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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 1,639 records · Page 91
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Ge{sub 1-y}Sn{sub y} (y = 0.01-0.10) alloys on Ge-buffered Si: Synthesis, microstructure, and optical properties

Novel hydride chemistries are employed to deposit light-emitting Ge{sub 1-y}Sn{sub y} alloys with y ≤ 0.1 by Ultra-High Vacuum Chemical Vapor Deposition (UHV-CVD) on Ge-buffered Si wafers. The properties of the resultant materials are systematically compared with similar alloys grown directly on Si wafers. The fundamental difference between the two systems is a fivefold (and higher) decrease in lattice mismatch between film and virtual substrate, allowing direct integration of bulk-like crystals with planar surfaces and relatively low dislocation densities. For y ≤ 0.06, the CVD precursors used were digermane Ge₂H₆ and deuterated stannane SnD₄. For y ≥ 0.06, the Ge precursor was changed to trigermane Ge₃H₈, whose higher reactivity enabled the fabrication of supersaturated samples with the target film parameters. In all cases, the Ge wafers were produced using tetragermane Ge₄H₁₀ as the Ge source. The photoluminescence intensity from Ge{sub 1–y}Sn{sub y}/Ge films is expected to increase relative to Ge{sub 1–y}Sn{sub y}/Si due to the less defected interface with the virtual substrate. However, while Ge{sub 1–y}Sn{sub y}/Si films are largely relaxed, a significant amount of compressive strain may be present in the Ge{sub 1–y}Sn{sub y}/Ge case. This compressive strain can reduce the emission intensity by increasing the separation between the direct and indirect edges. In this context, it is shown here that the proposed CVD approach to Ge{sub 1–y}Sn{sub y}/Ge makes it possible to approach film thicknesses of about 1 μm, for which the strain is mostly relaxed and the photoluminescence intensity increases by one order of magnitude relative to Ge{sub 1–y}Sn{sub y}/Si films. The observed strain relaxation is shown to be consistent with predictions from strain-relaxation models first developed for the Si{sub 1–x}Ge{sub x}/Si system. The defect structure and atomic distributions in the films are studied in detail using advanced electron-microscopy techniques, including aberration corrected STEM imaging and EELS mapping of the average diamond–cubic lattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Quantification of ordering at a solid-liquid interface using plasmon electron energy loss spectroscopy

We present an in situ electron energy loss spectroscopy (EELS) study of ordering of liquid Al at various Al-Al{sub 2}O{sub 3} interfaces. This technique utilizes precise measurements of the shifts in bulk plasmon resonance and their sensitivity to the valence electron density. Plasmon EELS combined with high resolution transmission electron microscopy provides information regarding the chemical composition in liquid Al at Al-Al{sub 2}O{sub 3} interfaces. Preferential oxygen segregation to the (0006) Al{sub 2}O{sub 3} plane was verified, and the (101{sup ¯}2) Al{sub 2}O{sub 3} plane was found to contain the lowest amount of segregated species.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Structural, electronic and thermal properties of Mo{sub 3}Ir superconductors

Self consistent first principle calculations on superconducting material Mo{sub 3}Ir of A15 phase have been performed to understand their fundamental characteristics of the structural, electronic and thermal properties. The bulk modulus (B{sub 0}), Debye temperature (θ{sub D}), density of states (N (E{sub F})) and electronic specific heat coefficient (γ) have been computed in terms of the electronic structure results obtained by using the tight-binding linear muffin tin orbital (TB-LMTO) method based on the density functional theory (DFT) within the local density approximation (LDA). Structural, electronic and thermal properties calculated here are found to corroborate well with the experimental and theoretical results of literature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Structural, mechanical and electronic properties of in-plane 1T/2H phase interface of MoS{sub 2} heterostructures

Two-dimensional (2D) molybdenum disulfide (MoS{sub 2}) phase hybrid system composed by 2H and 1T phase is a natural metal/semiconductor heterostructures and promised a wide range of potential applications. Here, we report the first principle investigations on the structural, mechanical and electronic properties of hybrid system with armchair (AC) and zigzag (ZZ) interfaces. The ZZ type 1T/2H interface are more energy favorable than AC type interface with 3.39 eV/nm. Similar with that of bulked 1T MoS{sub 2}, the intrinsic strengths of the heterostructures are lower than that of the bulk 2H, especially for that with ZZ interface. Analysis of density of states shows that the electronic properties gradually transmitted from the metallic 1T phase to the semiconducting 2H phase for the structural abrupt interface. The present theoretical results constitute a useful picture for the 2D electronic devices using current MoS{sub 2} 1T/2H heterostructures and provide vital insights into the other 2D hybrid materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Carrier mobilities of (001) cadmium arsenide films

We investigate (001)-oriented films of the topological semimetal cadmium arsenide (Cd 3 As 2 ) grown by molecular beam epitaxy on lattice-matched III–V Al x In 1-x Sb buffer layers. Magnetotransport studies and analysis of thin film microstructures are used to determine the influence of dislocations on their carrier mobilities. We show that only a minority of the threading dislocations present in the buffer layers extend into the Cd 3 As 2 films. Threading dislocations are shown to reduce the mobilities of carriers residing in the topological surface states, while bulk transport was unaffected by a change in the dislocation density across an order of magnitude. Thick (001) Cd 3 As 2 films exhibit electron mobilities of up to 41 000 cm 2 V -1 s -1 at 2 K. The results provide insights into the influence of extended defects on the transport properties of a prototype topological semimetal.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Analysis of optical and magnetooptical spectra of Fe{sub 5}Si{sub 3} and Fe{sub 3}Si magnetic silicides using spectral magnetoellipsometry

The optical, magnetooptical, and magnetic properties of polycrystalline (Fe{sub 5}Si{sub 3}/SiO{sub 2}/Si(100)) and epitaxial Fe{sub 3}Si/Si(111) films are investigated by spectral magnetoellipsometry. The dispersion of the complex refractive index of Fe{sub 5}Si{sub 3} is measured using multiangle spectral ellipsometry in the range of 250–1000 nm. The dispersion of complex Voigt magnetooptical parameters Q is determined for Fe{sub 5}Si{sub 3} and Fe{sub 3}Si in the range of 1.6–4.9 eV. The spectral dependence of magnetic circular dichroism for both silicides has revealed a series of resonance peaks. The energies of the detected peaks correspond to interband electron transitions for spin-polarized densities of electron states (DOS) calculated from first principles for bulk Fe{sub 5}Si{sub 3} and Fe{sub 3}Si crystals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Understanding the Role of Complexation in the Charge-Transfer Kinetics of the Cu 2+ + e ↔ Cu 1+ Redox Reaction in Ethaline Deep Eutectic Solvent

Deep eutectic solvent (DES) based electrolytes are gaining attention for electrochemical applications. As such, knowledge of the charge transfer kinetics in DES and its dependence on electrolyte composition and temperature is important. Using Cu 2+ + e ↔ Cu 1+ as a model system, we demonstrate that metal redox reactions in chloride-containing DES media suffer from sluggish charge transfer kinetics. The exchange current density, i 0 , displayed a peculiar inverse relationship with the bulk chloride concentration, [Cl – ] b . The i 0 decreased from 7.9 to 3.0 mA/cm 2 when [Cl – ] b increased from 2.8 to 4.6 M at 30°C. Such dependence is shown to originate from Cl – complexation with reactant and product species. Furthermore, i 0 increased with an increase in Cu n + bulk concentration in the 50–200 mM range. Also, increase in temperature elevated i 0 . The charge transfer coefficient α c , however, remained constant (~0.5) and was unaffected by Cu n + or Cl – concentrations or by temperature. To explain how charge transfer kinetics depend on the various system parameters, a model incorporating complexation phenomena was developed and its predictions were compared to experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Handbook on the Material Properties of Yttrium Hydride for High Temperature Moderator Applications

Yttrium hydride is an optimal choice for a high-temperature moderator material in advanced thermal neutron spectrum reactors that require small core volumes. A complete database of the thermomechanical properties of yttrium hydride is not yet available, although it is much needed to understand and predict the moderator performance during service in reactors. This milestone report presents the properties of unirradiated bulk yttrium hydride as a function of hydrogen concentration—including density, crystal structure, specific heat capacity, thermal diffusivity, thermal conductivity, hardness, elastic/shear moduli, Poisson’s ratio, fracture strength, microstructure, and thermal stability. This information provides a baseline measurement for the subsequent neutron irradiation response study of yttrium hydride. The recommended empirical treatment of the data is suggested. In addition, other properties (i.e., hydrogen retention, thermal hydrogen migration, and irradiation response) requiring investigation are discussed. Also included are the Preliminary post-irradiation examination (PIE) data of yttrium hydride irradiated at 600 and 900°C to 0.1 dpa in the High Flux Isotope Reactor (HFIR). The thermophysical properties have insignificant change following this low dpa irradiation for both irradiation temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Atomistic theories and Simulations of Multiferroics

The goal of this award was to build a research program aimed at investigating puzzling complex phenomena in multiferroics, that are systems possessing electric and magnetic dipoles. We first emphasized the study of multiferroic nanostructures, that are 0D, 1D, 2D systems as well as superlattices and then also study multiferroics as a whole, i.e., bulks as well. In order to fully understand such complex systems, we also decided to study magnetic systems and ferroelectrics, both in their nanostructure and bulk forms. For that and in addition to use standard Density Functional Theory codes, we developed and used ab-initio tools that are able to model properties of large supercells (about a million atoms nowadays) at finite temperature and for any mechanical and boundary conditions. We also collaborated with experimentalists to fully understand the systems under study. The whole program resulted in 108 publications that are listed at the end of this report. In the following, I will put an emphasis on some publications before the last award period and also indicate a description of the last award period.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1972

Fuel cells and the theory of metals.

Metal theory is used to study the role of metal catalysts in electrocatalysis, with particular reference to alkaline hydrogen-oxygen fuel cells. Use is made of a simple model, analogous to that used to interpret field emission in vacuum. Theoretical values for all the quantities in the Tafel equation are obtained in terms of bulk properties of the metal catalysts (such as free electron densities and Fermi level). The reasons why some processes are reversible (H-electrodes) and some irreversible (O-electrodes) are identified. Selection rules for desirable properties of catalytic materials are established.

Bocciarelli, C. V.↗
NASA NTRS1984

Method and apparatus for coating substrates using a laser

Metal substrates, preferably of titanium and titanium alloys, are coated by alloying or forming TiN on a substrate surface. A laser beam strikes the surface of a moving substrate in the presence of purified nitrogen gas. A small area of the substrate surface is quickly heated without melting. This heated area reacts with the nitrogen to form a solid solution. The alloying or formation of TiN occurs by diffusion of nitrogen into the titanium. Only the surface layer of the substrate is heated because of the high power density of the laser beam and short exposure time. The bulk of the substrate is not affected, and melting of the substrate is avoided because it would be detrimental.

Zaplatynsky, I.↗
NASA NTRS1985

The detection of eclipses in the Pluto-Charon system

The first eclipses between Pluto and its satellite ('Charon') were detected in January and February 1985, confirming the satellite's existence. Eclipses lasting a few hours will now occur at 3.20 day intervals for the next 5 to 6 years and then will cease for about 120 years. Careful observations of these eclipses will allow greatly improved determinations to be made of several physical parameters for the Pluto-Charon system: the diameters of the planet and satellite, the surface albedo distribution on one hemisphere of the planet, the orbit of the satellite, and the mass of the planet and hence its density. Knowledge of the density will provide a constraint on models of Pluto's bulk composition.

Binzel, R. P.↗
NASA NTRS1989

Physical conditions in molecular clouds

Recent developments have complicated the picture of the physical conditions in molecular clouds. The discoveries of widespread emission from high-J lines of CD and 12-micron IRAS emission have revealed the presence of considerably hotter gas and dust near the surfaces of molecular clouds. These components can complicate interpretation of the bulk of the cloud gas. Commonly assumed relations between column density or mean density and cloud size are called into question by conflicting results and by consideration of selection effects. Analysis of density and density structure through molecular excitation has shown that very high densities exist in star formation regions, but unresolved structure and possible chemical effects complicate the interpretation. High resolution far-IR and submillimeter observations offer a complementary approach and are beginning to test theoretical predictions of density gradients in clouds.

Evans, Neal J., II↗
NASA NTRS1988

The development of new, low-cost perfluoroalkylether fluids with excellent low and high-temperature properties

A series of perfluoroalkylether (PFAE) fluids were synthesized by direct fluorination. Viscosity-temperature properties, oxidation stabilities, oxidation-corrosion properties, and lubricity were determined. The fluids were tested in the presence of common elastomers to check for compatibility. The bulk modulus of each was measured to determine if any could be used as nonflammable aircraft hydraulic fluid. It was determined that as the carbon to oxygen ratio decreases, the viscometric properties improve, the fluids may become poor lubricants, the bulk modulus increases, the surface tension increases, and the fluid density increases. The presence of difluoromethylene oxide units in the polymer does not seriously lower the oxidation and oxidation-corrosion stabilities as long as the difluoromethylene oxide units are separated by other units.

Bierschenk, Thomas R.↗
NASA NTRS1995

The Honeycomb supernova remnant

At 2.5 min southeast of SN 1987A, the Honeycomb Nebula Supernova remnant (SNR) is named after its interesting morphology, which consists of over ten loops with sizes of 2-3 pc. High-dispersion spectra of these loops show hemispheres expanding toward the observer at 100-300 km/s. Using archival data X-ray data and a combination of new and archival radio data, we find bright X-ray and nonthermal radio emisssion associated with the Honeycomb Nebula. New CCD images further show enhanced (S II) H-alpha ratios. These results confirm a model in which the Honeycomb Nebula is due to a supernova shock front, traveling toward the observer, encountering an intervening sheet of dense, but porous, interstellar gas. The bulk of the supernova remnant resides in a low-density cavity, and is not otherwise visible. The situation is similar to the hidden supernova remnants postulated for the X-ray bright superbubbles. The Honeycomb Nebula has an unusually steep radio spectral index (S(sub nu) is proportional to nu(exp -1.2)), normally associated with young SNRs.

Chu, You-Hua↗
NASA NTRS1989

Simulations and Observations of Heating of Auroral Ion Beams

In the auroral zone, quasi-static parallel electric fields produce beams of ionospheric ions (e.g., H(+), He(+) and 0(+)), which flow outward into the magnetosphere, providing a significant source of ions for the ring current and plasma sheet. Because the velocities to which these beams are accelerated is dependent on the mass of the ions, differential flows between the various ion species can develop which are unstable to an ion-ion streaming instability. Particle simulations and observations from DE 1 are used to investigate the heating of the ion beams produced by this instability. It is shown that there is net transfer of energy from the light ions to the heavy ions, with the heavy ions reaching maximum velocities near the beam velocity of the light ions. Bulk heating of the heavy ions occurs when their relative density is low while high-energy tails are produced when their relative density is high. The heating is primarily parallel to the magnetic field if the difference in the heavy and light ion beam velocities is subsonic while both perpendicular and parallel heating can occur if it is supersonic. In the latter case, very strong heating of an intermediate ion's species such as He(+) can also occur. Comparison with observations shows features consistent with heating via the ion-ion instability including perpendicular heating in the supersonic regime and parallel heating in the subsonic regime and a change in the heating between these regimes as the ratio of the H(+) beam speed to the local sound speed is observed to decrease. This heating is, however, not always observed in association with enhanced wave emissions. This lack of waves is attributed to reabsorption of the waves as the ions become heated.

Winglee, R. M.↗
DOE OSTI2012

Electrochemical Sensors Based on Nanomaterials for Environmental Monitoring

This article review work relevant to the two fastest growing nanomaterials in electrochemical sensing of metal ions: organically modified ordered mesoporous silicas (OMSs) and carbon nanotubes (CNTs). Nanostructured self-assembled monolayers on mesoporous silicas (SAMMS) materials are highly effective as electrode modifiers; they can be either mixed with conductive materials or spin-cast as a thin-film on electrode surface. The interfacial chemistry of SAMMS can be fine-tuned to selectively preconcentrate the specific metal ions of interest. The functional groups on SAMMS materials enable the preconcentration to be done without mercury, supporting electrolytes, applied potential, and solution degassing, all of which are often required in conventional adsorptive stripping voltammetric sensors. Since it was first introduced in 1991, CNTs have been widely investigated for electrochemical sensors of many important biomolecules because of their electrocatalytic and antifouling properties, biocompatibility, high surface, and mechanical strength. For trace metal analysis, CNT thin-film created by drop-coating of CNT-solvent suspensions on electrode surfaces has been explored in order to develop mercury-free sensors by exploiting the bulk properties of the CNTs. Array of low-site-density aligned carbon nanotubes has been grown on metal substrates by a non-lithographic method. Each CNT serves as a nanoelectrode which normally has greater mass transfer rate and higher mass sensitivity than conventional macroelectrodes. The array of millions of CNT nanoelectrodes provides magnified voltammetric signals for trace metal ions without the need for a signal amplifier.

Electrochemical Sensors↗
DOE OSTI2015

Final Technical Report for the project titled "Manganese Based Permanent Magnet with 40 MGOe at 200°C"

The objective of project was to develop MnBi based permanent magnet for high temperature application (~150°C). This objective is derived based on MnBi’s unique positive temperature dependence of coercivity, which is doubled from ~1 T at RT to ~2.5 T at 200°C. Because of its limited magnetization (<0.9 T at RT), the MnBi magnet is best suited to fill in the gap between rare earth based NdFeB-Dy or SmCo magnet (20 MGOe) and the AlNiCo magnet (10 MGOe) at 150°C. It is expected that if successfully developed, MnBi will effectively mitigate the world’s demand on Dy. Before this project, the highest LTP content in MnBi powder is about 90% if the quantity of the powder is less than 5 gram (using melt-spin method); or 80% if the quantity is greater than 100 gram (using conventional powder metallurgical method such as arc melting and annealing). After this project, large quantities (5kg/batch) with high LPT phase content (>92 wt%) can be routinely synthesized. This achievement is made possible by the newly developed synthesis method based on conventional metallurgical processing technique involving arc melting, two-stage ingot annealing, grinding, sieving, and vacuum annealing. Before this project, the finest powder particle size is about 35 μm with overall powder composition maintaining at about 85% LTP phase. The reason why LTP phase content is listed along with particle size is because LTP MnBi is easy to decompose when exposed to temperature higher than 350 °C. As result, only low energy ball milling can be used to refine the particle size; moreover, the ball milling time cannot exceed 4 hrs, or else the decomposed LTP MnBi phase will exceed 10%. After this project, the finest powder size is reduced to 1~5 μm while maintain the 90% LTP MnBi phase content. This achievement is made possible by a newly developed cryogenic ball milling system, which provides -70 °C ambient for the rolling container. Before this project, it is not clear if MnBi will ferromagnetically exchange-couple with soft magnetic phase such as Fe or Co. After this project, it is established that MnBi will ferromagnetically exchange couple with Co, but not with Fe. It is also possible for MnBi to ferromagnetically exchange couple with Fe-Co alloy, but the amount of Fe cannot be more than 50 at.%. This conclusion is made possible by a series of electronic structure calculation followed by a series of thin film experimentation. As the result, 25 MGOe energy product was demonstrated using a MnBi-Co film. Before this project, the highest energy product for a bulk MnBi magnet is about 5 MGOe with 70% green density, and near-fully dense magnet is not available. After this project, the highest energy density is about 8.6 MGOe with 95% green density. This achievement is made possible by a modified warm-compaction system developed at University of Texas at Arlington. This system has 2.1 T alignment field vs the previous 1.8 T, and the compaction ambient maintains <1 ppm oxygen partial pressure. The estimated cost of MnBi magnet is about $110/kg when conventional magnet fabrication method is used, and about $84/kg when warm extrusion method is used. In comparison the cost of NdFeB, SmCo, AlNiCo, and Sr-Ferrite magnets is $150/kg, $180/kg, $119/kg, and $20/kg, respectively. The near term future work should focus on further improve the purity of the LTP MnBi, pushing it from the current 91 wt.% to 99 wt.%. If successful, the increased 8% LTP phase will increase the remanent magnetization, which in turn, increase the energy product. In addition, high reduction ratio warm extrusion method should be investigated to further push the texture to >90%.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗