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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Uniaxial Néel vector control in perovskite oxide thin films by anisotropic strain engineering

Antiferromagnetic (AF) thin films typically exhibit a multidomain state, and control of the AF Néel vector is challenging, as AF materials are robust to magnetic perturbations. In this paper, uniaxial Néel vector control is demonstrated by relying on anisotropic strain engineering of epitaxial thin films of the prototypical AF material LaFeO 3 (LFO). Orthorhombic (011)- and (101)-oriented DyScO 3 , GdScO 3 , and NdGaO 3 substrates are used to engineer different anisotropic in-plane strain states. The anisotropic in-plane strain stabilizes structurally monodomain monoclinic LFO thin films. The uniaxial Néel vector is found along the tensile strained b axis, contrary to bulk LFO having the Néel vector along the shorter a axis, and no magnetic domains are found. Hence, anisotropic strain engineering is a viable tool for designing unique functional responses, further enabling AF materials for mesoscopic device technology.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Orientational analysis of atomic pair correlations in nanocrystalline indium oxide thin films

The application of grazing-incidence total X-ray scattering (GITXS) for pair distribution function (PDF) analysis using >50 keV X-rays from synchrotron light sources has created new opportunities for structural characterization of supported thin films with high resolution. Compared with grazing-incidence wide-angle X-ray scattering, which is only useful for highly ordered materials, GITXS/PDFs expand such analysis to largely disordered or nanostructured materials by examining the atomic pair correlations dependent on the direction relative to the surface of the supporting substrate. A characterization of nanocrystalline In 2 O 3 -derived thin films is presented here with in-plane-isotropic and out-of-plane-anisotropic orientational ordering of the atomic structure, each synthesized using different techniques. The atomic orientations of such films are known to vary based on the synthetic conditions. Here, an azimuthal orientational analysis of these films using GITXS with a single incident angle is shown to resolve the markedly different orientations of the atomic structures with respect to the planar support and the different degrees of long-range order, and hence, the terminal surface chemistries. It is anticipated that orientational analysis of GITXS/PDF data will offer opportunities to extend structural analyses of thin films by providing a means to qualitatively determine the major atomic orientation within nanocrystalline and, eventually, non-crystalline films.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Impact of high-power impulse magnetron sputtering pulse width on the nucleation, crystallization, microstructure, and ferroelectric properties of hafnium oxide thin films

The impact of the high-power impulse magnetron sputtering (HiPIMS) pulse width on the crystallization, microstructure, and ferroelectric properties of undoped HfO 2 films is investigated. HfO 2 films were sputtered from a hafnium metal target in an Ar/O 2 atmosphere, varying the instantaneous power density by changing the HiPIMS pulse width with fixed time-averaged power and pulse frequency. The pulse width is shown to affect the ion-to-neutral ratio in the depositing species with the shortest pulse durations leading to the highest ion fraction. In situ x-ray diffraction measurements during crystallization demonstrate that the HiPIMS pulse width impacts nucleation and phase formation, with an intermediate pulse width of 110 μ s stabilizing the ferroelectric phase over the widest temperature range. Although the pulse width impacts the grain size with the lowest pulse width resulting in the largest grain size, the grain size does not strongly correlate with the phase content or ferroelectric behavior in these films. In conclusion, these results suggest that precise control over the energetics of the depositing species may be beneficial for forming the ferroelectric phase in this material.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Dynamic asymmetric strain imprinted into substrates by an oxide thin film

In film-substrate systems, the substrate role is often considered to be limited to providing static mechanical constraints. Dynamic film-substrate interactions when a structural change in the film modifies the substrate are generally disregarded. Here, using combined x-ray and electron microscopies, we observed that an electrically induced filament in a vanadium dioxide film created strong asymmetric strain in an underlying sapphire substrate. This asymmetric substrate strain fed back into the film and defined the filament expansion direction, revealing the importance of film-substrate dynamic interactions in determining film functionality. Furthermore, the strain imprint propagated at least tens of micrometers deep into the substrate, exceeding the film thickness by more than 200-fold, potentially enabling substrate functionalization as an active mechanical coupling media in three-dimensional integrated microelectronic architectures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Effect of Applied Stress on the Selective Oxidation of Alloy 600 Exposed to PWR Primary Water and Rhines Pack Environments

A mechanistic understanding of corrosion and oxidation processes is crucial to ensure long-term resistance to stress corrosion cracking of Ni-base structural alloys in pressurized water reactor (PWR) primary and secondary systems. Aqueous corrosion of Ni-base alloys under PWR primary water conditions was previously compared to gaseous oxidation with comparable oxygen potentials. However, those studies considered only stress-free conditions, which removes a critical parameter for understanding stress corrosion behaviors. A significant knowledge gap exists for the role of applied stresses on selective internal oxidation in gaseous environments. A micro-4-point-bend jig was designed to facilitate stress in a Rhines Pack set-up. Selective oxidation at different stress and strain conditions was investigated in a series of Rhines Pack experiments for Alloy 600. Focused ion beam milling enabled the extraction of site-specific specimens containing selected high-energy grain boundaries from tensile and compressive stress regions. Analytical transmission electron microscopy was employed to analyze the microstructure and chemical composition of the resulting oxides. Protective surface oxide films and selective intergranular oxides were observed at different conditions. The implications of these fundamental differences are discussed relative to intergranular attack and stress corrosion cracking mechanisms in PWR primary water.

stress, 4-point-bend, selective oxidation, Alloy 6↗
DOE OSTI2024

Intermittent oxidation kinetics and metal/oxide interfacial undulation

The phenomenon of oxygen-adsorption-induced surface restructuring is widespread across various metal-oxygen systems, yet its impact on initiating bulk oxide formation remains largely unexplored. In this study, through in-situ atomic-resolution electron microscopy observations of surface oxidation of Cu(110) and Cu 85 Au 15 (110), we unveil intermittent oxide-film growth modulated by oxygen-induced surface restructuring. This modulation is evidenced by repeated pinning of Cu 2 O growth front at isolated Cu columns of the c(6×2)-O reconstruction, owing to required long-range diffusion of Cu and O atoms to the Cu 2 O growth front. We reveal that Cu vacancies, generated at the Cu 2 O growth front, are injected into the Cu 2 O/Cu interface, inducing hill-and-valley undulation of the Cu 2 O film. In contrast, atomic vacancies produced during the Cu 85 Au 15 (110) oxidation preferentially migrate into interfaces between Au-rich and Au-poor regions in the bulk, resulting in a flat and adherent Cu 2 O film. These findings demonstrate the critical role of oxygen-induced surface restructuring in modulating oxide-film-growth kinetics and manipulability of the fate of injected vacancies by alloying, thereby offering insights applicable to a broader range of metal-oxygen systems for fine-tuning oxidation kinetics and enhancing oxide/metal interfacial adhesion.

25 ENERGY STORAGE↗
DOE OSTI2021

Understanding the Electronic Structure Evolution of Epitaxial LaNi1-xFexO3 Thin Films for Water Oxidation

Rare earth nickelates including LaNiO3 are promising catalysts for water electrolysis to produce oxygen gas. Recent studies report that Fe substitution for Ni can significantly enhance the oxygen evolution reaction (OER) activity of LaNiO3. However, the role of Fe in increasing activity remains ambiguous, with potential origins both structural and electronic in nature. Here, by utilizing a series of epitaxial LaNi1-xFexO3 thin films synthesized by oxygen-assisted molecular beam epitaxy, we report that Fe substitution tunes the oxidation state of Ni in LaNi1-xFexO3 and a volcano-like OER trend is observed with x = 0.375 being the most active. Spectroscopy and ab initio modeling reveal that the high-valent Fe3+? B-site cationic species strongly increases the transition metal (TM) 3d bandwidth via Ni-O-Fe bridges and enhances the TM 3d-O 2p hybridization, boosting the OER activity. Furthermore, pH-dependent electrochemical measurements suggest that the OER on LaNi1-xFexO3 involves a lattice oxygen-mediated mechanism.

LaNiO3, Fe substitution, charge transfer, lattice ↗
DOE OSTI2020

Aqueous passivation of multi-principal element alloy Ni 38 Fe 20 Cr 22 Mn 10 Co 10 : Unexpected high Cr enrichment within the passive film

The aqueous passivation of a non-equiatomic Ni 38 Fe 20 Cr 22 Mn 10 Co 10 - at.% (Ni 40 Fe 20 Cr 20 Mn 10 Co 10 - wt.%) multi-principal element alloy (MPEA) was investigated in 0.1 M NaCl at pH 4 and compared to a conventional binary Ni 76 Cr 24 – at.% (Ni 78 Cr 22 – wt.%) alloy. The electrochemical behavior and oxide film characteristics were explored utilizing in-situ electrochemical and ex-situ surface-sensitive techniques. The passive film composition, thickness, and elemental valence states, as well as, the fate of each element were studied by in-situ atomic emission spectro-electrochemistry, ex-situ X-ray photoelectron spectroscopy, and atom probe tomography. The Ni 38 Fe 20 Cr 22 Mn 10 Co 10 MPEA demonstrated slightly better corrosion resistance compared to the binary Ni 76 Cr 24 , alloy. Passive films on the MPEA contained primarily Cr, and small amounts of Ni, Fe, Co and Mn, while dissolution of Ni, Fe, Co was observed. Ni 0 was enriched at the oxide/metal interface while Cr was depleted. Enrichment of Cr in the passive film occurred to a greater extent in the MPEA than for the Ni-Cr binary alloy. As a result, enrichment factors were determined and the origins of enrichment are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Thermal stability of oxidized ultrathin Li films on TZM for plasma facing components

For improved understanding of the behavior of Li plasma facing components (PFCs) in the presence of oxygen impurities, we report on the thermal stability of ultrathin (up to 1.0 nm) LiO x films on a titanium-zirconium-molybdenum (TZM) alloy substrate over the temperature range of 310–1400 K. LiO x films were prepared by either post-oxidation of Li films or Li films deposited on an oxygen-precovered TZM surface. Thermal stability of these films was studied using a combination of temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and low-energy ion scattering (LEIS). For post-oxidized Li films, TPD showed that no Li desorption occurred until temperatures above 620 K, and then Li desorbed from the surface via at least three desorption peaks. The O 1s XPS spectra on the post-oxidized films at 310 K indicate the formation of lithium oxide (Li2O) and peroxide/hydroxide (Li 2 O 2 /LiOH). The peroxide/hydroxide converts to oxide after heating to 680 K with no desorption of Li or O 2 , and then this film decomposes to liberate Li into the gas phase while leaving oxygen at the TZM surface. Heating the LiO x films to 1070 K led to a solid-state reaction with surface Mo atoms of the substrate to form a condensed binary lithium molybdenum oxide (LixMoOy) phase, which upon further heating decomposed to liberate gas phase binary lithium molybdenum oxide species. Li deposition on an oxygen-precovered TZM surface formed a complex, highly stable, oxygen rich, Li-O-Mo interfacial oxide. Li desorption from multilayer Li films on oxygen-precovered TZM surfaces occurred in a metallic Li multilayer peak and three other oxide-derived peaks. These results support the improved thermal stability of oxidized lithium as compared to metallic Li and have implications for Mo impurity transport into the plasma at high temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Heterogeneous Structural Evolution of In–Zn–O Thin Films during Annealing

Amorphous In-Zn-O (a-IZO) thin films are among the most promising transparent conducting materials. Applications of a-IZO include thin film transistors for display technology and photovoltaic devices. However, the use of this material in practical devices has been impeded by limitations in our understanding of the relationship between a-IZO film structure and electrical properties. Here, we use in situ X-ray reflectivity to provide experimental evidence for a vertically heterogeneous, thermally induced structural relaxation that had been predicted for amorphous oxide films but not previously observed. The structural relaxation is shown to be dependent on the thermal annealing environment. Complementary in situ current-voltage curves and ex situ Van der Pauw measurements further show that thermal annealing also influences the electrical performance of the films. Here our results suggest that both oxygen uptake and structural relaxation contribute to the reduction in free carriers within a-IZO films during postdeposition processing. The structural heterogeneity and loss of carriers that occur during thermal annealing are only partly reversible. We anticipate that this insight into the structure-processing-property relationships within a-IZO will help to enable a-IZO-based devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Photonic curing of solution-deposited ZrO 2 dielectric on PEN: a path towards high-throughput processing of oxide electronics

High-throughput manufacturing of oxide electronics will enable new applications ranging from large-area displays to flexible medical devices and low-cost solar panels. However, high quality oxide films from solution-based precursors typically require 20 minutes or more of thermal annealing at high temperature (> 250 °C) for each layer, severely limiting both the throughput and substrate choice. Here, we report high speed photonic curing of ZrO 2 dielectric thin films on flexible plastic substrates. The curing and patterning processes can be achieved simultaneously by using shadow mask patterning or adjusting conditions to convert oxide only on top of underlying metal contacts, i.e. self-aligned patterning. Metal-insulator-metal capacitors using two layers of ZrO 2 films photonically cured in just 100 seconds per layer show non-dispersive capacitance-frequency behavior from 10 2 to 10 6 Hz, high areal capacitance of 200 nF/cm 2 and low dissipation factor of 0.03 at 10 5 Hz, leakage current density of ~ 10 -7 A/cm 2 at an applied field of 2 MV/cm, and a breakdown field of nearly 8 MV/cm. Using an upgraded tool, similar dielectric properties are achieved in as short as 100 milliseconds using a single pulse of light, revealing a pathway to oxide film processing beyond 30 m/min.

14 SOLAR ENERGY↗
DOE OSTI2021

Mesoscale Confinement Effects and Emergent Quantum Interference in Titania Antidot Thin Films

The effect of confinement on electron and ion transport in oxide films is of interest both fundamentally and technologically for the design of next-generation electronic devices. In metal oxides with mobile ions and vacancies, it is the interplay of the different modes of charge transport and the corresponding current–voltage signatures that is of interest. We developed a patterned structure in titania films, with feature sizes of 11–20 nm, that allow us to explore confined transport. In this study, we describe how confinement changes the competing charge transport mechanisms, the patterned antidot array leads to displacement fields and confines the charge density that results in modified and emergent electron transport with an increase in conductivity. This emergent behavior can be described by considering electron interference effects. Characterization of the charge transport with electron holography and impedance spectroscopy, and through comparison with modeling, show that nanoscale confinement is a way to control quantum interference.

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

Effects of size of an oxide layer on the surface properties of lithium irradiated by deuterium plasma

We investigate how growth of an oxide film will influence the deuterium recycling properties of Li on plasma facing surfaces. Lithium films on the walls or plasma-facing material surfaces of a fusion vacuum vessel improves plasma performance in part by removing residual impurity atoms from the plasma. Oxygen atoms, from residual water vapor or eroded oxide surfaces, are a prominent ubiquitous impurity that can create a layer of oxide on lithium films. The results of the work herein also indicate a possibility for determining the thickness of the oxide layer on such Li films by measuring the reflection probability of incident deuterium particles from the surface.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗