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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Large Silver Halide Single Crystals as Charged Particle Track Detectors

The trajectory of the particle is made visible under a microscope by the accumulation of metallic silver at regions of the lattice damaged by the particle. This decoration of the particle track is accomplished by exposure of the crystal to light. The decoration of normally present lattice imperfections such as dislocations can be suppressed by the addition to the crystal of less than ten parts per million of a suitable polyvalent metal impurity. An account of some preliminary attempts to grow thin single crystals of AgCl is given also, and suggestions for a more refined technique are offered.

Kusmiss, J. H.↗
NASA NTRS1983

Production of large-area single-crystal wafers of cubic SiC for semiconductor devices

A reproducible process is described for growing a thick single-crystal layer of cubic SiC on a single-crystal Si wafer by chemical vapor deposition. A buffer layer, grown in situ, is used between the cubic SiC and the Si substrate to minimize the effect of lattice mismatch. Layers of up to 34 microns thick and several sq cm in area have been grown. Wafers are obtained by chemically removing the Si substrates from the grown layers. Excellent electron channeling patterns produced by these wafers indicate very good crystal quality. Preliminary electrical measurements have yielded electron mobilities up to 380 sq cm/Vs.

Nishino, S.↗
NASA NTRS1987

Simultaneous SMM flat crystal spectrometer and Very Large Array observations of solar active regions

High-resolution images of the quiescent emission from two solar active regions at 20 cm (VLA) and soft X-ray (SMM FCS) wavelengths are compared. There are regions where the X-ray coronal loops have been completely imaged at 20 cm wavelength. In other regions, the X-ray radiation was detected without detectable 20 cm radiation, and vice versa. The X-ray data were used to infer average electron temperatures of about 3-million K and average electron densities of about 2.5 x 10 to the 9th/cu cm for the X-ray emitting plasma in the two active regions. The thermal bremsstrahlung of the X-ray emitting plasma is optically thin at 20 cm wavelength. The 20 cm brightness temperatures were always less than T(e), which is consistent with optically thin bremsstrahlung. The low T(B) can be explained if a higher, cooler plasma covers the hotter X-ray emitting plasma. Thermal gyroresonance radiation must account for the intense 20 cm radiation near and above sunspots where no X-ray radiation is detected.

Lang, Kenneth R.↗
NASA NTRS2004

Steps in Solution Growth: Revised Gibbs-Thomson Law, Turbulence and Morphological Stability

Two groups of new phenomena revealed by AFM and high resolution optical interferometry on crystal faces growing from solutions will be discussed. 1. Spacing between strongly polygonized spiral steps with low less than 10(exp -2) kink density on lysozyme and K- biphtalate do not follow the Burton-cabrera-Frank theory. The critical length of the yet immobile first Short step segment adjacent to a pinning defect (dislocation, stacking fault) is many times longer than that following from the step free energy. The low-kink density steps are typical of many growth conditions and materials, including low temperature gas phase epitaxy and MBE. 2. The step bunching pattern on the approx. 1 cm long { 110) KDP face growing from the turbulent solution flow (Re (triple bonds) 10(exp 4), solution flow rate approx. 1 m/s) suggests that the step bunch height does not increase infinitely as the bunch path on the crystal face rises, as is usually observed on large KDP crystals. The mechanism controlling the maximal bunch width and height is based on the drag of the solution depleted by the step bunch down thc solution stream. It includes splitting, coagulation and interlacing of bunches

Chernov, A. A.↗
NASA NTRSDate not supplied

Higher-Order Approximations for Stabilizing Zero-Energy Modes in Peridynamics Crystal Plasticity Models with Large Horizon Interactions

The non-ordinary state-based peridynamics theory combines non-local dynamic techniques with a desirable correspondence material principle, allowing for the use of continuum mechanics constitutive models. Such an approach presents a unique capability for solving problems involving discontinuities (e.g., strain localization, fracture, and fragmentation). However, the correspondence-based peridynamics models often suffer from zero-energy mode instabilities in numerical implementation, primarily due to the approximations of the non-local deformation gradient tensor. This paper focuses on a computational scheme for eliminating the zero-energy mode oscillations using a choice of influence functions that improve the truncation error in a higher-order Taylor series expansion of the deformation gradient. The novelty here is a tensor-based derivation of the linear constraint equations, which can be used to systematically identify the particle interaction weight functions for various user-specified horizon radii. In this paper, the proposed higher-order stabilization scheme is demonstrated for multi-dimensional examples involving polycrystalline and composite microstructures, along with comparisons against conventional finite element methods. The proposed stabilization scheme is shown to be highly effective in suppressing the spurious zero-energy mode oscillations in all numerical examples while enabling efficient simulations of strain localizations across material interfaces.

Non-Ordinary State-Based Peridynamics↗
DOE OSTI2015

Growth of large aluminum nitride single crystals with thermal-gradient control

In various embodiments, non-zero thermal gradients are formed within a growth chamber both substantially parallel and substantially perpendicular to the growth direction during formation of semiconductor crystals, where the ratio of the two thermal gradients (parallel to perpendicular) is less than 10, by, e.g., arrangement of thermal shields outside of the growth chamber.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Growth of large aluminum nitride single crystals with thermal-gradient control

In various embodiments, non-zero thermal gradients are formed within a growth chamber both substantially parallel and substantially perpendicular to the growth direction during formation of semiconductor crystals, where the ratio of the two thermal gradients (parallel to perpendicular) is less than 10, by, e.g., arrangement of thermal shields outside of the growth chamber.

36 MATERIALS SCIENCE↗
DOE OSTI2018

System for growth of large aluminum nitride single crystals with thermal-gradient control

In various embodiments, non-zero thermal gradients are formed within a growth chamber both substantially parallel and substantially perpendicular to the growth direction during formation of semiconductor crystals, where the ratio of the two thermal gradients (parallel to perpendicular) is less than 10, by, e.g., arrangement of thermal shields outside of the growth chamber.

36 MATERIALS SCIENCE↗
DOE OSTI2016

A study of the piezoelectric resonance in metal organic NLO single crystals: Sodium D-isoascorbate monohydrate and Lithium L-ascorbate dihydrate

Large single crystals of Sodium D-isoacsorbate monohydrate and Lithium L-ascorbate dehydrate were grown using solution growth technique. Dielectric constant and dielectric loss were monitored as a function of frequency at different temperatures. These are typically characterized by strong resonance peaks. The piezoelectric coefficients d{sub 31}, elastic coefficient (S{sub 11}) and electromechanical coupling coefficient (k{sub 31}) were estimated by resonance-antiresonance method. The temperature dependence of the resonance-peaks frequencies was studied.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Symmetry-lowering lattice distortion at the spin reorientation in MnBi single crystals

Here we report structural and physical properties determined by measurements on large single crystals of the anisotropic ferromagnet MnBi. The findings support the importance of magnetoelastic effects in this material. X-ray diffraction reveals a structural phase transition at the spin reorientation temperature T SR = 90 K. The distortion is driven by magneto-elastic coupling, and upon cooling transforms the structure from hexagonal to orthorhombic. Heat capacity measurements show a thermal anomaly at the crystallographic transition, which is suppressed rapidly by applied magnetic fields. Effects on the transport and anisotropic magnetic properties of the single crystals are also presented. Increasing anisotropy of the atomic displacement parameters for Bi with increasing temperature above T SR is revealed by neutron diffraction measurements. It is likely that this is directly related to the anisotropic thermal expansion in MnBi, which plays a key role in the spin reorientation and magnetocrystalline anisotropy. Finally, the identification of the true ground state crystal structure reported here may be important for future experimental and theoretical studies of this permanent magnet material, which have to date been performed and interpreted using only the high temperature structure.

36 MATERIALS SCIENCE↗
NASA NTRS1969

Method for the preparation of inorganic single crystal and polycrystalline electronic materials

Large area, semiconductor crystals selected from group 3-5 compounds and alloys are provided for semiconductor device fabrication by the use of a selective etching operation which completely removes the substrate on which the desired crystal was deposited. The substrate, selected from the same group as the single crystal, has a higher solution rate than the epitaxial single crystal which is essentially unaffected by the etching solution. The preparation of gallium phosphide single crystals using a gallium arsenide substrate and a concentrated nitric acid etching solution is described.

Groves, W. O.↗
DOE OSTI2024

Molten flux growth of single crystals of quasi-1D hexagonal chalcogenide BaTiS3

Abstract BaTiS 3 , a quasi-1D complex chalcogenide, has gathered considerable scientific and technological interest due to its giant optical anisotropy and electronic phase transitions. However, the synthesis of high-quality BaTiS 3 crystals, particularly those featuring crystal sizes of millimeters or larger, remains a challenge. Here, we investigate the growth of BaTiS 3 crystals utilizing a molten salt flux of either potassium iodide, or a mixture of barium chloride and barium iodide. The crystals obtained through this method exhibit a substantial increase in volume compared to those synthesized via the chemical vapor transport method, while preserving their intrinsic optical and electronic properties. Our flux growth method provides a promising route toward the production of high-quality, large-scale single crystals of BaTiS 3 , which will greatly facilitate advanced characterizations of BaTiS 3 and its practical applications that require large crystal dimensions. Additionally, our approach offers an alternative synthetic route for other emerging complex chalcogenides. Graphical Abstract

Materials Science↗
DOE OSTI2024

Optical and photoelectric properties of surface barrier diodes based on n- Hg3In2Te6 crystals

The high radiation resistance of Hg3In2Te6 (MIT) single crystals to large doses of ionizing radiation makes devices quite attractive. Such a feature of the crystal structure has not only important advantages, but also causes serious technological difficulties in doping and controlling the specific resistance within the required limits and type of conductivity of single crystals. These technological difficulties create serious problems when creating structures with a potential barrier, especially with a p-n junction. At the moment, there are no publications on the creation of a p-n junction based on MIT. The only alternative is to create a potential barrier such as a Schottky diode or a metal-dielectric-semiconductor structure. This limits the use of MIT to produce, for example, rectifier diodes that can operate at relatively high reverse bias voltages. The typical resistivity of single crystals of MIT of n-type conductivity, which are used for the manufacture of diodes and photodiodes, is approximately equal to ρ≈103-104 Ω×cm. Such a specific resistance leads to a relatively large resistance of the neutral part of the single crystal, which in turn limits the direct currents of the rectifier diodes and significantly limits an important parameter of photodiodes - the dynamic range of the watt-ampere characteristic. This problem arises from the relatively high series resistance of the substrate. For rectifier diodes, this relatively large series resistance leads to a significant forward bias voltage drop, which reduces both the rectification factor and the amount of rectified current. We have already created diodes and photodiodes on Cr/MIT/Cr single crystals with a specific resistance of ρ≈103-104 Ω×cm. The diodes had relatively small dark currents but had the disadvantage of a relatively large specific resistance of the substrate, which we have already discussed above [1,2,3].

Sklyarchuk, V.↗
DOE OSTI2017

Reconstructing three-dimensional protein crystal intensities from sparse unoriented two-axis X-ray diffraction patterns

Recently, there has been a growing interest in adapting serial microcrystallography (SMX) experiments to existing storage ring (SR) sources. For very small crystals, however, radiation damage occurs before sufficient numbers of photons are diffracted to determine the orientation of the crystal. The challenge is to merge data from a large number of such `sparse' frames in order to measure the full reciprocal space intensity. To simulate sparse frames, a dataset was collected from a large lysozyme crystal illuminated by a dim X-ray source. The crystal was continuously rotated about two orthogonal axes to sample a subset of the rotation space. With the EMC algorithm [expand–maximize–compress; Loh & Elser (2009). Phys. Rev. E , 80 , 026705], it is shown that the diffracted intensity of the crystal can still be reconstructed even without knowledge of the orientation of the crystal in any sparse frame. Moreover, parallel computation implementations were designed to considerably improve the time and memory scaling of the algorithm. The results show that EMC-based SMX experiments should be feasible at SR sources.

Chemistry↗