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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Improving qubit coherence time through detailed materials analysis

This study investigates the defects, imperfections, and variations in superconducting Nb thin films deposited on sapphire substrates. Two samples, W114 and W118, were fabricated using DC Magnetron Sputtering and Electron Cyclotron Resonance (ECR), respectively. Each sample was analyzed at five distinct spots to compare elemental homogeneity and thickness variations. Scanning Electron Microscopy (SEM) was employed to examine surface morphology, while Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) provided elemental and chemical state analyses. SEM revealed distinct structures in W114 and a uniform surface in W118. EDS showed higher aluminum and oxygen signals in W118, indicating a thicker film. XPS detected a higher Nb₂O₅ signal in W118, attributed to a thicker oxygen layer. These findings highlight the critical role of precise material characterization in advancing quantum computing technologies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Synthesis and Characterization of Superconductor Diodes

In the era of modern computing, quantum bits (or qubits) are extensively researched due to their ability to perform computations exponentially faster than classical computers. One promising method for synthesizing qubits on a macroscopic scale is through superconductor diodes (SDs). Unfortunately, SDs are currently limited by their dependence on extremely low temperatures (T ≈ 0K), which restricts their practical usability at larger scales. To address this limitation, researchers are exploring new materials and methods to identify superconductors with higher critical temperatures. My research at the Lawrence Livermore National Laboratory (LLNL) focuses on synthesizing and characterizing superconductor diodes to determine their efficiency for quantum computing applications. Bismuth thin films were synthesized with magnetron sputtering with separate thicknesses which provides information on methods to alter their resistivity. Bismuth was characterized as the topological insulator used in the diode, and its resistivity was measured using a standard four-point probe technique with 1 mA current. Bismuth (99.99% pure) was then purified in a tubular furnace at 400C to use within a Josephson junction as a topological insulator. Niobium and Tantalum Josephson junctions were then synthesized, and they were characterized using a lock-in amplifier four-point probe technique. Materials such as niobium and tantalum are used in high-entropy alloy research, which is a relatively new class of material that has little research within the superconductor diode community, yet the current research shows promise. We anticipate that testing high-entropy superconductors will reveal crucial factors, potentially leading to the development of high-temperature superconductors in the future.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Theoretical Analysis of Experimental Data of Sodium Diffusion in Oxidized Molybdenum Thin Films

In this work, the diffusion process of sodium (Na) in molybdenum (Mo) thin films while it was deposited on soda lime glass (SLG) was studied. A small amount of oxygen was present in the chamber while the direct-current (DC) magnetron sputtering was used for the deposition. The substrate temperatures were varied to observe its effect. Such molybdenum films, with or without oxidations, are often used in thin film solar cells, either as back contact or as hole transport layers. Secondary ion mass spectrometry (SIMS) was used to quantify the concentration of the species. A grain diffusion mechanistic model incorporating the effect of grain and grain boundary geometrical shape and size was developed. The model was used to provide an in-depth theoretical analysis of the sodium diffusion in molybdenum thin films that lead to the measured SIMS data. It was observed that not only diffusion coefficients should be considered when analyzing diffusion processes in thin films but also the ratio of grain boundary size to grain size. Both depend on substrate temperature and directly affect the amount of diffused species in the film. The data were analyzed under the light of the film growth speed versus diffusion front speed, the effect of oxygen content, and the effect of substrate temperature on the overall diffusion process. The temperature inversely affects the ratio of grain boundary size and grain size and directly affects the diffusion coefficient, which leads to a preferable temperature at which the highest amount of alkali can be found in the film.

36 MATERIALS SCIENCE↗
DOE OSTI2022

An Overview of Nano Multilayers as Model Systems for Developing Nanoscale Microstructures

The microstructural transformations of binary nanometallic multilayers (NMMs) to equiaxed nanostructured materials were explored by characterizing a variety of nanoscale multilayer films. Four material systems of multilayer films, Hf-Ti, Ta-Hf, W-Cr, and Mo-Au, were synthesized by magnetron sputtering, heat treated at 1000 °C, and subsequently characterized by transmission electron microscopy. Binary systems were selected based on thermodynamic models predicting stable nanograin formation with similar global compositions around 20–30 at.%. All NMMs maintained nanocrystalline grain sizes after evolution into an equiaxed structure, where the systems with highly mobile incoherent interfaces or higher energy interfaces showed a more significant increase in grain size. Furthermore, varying segregation behaviors were observed, including grain boundary (GB) segregation, precipitation, and intermetallic formation depending on the material system selected. The pathway to tailored microstructures was found to be governed by key mechanisms and factors as determined by a film’s initial characteristics, including global and local composition, interface energy, layer structure, and material selection. This work presents a global evaluation of NMM systems and demonstrates their utility as foundation materials to promote tailored nanomaterials.

Appleget, Chelsea D.↗
DOE OSTI2022

Hydriding, Oxidation, and Ductility Evaluation of Cr-Coated Zircaloy-4 Tubing

Accident-tolerant fuel concepts have been developed recently in diverse research programs. Recent research has shown clear advantages of Cr-coated Zr cladding over bare cladding tubes regarding oxidation behavior under the design basis loss-of-coolant accident condition. However, limited data are available about the hydriding behavior of the Cr coating. For that purpose, Cr-coated Zricaloy-4 tubes were tested to investigate the effects of hydriding, oxidation, and postquench ductility behavior on coated Zr cladding. A high-power impulse magnetron sputtering (HiPIMS) process was used to produce a high-density coating on the Zircaloy-4 tube surface. Coated and uncoated Zircaloy-4 tube specimens underwent one-sided hydriding in a tube furnace filled with pure hydrogen gas at 425 °C. The tubing specimen ends were sealed with Swagelok plugs before the hydriding runs. For uncoated specimens, H analysis of the hydrided specimens indicated that the H content increased as the test time and initial pressure increased. However, almost no change was observed for the coated specimens that were hydrided under the same test conditions. After one-sided hydriding, the hydrided coated and uncoated specimens were exposed to steam at high temperatures for two-sided oxidation studies to simulate accident conditions. The coated specimens showed a slower oxidation: oxygen pickup was 50% lower than the uncoated specimens tested under the same conditions. Ring compression testing was performed to evaluate the embrittlement behavior of the Cr-coated specimens after hydriding and oxidation. The results indicated that the HiPIMS coating provides excellent protection from hydriding and oxidation at high temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Inhibited Surface Diffusion in Nanoporous Multi-Principal Element Alloy Thin Films Prepared by Vacuum Thermal Dealloying

Nanoporous structures with 3D interconnected networks are traditionally made by dealloying a binary precursor. Certain approaches for fabricating these materials have been applied to refractory multi-principal element alloys (RMPEAs), which can be suitable candidates for high-temperature applications. In this study, nanoporous refractory multi-principal element alloys (np-RMPEAs) were fabricated from magnesium-based thin films (VMoNbTaMg) that had been prepared by magnetron sputtering. Vacuum thermal dealloying (VTD), which involves sublimation of a higher vapor pressure element, is a novel technique for synthesizing nanoporous refractory elements that are prone to oxidation. When VMoNbTaMg was heated under vacuum, a nanoporous structure was created by the sublimation of the highest vapor pressure element (Mg). X-ray photoelectron spectroscopy depth profiling indicated significantly less ligament oxidation during VTD as compared to traditional dealloying methods. Furthermore, np-RMPEAs exhibited outstanding stability against coarsening, retaining smaller ligaments (~25 nm) at elevated temperature (700 °C) for a prolonged period (48 h).

Das Gupta, Tibra (ORCID:0000000317103025)↗
DOE OSTI2022

High-Temperature Ferroelectric Behavior of Al 0.7 Sc 0.3 N

Currently, there is a lack of nonvolatile memory (NVM) technology that can operate continuously at temperatures > 200 °C. While ferroelectric NVM has previously demonstrated long polarization retention and >10 13 read/write cycles at room temperature, the largest hurdle comes at higher temperatures for conventional perovskite ferroelectrics. Here, we demonstrate how AlScN can enable high-temperature (>200 °C) nonvolatile memory. The c-axis textured thin films were prepared via reactive radiofrequency magnetron sputtering onto a highly textured Pt (111) surface. Photolithographically defined Pt top electrodes completed the capacitor stack, which was tested in a high temperature vacuum probe station up to 400 °C. Polarization–electric field hysteresis loops between 23 and 400 °C reveal minimal changes in the remanent polarization values, while the coercive field decreased from 4.3 MV/cm to 2.6 MV/cm. Even at 400 °C, the polarization retention exhibited negligible loss for up to 1000 s, demonstrating promise for potential nonvolatile memory capable of high–temperature operation. Fatigue behavior also showed a moderate dependence on operating temperature, but the mechanisms of degradation require additional study.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Electrical Behavior of Combinatorial Thin-Film Zr x Ta 1−x O y

Combinatorial magnetron sputtering and electrical characterization were used to systematically study the impact of compositional changes in the resistive switching of transition metal oxides, specifically the Zr x Ta 1−x O y system. Current-voltage behavior across a range of temperatures provided insights into the mechanisms that contribute to differences in the electrical conductivity of the pristine Ta 2 O 5 and ZrO 2 , and mixed Zr x Ta 1−x O y devices. The underlying conductive mechanism was found to be a mixture of charge trapping and ionic motion, where charge trapping/emission dictated the short-term cycling behavior while ion motion contributed to changes in the conduction with increased cycling number. ToF-SIMS was used to identify the origin of the “wake-up” behavior of the devices, revealing an ionic motion contribution. This understanding of how cation concentration affects conduction in mixed valence systems helps provide a foundation for a new approach toward manipulating resistive switching in these active layer materials.

36 MATERIALS SCIENCE↗
NASA NTRS1978

Multilevel metallization method for fabricating a metal oxide semiconductor device

An improved method is described of constructing a metal oxide semiconductor device having multiple layers of metal deposited by dc magnetron sputtering at low dc voltages and low substrate temperatures. The method provides multilevel interconnections and cross over between individual circuit elements in integrated circuits without significantly reducing the reliability or seriously affecting the yield.

Hollis, B. R., Jr.↗
NASA NTRS1979

Materials and techniques for spacecraft static charge control 2

Results of exploratory development on the design, fabrication and testing of transparent conductive coatings, conductive bulk materials and grounding techniques for application to high resistivity spacecraft dielectric materials to obtain control of static charge buildup are presented. Deposition techniques for application of indium oxide, indium/tin oxide and other metal oxide films on Kapton, FEP Teflon, OSR and solar cell coverglasses discussed include RF and Magnetron sputtering and vapor deposition. Development, fabrication and testing of conductive glass tiles for OSR and solar cell coverglass applications is discussed. Several grounding techniques for rapid charge dissipation from the conductively coated polymer and glass dielectrics which were developed and tested in thermal cycled and electron plasma environments are described. The optical and electrical characterization and aging effects of these coatings, bulk materials and grounding techniques are reviewed as they apply to the performance of their design functions in a geosynchronous orbit environment.

Schmidt, R. E.↗
NASA NTRS1985

Internal stresses in wear and corrosion resistant amorphous metallic coatings of (W/0.6/Re/0.4/)76B24 and (Mo/0.6/Ru/0.4/)82B18

Hard protective coatings in the W-Re-B and Mo-Ru-B alloy systems have been deposited by magnetron sputtering onto soda-lime glass and heat-treated AISI 52100 steel substrates. X-ray diffraction has confirmed the amorphous nature of the as-deposited coatings, and their crystallization temperatures were determined by differential thermal analysis to be 1000 and 790 C for W-Re-B and Mo-Ru-B coatings, respectively. Both coatings exhibit high microhardness; Mo-Ru-B, in addition, has excellent corrosion resistance by comparison with pure Mo at high anodic potentials. Attention is given to the influence of internal stresses on the protective properties of the coatings deposited under different conditions.

Thakoor, A. P.↗
NASA NTRS1986

Room-Temperature Deposition of NbN Superconducting Films

Films with high superconducting transition temperatures deposited by reactive magnetron sputtering. Since deposition process does not involve significantly high substrate temperatures, employed to deposit counter electrode in superconductor/insulator/superconductor junction without causing any thermal or mechanical degradation of underlying delicate tunneling barrier. Substrates for room-temperature deposition of NbN polymeric or coated with photoresist, making films accessible to conventional lithographic patterning techniques. Further refinements in deposition technique yield films with smaller transition widths, Tc of which might approach predicted value of 18 K.

Thakoor, S.↗
NASA NTRS1985

Refractory amorphous metallic (W/0.6/ Re/0.4/)76B24 coatings on steel substrates

Refractory metallic coatings of (W/0.6/ Re/0.4/)76B24 (WReB) have been deposited onto glass, quartz, and heat-treated AISI 52100 bearing steel substrates by dc magnetron sputtering. As-deposited WReB films are amorphous, as shown by their diffuse X-ray diffraction patterns; chemically homogeneous, according to secondary ion mass spectrometry (SIMS) analysis; and they exhibit a very high (approximately 1000 C) crystallization temperature. Adhesion strength of these coatings on heat-treated AISI 52100 steel is in excess of approximately 20,000 psi and they possess high microhardness (approximately 2400 HV50). Unlubricated wear resistance of such hard and adherent amorphous metallic coatings on AISI 52100 steel is studied using the pin-on-disc method under various loading conditions. Amorphous metallic WReB coatings, about 4 microns thick, exhibit an improvement of more than two and a half orders of magnitude in the unlubricated wear resistance over that of the uncoated AISI 52100 steel.

Thakoor, A. P.↗
NASA NTRS1985

Rolling contact fatigue behavior of Cu and TiN coatings on bearing steel substrates

The resistance of copper and TiN coatings on various bearing substrates to high-load rolling contact fatigue (RCF) is investigated. Special attention is given to the lubricating characteristics of copper deposited by ion plating, and the wear resistant characteristics of TiN deposited by ion plating and magnetron sputtering techniques. RCF samples of 440C and AMS 5749 bearing steels were coated. Sputter deposited and ion plated films were on the RCF samples in a range of thickness from about 2000 A to 2 microns. Results showed a marked improvement of the RCF for pure copper tested on 440C, but a degradation for copper on AMS 5749. It is also found that the 2000 A TiN films behave favorably on the 440C and AMS 5749 bearing steels at RCF stress levels of 786 ksi. Scanning electron microscopy, X-ray diffraction, and electron spectroscopy for chemical analysis were used during the investigation.

Hochman, R. F.↗
NASA NTRS1985

High T(c) superconducting NbN films deposited at room temperature

The dc reactive magnetron sputtering process yields stoichiometric NbN films with superconducting transition temperature T(c) as high as 15.7 K on substrates as varied as glass, glazed ceramic, fused quartz, and sapphire. These films posses fcc (B1) structure and (111) texture. The most dominant factors governing the formation of the transition metal nitrides are the relative metal and nitrogen fluxes incident on the substrate and the background argon pressure (which dictates the overall reactive sites and residence times for nitrogen).

Thakoor, S.↗
NASA NTRS1986

Room temperature deposition of superconducting NbN for superconductor-insulator-superconductor junctions

The deposition of stoichiometric B1-crystal-structure (111) NbN films on glass or sapphire substrates by reactive dc magnetron sputtering is reported. High-purity Ar-N2 mixtures are used in the apparatus described by Thakoor et al. (1985), and typical deposition parameters are given as background pressure about 10 ntorr, voltage -325 V, current 1 A, deposition rate 1.35 nm/s, film thickness 500 nm, P(Ar) 5-17 mtorr, initial P(N2) 2-6 mtorr, and room temperature. The N2 consumption-injection characteristics are studied and found to control NbN formation using well-conditioned Nb targets. Films with transition temperatures 15-16 K are obtained at P(Ar) = 12.9 + or - 0.2 mtorr and P(N2) = 3.7 + or - 0.1 mtorr. SIS junctions of area about 0.001 sq cm fabricated using the NbN films are shown to have I-V characteristics with nonlinearity parameter about 110 and NbN superconducting-gap parameter Delta = about 2.8 meV.

Thakoor, S.↗
NASA NTRS1988

Radiation resistance and comparative performance of ITO/InP and n/p InP homojunction solar cells

The radiation resistance of ITO/InP cells processed by DC magnetron sputtering is compared to that of standard n/p InP and GaAs homojunction cells. After 20 MeV proton irradiations, it is found that the radiation resistance of the present ITO/InP cell is comparable to that of the n/p homojunction InP cell and that both InP cell types have radiation resistance significantly greater than GaAs. The relatively lower radiation resistance, observed at higher fluence, for the InP cell with the deepest junction depth, is attributed to losses in the cells emitter region. Diode parameters obtained from I sub sc - V sub oc plots, data from surface Raman spectroscopy, and determinations of surface conductivity types are used to investigate the configuration of the ITO/InP cells. It is concluded that thesee latter cells are n/p homojunctions, the n-region consisting of a disordered layer at the oxide semiconductor.

Weinberg, I.↗
NASA NTRS1989

High-efficiency indium tin oxide/indium phosphide solar cells

Improvements in the performance of indium tin oxide (ITO)/indium phosphide solar cells have been realized by the dc magnetron sputter deposition of n-ITO onto an epitaxial p/p(+) structure grown on commercial p(+) bulk substrates. The highest efficiency cells were achieved when the surface of the epilayer was exposed to an Ar/H2 plasma before depositing the bulk of the ITO in a more typical Ar/O2 plasma. With H2 processing, global efficiencies of 18.9 percent were achieved. It is suggested that the excellent performance of these solar cells results from the optimization of the doping, thickness, transport, and surface properties of the p-type base, as well as from better control over the ITO deposition procedure.

Li, X.↗