Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Atomic Interface”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,765 records · Page 98
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Water reduction by a p-GaInP2 photoelectrode stabilized by an amorphous TiO2 coating and a molecular cobalt catalyst

Producing hydrogen through solar water splitting requires the coverage of large land areas. Abundant metal-based molecular catalysts offer scalability, but only if they match noble metal activities. We report on a highly active p-GaInP2 photocathode protected through a 35-nm TiO2 layer functionalized by a cobaloxime molecular catalyst (GaInP2-TiO2-cobaloxime). This photoelectrode mediates H2 production with a current density of ~9"0mA"0cm-2 at a potential of 0"0V versus RHE under 1-sun illumination at pH"013. The calculated turnover number for the catalyst during a 20-h period is 139,000, with an average turnover frequency of 1.9"0s-1. Bare GaInP2 shows a rapid current decay, whereas the GaInP2-TiO2-cobaloxime electrode shows </=5% loss over 20"0min, comparable to a GaInP2-TiO2-Pt catalyst particle-modified interface. The activity and corrosion resistance of the GaInP2-TiO2-cobaloxime photocathode in basic solution is made possible by an atomic layer-deposited TiO2 and an attached cobaloxime catalyst.

14 SOLAR ENERGY↗
DOE OSTI2020

Copper-zirconia interfaces in UiO-66 enable selective catalytic hydrogenation of CO 2 to methanol

Molecular interactions with both oxides and metals are essential for heterogenous catalysis, leading to remarkable synergistic impacts on activity and selectivity. Here, we show that the direct link between the two phases (and not merely being together) is required to selectively hydrogenate CO 2 to methanol on catalysts containing Cu and ZrO 2 . Materials consisting of isolated Cu particles or atomically dispersed Cu–O–Zr sites only catalyze the reverse watergas shift reaction. In contrast, a metal organic framework structure (UiO-66) with Cu nanoparticles occupying missing-linker defects maximizes the fraction of metallic Cu interfaced to ZrO 2 nodes leading to a material with high adsorption capacity for CO 2 and high activity and selectivity for low-temperature methanol synthesis.

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

Ubiquitous short-range order in multi-principal element alloys

Recent research in multi-principal element alloys (MPEAs) has increasingly focused on the role of short-range order (SRO) on material performance. However, the mechanisms of SRO formation and its precise control remain elusive, limiting the progress of SRO engineering. Here, leveraging advanced additive manufacturing techniques that produce samples with a wide range of cooling rates (up to 10 7 K s –1 ) and an enhanced semi-quantitative electron microscopy method, we characterize SRO in three CoCrNi-based face-centered-cubic (FCC) MPEAs. Surprisingly, irrespective of the processing and thermal treatment history, all samples exhibit similar levels of SRO. Atomistic simulations reveal that during solidification, prevalent local chemical order arises in the liquid-solid interface (solidification front) even under the extreme cooling rate of 10 11 K s –1 . This phenomenon stems from the swift atomic diffusion in the supercooled liquid, which matches or even surpasses the rate of solidification. Therefore, SRO is an inherent characteristic of most FCC MPEAs, insensitive to variations in cooling rates and even annealing treatments typically available in experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Concomitant ion effects on isotope ratio measurements with liquid sampling – atmospheric pressure glow discharge ion source Orbitrap mass spectrometry

RATIONALE: The field of highly accurate and precise isotope ratio (IR) analysis has been dominated by inductively coupled plasma and thermal ionization mass spectrometers. While these instruments are considered the gold standard for IR analysis, the International Atomic Energy Agency desires a field deployable instrument capable of accurately and precisely measuring U isotope ratios. METHODS: The proposed system interfaces the liquid sampling – atmospheric pressure glow discharge (LS-APGD) ion source with a high resolution Exactive Orbitrap mass spectrometer. With this experimental setup certified U isotope standards and unknown samples were analyzed. The accuracy and precision of the system were then determined. RESULTS: The LS-APGD /Exactive instrument measures a certified reference material of natural U (235U/238U = 0.007258) as 0.007041 with a relative standard deviation of 0.158% meeting the International Target Values for Uncertainty for the destructive analysis of U. Additionally, when three unknowns measured and compared to the results from an ICP multi collector instrument, there is no statistical difference between the two instruments. CONCLUSIONS: The LS-APGD / Orbitrap system, while still in the preliminary stages of development, offers highly accurate and precise IR analysis that suggest a paradigm shift in the world of IR analysis. Furthermore, the portability of the LS-APGD as an elemental ion source combined with the low overhead and small size of the Orbitrap suggest that the instrumentation is capable of being field deployable. With liquid sampling glow discharge-Orbitrap MS, isotope ratio and precision performance improves with rejection of concomitant ion species.

atmospheric pressure sampling↗
DOE OSTI2019

Evidence of a purely electronic two-dimensional lattice at the interface of TMD/Bi 2 Se 3 heterostructures

When 2D materials are vertically stacked, new physics emerges from interlayer orbital interactions and charge transfer modulated by the additional periodicity of interlayer atomic registry (moiré superlattice). Surprisingly, relatively little is known regarding the real-space distribution of the transferred charges within this framework. In this paper we provide the first experimental indications of a real-space, non-atomic lattice formed by interlayer coupling induced charge redistribution in vertically stacked Bi 2 Se 3 /transition metal dichalcogenide (TMD) 2D heterostructures. Robust enough to scatter 200 keV electron beams, this non-atomic lattice generates selected area diffraction patterns that correspond excellently with simulated patterns from moiré superlattices of the parent crystals suggesting their location at sites of high interlayer atomic registry. Density functional theory (DFT) predicts concentrated charge pools reside in the interlayer region, located at sites of high nearest-neighbor atomic registry, suggesting the non-atomic lattices are standalone, reside in the interlayer region, and are purely electronic.

2D materials↗
DOE OSTI2013

Surface and interfacial reaction study of half cycle atomic layer deposited HfO{sub 2} on chemically treated GaSb surfaces

An in situ half-cycle atomic layer deposition/X-ray photoelectron spectroscopy (XPS) study was conducted in order to investigate the evolution of the HfO{sub 2} dielectric interface with GaSb(100) surfaces after sulfur passivation and HCl etching, designed to remove the native oxides. With the first pulses of tetrakis(dimethylamido)hafnium(IV) and water, a decrease in the concentration of antimony oxide states present on the HCl-etched surface is observed, while antimony sulfur states diminished below the XPS detection limit on sulfur passivated surface. An increase in the amount of gallium oxide/sulfide is seen, suggesting oxygen or sulfur transfers from antimony to gallium during antimony oxides/sulfides decomposition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Layered insulator hexagonal boron nitride for surface passivation in quantum dot solar cell

Single crystalline, two dimensional (2D) layered insulator hexagonal boron nitride (h-BN), is demonstrated as an emerging material candidate for surface passivation on mesoporous TiO{sub 2}. Cadmium selenide (CdSe) quantum dot based bulk heterojunction (BHJ) solar cell employed h-BN passivated TiO{sub 2} as an electron acceptor exhibits photoconversion efficiency ∼46% more than BHJ employed unpassivated TiO{sub 2}. Dominant interfacial recombination pathways such as electron capture by TiO{sub 2} surface states and recombination with hole at valence band of CdSe are efficiently controlled by h-BN enabled surface passivation, leading to improved photovoltaic performance. Highly crystalline, confirmed by transmission electron microscopy, dangling bond-free 2D layered h-BN with self-terminated atomic planes, achieved by chemical exfoliation, enables efficient passivation on TiO{sub 2}, allowing electronic transport at TiO{sub 2}/h-BN/CdSe interface with much lower recombination rate compared to an unpassivated TiO{sub 2}/CdSe interface.

14 SOLAR ENERGY↗
DOE OSTI2014

Atomic oxidation of large area epitaxial graphene on 4H-SiC(0001)

Structural and electronic properties of epitaxial graphene on 4H-SiC were studied before and after an atomic oxidation process. X-ray photoemission spectroscopy indicates that oxygen penetrates into the substrate and decouples a part of the interface layer. Raman spectroscopy demonstrates the increase of defects due to the presence of oxygen. Interestingly, we observed on the near edge x-ray absorption fine structure spectra a splitting of the π* peak into two distinct resonances centered at 284.7 and 285.2 eV. This double structure smears out after the oxidation process and permits to probe the interface architecture between graphene and the substrate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Superconducting contact and quantum interference between two-dimensional van der Waals and three-dimensional conventional superconductors

Atomically thin two-dimensional (2D) transition-metal dichalcogenide (TMD) superconductors enable uniform, flat, and clean van der Waals tunneling interfaces, motivating their integration into conventional superconducting circuits. However, fully superconducting contact must be made between the 2D material and three-dimensional (3D) superconductors to employ the standard microwave drive and readout of qubits in such circuits. We present a method for creating zero-resistance contacts between 2D NbSe 2 and 3D aluminum that behave as Josephson junctions (JJs) with large effective areas compared to 3D-3D JJs. The devices formed from 2D TMD superconductors are strongly influenced by the geometry of the flakes themselves as well as the placement of the contacts to bulk 3D superconducting leads. We present a model for the supercurrent flow in a 2D-3D superconducting structure by a numerical solution of the Ginzburg-Landau equations and find good agreement with experiment. Finally, these results demonstrate a crucial step towards a new generation of hybrid superconducting quantum circuits.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effect of GaN surface treatment on Al 2 O 3 /n-GaN MOS capacitors

The surface preparation for depositing Al 2 O 3 for fabricating Au/Ni/Al 2 O 3 /n-GaN (0001) metal oxide semiconductor (MOS) capacitors was optimized as a step toward realization of high performance GaN MOSFETs. The GaN surface treatments studied included cleaning with piranha (H 2 O 2 :H 2 SO 4 = 1:5), (NH 4 )(2)S, and 30% HF etches. By several metrics, the MOS capacitor with the piranha-etched GaN had the best characteristics. It had the lowest capacitance-voltage hysteresis, the smoothest Al 2 O 3 surface as determined by atomic force microscopy (0.2nm surface roughness), the lowest carbon concentration (similar to 0.78%) at the Al 2 O 3 /n-GaN interface (from x-ray photoelectron spectroscopy), and the lowest oxide-trap charge (Q(T) = 1.6 x 10(11) cm(-2) eV(-1)). Its interface trap density (D-it = 3.7 x 10(12) cm(-2) eV(-1)), as measured with photon-assisted capacitance- voltage method, was the lowest from conduction band-edge to midgap. (C) 2015 American Vacuum Society.

36 MATERIALS SCIENCE↗
DOE OSTI2021

PYSEQM

PYSEQM is a package for performing semi-empirical quantum mechanical (SEQM) simulations on molecular systems utilizing PyTorch. SEQM simulations determine molecular properties (energy, electron density, dipole moment, ect.) by solving an approximate Schrödinger equation for the motions of electrons in a molecule. The use of PyTorch provides three specific advantages. First, it allows the calculations to be offloaded to GPU accelerators, giving an order of magnitude increase in speed. Second, back propagation is used to get atomic forces (derivative of the total energy with respect to atomic position) at the same computational cost as the energy calculation itself. Finally, the use of PyTorch makes for a natural interface to modern machine learning methods, which can be used to adjust the semi-empirical parameters build into SEQM methods. Additionally, PYSEQM implements various other optimizations for performing quantum mechanics based molecular dynamics, including SP2 for rapid GPU based solution of the self-consistent field algorithm, and the extended Lagrangian method for rapid QM-MD.

Nebgen, Benjamin↗
NASA NTRS1983

Explosive Joining for Nuclear-Reactor Repair

In explosive joining technique, adapter flange from fuel channel machined to incorporate a V-notch interface. Ribbon explosive, 1/2 inch (1.3 cm) in width, drives V-notched wall of adapter into bellows assembly, producing atomic-level metallurgical bond. Ribbon charge yields joint with double parent metal strength.

Bement, L. J.↗
NASA NTRS2009

Graded Index Silicon Geranium on Lattice Matched Silicon Geranium Semiconductor Alloy

A lattice matched silicon germanium (SiGe) semiconductive alloy is formed when a {111} crystal plane of a cubic diamond structure SiGe is grown on the {0001} C-plane of a single crystalline Al2O3 substrate such that a <110> orientation of the cubic diamond structure SiGe is aligned with a <1,0,-1,0> orientation of the {0001} C-plane. A lattice match between the substrate and the SiGe is achieved by using a SiGe composition that is 0.7223 atomic percent silicon and 0.2777 atomic percent germanium. A layer of Si(1-x), ,Ge(x) is formed on the cubic diamond structure SiGe. The value of X (i) defines an atomic percent of germanium satisfying 0.2277<X<1.0,(ii) is approximately 0.2777 where the layer of Si(1-x)Ge(x)interfaces with the cubic diamond structure SiGe, and (iii) increases linearly with the thickness of the layer of Si(1-x)Ge(x).

Park, Yeonjoon↗
DOE OSTI2016

Combined analysis of energy band diagram and equivalent circuit on nanocrystal solid

We investigate a combined analysis of an energy band diagram and an equivalent circuit on nanocrystal (NC) solids. We prepared a flat silicon-NC solid in order to carry out the analysis. An energy band diagram of a NC solid is determined from DC transport properties. Current-voltage characteristics, photocurrent measurements, and conductive atomic force microscopy images indicate that a tunneling transport through a NC solid is dominant. Impedance spectroscopy gives an equivalent circuit: a series of parallel resistor-capacitors corresponding to NC/metal and NC/NC interfaces. The equivalent circuit also provides an evidence that the NC/NC interface mainly dominates the carrier transport through NC solids. Tunneling barriers inside a NC solid can be taken into account in a combined capacitance. Evaluated circuit parameters coincide with simple geometrical models of capacitances. As a result, impedance spectroscopy is also a useful technique to analyze semiconductor NC solids as well as usual DC transport. The analyses provide indispensable information to implement NC solids into actual electronic devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

DE-NE0000533 2015 final report

The objective of this work was to explore the development of advanced metal/ceramic composites with greatly improved radiation tolerance and stability above 500°C. Such composites combine the good properties of glasses (high strength and elastic limit, corrosion resistance) with those of crystals (high toughness, strain hardening). The ceramic component of the composite consisted of a high crystallization temperature amorphous material composed of Si-O-C while the metal component was Fe, chosen as a model material for steel. The potential impact of this work is the development of a new class of ceramic/metal composites that can be adapted for engineering applications, resulting in dramatically improved materials performance for advanced reactors. We observed that the combination of the composite constituents, as well as the interfaces between them, provided significantly enhanced radiation tolerance. Our research showed the SiOC materials to be extremely radiation tolerant up to 20 displacements per atom (dpa) at 600 °C. The composites of SiOC/Fe were also studies and found to be radiation tolerant up to 5 dpa at 300°C The approached used for the synthesis of these composites (physical vapor deposition) allowed for rapid alloy and composite prototype development and was therefore appropriate for the proposed exploratory study. It does not, however, limit the engineering applicability of the class of materials we have investigated because, in engineering practice, the amorphous ceramic can be made by a variety of chemical methods, including pyrolysis, and the amorphous-ceramic/steel composite can be manufactured by ball milling. The need to develop advanced cladding that does not react with hydrogen or other structural materials is urgent considering past accidents at Fukushima. Ceramic composites are therefore a strong option with stream reactions rates orders of magnitude lower than the Ziracloy currently in use. Different from its crystalline counterparts, the conventional concept of point defects does not apply to amorphous ceramics, so these materials are expect to have higher radiation tolerance. Furthermore, the interfaces created between amorphous-ceramics and metals represent a new type of defect sink that also improves the radiation resistance of the composite’s crystalline component. This project has shown that it is possible to develop high temperature irradiation resistant materials that are in critical need for nuclear applications under extreme conditions where in-core materials have to withstand neutron damage and high temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2017

A mass and momentum conserving unsplit semi-Lagrangian framework for simulating multiphase flows

In this work, we present a computational methodology for convection and advection that handles discontinuities with second order accuracy and maintains conservation to machine precision. This method can transport a variety of discontinuous quantities and is used in the context of an incompressible gas–liquid flow to transport the phase interface, momentum, and scalars. The proposed method provides a modification to the three-dimensional, unsplit, second-order semi-Lagrangian flux method of Owkes & Desjardins (JCP, 2014). The modification adds a refined grid that provides consistent fluxes of mass and momentum defined on a staggered grid and discrete conservation of mass and momentum, even for flows with large density ratios. Additionally, the refined grid doubles the resolution of the interface without significantly increasing the computational cost over previous non-conservative schemes. This is possible due to a novel partitioning of the semi-Lagrangian fluxes into a small number of simplices. The proposed scheme is tested using canonical verification tests, rising bubbles, and an atomizing liquid jet.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Copper Defects and Charge Collection in Cadmium Telluride Photovoltaic Devices

In CdTe photovoltaic devices, the CdTe layer must be doped with Cu to reduce its resistivity, increase carrier lifetime, and improve hole transport. However, the Cu concentration is typically very low around the interfaces and within the CdTe layer, making it difficult to determine the influence Cu has on charge transport at the nanoscale; Cu concentrations are difficult to detect due to low ionization probability of Cu atoms [1]. Here, we use synchrotron X-ray microscopy to probe the nanoscale distribution of Cu and correlate it to local charge collection in CdTe photovoltaic devices. We demonstrate Cu segregation around grain boundaries, and, using cross-section charge collection measurements and transport modelling, show recombination center concentration in the CdTe layer dictates the interface at which charge collection occurs. The work gives insights on how Cu distributes in CdTe photovoltaic systems, and an understanding of how these distributions affect charge transport.

Walker, Trumann↗
DOE OSTI2015

Magnetic leverage effects in amorphous SmCo/CoAlZr heterostructures

Although magnetic heterostructures are the basis of many magnetic technologies, the mechanisms involved in magnetization reversals in such structures are not fully understood, especially in amorphous multilayers. Here, we report on the SmCo/CoAlZr system and exploit resonant magnetic x-ray scattering to probe the element specific magnetization reversals. When combined into a tri-layer structure, two different switching fields and reversal mechanisms are observed for the Sm and Co sub-lattices. We argue that the decoupling of the sub-lattices arises from the local distribution of atomic species within the amorphous matrix leading to a strong magnetic leverage effect and exchange pinning. The decoupling arises due to strong interactions between regions of high Co density which span the interface. The relatively sparse interactions between Sm and Co induce a localized pinning of the Co-rich areas, resulting in an exchange bias in minor loops and an enhanced coercivity.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗