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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Anomalous Hall Effect in Epitaxial Ni–Mn–Ga Thin Films Grown on MgO(001) Substrate during the Martensitic Transformation

Epitaxial Ni–Mn–Ga thin films had been grown on MgO (001) by DC magnetron sputtering. And the anomalous Hall effect (AHE), microstructures, magnetism, and magnetoresistance (MR) were investigated. The AHE was measured in the film of Ni{sub 47.8}Mn{sub 30.8}Ga{sub 21.4} during the martensitic transformation. Meanwhile, the mechanism of the AHE was explained which indicates that the hall resistivity measured in our sample is primarily determined by AHE. The microstructures of the austenite phase and 7M martensite plates at room temperature had been observed on the film of Ni{sub 46.7}Mn{sub 31.7}Ga{sub 21.6} and Ni{sub 47.8}Mn{sub 30.8}Ga{sub 21.4}, respectively. Magnetic measurements reveal that all films possessed the martensitic transformation during the heating and cooling processes. In addition, the MR showed a negative value during the martensitic transformation which is mainly due to the reduction of spin-dependent scattering.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Influence of argon flow rate on structural and optical properties of transparent Nb{sub 2}O{sub 5} thin films

Transparent niobium pentoxide (Nb{sub 2}O{sub 5}) thin films deposited on glass substrates by RF sputtering at different argon (Ar) flow rate were contrastively studied. Analytical methods such as X-ray fluorescence, Fourier-transform infrared spectroscopy and field emission scanning electron microscope were utilized to investigate the morphological surface and structural properties of Nb{sub 2}O{sub 5} thin films deposited at different Ar flow rate. UV–Vis–NIR and photoluminescence (PL) spectroscopy were used to explore the optical properties of Nb{sub 2}O{sub 5} thin films deposited at different Ar flow rate. The allowed optical band gap (E{sub g}{sup d}) of the Nb{sub 2}O{sub 5} thin films varies from 3.88 to 3.80 eV with increasing Ar flow rate from 30 to 90 sccm. The PL of the Nb{sub 2}O{sub 5} thin films showed strong emission peak around 400 nm. The real values of the refractive index are increase with increasing Ar flow rate. Optical quantities related to the optical constants of Nb{sub 2}O{sub 5} thin films thin films such as single oscillator parameters and third-order nonlinear susceptibility were assessed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Relation between carriers hopping rate and structural constants in amorphous carbon nickel films with different nickel nanoparticles distributions

In this paper, the films were prepared by radio frequency magnetron co-sputtering technique. The effect of different mosaic targets made of nickel strips and graphite pure on the dielectric relaxation time, the carriers hopping rate, the fractal dimensions and the optical loss of films were studied. The values of the optical band gap of films using the cross-point between the tangent of the plot of lower and higher values of the photon energy were calculated. The films deposited at 4.64% have maximum hopping rate of about 8.6 × 10{sup 12} S{sup −1}. It can be seen that the films deposited at 3.92% have minimum value of fractal dimension of 2.27. With increasing Ni content of films a nonmetal–metal transition is observed which it is explainable by the power law of percolation theory. Critical metal content and the critical exponent of films were 87.25% and 1, respectively. With increasing Ni content, the carriers effective mass of films decreased and average lattice separation values of films increased. Films deposited at 3.92% have minimum value of Debye frequency ν{sub D} of about 1.09 × 10{sup 12} Hz. The value of energy loss by free charge carriers when traversing the bulk and surface of films at 3.92% has maximum value and it has an increasing function behavior with energy.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Liquid-Phase Surface Alloying of Copper with Stainless Steel Using Low-Energy, High-Current Electron Beam

The paper deals with the formation of the stainless steel-copper surface alloy which occurs during the single vacuum cycle. Deposition of the stainless steel film onto a copper substrate is performed via successive magnetron sputtering followed by its liquid-phase mixing with copper using the low-energy, high-current electron beam of microsecond length. Numerical calculations are used to identify the optimum irradiation modes for the surface alloying. It is found that the optimum irradiation modes provide the homogeneous surface alloying, and the copper concentration in the obtained layer increases with the increase in energy density of the low-energy, high-current electron beam. The formation of the stainless steel-copper surface alloy increases the wear resistance of copper specimens by 7.5 times as compared to the original specimens. In addition, it is ascertained that the wear resistance of the surface alloy exceeds that of the common film coating (1 μm) more than 5 times.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Characteristics of Hydrogen Sensors Based on Thin Tin Dioxide Films Modified with Platinum, Palladium, Silver, and Yttrium

The dependence of the characteristics of hydrogen sensors based on thin Pt/Pd/SnO{sub 2}:Sb, Ag, Y and Ag/SnO{sub 2}:Sb, Ag, Y films obtained by the method of magnetron sputtering at a direct current on the humidity level of the gas mixture during operation in thermal cyclic mode is investigated. The analysis of the experimental data was carried out using the expressions obtained on the basis of the dissociative adsorption model of hydrogen and water molecules on the SnO{sub 2} surface, taking into account the presence of three types of adsorbed particles: O{sup –}, OH, OН{sup –}. The use of complex modifiers Pt/Pd, Ag on the surface and Ag + Y in the bulk of tin dioxide films allows to reduce the influence of humidity on the characteristics of sensors. The role of these modifying additives in the process of dissociative adsorption of hydrogen molecules on the surface of SnO{sub 2} films in humid environment is established.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Physical Properties of Solid Solutions In{sub x}Al{sub 1–x}N

The phase diagrams and the results of studies of the GaN, AlN and InN ternary solid solutions grown using the magnetron sputtering, molecular beam epitaxy, and metalorganic vapour-phase epitaxy technologies and intended for the production of ultrahigh-frequency InAlN/GaN HEMT transistors are analyzed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Perspectives on novel refractory amorphous high-entropy alloys in extreme environments

Two new refractory amorphous high-entropy alloys (RAHEAs) within the W–Ta–Cr–V and W–Ta–Cr–V–Hf systems were herein synthesized using magnetron-sputtering and tested under high-temperature annealing and displacing irradiation using in situ Transmission Electron Microscopy. While the 14W-41Ta-26Cr-19V in at.% RAHEA (defined as WTaCrV RAHEA) was found to be unstable under such tests, additions of Hf in this system composing a new quinary 24W-40Ta-18Cr-5V-13Hf in at.% RAHEA (defined as WTaCrVHf RAHEA) was found to be a route to achieve stability both under annealing and irradiation. A new effect of nanoprecipitate reassembling observed to take place within the WTaCrVHf RAHEA under irradiation indicates that a duplex microstructure composed of an amorphous matrix with crystalline nanometer-sized precipitates enhances the radiation response of the system. Further, it is demonstrated that tunable chemical complexity arises as a new alloy design strategy to foster the use of novel RAHEAs within extreme environments. New perspectives for the alloy design and application of chemically-complex amorphous metallic alloys in extreme environments are presented with focus on their thermodynamic phase stability when subjected to high-temperature annealing and displacing irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Orientation-dependent structural properties during growth and growth mechanism of CoO films

The orientation-dependent local structural properties of CoO films on sapphire substrates during growth were investigated through linearly-polarized extended X-ray absorption fine structure (EXAFS) measurements. Specifically, CoO(1 1 1) and (100) crystals with a rock-salt structure (Fm3m) were epitaxially grown on alpha-Al2O3(0001) and (1012) substrates, respectively, at 700 degrees C using a radio-frequency sputtering system. The local structural properties of CoO films in the in-plane and out-of-plane orientations were quantitatively determined using linearly-polarized EXAFS at the Co K-edge during growth. The EXAFS analysis revealed that during the initial stages of growth, the local structural properties exhibit significant differences compared to thick films, with short atomic distances and large (small) Debye-Waller factors observed in the out-of-plane (in-plane) orientations. The local structural strain mostly diminished when approximately 20 CoO layers accumulated on the substrate. Density functional theory (DFT) calculations further supported these findings by confirming that cobalt atoms initially form stable bonds with the sapphire surface, leading to the simultaneous growth of oxygen and cobalt layers in a coordinated manner through layer-by-layer growth.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Tailoring the coefficient of thermal expansion of ternary nickel alloys through compositional control and non-contact measurements

The majority of microelectromechanical systems (MEMS) are made of silicon, however, future applications will be used in extreme environments, especially at elevated temperatures, and require materials with enhanced properties. Use of metal alloys in these applications will require microscale manufacturability, a balance of physical and mechanical properties and dimensional stability. Here in this paper, we emphasized dimensional stability by reducing the coefficient of thermal expansion (CTE) and present an optical non-contact method for measuring the thermal expansion of planar thin films. A combinatorial approach was employed to determine the CTE of nickel-molybdenum-tungsten (Ni-Mo-W) sputter deposited films over a range of compositions, and the addition of Mo and W is shown to significantly decrease and provide a route for tailoring the CTE with compositional control. Ni-Mo-W alloys were revealed to have CTE values ranging from 8–12 × 10 -6 /°C, matching that of commercial glass substrates that are employed in numerous MEMS devices.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enabling high resolution strain mapping in zirconium alloys

Highlights: • Optimisation of speckle patterns suitable for high resolution digital image correlation in a zirconium alloy • Evidence of distinct strain patterning at the macro and micro scale • Analysis of strain heterogeneity in a neighbouring low and high strain band • Paved the way for future studies on strain localization in zirconium alloys subjected to hydriding and irradiation damage - Abstract: High Resolution Digital Image Correlation (HRDIC) has been established recently as a novel displacement mapping technique during mechanical loading experiments to quantify strain localisation down to the level of individual slip traces. This is achieved by the creation of a nano-scale gold pattern naturally formed during remodelling of a thin gold layer that was sputtered onto the region of interest. To date, the gold remodelling is carried out in a water vapourisation environment, which excludes the technique to be applied to materials that readily form noticeable oxide layers in such environments. The current paper describes a recently developed gold remodelling technique using a styrene-argon environment at substantially lower temperatures than the water-vapour based technique. The material used in the present work is a zirconium alloy where we first demonstrate the problem of oxide formation during remodelling in water vapour and the benefit of the modified remodelling procedure. The error associated with the spatial drift was assessed for different interrogation window sizes followed by detailed analysis of the subsequent strain maps produced using the styrene remodelled patterns after tensile deformation to nominal applied strains of ~3.5% and ~7.0%. The level of detail captured demonstrate the suitability of styrene-argon-based remodelling for materials like Zr alloys with the strain maps showing clear strain patterning on both a transgranular and single grain scale with the possibility of quantifying strain across a single slip trace.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Diffusion behavior of Ag in TiO2 nanofilms

Highlights: • We prepared Ag/TiO{sub 2} bilayer nanofilms and heat treatment at 400 °C lead to the formation of Ag nanoparticles, which evenly distributed inside TiO{sub 2} nanofilms. • Ag is not oxidized during the heat treatment. • The morphology and size of Ag nanoparticles after heat treatment is temperature related, higher temperature lead to larger Ag nanoparticles on the surface of the film. • The diffusion process is of Ag much easier in amorphous than in anatase structure. - Abstract: Using magnetron sputtering, Ag/TiO{sub 2} bilayer nanofilms were deposited on glass substrates. Heat-treating the Ag/TiO{sub 2} nanofilms at 400 °C led to the formation of Ag nanoparticles, which dispersed inside the TiO{sub 2} films as well as the free surface of the TiO{sub 2} films. After heat treatment the sample at 500 °C, larger Ag nanoparticles could be observed on the surface, which means the particle size after heat treatment is temperature related. Anatase TiO{sub 2} phase was formed after the Ag/TiO{sub 2} films were heat-treated at 400 °C. SEM and TEM were used to investigate the morphology and structure of the films and it was found that Ag was not oxidized during heat treatment. The diffusion process of Ag in TiO{sub 2} film is also related to the order of Ag layer and TiO{sub 2} layer on glass substrate. Moreover, the diffusion process is much easier in amorphous than that in anatase structure.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Unraveling the surface chemistry processes in lithiated and boronized plasma material interfaces under extreme conditions

The review of recent theoretical and experimental research on the complex surface chemistry processes that evolve from low-Z material conditioning on plasma-facing materials under extreme fusion plasma conditions is presented. A combination of multi-scale computational physics and chemistry modeling with real-time diagnosis of the plasma-material interface in tokamak fusion plasma edge is complemented by ex-vessel in-situ single-effect experimental facilities to unravel the evolving characteristics of low-Z components under irradiation. Effects of the lithium and boron coatings at carbon surfaces to the retention of deuterium and chemical sputtering of the plasma-facing surfaces are discussed in detail. The critical role of oxygen in the surface chemistry during hydrogen-fuel irradiation is found to drive the kinetics and dynamics of these surfaces as they interact with fusion edge plasma that ultimately could have profound effects on fusion plasma confinement behavior. Computational studies also extend in spatio-temporal scales not accessible by empirical means and therefore open the opportunity for a strategic approach at irradiation surface science studies that combined these powerful computational tools with in-vessel and ex-vessel in-situ diagnostics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Strain-rate dependent deformation mechanisms in single-layered Cu, Mo, and multilayer Cu/Mo thin films

Here, strain-rate sensitivity and rate-dependent hardness, over a range of 10 -2 to 10 2 s -1 , of sputter-deposited single-layered Cu, Mo, and 5 nm Cu/ 5 nm Mo, and 100 nm Cu/ 100 nm Mo multilayer films with a total film thickness of 5 μm were measured using nanoindentation. The plastic zone underneath the nanoindents was characterized via cross-sectional transmission electron microscopy (XTEM). The multilayer films exhibited enhanced hardness but slightly reduced strain-rate sensitivity with decreasing layer thickness from 100 nm to 5 nm. Only the 5 nm Cu/ 5 nm Mo multilayer film exhibited shear bands underneath the nanoindents, and the size of the shear bands increased with increasing strain rate. In contrast, the 100 nm Cu/ 100 nm Mo multilayer film exhibited material pile-up around the indents and significant nanotwinning within Cu grains. The effect of strain rate and layer thickness on the hardness and strain rate sensitivity of the multilayer thin films is interpreted using a modified confined layer slip (CLS) model. The reduced rate sensitivity at 5 nm as compared to 100 nm correlates with abundant growth nanotwins in the Cu grains in 100 nm and formation of shear bands in 5 nm multilayers. In single layer films, a substructure with a high density of dislocations was observed consistent with the plastic strain gradient in the indent plastic zone. No evidence of deformation twins was noted in any of the samples.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Cr plasma-material-interaction in PISCES-RF: D thermal release, retention, and erosion

Pure chromium (Cr) targets were exposed to high-flux deuterium (D) plasmas in the Pisces-RF linear plasma device, and measurements of D retention, release, and erosion were subsequently performed. Post-exposure D retention was quantified using temperature-programmed desorption on Cr targets irradiated by 50 eV ions over a broad range of exposure temperatures (423–873 K) and ion fluences (3 × 10 24 – 3 × 10 26 m −2 ). The retained D inventory was observed to decrease rapidly with increased exposure temperature, from approximately ∼7 × 10 20 m −2 at ∼ 420 K, to then saturate near ∼ 10 20 m −2 for exposure temperatures above ∼550 K. Separately, at fixed exposure temperature (∼450 K), D retention was found to have only a weak dependence on increasing ion fluence. Lastly, the erosion of Cr in D plasma was investigated for ion impact energies in the range 40 ≤ E i ≤ 250 eV. Erosion was inferred using optical emission spectroscopy (OES) from the ratio of emission lines (Cr I (425.4 nm)/D I (656.1 nm)) measured close to the target. Conversion of the OES yield data to net erosion yield was made with singular ion energy target mass-loss measurements. These net erosion yield data were then further corrected to obtain gross erosion yield by accounting for a re-deposition factor, computed using a simple model. The gross erosion yield is found to be 2–4 times lower than predicted by SDTrimSP, consistent with that typically observed for light-ion sputtering under high-flux plasma conditions.

Chromium↗
DOE OSTI2024

Tailoring the nanotwin spacing of Ni-Mo-W alloys via composition and substrate temperature control

Alloy chemistry and deposition conditions can strongly influence the structure and properties of nanostructured materials. However, in Ni-Mo-W alloys, the limited influence of deposition rate on the twin spacing compels the exploration of other routes to tailor the structure and properties. This study was undertaken to investigate the effect of composition and substrate temperature on the nanotwin spacing of sputter-deposited Ni-Mo-W alloys. Increasing the Ni content from 84 at.% to 93 at.% doubled the average twin spacing from 1.8 nm to 3.8 nm, while raising the substrate temperature from room temperature to 200°C for a fixed Ni content of 91 at.% resulted in an increase from 2.9 nm to 5.0 nm. Concurrent weakening of the {111} texture occurred with both increased Ni and temperature. Furthermore, the combined effectiveness of composition and temperature demonstrated here provides a potential process window for tuning the twin spacing while maintaining the strongly textured columnar structure.

36 MATERIALS SCIENCE↗
DOE OSTI2025

The physical origin of heterogeneous solute clustering and nanoprecipitation at grain boundaries in ultrafine-grained immiscible alloys

Here, grain-boundary segregation effects on heterogeneous solute clustering and nanoprecipitation at low solute concentrations were investigated in sputter-deposited ultrafine-grained Ag-Cu alloy films. X-ray diffraction and scanning transmission electron microscopy revealed extended solubility of Cu in Ag matrix, accompanied by the formation of Cu-rich nanoprecipitates and solute clusters at grain boundaries and their junctions. Atomistic simulations further demonstrated that Cu solutes heterogeneously segregate to Ag GBs and form small clusters that grow into nuclei for Cu nanoprecipitates. These findings provide critical insights into the role of heterogeneous grain-boundary segregation in governing the phase separation pathways of immiscible nanocrystalline and ultrafine-grained alloys.

Heterogeneous segregation↗
DOE OSTI2025

Solid solutions limited by grain-boundary solute clustering in ultrafine-grained alloys

Immiscible Ag-Cu alloys exhibit complex behavior due to varying Cu solid solubilities reported under equilibrium and metastable conditions. In ultrafine-grained alloys, these limits are further complicated by a high fraction of grain boundaries, where solute atoms tend to segregate and, in some cases, form clusters. Here, this study investigates the influence of Cu solute segregation and clustering on solid-solution limits in ultrafine-grained Ag-Cu alloys synthesized by magnetron sputtering with varying Cu content. X-ray diffraction peak shifts reveal a solid-solution concentration plateau for Cu contents from 4.9 to 11.7 at %, in contrast to the peak shifts predicted by density-functional theory for Ag-Cu alloys. Scanning transmission electron microscopy further reveals limited solid solubility and the formation of numerous Cu-rich clusters at grain boundaries. Atomistic simulations demonstrate that such limited solubility does not arise from grain boundary segregation alone, but only when strong solute-solute interactions promote the formation of grain-boundary Cu solute clusters.

Density-functional theory↗
DOE OSTI2018

Effect of the addition of Si into V 2 O 5 coatings: Structure and tribo-mechanical properties

Vanadium oxide (V2O5) is one of the lubricious oxides with the potential to be used as a solid lubricant at elevated temperatures. However, the material itself is not hard wear-resistant, so most of the research has focused on adding V into hard nitride coatings that could lead to the formation of a self-lubricating V(2)O(5)layer when heated. The other possible solution, which has been less studied, is to look for mechanisms to enhance the hardness of the oxide coating. In this research, we investigate the effect of the addition of Si into the V2O5 coatings, aiming to find conditions that lead to enhance hardness and/or reduced wear while keeping the high temperature lubricity of the V2O5 structure. For this, Si modified V2O5 coatings were deposited using a dual magnetron sputtering system. The results showed that small additions of Si (< 2.0 at%) improved the hardness of the V2O5 coatings up to 5 times while keeping the same temperature dependence of the coefficient of friction than V2O5. Dry sliding experiments using the pin-on-disc configuration against silicon nitride balls were performed at 25, 300 and 600 degrees C. Wear factors in the 10(-7) mm(3)/Nm range were obtained, indicating a good wear resistance. Further addition of Si into the V2O5 structure led to a loss of the crystalline ordering and a significant reduction in the hardness.

Hall-Petch↗