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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Photocatalytic activity of anatase titanium dioxide nanostructures prepared by reactive magnetron sputtering technique

In this work, nanostructured titanium dioxide (TiO{sub 2}) photocatalysts with high optical and structural homogeneity were successfully synthesized by dc reactive magnetron sputtering technique. The TiO{sub 2} thin films were produced with high structural homogeneity without any heat treatment. Analysis of the X-ray diffraction patterns and UV–visible spectroscopy gave an indication that the structure of prepared films is anatase with energy band gap of 3.23 eV. The Fourier-transform infrared spectroscopy has confirmed the formation of Ti–O bond. The average size of TiO{sub 2} particles in the deposited films was ranging in 5–7 nm. These nanostructures are very applicable as photocatalysts as their photocatalytic activity was determined from the degradation rate with UV irradiation time as the first order reaction rate constant was determined to be 2.4 × 10{sup −3} min{sup −1}.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Physical properties of RF magnetron sputtered GaN/n-Si thin film: impacts of RF power

GaN thin film was successfully produced on n-Si(100) substrate by RF magnetron sputter under different RF power. Experimental measurement techniques such as UV/Vis spectroscopy, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and Micro-Raman Spectroscopy were used to research effects of Radio Frequency power on physical properties of produced thin film. It has been found that produced thin film was polycrystalline structure with (100) and (110) planes of hexagonal GaN from X-ray diffraction measurement result. It also proved that increasing RF power gives rise to deterioration in crystal quality of GaN thin film. Reason of this deterioration was discussed. It has been achieved that increasing RF power has resulted in decreasing optical band gap energy of GaN thin film. Reasons for these changes in optical band gap energy were explained. It was seen that some thin films were grown as layer-plus-island mode (Stranski–Krastanov growth mode) and others were grown as layer-by-layer growth mode (Frank van der Merwe mode) from AFM analysis. It has been found that increasing RF power has resulted in improvement of surface morphology of thin film from field emission scanning electron microscopy analysis. However, reaching RF power to 125 W leads to start to deteriorate of surface of GaN thin film. The reasons for this have been discussed. E{sub 1}(TO) transverse optical phonon mode of hexagonal GaN with different intensity was detected from Micro-Raman Spectroscopy measurement. The reasons for this difference have been discussed. It was concluded that RF power has played a significant role in growing high quality GaN thin film. Morphological, structural, and optical properties of GaN thin film were enhanced by controlling RF power, making them a potential candidate for LED, solar cell, diode application.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Role of oxygen concentrations on structural and optical properties of RF magnetron sputtered ZnO thin films

We report an investigation on the effect of oxygen flow rate on the structural and optical properties of zinc oxide thin films prepared by RF magnetron sputtering. The structural measurements were carried using grazing incidence X-ray diffraction, atomic force microscopy and Raman spectroscopy. The role of oxygen partial pressure on the crystallinity, the surface morphology and vibrational modes has been established. The optical properties of the films were investigated using FR-Basic-VIS/NIR fitted with FR-Monitor software for film thickness, refractive index and color determination. The film thickness is observed to increase when oxygen is introduced at 4 sccm but eventual decrease with increase in the flow rate an indication of initial increase in rate of deposition followed by reduction. Elaborate explanations of these trends are provided.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Properties of Gallium Oxide Films Obtained by HF-Magnetron Sputtering

The results of an analysis of structure and phase composition of gallium oxide films obtained by HF-magnetron sputtering are presented. It is shown that in the interval 290–350 K, the increase in the film conductivity with increasing temperature is due to the excitation of electrons from a local level Е{sub t} located 0.95 eV below the conduction band bottom.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Preparation and Oxidation Performance of a NiCoCrAlYSiHf + NiAl Composite Coating Deposited by Arc Ion Plating and Magnetron Sputtering Techniques

A NiCoCrAlYSiHf+NiAl composite coating was deposited onto a second-generation single-crystal superalloy René N5 by methods of arc ion plating and magnetron sputtering. After vacuum annealing, the composite coating exhibited a gradient distribution of elements, in which Al was enriched in outer layer and Cr was enriched in inner layer. Compared with conventional NiCoCrAlYSiHf and β-NiAl coatings, the composite coating was evaluated in isothermal and cyclic oxidation tests at 1100 °C in ambient air. The results showed that the oxidation rate of the composite coating was lower than that of NiCoCrAlYSiHf coating. Meanwhile, the extent of interdiffusion between coating and substrate in the composite coating was slighter compared with that in the β-NiAl coating. Microstructure evolutions of the composite coating after annealing and further oxidation test are investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Properties of Nb3Sn films fabricated by magnetron sputtering from a single target

Superconducting Nb3Sn films were fabricated on sapphire and fine grain Nb substrates by magnetron sputtering from a single stoichiometric Nb3Sn target. The structural, morphological and superconducting properties of the films annealed for 24 h at temperatures of 800-1000 {\deg}C were investigated. The effect of the annealing time at 1000 {\deg}C was examined for 1, 12, and 24 h. The film properties were characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, energy dispersive X-ray spectroscopy, and Raman spectroscopy. The DC superconducting properties of the films were characterized by a four-point probe measurement down to cryogenic temperatures. The RF surface resistance of films was measured over a temperature range of 6-23 K using a 7.4 GHz sapphire-loaded Nb cavity. As-deposited Nb3Sn films on sapphire had a superconducting critical temperature of 17.21 K, which improved to 17.83 K when the film was annealed at 800 {\deg}C for 24 h. For the films annealed at 1000 {\deg}C, the surface Sn content was reduced to ~11.3 % for an annealing time of 12 h and to ~4.1 % for an annealing time of 24 h. The Raman spectra of the films confirmed the microstructural evolution after annealing. The RF superconducting critical temperature of the as-deposited Nb3Sn films on Nb was 16.02 K, which increased to 17.44 K when the film was annealed at 800 {\deg}C for 24 h.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Effect of annealing on Curie temperature and phase transition in La{sub 0.55}Sr{sub 0.08}Mn{sub 0.37}O{sub 3} epitaxial films grown on SrTiO{sub 3} (100) substrates by reactive radio frequency magnetron sputtering

Mn-poor LaSrMnO{sub 3} (LSMO) epitaxial films were grown on SrTiO{sub 3} (100) substrates by radio frequency magnetron sputtering in an argon and oxygen gas mix, and then the samples were annealed in air at various temperatures (T{sub a}). 2 theta-chi X-ray diffraction mapping, nano-beam diffraction analysis through transmission electron microscopy, and electron back scatter diffraction through scanning electron microscopy revealed that the crystal symmetry of the LSMO films changed from monoclinic/orthorhombic to rhombohedral on annealing in air. Curie temperature (T{sub C}) of the LSMO films was found to increase with increasing T{sub a}, and become higher than the room temperature at T{sub a} ≥ 861 °C, indicating that the cause of these changes was the filling of oxygen and the transition of the crystal symmetry into rhombohedral. - Highlights: •Mn-poor LSMO changed from monoclinic/orthorhombic to rhombohedral by oxygen supply. •Mn-poor LSMO was increased T{sub C} by changed crystal symmetry, and it showed T{sub C} above RT. •Annealed in air effectively supplied O{sub 2} more than O{sub 2} gas during sputtering •EBSD is useful to evaluate crystal symmetry of complex oxide film from the substrate.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Length-scale-dependent nanoindentation creep behaviour of Ti/Al multilayers by magnetron sputtering

This study presented length-scale-dependent room temperature creep behaviour of Ti/Al multilayers by nanoindentation. Ti/Al multilayers with individual layer thickness ranging from 10 nm to 250 nm were prepared by a direct current magnetron sputtering method. Microstructural analysis showed that the prepared Ti/Al multilayers were polycrystalline, with strong Ti (0002) and Al (111) texture. Nanoindentation creep tests were performed to examine the time-dependent creep deformation, stress exponent, creep strain rate sensitivity and contact creep compliance of the multilayers at room temperature. It was found that both the maximum creep deformation and the creep strain rate sensitivity increase with an increase in the individual layer thickness, indicating a length-scale-dependent creep behaviour of the Ti/Al multilayers. The values of stress exponent were found to lay in the range of 15.74–61.46, implying that the creep behaviour of the multilayers was controlled by the dislocation creep mechanism. Finally, the contact creep compliances of the Ti/Al multilayers were well modelled by a two-element Kelvin-Voigt model. From this, it was determined that the creep numbers and retardation times increased with increased individual layer thickness.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Correlation between structural and mechanical properties of RF magnetron sputter deposited hydroxyapatite coating

Highlights: • Microstructure and mechanical properties of textured hydroxyapatite (HA) coatings were evaluated. • TEM results revealed two types of coating microstructure corresponding to the film texture. • Elastic performance of the coating was determined by the texture of the HA coating. • HA coating with (300) texture showed larger elastic recovery. - Abstract: In the present study hydroxyapatite (HA) thin films with a,b-plain and c-plain preferential orientation were prepared by means of RF-magnetron sputtering with water vapor addition into a working gas atmosphere to investigate the influence of microstructural features on mechanical performance of the coating at nanoscale. The mechanical properties of the HA coatings textured along a,b- and c-axes by nanoindentation conclusively highlight that elastic modulus, H/E ratio, H{sup 3}/E{sup 2} parameter and percent of elastic recovery are determined by preferential orientation of the film. Nanoindentation reveals that the HA films exhibiting (300) texture possess commensurate nanohardness and lower elastic modulus compared to (002) oriented films, indicating that the former films possess higher resistance to cracking. The (002) and (300) textured coatings exhibited a nanohardness of 4.7 ± 2.0 GPa and 4.4 ± 2.2 GPa, respectively. The elastic modulus of the HA film with (300) and (002) preferential orientation was 75 ± 40 GPa and 103 ± 40 GPa, respectively. The HA coating with (300) texture showed a higher percentage of elastic recovery of 92% within unloading than that of the (002) textured film (69%).

36 MATERIALS SCIENCE↗
DOE OSTI2017

Ferroelectric and dielectric study of strontium tantalum based perovskite oxynitride films deposited by reactive rf magnetron sputtering

Highlights: • Oxynitride perovskite thin films were deposited by reactive sputtering. • Films are textured or epitaxially grown on MgO and Nb-SrTiO{sub 3} substrates. • Local piezoelectric and ferroelectric behavior was highlighted by PFM. • A 1600 nm-thick film presents a permittivity of 175 at 10 kHz and RT. • Permittivity is around 65 in high frequency range. - Abstract: Strontium and tantalum based oxynitride perovskite thin films were deposited by reactive magnetron sputtering. Epitaxial films deposited on Nb-SrTiO{sub 3} substrates show smooth surfaces with roughness values from 1.5 to 3.6 nm for a thickness of films in the range 20–1600 nm. The samples are yellow with band gap values around 2.35 eV. Piezo-force microscopy characterization pointed out the local piezoelectric and ferroelectric behavior of the oxynitride perovskite films. In the low frequency range, the 1600 nm-thick film exhibits a permittivity of 175 at 10 kHz, with dielectric losses of 0.055. Permittivity is lowered in high frequencies with a value around 65 obtained on a 1520 nm-thick film deposited on MgO substrate, which is textured with a preferential c-axis orientation. No accordability of the permittivity was highlighted at a macroscopic scale. The moderate crystallographic strain evidenced in the 20 nm thin film does not induce a high permittivity.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effects of growth rate and dynamic substrate tilt on properties of Au-Ta alloy films deposited by high-power impulse magnetron sputtering

Gold-tantalum (Au—Ta) alloys are promising for next-generation hohlraums for magnetically-assisted indirect-drive inertial confinement fusion. Hohlraum fabrication involves sputter deposition of ultrathick coatings on sphero-cylindrical substrates. The control of physical properties of such coatings remains a challenge. Here, in this work, we systematically study effects of the growth rate and dynamic substrate tilt on properties of AuTa 4 films deposited onto rotating planar substrates mounted at different tilt angles to mimic different regions of the sphero-cylindrical surface of a hohlraum. We use high-power impulse magnetron sputtering (HiPIMS) in the constant charge per pulse mode with a pulse duration of 100 μs, a charge per pulse of 190 μC, a peak target current of about 3 A, and the pulse frequency varied in the range of 400–1400 Hz. The Langmuir probe, mass-resolved ion energy spectrometry, and optical emission spectroscopy are used to monitor plasma discharge characteristics in order to isolate and study effects of the growth rate. The deposition rate and the ballistics and energetics of depositing species are estimated by Monte Carlo simulations. Results show that the film microstructure, crystallographic phase, residual stress, and electrical resistivity strongly depend on both the deposition rate and substrate tilt, highlighting their critical role in tailoring properties of Au—Ta films during hohlraum fabrication.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Deposition of very thick Mo/Al multilayer films using magnetron sputtering

To understand materials at extreme conditions dynamic ramp compression techniques/experiments are critical, and gradient density impactors (GDIs) have the potential to enable high quality experiments. Very thick (i.e., hundreds of μm thick) multilayer films consisting of high z/low z layers with a gradient in z through the stack can serve as a GDI. Surprisingly while there is a large amount of literature on the topic of multilayer films, there is an absence of literature on very thick multilayer films. A number of multilayer film systems deposited by dc magnetron sputtering were evaluated as potential candidates, including Cu/Al, Ta/Al, and Mo/Al. The Mo/Al multilayer system was observed to be the most promising candidate and is the primary focus of this paper. Mo/Al multilayer films up to ∼400 μm thick with reasonable thickness uniformity were deposited.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

High-rate deposition of ultrathick bismuth films by direct-current magnetron sputtering

Bismuth coatings deposited at room temperature by physical vapor deposition typically feature irregularly-shaped grains and a high density of voids, thereby preventing their use in many potential applications. Here, we demonstrate the deposition of low-stress, high-density 40-μm-thick Bi films by systematically studying the effect of the deposition rate and substrate tilt on the properties of Bi films deposited at room temperature by direct-current magnetron sputtering. Furthermore, results show that, with increasing deposition rate, the morphology, structure, and properties of Bi films greatly improve, while an increase in substrate tilt leads to a monotonic decrease in film thickness, density, and electrical conductivity.

Bismuth↗
DOE OSTI2016

Novel high power impulse magnetron sputtering enhanced by an auxiliary electrical field

The high power impulse magnetron sputtering (HIPIMS) technique is a novel highly ionized physical vapor deposition method with a high application potential. However, the electron utilization efficiency during sputtering is rather low and the metal particle ionization rate needs to be considerably improved to allow for a large-scale industrial application. Therefore, we enhanced the HIPIMS technique by simultaneously applying an electric field (EF-HIPIMS). The effect of the electric field on the discharge process was studied using a current sensor and an optical emission spectrometer. Furthermore, the spatial distribution of the electric potential and electric field during the EF-HIPIMS process was simulated using the ANSYS software. The results indicate that a higher electron utilization efficiency and a higher particle ionization rate could be achieved. The auxiliary anode obviously changed the distribution of the electric potential and the electric field in the discharge region, which increased the plasma density and enhanced the degree of ionization of the vanadium and argon gas. Vanadium films were deposited to further compare both techniques, and the morphology of the prepared films was investigated by scanning electron microscopy. The films showed a smaller crystal grain size and a denser growth structure when the electric field was applied during the discharge process.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Comparison of 1D and 2D particle-in-cell simulations for DC magnetron sputtering discharges

One-dimensional and two-dimensional particle-in-cell (PIC)/Monte Carlo collision simulations are performed for a balanced direct current magnetron sputtering (DCMS) discharge. The plasma parameters obtained by both simulations above the target racetrack share similar features and magnitudes under similar discharge intensities, i.e., similar local discharge current densities. The commonly observed high-energy tail of electron energy distribution in DCMS discharges is reproduced in both simulations. Additionally, the accuracy and applicability of using onedimensional simulations to qualitatively investigate the characteristics of balanced DCMS discharge are confirmed. In terms of capturing the key physical mechanisms in DCMS, one-dimensional PIC simulation is an efficient method, which could largely alleviate the computational expense and preserve the physical fidelity of modeling results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Gold-tantalum alloy films deposited by high-density-plasma magnetron sputtering

Gold-tantalum alloy films are of interest for biomedical and magnetically-assisted inertial confinement fusion applications. Here, we systematically study the effects of substrate tilt (0°–80°) and negative substrate bias (0–100 V) on properties of ≲3-μm-thick films deposited by high-power impulse magnetron sputtering (HiPIMS) from a Au–Ta alloy target (with 80 at. % of Ta). Results reveal that, for all the substrate bias values studied, an increase in substrate tilt leads to a monotonic decrease in film thickness, density, residual compressive stress, and electrical conductivity. Larger substrate bias favors the formation of a body-centered cubic phase, with films exhibiting lower column tilt and higher density, electrical conductivity, and residual compressive stress. Furthermore, these changes are attributed to metal atom ionization effects, based on the lack of correlation with distributions of landing energies and incident angles of depositing species as calculated by Monte Carlo simulations of ballistic collisions and gas phase atomic transport. By varying substrate tilt and bias in HiPIMS deposition, properties of Au–Ta alloy films can be controlled in a very wide range, including residual stress from –2 to +0.5 GPa, density from 12 to 17 g/cm 3 , and the electrical resistivity from 50 to 4500 μΩ cm, enabling optimum deposition conditions to be selected for specific applications.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Oblique angle deposition of boron carbide films by magnetron sputtering

Many applications of boron carbide (B4C) films entail deposition on non-planar substrates, necessitating a better understanding of oblique angle deposition phenomena. Here, we systematically study the effect of substrate tilt on properties of B 4 C films with thicknesses up to 10 μm deposited by direct current magnetron sputtering. Results show that all films are amorphous and columnar with an average column width of ~100 nm, independent of substrate tilt. Column tilt angles are limited to ~20° even for substrate tilt of 80°. Film density, residual stress, and the refractive index weakly (within ≲20%) depend on substrate tilt. Furthermore, oxygen impurities bond preferentially with carbon atoms in inter-columnar regions. Substrate tilt has a major effect on mechanical properties that decrease by ~50%, suggesting weak interconnection between nano-columns. Implications of these observations for the deposition onto non-planar substrates are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Deposition of ultrathick heavy-metal alloys on rotating substrates by high-power impulse magnetron sputtering: Target erosion effects

Sputter deposition of ultrathick (≈20μm) Au–Ta alloy coatings on sphero-cylindrical substrates is key for the fabrication of hohlraums for magnetically assisted inertial confinement fusion. In this work, we study the deposition of AuTa 4 alloy coatings onto rotating substrates. We use high-power impulse magnetron sputtering (HiPIMS) in a constant peak target voltage mode. Results show that the target erosion state has a strong impact on the dominant crystallographic phase, microstructure, surface morphology, and electrical resistivity of AuTa 4 films. This is due to effects of changes in the confining magnetic field with target erosion on the HiPIMS discharge characteristics and the sputter source output. We quantify these effects via plasma diagnostics and discuss the optimization of HiPIMS deposition of ultrathick films for cases when target erosion effects dominate film properties.

36 MATERIALS SCIENCE↗