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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 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Integration of amorphous ferromagnetic oxides with multiferroic materials for room temperature magnetoelectric spintronics

A room temperature amorphous ferromagnetic oxide semiconductor can substantially reduce the cost and complexity associated with utilizing crystalline materials for spintronic devices. We report a new material (Fe 0.66 Dy 0.24 Tb 0.1 ) 3 O 7-x (FDTO), which shows semiconducting behavior with reasonable electrical conductivity (~500 mOhm-cm), an optical band-gap (2.4 eV), and a large enough magnetic moment (~200 emu/cc), all of which can be tuned by varying the oxygen content during deposition. Magnetoelectric devices were made by integrating ultrathin FDTO with multiferroic BiFeO 3 . A strong enhancement in the magnetic coercive field of FDTO grown on BiFeO 3 validated a large exchange coupling between them. Additionally, FDTO served as an excellent top electrode for ferroelectric switching in BiFeO3 with no sign of degradation after ~10 10 switching cycles. RT magneto-electric coupling was demonstrated by modulating the resistance states of spin-valve structures using electric fields.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Kinetic analyses for solid-state phase transition of metastable amorphous-AlO x (2.5 < x ≤ 3.0) nanostructures into crystalline alumina polymorphs

Solid-solid phase change materials (SS-PCMs) hold promise for energy storage/dissipation in batteries and energetic materials. Yet, phase change kinetics for SS-PCMs undergoing metastable to semi-stable/stable phase transformations remain relatively ill-studied because trapping metastable phases remain challenging. Recently, we demonstrated the kinetic entrapment and stabilization of a highly disordered and amorphous Al-oxide phase m-AlO x @C (x~2.5-3.0) via laser ablation synthesis in solution (LASiS). We report here, to our knowledge, the first chemical kinetics analysis for S-S phase transition of the m-AlO 3 @C nanocomposites (< 5–8 nm sizes) into semi-stable equilibrium alumina phases (θ/γ-Al 2 O 3 ) via disproportionation reaction, while releasing excess trapped gases. Our results indicate the atomic density of the AlO 3 structures to be ~5–10 times less than that of the final Al 2 O 3 phases, which led to the hypothesis of a volume shrinkage process during their phase transition. Temperature-dependent X-ray diffraction studies reveal the high-temperature phase transition for m-AlO 3 → θ/γ-Al 2 O 3 to follow contracting volume kinetics model, thereby validating our earlier hypothesis. Using the geometric volume contraction model, reaction kinetics analyses from Arrhenius plots reveal the activation energy barrier for the phase transition to be ~270±11 kJ/mol. This makes the activation energy barrier nearly identical to the oxidation of micron-sized Al particles.

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

Ultrasmall amorphous zirconia nanoparticles catalyse polyolefin hydrogenolysis

Carbon–carbon bond cleavage reactions, adapted to deconstruct aliphatic hydrocarbon polymers and recover the intrinsic energy and carbon value in plastic waste, have typically been catalysed by metal nanoparticles or air-sensitive organometallics. Metal oxides that serve as supports for these catalysts are typically considered to be inert. Here we show that Earth-abundant, non-reducible zirconia catalyses the hydrogenolysis of polyolefins with activity rivalling that of precious metal nanoparticles. To harness this unusual reactivity, our catalytic architecture localizes ultrasmall amorphous zirconia nanoparticles between two fused platelets of mesoporous silica. Macromolecules translocate from bulk through radial mesopores to the highly active zirconia particles, where the chains undergo selective hydrogenolytic cleavage into a narrow, C18-centred distribution. Calculations indicated that C–H bond heterolysis across a Zr–O bond of a Zr(O) 2 adatom model for unsaturated surface sites gives a zirconium hydrocarbyl, which cleaves a C–C bond via β-alkyl elimination.

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

Spin-on deposition of amorphous zeolitic imidazolate framework films for lithography applications

Amorphous zeolitic imidazolate framework (aZIF) films have been recently introduced as resists for electron beam and extreme ultraviolet lithography. aZIFs are also being considered for separation applications, including thin film membranes. However, the reported methods for aZIF deposition are currently based on highly empirical trial-and-error approaches that hinder control of film composition, thickness and uniformity as well as scale-up and transferability to different coating geometries. This work presents a method for depositing aZIF films with controllable thickness using dilute precursors mixed immediately before encountering the substrate. Importantly, the method is amenable to quantitative analysis by computational fluid dynamics to extract intrinsic deposition rates and limiting reactant transport diffusivities, enabling predictive physics-based modeling of the deposition process. This allows the deposition method to be adapted for spin coating on silicon wafers to prepare high-quality aZIF films with consistently controlled thickness. Using this approach, high-resolution resist performance and wafer-scale use for beyond extreme-ultraviolet lithography of aZIF films is demonstrated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Hydrogen reverses the clustering tendency of carbon in amorphous silicon oxycarbide

Amorphous silicon oxycarbide (SiOC) is of great technological interest. However, its atomic-level structure is not well understood. Using density functional theory calculations, we show that the clustering tendency of C atoms in SiOC is extremely sensitive to hydrogen (H): without H, the C-C interaction is attractive, leading to enrichment of aggregated SiC 4 tetrahedral units; with hydrogen, the C-C interaction is repulsive, leading to enrichment of randomly distributed SiCO 3 tetrahedral units. Our results suggest that conflicting experimental characterizations of C distributions may be due to differing amounts of H present in the samples investigated. Our work also opens a path for tailoring the properties of SiOC by using the total H content to control the C distribution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Novel Iron-based ternary amorphous oxide semiconductor with very high transparency, electronic conductivity, and mobility

We report that ternary metal oxides of type (Me) 2 O 3 with the primary metal (Me) constituent being Fe (66 atomic (at.) %) along with the two Lanthanide elements Tb (10 at.%) and Dy (24 at.%) can show excellent semiconducting transport properties. Thin films prepared by pulsed laser deposition at room temperature followed by ambient oxidation showed very high electronic conductivity (>5 × 10 4 S/m) and Hall mobility (>30 cm 2 /V-s). These films had an amorphous microstructure which was stable to at least 500 °C and large optical transparency with a direct band gap of 2.85 ± 0.14 eV. This material shows emergent semiconducting behavior with significantly higher conductivity and mobility than the constituent insulating oxides. In conclusion, since these results demonstrate a new way to modify the behaviors of transition metal oxides made from unfilled d- and/or f-subshells, a new class of functional transparent conducting oxide materials could be envisioned.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Cucurbit[7]uril: an Amorphous Molecular Material for Highly Selective Carbon Dioxide Uptake

Cucurbit[7]uril (CB[7]), in its amorphous solid state, shows one of the highest CO2 sorption capacities among the known organic molecular porous materials at 298 K and 0.1~ and 1 bar. Apart from the highest CO2 capacity, CB[7] shows a remarkable selectivity of CO2 over N2 and CH4. These properties along with the readily available precursors makes this materials a very attractive for CO2 sequestration particularly when considering the easy synthesis and low manufacturing costs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Probing the Interaction of Amorphous Solid Water on a Hydrophobic Surface: Dewetting and Crystallization Kinetics of ASW on Carbon Tetrachloride

Desorption of carbon tetrachloride from beneath an amorphous solid water (ASW) overlayer is explored utilizing a combination of temperature programmed desorption and infrared spectroscopy. Otherwise inaccessible information about the dewetting and crystallization of ASW is revealed by monitoring desorption of the CCl4 underlayer. The desorption maximum of CCl4 on graphene occurs at ~140 K. When ASW wets the CCl4 no desorption below 140 K is observed. However, the mobility of the water molecules increases with ASW deposition temperature, leading to a thermodynamically driven dewetting of water from the hydrophobic CCl4 surface. This dewetting exposes some CCl4 to the ambient environment, allowing unhindered desorption of CCl4 below 140 K. When ASW completely covers the underlayer, desorption of CCl4 is delayed until crystallization induced cracking of the ASW overlayer opens an escape path to the surface. The subsequent rapid episodic release of CCl4 is termed a “molecular volcano”. Reflection adsorption infrared spectroscopy (RAIRS) measurements indicate that the onset and duration of the molecular volcano is directly controlled by the ASW crystallization kinetics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Stabilization of Si microwire arrays for solar-driven H 2 O oxidation to O 2 (g) in 1.0 M KOH(aq) using conformal coatings of amorphous TiO 2

In this work, conductive, amorphous TiO 2 coatings deposited by atomic-layer deposition, in combination with a sputter deposited NiCrO x oxygen-evolution catalyst, have been used to protect Si microwire arrays from passivation or corrosion in contact with aqueous electrolytes. Coated np + -Si/TiO 2 /NiCrO x as well as heterojunction n-Si/TiO 2 /NiCrO x Si microwire-array photoanodes exhibited stable photoelectrochemical operation in aqueous ferri-/ferro-cyanide solutions. The coatings also allowed for photoanodic water oxidation in 1.0 M KOH(aq) solutions for >2200 h of continuous operation under simulated 1 Sun conditions with ~100% Faradaic efficiency for the evolution of O 2 (g).

Shaner, Matthew R.↗
DOE OSTI2014

Chemical Bonding In Amorphous Si Coated-carbon Nanotube As Anodes For Li ion Batteries: A XANES Study

The chemical bonding nature and its evolution upon electrochemical cycling in amorphous Si coated-carbon nanotube (Si-CNT) anode has been investigated using comprehensive X-ray absorption spectroscopy (XANES) at Si L- and K-edges along with C and O K-edges. The Si nanolayer on CNT is found to be anchored to CNT via Si-O-C bonding. This bond weakens upon electrochemical cycling accompanied with generation of Li2CO3 on the surface of Si-CNT. Those findings are crucial in designing further improved Si-C composite anode for lithium ion battery.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2015

A monolithically integrated, intrinsically safe, 10% efficient, solar-driven water-splitting system based on active, stable earth-abundant electrocatalysts in conjunction with tandem III–V light absorbers protected by amorphous TiO 2 films

A monolithically integrated device consisting of a tandem-junction GaAs/InGaP photoanode coated by an amorphous TiO 2 stabilization layer, in conjunction with Ni-based, earth-abundant active electrocatalysts for the hydrogen-evolution and oxygen-evolution reactions, was used to effect unassisted, solar-driven water splitting in 1.0 M KOH(aq). When connected to a Ni–Mo-coated counterelectrode in a two-electrode cell configuration, the TiO 2 -protected III–V tandem device exhibited a solar-to-hydrogen conversion efficiency, η STH , of 10.5% under 1 sun illumination, with stable performance for >40 h of continuous operation at an efficiency of η STH > 10%. The protected tandem device also formed the basis for a monolithically integrated, intrinsically safe solar-hydrogen prototype system (1 cm 2 ) driven by a NiMo/GaAs/InGaP/TiO 2 /Ni structure. The intrinsically safe system exhibited a hydrogen production rate of 0.81 μL s –1 and a solar-to-hydrogen conversion efficiency of 8.6% under 1 sun illumination in 1.0 M KOH(aq), with minimal product gas crossover while allowing for beneficial collection of separate streams of H 2 (g) and O 2 (g).

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

Electronic and optical properties of oxygen vacancies in amorphous Ta 2 O 5 from first principles

Oxygen vacancies are important defects considered to play a central role in the electronic and optical properties of tantalum pentoxide (Ta2O5) films and devices. Despite extensive experimental studies on oxygen vacancies in Ta2O5, the reported defect states are ambiguously identified due to the absence of accurate and conclusive theoretical evidence. Here we investigate the thermodynamic, electronic, and optical properties of oxygen vacancies in amorphous Ta2O5 by first-principles calculations based on hybrid-functional density functional theory (DFT). The calculated thermodynamic and optical transition levels are in good agreement with a broad range of diverse measured properties with various experimental methods, providing conclusive evidence for the identification of the defect states observed in experiments as originating from oxygen vacancies. Our calculations also predict the formation of spin-polarized polarons. Our results elucidate the fundamental atomistic properties of oxygen vacancies in various oxidation states as a function of growth conditions and provide guidance to control the properties of Ta2O5 films/devices.

Lee, Jihang↗