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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 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Atomic state and characterization of nitrogen at the SiC/SiO{sub 2} interface

We report on the concentration, chemical bonding, and etching behavior of N at the SiC(0001)/SiO{sub 2} interface using photoemission, ion scattering, and computational modeling. For standard NO processing of a SiC MOSFET, a sub-monolayer of nitrogen is found in a thin inter-layer between the substrate and the gate oxide (SiO{sub 2}). Photoemission shows one main nitrogen related core-level peak with two broad, higher energy satellites. Comparison to theory indicates that the main peak is assigned to nitrogen bound with three silicon neighbors, with second nearest neighbors including carbon, nitrogen, and oxygen atoms. Surprisingly, N remains at the surface after the oxide was completely etched by a buffered HF solution. This is in striking contrast to the behavior of Si(100) undergoing the same etching process. We conclude that N is bound directly to the substrate SiC, or incorporated within the first layers of SiC, as opposed to bonding within the oxide network. These observations provide insights into the chemistry and function of N as an interface passivating additive in SiC MOSFETs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Understanding the Solid-State Electrode–Electrolyte Interface of a Model System Using First-Principles Statistical Mechanics and Thin-Film X-ray Characterization

Intermixing of atomic species at the electrode-electrolyte boundaries can impact the properties of the interfaces in solid-state batteries. Herein, this work uses first-principles statistical mechanics along with experimental characterization to understand intermixing at the electrode-electrolyte interface. For the model presented in this work, lithium manganese oxide (LiMn 2 O 4 , LMO) and lithium lanthanum titanate (Li 3x La 2/3-x TiO 3 , LLTO) are employed as the cathode and electrolyte, respectively. The results of the computational work show that Ti-Mn intermixing at the interface is significant at synthesis temperatures. The experimental results in this work find that, at some critical temperatures between 600 and 700 degrees C for material preparation, the interface of LLTO-LMO becomes blurred. Calculations predict that the interface is unstable with regard to Ti-Mn intermixing starting at 0 K, suggesting that the critical temperature found in the experiment is related to kinetics. The work overall suggests that, in designing a solid-state battery, the fundamental reactions such as intermixing need to be considered.

25 ENERGY STORAGE↗
DOE OSTI2015

Elimination of surface band bending on N-polar InN with thin GaN capping

0.5–1 μm thick InN (0001) films grown by molecular-beam epitaxy with N- or In-polarity are investigated for the presence of native oxide, surface energy band bending, and effects introduced by 2 to 4 monolayers of GaN capping. Ex situ angle-resolved x-ray photo-electron spectroscopy is used to construct near-surface (GaN)/InN energy profiles, which is combined with deconvolution of In3d signal to trace the presence of InN native oxide for different types of polarity and capping. Downwards surface energy band bending was observed on bare samples with native oxide, regardless of the polarity. It was found that the In-polar InN surface is most readily oxidized, however, with only slightly less band bending if compared with the N-polar sample. On the other hand, InN surface oxidation was effectively mitigated by GaN capping. Still, as confirmed by ultra-violet photo-electron spectroscopy and by energy band diagram calculations, thin GaN cap layer may provide negative piezoelectric polarization charge at the GaN/InN hetero-interface of the N-polar sample, in addition to the passivation effect. These effects raised the band diagram up by about 0.65 eV, reaching a flat-band profile.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Spatially Precise Light‐Activated Dedoping in Wafer‐Scale MoS 2 Films

2D materials, particularly transition metal dichalcogenides (TMDCs), have shown great potential for microelectronics and optoelectronics. However, a major challenge in commercializing these materials is the inability to control their doping at a wafer scale with high spatial fidelity. Interface chemistry is used with the underlying substrate oxide and concomitant exposure to visible light in ambient conditions for photo-dedoping wafer scale MoS 2 . It is hypothesized that the oxide layer traps photoexcited holes, leaving behind long-lived electrons that become available for surface reactions with ambient air at sulfur vacancies (defect sites) resulting in dedoping. Additionally, high fidelity spatial control is showcased over the dedoping process, by laser writing, and fine control achieved over the degree of doping by modulating the illumination time and power density. This localized change in MoS 2 doping density is very stable (at least 7 days) and robust to processing conditions like high temperature and vacuum. The scalability and ease of implementation of this approach can address one of the major issues preventing the “Lab to Fab” transition of 2D materials and facilitate its seamless integration for commercial applications in multi-logic devices, inverters, and other optoelectronic devices.

14 SOLAR ENERGY↗
DOE OSTI2015

Blending Cr 2 O 3 into a NiO-Ni electrocatalyst for sustained water splitting

The rising H 2 economy demands active and durable electrocatalysts based on low-cost, earth-abundant materials for water electrolysis/photolysis. Here we report nanoscale Ni metal cores over-coated by a Cr 2 O 3 -blended NiO layer synthesized on metallic foam substrates. The Ni@NiO/Cr 2 O 3 triphase material exhibits superior activity and stability similar to Pt for the hydrogen-evolution reaction in basic solutions. The chemically stable Cr 2 O 3 is crucial for preventing oxidation of the Ni core, maintaining abundant NiO/Ni interfaces as catalytically active sites in the heterostructure and thus imparting high stability to the hydrogen-evolution catalyst. The highly active and stable electrocatalyst enables an alkaline electrolyzer operating at 20 mA cm –2 at a voltage lower than 1.5 V, lasting longer than 3 weeks without decay. Thus, the non-precious metal catalysts afford a high efficiency of about 15 % for light-driven water splitting using GaAs solar cells.

08 HYDROGEN↗
DOE OSTI2023

A Dual Anion Chemistry-Based Superionic Glass Enabling Long-Cycling All-Solid-State Sodium-Ion Batteries

Glassy Na-ion solid-state electrolytes (GNSSEs) are an important group of amorphous SSEs. However, the insufficient ionic conductivity of state-of-the-art GNSSEs at room temperature lessens their promise in the development of all-solid-state Na-ion batteries (ASSNIBs) with high energy density and improved safety. Here we report the discovery of a new sodium superionic glass, 0.5Na 2 O 2 -TaCl 5 (NTOC), based on dual-anion sublattice of oxychlorides. The unique local structures with abundant bridging and non-bridging oxygen atoms contributes to a highly disordered Na-ion distribution as well as low Na + migration barrier within NTOC, enabling an ultrahigh ionic conductivity of 4.62 mS cm −1 at 25 °C (more than 20 times higher than those of previously reported GNSSEs). Moreover, the excellent formability of glassy NTOC electrolyte and its high electrochemical oxidative stability ensure a favourable electrolyte-electrode interface, contributing to superior cycling stability of ASSNIBs for over 500 cycles at room temperature. The discovery of glassy NTOC electrolyte would reignite research enthusiasm in superionic glassy SSEs based on multi-anion chemistry.

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

The evaluation of aluminum and iron metal oxide settling behaviors for Hanford insoluble solids waste preprocessing

The Hanford site is currently one of the largest and most expensive cleanup sites for hazardous, radioactive waste. Over 20% of the waste found at the Hanford site is in the form of a high activity sludge. The insoluble solids in the sludge will need to be concentrated prior to vitrification in the high-level waste (HLW) melter. This will minimize the amount of liquid that will be evaporated during the melting process and expedite the melter processing rate. One proposed option for concentrating the insoluble solids is gravity settling in the storage tanks. Metal oxide compounds containing aluminum and iron make up the majority of the insoluble solids in the sludge, therefore understanding the behavior of these compounds in various tank waste matrices can facilitate sludge pretreatment options. A study of non-radioactive slurry solutions containing Al(OH) 3 (gibbsite), AlO(OH) (boehmite), and Fe 2 O 3 (iron (III) oxide) was conducted to determine the time dependent interface behavior and settling rates of these compounds. Variations in solids loading and sodium concentration were evaluated to represent waste processing conditions and the results of these settling studies were compared with prior tank waste settling tests. Information gathered from these studies can be used to inform future decisions on sludge treatment processes of the insoluble solids processed at the Hanford site.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

Characterization of SiO 2 Thermally Grown Oxide Stress Evolution of EBCs with Al-Containing Dopants

SiC/SiC ceramic matrix composites (CMCs) are desired for use in combustion environments to achieve higher turbine operating temperatures. However, CMCs require environmental barrier coatings (EBCs) for protection from the gas environment. EBC systems are known to primarily fail through coating delamination via growth of a thermally grown oxide (TGO) at the EBC—silicon bond coating interface when exposed to steam, which accelerates the TGO growth rate. The TGO undergoes a phase transformation during thermal cycling, which results in stresses that may encourage EBC spallation. Yb-silicate EBCs with mullite and yttrium aluminum garnet (YAG) dopant additions were deposited on SiC substrates with a Si intermediate bond coating and exposed to thermal cycling in steam at 1350 °C. The impact of Al dopant additions on the TGO growth rate and the SiO 2 phase transformation was assessed. Photo-stimulated luminescence spectroscopy (PSLS) was used to characterize the Al-containing phases and to measure stress evolution in the EBC following exposure using the stress-induced peak shift of the R-lines of mullite. Raman microscopy was used to map the stresses in the Si bond coating following exposure. It was found that the TGO phase transformation upon cooling increased compressive stress in the Si bond coating within 15 µm of the TGO.

Building Materials↗
DOE OSTI2021

Mediated electrochemistry for redox-based biological targeting: entangling sensing and actuation for maximizing information transfer

Biology and electronics are both expert at receiving, analyzing, and responding to information, yet they use entirely different information processing paradigms. Biology processes information using networks that are intrinsically molecular while electronics process information through circuits that control the flow of electrons. There is great interest in coupling the molecular logic of biology with the electronic logic of technology, and we suggest that redox (reduction-oxidation) is a uniquely-suited modality for interfacing biology with electronics. Specifically, redox is a native biological modality and is accessible to electronics through electrodes. Here, we summarize recent advances in mediated electrochemistry to direct information transfer into biological systems intentionally altering function, exposing it for more advanced interpretation, which can dramatically expand the biotechnological toolbox.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Preparation and characterization of biodegradable Mg-Zn-Ca/MgO nanocomposites for biomedical applications

Highlights: • Novel biodegradable Mg-Zn-Ca/MgO matrix composites, were devised and prepared using high shear melt conditioning. • The excellent interfacial bonding between MgO particles and α-Mg matrix was observed via HRTEM and FFT pattern analysis. • The optimum solution treatment and the addition of MgO nanoparticles hugely enhanced corrosion resistance of nanocomposites. • The yield tensile strength (YTS) increased by 22.81% with 0.5% MgO addition, while the ductility did not mainly deteriorate. - Abstract: In order to improve the corrosion resistance and mechanical properties of magnesium alloys for biomedical implant applications, novel biodegradable Mg-3Zn-0.2Ca (wt%) matrix composites, reinforced by adding various contents of MgO nanoparticles (0.1, 0.2, 0.3, 0.5 wt%), were devised and prepared using high shear melt conditioning. An optimum solution treatment (450 °C, 48 h) and subsequent hot extrusion was carried out to produce the Mg-3Zn-0.2Ca/MgO composites. It was found that the as-extruded composite exhibited a fine grain structure with relatively uniformly distributed MgO particles. The orientation relationships (ORs) of (1 1 1){sub MgO} ~ 2.62° from (0 0 0 2){sub α-Mg} and [0 −1 1]{sub MgO} // [2 −1 −1 0]{sub α-Mg}, were observed between the MgO particles and the α-Mg matrix via high resolution transmission electron microscopy (HRTEM) investigation and fast Fourier transform (FFT) pattern analysis, verifying the excellent interfacial bonding between the phases. Additionally, a substantial reduction in the secondary phase content was found in the solution treated sample. In vitro immersion, electrochemical, and mechanical tensile tests were used to characterize the corrosion behavior and mechanical properties. The ultimate tensile strength (UTS) increased to 329.03 ± 2.01 MPa and the yield tensile strength (YTS) increased by 22.81% with 0.5 wt% MgO loading, while the ductility did not substantially deteriorate. The polarization resistance (R{sub p}) of the composite was shown to increase from 0.95 kΩ cm{sup 2} to 2.02 kΩ cm{sup 2} with the addition of 0.2 wt% MgO. With increasing MgO content, agglomeration of the MgO particles was detected in the analyzed composite, resulting in decreased ductility and the occurrence of pitting corrosion.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Tailoring Interfaces in Solid-State Batteries Using Interfacial Thermochemistry and Band Alignment

Solid-state lithium ion batteries have enhanced thermal stability compared to batteries using liquid electrolytes. Although their practical implementation is limited by undesired side reactions between the electrode and electrolyte, different modification strategies have been proposed to stabilize these reactive interfaces. These approaches have been primarily based upon bulk materials properties, however, which may not necessarily be representative of the chemistry at the solid/solid interface. In this work, first principles calculations and X-ray scattering experiments are used to elucidate molecular-level reactivity and develop design principles for tailored interfaces based on surface and interfacial properties. Because of its well-known instability, the interface between the Li metal anode and the lithium lanthanum titanate (LLTO) solid electrolyte is applied as a model system. Density functional theory calculations are used to describe bulk, surface, and interfacial thermochemistry of the Li/LLTO system, and interfacial reconstruction is probed using ab initio molecular dynamics. These simulations of the Li/LLTO interface demonstrate facile decomposition concomitant with reduction of Ti 4+ ions. Based on further insights from computational analysis of the surface band edge positions, La 2 O 3 is proposed as an interlayer coating and is shown to provide an energetic barrier for interfacial charge transfer and decomposition reactions from X-ray reflectivity measurements and theoretical calculations. The findings in this work suggest that design strategies based on surface and interfacial properties can be used to kinetically stabilize electrode/electrolyte interfaces in solid-state batteries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Controlling the Schottky Barrier at the Pt/TiO 2 Interface by Intercalation of a Self-Assembled Monolayer with Oriented Dipole Moments

Interfacial Schottky barriers can impact the catalytic function of Pt on TiO 2 . Since the electronic structure is characteristic of each material, it may be advantageous to tailor the interfacial Schottky barrier by the addition of adsorbed layers. Here, we show that the Schottky barrier in Pt/TiO 2 can be mitigated by the insertion of self-assembled monolayers (SAM) of carboranethiols that possess an oriented dipole moment. A Pt substrate with the SAM on which TiO 2 nanoparticles are deposited is used to that effect. Kelvin Probe Force Microscopy shows thatm-9-carboranethiolate SAM with perpendicular dipole moments decreases the potential difference between TiO 2 and Pt by ~0.3 eV due to the interfacial electric field of the SAM. Furthermore, our findings open new opportunities for tailoring interfacial electronic structures not only in the metal-semiconductor junction, but also the semiconductor heterojunctions.

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

Tuning In-Plane Magnetic Anisotropy and Interfacial Exchange Coupling in Epitaxial La 2/3 Sr 1/3 CoO 3 /La 2/3 Sr 1/3 MnO 3 Heterostructures

Controlling the in-plane magnetocrystalline anisotropy and interfacial exchange coupling between ferromagnetic (FM) layers plays a key role in next-generation spintronic and magnetic memory devices. In this work, we explored the effect of tuning the magnetocrystalline anisotropy of La 2/3 Sr 1/3 CoO 3 (LSCO) and La 2/3 Sr 1/3 MnO 3 (LSMO) layers and the corresponding effect on interfacial exchange coupling by adjusting the thickness of the LSCO layer (t LSCO ). The epitaxial LSCO/LSMO bilayers were grown on (110) o -oriented NdGaO 3 (NGO) substrates with a fixed LSMO (top layer) thickness of 6 nm and LSCO (bottom layer) thicknesses varying from 1 to 10 nm. Despite the small difference (~0.2%) in lattice mismatch between the two in-plane directions, [001] o and [11̅0] o , a pronounced in-plane magnetic anisotropy was observed. Soft X-ray magnetic circular dichroism hysteresis loops revealed that for t LSCO ≤ 4 nm, the easy axes for both LSCO and LSMO layers were along the [001] o direction, and the LSCO layer was characterized by magnetically active Co 2+ ions that strongly coupled to the LSMO layer. No exchange bias effect was observed in the hysteresis loops. In contrast, along the [11̅0] o direction, the LSCO and LSMO layers displayed a small difference in their coercivity values, and a small exchange bias shift was observed. As t LSCO increased above 4 nm, the easy axis for the LSCO layer remained along the [100] o direction, but it gradually rotated to the [11̅0] o direction for the LSMO layer, resulting in a large negative exchange bias shift. Therefore, we provide a way to control the magnetocrystalline anisotropy and exchange bias by tuning the interfacial exchange coupling between the two FM layers.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Comparative Study of Vinylene Carbonate and Lithium Difluoro(oxalate)borate Additives in a SiO x /Graphite Anode Lithium-Ion Battery in the Presence of Fluoroethylene Carbonate

The SiO x /graphite composite is recognized as a promising anode material for lithium-ion batteries (LIBs), owing to the high theoretical capacity of SiO x combined with the excellent stability of graphite. However, the inherent disadvantage of volume expansion in silicon-based anodes places significant challenges on the solid electrolyte interphase (SEI) and severely degrades the electrochemical performance. Rational formulation of electrolyte, including its additives, is crucial in accommodating and optimizing the composition of the SEI and enhancing the cell performance. In this work, we present a comparative study of vinylene carbonate (VC) and lithium difluoro(oxalate)borate (LiDFOB) additives combined with fluoroethylene carbonate (FEC) in the electrolyte for SiO x /graphite∥LiNi 1–x–y–z Co x Mn y Al z O 2 full cells. VC outperformed LiDFOB as an additive, delivering higher capacity cycling, higher Coulombic efficiency, and better cycle stability up to 400 cycles. XPS and impedance analyses reveal that LiDFOB contributed to SEI/CEI with both a lower proportion of LiF and a higher proportion of poly(VC), which tended to produce higher cell impedance. XRD and XANES further indicated that using the LiDFOB additive, the NCMA cycled to a shallower degree than that of the VC additive. Although the VC additive maintained a higher capacity up to 400 cycles, microstrain and SEM analyses show a higher strained NCMA along with clear evidence of cracking over the surface of the NCMA particle in VC-based electrolyte but not in LiDFOB. In conclusion, this suggests that the negative influence of LiDFOB at the anode (inferior SEI) supersedes the negative impact of both a cracked NCMA and a deeper cycled NCMA and SiO x -based anode.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Activation and Conversion of Methane to Syngas over ZrO 2 /Cu(111) Catalysts near Room Temperature

Enzymatic systems achieve the catalytic conversion of methane at room temperature under mild conditions. Here, in this study, varying thermodynamic and kinetic parameters, we show that the reforming of methane by water (MWR, CH 4 + H 2 O → CO + 3H 2 ) and the water-gas shift reaction (WGS, CO + H 2 O → H 2 + CO 2 ), two essential processes to integrate fossil fuels toward a H2 energy loop, can be achieved on ZrO 2 /Cu(111) catalysts near room temperature. Measurements of ambient-pressure X-ray photoelectron spectroscopy and mass spectrometry, combined with density functional calculations and kinetic Monte Carlo simulations, were used to study the behavior of the inverse oxide/metal catalysts. The superior performance is associated with a unique zirconia-copper interface, where multifunctional sites involving zirconium, oxygen, and copper work coordinatively to dissociate methane and water at 300 K and move forward the MWR and WGS processes.

03 NATURAL GAS↗
DOE OSTI2018

Methanotrophy across a natural permafrost thaw environment

The fate of carbon sequestered in permafrost is a key concern for future global warming as this large carbon stock is rapidly becoming a net methane source due to widespread thaw. Methane release from permafrost is moderated by methanotrophs, which oxidise 20-60% of this methane before emission to the atmosphere. Despite the importance of methanotrophs to carbon cycling, these microorganisms are under-characterised and have not been studied across a natural permafrost thaw gradient. Here, we examine methanotroph communities from the active layer of a permafrost thaw gradient in Stordalen Mire (Abisko, Sweden) spanning three years, analysing 188 metagenomes and 24 metatranscriptomes paired with in situ biogeochemical data. Methanotroph community composition and activity varied significantly as thaw progressed from intact permafrost palsa, to partially-thawed bog and fully-thawed fen. Thirteen methanotroph population genomes were recovered, including two novel genomes belonging to the uncultivated upland soil cluster alpha (USCα) group and a novel potentially methanotrophic Hyphomicrobiaceae . Combined analysis of porewater δ 13 C-CH 4 isotopes and methanotroph abundances showed methane oxidation was greatest below the oxic-anoxic interface in the bog. Here, these results detail the direct effect of thaw on autochthonous methanotroph communities, and their consequent changes in population structure, activity, and methane moderation potential.

54 ENVIRONMENTAL SCIENCES↗