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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Turning Catalysts on by Light-Induced Stress: When Red Means Go

We report the activation of platinum catalyst thin films for oxygen reduction reaction in perchloric acid electrolytes when the films are subjected to mechanical stress. The catalysts films were deposited by magnetron sputtering on photosensitive chalcogenide As 20 Se 80 semiconductor glass layer. When platinum films are illuminated by red laser light the glass under semitransparent platinum film exhibits photo-induced flow. The material flow underneath platinum film induces mechanical stress resulting in film wrinkling and significant increase in its catalytic activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Underlying Substrate Effect on Electrochemical Activity for Hydrogen Evolution Reaction with Low‐Platinum‐Loaded Catalysts

Platinum is known as the best catalyst for the hydrogen evolution reaction (HER) but the scarcity and high cost of Pt limit its widespread applicability. Herein, the role of the underlying substrate on the HER activity of dispersed Pt atoms is uncovered. A direct current magnetron sputtering technique is utilized to deposit transition metal (TM) thin films of W, Ti, and Ta as underlying substrates for extremely low loading of Pt (<1.5 at%). The electrocatalytic performance of as‐synthesized samples for the HER is examined in both alkali and acidic media. The results show that despite the low loading of Pt, the Pt/TM catalysts produce hydrogen at a rate comparable to that of pristine bulk Pt. Pt/TM catalysts also display good stability with less than 5% decay in performance after 10 h of continuous HER operation. Based on the computational study, the excellent performance is attributed to the modified electronic properties of the Pt atoms, offering ideal binding energy for HER due to interaction with the underlying substrates. This work provides a robust and industry‐friendly route toward designing efficient catalytic systems for important electrochemical reactions such as HER and others.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Effect of Deposition Pressure, Nitrogen Content and Substrate Temperature on Optical and Mechanical Behavior of Nanocomposite Al-Si-N Hard Coatings for Solar Thermal Applications

Hard and optically transparent nanocomposite Al-Si-N thin films were deposited using DC magnetron sputtering at different process parameters. There was a significant effect of these parameters on the film properties affecting its mechanical and optical behavior. The nitrogen content or pressure, deposition pressure and substrate temperature strongly influence the phase formation which governs the hardness and optical transparency of the coating. Hardness was measured between 18 and 30 GPa. The band gap could be varied in the range of 3.8-4.2 eV by varying nitrogen pressures in the chamber during deposition. The films showed (0-80)% transparency in UV and visible region depending on the sputtering conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structure and Tribological Properties of CrTiAlCN Coatings with Various Carbon Contents

Multi-component CrTiAlCN coatings with different carbon contents were deposited on AISI M2 high-speed steels using unbalanced magnetron sputtering via adjusting the C{sub 2}H{sub 2} flow rates, and their microstructures and mechanical properties were characterized by using SEM, EDS, XRD, Vickers hardness tester and scratch tester, respectively. The tribological properties of CrTiAlCN coatings sliding against SUS440C high carbon martensitic balls were performed using ball-on-disk tribo-tester. The results showed that CrTiAlCN coatings were mainly comprised of (111) and (200) crystal orientation. The maximum hardness of coatings was 29.4 ± 1.5 GPa as the carbon content was 22.5 at.%. With an increase in the carbon content of coatings, the friction coefficients and wear rates of CrTiAlCN/SUS440C tribo-pairs were significantly reduced, and the wear mechanism of coatings changed from adhesive wear to abrasive wear.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Influence of Substrate Bias Voltage on Corrosion and Wear Behavior of Physical Vapor Deposition CrN Coatings

The objective of the present paper is to study the influence of the substrate bias voltage on the microstructure, composition, deposition rate, tribological and corrosion properties of CrN coatings obtained by DC magnetron sputtering on 90CrMoV8 steel and Si (100) substrates. The substrate bias voltage varied from 0 to − 700 V. The deposited films were characterized by SEM, XRD and potentiodynamic polarization. The wear behavior and coefficient of friction were determined and investigated after rotative tribometer tests. The results indicated that the substrate bias voltage considerably affected the intrinsic properties of the CrN films. Indeed, it significantly influenced the grain size and the root-mean-squared roughness which varied from 20 to 29 nm, and from 9 to 19 nm, respectively, when polarization changed from 0 to − 700 V. All the CrN coatings have a dense columnar structure and are well crystallized according to the XRD analyses. Nevertheless, it has been shown that the peaks intensity decreased by increasing the substrate bias voltage. By applying a substrate bias voltage, it was obvious that the friction behavior was enhanced, and the wear volume was decreased. Finally, the CrN coating obtained under a substrate bias voltage of − 500 V presented the best corrosion resistance and wear resistance probably due to its dense microstructure.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Ni Content on Double-Target Co-sputtered CrNiN Coatings

Double-target co-sputtered CrNiN coatings were deposited by DC-pulsed magnetron reactive sputtering. The nickel content increases from 0.7 to 5.0 at.% with the increased Ni target current from 0.10 to 0.40 A. The influence of Ni content on preferred orientation and properties of CrNiN coatings was investigated. The results show that the doped Ni enters CrN to form (Cr,Ni)N solid solution. CrNiN coatings are mainly composed of CrN phase and demonstrate CrN(111) preferred orientation. All the coatings present columnar growth pattern. And the less obvious the preferred orientation, the more intense competitive growth, the less sufficient the columnar growth, the finer the columnar crystal and the denser the microstructure. In spite of the most dense structure with finest grains, the hardness of CrNiN coating containing 0.7 at.% Ni is the lowest. The hardness is affected by multiple effects of preferred orientation, grain size, solid solution strengthening, morphology and stress, especially the intensity degree of preferred orientation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Mechanical and Frictional Performance of Ta and Ta-Ag Alloy Films Deposited at Different Sputtering Powers

The mechanical and tribological properties of tantalum and its alloy films are greatly influenced by their phase transformation. In this study, Ta and Ta-Ag films were prepared on carbon steel substrate by DC magnetron sputtering with various sputtering powers. The amorphous and nanocrystalline Ta and Ta-Ag film were produced at different sputtering powers from 40 to 110 W. The frictional properties of Ta and Ta-Ag films were investigated by rubbing against Si{sub 3}N{sub 4} ball from RT to 700 °C. The nanocrystalline Ta-Ag films shows higher hardness values (12 GPa) compared with amorphous phase. The nanocrystalline Ta90-Ag8 film shows a low friction coefficient of about 0.20-0.30 when rubbing against Si{sub 3}N{sub 4} ball at 700 °C. The segregation of Ag can effectively reduce friction coefficients of Ta-Ag film at 700 °C. The Ta-Ag films show high structure stability even after friction at 700 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Optimization of Interlayer/CrWN Bilayer Films Fabricated and Monitored under Shewhart Control

Chromium tungsten nitride (CrWN) films were deposited onto SUS 304 stainless steel, cutter inserts and glass substrates using direct current reactive magnetron sputtering, with pure W and Cr metal targets. The deposition parameters for the interlayer (W and WN) with multiple qualities were optimized using the gray Taguchi method. The microstructure of these coatings was determined using x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and transmission electron microscopy. The results showed that the mechanical properties of bilayer samples with an interlayer of WN nitride film are superior to those with a W metal interlayer. Moreover, increasing the N{sub 2}/(N{sub 2} + Ar) flow ratio and working pressure enhanced the microhardness and the elastic recovery for coatings with an interlayer/CrWN bilayer. Dry milling tests also showed that bilayer film coatings have better mechanical performance. This increase in multiple performance characteristics is attributed to a bilayer that is manufactured using the gray Taguchi method. Control charts, which are powerful tools and widely used, were employed to monitor and ensure high-quality fabrication of the interlayer/CrWN bilayer and to show the coating processes to be stable and well regulated.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Atomic Layer-Deposited Al{sub 2}O{sub 3} Interlayer for Improved Tribological and Anti-corrosion Properties of TiN Hard Coating on 316L Stainless Steel

A dense Al{sub 2}O{sub 3} interlayer was inserted into TiN to enhance the tribological and anti-corrosion properties of TiN hard coating via a hybrid process of magnetron sputtering and atomic layer deposition (ALD). The influence of the ALD-Al{sub 2}O{sub 3} layer on the microstructure, mechanical, tribological and anti-corrosion properties of TiN was examined. The TiN-Al{sub 2}O{sub 3} coating exhibits low friction coefficient and specific wear rate, due to the structure change and columnar refinement caused by the addition of amorphous ALD-Al{sub 2}O{sub 3} interlay which improves the mechanical properties of hard coating. The improved corrosion properties of TiN are attributed to the fact that the insulating ALD-Al{sub 2}O{sub 3} used as a sealing layer can prevent the corrosive chlorine ions migrating into the lower TiN layer and block the charge transport in coatings. Moreover, raising the insertion position of ALD-Al{sub 2}O{sub 3} layer away from the steel substrate results in a further increase in the anti-corrosion property of TiN-Al{sub 2}O{sub 3} composite coating.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Unusual size dependent strengthening mechanisms of Cu/amorphous CuNb multilayers

Nanostructured crystalline/amorphous metallic multilayers have been increasingly studied due to their high strength and potential enhancement of plasticity in amorphous metals. Here we report on mechanical behaviors of Cu/amorphous CuNb multilayers that were prepared by magnetron sputtering with equal individual layer thickness (h) varying from 1 to 200 nm. A medium-range-order amorphous CuNb layer formed between Cu and amorphous CuNb layers. This intermediate layer facilitates transmission of plasticity from Cu to amorphous layers by preventing the smear of dislocation core on the interface. The maximum hardness of Cu/amorphous CuNb multilayers is achieved when h ≤ 50 nm, and is much lower than the hardness of single-layer amorphous CuNb films. Molecular dynamics simulations show that, comparing with single-layer amorphous CuNb, the pile-up of dislocations in Cu layers lowers the stress for the activation of shear transformation zones in amorphous CuNb layers in multilayers.

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

Mechanical properties of metal-ceramic nanolaminates: Effect of constraint and temperature

Al/SiC nanolaminates with equal nominal thicknesses of the Al and SiC layers (10, 25, 50 and 100 nm) were manufactured by magnetron sputtering. The mechanical properties were measured at 25 °C and 100 °C by means of nanoindentation and micropillar compression tests and the deformation mechanisms were analyzed by in situ micropillar compression tests in the transmission electron microscope. In addition, finite element simulations of both tests were carried out to ascertain the role played by the strength of the Al layers and by the elastic constraint of the ceramic layers on the plastic flow of Al in the mechanical response. It was found that the mechanical response was mainly controlled by the constraint during nanoindentation or micropillar compression tests of very thin layered (≈10 nm) laminates, while the influence of the strength of Al layers was not as critical. This behavior was reversed, however, for thick layered laminates (100 nm). Here, these mechanisms point to the different effects of layer thickness during nanoindentation and micropillar compression, at both temperatures, and showed the critical role played by constraint on the mechanical response of nanolaminates made of materials with a very large difference in the elasto-plastic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Switching kinetics in ferroelectric zinc magnesium oxide thin films

The switching kinetics of RF-magnetron reactively sputtered ~200 nm thick Zn 1-x Mg x O (ZMO) ferroelectric thin films with x = 0.41 and x = 0.27 prepared on Pt/Ti/SiO 2 /Si substrates were studied at applied fields near the coercive fields, ranging from 3.4 to 5.1 MV cm -1 , and at temperatures ranging from room temperature to 100 °C. Polarization reversal in ZMO followss the Kolmogorov-Avrami-Ishibashi kinetics model for nucleation and growth at applied fields near the coercive field, and obeys an individual column switching (ICS) model at higher applied fields required to switch most of the spontaneous polarization. Switching in the high-applied field regime can be described using either the Gaussian or inverse gamma distribution functions depending on the mole fraction of magnesium in the film. The switching current transients of the high-Mg content ZMO film (x = 0.41) are always bi-modal, whereas the low Mg composition film (x = 0.27) is described by the Gaussian distribution initially following wake-up, and becomes bimodal with continued cycling. Rayleigh-like behavior of the dielectric constant revealed a simultaneous increase of the irreversible and decrease of the reversible contributions to the dielectric constant, which was ascribed to an increase in the density of mobile domain walls with cycling and resulted in faster switching.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2023

Effects of Cr/Zircaloy-4 coating qualities for enhanced accident tolerant fuel cladding

Cr-coated zirconium alloys represent a modern approach to enhance cladding safety during accident scenarios. Two high-power impulse magnetron sputtered Cr-coated Zry-4 systems were subjected to simulated loss-of-coolant accident conditions to investigate cladding performance. The first Cr-coating (4.8 µm thick) was deposited onto Zry-4 cladding and exhibited through-thickness cracking while the second Cr-coating (6.8 µm thick) was deposited with improved deposition parameters onto polished Zry-4 and exhibited no cracking. During burst testing, the coating with a higher density of defects failed to consistently reduce oxidation and exhibited similar burst behavior as Zry-4. In contrast, the second Cr-coating reduced ZrO 2 formation through formation of Cr 2 O 3 and displayed enhanced burst temperatures by ~80 °C compared to Zry-4. Utilizing an empirical relation for burst behavior of zirconium alloys, the 6.8 µm Cr/Zry-4 system displayed enhanced burst temperatures equivalent to an effective 0.464 mm increase in Zry-4 wall thickness, highlighting the value of continuous Cr coatings for accident scenarios.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2021

Effect of substrate tilt on sputter-deposited AuTa films

Gold-tantalum alloy films are of interest for biomedical and magnetically-assisted inertial confinement fusion applications. However, growth mechanisms of such Au-Ta alloy films are not well understood. Here, we systematically study the effect of substrate tilt on properties of films deposited by direct current magnetron sputtering from a AuTa alloy target. Experimental data is correlated with distributions of landing energies and incident angles of sputtered and backscattered species calculated by Monte Carlo simulations of ballistic collisions and gas phase atomic transport. Results reveal that the deposition rate and film density monotonically decrease with increasing substrate tilt. Properties are similar for films with a tilt of 40° and below: films are amorphous, with an average compressive stress of 0.5 GPa, a density of 16 g/cm 3 , and electrical resistivity of 200 μΩ cm. The critical substrate tilt angle for the onset of porosity, a transition to a reduced stress state, and an increase in electrical resistivity lies between 40 and 60°. Based on Monte Carlo simulations, these changes in film properties are correlated with an increase in the average impact angle of the ballistic component of atomic flux. Implications of these results to deposition onto non-planar substrates are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A thermal study of amorphous and textured carbon and carbon nitride thin films via transient grating spectroscopy

Here in this study, we are considering a novel way of growing carbon nitride (CN) films by using High Power Impulse Magnetron Sputtering (HiPIMS). Carbon and CN thin films were grown on silicon substrate with varying nanocrystalline texturing: some samples were amorphous while others were either nanocrystalline graphite (for the carbon sample) or fullerene-like (for the CN sample), with both samples having a graphitic nanostructure vertically ordered throughout the film. Their thermal diffusivity was computed using transient grating spectroscopy in order to compare the impact of the material's nanostructure on its thermal property as well as benchmarking the performance of CN. It was found that the thermal properties of carbon thin films were decreased when doped with nitrogen, which is attributed to the increased atomic disorder introduced by the nitrogen cross-linking, impacting the phonon propagation. The impact of nitrogen doping on thermal properties opens new avenues in engineering materials with tailored and varying thermal properties at the microscale.

42 ENGINEERING↗
DOE OSTI2018

Comprehensive characterization of CIGS absorber layers grown by one-step sputtering process

We have demonstrated that the use of a one-step sputtering process allowed for the fabrication of copper indium gallium diselenide (CIGS) thin films by RF magnetron sputtering without an additional selenization process. The CIGS thin films deposited at different substrate temperatures were synthesized on soda-lime glass (SLG) substrates using a single quaternary CIGS target. The film composition ratios of ([Cu]/[In]+[Ga]), ([Ga]/[In]+[Ga]), and ([Se]/[Cu]+[In]+[Ga]) were almost consistent with those of the sputtering target. X-ray diffraction (XRD) and Raman results showed that the crystallinity of the CIGS thin films was gradually improved as substrate temperatures increased. Transmission electron microscopy (TEM) showed that the films grown at 600 degrees C have a columnar structure with the grain size of ~100 nm. In addition, for the CIGS films grown at 600 degrees C, TEM-EDX analysis revealed that the synchronized fluctuation of the Cu and Se signals was observed in the direction of the film depth, while the In and Ga signals were constant. As a result, the CIGS solar cell made using the film showed a degraded cell efficiency of 2.5%, which might be have been caused by not only Cu-rich and Se-poor compositions but the locally unstable composition in the CIGS films fabricated by one-step sputtering.

14 SOLAR ENERGY↗
DOE OSTI2021

Characterization data of an (AlFeNiTiVZr) 1-x Cr x multi-principal element alloy continuous composition spread library

The data provided in this article is related to the research article entitled “Phase stabilization and oxidation of a continuous composition spread multi-principal element (AlFeNiTiVZr) 1-x Cr x alloy”. This data article describes the high-throughput synthesis and characterization processes of an (AlFeNiTiVZr) 1-x Cr x alloy system. Continuous composition spread (CCS) thin-film libraries were synthesized by co-depositing an AlFeNiTiVZr metal alloy target and Cr target via magnetron sputtering. Post-processing was performed on the sample libraries with a vacuum anneal at 873 K and an air anneal at 873 K. Compositional data was determined via WDS in order to verify parameters provided by an in-house sputter model. Crystallographic data was captured via synchrotron diffraction and diffractograms were compared as a function of the change in Cr concentration. These measurements were taken in order to observe phase behavior after oxidation throughout the composition library. Furthermore, vibrational spectrographic data is provided of the oxidized library to show surface speciation along the composition gradient of the alloy system. The structural and oxidative behavior of the (AlFeNiTiVZr) 1-x Cr x alloy can be analysed using the data provided in this article. Additionally, this characterization dataset can be utilized in machine learning algorithms for determining important features and parameters for future hypothesis generation of functional multi-principal element alloys (MPEAs).

36 MATERIALS SCIENCE↗
DOE OSTI2019

Evaluation of hydrogen evolution reaction activity of molybdenum nitride thin films on their nitrogen content

We report preparation and electrochemical properties of molybdenum nitride Mo x N (x from 1 to 2) and Mo thin films prepared by the magnetron sputtering. We adjusted amount of nitrogen during reactive sputtering, to achieve different ratios of Mo:N in the films.We could prepare well-defined and extremely smooth films. We determined hydrogen evolution reaction (HER) activity and other kinetics parameters such as Tafel slopes and exchange current densities. Corrosion stability at anodic potentials was also evaluated from onset potentials of dissolution of prepared films. We found that Mo x N thin film HER activity dependence on nitrogen content in the film exhibits volcano-like diagram. From XRD measurements we identified several phases present in the films from pure Mo to β-Mo 2 N and δ-MoN. We find that β-Mo 2 N phase has the highest HER activity. Stability of studied nitrides at anodic potentials increases with increasing content of nitrogen. Mo films sputtered at high substrate temperatures exhibit higher HER activity than Mo x N systems. Furthermore, with increasing substrate temperature during sputtering, HER activity of pure Mo thin films increases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗