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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Stimulated Emission and Optical Properties of Solid Solutions of Cu(In,Ga)Se{sub 2} Direct Band Gap Semiconductors

Stimulated emission, optical properties, and structural characteristics of non-irradiated and proton-irradiated Cu(In,Ga)Se{sub 2} thin films deposited on soda lime glass substrates using co-evaporation of elements in a multistage process were investigated. X-ray diffraction analysis, scanning electron microscopy, X-ray spectral analysis with energy dispersion, low-temperature photoluminescence, optical transmittance and reflectance were used to study the films. Stimulated emission at low temperatures of ~20 K was found in non-irradiated and proton-irradiated Cu(In,Ga)Se{sub 2} thin films upon excitation by laser pulses of nanosecond duration with a threshold power density of ~20 kW/cm{sup 2}. It was shown that the appearance and parameters of the stimulated emission depend strongly on the concentration of ion-induced defects in Cu(In,Ga)Se{sub 2} thin films.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Time-Dependent Diffusion Coefficient of Fe in MgB{sub 2} Superconductors

The iron (Fe) diffusion in superconducting MgB{sub 2} bulk samples has been studied for sintering time durations of 15 min, 30 min, 1 h, 2 h, and 4 h at 900{sup ∘}C. Fe coating bulk polycrstalline superconducting MgB{sub 2} samples for Fe coating were prepared by pelletizing and used in the diffusion experiments with initial sintering at 800{sup ∘}C for 1 h. A thin layer of Fe was coated on MgB{sub 2} pellets by evaporation in vacuum. Effects of Fe diffusion on the structural, electrical, and superconducting properties of MgB{sub 2} have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), energy-dispersive X-ray spectroscopy (EDS), and resistivity measurements. Fe diffused samples have slightly increased critical transition temperatures and have larger lattice parameter c values, in comparison with bare samples. Fe diffusion coefficients were calculated from depth profiles of c parameter and room temperature resistivity values. Depth profiles were obtained by successive removal of thin layers from Fe diffused surfaces of the samples. Our results have shown that the Fe diffusion coefficient decreases with increasing sintering time and resistivity measurements can be utilized for determination of diffusion coefficient.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Influence of Fe ions on structural, optical and thermal properties of SnO{sub 2} nanoparticles

In the present work, Fe doped SnO{sub 2} nanoparticles with the composition Sn{sub 1-x}Fe{sub x}O{sub 2} (x = 0, 0.02, 0.04 and 0.06) have been successfully synthesized using sol-gel auto combustion technique. The samples are characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDAX), Ultraviolet (UV-Visible) absorption spectroscopy and thermal gravimetric analysis (TGA). The XRD study shows that all the samples have been found in tetragonal rutile structure without any extra phase and average crystallite size which lies in the range of 6-17 nm. The EDAX spectrum confirmed the doping of Fe ion into tin oxide nanomaterial. The optical band gap of doped SnO{sub 2} is found to decrease with increasing Fe ion concentration, which is due to the formation of donor energy levels in the actual band gap of SnO{sub 2}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Utah FORGE: Well 78B-32 Core Sample Petrographic Analysis Data

This dataset contains an overview of the petrographic, X-ray Diffraction and scanning electron microscopy analyses of core samples from Utah FORGE Well 78B-32 and related data as described in the .zip folder's Description below.

15 GEOTHERMAL ENERGY↗
DOE OSTI2025

Epitaxial columnar growth of strain-free antiferromagnetic Weyl semimetal Mn 3 Sn on wurtzite c -plane GaN/Al 2 O 3 (0001)

Weyl semimetal thin films with excellent crystalline quality are of great interest for antiferromagnetic spintronics. Mn 3 Sn is one Weyl semimetal with great properties and promise for exciting science and applications. It has proven very challenging, however, to grow Mn 3 Sn thin films with smooth surfaces, negligible strain, and excellent crystallinity. In this work, we discuss the successful preparation of epitaxial Mn 3 Sn (0001)-oriented thin films via molecular beam epitaxial growth on c -plane wurtzite GaN which was grown by MBE on Al 2 O 3 (0001). We present the reflection high energy electron diffraction analysis along with x-ray diffraction in order to demonstrate the crystalline quality of the film, and we give atomic models to explain the epitaxial orientation relationships between the crystal lattices of the substrate, GaN layer, and Mn 3 Sn layer. Importantly, we discuss the film lattice parameters as compared to expected values, demonstrating negligible strain both in-plane and out-of-plane . Atomic force microscopy reveals an epitaxial columnar growth mode characterized by flat-top-mesa islands, while scanning tunneling microscopy shows the atomically smooth surfaces of the mesa-top structures. Finally, Rutherford backscattering informs the stoichiometry of the film as well as the layer thicknesses.

Chiral antiferromagnetic material↗
DOE OSTI2022

Influence of Copper Composition on Cu 2 BaSn(S,Se) 4 Solution-Deposited Films and Photovoltaic Devices with Over 5% Efficiency

Cu 2 BaSn(S,Se) 4 is currently in the spotlight for prospective environmentally friendly, stable, thin-film solar cell application, with demonstrated device power conversion efficiency (PCE) exceeding 5% for vacuum-deposited absorbers. As suggested by first-principles calculations, experimental studies involving related Cu 2 ZnSn(S,Se) 4 and Cu(In,Ga)(S,Se) 2 absorbers prove that the detailed chemical composition typically plays a sensitive role in altering defects and electronic properties of these complicated compound semiconductors. Herein, the copper composition of Cu 2 BaSn(S,Se) 4 has been systematically modified, employing a solution-based deposition approach, to provide a more complete picture of the phase stability and optoelectronic property sensitivity for this material. X-ray diffraction and scanning electron microscopy show that phase purity is preserved over a film Cu content range of nominally 0.94 ≤ [Cu]/[Ba + Sn] ≤ 1.01. Terahertz spectroscopy and Hall effect measurements reveal that the majority carrier hole density of ~10 13 cm –3 and mobility (~5 cm 2 /V s), as well as the minority carrier lifetime (a bulk lifetime of 180 ps and a surface recombination velocity >106 cm/s), are nominally independent of Cu content. The champion PCEs exceed 4.7% for all copper compositions in the phase-pure region, with a record value of 5.1%, similar to the reported values for record vacuum-deposited devices. Furthermore, these results suggest that Cu 2 BaSn(S,Se) 4 films and solar cells (at the current performance level) may be less sensitive to Cu stoichiometry compared to kesterite materials and therefore may provide a more stable material platform to prepare thin-film solar cells.

(CBTSSe)↗
DOE OSTI2016

Charge transport mechanism analysis of Al/CdS:Sr{sup 2+}/ITO device under dark and light

In this study, we have synthesized CdS:Sr{sup 2+} by hydrothermal technique. Material property has been studied by X-ray diffraction (XRD), Scanning electron microscope (SEM) and UV-vis absorption spectroscopy. XRD data revealed that there are mixed phases of CdS and SrS in the synthesized sample. The optical band gap of the material was estimated as 3.15 eV from UV-vis data. The synthesized material has been applied in metal-semiconductor device and transport properties have been analyzed by measuring current–voltage characteristics under dark and light conditions at room temperature. Variation in different device parameters like ideality factor, barrier height and series resistance of Al/CdS:Sr{sup 2+}/ITO device were analyzed by using Cheung’s function.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Corrosion and interdiffusion studies of U{sub 3}Si{sub 2}

U{sub 3}Si{sub 2} is a candidate fissile phase for use in accident tolerant fuel systems in light-water reactors because of its higher fissile density, higher thermal conductivity when compared to uranium dioxide. It is also expected to have acceptable performance in contact with high temperature water (e.g., a leaker event from breached cladding) and in regards to interaction with different cladding materials. In high temperature water, U{sub 3}Si{sub 2} is expected to form a protective SiO{sub 2} coating. However, the resistance of U{sub 3}Si{sub 2} to corrosion under light water reactor service conditions has been previously unknown. In this study, the corrosion tests of sintered U{sub 3}Si{sub 2} discs were conducted in pressurized water at 300 C. degrees in an autoclave. The exposure times to corrosion were 6 hours and 24 hours. Detailed composition and microstructural analysis were carried out using a combination of techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) equipped with energy dispersive X-ray spectroscopy (EDS). Only slight weight change of U{sub 3}Si{sub 2} discs can be detected in corrosion tests up to 24 hours. A layered structure of corrosion products formed on U{sub 3}Si{sub 2}, with a glassy silicon oxide layer at the top followed by a nanocrystalline UO{sub 2} layer, a Si-rich oxide layer and then a mixture oxide layer of U and Si. A diffusion couple of U{sub 3}Si{sub 2} in contact with Zircaloy-4 has been tested at 800 C. degrees up to 100 hours. The resulting microstructure and interdiffusion have been studied with SEM/EDS. Some limited interdiffusion has been observed in these tests as well as a layer containing Zr and Si forms between the U{sub 3}Si{sub 2} disc and the Zircaloy-4 disc. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Continuously Doping BiM 2 Sr 2 CaCu 2 O 8+δ into Electron-Doped Superconductor by CaH 2 Annealing Method

As a typical hole-doped cuprate superconductor, Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) carrier doping is mostly determined by its oxygen content. Traditional doping methods can regulate its doping level within the range of hole doping. Here we report the first application of CaH 2 annealing method in regulating the doping level of Bi2212. By continuously controlling the anneal time, a series of differently doped samples can be obtained. The combined experimental results of x-ray diffraction, scanning transmission electron microscopy, resistance and Hall measurements demonstrate that the CaH 2 induced topochemical reaction can effectively change the oxygen content of Bi2212 within a very wide range, even switching from hole doping to electron doping. Further, we also found evidence of a low-T c superconducting phase in the electron doping side.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Epitaxial growth of monolayer PdTe 2 and patterned PtTe 2 by direct tellurization of Pd and Pt surfaces

Two-dimensional (2D) palladium ditelluride (PdTe 2 ) and platinum ditelluride (PtTe 2 ) are two Dirac semimetals, which have fascinating quantum properties such as superconductivity, magnetism and topological order and show the promising applications in future nanoelectronics and optoelectronics. However, the synthesis of PdTe 2 and PtTe 2 monolayers (MLs) is hindered by a strong interlayer coupling and orbital hybridization. Here, in this study, we demonstrate an efficient synthesis of PdTe 2 and PtTe 2 MLs Large-area and high quality MLs of PdTe 2 and patterned PtTe 2 were epitaxially grown on the Pd(111) and Pt(111) surfaces by direct telurization in ultra-high vacuum. This was confirmed by x-ray photoelectron spectroscopy, low energy electron diffraction and scanning tunnelling microscopy. PdTe 2 ML demonstrated high thermal stability showing no decomposition sign after annealing at 470 °C. A well-ordered (2 × 2) PtTe 2 structure with Kagome lattice was observed on Te/Pt(111) surface following annealing at 200 °C in UHV, where the (2 × 2) pattern was formed by Te atom vacancies. PtTe 2 multilayer film was prepared as well, and it demonstrated the excitation of the Dirac plasmons as measured by high-resolution electron energy loss spectroscopy. The direct tellurization offers the simple and reliable protocol for the preparation of the ML of PdTe 2 and patterned PtTe 2 , and this opens new opportunities for quantum phenomena research and for practical optoelectronics applications.

2D materials↗
DOE OSTI2021

Electronic and structural properties of single-crystal Jahn–Teller active Co 1+x Mn 2–x O 4 thin films

Recent investigations on spinel CoMn 2 O 4 have shown its potential for applications in water splitting and fuel cell technologies as it exhibits strong catalytic behavior through oxygen reduction reactivity. To further understand this material, we report for the first time the synthesis of single-crystalline Co 1+x Mn 2-x O 4 thin films using molecular beam epitaxy. By varying sample composition, we establish links between cation stoichiometry and material properties using in-situ x-ray photoelectron spectroscopy, x-ray diffraction, scanning transmission electron microscopy, x-ray absorption spectroscopy, and spectroscopic ellipsometry. Our results indicate that excess Co ions occupy interstitial tetrahedral sites up to a certain stoichiometry, then are substitutional for octahedrally-coordinated Mn beyond this threshold. Here, we compare these results with density functional theory models of stoichiometric CoMn 2 O 4 to understand how the Jahn-Teller distortion and hybridization in Mn-O bonds impact the ability to hole dope the material with excess Co. The findings provide important insights into CoMn 2 O 4 and related spinel oxides for future application as inexpensive oxygen reduction reaction catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

The Surface Chemistry of Methanol on Cu 3 Pd(111): Effects of Metal Alloying and Reaction with Hydrogen

Synchrotron-based ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) was used to study the adsorption and surface chemistry of methanol on a Cu 3 Pd(111) model surface. The composition and morphological properties of the pristine Cu 3 Pd(111) substrate were analyzed using a combination of low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and low-energy ion scattering (LEIS). The results of ion scattering showed segregation of Pd toward the surface, with a Pd/Cu ratio close to 0.5, a larger value than the ratio of 0.33 expected for a Cu 3 Pd bimetallic structure. The surface of the alloy exhibited a good LEED pattern with three-fold long-range periodicities. In STM, clusters of palladium with hexagonal arrays and Pd- Pd distances of 2.7-2.8 Å were detected. Bonding to copper perturbed the electronic properties of the atoms in the Pd clusters, shifting their 4d states toward higher binding energy with respect to the Fermi level. Further, the valence band spectrum of Cu 3 Pd(111) exhibited a line shape that was very different from those displayed by Cu(111) or Pd(111). At low pressures, the adsorption of methanol on Cu 3 Pd(111) at 300 K mainly produced CH 3 O, CO and CH x species. AP-XPS showed that most Pd atoms in the surface of the Cu 3 Pd(111) alloy interacted with the decomposition products of methanol. No significant changes were observed in the core levels of copper upon the adsorption and dissociation of methanol, suggesting that the molecule mainly interacted with Pd sites of the alloy. Reaction with hydrogen led to fast removal of CH x , C and PdC x species from Cu 3 Pd(111) at moderate (< 450 K) temperatures and prevented a CH x → C transformation. If the stability of adsorbed CH 3 O is used as a descriptor for the hydrogenation of CO 2 to methanol, Cu 3 Pd should be a much better catalyst than monometallic palladium. This may be a consequence of electronic and ensemble effects in the alloy that moderate the reactivity of Pd sites.

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

Direct Deposition of Nonaqueous SnO 2 Dispersion by Blade Coating on Perovskites for the Scalable Fabrication of p–i–n Perovskite Solar Cells

Tin(IV) oxide materials have been extensively used as electron transport materials in n–i–p perovskite solar cells (PSCs) due to their superior optoelectronic properties, low-temperature processability, and high chemical stability. However, solvent incompatibility and processing temperature have limited the direct deposition of fully solution-processed SnO 2 in p–i–n devices. In this study, we overcome this limitation by the functionalization of SnO 2 nanoparticles with acetate through ligand exchange, allowing their dispersion in anhydrous ethanol. The SnO 2 dispersion was deposited on the perovskite absorber by blade coating without damaging the underlying perovskite layer, as determined by X-ray diffraction and scanning electron microscopy. Photoluminescence spectroscopy confirmed effective electron extraction. The champion device shows 14.1% initial power conversion efficiency (PCE) which is unprecedented for a p–i–n device employing solution-phase SnO 2 . Finally, PSCs stored for 40 days in a nitrogen flow box retained an average of 95.8% of the initial PCE.

14 SOLAR ENERGY↗
DOE OSTI2016

Investigating the effect of zirconium oxide microstructure on corrosion performance: a comparison between neutron, proton, and nonirradiated oxides - 2016-0069

Scanning precession electron diffraction in the transmission electron microscope has been used to simultaneously map the phase, orientation, and grain morphology of oxides formed on Zircaloy-2 after three and six cycles in a boiling water reactor in unprecedented detail. For comparison, a region of a preoxidized autoclave-formed oxide was also proton-irradiated at the Dalton Cumbrian Facility. The proton irradiation was observed to cause additional stabilization of the tetragonal phase that was attributed to the stabilizing effect of irradiation- induced defects in the oxide. In the reactor-formed oxides, no extra stabilization of the tetragonal grains was observed under neutron irradiation, as indicated by the similar tetragonal phase fraction and transformation twin-boundary distributions between the nonirradiated and reactor-formed oxides. It is suggested that the damage rate is too low in the newly formed oxide to cause significant stabilization of the tetragonal phase. This technique also reveals that the oxide formed under reactor conditions has a more heterogeneous microstructure, and the growth of well-oriented columnar monoclinic grains is significantly reduced compared with a nonirradiated oxide. High-angle annular dark-field scanning transmission electron microscopy also revealed the development of extensive networks of intergranular porosity and eventually grain de-cohesion in the reactor-formed oxides. These results suggest that the tetragonal-monoclinic transformation is not responsible for the accelerated corrosion exhibited under reactor conditions. It is proposed that the usual out-of-reactor oxide growth and nucleation processes are significantly modified under reactor conditions, resulting in a more heterogeneous and randomly oriented oxide microstructure with reduced columnar grain growth. It is suggested that this disordered oxide microstructure allows for the formation of extensive intergranular porosity that could lead to accelerated in-reactor corrosion. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of niobium and phase transformation temperature on the microstructure and texture of a novel 0.40% C thermomechanically processed steel

Field emission scanning electron microscopy, electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) have been employed to investigate the effect of niobium and phase transformation temperature on the evolution of microstructure and texture in a novel thermomechanically processed, medium‑carbon, low-alloy steel intended for slurry pipeline applications. Thermomechanical processing consisted of hot-rolling in the austenitic region with deformation both above the recrystallization limit temperature and below the recrystallization stop temperature. Immediately after rolling, specimens were directly quenched in water to two different temperatures of 560 °C and 420 °C and subsequently furnace cooled from those temperatures to simulate the cooling of coiled strip on a hot strip mill. The microstructure of samples quenched to 560 °C mostly comprised of upper bainite, whereas the samples quenched to 420 °C mainly consisted of lath-type lower bainite. The transformation texture of all samples at the mid-thickness position consisted of α, γ and ε-fibers with high intensities close to the transformed copper, transformed brass and rotated cube components. The addition of 0.013 wt% Nb refined the microstructure and sharpened the texture. The texture of the small fraction of retained austenite present in the final microstructures indicated that the main bcc texture components result from the brass and copper components in the parent austenite.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Erosion and cathodic arc plasma of Nb–Al cathodes: composite versus intermetallic

Many properties of cathodic arcs from single-element cathodes show a correlation to the cohesive energy of the cathode material. For example, the burning voltage, the erosion rate, or, to a lesser extent, plasma properties like electron temperatures or average ion energy and charge states. For multi-element cathodes, various phases with different cohesive energies can initially be present in the cathode, or form due to arc exposure, complicating the evaluation of such correlations. To test the influence of morphology and phase composition of multi-element cathodes on cathodic arc properties, a Nb–Al cathode model system was used that includes: pure Nb and Al cathodes; intermetallic Nb 3 Al, Nb 2 Al and NbAl 3 cathodes; and three composite Nb–Al cathodes with atomic ratios corresponding to the stoichiometric ratios of the intermetallic phases. Pulsed cathodic arc plasmas from these cathodes were examined using a mass-per-charge and energy-per-charge analyzer, showing that charge-state-resolved ion energy distributions of plasmas from the intermetallic and corresponding composite cathodes are nearly identical. An examination of converted layers of eroded cathodes using x-ray diffraction and scanning electron microscopy indicates the formation of a surface layer with similar phase composition for intermetallic and their corresponding composite cathode types. The average arc voltages do not follow the trend of cohesive energies of Nb, Al and intermetallic Nb–Al phases, which have been calculated using density functional theory. Possible reasons for this effect are discussed based on the current knowledge of multi-element arc cathodes and their arc plasma available in literature.

36 MATERIALS SCIENCE↗
NASA NTRS1989

Sequentially evaporated thin Y-Ba-Co-O superconducting films on microwave substrates

The development of high T sub c superconducting thin films on various microwave substrates is of major interest in space electronic systems. Thin films of YBa2Cu3O(7-Delta) were formed on SrTiO3, MgO, ZrO2 coated Al2O3, and LaAlO3 substrates by multi-layer sequential evaporation and subsequent annealing in oxygen. The technique allows controlled deposition of Cu, BaF2 and Y layers, as well as the ZrO buffer layers, to achieve reproducibility for microwave circuit fabrication. The three layer structure of Cu/BaF2/Y is repeated a minimum of four times. The films were annealed in an ambient of oxygen bubbled through water at temperatures between 850 C and 900 C followed by slow cooling (-2 C/minute) to 450 C, a low temperature anneal, and slow cooling to room temperature. Annealing times ranged from 15 minutes to 5 hrs. at high temperature and 0 to 6 hr. at 450 C. Silver contacts for four probe electrical measurements were formed by evaporation followed with an anneal at 500 C. The films were characterized by resistance-temperature measurements, energy dispersive X-ray spectroscopy, X-ray diffraction, and scanning electron microscopy. Critical transition temperatures ranged from 30 K to 87 K as a function of the substrate, composition of the film, thicknesses of the layers, and annealing conditions. Microwave ring resonator circuits were also patterned on these MgO and LaAlO3 substrates.

Valco, G. J.↗
DOE OSTI2023

Targeted Dy intercalation under graphene/SiC for tuning its electronic band structure

Metal intercalation of graphene is a promising method to tune its electronic band structure and generate novel electronic and topological phases. The tuning depends critically on the ability to bond the intercalated atoms at predesigned, subsurface interlayer locations because the emerging band structure depends on metal location. In this work, we have studied Dy intercalation under single-layer graphene (SLG) on SiC using spot profile analysis–low-energy electron diffraction and scanning tunneling microscopy (STM). The experimental work is complemented with density-functional theory (DFT) analysis. Because different diffraction spots originate from different subsurface interlayer regions, it is possible to identify changes in the intercalation location by monitoring the spot intensity as a function of growth conditions. DFT calculations of the chemical potential as a function of intercalated Dy coverage support the variation of the stability of the intercalated phase at different intercalated locations. The preferred location is confirmed from STM studies showing the removal of the 6 × 6 moiré corrugation at the preferred location, observed at higher Dy coverage.

2-dimensional systems↗