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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 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Stereochemistry of silicon in oxygen-containing compounds

Specific stereochemical features of silicon in oxygen-containing compounds, including hybrid silicates with all oxygen atoms of SiO{sub n} groups ({sub n} = 4, 5, or 6) entering into the composition of organic anions or molecules, are described by characteristics of Voronoi—Dirichlet polyhedra. It is found that in rutile-like stishovite and post-stishovite phases with the structures similar to those of СаСl{sub 2}, α-PbO{sub 2}, or pyrite FeS{sub 2}, the volume of Voronoi—Dirichlet polyhedra of silicon and oxygen atoms decreases linearly with pressure increasing to 268 GPa. Based on these results, the possibility of formation of new post-stishovite phases is shown, namely, the fluorite-like structure (transition predicted at ~400 GPa) and a body-centered cubic lattice with statistical arrangement of silicon and oxygen atoms (~900 GPa).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Non-isothermal crystallization kinetics of Fe{sub 2}O{sub 3}–CaO–SiO{sub 2} glass containing nucleation agent P{sub 2}O{sub 5}/TiO{sub 2}

Fe{sub 2}O{sub 3}–CaO–SiO{sub 2} glass ceramics containing nucleation agent P{sub 2}O{sub 5}/TiO{sub 2} were prepared by sol-gel method. The samples were characterized by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The activation energy and kinetic parameters for crystallization of the samples were calculated by the Johnson-Mehi-Avrami (JMA) model and Augis-Bennett method according to the results of DSC. The results showed that the crystallization mechanism of Fe{sub 2}O{sub 3}–CaO–SiO{sub 2} glass, whose non-isothermal kinetic parameter n = 2.3, was consistent with surface crystallization of the JMA model. The kinetics model function of Fe{sub 2}O{sub 3}–CaO–SiO{sub 2} glass, f(α) = 2.3(1–α)[–ln(1–α)]{sup 0.57}, was also obtained. The addition of nucleation agent P{sub 2}O{sub 5}/TiO{sub 2} could reduce the activation energy, which made the crystal growth modes change from onedimensional to three-dimensional.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Crystal Structure of a Nickel(II) Complex with the Macrocyclic Azadibenzo-14-crown-4 Ether Ligand Containing the Embedded Di(α-pyridyl)bispidone Moiety

The crystal structure of the nickel(II) complex with substituted azadibenzo-14-crown-4 ether containing the embedded di(α-pyridyl)bispidone moiety having the formula [L(H{sub 2}O)Ni(NO{sub 3}) Ni(H{sub 2}O)L](ClO{sub 4}){sub 3} · 0.7EtOH was studied by X-ray diffraction (T = 150(2) K, R = 0.0628). In the complex cation two five-coordinate nickel complexes are bridged by the nitrate anion to form a dimer. The distorted octahedral environment of Ni atoms is formed by four nitrogen atoms of the molecule L and the oxygen atoms of the water molecule and the NO{sub 3}{sup -} anion. In the nickel complex, like in the cobalt and copper complexes studied previously, the bispidine moiety of the molecule L adopts a chair-chair conformation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Influence of radiative processes on the ignition of deuterium–tritium plasma containing inactive impurities

The degree of influence of radiative processes on the ignition of deuterium–tritium (DT) plasma has been theoretically studied as dependent on the content of inactive impurities in plasma. The analytic criterion of plasma ignition in inertial confinement fusion (ICF) targets is modified taking into account the absorption of intrinsic radiation from plasma in the ignition region. The influence of radiative processes on the DT plasma ignition has been analytically and numerically studied for plasma that contains a significant fraction of inactive impurities either as a result of DT fuel mixing with ICF target ablator material or as a result of using light metal DT-hydrides as solid noncryogenic fuel. It has been shown that the effect of the absorption of intrinsic radiation leads to lower impurity-induced increase in the ignition energy as compared to that calculated in the approximation of optically transparent ignition region.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

XAFS Spectroscopy Study of Microstructure and Electronic Structure of Heterosystems Containing Si/GeMn Quantum Dots

Using X-ray absorption near edge structure spectroscopy, extended X-ray absorption fine structure spectroscopy, atomic force microscopy, and Rutherford backscattering spectroscopy, the features of the microstructure and elemental composition of Si/GeMn magnetic systems obtained by molecular beam epitaxy and containing quantum dots are studied. Intense mixing of Ge and Si atoms is found in all samples. The degree of mixing (diffusion) correlates with the conditions of synthesis of Si/GeMn samples. For these systems, direct contacts of germanium atoms with manganese atoms are characterized and the presence of interstitial manganese with tetrahedral coordination and substitution of manganese for germanium and silicon in the lattice sites is found. The presence of stoichiometric phases Ge{sub 8}Mn{sub 11}, Ge{sub 3}Mn{sub 5} is not detected. The correlations of the Ge, Si, and Mn coordination numbers in the Ge environment are determined both with the Mn flux value (evaporator temperature) and with the temperature at which quantum dots are grown, as well as with other synthesis conditions. The manganese concentration in the samples is determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Coherent fragmentation of {sup 12}C nuclei of momentum 4.5 GeV/c per nucleon through the {sup 8}Be{sub g.s.}+{sup 4}He channel in a nuclear photoemulsion containing lead nuclei

A two-particle channel in which an unbound nucleus of {sup 8}Be in the ground state ({sup 8}Be{sub g.s.}) was one of the fragments was selected among events where {sup 12}C nuclei of momentum 4.5 GeV/c per nucleon undergo coherent dissociation into three alpha particles. The events in question were detected in a track nuclear photoemulsion containing lead nuclei, which was irradiated at the synchrophasotron of the Laboratory of High Energies at the Joint Institute for Nuclear Research (JINR, Dubna). The average transverse momentum of alpha particles produced upon the decay of {sup 8}Be{sub g.s.} nuclei was 87±6 MeV/c, while that for “single” alpha (α{sub s}) particles was 123±15 MeV/c. The average value of the transverse-momentum transfer in the reaction being considered, Pt(12C), was 223 ± 20 MeV/c. The average value of the cross section for this channel involving Ag and Br target nuclei was 13 ± 4 mb, while the cross section for the reaction on the Pb nucleus was 40 ± 15 mb. The Coulomb dissociation contribution evaluated on the basis of the number of events where the momentum P{sub t}({sup 12}C) did not exceed 0.1 GeV/c saturated about 20%. In nine events, the measured total transverse energy of the fragments in the reference frame comoving with the decaying carbon nucleus did not exceed 0.45 MeV, which did not contradict the excitation of the participant {sup 12}C nucleus to the level at 7.65 MeV. The average value of the transverse momentum in those events was 234 ± 25 MeV/c.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Effect of dust charge fluctuations on dust acoustic structures in magnetized dusty plasma containing nonextensive electrons and two-temperature isothermal ions

Effect of dust electrical charge fluctuations on the nature of dust acoustic solitary waves (DASWs) in a four-species magnetized dusty plasma containing nonextensive electrons and two-temperature isothermal ions has been investigated. In this model, the negative dust electric charge is considered to be proportional to the plasma space potential. The nonlinear Zakharov–Kuznetsov (ZK) and modified Zakharov–Kuznetsov (mZK) equations are derived for DASWs by using the standard reductive perturbation method. The combined effects of electron nonextensivity and dust charge fluctuations on the DASW profile are analyzed. The different ranges of the nonextensive q-parameter are considered. The results show that solitary waves the amplitude and width of which depend sensitively on the nonextensive q-parameter can exist. Due to the electron nonextensivity and dust charge fluctuation rate, our dusty plasma model can admit both positive and negative potential solitons. The results show that the amplitude of the soliton increases with increasing electron nonextensivity, but its width decreases. Increasing the electrical charge fluctuations leads to a decrease in both the amplitude and width of DASWs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Study of Gallium Arsenide Etching in a DC Discharge in Low-Pressure HCl-Containing Mixtures

Halogen-containing plasmas are often used to form topological structures on semiconductor surfaces; therefore, spectral monitoring of the etching process is an important diagnostic tool in modern electronics. In this work, the emission spectra of gas discharges in mixtures of hydrogen chloride with argon, chlorine, and hydrogen in the presence of a semiconducting gallium arsenide plate were studied. Spectral lines and bands of the GaAs etching products appropriate for monitoring the etching rate were determined. It is shown that the emission intensity of the etching products is proportional to the GaAs etching rate in plasmas of HCl mixtures with Ar and Cl{sub 2}, which makes it possible to monitor the etching process in real time by means of spectral methods.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Electrical properties of silicon schottky diodes containing metal films of various compositions

Au{sub x}Ti{sub 100{sub -}} {sub x}/n-Si Schottky diodes are fabricated and studied; in addition, the electrical properties of diodes containing metal films with varying composition (x = 0, 14, 30, 38, 60, 80, and 100) are also studied. Using X-ray phase analysis, it is established that the film of Au{sub 38}Ti{sub 62} composition has the amorphous structure, while the remaining films Au{sub x}Ti{sub 100-x} possess the polycrystalline structure. The main parameters of the Schottky diodes are determined in relation to the composition and structure of the metal films. As a result, it is shown that the electrical properties of Au{sub x}Ti{sub 100-x}/n-Si Schottky diodes are related to variations in the composition and structure of metal films.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Simulation of the effective concentration profiles in InGaAs/GaAs heterostructures containing δ-doped layers

InGaAs/GaAs heterostructures containing quantum wells and δ-doped layers are studied theoretically and experimentally. On the basis of the procedure of self-consistently solving the Schrödinger equation and Poisson equation, the differential capacitance and the apparent electron concentration profiles are numerically calculated for structures with different mutual arrangements of the quantum well and the δ layer. The results of the calculations are compared with the result of analyzing the experimental capacitance-voltage characteristics of the structures. The systematic features of the behavior of the apparent concentration profiles and capacitance-voltage characteristics in relation to the geometric properties of the structure, the temperature, and the doping level are established.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Specific features of the photoluminescence of HEMT nanoheterostructures containing a composite InAlAs/InGaAs/InAs/InGaAs/InAlAs quantum well

The specific features of the photoluminescence and the electrical properties of doped nanoheterostructures containing a composite InAlAs/InGaAs/InAlAs quantum well with a thin InAs insert in the middle are studied. The insert thickness is varied in the range from 1.7 to 3.0 nm. It is established that the position of the peaks in the photoluminescence spectra in the photon energy range 0.6–0.8 eV correlates with the InAs insert thickness. Simulation of the band structure shows that the experimentally observed variation in the energy of optical transitions is associated with lowering of the energy of electron and hole states in the quantum well with increasing insert thickness. In the photon energy range 1.24–1.38 eV, optical transitions in the region of the InAlAs buffer-InP substrate interface are observed. The signal photon energy and intensity depend on the features of the formation of this heterointerface and on the conditions of substrate annealing. It is conceived that this is due to the formation of a transition region between the InAlAs buffer and the substrate.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Photoluminescence of heterostructures containing an In{sub x}Ga{sub 1–x}As quantum well with a high in content at different excitation powers

The results of studies of the photoluminescence spectra of heterostructures containing an In{sub x}Ga{sub 1–x}As quantum well with a high In content x at different laser-radiation powers are reported. It is found that, as the radiation power density is increased, the luminescence spectrum of In{sub 0.70}Al{sub 0.30}As/In{sub 0.76}Ga{sub 0.24}As quantum-well heterostructures exhibits a decrease in the half-width and a shift of the peak to higher energies. It is shown that, for Al{sub 0.27}Ga{sub 0.73}As/In{sub 0.20}Ga{sub 0.80}As quantum-well heterostructures, no shift of the peak and no change in the shape of the spectrum is observed. It is established that the integrated photoluminescence intensity is related to the laser-radiation power density by a power law with the exponent α ≈ 1.3 for heterostructures with x ≈ 0.76, suggesting the predominantly excitonic character of the radiative recombination of charge carriers.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Luminescence properties of Si-containing porous matrix–PbS nanoparticle systems

The luminescence properties of systems that contain lead-sulfide nanoparticles deposited onto substrates fabricated from porous silicon, oxidized porous silicon, and porous (tin-oxide)–(silicon-oxide) layers are studied. It is shown that the structure and composition of the matrix induce a strong effect on the luminescence spectra of colloidal quantum dots, defining their emission wavelength.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Photoluminescence properties of thallium-containing GeSe{sub 2} and GeSe{sub 3} vitreous semiconductors

The photoluminescence properties of thallium-containing vitreous semiconductor systems with stoichiometric and nonstoichiometric compositions (GeSe{sub 2}){sub 1–x}Tl{sub x} and (GeSe{sub 3}){sub 1–x}Tl{sub x} (0 ⩽ x ⩽ 0.1) are studied at a temperature of T = 77 K. Intrinsic defects with negative correlation energy are responsible for the Gaussian shape of the photoluminescence spectra. It is established that an increase in x in the systems does not affect the shape of the spectrum, does not generate new emission bands, shifts the photoluminescence spectra to the region of low energies, reduces the intensity of radiation, and increases its half-width. Kinetics of the fatigue of photoluminescence is different for both systems and is characterized by one curve irrespective of Tl content in the systems.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Polarization Properties of Photoluminescence of Anisotropic Polymer Films Containing Aligned Au Nanorods and Semiconductor Nanoparticles of Various Shape

Anisotropic polymer films containing aligned Au nanorods and semiconductor nanoparticles of various shape were fabricated. The photoluminescence of semiconductor nanoparticles in these films is partially polarized. The value of the photoluminescence polarization degree of quantum dots embedded in an anisotropic PVA-film after 4.5-fold stretching P = 0.27 has been obtained.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Phase Equilibrium and Surface Properties of a Binary System Containing Nanoparticles

A consistent description of phase equilibrium and surface phenomena in binary systems containing monodisperse spherical nanoparticles of arbitrary (including nanoscale) size is presented in the context of the classical method with separating surfaces. Using the obtained relations, we have calculated the composition of coexisting phases and interface layer, and interfacial tension on the boundary between nanoparticles and the matrix at different temperatures in Ti-Mo system. The results of the calculations are consistent with the available experimental data.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Features of the Electrical Properties of Lithium Niobate Crystals Grown from a Melt Containing K{sub 2}O Flux

The variations of electrical conductivity and the primary pyroelectric coefficient with temperature for lithium niobate (LiNbO{sub 3}) crystals grown from melt containing K{sub 2}O flux are studied in the range of 292–450 K. These crystals are found to exhibit considerable anisotropy of electrical conductivity, and the proton conductivity is dominant in the studied temperature range.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗