behave similarly while the basal plane (0001) behaved in a substantially different manner.

  8. Mechanical, thermal and optical properties of the SPS-processed polycrystalline Nd:YAG

    NASA Astrophysics Data System (ADS)

    Sokol, M.; Kalabukhov, S.; Kasiyan, V.; Rothman, A.; Dariel, M. P.; Frage, N.

    2014-12-01

    The present study deals with a comprehensive comparison of the mechanical and functional properties of Nd:YAG single crystals with those of the polycrystalline ceramics (PCs), undoped and LiF-doped, processed by Spark Plasma Sintering (SPS). The polycrystalline ceramics have higher mechanical properties (hardness, bending strength and thermal shock resistance) than the single crystals. The optical transmittance of the LiF-doped PC Nd:YAG is significantly higher than that of the undoped one and is close to that of the single crystal. With respect to other optical and thermal properties, i.e. refraction index, absorption coefficient, extinction ratio, thermo-optic coefficient, fluorescence and thermal conductivity, no significant differences were observed between the single crystals and the polycrystalline ceramic.

  9. The importance of stress percolation patterns in rocks and other polycrystalline materials.

    PubMed

    Burnley, P C

    2013-01-01

    A new framework for thinking about the deformation behavior of rocks and other heterogeneous polycrystalline materials is proposed, based on understanding the patterns of stress transmission through these materials. Here, using finite element models, I show that stress percolates through polycrystalline materials that have heterogeneous elastic and plastic properties of the same order as those found in rocks. The pattern of stress percolation is related to the degree of heterogeneity in and statistical distribution of the elastic and plastic properties of the constituent grains in the aggregate. The development of these stress patterns leads directly to shear localization, and their existence provides insight into the formation of rhythmic features such as compositional banding and foliation in rocks that are reacting or dissolving while being deformed. In addition, this framework provides a foundation for understanding and predicting the macroscopic rheology of polycrystalline materials based on single-crystal elastic and plastic mechanical properties. PMID:23823992

  10. Polycrystalline indium phosphide on silicon by indium assisted growth in hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Metaferia, Wondwosen; Sun, Yan-Ting; Pietralunga, Silvia M.; Zani, Maurizio; Tagliaferri, Alberto; Lourdudoss, Sebastian

    2014-07-01

    Polycrystalline InP was grown on Si(001) and Si(111) substrates by using indium (In) metal as a starting material in hydride vapor phase epitaxy (HVPE) reactor. In metal was deposited on silicon substrates by thermal evaporation technique. The deposited In resulted in islands of different size and was found to be polycrystalline in nature. Different growth experiments of growing InP were performed, and the growth mechanism was investigated. Atomic force microscopy and scanning electron microscopy for morphological investigation, Scanning Auger microscopy for surface and compositional analyses, powder X-ray diffraction for crystallinity, and micro photoluminescence for optical quality assessment were conducted. It is shown that the growth starts first by phosphidisation of the In islands to InP followed by subsequent selective deposition of InP in HVPE regardless of the Si substrate orientation. Polycrystalline InP of large grain size is achieved and the growth rate as high as 21 μm/h is obtained on both substrates. Sulfur doping of the polycrystalline InP was investigated by growing alternating layers of sulfur doped and unintentionally doped InP for equal interval of time. These layers could be delineated by stain etching showing that enough amount of sulfur can be incorporated. Grains of large lateral dimension up to 3 μm polycrystalline InP on Si with good morphological and optical quality is obtained. The process is generic and it can also be applied for the growth of other polycrystalline III-V semiconductor layers on low cost and flexible substrates for solar cell applications.

  11. Polycrystalline indium phosphide on silicon by indium assisted growth in hydride vapor phase epitaxy

    SciTech Connect

    Metaferia, Wondwosen; Sun, Yan-Ting Lourdudoss, Sebastian; Pietralunga, Silvia M.; Zani, Maurizio; Tagliaferri, Alberto

    2014-07-21

    Polycrystalline InP was grown on Si(001) and Si(111) substrates by using indium (In) metal as a starting material in hydride vapor phase epitaxy (HVPE) reactor. In metal was deposited on silicon substrates by thermal evaporation technique. The deposited In resulted in islands of different size and was found to be polycrystalline in nature. Different growth experiments of growing InP were performed, and the growth mechanism was investigated. Atomic force microscopy and scanning electron microscopy for morphological investigation, Scanning Auger microscopy for surface and compositional analyses, powder X-ray diffraction for crystallinity, and micro photoluminescence for optical quality assessment were conducted. It is shown that the growth starts first by phosphidisation of the In islands to InP followed by subsequent selective deposition of InP in HVPE regardless of the Si substrate orientation. Polycrystalline InP of large grain size is achieved and the growth rate as high as 21 μm/h is obtained on both substrates. Sulfur doping of the polycrystalline InP was investigated by growing alternating layers of sulfur doped and unintentionally doped InP for equal interval of time. These layers could be delineated by stain etching showing that enough amount of sulfur can be incorporated. Grains of large lateral dimension up to 3 μm polycrystalline InP on Si with good morphological and optical quality is obtained. The process is generic and it can also be applied for the growth of other polycrystalline III–V semiconductor layers on low cost and flexible substrates for solar cell applications.

  12. Shock waves in complex binary solids: Cubic Laves crystals, quasicrystals, and amorphous solids

    NASA Astrophysics Data System (ADS)

    Roth, Johannes

    2005-02-01

    Shock waves have been simulated by molecular dynamics in the cubic Laves phase C15, in related Frank-Kasper-type (AlCu)Li quasicrystals, and in an amorphous solid of the same composition and potential parameters. The goal of this study was to generate shock waves in periodic and aperiodic structures and to compare their behavior. The expectation was that new types of defects would show up in aperiodic materials. Three regimes are observed in the Laves phase: at low shock wave intensity the system reacts elastically, at high intensities it turns disordered. In the intermediate region the velocity of the elastic wave saturates and an additional plastic wave appears. Extended defects are created which form a network of walls of finite width. The crystallites in between are rotated by the shock wave. If the samples are quenched a polycrystalline phase is obtained. The size of the grains decreases with increasing shock wave intensity until complete fragmentation occurs in the third regime. The behavior of the quasicrystal models is similar, except that there is a continuous transition from a quasielastic behavior to the plastic regime. Ring processes are observed which break up into open paths when the shock wave energy grows. The transition to a complete destruction of the structure is continuous. In the amorphous solid a linear us-up relation is found over the whole range of piston velocities. Two regimes are present, with unsteady plastic waves at weak shock strengths and steady waves in the range coinciding with the upper regime in the ordered structures.

  13. Nucleation and growth of cubic boron nitride films produced by ion-assisted pulsed laser deposition

    SciTech Connect

    Friedmann, T.A.; Medlin, D.L.; Mirkarimi, P.B.; McCarty, K.F.; Klaus, E.J.; Boehme, D.R.; Johnsen, H.A.; Mills, M.J.; Ottesen, D.K.

    1993-12-31

    We are studying the boron nitride system using a pulsed excimer laser to ablate from hexagonal BN (cBN) targets to form cubic BN (cBN) films. We are depositing BN films on heated (25--800C) Si (100) surfaces and are using a broad-beam ion source operated with Ar and N{sub 2} source gases to produce BN films with a high percentage of sp{sup 3}-bonded cBN. In order to optimize growth and nucleation of cBN films, parametric studies of the growth parameters have been performed. The best films to date show >85% sp{sup 3}-bonded BN as determined from Fourier-transform infrared (FTIR) reflection spectroscopy. High resolution transmission electron microscopy (TEM) and selected area electron diffraction confirm the presence of cBN in these samples. The films are polycrystalline and show grain sizes up to 30--40 mn. We find from both the FTIR and TEM analyses that the cBN content in these films evolves with growth time. Initially, the films are deposited as hBN and the cBN nucleates on this hBN underlayer. Importantly, the position of the cBN IR phonon also changes with growth time. Initially this mode appears near 1130 cm{sup {minus}1} and the position decreases with growth time to a constant value of 1085 cm{sup {minus}1}. Since in bulk cBN this IR mode appears at 1065 cm{sup {minus}1}, a large compressive stress induced by the ion bombardment is suggested. In addition, we report on the variation in cBN percentage with temperature.

  14. Effect of grain size of polycrystalline diamond on its heat spreading properties

    NASA Astrophysics Data System (ADS)

    Simon, Roland B.; Anaya, Julian; Faili, Firooz; Balmer, Richard; Williams, Gruffudd T.; Twitchen, Daniel J.; Kuball, Martin

    2016-06-01

    The exceptionally high thermal conductivity of polycrystalline diamond (>2000 W m‑1 K‑1) makes it a very attractive material for optimizing the thermal management of high-power devices. In this paper, the thermal conductivity of a diamond sample capturing grain size evolution from nucleation towards the growth surface is studied using an optimized 3ω technique. The thermal conductivity is found to decrease with decreasing grain size, which is in good agreement with theory. These results clearly reveal the minimum film thickness and polishing thickness from nucleation needed to achieve single-crystal diamond performance, and thus enable production of an optimal polycrystalline diamond for heat-spreading applications.

  15. Effects of grain size distribution on the creep damage evolution of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Yu, Tao; Shi, Huiji

    2010-04-01

    It is evident that realistic microstructures of polycrystalline materials demonstrate a certain distribution of grain size, which has not been widely studied in most analyses of mechanical properties of materials at high temperatures. In this work, the effects of grain size distribution on the creep damage evolution induced by void growth of polycrystalline materials were investigated by the Voronoi tessellation approach, taking into account the void evolution on the grain boundaries in a grain aggregate cell. The results indicate that with the decrease in mean grain size, the damage variable increases faster. When the mean grain sizes are the same, the more uniform the grain size is, the faster the damage variable increases.

  16. Time-resolved photoluminescence of polycrystalline CdTe grown by close-spaced sublimation

    SciTech Connect

    Keyes, B.; Dhere, R.; Ramanathan, K. )

    1994-06-30

    Polycrystalline CdTe has shown great promise as a low-cost material for thin-film, terrestrial photovoltaic applications, with efficiencies approaching 16% achieved with close-spaced sublimation (CSS)-grown CdTe. Due to the inherent complexities of polycrystalline material, much of the progress in this area has occurred through a slow trial-and-error process. This report uses time-resolved photoluminescence (TRPL) to characterize the CdTe material quality as a function of one basic growth parameter---substrate temperature. This characterization is done for two different glass substrate materials, soda-lime silicate and borosilicate.

  17. Electronic structure of polycrystalline Cd metal using {sup 241}Am radioisotope

    SciTech Connect

    Dhaka, M. S.; Sharma, G.; Mishra, M. C.; Sharma, B. K.

    2014-04-24

    Electronic structure study of the polycrystalline cadmium metal is reported. The experimental measurement is undertaken on a polycrystalline sheet sample using 59.54 keV radioisotope of {sup 241}Am. These results are compared with the ab initio calculations. The theoretical calculations are performed using linear combination of atomic orbitals (LCAO) method employing the density functional theories (DFT) and Hartree-Fock (HF) and augmented plane wave (APW) methods. The spherically averaged APW and LCAO based theoretical Compton profiles are in good agreement with the experimental measurement however the APW based theoretical calculations show best agreement.

  18. Investigation of lifetime limiting microdefects in polycrystalline silicon for photovoltaic applications

    SciTech Connect

    Werner, M.; Weber, E.R.; McHugo, S.; Bailey, J.

    1994-12-31

    Electron Microscopy techniques were applied to the study of intragranular microdefects in as-grown and intentionally Fe contaminated polycrystalline silicon solar cell material. Electron-Energy-Loss Spectroscopy (EELS) imaging revealed bright contrasts in metal diffused samples and with smaller concentration in as-grown material, probably due to metal precipitates. High-resolution and analytical electron microscopy identified Cu- and Fe-silicide particles in the contaminated specimen. These results demonstrate that intragranular microdefects exist in polycrystalline Si which act as nucleation sites for metal contaminants and lend support to the model that metal-decorated microdefects are decisive lifetime killers in as-grown material.

  19. Polycrystalline nanowires of gadolinium-doped ceria via random alignment mediated by supercritical carbon dioxide

    PubMed Central

    Kim, Sang Woo; Ahn, Jae-Pyoung

    2013-01-01

    This study proposes a seed/template-free method that affords high-purity semiconducting nanowires from nanoclusters, which act as basic building blocks for nanomaterials, under supercritical CO2 fluid. Polycrystalline nanowires of Gd-doped ceria (Gd-CeO2) were formed by CO2-mediated non-oriented attachment of the nanoclusters resulting from the dissociation of single-crystalline aggregates. The unique formation mechanism underlying this morphological transition may be exploited for the facile growth of high-purity polycrystalline nanowires. PMID:23572061

  20. An experimental investigation of domain wall motion in polycrystalline Ni during high-rate compressive loading

    NASA Astrophysics Data System (ADS)

    Ghosh, Dipankar; Bah, Abubakarr; Carman, Gregory P.; Ravichandran, Guruswami

    2016-01-01

    This paper describes experimental data on a polycrystalline nickel subjected to compressive loads induced in a split Hopkinson pressure bar test. A perpendicular bias magnetic field with respect to the loading direction is used to orient the domains and a pick-up coil measures the magnetic response of the sample during loading. Utilizing this experimental configuration, this study investigated the coupled effects of the magnetic and mechanical fields on domain wall motion in a polycrystalline magnetostrictive material (Ni) during the high-rate elastic loading. The experimental measurements reveal that the magnitude of the stress-induced magnetization change is dependent upon bias magnetic field.

  1. Role of polycrystallinity in CdTe and CuInSe[sub 2] photovoltaic cells

    SciTech Connect

    Sites, J.R. )

    1992-11-01

    The limiting role of polycrystallinity in thin-film solar calls has been reduced somewhat during the past year, and efficiencies of both CdTe and CuInSe[sub 2] cells are approaching 15%. Quantitative separation of loss mechanisms shows that individual losses, with the exception of forward recombination current, can be made comparable to their single crystal counterparts. One general manifestation of the extraneous trapping states in that the voltage of all polycrystalline thin-film cells drifts upward by 10--50 mV following the onset of illumination.

  2. Single crystal and polycrystalline GaAs solar cells using AMOS technology

    NASA Technical Reports Server (NTRS)

    Stirn, R. J.; Yeh, Y. C. M.

    1976-01-01

    A description is given of current technology for fabricating single AMOS (antireflection-coated metal oxide semiconductor) solar cells, with attention given to thermal, plasma, and anodic oxidation, native oxide stripping, and X-ray photoelectron spectroscopy results. Some preliminary results are presented on the chemistry and electrical characterization of such cells, and the characteristics of cells fabricated on sliced polycrystalline GaAs wafers are examined. Consideration is also given to the recrystallization of evaporated Ge films for use as low-cost substrates for polycrystalline GaAs solar cells.

  3. Elasticity and sound velocities of polycrystalline grossular garnet (Ca3Al2Si3O12) at simultaneous high pressures and high temperatures

    NASA Astrophysics Data System (ADS)

    Gwanmesia, Gabriel D.; Wang, Liping; Heady, Adaire; Liebermann, Robert C.

    2014-03-01

    The elastic wave velocities of a dense polycrystalline specimen (99.7% of theoretical density) of synthetic grossular garnet (Ca3Al2Si3O12) were measured to pressures of ∼10 GPa and temperatures of 1000 K by transfer-function ultrasonic interferometry in conjunction with energy-dispersive synchrotron X-radiation in a deformation DIA-type cubic-anvil apparatus. The calculated elastic bulk (Ks) and shear (G) moduli data were fitted to functions of Eulerian strain to 3rd order, yielding the zero-pressure values [Ks = 171.2 (8) GPa; G = 107.4 (2) GPa] and their pressure derivatives [(∂Ks/∂P)T = 4.47 (2); (∂G/∂P)T = 1.29 (5)]. The temperature dependences of the elastic moduli obtained from linear regression of entire P-T-Ks and P-T-G data are: (∂Ks/∂T)P = -1.38 (3) × 10-2 GPa/K and (∂G/∂T)P = -1.28 (2) × 10-2 GPa/K. These results together with those from previous studies for garnets with varying compositions suggest that most of the thermo-elastic properties of garnet are insensitive to grossular content, with the exception of the shear modulus, which significantly depends on the calcium content.

  4. Nonlinear surface acoustic waves in cubic crystals

    NASA Astrophysics Data System (ADS)

    Kumon, Ronald Edward

    Model equations developed by Hamilton, Il'inskii, and Zabolotskaya [J. Acoust. Soc. Am. 105, 639-651 (1999)] are used to perform theoretical and numerical studies of nonlinear surface acoustic waves in a variety of nonpiezoelectric cubic crystals. The basic theory underlying the model equations is outlined, quasilinear solutions of the equations are derived, and expressions are developed for the shock formation distance and nonlinearity coefficient. A time-domain equation corresponding to the frequency-domain model equations is derived and shown to reduce to a time-domain equation introduced previously for Rayleigh waves [E. A. Zabolotskaya, J. Acoust. Soc. Am. 91, 2569-2575 (1992)]. Numerical calculations are performed to predict the evolution of initially monofrequency surface waves in the (001), (110), and (111) planes of the crystals RbCl, KCl, NaCl, CaF2, SrF2, BaF2, C (diamond), Si, Ge, Al, Ni, Cu in the moverline 3m point group, and the crystals Cs-alum, NH4- alum, and K-alum in the moverline 3 point group. The calculations are based on measured second- and third- order elastic constants taken from the literature. Nonlinearity matrix elements which describe the coupling strength of harmonic interactions are shown to provide a powerful tool for characterizing waveform distortion. Simulations in the (001) and (110) planes show that in certain directions the velocity waveform distortion may change in sign, generation of one or more harmonies may be suppressed and shock formation postponed, or energy may be transferred rapidly to the highest harmonics and shock formation enhanced. Simulations in the (111) plane show that the nonlinearity matrix elements are generally complex-valued, which may lead to asymmetric distortion and the appearance of low frequency oscillations near the peaks and shocks in the velocity waveforms. A simple transformation based on the phase of the nonlinearity matrix is shown to provide a reasonable approximation of asymmetric waveform

  5. Lattice matched crystalline substrates for cubic nitride semiconductor growth

    SciTech Connect

    Norman, Andrew G; Ptak, Aaron J; McMahon, William E

    2015-02-24

    Disclosed embodiments include methods of fabricating a semiconductor layer or device and devices fabricated thereby. The methods include, but are not limited to, providing a substrate having a cubic crystalline surface with a known lattice parameter and growing a cubic crystalline group III-nitride alloy layer on the cubic crystalline substrate by coincident site lattice matched epitaxy. The cubic crystalline group III-nitride alloy may be prepared to have a lattice parameter (a') that is related to the lattice parameter of the substrate (a). The group III-nitride alloy may be a cubic crystalline In.sub.xGa.sub.yAl.sub.1-x-yN alloy. The lattice parameter of the In.sub.xGa.sub.yAl.sub.1-x-yN or other group III-nitride alloy may be related to the substrate lattice parameter by (a')= 2(a) or (a')=(a)/ 2. The semiconductor alloy may be prepared to have a selected band gap.

  6. Evolution of cubic membranes as antioxidant defence system.

    PubMed

    Deng, Yuru; Almsherqi, Zakaria A

    2015-08-01

    Possibly the best-characterized cubic membrane transition has been observed in the mitochondrial inner membranes of free-living giant amoeba (Chaos carolinense). In this ancient organism, the cells are able to survive in extreme environments such as lack of food, thermal and osmolarity fluctuations and high levels of reactive oxygen species. Their mitochondrial inner membranes undergo rapid changes in three-dimensional organization upon food depletion, providing a valuable model to study this subcellular adaptation. Our data show that cubic membrane is enriched with unique ether phospholipids, plasmalogens carrying very long-chain polyunsaturated fatty acids. Here, we propose that these phospholipids may not only facilitate cubic membrane formation but may also provide a protective shelter to RNA. The potential interaction of cubic membrane with RNA may reduce the amount of RNA oxidation and promote more efficient protein translation. Thus, recognizing the role of cubic membranes in RNA antioxidant systems might help us to understand the adaptive mechanisms that have evolved over time in eukaryotes. PMID:26464785

  7. Evolution of cubic membranes as antioxidant defence system

    PubMed Central

    Deng, Yuru; Almsherqi, Zakaria A.

    2015-01-01

    Possibly the best-characterized cubic membrane transition has been observed in the mitochondrial inner membranes of free-living giant amoeba (Chaos carolinense). In this ancient organism, the cells are able to survive in extreme environments such as lack of food, thermal and osmolarity fluctuations and high levels of reactive oxygen species. Their mitochondrial inner membranes undergo rapid changes in three-dimensional organization upon food depletion, providing a valuable model to study this subcellular adaptation. Our data show that cubic membrane is enriched with unique ether phospholipids, plasmalogens carrying very long-chain polyunsaturated fatty acids. Here, we propose that these phospholipids may not only facilitate cubic membrane formation but may also provide a protective shelter to RNA. The potential interaction of cubic membrane with RNA may reduce the amount of RNA oxidation and promote more efficient protein translation. Thus, recognizing the role of cubic membranes in RNA antioxidant systems might help us to understand the adaptive mechanisms that have evolved over time in eukaryotes. PMID:26464785

  8. Ultratough, Thermally Stable Polycrystalline Diamond/Silicon Carbide Nanocomposites for Drill Bits

    SciTech Connect

    2009-03-01

    This factsheet describes a research project whose goal is to develop and produce in quantity novel superhard and ultratough thermally stable polycrystalline (TSP) diamond/SiC nanocomposites reinforced with SiC/C nanofibers for drill-bit applications and multiple industrial functions.

  9. The production of oxygenated polycrystalline graphene by one-step ethanol-chemical vapor deposition.

    PubMed

    Paul, Rajat K; Badhulika, Sushmee; Niyogi, Sandip; Haddon, Robert C; Boddu, Veera M; Costales-Nieves, Carmen; Bozhilov, Krassimir N; Mulchandani, Ashok

    2011-10-01

    Large-area mono- and bilayer graphene films were synthesized on Cu foil (~ 1 inch(2)) in about 1 min by a simple ethanol-chemical vapor deposition (CVD) technique. Raman spectroscopy and high resolution transmission electron microscopy revealed the synthesized graphene films to have polycrystalline structures with 2-5 nm individual crystallite size which is a function of temperature up to 1000°C. X-ray photoelectron spectroscopy investigations showed about 3 atomic% carboxylic (COOH) functional groups were formed during growth. The field-effect transistor devices fabricated using polycrystalline graphene as conducting channel (L(c)=10 μm; W(c)=50 μm) demonstrated a p-type semiconducting behavior with high drive current and Dirac point at ~35 V. This simple one-step method of growing large area polycrystalline graphene films with semiconductor properties and easily functionalizable groups should assist in the realization of potential of polycrystalline graphene for nanoelectronics, sensors and energy storage devices. PMID:22408276

  10. Rubrene polycrystalline films growth from vacuum deposition at various substrate temperatures

    NASA Astrophysics Data System (ADS)

    Lin, Ku-Yen; Wang, Yan-Jun; Chen, Ko-Lun; Yang, Chun-Chuen; Ho, Ching-Yuan; Lee, Kueir-Rarn; Shen, Ji-Lin; Chiu, Kuan-Cheng

    2016-04-01

    Rubrene polycrystalline films growth from vacuum deposition (with a fixed source temperature of 300 °C) were characterized with respect to various substrate temperatures (Tsub=103-221 °C). First, the growth behavior of these as-deposited polycrystalline films is confirmed to follow an activated surface-adsorption process with an activation energy EA=0.69±0.01 eV. A comparison of EA for the growth of some other small organic molecular solid films is given. Then, the surface morphology and the temporal evolution of the grain size in these polycrystalline films with respect to Tsub are described and discussed. Furthermore, by X-ray diffraction, these rubrene crystalline grains are confirmed to have an orthorhombic structure, and the average coherent length and lattice microstrain of the crystallites deposited at high Tsub (189-221 °C) are estimated and compared. This experimental work reveals that Tsub has a strong influence on the growth rate, the surface morphology, and the structural properties of the as-deposited rubrene polycrystalline films.

  11. A method for polycrystalline silicon delineation applicable to a double-diffused MOS transistor

    NASA Technical Reports Server (NTRS)

    Halsor, J. L.; Lin, H. C.

    1974-01-01

    Method is simple and eliminates requirement for unreliable special etchants. Structure is graded in resistivity to prevent punch-through and has very narrow channel length to increase frequency response. Contacts are on top to permit planar integrated circuit structure. Polycrystalline shield will prevent creation of inversion layer in isolated region.

  12. Ion beam-induced luminescence as method of characterization of radiation damage in polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Jozwik, Iwona; Jagielski, Jacek; Gawlik, Grzegorz; Panczer, Gerard; Moncoffre, Nathalie; Ratajczak, Renata; Jozwik, Przemyslaw; Wajler, Anna; Sidorowicz, Agata; Thomé, Lionel

    2015-12-01

    The problem of information about damage build-up, intensively studied for single crystals, poses many difficulties for polycrystalline materials. The Rutherford Backscattering/Channeling (RBS/C) technique could be applied for single crystals only, but its use is excluded in polycrystalline materials. Therefore the development of a quantitative method well suited for the evaluation of damage level in polycrystalline materials is a must, and still constitutes a major challenge in materials analysis. A comparative study of damage accumulation in magnesium aluminate spinel (MgAl2O4) has been conducted using ionoluminescence (IL) and RBS/C techniques. The results obtained by both methods, demonstrate a two-step character of damage build-up process. The values of the cross-section on the damage creation in each case were estimated using MSDA model. The results presented here confirm the huge potential of the luminescence techniques for damage analysis in single- and polycrystalline samples, and ability of the IL method to perform fast, in situ analysis of damage accumulation process.

  13. Mesoscopic deformation features of shocked porous ceramic: Polycrystalline modeling and experimental observations

    NASA Astrophysics Data System (ADS)

    Yu, Yin; Wang, Wenqiang; He, Hongliang; Jiang, Tailong; Huan, Qiang; Zhang, Fuping; Li, Yongqiang; Lu, Tiecheng

    2015-03-01

    To prevent functional failure, the macroscopic shock response of ceramics needs to be understood. We explored the mesoscopic deformation features of porous ceramics, which are responsible for the measured macroscopic "plastic" wave profiles, using polycrystalline modeling and experiments. A polycrystalline model is established that considers the influence of two major microstructures (multi-voids and grain boundaries) in the porous ceramics. Shock experiments with the recovery of shocked porous lead zirconate titanate ceramics were conducted. The computational results show that shear cracks nucleate around voids under shock because of severe shear stress concentrations. Broken fragments fill the voids and lead to void collapse. Representative long-distance extended cracks and thick crevices are observed in the recovered sample subjected to 3.3 GPa compression. These representative features are reproduced by the polycrystalline model. An initial transgranular crack translates into an intergranular crack after a certain propagation range to form a long-distance extended crack. Intergranular cracks branch from the main transgranular crack during main crack propagation to form a thick crevice. The simultaneous propagation of main and branching cracks results in a more effective shock energy dissipation. Slippage and rotation deformation induced by multi-cracks allows the shocked porous ceramic to deform even after all the voids have collapsed. Mesoscopic deformations of porous ceramics induce significant stress relaxations and lead to macroscopic "plastic" wave profiles. The polycrystalline model will aid microstructures design and provide guidance for preventing the shock failure of functional ceramics.

  14. Ferromagnetic Ground States in Face-Centered Cubic Hubbard Clusters.

    PubMed

    Souza, T X R; Macedo, C A

    2016-01-01

    In this study, the ground state energies of face-centered cubic Hubbard clusters are analyzed using the Lanczos method. Examination of the ground state energy as a function of the number of particle per site n showed an energy minimum for face-centered cubic structures. This energy minimum decreased in n with increasing coulombic interaction parameter U. We found that the ground state energy had a minimum at n = 0.6, when U = 3W, where W denotes the non-interacting energy bandwidth and the face-centered cubic structure was ferromagnetic. These results, when compared with the properties of nickel, shows strong similarity with other finite temperature analyses in the literature and supports the Hirsh's conjecture that the interatomic direct exchange interaction dominates in driving the system into a ferromagnetic phase. PMID:27583653

  15. High-temperature fiber optic cubic-zirconia pressure sensor

    NASA Astrophysics Data System (ADS)

    Peng, Wei; Pickrell, Gary R.; Wang, Anbo

    2005-12-01

    There is a critical need for pressure sensors that can operate reliably at high temperatures in many industrial segments such as in the combustion section of gas turbine engines for both transportation and power generation, coal gasifiers, coal fired boilers, etc. Optical-based sensors are particularly attractive for the measurement of a wide variety of physical and chemical parameters in high-temperature and high-pressure industrial environments due to their small size and immunity to electromagnetic interference. A fiber optic pressure sensor utilizing single-crystal cubic zirconia as the sensing element is reported. The pressure response of this sensor has been measured at temperatures up to 1000 °C. Additional experimental results show that cubic zirconia could be used for pressure sensing at temperatures over 1000 °C. This study demonstrates the feasibility of using a novel cubic-zirconia sensor for pressure measurement at high temperatures.

  16. Use of Pom Pons To Illustrate Cubic Crystal Structures

    NASA Astrophysics Data System (ADS)

    Cady, Susan G.

    1997-07-01

    In general chemistry classes, students are introduced to the ways in which atoms are arranged in cubic crystal structures. Transposing the textbook illustrations into three dimensional structures is difficult for some students. This transitions is easier if a three dimensional model is available for examination. Several 3D models are cited. A quick to assemble, inexpensive, colorful, and durable alternative to these models and styrofoam balls is the use of olefin pom pons. Different sized pom pons can be used to demonstrate how the atomic radius will vary when comparing the different types of cubic crystal unit cells. Being made of a coarse material, pom pons can be stacked to illustrate different packing arrangements such as hexagonal close-packed and cubic close-packed structures. Pom pons make great atoms.

  17. Extended temperature dependence of elastic constants in cubic crystals.

    PubMed

    Telichko, A V; Sorokin, B P

    2015-08-01

    To extend the theory of the temperature dependence of the elastic constants in cubic crystals beyond the second- and third-order elastic constants, the fourth-order elastic constants, as well as the non-linearity in the thermal expansion temperature dependence, have been taken into account. Theoretical results were represented as temperature functions of the effective elastic constants and compared with experimental data for a number of cubic crystals, such as alkali metal halides, and elements gold and silver. The relations obtained give a more accurate description of the experimental temperature dependences of second-order elastic constants for a number of cubic crystals, including deviations from linear behavior. A good agreement between theoretical estimates and experimental data has been observed. PMID:25819879

  18. Compensation in epitaxial cubic SiC films

    NASA Technical Reports Server (NTRS)

    Segall, B.; Alterovitz, S. A.; Haugland, E. J.; Matus, L. G.

    1986-01-01

    Hall measurements on four n-type cubic SiC films epitaxially grown by chemical vapor deposition on SiC substrates are reported. The temperature dependent carrier concentrations indicate that the samples are highly compensated. Donor ionization energies, E sub D, are less than one half the values previously reported. The values for E sub D and the donor concentration N sub D, combined with results for small bulk platelets with nitrogen donors, suggest the relation E sub D (N sub D) = E sub D(O) - alpha N sub N sup 1/3 for cubic SiC. A curve fit gives alpha is approx 2.6x10/5 meV cm and E sub D (O) approx 48 meV, which is the generally accepted value of E sub D(O) for nitrogen donors in cubic SiC.

  19. Development and evaluation of polycrystalline cadmium telluride dosimeters for accurate quality assurance in radiation therapy

    NASA Astrophysics Data System (ADS)

    Oh, K.; Han, M.; Kim, K.; Heo, Y.; Moon, C.; Park, S.; Nam, S.

    2016-02-01

    For quality assurance in radiation therapy, several types of dosimeters are used such as ionization chambers, radiographic films, thermo-luminescent dosimeter (TLD), and semiconductor dosimeters. Among them, semiconductor dosimeters are particularly useful for in vivo dosimeters or high dose gradient area such as the penumbra region because they are more sensitive and smaller in size compared to typical dosimeters. In this study, we developed and evaluated Cadmium Telluride (CdTe) dosimeters, one of the most promising semiconductor dosimeters due to their high quantum efficiency and charge collection efficiency. Such CdTe dosimeters include single crystal form and polycrystalline form depending upon the fabrication process. Both types of CdTe dosimeters are commercially available, but only the polycrystalline form is suitable for radiation dosimeters, since it is less affected by volumetric effect and energy dependence. To develop and evaluate polycrystalline CdTe dosimeters, polycrystalline CdTe films were prepared by thermal evaporation. After that, CdTeO3 layer, thin oxide layer, was deposited on top of the CdTe film by RF sputtering to improve charge carrier transport properties and to reduce leakage current. Also, the CdTeO3 layer which acts as a passivation layer help the dosimeter to reduce their sensitivity changes with repeated use due to radiation damage. Finally, the top and bottom electrodes, In/Ti and Pt, were used to have Schottky contact. Subsequently, the electrical properties under high energy photon beams from linear accelerator (LINAC), such as response coincidence, dose linearity, dose rate dependence, reproducibility, and percentage depth dose, were measured to evaluate polycrystalline CdTe dosimeters. In addition, we compared the experimental data of the dosimeter fabricated in this study with those of the silicon diode dosimeter and Thimble ionization chamber which widely used in routine dosimetry system and dose measurements for radiation

  20. Complex dielectric properties of anhydrous polycrystalline glucose in the terahertz region

    NASA Astrophysics Data System (ADS)

    Sun, P.; Liu, W.; Zou, Y.; Jia, Qiong Z.; Li, Jia Y.

    2015-03-01

    We utilized terahertz time-domain spectroscopy (THz-TDS) to investigate the complex dielectric properties of solid polycrystalline material of anhydrous glucose (D-(+)-glucose with purity >99.9%). THz transmission spectra of samples were measured from 0.2 to 2.2 THz. The samples were prepared into tablets with thicknesses of 0.362, 0.447, 0.504, 0.522 and 0.626 mm, respectively. The imaginary part of the complex dielectric function of polycrystalline glucose showed that there were multiple characteristic absorption peaks at 1.232, 1.445, 1.522, 1.608, 1.811 and 1.987 THz, respectively. Moreover, for a given characteristic absorption peak, the real part of the complex dielectric function showed anomalous dispersion within the full width half maximum (FWHM) of the absorption peak. Both finite difference time-domain (FDTD) numerical simulations and experimental results showed that the complex dielectric function of anhydrous polycrystalline glucose fits well with the Lorentz dielectric mode. The plasma oscillation frequency was below the frequency of the light waves suggesting that the light waves passed through the polycrystalline glucose tablets. Calculations based on density functional theory (DFT) showed that the characteristic absorption peaks of polycrystalline glucose originated mainly from collective intermolecular vibrations such as hydrogen bonds and crystal phonon modes. The THz radiation can excite the vibrational or rotational energy levels of the biological macromolecules. This leads to changes in their spatial configuration or interactions. This study showed that THz-TDS has potential applications in biological and pharmaceutical research and food industry.

  1. Ultrasonic radiation from wedges of cubic profile: Experimental results.

    PubMed

    Anderson, Brian E; Remillieux, Marcel C; Le Bas, Pierre-Yves; Ulrich, T J; Pieczonka, Lukasz

    2015-12-01

    This paper presents experimental results demonstrating the increase in ultrasonic radiation obtained from a wedge of cubic profile relative to a plate of uniform thickness. The wedge of cubic profile provides high efficiency sound radiation matching layer from a mounted piezoelectric transducer into the surrounding air. Previous research on structures with indentations of power-law profile has focused on vibration mitigation using the so called "acoustic black-hole" effect, whereas here such structures are used to enhance ultrasonic radiation. The work provides experimental verification of the numerical results of Remillieux et al. (2014). PMID:26166628

  2. Cubic C8 : An Observable Allotrope of Carbon?

    PubMed

    Sharapa, Dmitry; Hirsch, Andreas; Meyer, Bernd; Clark, Timothy

    2015-07-20

    Ab initio and DFT calculations are used to investigate the structure, electronic properties, spectra and reactivity of cubic C8 , which is predicted to be aromatic according to Hirsch's rule. Although highly strained and with a small amount of diradical character, the carbon cube represents a surprisingly deep minimum and should therefore be observable as an isolated molecule. It is, however, predicted to be very reactive, both with itself and triplet oxygen. Calculated IR, Raman, and UV/Vis spectra are provided to aid identification of cubic C8 should it be synthesized. PMID:26013967

  3. Process for producing wurtzitic or cubic boron nitride

    DOEpatents

    Holt, J.B.; Kingman, D.D.; Bianchini, G.M.

    1992-04-28

    Disclosed is a process for producing wurtzitic or cubic boron nitride comprising the steps of: [A] preparing an intimate mixture of powdered boron oxide, a powdered metal selected from the group consisting of magnesium or aluminum, and a powdered metal azide; [B] igniting the mixture and bringing it to a temperature at which self-sustaining combustion occurs; [C] shocking the mixture at the end of the combustion thereof with a high pressure wave, thereby forming as a reaction product, wurtzitic or cubic boron nitride and occluded metal oxide; and, optionally [D] removing the occluded metal oxide from the reaction product. Also disclosed are reaction products made by the process described.

  4. Process for producing wurtzitic or cubic boron nitride

    DOEpatents

    Holt, J. Birch; Kingman, deceased, Donald D.; Bianchini, Gregory M.

    1992-01-01

    Disclosed is a process for producing wurtzitic or cubic boron nitride comprising the steps of: [A] preparing an intimate mixture of powdered boron oxide, a powdered metal selected from the group consisting of magnesium or aluminum, and a powdered metal azide; [B] igniting the mixture and bringing it to a temperature at which self-sustaining combustion occurs; [C] shocking the mixture at the end of the combustion thereof with a high pressure wave, thereby forming as a reaction product, wurtzitic or cubic boron nitride and occluded metal oxide; and, optionally [D] removing the occluded metal oxide from the reaction product. Also disclosed are reaction products made by the process described.

  5. The singular cubical set of a topological space

    NASA Astrophysics Data System (ADS)

    Antolini, Rosa; Wiest, Bert

    1999-01-01

    For any topological space X let C(X) be the realization of the singular cubical set of X; let * be the topological space consisting of one point. In [1] Antolini proves, as a corollary to a general theorem about cubical sets, that C(X) and X×C(*) are homotopy equivalent, provided X is a CW-complex. In this note we give a short geometric proof that for any topological space X there is a natural weak homotopy equivalence between C(X) and X×C(*).

  6. Stationary phase analysis of generalized cubic phase mask wavefront coding

    NASA Astrophysics Data System (ADS)

    Liu, Ming; Dong, Liquan; Zhao, Yuejin; Hui, Mei; Jia, Wei

    2013-07-01

    The modified generalized cubic phase mask (GCPM) has recently been applied in wavefront coding systems including infrared imaging and microscopy. In this paper, the stationary phase method is employed to analyze the GCPM characteristics. The SPA of the modulation transfer function (MTF) under misfocus aberration is derived for a wavefront coding system with a GCPM. The approximation corresponds with the Fast Fourier Transform (FFT) approach. On the basis of this approximation, we compare the characteristics of GCPM and cubic phase masks (CPM). A GCPM design approach based on stationary phase approximation is presented which helps to determine the initial parameter of phase mask, significantly decreasing the computational time required for numerical simulation.

  7. Measurement of the electrical properties of a polycrystalline cadmium telluride for direct conversion flat panel x-ray detector

    NASA Astrophysics Data System (ADS)

    Oh, K. M.; kim, D. K.; Shin, J. W.; Heo, S. U.; Kim, J. S.; Park, J. G.; Nam, S. H.

    2014-01-01

    Cadmium telluride (CdTe) is one of the best candidate direct conversion material for medical X-ray application because it satisfies the requirements of direct conversion x-ray material such as high atomic absorption, density, bandgap energy, work fuction, and resistivity. With such properties, single crystal CdTe exhibits high quantum efficiency and charge collection efficiency. However, for the development of low-cost large area detector, the study of the improvement of polycrystalline CdTe property is desirable. In this study, in order to improve the properties of polycrystalline CdTe, we produced polycrystalline CdTe with different kinds of raw materials, high purity Cd and Te powder compounds and bulk CdTe compound synthesized from single crystal CdTe. The electric properties including resistivity, x-ray sensitivity, and charge transport properties were investigated. As a result, polycrystalline CdTe exhibited simular level of resistivity and x-ray sensitivity to single crystal CdTe. The carrier transport properties of polycrystalline CdTe showed poorer properties than those of single crystal CdTe due to significant charge trapping. However, the polycrystalline CdTe fabricated with bulk CdTe compound synthesized from single crystal CdTe showed better charge transport properties than the polycrystalline CdTe fabricated with CdTe powder compounds. This is suitable for diagnostic x-ray detectors, especially for digital fluoroscopy.

  8. Ferroelectric domain switching of individual nanoscale grains in polycrystalline lead zirconate titanate thin films

    NASA Astrophysics Data System (ADS)

    Jing, Yuanyuan

    2011-12-01

    This thesis will focus on the switching behavior of nanoscale ferroelectric domains in polycrystalline thin films. Ferroelectrics are a class of dielectric materials that demonstrate spontaneous polarizations under zero applied electric field. A region with the same polarization is called a ferroelectric domain. One important attribute of ferroelectrics is the domain switching from one thermodynamically stable state to another by application of an external electric field. Ferroelectric domain switching has been intensively investigated in epitaxial thin films. However, little is known about the domain switching in polycrystalline thin films. The main reason is that each grain is differently orientated and each is in a unique local stress and electric field determined by neighboring grains. To understand and deterministically control the nanoscale domain switching in polycrystalline thin films, it's critical to experimentally identify the effect of local microstructure (grain orientation and grain boundary misorientation) on the individual grain switching behavior. In this thesis, the effect of local microstructure on domain switching has been quantitatively analyzed in a 100 nm thick polycrystalline PbZr 0.2Ti0.8O3 thin film. The ferroelectric domains are characterized by Piezoresponse Force Microscopy (PFM), with their switching behavior analyzed by Polarization Difference Maps (PDMs, an analytical technique developed in this work). The local microstructure is determined by Electron Back Scattering Diffraction (EBSD). The results are discussed in chapter 3 to 6. Chapter 3 introduces the PDMs technique that enables the rapid identification of 0o, 90o switching and 180o switching in polycrystalline thin films. By assigning different colors to different types of switching, the full nature of polarization switching can be visualized simultaneously for large number of domains or grains in one map. In chapter 4, an external electric field reversal experiment has been

  9. 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.

  10. Identification and quantification of oxygen species adsorbed on Pt(111) single-crystal and polycrystalline Pt electrodes by photoelectron spectroscopy.

    PubMed

    Wakisaka, Mitsuru; Suzuki, Hirokazu; Mitsui, Satoshi; Uchida, Hiroyuki; Watanabe, Masahiro

    2009-02-17

    We have positively identified oxygen species on Pt(111) single-crystal and polycrystalline Pt electrodes in N2-purged 0.1 M HF solution by X-ray photoelectron spectroscopy combined with an electrochemical cell. Four oxygen species (Oad, OHad, and two types of water molecules) were distinguished. The binding energies of each species were nearly constant over the whole potential region and independent of the single- or polycrystalline electrodes. The coverages, however, varied considerably and were dependent on the electrode potential. We have for the first time demonstrated clear differences in the surface oxidation processes for Pt(111) and polycrystalline Pt electrodes. PMID:19152331

  11. Spatial dependence of polycrystalline FTO’s conductance analyzed by conductive atomic force microscope (C-AFM)

    SciTech Connect

    Peixoto, Alexandre Pessoa; Costa, J. C. da

    2014-05-15

    Fluorine-doped Tin oxide (FTO) is a highly transparent, electrically conductive polycrystalline material frequently used as an electrode in organic solar cells and optical-electronic devices [1–2]. In this work a spatial analysis of the conductive behavior of FTO was carried out by Conductive-mode Atomic Force Microscopy (C-AFM). Rare highly oriented grains sample give us an opportunity to analyze the top portion of polycrystalline FTO and compare with the border one. It is shown that the current flow essentially takes place through the polycrystalline edge at grain boundaries.

  12. Tangent Lines without Derivatives for Quadratic and Cubic Equations

    ERIC Educational Resources Information Center

    Carroll, William J.

    2009-01-01

    In the quadratic equation, y = ax[superscript 2] + bx + c, the equation y = bx + c is identified as the equation of the line tangent to the parabola at its y-intercept. This is extended to give a convenient method of graphing tangent lines at any point on the graph of a quadratic or a cubic equation. (Contains 5 figures.)

  13. Rheology of cubic particles suspended in a Newtonian fluid.

    PubMed

    Cwalina, Colin D; Harrison, Kelsey J; Wagner, Norman J

    2016-05-18

    Many real-world industrial processes involve non-spherical particles suspended in a fluid medium. Knowledge of the flow behavior of these suspensions is essential for optimizing their transport properties and designing processing equipment. In the present work, we explore and report on the rheology of concentrated suspensions of cubic-shaped colloidal particles under steady and dynamic shear flow. These suspensions exhibit a rich non-Newtonian rheology that includes shear thickening and normal stress differences at high shear stresses. Scalings are proposed to connect the material properties of these suspensions of cubic particle to those measured for suspensions of spherical particles. Negative first normal stress differences indicate that lubrication hydrodynamic forces dominate the stress in the shear-thickened state. Accounting for the increased lubrication hydrodynamic interactions between the flat surfaces of the cubic particles allows for a quantitative comparison of the deviatoric stress in the shear-thickened state to that of spherical particles. New semi-empirical models for the viscosity and normal stress difference coefficients are presented for the shear-thickened state. The results of this study indicate that cubic particles offer new and unique opportunities to formulate colloidal dispersions for field-responsive materials. PMID:27112791

  14. Moufang loops of class 2 and cubic forms

    NASA Astrophysics Data System (ADS)

    Hsu, Tim

    2000-03-01

    We classify finite Moufang loops which are centrally nilpotent of class 2 in terms of certain cubic forms, concentrating on small Frattini Moufang loops, or SFMLs, which are Moufang loops L with a central subgroup Z of order p such that L/Z is an elementary abelian p-group. (For example, SFM 2-loops are precisely the class of code loops, in the sense of Griess.)More specifically, we first show that the nuclearly-derived subloop (normal associator subloop) of a Moufang loop of class 2 has exponent dividing 6. It follows that the subloop of elements of p-power order is associative for p > 3. Next, we show that if L is an SFML, then L/Z has the structure of a vector space with a symplectic cubic form. We then show that every symplectic cubic form is realized by some SFML and that two SFMLs are isomorphic in a manner preserving the central subgroup Z if and only if their symplectic cubic spaces are isomorphic up to scalar multiple. Consequently, we also obtain an explicit characterization of isotopy in SFM 3-loops. Finally, we extend many of our results to all finite Moufang loops of class 2.

  15. Assessing Inquiry Learning: How Much Is a Cubic Metre?

    ERIC Educational Resources Information Center

    Fry, Kym

    2014-01-01

    In this article, Kym Fry uses the "Programme for International Student Assessment" (PISA) assessment framework to break down what her Year 6 students learned as they explored the inquiry question, "How much is a cubic metre?" First, an overview of the lessons in the unit is provided. Quality assessment opportunities are…

  16. Hydrophobic Surfactant Proteins Induce a Phosphatidylethanolamine to Form Cubic Phases

    PubMed Central

    Chavarha, Mariya; Khoojinian, Hamed; Schulwitz, Leonard E.; Biswas, Samares C.; Rananavare, Shankar B.; Hall, Stephen B.

    2010-01-01

    Abstract The hydrophobic surfactant proteins SP-B and SP-C promote rapid adsorption of pulmonary surfactant to an air/water interface. Previous evidence suggests that they achieve this effect by facilitating the formation of a rate-limiting negatively curved stalk between the vesicular bilayer and the interface. To determine whether the proteins can alter the curvature of lipid leaflets, we used x-ray diffraction to investigate how the physiological mixture of these proteins affects structures formed by 1-palmitoyl-2-oleoyl phosphatidylethanolamine, which by itself undergoes the lamellar-to-inverse hexagonal phase transition at 71°C. In amounts as low as 0.03% (w:w) and at temperatures as low as 57°C, the proteins induce formation of bicontinuous inverse cubic phases. The proteins produce a dose-related shift of diffracted intensity to the cubic phases, with minimal evidence of other structures above 0.1% and 62°C, but no change in the lattice-constants of the lamellar or cubic phases. The induction of the bicontinuous cubic phases, in which the individual lipid leaflets have the same saddle-shaped curvature as the hypothetical stalk-intermediate, supports the proposed model of how the surfactant proteins promote adsorption. PMID:20409474

  17. Analytical properties of the anisotropic cubic Ising model

    SciTech Connect

    Hansel, D.; Maillard, J.M.; Oitmaa, J.; Velgakis, M.J.

    1987-07-01

    The authors combine an exact functional relation, the inversion relation, with conventional high-temperature expansions to explore the analytic properties of the anisotropic Ising model on both the square and simple cubic lattice. In particular, they investigate the nature of the singularities that occur in partially resummed expansions of the partition function and of the susceptibility.

  18. Morphosynthesis of cubic silver cages on monolithic activated carbon.

    PubMed

    Wang, Fei; Zhao, Hong; Lai, Yijian; Liu, Siyu; Zhao, Binyuan; Ning, Yuesheng; Hu, Xiaobin

    2013-11-14

    Cubic silver cages were prepared on monolithic activated carbon (MAC) pre-absorbed with Cl(-), SO4(2-), or PO4(3-) anions. Silver insoluble salts served as templates for the morphosynthesis of silver cages. The silver ions were reduced by reductive functional groups on MAC micropores through a galvanic cell reaction mechanism. PMID:24080952

  19. Integrability of Lotka-Volterra Planar Complex Cubic Systems

    NASA Astrophysics Data System (ADS)

    Dukarić, Maša; Giné, Jaume

    In this paper, we study the Lotka-Volterra complex cubic systems. We obtain necessary conditions of integrability for these systems with some restriction on the parameters. The sufficiency is proved for all conditions, except one which remains open, using different methods.

  20. A Unified Approach to Teaching Quadratic and Cubic Equations.

    ERIC Educational Resources Information Center

    Ward, A. J. B.

    2003-01-01

    Presents a simple method for teaching the algebraic solution of cubic equations via completion of the cube. Shows that this method is readily accepted by students already familiar with completion of the square as a method for quadratic equations. (Author/KHR)

  1. Natural convection of a magnetic fluid in a cubic enclosure

    NASA Astrophysics Data System (ADS)

    Kikura, H.; Sawada, T.; Tanahashi, T.

    1993-04-01

    Laminar natural convection heat transfer of a magnetic fluid in a cubic enclosure is examined experimentally. Wall-temperature distributions are visualized by thermosensitive liquid crystal sheets. The effect of the magnetic field on the transient temperature distributions, and the local and averaged Nusselt numbers are discussed.

  2. Failure of semiclassical models to describe resistivity of nanometric, polycrystalline tungsten films

    SciTech Connect

    Choi, Dooho; Liu, Xuan; Schelling, Patrick K.; Coffey, Kevin R.; Barmak, Katayun

    2014-03-14

    The impact of electron scattering at surfaces and grain boundaries in nanometric polycrystalline tungsten (W) films was studied. A series of polycrystalline W films ranging in thickness from 10 to 310 nm and lateral grain size from 74 to 133 nm were prepared on thermally oxidized Si. The Fuchs-Sondheimer surface-scattering model and Mayadas-Shatzkes grain-boundary scattering model were employed for quantitative analyses. Predictions from the theoretical models were found to deviate systematically from the experimental data. Possible reasons for the failure of the theoretical models to describe the experimental data are explored. Finally, a discussion of the crucial features lacking from existing models is presented, along with possible avenues for improving the models to result in better agreement with experimental data.

  3. Comparison of Deformation in High-Purity Single/Large Grain and Polycrystalline Niobium Superconducting Cavities

    SciTech Connect

    Ganapati Rao Myneni; Peter Kneisel

    2005-07-10

    The current approach for the fabrication of superconducting radio frequency (SRF) cavities is to roll and deep draw sheets of polycrystalline high-purity niobium. Recently, a new technique was developed at Jefferson Laboratory that enables the fabrication of single-crystal high-purity Nb SRF cavities. To better understand the differences between SRF cavities fabricated out of fine-grained polycrystalline sheet in the standard manner and single crystal cavities fabricated by the new technique, two half-cells were produced according to the two different procedures and compared using a variety of analytical techniques including optical microscopy, scanning laser confocal microscopy, profilometry, and X-ray diffraction. Crystallographic orientations, texture, and residual stresses were determined in the samples before and after forming and this poster presents the results of this ongoing study.

  4. The SEM-EBIV signals near the grain boundary in a polycrystalline solar cell

    NASA Astrophysics Data System (ADS)

    Romanowski, A.; Buczkowski, A.

    1985-12-01

    A new technique of EBIV measurements has been proposed. The open-circuit voltage signal modified by a grain boundary (GB) assuming a simple equivalent circuit of a polycrystalline solar cell has been analyzed. The numerical calculations of the voltage contrast as a function of the distance between the electron-hole generation sphere and the GB were performed. The EBIC and EBIV characteristics have been compared on account of their usefulness for evaluating the carrier diffusion length. The recombination velocity at the grain boundary, and the shunt resistance of the cell. It was found that EBIV measurements provided more detailed information about the electrical properties of the GB and the junction parameters of a polycrystalline solar cell.

  5. Elasticity and hardness of nano-polycrystalline boron nitrides: The apparent Hall-Petch effect

    SciTech Connect

    Nagakubo, A.; Ogi, H. Hirao, M.; Sumiya, H.

    2014-08-25

    Nano-polycrystalline boron nitride (BN) is expected to replace diamond as a superhard and superstiff material. Although its hardening was reported, its elasticity remains unclear and the as-measured hardness could be significantly different from the true value due to the elastic recovery. In this study, we measured the longitudinal-wave elastic constant of nano-polycrystalline BNs using picosecond ultrasound spectroscopy and confirmed the elastic softening for small-grain BNs. We also measured Vickers and Knoop hardness for the same specimens and clarified the relationship between hardness and stiffness. The Vickers hardness significantly increased as the grain size decreased, while the Knoop hardness remained nearly unchanged. We attribute the apparent increase in Vickers hardness to the elastic recovery and propose a model to support this insight.

  6. The properties of polycrystalline silicon solar cells with controlled titanium additions

    NASA Technical Reports Server (NTRS)

    Rohatgi, A.; Hopkins, R. H.; Davis, J. R., Jr.

    1981-01-01

    By coupling the results of electrical measurements, such as spectral response, lighted and dark I-V determinations, and deep-level-transient spectroscopy with optical and laser scan photomicroscopy, the effects of grain boundaries and impurities on silicon solar cells were evaluated. Titanium, which produces two deep levels in silicon, degrades cell performance by reducing bulk lifetime and thus cell short-circuit current. Electrically active grain boundaries induce carrier recombination in the bulk and depletion regions of the solar cell. Experimental data imply a small but measurable segregation of titanium into some grain boundaries of the polycrystalline silicon containing high Ti concentration. However, for the titanium-contaminated polycrystalline material used in this study, solar cell performance is dominated by the electrically active titanium concentration in the grains. Microstructural impacts on the devices are of secondary importance

  7. Nucleation and growth of damage in polycrystalline aluminum under dynamic tensile loading

    SciTech Connect

    Qi, M. L.; Yao, Y.; Ran, X. X.; Ye, W.; Bie, B. X.; Fan, D.; Li, P.

    2015-03-15

    Plate-impact experiments were conducted to study the features and mechanisms of void nucleation and growth in the polycrystalline of pure aluminum under dynamic loading. Soft-recovered samples have been analyzed by metallographic microscopy, electron back scattering diffraction (EBSD), and synchrotron radiation x-ray tomography technology. It was found that most of the void nucleation in grains neared the boundaries of “weak-orientation” grains and grew toward the grain boundaries with fractured small grains around the boundaries. This was mainly caused by the accumulation and interaction of slip systems in the “weak-orientation” grains. In addition, the micro voids were nearly octahedron because the octahedral slip systems were formed by 8 slip planes in the polycrystalline of pure aluminum. The EBSD results are consistent with the three-dimensional structure observed by synchrotron radiation x-ray.

  8. Electrically Benign Behavior of Grain Boundaries in Polycrystalline CuInSe2 Films

    SciTech Connect

    Yan, Y.; Jiang, C. S.; Noufi, R.; Wei, S. H.; Moutinho, H. R.; Al-Jassim, M. M.

    2007-12-07

    The classic grain-boundary (GB) model concludes that GBs in polycrystalline semiconductors create deep levels that are extremely harmful to optoelectronic applications. However, our first-principles density-functional theory calculations reveal that, surprisingly, GBs in CuInSe{sub 2} (CIS) do not follow the classic GB model: GBs in CIS do not create deep levels due to the large atomic relaxation in GB regions. Thus, unlike the classic GB model, GBs in CIS are electrically benign, which explains the long-standing puzzling fact that polycrystalline CIS solar cells with remarkable efficiency can be achieved without deliberate GB passivation. This benign electrical character of GBs in CIS is confirmed by our scanning Kelvin probe microscopy measurements on Cu(In,Ga)Se{sub 2} chalcopyrite films.

  9. Grain-Boundary Physics in Polycrystalline CuInSe2 Revisited: Experiment and Theory

    SciTech Connect

    Yan, Y.; Noufi, R.; Al-Jassim, M. M.

    2006-01-01

    Current studies have attributed the remarkable performance of polycrystalline CuInSe{sub 2} (CIS) to anomalous grain-boundary (GB) physics in CIS. The recent theory predicts that GBs in CIS are hole barriers, which prevent GB electrons from recombining. We examine the atomic structure and chemical composition of (112) GBs in Cu(In,Ga)Se{sub 2} (CIGS) using high-resolution Z-contrast imaging and nanoprobe x-ray energy-dispersive spectroscopy. We show that the theoretically predicted Cu-vacancy rows are not observed in (112) GBs in CIGS. Our first-principles modeling further reveals that the (112) GBs in CIS do not act as hole barriers. Our results suggest that the superior performance of polycrystalline CIS should not be explained solely by the GB behaviors.

  10. Method of azimuthally stable Mueller-matrix diagnostics of blood plasma polycrystalline films in cancer diagnostics

    NASA Astrophysics Data System (ADS)

    Ushenko, Yu. A.; Prysyazhnyuk, V. P.; Gavrylyak, M. S.; Gorsky, M. P.; Bachinskiy, V. T.; Vanchuliak, O. Ya.

    2015-02-01

    A new information optical technique of diagnostics of the structure of polycrystalline films of blood plasma is proposed. The model of Mueller-matrix description of mechanisms of optical anisotropy of such objects as optical activity, birefringence, as well as linear and circular dichroism is suggested. The ensemble of informationally topical azimuthally stable Mueller-matrix invariants is determined. Within the statistical analysis of such parameters distributions the objective criteria of differentiation of films of blood plasma taken from healthy and patients with liver cirrhosis were determined. From the point of view of probative medicine the operational characteristics (sensitivity, specificity and accuracy) of the information-optical method of Mueller-matrix mapping of polycrystalline films of blood plasma were found and its efficiency in diagnostics of liver cirrhosis was demonstrated. Prospects of application of the method in experimental medicine to differentiate postmortem changes of the myocardial tissue was examined.

  11. Photonic-band-gap effects in two-dimensional polycrystalline and amorphous structures

    SciTech Connect

    Yang, Jin-Kyu; Noh, Heeso; Liew, Seng-Fatt; Schreck, Carl; Guy, Mikhael I.; O'Hern, Corey S.; Cao, Hui

    2010-11-15

    We study numerically the density of optical states (DOS) in two-dimensional photonic structures with short-range positional order and observe a transition from polycrystalline to amorphous photonic systems. In polycrystals, photonic band gaps (PBGs) are formed within individual domains, which leads to a depletion of the DOS similar to that in periodic structures. In amorphous photonic media, the domain sizes are too small to form PBGs, thus the depletion of the DOS is weakened significantly. The critical domain size that separates the polycrystalline and amorphous regimes is determined by the attenuation length of Bragg scattering, which depends not only on the degree of positional order but also the refractive-index contrast of the photonic material. Even with relatively low-refractive-index contrast, we find that modest short-range positional order in photonic structures enhances light confinement via collective scattering and interference.

  12. Elasticity and hardness of nano-polycrystalline boron nitrides: The apparent Hall-Petch effect

    NASA Astrophysics Data System (ADS)

    Nagakubo, A.; Ogi, H.; Sumiya, H.; Hirao, M.

    2014-08-01

    Nano-polycrystalline boron nitride (BN) is expected to replace diamond as a superhard and superstiff material. Although its hardening was reported, its elasticity remains unclear and the as-measured hardness could be significantly different from the true value due to the elastic recovery. In this study, we measured the longitudinal-wave elastic constant of nano-polycrystalline BNs using picosecond ultrasound spectroscopy and confirmed the elastic softening for small-grain BNs. We also measured Vickers and Knoop hardness for the same specimens and clarified the relationship between hardness and stiffness. The Vickers hardness significantly increased as the grain size decreased, while the Knoop hardness remained nearly unchanged. We attribute the apparent increase in Vickers hardness to the elastic recovery and propose a model to support this insight.

  13. Optimized growth and dielectric properties of barium titanate thin films on polycrystalline Ni foils

    NASA Astrophysics Data System (ADS)

    Liang, Wei-Zheng; Ji, Yan-Da; Nan, Tian-Xiang; Huang, Jiang; Zeng, Hui-Zhong; Du, Hui; Chen, Chong-Lin; Lin, Yuan

    2012-06-01

    Barium titanate (BTO) thin films were deposited on polycrystalline Ni foils by using the polymer assisted deposition (PAD) technique. The growth conditions including ambient and annealing temperatures were carefully optimized based on thermal dynamic analysis to control the oxidation processing and interdiffusion. Crystal structures, surface morphologies, and dielectric performance were examined and compared for BTO thin films annealed under different temperatures. Correlations between the fabrication conditions, microstructures, and dielectric properties were discussed. BTO thin films fabricated under the optimized conditions show good crystalline structure and promising dielectric properties with inr ~ 400 and tan δ < 0.025 at 100 kHz. The data demonstrate that BTO films grown on polycrystalline Ni substrates by PAD are promising in device applications.

  14. Enhanced photovoltaic properties in graphene/polycrystalline BiFeO3/Pt heterojunction structure

    NASA Astrophysics Data System (ADS)

    Zang, Yongyuan; Xie, Dan; Wu, Xiao; Chen, Yu; Lin, Yuxuan; Li, Mohan; Tian, He; Li, Xiao; Li, Zhen; Zhu, Hongwei; Ren, Tianling; Plant, David

    2011-09-01

    We report the enhanced photovoltaic properties in polycrystalline BiFeO3 (BFO) thin films with graphene as top electrodes. The short circuit current density (Jsc) and open circuit voltage of the heterojunction are measured to be 25 μA/cm2 and 0.44 V, respectively, much higher than the reported values for polycrystalline BFO with indium tin oxide (ITO) as top electrodes. Influence of HNO3 treatment on the photovoltaic properties is studied, and a significant photocurrent density improvement from 25 μA/cm2 to 2.8 mA/cm2 is observed. A metal-intrinsic semiconductor-metal model is proposed to explain the graphene induced enhancement comparing with traditional ITO.

  15. Annealing Effects on Creep and Rupture of Polycrystalline Alumina-Based Fibers

    NASA Technical Reports Server (NTRS)

    Goldsby, J. C.; Yun, H. M.; Morscher, G. N.; DiCarlo, J. A.

    1998-01-01

    Continuous-length polycrystalline aluminum-oxide-based fibers are being considered as reinforcements for advanced high-temperature composite materials. For these fine-grained fibers, basic issues arise concerning grain growth and microstructural instability during composite fabrication and the resulting effects on the fiber's thermo-mechanical properties. To examine these issues, commercially available Nextel 610 (alumina) and Altex (alumina-silica) fibers were annealed at 1100 and 1300 C for up to 100 hr in air. Changes in fiber microstructure, fiber tensile creep, stress rupture, and bend stress relaxation (BSR) that occurred with annealing were then determined. BSR tests were also used to compare as-received and annealed fibers to other polycrystalline oxide fibers. Annealing was shown to have a significant effect, particularly on the Altex fiber, and caused it to have increased creep resistance.

  16. Stable powders made from photosensitive polycrystalline complexes of heterocyclic monomers and their polymers

    NASA Technical Reports Server (NTRS)

    Hodko, Dalibor (Inventor); Murphy, Oliver J. (Inventor); Hitchens, G. Duncan (Inventor)

    1999-01-01

    The present invention relates to a low electronic conductivity polymer composition having well dispersed metal granules, a stable powder made from photosensitive polycrystalline complexes of pyrrole, or its substituted derivatives and silver cations for making the polymer composition, and methods of forming the stable powder and polymer composition, respectively. A polycrystalline complex of silver and a monomer, such as pyrrole, its substituted derivatives or combinations thereof, is precipitated in the form of a stable photosensitive powder upon addition of the monomer to a solvent solution, such as toluene containing an electron acceptor. The photosensitive powder can be stored in the dark until needed. The powder may be dissolved in a solvent, cast onto a substrate and photopolymerized.

  17. Solar cells utilizing pulsed-energy crystallized microcrystalline/polycrystalline silicon

    DOEpatents

    Kaschmitter, James L.; Sigmon, Thomas W.

    1995-01-01

    A process for producing multi-terminal devices such as solar cells wherein a pulsed high energy source is used to melt and crystallize amorphous silicon deposited on a substrate which is intolerant to high processing temperatures, whereby to amorphous silicon is converted into a microcrystalline/polycrystalline phase. Dopant and hydrogenization can be added during the fabrication process which provides for fabrication of extremely planar, ultra shallow contacts which results in reduction of non-current collecting contact volume. The use of the pulsed energy beams results in the ability to fabricate high efficiency microcrystalline/polycrystalline solar cells on the so-called low-temperature, inexpensive plastic substrates which are intolerant to high processing temperatures.

  18. Boron- and phosphorus-doped polycrystalline silicon thin films prepared by silver-induced layer exchange

    SciTech Connect

    Antesberger, T.; Wassner, T. A.; Jaeger, C.; Algasinger, M.; Kashani, M.; Scholz, M.; Matich, S.; Stutzmann, M.

    2013-05-27

    Intentional boron and phosphorus doping of polycrystalline silicon thin films on glass prepared by the silver-induced layer exchange is presented. A silver/(titanium) oxide/amorphous silicon stack is annealed at temperatures below the eutectic temperature of the Ag/Si system, leading to a complete layer exchange and simultaneous crystallization of the amorphous silicon. Intentional doping of the amorphous silicon prior to the exchange process results in boron- or phosphorus-doped polycrystalline silicon. Hall effect measurements show carrier concentrations between 2 Multiplication-Sign 10{sup 17} cm{sup -3} and 3 Multiplication-Sign 10{sup 20} cm{sup -3} for phosphorus and 4 Multiplication-Sign 10{sup 18} cm{sup -3} to 3 Multiplication-Sign 10{sup 19} cm{sup -3} for boron-doped layers, with carrier mobilities up to 90 cm{sup 2}/V s.

  19. Effect of the microstructure on the thermoelectric properties of polycrystalline lanthanum chalcogenides

    NASA Technical Reports Server (NTRS)

    Lockwood, A.; Wood, C.; Vandersande, J.; Zoltan, A.; Parker, J.; Danielson, L.; Alexander, M.; Whittenberger, D.

    1987-01-01

    Small amounts of second phase materials can have important effects on the thermoelectric properties of polycrystalline gamma-La(3-x)X4 (X-S, Te; X in the range of 0 to 1/3). Microscopic examination by SEM of hot pressed La(3-x)Te4 samples has revealed from 1-5 vol. pct of La2O2Te, an amount which is not detected by X-ray powder diffraction measurements. This amount of La2O2Te resulting from oxygen contamination can reduce the concentration of electrons by as much as 10 to 75 percent below the electron concentration calculated for single phase La(3-x)Te4 in the composition range of greatest interest. Small amounts of second phase materials can also lower the lattice thermal conductivity by scattering low frequency phonons. These results indicate that microstructural effects should be considered when electrical and thermal properties of polycrystalline materials are analyzed.

  20. Synthesis and absorbing mechanism of two-layer microwave absorbers containing polycrystalline iron fibers and carbonyl iron

    NASA Astrophysics Data System (ADS)

    Ding, Qingwei; Zhang, Mingang; Zhang, Cunrui; Qian, Tianwei

    2013-04-01

    Polycrystalline iron fibers were fabricated by α-FeOOH fiber precursors. Two-layer microwave absorber had been prepared by as-prepared polycrystalline iron fibers and carbonyl iron. The structure, morphology and properties of the composites were characterized with X-ray diffraction, scanning electron microscope and Network Analyzer. The complex permittivity and reflection loss (dB) of the composites were measured employing vector network analyzer model PNA 3629D vector in the frequency range between 30 and 6000 MHz. The thickness effect of the carbonyl iron layer on the microwave loss properties of the composites was investigated. A possible microwave-absorbing mechanism of polycrystalline iron fibers/carbonyl iron composite was proposed. The polycrystalline iron fibers/carbonyl iron composite can find applications in suppression of electromagnetic interference, and reduction of radar signature.

  1. Theory of transport phenomena in polycrystalline lead chalcogenide films. Mobility. Nondegenerate statistics

    SciTech Connect

    Atakulov, Sh. B. Zaynolobidinova, S. M.; Nabiev, G. A.; Nabiyev, M. B.; Yuldashev, A. A.

    2013-07-15

    The mobility of nondegenerate electrons in quasi-single-crystal and polycrystalline PbTe films is experimentally investigated. The results obtained are compared with the data for bulk crystals at the same charge-carrier concentration. Under the assumption of limitation of the charge-carrier mobility by intercrystallite potential barriers, electron transport in an electric field is theoretically considered. The theoretical results are in good agreement with the experiment.

  2. Polycrystalline CVD diamond detector: Fast response and high sensitivity with large area

    SciTech Connect

    Liu, Linyue Zhang, Xianpeng; Zhong, Yunhong; Ouyang, Xiaoping Zhang, Jianfu

    2014-01-15

    Polycrystalline diamond was successfully used to fabricate a large area (diameter up to 46 mm) radiation detector. It was proven that the developed detector shows a fast pulsed response time and a high sensitivity, therefore its rise time is lower than 5 ns, which is two times faster than that of a Si-PIN detector of the same size. And because of the large sensitive area, this detector shows good dominance in fast pulsed and low density radiation detection.

  3. Second- and third-order elastic coefficients in polycrystalline aluminum alloy AMg6

    NASA Astrophysics Data System (ADS)

    Volkov, A. D.; Kokshaiskii, A. I.; Korobov, A. I.; Prokhorov, V. M.

    2015-11-01

    All independent second- and third-order elastic coefficients were measured in the isotropic polycrystalline aluminum alloy AMg6 (Al-Mg-Mn system) using the Ritec RAM-5000 SNAP SYSTEM ultrasonic automated complex operating in the pulsed mode. The third-order elastic coefficients were determined using the Thurston-Bragger method from the experimentally measured velocity of shear and longitudinal elastic waves in AMg6 alloy as a function of uniaxial compression.

  4. Nano-scale machining of polycrystalline coppers - effects of grain size and machining parameters

    PubMed Central

    2013-01-01

    In this study, a comprehensive investigation on nano-scale machining of polycrystalline copper structures is carried out by molecular dynamics (MD) simulation. Simulation cases are constructed to study the impacts of grain size, as well as various machining parameters. Six polycrystalline copper structures are produced, which have the corresponding equivalent grain sizes of 5.32, 6.70, 8.44, 13.40, 14.75, and 16.88 nm, respectively. Three levels of depth of cut, machining speed, and tool rake angle are also considered. The results show that greater cutting forces are required in nano-scale polycrystalline machining with the increase of depth of cut, machining speed, and the use of the negative tool rake angles. The distributions of equivalent stress are consistent with the cutting force trends. Moreover, it is discovered that in the grain size range of 5.32 to 14.75 nm, the cutting forces and equivalent stress increase with the increase of grain size for the nano-structured copper, while the trends reserve after the grain size becomes even higher. This discovery confirms the existence of both the regular Hall–Petch relation and the inverse Hall–Petch relation in polycrystalline machining, and the existence of a threshold grain size allows one of the two relations to become dominant. The dislocation-grain boundary interaction shows that the resistance of the grain boundary to dislocation movement is the fundamental mechanism of the Hall–Petch relation, while grain boundary diffusion and movement is the reason of the inverse Hall–Petch relation. PMID:24267785

  5. Effect of small perturbations on the evolution of polycrystalline structure during plastic deformation

    NASA Astrophysics Data System (ADS)

    Korznikova, E. A.; Baimova, Yu. A.; Kistanov, A. A.; Dmitriev, S. V.; Korznikov, A. V.

    2014-09-01

    The method of molecular dynamics has been used to study the influence of initial perturbations on the evolution of grain boundaries during the shear plastic deformation of a two-dimensional polycrystalline material with nanoscale grains. It has been shown that short-term thermalization-induced small perturbations result in noticeable differences in grain boundaries configurations at the deformation of 0.05 and the polycrystal completely loses its initial grain boundary structure at the deformation of 0.4.

  6. Laser generation in polycrystalline Cr{sup 2+}:ZnSe with undoped faces

    SciTech Connect

    Savin, D V; Gavrishchuk, E M; Ikonnikov, V B; Eremeykin, O N; Egorov, A S

    2015-01-31

    An original method has been suggested for producing polycrystalline Cr{sup 2+}:ZnSe samples with undoped faces. Generation characteristics of a Cr{sup 2+}:ZnSe laser are studied under pulse-periodic pumping by a Tm{sup 3+}:YLF-laser. The efficiency of converting the pump radiation into laser generation at a wavelength of 2350 nm is 20%. Cr{sup 2+}:ZnSe samples exhibit high resistance to surface breakdown. (lasers)

  7. Implementation of Two-Dimensional Polycrystalline Grains in Object Oriented Micromagnetic Framework

    PubMed Central

    Lau, J. W.; McMichael, R. D.; Donahue, M. J.

    2009-01-01

    In response to the growing need for a more accurate micromagnetic model to understand switching phenomenon in nanoscale magnets, we developed the capability to simulate two-dimensional polycrystalline grains using the Object Oriented Micromagnetic Framework (OOMMF). This addition allows users full flexibility in determining the magnetocrystalline anisotropy and axe in each grain as well as the inter- and intragranular exchange coupling strength. PMID:27504213

  8. Thin-film polycrystalline n-ZnO/p-CuO heterojunction

    SciTech Connect

    Lisitski, O. L.; Kumekov, M. E.; Kumekov, S. E. Terukov, E. I.

    2009-06-15

    Results of X-ray diffraction and spectral-optical studies of n-ZnO and p-CuO films deposited by gas-discharge sputtering with subsequent annealing are presented. It is shown that, despite the difference in the crystal systems, the polycrystallinity of n-ZnO and p-CuO films enables fabrication of a heterojunction from this pair of materials.

  9. Constitutive model of creep in polycrystalline halite based on workhardening and recovery

    SciTech Connect

    Munson, D.E.

    1993-07-01

    A multimechanism constitutive model of creep has been developed which incorporates the workhardening and recovery transient creep behavior. This model has been applied to the creep of polycrystalline halite. The specific application of the model is in the calculation of the closure of underground rooms in layered salt deposits. Through the use of finite element calculations, this model, with appropriate laboratory material parameters and a Tresca flow potential, has predicted the measured closure of a number of large in situ experimental rooms.

  10. Performance study of polycrystalline CVD diamond detectors for fast neutron monitoring

    SciTech Connect

    Singh, Arvind Kumar, Amit Topkar, Anita

    2014-04-24

    Diamond detectors using polycrystalline CVD diamond substrates of thickness 300μm and 100μm were fabricated for fast neutron monitoring application.. The characterization of detectors was carried out using various tests such as leakage current, capacitance and alpha particle response. The performance of detectors was evaluated for fast neutrons at different neutron yields. The results presented in this work demonstrate that the diamond detectors will be suitable for monitoring fast neutrons.

  11. A new phase in polycrystalline magnetoresistive Sr 2FeMoO 6

    NASA Astrophysics Data System (ADS)

    Dai, M. X.; Su, C.; Wang, R.; Wang, Z. L.

    2001-07-01

    A new layered body-centered tetragonal perovskite structure was observed in polycrystalline Sr 2FeMoO 6 materials by transmission electron microscopy (TEM). Together with the double perovskite (DB) and the layered superstructure with tripled c-axis (ST) reported previously, the three ordered perovskite phases co-exists in the grain by sharing a common atomic plane of (001). The translation periodicity along the direction perpendicular to the layer plane is about 20 Å.

  12. Polycrystalline VO2 thin films via femtosecond laser processing of amorphous VO x

    NASA Astrophysics Data System (ADS)

    Charipar, N. A.; Kim, H.; Breckenfeld, E.; Charipar, K. M.; Mathews, S. A.; Piqué, A.

    2016-05-01

    Femtosecond laser processing of pulsed laser-deposited amorphous vanadium oxide thin films was investigated. Polycrystalline VO2 thin films were achieved by femtosecond laser processing in air at room temperature. The electrical transport properties, crystal structure, surface morphology, and optical properties were characterized. The laser-processed films exhibited a metal-insulator phase transition characteristic of VO2, thus presenting a pathway for the growth of crystalline vanadium dioxide films on low-temperature substrates.

  13. Development and Testing of a Jet Assisted Polycrystalline Diamond Drilling Bit. Phase II Development Efforts

    SciTech Connect

    David S. Pixton

    1999-09-20

    Phase II efforts to develop a jet-assisted rotary-percussion drill bit are discussed. Key developments under this contract include: (1) a design for a more robust polycrystalline diamond drag cutter; (2) a new drilling mechanism which improves penetration and life of cutters; and (3) a means of creating a high-pressure mud jet inside of a percussion drill bit. Field tests of the new drill bit and the new robust cutter are forthcoming.

  14. 16 CFR 500.14 - Statements of cubic measure and dry measure.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 16 Commercial Practices 1 2012-01-01 2012-01-01 false Statements of cubic measure and dry measure... UNDER SECTION 4 OF THE FAIR PACKAGING AND LABELING ACT § 500.14 Statements of cubic measure and dry measure. Statements of cubic measure and dry measure shall be expressed in terms most appropriate to...

  15. 16 CFR 500.14 - Statements of cubic measure and dry measure.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 16 Commercial Practices 1 2011-01-01 2011-01-01 false Statements of cubic measure and dry measure... UNDER SECTION 4 OF THE FAIR PACKAGING AND LABELING ACT § 500.14 Statements of cubic measure and dry measure. Statements of cubic measure and dry measure shall be expressed in terms most appropriate to...

  16. 16 CFR 500.14 - Statements of cubic measure and dry measure.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 16 Commercial Practices 1 2010-01-01 2010-01-01 false Statements of cubic measure and dry measure... UNDER SECTION 4 OF THE FAIR PACKAGING AND LABELING ACT § 500.14 Statements of cubic measure and dry measure. Statements of cubic measure and dry measure shall be expressed in terms most appropriate to...

  17. Helium irradiation effects in polycrystalline Si, silica, and single crystal Si

    NASA Astrophysics Data System (ADS)

    Abrams, K. J.; Hinks, J. A.; Pawley, C. J.; Greaves, G.; van den Berg, J. A.; Eyidi, D.; Ward, M. B.; Donnelly, S. E.

    2012-04-01

    Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6 keV helium ion irradiation of a thin (≈55 nm thick) tri-layer consisting of polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the TEM under conditions where approximately 24% of the incident ions came to rest in the specimen. This paper reports on the comparative development of irradiation-induced defects (primarily helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides direct measurement of a radiation-induced increase in the width of the polycrystalline layer and shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiation-induced viscoelastic flow processes in the silica under the influence of stresses applied by the swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion irradiation; however, this is estimated to be a relatively minor effect with swelling and stress-related viscoelastic flow being the dominant mechanisms of dimensional change.

  18. Calculation of Debye-Scherrer diffraction patterns from highly stressed polycrystalline materials

    NASA Astrophysics Data System (ADS)

    MacDonald, M. J.; Vorberger, J.; Gamboa, E. J.; Drake, R. P.; Glenzer, S. H.; Fletcher, L. B.

    2016-06-01

    Calculations of Debye-Scherrer diffraction patterns from polycrystalline materials have typically been done in the limit of small deviatoric stresses. Although these methods are well suited for experiments conducted near hydrostatic conditions, more robust models are required to diagnose the large strain anisotropies present in dynamic compression experiments. A method to predict Debye-Scherrer diffraction patterns for arbitrary strains has been presented in the Voigt (iso-strain) limit [Higginbotham, J. Appl. Phys. 115, 174906 (2014)]. Here, we present a method to calculate Debye-Scherrer diffraction patterns from highly stressed polycrystalline samples in the Reuss (iso-stress) limit. This analysis uses elastic constants to calculate lattice strains for all initial crystallite orientations, enabling elastic anisotropy and sample texture effects to be modeled directly. The effects of probing geometry, deviatoric stresses, and sample texture are demonstrated and compared to Voigt limit predictions. An example of shock-compressed polycrystalline diamond is presented to illustrate how this model can be applied and demonstrates the importance of including material strength when interpreting diffraction in dynamic compression experiments.

  19. Influence of lattice distortion on phase transition properties of polycrystalline VO2 thin film

    NASA Astrophysics Data System (ADS)

    Lin, Tiegui; Wang, Langping; Wang, Xiaofeng; Zhang, Yufen; Yu, Yonghao

    2016-08-01

    In this work, high power impulse magnetron sputtering was used to control the lattice distortion in polycrystalline VO2 thin film. SEM images revealed that all the VO2 thin films had crystallite sizes of below 20 nm, and similar configurations. UV-vis-near IR transmittance spectra measured at different temperatures showed that most of the as-deposited films had a typical metal-insulator transition. Four-point probe resistivity results showed that the transition temperature of the films varied from 54.5 to 32 °C. The X-ray diffraction (XRD) patterns of the as-deposited films revealed that most were polycrystalline monoclinic VO2. The XRD results also confirmed that the lattice distortions in the as-deposited films were different, and the transition temperature decreased with the difference between the interplanar spacing of the as-deposited thin film and standard rutile VO2. Furthermore, a room temperature rutile VO2 thin film was successfully synthesized when this difference was small enough. Additionally, XRD patterns measured at varied temperatures revealed that the phase transition process of the polycrystalline VO2 thin film was a coordinative deformation between grains with different orientations. The main structural change during the phase transition was a gradual shift in interplanar spacing with temperature.

  20. Atomistically derived cohesive zone model of intergranular fracture in polycrystalline graphene

    NASA Astrophysics Data System (ADS)

    Guin, Laurent; Raphanel, Jean L.; Kysar, Jeffrey W.

    2016-06-01

    Pristine single crystal graphene is the strongest known two-dimensional material, and its nonlinear anisotropic mechanical properties are well understood from the atomic length scale up to a continuum description. However, experiments indicate that grain boundaries in the polycrystalline form reduce the mechanical behavior of polycrystalline graphene. Herein, we perform atomistic-scale molecular dynamics simulations of the deformation and fracture of graphene grain boundaries and express the results as continuum cohesive zone models (CZMs) that embed notions of the grain boundary ultimate strength and fracture toughness. To facilitate energy balance, we employ a new methodology that simulates a quasi-static controlled crack propagation which renders the kinetic energy contribution to the total energy negligible. We verify good agreement between Griffith's critical energy release rate and the work of separation of the CZM, and we note that the energy of crack edges and fracture toughness differs by about 35%, which is attributed to the phenomenon of bond trapping. This justifies the implementation of the CZM within the context of the finite element method (FEM). To enhance computational efficiency in the FEM implementation, we discuss the use of scaled traction-separation laws (TSLs) for larger element sizes. As a final result, we have established that the failure characteristics of pristine graphene and high tilt angle bicrystals differ by less than 10%. This result suggests that one could use a unique or a few typical TSLs as a good approximation for the CZMs associated with the mechanical simulations of the polycrystalline graphene.

  1. Bottom-up processing and low temperature transport properties of polycrystalline SnSe

    SciTech Connect

    Ge, Zhen-Hua; Wei, Kaya; Lewis, Hutton; Martin, Joshua; Nolas, George S.

    2015-05-15

    A hydrothermal approach was employed to efficiently synthesize SnSe nanorods. The nanorods were consolidated into polycrystalline SnSe by spark plasma sintering for low temperature electrical and thermal properties characterization. The low temperature transport properties indicate semiconducting behavior with a typical dielectric temperature dependence of the thermal conductivity. The transport properties are discussed in light of the recent interest in this material for thermoelectric applications. The nanorod growth mechanism is also discussed in detail. - Graphical abstract: SnSe nanorods were synthesized by a simple hydrothermal method through a bottom-up approach. Micron sized flower-like crystals changed to nanorods with increasing hydrothermal temperature. Low temperature transport properties of polycrystalline SnSe, after SPS densification, were reported for the first time. This bottom-up synthetic approach can be used to produce phase-pure dense polycrystalline materials for thermoelectrics applications. - Highlights: • SnSe nanorods were synthesized by a simple and efficient hydrothermal approach. • The role of temperature, time and NaOH content was investigated. • SPS densification allowed for low temperature transport properties measurements. • Transport measurements indicate semiconducting behavior.

  2. Deformation and fracture of single-crystal and sintered polycrystalline silicon carbide produced by cavitation

    NASA Technical Reports Server (NTRS)

    Miyoshi, Kazuhisa; Hattori, Shuji; Okada, Tsunenori; Buckley, Donald H.

    1987-01-01

    An investigation was conducted to examine the deformation and fracture behavior of single-crystal and sintered polycrystalline SiC surfaces exposed to cavitation. Cavitation erosion experiments were conducted in distilled water at 25 C by using a magnetostrictive oscillator in close proximity (1 mm) to the surface of SiC. The horn frequency was 20 kHz, and the double amplitude of the vibrating disk was 50 microns. The results of the investigation indicate that the SiC (0001) surface could be deformed in a plastic manner during cavitation. Dislocation etch pits were formed when the surface was chemically etched. The number of defects, including dislocations in the SiC (0001) surface, increased with increasing exposure time to cavitation. The presence of intrinsic defects such as voids in the surficial layers of the sintered polycrystalline SiC determined the zones at which fractured grains and fracture pits (pores) were generated. Single-crystal SiC had superior erosion resistance to that of sintered polycrystalline SiC.

  3. Scatter properties of polycrystalline YAG in the visible and near-infrared

    NASA Astrophysics Data System (ADS)

    Springer, R. M.; Thomas, M. E.; Brown, A. M.

    2014-05-01

    Yttrium Aluminum Garnet (YAG) is an important laser host material. Ideal host materials have low loss at the laser transition frequency. This becomes more important as the gain length increases or a low gain transition is of interest. Unfortunately, single crystal YAG suffers from relatively high scatter caused by strain induced index of refraction variations generated by the growth method. For this reason polycrystalline YAG has been developed with virtually no strain. Furthermore, this material can be doped with concentrations that vary spatially. This can provide a tremendous advantage in matching the gain volume to the mode volume in a laser. However, because of the grain boundaries and porosity, polycrystalline materials have scatter loss. Angle resolved, in-plane scatter measurements of polycrystalline YAG and Nd:YAG are reported from 405 to 1064 nm. This covers the range of interest for laser operation but also with enough bandwidth to derive a physical understanding of the scatter mechanisms. A model is also applied to provide physical insight and interpolation and meaningful extrapolation of the experimental results.

  4. Stress Distribution During Deformation of Polycrystalline Aluminum by Molecular-Dynamics and Finite-Element Modeling

    NASA Technical Reports Server (NTRS)

    Yamakov, V.; Saether, E.; Phillips, D.; Glaessgen, E. H.

    2004-01-01

    In this paper, a multiscale modelling strategy is used to study the effect of grain-boundary sliding on stress localization in a polycrystalline microstructure with an uneven distribution of grain size. The development of the molecular dynamics (MD) analysis used to interrogate idealized grain microstructures with various types of grain boundaries and the multiscale modelling strategies for modelling large systems of grains is discussed. Both molecular-dynamics and finite-element (FE) simulations for idealized polycrystalline models of identical geometry are presented with the purpose of demonstrating the effectiveness of the adapted finite-element method using cohesive zone models to reproduce grain-boundary sliding and its effect on the stress distribution in a polycrystalline metal. The yield properties of the grain-boundary interface, used in the FE simulations, are extracted from a MD simulation on a bicrystal. The models allow for the study of the load transfer between adjacent grains of very different size through grain-boundary sliding during deformation. A large-scale FE simulation of 100 grains of a typical microstructure is then presented to reveal that the stress distribution due to grain-boundary sliding during uniform tensile strain can lead to stress localization of two to three times the background stress, thus suggesting a significant effect on the failure properties of the metal.

  5. Governing parameter for electromigration damage in the polycrystalline line covered with a passivation layer

    NASA Astrophysics Data System (ADS)

    Sasagawa, Kazuhiko; Hasegawa, Masataka; Saka, Masumi; Abé, Hiroyuki

    2002-02-01

    A governing parameter, called AFDgen*, which reflects electromigration damage in a polycrystalline line covered with a passivation layer is proposed. The formulation is based on the parameter AFDgen previously introduced in our studies. With the help of AFDgen we can calculate the atomic flux divergence due to electromigration by considering two-dimensional distributions of current density and temperature and also by simply considering the microstructure of polycrystalline lines and bamboo lines. AFDgen has been identified as a governing parameter for electromigration damage in unpassivated polycrystalline lines and bamboo lines through experimental verification. As the first step in the development of a practical and universal prediction method for electromigration damage, we treated metal lines not covered with a passivation layer. On the other hand, metal lines used in packaged silicon integrated circuits are covered with passivation. Electromigration induces a mechanical stress (atomic density) gradient in such lines. This gradient plays an important role in the mechanism of electromigration damage. The new parameter proposed here, AFDgen*, includes the effect of the atomic density gradient. We develop also an AFDgen*-based method for determination of film characteristics. This method is applied to both covered and uncovered metal lines made of the same Al film. The film characteristics of both line types are obtained experimentally. Based on a discussion about the validity of the obtained characteristic constants, we were finally able to conclude that the AFDgen* parameter and the proposed method for deriving film characteristics are useful.

  6. Infrared detection of hydrogen-generated free carriers in polycrystalline ZnO thin films

    SciTech Connect

    Wolden, Colin A.; Barnes, Teresa M.; Baxter, Jason B.; Aydil, Eray S.

    2005-02-15

    The changes in the free-carrier concentration in polycrystalline ZnO films during exposure to H{sub 2} and O{sub 2} plasmas were studied using in situ attenuated total reflection Fourier transform infrared spectroscopy. The carrier concentration and mobility were extracted from the free-carrier absorption in the infrared using a model for the dielectric function. The electron density in polycrystalline zinc oxide films may be significantly increased by >10{sup 19} cm{sup -3} by brief exposures to hydrogen plasma at room temperature and decreased by exposure to O{sub 2} plasmas. Room-temperature oxygen plasma removes a fraction of the H at donor sites but both elevated temperatures ({approx}225 deg. C) and O{sub 2} plasma were required to remove the rest. We demonstrate that combinations of O{sub 2} and H{sub 2} plasma treatments can be used to manipulate the carrier density in ZnO films. However, we also show the existence of significant drifts ({approx}15%) in the carrier concentrations over very long time scales (hours). Possible sites for H incorporation in polycrystalline films and reasons for the observed carrier-concentration changes are proposed.

  7. Polycrystalline thin film materials and devices. Final subcontract report, 16 January 1990--15 January 1993

    SciTech Connect

    Birkmire, R.W.; Phillips, J.E.; Shafarman, W.N.; Hegedus, S.S.; McCandless, B.E.; Yokimcus, T.A.

    1993-08-01

    This report describes results and conclusions of the final phase (III) of a three-year research program on polycrystalline thin-film heterojunction solar cells. The research consisted of the investigation of the relationships between processing, materials properties, and device performance. This relationship was quantified by device modeling and analysis. The analysis of thin-film polycrystalline heterojunction solar cells explains how minority-carrier recombination at the metallurgical interface and at grain boundaries can be greatly reduced by the proper doping of the window and absorber layers. Additional analysis and measurements show that the present solar cells are limited by the magnitude of the diode current, which appears to be caused by recombination in the space charge region. Developing an efficient commercial-scale process for fabricating large-area polycrystalline, thin-film solar cells from a research process requires a detailed understanding of the individual steps in making the solar cell, and their relationship to device performance and reliability. The complexities involved in characterizing a process are demonstrated with results from our research program on CuInSe{sub 2}, and CdTe processes.

  8. Granular behavior observed in the polycrystalline superconducting LiFeAs

    NASA Astrophysics Data System (ADS)

    Singh, Shiv Jee; Beck, Robert; Wurmehl, Sabine; Hess, Christian; Büchner, Bernd

    2015-02-01

    Stoichiometric polycrystalline LiFeAs has been synthesized by a two-step solid state reaction method at low sintering temperature (600 °C) and its physical properties have been characterized. Room temperature x-ray diffraction confirms the phase purity of the samples, and microstructural analysis provides evidence that polycrystalline LiFeAs samples have a dense and nearly homogeneous microstructure with disk-shaped grains. Bulk superconductivity is established at the onset transition temperature (Tc) of 19.2 K. Both the onset and offset resistive transition temperatures shift to lower temperature in applied magnetic field (≤15 T) which yield an estimated upper critical field [Hc2(0)] at zero temperature of about 41 T. Two distinct scales of current flow corresponding to inter- and intragranular shielding currents are revealed by remanent magnetization measurements of bulk samples. The calculated intergranular current density at self-field and 5 K is ˜4.4 × 102 A cm-2. The analysis of the superconducting properties suggests evidence of weak-links and the electromagnetic granular nature of polycrystalline LiFeAs similar to other pnictide superconductors.

  9. Effect of flash lamp annealing on electrical activation in boron-implanted polycrystalline Si thin films

    SciTech Connect

    Do, Woori; Jin, Won-Beom; Choi, Jungwan; Bae, Seung-Muk; Kim, Hyoung-June; Kim, Byung-Kuk; Park, Seungho; Hwang, Jin-Ha

    2014-10-15

    Highlights: • Intensified visible light irradiation was generated via a high-powered Xe arc lamp. • The disordered Si atomic structure absorbs the intensified visible light. • The rapid heating activates electrically boron-implanted Si thin films. • Flash lamp heating is applicable to low temperature polycrystalline Si thin films. - Abstract: Boron-implanted polycrystalline Si thin films on glass substrates were subjected to a short duration (1 ms) of intense visible light irradiation generated via a high-powered Xe arc lamp. The disordered Si atomic structure absorbs the intense visible light resulting from flash lamp annealing. The subsequent rapid heating results in the electrical activation of boron-implanted Si thin films, which is empirically observed using Hall measurements. The electrical activation is verified by the observed increase in the crystalline component of the Si structures resulting in higher transmittance. The feasibility of flash lamp annealing has also been demonstrated via a theoretical thermal prediction, indicating that the flash lamp annealing is applicable to low-temperature polycrystalline Si thin films.

  10. Oxygen-aided synthesis of polycrystalline graphene on silicon dioxide substrates.

    PubMed

    Chen, Jianyi; Wen, Yugeng; Guo, Yunlong; Wu, Bin; Huang, Liping; Xue, Yunzhou; Geng, Dechao; Wang, Dong; Yu, Gui; Liu, Yunqi

    2011-11-01

    We report the metal-catalyst-free synthesis of high-quality polycrystalline graphene on dielectric substrates [silicon dioxide (SiO(2)) or quartz] using an oxygen-aided chemical vapor deposition (CVD) process. The growth was carried out using a CVD system at atmospheric pressure. After high-temperature activation of the growth substrates in air, high-quality polycrystalline graphene is subsequently grown on SiO(2) by utilizing the oxygen-based nucleation sites. The growth mechanism is analogous to that of growth for single-walled carbon nanotubes. Graphene-modified SiO(2) substrates can be directly used in transparent conducting films and field-effect devices. The carrier mobilities are about 531 cm(2) V(-1) s(-1) in air and 472 cm(2) V(-1) s(-1) in N(2), which are close to that of metal-catalyzed polycrystalline graphene. The method avoids the need for either a metal catalyst or a complicated and skilled postgrowth transfer process and is compatible with current silicon processing techniques. PMID:21988639

  11. Helium irradiation effects in polycrystalline Si, silica, and single crystal Si

    SciTech Connect

    Abrams, K. J.; Greaves, G.; Berg, J. A. van den; Hinks, J. A.; Donnelly, S. E.; Pawley, C. J.; Eyidi, D.; Ward, M. B.

    2012-04-15

    Transmission electron microscopy (TEM) has been used to investigate the effects of room temperature 6 keV helium ion irradiation of a thin ({approx_equal}55 nm thick) tri-layer consisting of polycrystalline Si, silica, and single-crystal Si. The ion irradiation was carried out in situ within the TEM under conditions where approximately 24% of the incident ions came to rest in the specimen. This paper reports on the comparative development of irradiation-induced defects (primarily helium bubbles) in the polycrystalline Si and single-crystal Si under ion irradiation and provides direct measurement of a radiation-induced increase in the width of the polycrystalline layer and shrinkage of the silica layer. Analysis using TEM and electron energy-loss spectroscopy has led to the hypothesis that these result from helium-bubble-induced swelling of the silicon and radiation-induced viscoelastic flow processes in the silica under the influence of stresses applied by the swollen Si layers. The silicon and silica layers are sputtered as a result of the helium ion irradiation; however, this is estimated to be a relatively minor effect with swelling and stress-related viscoelastic flow being the dominant mechanisms of dimensional change.

  12. Optical and electrical properties of polycrystalline and amorphous Al-Ti thin films

    NASA Astrophysics Data System (ADS)

    Canulescu, S.; Borca, C. N.; Rechendorff, K.; Davidsdóttir, S.; Pagh Almtoft, K.; Nielsen, L. P.; Schou, J.

    2016-04-01

    The structural, optical, and transport properties of sputter-deposited Al-Ti thin films have been investigated as a function of Ti alloying with a concentration ranging from 2% to 46%. The optical reflectivity of Al-Ti films at visible and near-infrared wavelengths decreases with increasing Ti content. X-ray absorption fine structure measurements reveal that the atomic ordering around Ti atoms increases with increasing Ti content up to 20% and then decreases as a result of a transition from a polycrystalline to amorphous structure. The transport properties of the Al-Ti films are influenced by electron scattering at the grain boundaries in the case of polycrystalline films and static defects, such as anti-site effects and vacancies in the case of the amorphous alloys. The combination of Ti having a real refractive index (n) comparable with the extinction coefficient (k) and Al with n much smaller than k allows us to explore the parameter space for the free-electron behavior in transition metal-Al alloys. The free electron model, applied for the polycrystalline Al-Ti films with Ti content up to 20%, leads to an optical reflectance at near infrared wavelengths that scales linearly with the square root of the electrical resistivity.

  13. The determination of minority carrier lifetime in polycrystalline silicon by the photoconductivity decay method

    NASA Astrophysics Data System (ADS)

    Singh, S. N.; Kishore, R.; Arora, N. K.

    1985-04-01

    Experiments were carried out to investigate the possible sources of error in estimates of the time constant of apparent minority carrier lifetime (tau-asterisk) in polycrystalline silicon. Tau-asterisk was measured in both single-crystal and polycrystalline silicon rods as a function of: (1) the intensity of background illumination; and (2) the temperature of the specimens. The background illumination source for the experiments was a tungsten-halogen lamp which operated in the intensity range 0-85 mW per sq cm. The temperatures of the specimens under illumination were in the range 25-140 C. The experimental results were explained on the basis of a theoretical analysis. It is shown that the photoconductivity of the specimens was generally dependent on the minority carrier mobility lifetime, as long as potential barriers were present at the grain boundaries of the specimens. On the basis of the theoretical analysis, it is concluded that the absence of potential barriers at the grain boundaries in polycrystalline silicon is a major source of error in estimates of minority carrier mobility lifetime. The apparent minority carrier mobility decay curves are reproduced in graphic form.

  14. Effect of mechanical stress on current-voltage characteristics of thin film polycrystalline diamond Schottky diodes

    SciTech Connect

    Zhao, G.; Charlson, E.M.; Charlson, E.J.; Stacy, T.; Meese, J.M. ); Popovici, G.; Prelas, M. )

    1993-02-15

    Schottky diodes utilized for mechanical stress effect studies were fabricated using aluminum contacts to polycrystalline diamond thin films grown by a hot-filament-assisted chemical vapor deposition process. Compressive stress was found to have a large effect on the forward biased current-voltage characteristics of the diode, whereas the effect on the reverse biased characteristics was relatively small. This stress effect on the forward biased diamond Schottky diode was attributed to piezojunction and piezoresistance effects that dominated the diode current-voltage characteristics in the small and large bias regions, respectively. At a large constant forward bias current, a good linear relationship between output voltage and applied force was observed for force of less than 10 N, as predicted by the piezoresistance effect. The measured force sensitivity of the diode was as high as 0.75 V/N at 1 mA forward bias. Compared to either silicon or germanium junction diodes and tunnel diodes, polycrystalline diamond Schottky diodes not only are very stress sensitive but also have good linearity. This study shows polycrystalline diamond Schottky diodes have potential as mechanical sensors.

  15. Nanofrictional behavior of amorphous, polycrystalline and textured Y-Cr-O films

    NASA Astrophysics Data System (ADS)

    Gervacio-Arciniega, J. J.; Flores-Ruiz, F. J.; Diliegros-Godines, C. J.; Broitman, E.; Enriquez-Flores, C. I.; Espinoza-Beltrán, F. J.; Siqueiros, J.; Cruz, M. P.

    2016-08-01

    Differences in friction coefficients (μ) of ferroelectric YCrO3, textured and polycrystalline films, and non-ferroelectric Y-Cr-O films are analyzed. The friction coefficient was evaluated by atomic force microscopy using a simple quantitative procedure where the dependence of friction force with the applied load is obtained in only one topographical image. A simple code was developed with the MATLAB® software to analyze the experimental data. The code includes a correction of the hysteresis in the forward and backward scanning directions. The quantification of load exerted on the sample surface was obtained by finite element analysis of the AFM cantilever starting from its experimental dynamic information. The results show that the ferroelectric YCrO3 film deposited on a Pt(150 nm)/TiO2(30 nm)/SiO2/Si (100) substrate is polycrystalline and has a lower friction coefficient than the deposited on SrTiO3 (110), which is highly textured. From a viewpoint of industrial application in ferroelectric memories, where the writing process is electrical or mechanically achieved by sliding AFM tips on the sample, polycrystalline YCrO3 films seem to be the best candidates due to their lower μ.

  16. Cast polycrystalline silicon photovoltaic module manufacturing technology improvements. Annual subcontract report, January 1, 1995--December 31, 1995

    SciTech Connect

    Wohlgemuth, J

    1996-06-01

    The objective of this three-year program is to advance Solarex`s cast polycrystalline silicon manufacturing technology, reduce module production cost, increase module performance and expand Solarex`s commercial production capacities. Two specific objectives of this program are to reduce the manufacturing cost for polycrystalline silicon PV modules to less than $1.20/watt and to increase the manufacturing capacity by a factor of three.

  17. Three-dimensional kinetic Monte Carlo simulations of cubic transition metal nitride thin film growth

    NASA Astrophysics Data System (ADS)

    Nita, F.; Mastail, C.; Abadias, G.

    2016-02-01

    A three-dimensional kinetic Monte Carlo (KMC) model has been developed and used to simulate the microstructure and growth morphology of cubic transition metal nitride (TMN) thin films deposited by reactive magnetron sputtering. Results are presented for the case of stoichiometric TiN, chosen as a representative TMN prototype. The model is based on a NaCl-type rigid lattice and includes deposition and diffusion events for both N and Ti species. It is capable of reproducing voids and overhangs, as well as surface faceting. Simulations were carried out assuming a uniform flux of incoming particles approaching the surface at normal incidence. The ballistic deposition model is parametrized with an interaction parameter r0 that mimics the capture distance at which incoming particles may stick on the surface, equivalently to a surface trapping mechanism. Two diffusion models are implemented, based on the different ways to compute the site-dependent activation energy for hopping atoms. The influence of temperature (300-500 K), deposition flux (0.1-100 monolayers/s), and interaction parameter r0 (1.5-6.0 Å) on the obtained growth morphology are presented. Microstructures ranging from highly porous, [001]-oriented straight columns with smooth top surface to rough columns emerging with different crystallographic facets are reproduced, depending on kinetic restrictions, deposited energy (seemingly captured by r0), and shadowing effect. The development of facets is a direct consequence of the diffusion model which includes an intrinsic (minimum energy-based) diffusion anisotropy, although no crystallographic diffusion anisotropy was explicitly taken into account at this stage. The time-dependent morphological evolution is analyzed quantitatively to extract the growth exponent β and roughness exponent α , as indicators of kinetic roughening behavior. For dense TiN films, values of α ≈0.7 and β =0.24 are obtained in good agreement with existing experimental data. At this

  18. Fluids Speciation in Deep Subduction Channels: Evidence From Polycrystalline Diamonds From UHPM Terranes

    NASA Astrophysics Data System (ADS)

    Dobrzhinetskaya, L.; Wirth, R.; Green, H. W.

    2011-12-01

    Geochemical characteristic of fluids circulating in deep subduction zones is of a great interest for many directions of geosciences. One of the intriguing processes is a fluid-rock interaction during subduction of the continental slab because the latter is characterized by contrast chemistry in comparison with the rocks of surrounding mantle and its fluids. Diamond due to its chemical inertness is the only mineral which contains "unchanged" fluid trapped during its crystallization at the peak of UHP metamorphism. Polycrystalline diamonds, that we have recently found within both the Kokchetav and the Earzgebirge UHPM terranes, represent an outstanding material to study geochemical diversity of the fluids circulating in deep subduction zones. Earlier studies of diamond monocrystals included in garnet, zircon, pyroxene and mica of the Kokchetav massif showed that the fluid responsible for diamond crystallization contains traces of both crustal and mantle components: Al, K, Ca, Mg, Fe, Si, Ti, V, Zn, Co, Fe F, Cl, S. The finding of polycrystalline diamonds in UHPM rocks of the Kokchetav and the Erzgebirge areas extends our knowledge related to UHP fluid composition. The polycrystalline diamonds consist of 5-15 single crystals of 0.3-5 micron size with a typical "zig-zag" grain boundaries and triangle voids filled with a C-O-H fluid with traces of Al, Co, F, V, Zn, Si, Cl, S, Ca, Mg, Fe, K in different combinations. Occurrences of "spider-like" dislocations, "zig-zag" boundaries, stacking faults and associated fluid pockets indicate presence of an internal stress accompanied diamond nucleation and growth from a fluid media. Observations of the carbonate (CaCO3) suggest an oxidizing environment of the fluids, close to the CCO buffer. Carbon isotopes speciation (delta 13C = -10 to -27 %) indicates organic carbon reservoir. Furthermore, studies by Sumino et al. (2011) showed that the Kokchetav diamonds, which are formed from organic carbon, are characterized by very high 3

  19. Anharmonic phonon decay in cubic GaN

    NASA Astrophysics Data System (ADS)

    Cuscó, R.; Domènech-Amador, N.; Novikov, S.; Foxon, C. T.; Artús, L.

    2015-08-01

    We present a Raman-scattering study of optical phonons in zinc-blende (cubic) GaN for temperatures ranging from 80 to 750 K. The experiments were performed on high-quality, cubic GaN films grown by molecular-beam epitaxy on GaAs (001) substrates. The observed temperature dependence of the optical phonon frequencies and linewidths is analyzed in the framework of anharmonic decay theory, and possible decay channels are discussed in the light of density-functional-theory calculations. The longitudinal-optical (LO) mode relaxation is found to occur via asymmetric decay into acoustic phonons, with an appreciable contribution of higher-order processes. The transverse-optical mode linewidth shows a weak temperature dependence and its frequency downshift is primarily determined by the lattice thermal expansion. The LO phonon lifetime is derived from the observed Raman linewidth and an excellent agreement with previous theoretical predictions is found.

  20. Alpha decay self-damage in cubic and monoclinic zirconolite

    SciTech Connect

    Clinard, F.W. Jr.; Land, C.C.; Peterson, D.E.; Rohr, D.L.; Roof, R.B.

    1981-01-01

    Samples of primarily-monoclinic /sup 238/Pu-doped zirconolite were stored at ambient temperature to allow accumulation of alpha decay self-damage to a dose of 1 x 10/sup 24/ ..cap alpha../m/sup 3/ (equivalent to a SYNROC age of approx. 10/sup 3/y). Bulk swelling reached 2.3 vol% with no tendency toward saturation, a damage response similar to that observed for cubic Pu-doped zirconolite. X-ray volumetric swelling at 4 x 10/sup 24/ ..cap alpha../m/sup 3/ was 1 vol%, considerably less than that for the cubic material. Changes in cell dimensions differed significantly from those reported by others for a monoclinic natural mineral. Extensive microcracking was observed, and is attributed at least partially to swelling differences between the matrix and minor phases.

  1. Structural Characterization of Polycrystalline 3C-SiC Films Prepared at High Rates by Atmospheric Pressure Plasma Chemical Vapor Deposition Using Monomethylsilane

    NASA Astrophysics Data System (ADS)

    Kakiuchi, Hiroaki; Ohmi, Hiromasa; Nakamura, Ryota; Aketa, Masatoshi; Yasutake, Kiyoshi

    2006-10-01

    Polycrystalline cubic silicon carbide (3C-SiC) films were deposited at a relatively low temperature of 1070 K on Si(001) substrates by atmospheric pressure plasma chemical vapor deposition. Monomethylsilane (CH3SiH3) was used as the single source. CH4 and SiH4 dual sources were also used to compare deposition characteristics. Under the present deposition conditions, very high deposition rates of more than 3 nm/s were obtained. The structure of the SiC films was evaluated by reflection high-energy electron diffraction, Fourier transform infrared absorption spectroscopy and cross-sectional transmission electron microscopy. In addition, optical emission spectroscopy was employed to study the chemical reactions in the CH4/SiH4 and CH3SiH3 plasmas. The results showed that increasing H2 concentration is essential in forming a high quality 3C-SiC film by enhancing the hydrogen elimination reaction at the film-growing surface. From the optical emission spectra, it was found that atomic hydrogen generated by adding H2 in the plasma increase the amount of principal precursors for the film growth. The utilization of CH3SiH3 also led to a higher concentration of principal precursors in the plasma, enhancing the incorporation of Si-C bonds into the film. As a consequence of simultaneously using a high H2 concentration and the CH3SiH3 single source, the columnar growth of 3C-SiC crystallites was achieved.

  2. Anodic etching of p-type cubic silicon carbide

    NASA Technical Reports Server (NTRS)

    Harris, G. L.; Fekade, K.; Wongchotigul, K.

    1992-01-01

    p-Type cubic silicon carbide was anodically etched using an electrolyte of HF:HCl:H2O. The etching depth was determined versus time with a fixed current density of 96.4 mA/sq cm. It was found that the etching was very smooth and very uniform. An etch rate of 22.7 nm/s was obtained in a 1:1:50 HF:HCl:H2O electrolyte.

  3. Higher-order numerical solutions using cubic splines

    NASA Technical Reports Server (NTRS)

    Rubin, S. G.; Khosla, P. K.

    1976-01-01

    A cubic spline collocation procedure was developed for the numerical solution of partial differential equations. This spline procedure is reformulated so that the accuracy of the second-derivative approximation is improved and parallels that previously obtained for lower derivative terms. The final result is a numerical procedure having overall third-order accuracy of a nonuniform mesh. Solutions using both spline procedures, as well as three-point finite difference methods, are presented for several model problems.

  4. Large scale structures and the cubic galileon model

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Sourav; Dialektopoulos, Konstantinos F.; Tomaras, Theodore N.

    2016-05-01

    The maximum size of a bound cosmic structure is computed perturbatively as a function of its mass in the framework of the cubic galileon, proposed recently to model the dark energy of our Universe. Comparison of our results with observations constrains the matter-galileon coupling of the model to 0.033lesssim α lesssim 0.17, thus improving previous bounds based solely on solar system physics.

  5. Lipidic cubic phase injector facilitates membrane protein serial femtosecond crystallography

    PubMed Central

    Weierstall, Uwe; James, Daniel; Wang, Chong; White, Thomas A.; Wang, Dingjie; Liu, Wei; Spence, John C.H.; Doak, R. Bruce; Nelson, Garrett; Fromme, Petra; Fromme, Raimund; Grotjohann, Ingo; Kupitz, Christopher; Zatsepin, Nadia A.; Liu, Haiguang; Basu, Shibom; Wacker, Daniel; Han, Gye Won; Katritch, Vsevolod; Boutet, Sébastien; Messerschmidt, Marc; Williams, Garth J.; Koglin, Jason E.; Seibert, M. Marvin; Klinker, Markus; Gati, Cornelius; Shoeman, Robert L.; Barty, Anton; Chapman, Henry N.; Kirian, Richard A.; Beyerlein, Kenneth R.; Stevens, Raymond C.; Li, Dianfan; Shah, Syed T.A.; Howe, Nicole; Caffrey, Martin; Cherezov, Vadim

    2014-01-01

    Lipidic cubic phase (LCP) crystallization has proven successful for high-resolution structure determination of challenging membrane proteins. Here we present a technique for extruding gel-like LCP with embedded membrane protein microcrystals, providing a continuously-renewed source of material for serial femtosecond crystallography. Data collected from sub-10 μm-sized crystals produced with less than 0.5 mg of purified protein yield structural insights regarding cyclopamine binding to the Smoothened receptor. PMID:24525480

  6. The Number of Real Roots of a Cubic Equation

    ERIC Educational Resources Information Center

    Kavinoky, Richard; Thoo, John B.

    2008-01-01

    To find the number of distinct real roots of the cubic equation (1) x[caret]3 + bx[caret]2 + cx + d = 0, we could attempt to solve the equation. Fortunately, it is easy to tell the number of distinct real roots of (1) without having to solve the equation. The key is the discriminant. The discriminant of (1) appears in Cardan's (or Cardano's) cubic…

  7. A highly ordered cubic mesoporous silica/graphene nanocomposite

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Wook; Roh, Kwang Chul; Kim, Kwang-Bum

    2013-09-01

    A highly ordered cubic mesoporous silica (KIT-6)/graphene nanocomposite and 2D KIT-6 nanoflakes were synthesized using a novel synthesis methodology. The non-ionic triblock copolymer, P123, played a dual role as a structure-directing agent in the formation of the cubic mesoporous structure and as a cross-linking agent between mesoporous silica and graphene. The prepared (KIT-6)/graphene nanocomposite could act as a template for the preparation of mesoporous material/graphene nanocomposites.A highly ordered cubic mesoporous silica (KIT-6)/graphene nanocomposite and 2D KIT-6 nanoflakes were synthesized using a novel synthesis methodology. The non-ionic triblock copolymer, P123, played a dual role as a structure-directing agent in the formation of the cubic mesoporous structure and as a cross-linking agent between mesoporous silica and graphene. The prepared (KIT-6)/graphene nanocomposite could act as a template for the preparation of mesoporous material/graphene nanocomposites. Electronic supplementary information (ESI) available: S1: TEM images of disordered mesoporous silica/graphene nanocomposite; S2: TEM images of KIT-6/GO nanocomposite; S3: Thermogravimetric analysis of KIT-6/GO and KG-400-700; S4: SEM and TEM images of KIT-6; S5: Low angle XRD, Raman spectra, N2 adsorption isotherms, pore size distribution and photographic images of the prepared samples; S6: TEM image and N2 adsorption isotherms of mesoporous carbon/graphene nanocomposite; S7: XPS C1s spectra of the prepared samples. See DOI: 10.1039/c3nr03108j

  8. Cubic and Hexagonal Liquid Crystals as Drug Delivery Systems

    PubMed Central

    Chen, Yulin; Ma, Ping; Gui, Shuangying

    2014-01-01

    Lipids have been widely used as main constituents in various drug delivery systems, such as liposomes, solid lipid nanoparticles, nanostructured lipid carriers, and lipid-based lyotropic liquid crystals. Among them, lipid-based lyotropic liquid crystals have highly ordered, thermodynamically stable internal nanostructure, thereby offering the potential as a sustained drug release matrix. The intricate nanostructures of the cubic phase and hexagonal phase have been shown to provide diffusion controlled release of active pharmaceutical ingredients with a wide range of molecular weights and polarities. In addition, the biodegradable and biocompatible nature of lipids demonstrates the minimum toxicity and thus they are used for various routes of administration. Therefore, the research on lipid-based lyotropic liquid crystalline phases has attracted a lot of attention in recent years. This review will provide an overview of the lipids used to prepare cubic phase and hexagonal phase at physiological temperature, as well as the influencing factors on the phase transition of liquid crystals. In particular, the most current research progresses on cubic and hexagonal phases as drug delivery systems will be discussed. PMID:24995330

  9. A study of accelerated radiation damage effects in PuO2 and gadolinia-stabilized cubic zirconia, Zr0.79Gd0.14Pu0.07O1.93, doped with 238Pu

    NASA Astrophysics Data System (ADS)

    Burakov, B. E.; Yagovkina, M. A.

    2015-12-01

    Polycrystalline samples of cubic zirconia, Zr0.79Gd0.14Pu0.07O1.93, doped with approximately 9.9 wt.% 238Pu, and PuO2 containing 11.0 wt. % 238Pu (and main isotope is 239Pu) have been repeatedly studied during many years by X-ray diffraction analysis. At a temperature of 25 °C the unit-cell parameter of PuO2 increases depending on accumulated dose, and is accompanied by decrease of coherent scattering region (CSR). Self-irradiation of Zr0.79Gd0.14Pu0.07O1.93 is accompanied with repeated change of unit-cell parameter and CSR.

  10. Effective work functions for ionic and electronic emissions from mono- and polycrystalline surfaces

    NASA Astrophysics Data System (ADS)

    Kawano, Hiroyuki

    2008-02-01

    The effective work functions ( ϕ+, ϕe and ϕ-) for positive-ionic, electronic, and negative-ionic emissions from mono- and polycrystalline surfaces are surveyed comprehensively and also investigated critically for the main purposes of (1) evaluating the most probable values of ϕ+, ϕe and ϕ- for a variety of surface species, (2) explicating both thermionic contrasts (Δ ϕ∗ ≡ ϕ+ - ϕe and Δ ϕ∗∗ ≡ ϕ- - ϕe) and their dependence on experimental conditions, and (3) demonstrating the necessity of employing ϕ+ (not ϕe) for quantitative analysis of those data on positive ion emission from polycrystalline surfaces. Careful examination of both theoretical results and experimental data on the work functions yield several conclusions. By both theory and experiment, clean monocrystalline surfaces are verified to have Δ ϕ∗ = 0.0 eV within an error of ±0.05 eV. Next, as the density of local surface irregularities increases, the homogeneity in the work function over the whole surface area decreases and, hence, Δ ϕ∗ increases. Also, the most probable values of ϕ+ and ϕe are recommended for many mono- and polycrystalline surfaces, mostly (∼70%) with a standard deviation of ±0.02-0.08 eV. Compared with the probable or typical values of ϕe accepted in influential handbooks, the most probable values of ϕe recommended here are typically (∼70%) equal to each other within a narrow gap of less than ∼0.1 eV, but some (∼20%) are different by ∼0.2 eV or more (up to ∼1 eV). Furthermore, polycrystalline surfaces of Nb, Mo, Ta, W, Re, Ir, Pt, etc. hold Δ ϕ∗ ≈ 0.3-0.8 eV since each surface has a mean value that is different between ϕ+ and ϕe. Also, at the degree of monocrystallization ( δm) below ∼50%, the theoretical value of Δ ϕ∗ depends little on δm and agrees well with experimental data on each polycrystalline surface. As δm increases beyond ∼80%, Δ ϕ∗ decreases rapidly to 0, showing again a good agreement between theory

  11. Synthesis and Characterization of Ru Cubic Nanocages with a Face-Centered Cubic Structure by Templating with Pd Nanocubes.

    PubMed

    Zhao, Ming; Figueroa-Cosme, Legna; Elnabawy, Ahmed O; Vara, Madeline; Yang, Xuan; Roling, Luke T; Chi, Miaofang; Mavrikakis, Manos; Xia, Younan

    2016-08-10

    Nanocages have received considerable attention in recent years for catalytic applications owing to their high utilization efficiency of atoms and well-defined facets. Here we report, for the first time, the synthesis of Ru cubic nanocages with ultrathin walls, in which the atoms are crystallized in a face-centered cubic (fcc) rather than hexagonal close-packed (hcp) structure. The key to the success of this synthesis is to ensure layer-by-layer deposition of Ru atoms on the surface of Pd cubic seeds by controlling the reaction temperature and the injection rate of a Ru(III) precursor. By selectively etching away the Pd from the Pd@Ru core-shell nanocubes, we obtain Ru nanocages with an average wall thickness of 1.1 nm or about six atomic layers. Most importantly, the Ru nanocages adopt an fcc crystal structure rather than the hcp structure observed in bulk Ru. The synthesis has been successfully applied to Pd cubic seeds with different edge lengths in the range of 6-18 nm, with smaller seeds being more favorable for the formation of Ru shells with a flat, smooth surface due to shorter distance for the surface diffusion of the Ru adatoms. Self-consistent density functional theory calculations indicate that these unique fcc-structured Ru nanocages might possess promising catalytic properties for ammonia synthesis compared to hcp Ru(0001), on the basis of strengthened binding of atomic N and substantially reduced activation energies for N2 dissociation, which is the rate-determining step for ammonia synthesis on hcp Ru catalysts. PMID:27458871

  12. Polycrystalline Diamonds from the Erzgebirge Ultrahigh-Pressure Metamorphic Terrane, Germany

    NASA Astrophysics Data System (ADS)

    Dobrzhinetskaya, L.; Wirth, R.; Green, H. W.

    2010-12-01

    Previous studies showed that microdiamonds from Erzgebirge terrane of Germany are crystallized from a C-O-H fluid (Stoeckhert et al., 2001, 2009; Dobrzhinetskaya et al., 2003, 2007) due to course of the UHPM. Usually metamorphic diamonds are presented by single crystals of 5 to 80 micron size, which are caracterized by a complicated morphology suggesting that their crystallization took place in a media rich in impurities. Within the microdiamonds population ocurred in the Erzgebirge quartz-feldspathic gneisses, we have recently found polycrystalline diamonds which extend our knowledge related to mechanisms of their formation. These polycrystalline diamonds occur as inclusions in zircons. Several focused ion beam foils were prepared from polished slide containing zircon with diamond inclusions, and studied with transmission electron microscopy. Bright Field images revealed that single diamond inclusions in zircon consist of 5 to 15 microcrystals which are characterized by ’zig-zag’ boundaries. The series of triangle fluid-pockets are situated at the interface diamond-zircon, and ’glue’ together microcrystals. The octahedral voids accountered by (111) crystal faces are observed within polycrystalline sectors of diamond. The octahedral voids are characterized by low density contrast what suggests that the void is a negative nanocrystal of diamond filled by fluid/gas. In many cases the fluid was evaporated during the foil preparation by high energy Ga-ions beam. The fluid consisted of Ti, Cl, S, K, Cr, Ba, Pb, Mo, Co, Al. The presence of the negative crystals of diamonds filled with a fluid, suggest that such a fluid was in equilibrium with the diamond, and represents the diamond-forming media. Triangle pockets of the former fluid situated at the zircon-diamond interface are also penetrated by FIB, the residual fluid composition is characterized by presence of Al, Ti, Ca, F, V, Zn, Si, Cl, and S, or Ca, Al, K, Cl, Fe and Mg, or Al, Co, F, V, Zn, Si, Cl, or

  13. High Cubic-Phase Purity InN on MgO (001) Using Cubic-Phase GaN as a Buffer Layer

    SciTech Connect

    Sanorpim, S.; Kuntharin, S.; Parinyataramas, J.; Yaguchi, H.; Iwahashi, Y.; Orihara, M.; Hijikata, Y.; Yoshida, S.

    2011-12-23

    High cubic-phase purity InN films were grown on MgO (001) substrates by molecular beam epitaxy with a cubic-phase GaN buffer layer. The cubic phase purity of the InN grown layers has been analyzed by high resolution X-ray diffraction, {mu}-Raman scattering and transmission electron microscopy. It is evidenced that the hexagonal-phase content in the InN overlayer much depends on hexagonal-phase content in the cubic-phase GaN buffer layer and increases with increasing the hexagonal-phase GaN content. From Raman scattering measurements, in addition, the InN layer with lowest hexagonal component (6%), only Raman characteristics of cubic TO{sub InN} and LO{sub InN} modes were observed, indicating a formation of a small amount of stacking faults, which does not affect on vibrational property.

  14. Amplitude equations for polycrystalline materials with interaction between composition and stress

    NASA Astrophysics Data System (ADS)

    Spatschek, Robert; Karma, Alain

    2010-06-01

    We investigate the ability of frame-invariant amplitude equations [G. H. Gunaratne, Q. Ouyang, and H. Swinney, Phys. Rev. E 50, 2802 (1994)] to describe quantitatively the evolution of polycrystalline microstructures and we extend this approach to include the interaction between composition and stress. Validations for elemental materials include studies of the Asaro-Tiller-Grinfeld morphological instability of a stressed crystal surface, polycrystalline growth from the melt, grain-boundary energies over a wide range of misorientation, and grain-boundary motion coupled to shear deformation. Amplitude equations with accelerated strain relaxation in the solid are shown to model accurately the Asaro-Tiller-Grinfeld instability. Polycrystalline growth is also well described. However, the survey of grain-boundary energies shows that the approach is only valid for a restricted range of misorientations as a direct consequence of an amplitude expansion. This range covers approximately half the complete range allowed by crystal symmetry for some fixed reference set of density waves used in the expansion. Over this range, coupled motion to shear is well described by known geometrical rules and a transition from coupling to sliding motion is also reproduced. Amplitude equations for alloys are derived phenomenologically in a Ginzburg-Landau spirit. Vegard’s law is shown to be naturally described by seeking a gauge-invariant form of those equations under a transformation that corresponds to a lattice expansion and deviations from Vegard’s law can be easily incorporated. Those equations realistically describe the dilute alloy limit and have the same flexibility as conventional phase-field models for incorporating arbitrary free-energy/composition curves. As a test of this approach, we recover known analytical expressions for open-system elastic constants [F. C. Larché and J. W. Cahn, Acta Metall. 33, 331 (1985)].

  15. Study on growth of large area mercuric iodide polycrystalline film and its x-ray imaging

    NASA Astrophysics Data System (ADS)

    Xu, Gang; Guo, Yanfei; Xi, Zengzhe; Gu, Zhi; Zhang, Lan; Yu, Wentao; Ma, Xuming; Li, Bo

    2014-11-01

    Tetragonal mercuric iodide, as a group of wide band gap semiconductors, has been widely investigation during most of the last half-century, applied on room-temperature X-ray and gamma-ray spectrometers. Up to the present, Mercuric iodide (HgI2) is still thought to be one of the most outstanding vitality semiconductor materials because of its wide band gap, for which the device was required to be high resistivity, high atomic number, adequate mechanical strength, long carrier lifetimes and high mobility-lifetime produces. Now, HgI2 polycrystalline films are being developed as a new detector technology for digital x-ray imaging. In this research, HgI2 polycrystalline films with different surface areas of 1 and 36 cm2 were grown by vapor sublimation method within a self-design growth furnace. XRD, SEM and J-V analysis were used to characterize the properties of these as-grown films. The results of XRD show that the ratio of (001) / (hkl) on all as-grown films is amount to be 90% for the area of 1 cm2 films. Grain size of 1 cm2 films was measured to be 120-150 μm. Their electrical resistivity were also determined to be about 1011 Ω·cm operated at the bias voltage of ~100 V by I-V characteristic measurement. Utilizing the polycrystalline film with the area of 36 cm2 deposited on TFT, we then prepared the direct image detector after capsulation for non-corrosive steel screw imaging. The results indicated that profile of screw was distinctly exhibited in digital x-ray imaging systems.

  16. Microstructure and nanohardness distribution in a polycrystalline Zn deformed by high strain rate impact

    SciTech Connect

    Dirras, G.; Ouarem, A.; Couque, H.; Gubicza, J.; Szommer, P.; Brinza, O.

    2011-05-15

    Polycrystalline Zn with an average grain size of about 300 {mu}m was deformed by direct impact Hopkinson pressure bar at a velocity of 29 m/s. An inhomogeneous grain structure was found consisting of a center region having large average grain size of 20 {mu}m surrounded by a fine-grained rim with an average grain size of 6 {mu}m. Transmission electron microscopy investigations showed a significant dislocation density in the large-grained area while in the fine-grained rim the dislocation density was negligible. Most probably, the higher strain yielded recrystallization in the outer ring while in the center only recovery occurred. The hardening effect of dislocations overwhelms the smaller grain size strengthening in the center part resulting in higher nanohardness in this region than in the outer ring. - Graphical Abstract: (a): EBSD micrograph showing the initial microstructure of polycrystalline Zn that was subsequently submitted to high strain rate impact. (b): an inhomogeneous grain size refinement was obtained which consists of a central coarse-grained area, surrounded by a fine-grained recrystallized rim. The black arrow points to the disc center. Research Highlights: {yields} A polycrystalline Zn specimen was submitted to high strain rate impact loading. {yields} Inhomogeneous grain refinement occurred due to strain gradient in impacted sample. {yields} A fine-grained recrystallized rim surrounded the coarse-grained center of specimen. {yields} The coarse-grained center exhibited higher hardness than the fine-grained rim. {yields} The higher hardness of the center was caused by the higher dislocation density.

  17. New Measurements on the Temperature Dependence of Elasticity of Polycrystalline Fe- Wadsleyite and Other Mantle Minerals

    NASA Astrophysics Data System (ADS)

    Isaak, D. G.; Gwanmesia, G. D.; Triplett, R. S.; Davis, M. G.; Donahue, L. K.; Stafford, A. M.; Stafford, S. C.

    2007-12-01

    Understanding the composition and structure of Earth's mantle requires accurate and precise information about the elastic properties of candidate minerals and how these elastic properties are affected by temperature, pressure, and chemical variations. New elasticity data from room temperature to 640 K at ambient pressure for hot-pressed polycrystalline iron-bearing wadsleyite (Fe:Mg ~ 1:9) will be presented. These data were obtained using resonant ultrasound spectroscopy (RUS) on a Fe-wadsleyite shaped into a right-rectangular parallelepiped with dimensions of 1.965 mm x 1.667 mm x 1.416 mm. From analysis of 42 modal frequencies, the room temperature adiabatic bulk (KS) and shear (G) moduli were found to be 171.3(0.7) GPa and 108.9(0.2) GPa, respectively, with numbers in parentheses indicating uncertainty. These results agree with room temperature values of KS = 170(3) GPa and G = 108(2) GPa found in an earlier study on single-crystal Fe- wadsleyite using Brillouin spectroscopy, and they provide a better anchor point for investigating the temperature dependence of the elasticity of polycrystalline wadsleyite than values of KS = 165.72(0.06) GPa and G = 105.43(0.02) GPa used by previous investigators. We carried out several temperature cycles from room temperature to 500 K (twice) and to 640 K (thrice) in order to determine the elastic properties at elevated temperature and to test reproducibility of the data. The temperature dependence of elastic moduli for Fe-bearing wadsleyite obtained from these experiments will be presented. We will also show recent results of high- temperature elasticity for other polycrystalline mantle minerals (forsterite, garnet).

  18. Observation and modeling of polycrystalline grain formation in Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Burr, Geoffrey W.; Tchoulfian, Pierre; Topuria, Teya; Nyffeler, Clemens; Virwani, Kumar; Padilla, Alvaro; Shelby, Robert M.; Eskandari, Mona; Jackson, Bryan; Lee, Bong-Sub

    2012-05-01

    The relationship between the polycrystalline nature of phase change materials (such as Ge2Sb2Te5) and the intermediate resistance states of phase change memory (PCM) devices has not been widely studied. A full understanding of such states will require knowledge of how polycrystalline grains form, how they interact with each other at various temperatures, and how the differing electrical (and thermal) characteristics within the grains and at their boundaries combine through percolation to produce the externally observed electrical (and thermal) characteristics of a PCM device. We address the first of these tasks (and introduce a vehicle for the second) by studying the formation of fcc polycrystalline grains from the as-deposited amorphous state in undoped Ge2Sb2Te5. We perform ex situ transmission electron microscopy membrane experiments and then match these observations against numerical simulation. Ramped-anneal experiments show that the temperature ramp-rate strongly influences the median grain size. By truncating such ramped-anneal experiments at various peak temperatures, we convincingly demonstrate that the temperature range over which these grains are established is quite narrow. Subsequent annealing at elevated temperature appears to change these established distributions of grain sizes only slightly. Our numerical simulator—which models nuclei formation through classical nucleation theory and then tracks the subsequent time- and temperature-dependent growth of these grains—can match these experimental observations of initial grain distributions and crystallization temperature both qualitatively and quantitatively. These simulations show that the particular narrow temperature range over which crystallization occurs shifts as a function of temperature ramp-rate, which allows us to quantify the lower portions of the time-temperature-transformation map for Ge2Sb2Te5. Future experiments and extensions of the simulator to investigate temperature

  19. Cast polycrystalline silicon photovoltaic module manufacturing technology improvements. Semiannual subcontract report, January 1--June 30, 1995

    SciTech Connect

    Wohlgemuth, J.

    1996-02-01

    The objective of this three-year program is to advance Solarex`s cast polycrystalline silicon manufacturing technology, reduce module production cost, increase module performance and expand Solarex`s commercial production capacities. Two specific objectives of this program are to reduce the manufacturing cost for polycrystalline silicon PV modules to less than $1.20/watt and to increase the manufacturing capacity by a factor of three. To achieve these objectives, Solarex is working in the following technical areas: casting, wire saws, cell process, module assembly, frameless module development, and automated cell handling. Accomplishments reported include: Cast first successful larger ingot producing 73% larger volume of usable Si; Increased the size of the ingot even further and cast an ingot yielding nine 11.4 {times} 11.4 cm bricks, representing a 125% increase in usable Si from a single casting; Operated the wire-saw in a semi-operational mode, producing 459,000 wafers at 94.1% overall yield; Reduced the cost of wire-saw consumables, spare parts, and waste disposal; Developed a cost-effective back surface field process that increases cell efficiency by 5% and began production trials; Developed a plan for increasing the capacity in the module assembly area; Completed qualification testing of modules built using Spire`s automated tabbing and stringing machine; Selected, tested, and qualified a low-cost electrical termination system; Completed long-term UV testing of experimental back sheets; Qualified the structure and adhesive-tape system for mounting frameless modules; and ARRI completed a study of the fracture properties of cast polycrystalline Si wafers and provided the information necessary to calculate the maximum stresses allowable during wafer handling.

  20. History of development of polycrystalline optical spinel in the U.S.

    NASA Astrophysics Data System (ADS)

    Harris, Daniel C.

    2005-05-01

    Optical quality polycrystalline spinel (MgAl2O4) has been sought as a visible- and infrared-transmitting material since the 1960s because of its potential for transparent armor and durable sensor windows. Its physical properties were known from synthetic crystals available since ~1950 from Linde Air Products. In the late 1960s, methods to process powder into transparent, polycrystalline spinel were investigated at North Carolina State University, General Electric Co., AVCO, and Westinghouse, mainly with Government support. The leading figure in the development of polycrystalline spinel was Don Roy, who began work on spinel at Coors Ceramics around 1970, initially for transparent armor. In the late 1970s, both Coors Ceramics and Raytheon Research Division were funded to make spinel for the infrared dome of the Advanced Short-Range Air-to-Air Missile, an application that disappeared by 1980. In the late 1980s, there was another burst of activity when spinel was a candidate for the Stinger Missile. By 1990, Raytheon had dropped spinel and the material was spun off by Coors Ceramics to Alpha Optical Systems, whose technical effort was led by Don Roy. With low commercial sales potential for spinel, Alpha was dissolved in 1993. RCS Technologies took over a Government contract seeking 200-mm spinel domes for the Harrier aircraft, but this effort ended in 1996 and RCS was dissolved. In 1998, the Army enlisted TA&T to make spinel for transparent armor. Other potential applications appeared and TA&T received numerous Government development contracts. Demand for the still-unavailable spinel drew Surmet to begin development in 2002. In early 2005, spinel is under active development at TA&T and Surmet.