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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 1,459 records · Page 81
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Hydrogen migration at restructuring palladium–silver oxide boundaries dramatically enhances reduction rate of silver oxide

Heterogeneous catalysts are complex materials with multiple interfaces. A critical proposition in exploiting bifunctionality in alloy catalysts is to achieve surface migration across interfaces separating functionally dissimilar regions. Herein, we demonstrate the enhancement of more than 10 4 in the rate of molecular hydrogen reduction of a silver surface oxide in the presence of palladium oxide compared to pure silver oxide resulting from the transfer of atomic hydrogen from palladium oxide islands onto the surrounding surface formed from oxidation of a palladium-silver alloy. The palladium-silver interface also dynamically restructures during reduction, resulting in silver-palladium intermixing. This study clearly demonstrates the migration of reaction intermediates and catalyst material across surface interfacial boundaries in alloys with a significant effect on surface reactivity, having broad implications for the catalytic function of bimetallic materials.

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

Understanding of Void Formation in Cu/Sn-Sn/Cu System During Transient Liquid Phase Bonding Process Through Diffusion Modeling

Transient Liquid Phase (TPL) bounding of Sn foil sandwiched between two Cu foils involves, in the temperature range above the melting point of Sn (232 °C) and below 350 °C, the formation and the growth of two intermetallic compounds (IMCs) Cu{sub 6}Sn{sub 5} and Cu{sub 3}Sn and mostly unintended micro-pores. The present study aims to analyze the mechanism of void development during the soldering process through an experimental and modeling approach of diffusion-controlled IMC transformation. This modeling couples the diffusion process and the interface motion with the volume shrinkage induced by the difference of partial molar volumes of atoms between each phase. We also consider two types of inter-diffusion transports: (i) inter-diffusion based on the exchange of Cu and Sn atoms and (ii) inter-diffusion of Sn atoms with vacancies allowing Kirkendall void formation. The simulations of IMC growth performed correspond to a sequence of planar phase layers, where the distinctive scallop morphology of the Cu{sub 6}Sn{sub 5} layer is described through an analytical function allowing to quantify the grain boundary diffusion pathway. We take into account of the volume diffusion mechanism for Cu{sub 3}Sn intermetallic. For Cu{sub 6}Sn{sub 5} intermetallic two mechanisms are considered, volume diffusion and grain boundary diffusion, limited by grain growth. The simulations of IMC growth kinetics, for different transport scenarios, are compared to the experimental evolving morphologies to determine the most likely mechanism of micro-void formation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Long-life LiNi 0.5 Mn 1.5 O 4 /graphite lithium-ion cells with an artificial graphite-electrolyte interface

The high operating voltage of a spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode leads to electrolyte decomposition and accelerated deterioration of the electrode/electrolyte interface in lithium-ion cells. Aggressive side reactions prevent long-term cycling and hinder its practical application. Advanced characterization shows that the high-voltage operation makes the graphite anode react with the electrolyte, particularly with the lithium salt in the electrolyte, resulting in massive active lithium inventory loss and capacity fade. The side reactions at the graphite are identified as the main culprit for the LNMO/graphite full cell decay. Here, we demonstrate that an artificial solid-electrolyte interface layer consisting of an ultra-thin Al 2 O 3 film, generated via atomic layer deposition (ALD) at the graphite surface, can successfully isolate the graphite from the electrolyte and inhibit the undesired reactions. Consequently, the capacity and cycling stability of the LNMO/graphite cell are drastically improved. After 300 cycles, the capacity retention of LNMO/graphite cell increases from 57.7% to 98.6% with the ALD-coated graphite. Furthermore, our findings provide valuable insights into the LNMO/graphite cell degradation and suggest a simple and robust, yet highly effective, approach for the practical viability of high-voltage lithium-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2022

Facile fabrication of 2D material multilayers and vdW heterostructures with multimodal microscopy and AFM characterization

Reliable transfer processes that enable manipulation of two-dimensional (2D) materials, e.g., transition metal dichalcogenides (TMDCs) and MXenes, from one substrate to another has been a necessity for successful device fabrication. Here, with both mechanical exfoliation and chemical vapor deposition (CVD) widely used, a versatile, clean, deterministic, and yet simple transfer technique is highly needed. To address such need, we developed a transfer method that takes advantage of wettability contrast between interfaces without the use of sacrificial layers or chemical processes. More importantly, a setup was developed to carry out this transfer method with high sample selectivity and fine control of the position and orientation of transferred TMDC crystals, a feature required for fabrication of the devices based on vertical 2D heterostructures. Using both exfoliated and CVD grown materials and subsequent atomic force microscopy (AFM), photoluminescence (PL), confocal Raman and tip enhanced Raman spectroscopy (TERS) characterization, we ascertained the quality of interfaces resulting from the transfer process while preserving excellent 2D material integrity. PL and TERS maps revealed nanometer-scale heterogeneities in the interfaces of fabricated heterostructures, which should enable further perfection of the transfer technique. TERS/TEPL information were employed to identify areas suitable for nanodevice fabrication, making the reported transfer and characterization methods ideal for making high quality assembly of 2D heterostructure more accessible, which should facilitate exploration of vertical 2D heterostructures for applications in electronics, batteries, solar cells, and twistronics.

2D material transfer↗
DOE OSTI2018

Imaging Coherent Structural Dynamics with Ultrafast Electron Microscopy

Development of ultrafast electron and X-ray scattering methods has enabled direct routes to probing atomic-scale structural dynamics. This in turn has led to new insight into lattice responses to a variety of dynamic processes associated with phase transformations, electron-lattice correlations, and nanoscale mechanical motion, to name a few. Presently, the most wide-spread approaches involve using table-top, laser-driven electron-scattering chambers or femtosecond (fs) X-ray beamlines to probe dynamics in reciprocal space and, in many instances, over specimen regions that are large relative to unit-cell dimensions and discrete (atomic and nanoscale) structural and morphological defects (e.g., vacancies, line and screw dislocations, grain boundaries, interfaces, etc.). As a result, the transients monitored for relatively large-spot-size reciprocal-space measurements – typically some aspect of a Bragg reflection (intensity, position, width, shape) – may be comprised of a range of responses occurring within the probed region. To directly resolve the role of distinct morphologies and structural features on dynamics associated with the nucleation, emergence, evolution, and decay of coherent phenomena, one would ideally directly image the local, nanoscale behaviors and precisely correlate responses to the nature of the feature. Here, I will show how such effects can be directly probed with ultrafast electron microscopy (UEM). After a brief overview of the operating principles of UEM, I will discuss how we are using real-space imaging to directly visualize coherent structural dynamics in a variety of nanostructured and nanoscale materials.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

Nonclassical Strong Metal–Support Interactions for Enhanced Catalysis

Strong metal–support interaction (SMSI), which encompasses reversible encapsulation and de-encapsulation and modulation of surface adsorption properties, imposes great impacts on the performance of heterogeneous catalysts. Recent development of SMSI has surpassed the prototypical encapsulated Pt-TiO 2 catalyst, affording a series of conceptually novel and practically advantageous catalytic systems. Here, in this work, we provide our perspective on recent progress in nonclassical SMSIs for enhanced catalysis. Unravelling the structural complexity of SMSI necessitates the combination of multiple characterization techniques at different scales. Synthesis strategies leveraging chemical, photonic, and mechanochemical driving forces further expand the definition and application scope of SMSI. Exquisite structure engineering permits elucidation of the interface, entropy, and size effect on the geometric and electronic characteristics. Materials innovation places the atomically thin two-dimensional materials at the forefront of interfacial active site control. A broader space is awaiting exploration, where exploitation of metal–support interactions brings compelling catalytic activity, selectivity, and stability.

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

How Rh surface breaks CO 2 molecules under ambient pressure

Utilization of carbon dioxide (CO 2 ) molecules leads to increased interest in the sustainable synthesis of methane (CH 4 ) or methanol (CH 3 OH). The representative reaction intermediate consisting of a carbonyl or formate group determines yields of the fuel source during catalytic reactions. However, their selective initial surface reaction processes have been assumed without a fundamental understanding at the molecular level. Here, we report direct observations of spontaneous CO 2 dissociation over the model rhodium (Rh) catalyst at 0.1 mbar CO 2 . The linear geometry of CO 2 gas molecules turns into a chemically active bent-structure at the interface, which allows non-uniform charge transfers between chemisorbed CO 2 and surface Rh atoms. By combining scanning tunneling microscopy, X-ray photoelectron spectroscopy at near-ambient pressure, and computational calculations, we reveal strong evidence for chemical bond cleavage of O-CO* with ordered intermediates structure formation of (2 × 2)-CO on an atomically flat Rh(111) surface at room temperature.

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

All-solid-state disordered LiTiS 2 pseudocapacitor

A lithium charge storage mechanism is discovered at the interface of nano-crystallites of LiTiS 2 in the solid state. The surface titanium atoms can be reduced reversibly at higher voltages. Electrochemically, this appears as a pseudocapacitive effect boosting capacity greater than theoretical at high rate with no liquid electrolyte.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Scanning transmission electron microscopy (STEM) study on surface modified CVD diamond/Si(111) film post implanted Fe-B and NiFe-B related to GMR properties

Nanostructure investigation on the post implantation by Fe-B and NiFe-B on CVD diamond/Si(111) film have been studied by means of STEM related to their GMR phenomena. Two samples were investigated carefully, firstly sample is post NiFe-B at E=70keV and dose= 10{sup 15} ions/cm{sup 2} (denoted as A-E3D1). Secondly, is post FeB at E=20 keV and dose= 10{sup 15} ions/cm{sup 2} (denoted as B-E1D1). Based on FPP measurement at room temperature (RT) and H{sub applied} = 8 kOe, A-E3D1 sample has MR ratio almost 80% and MR ratio in B-E1D1 sample is 45%. Based on STEM-EDX investigation, there are two aspects of how MR ratio of A-E3D1 more higher than those of B-E1D1. Firstly, surface nanostructure on the top of A-E3D1 film is more grazing than on the top of B-E1D1. Analysis with Scanning Transmission Electron Microscope (STEM) equipped with Electron Energy Loss Spectroscopy (EELS) the growth of amorphous carbon layer on top of the implanted diamond film with thickness around 100 nm and only 20 nm on the no implanted sample have observed. Boron atoms were found inside the carbon amorphous layer distributed homogenously. Secondly, oxygen content at the interface between diamond film and silicon substrate in sample A-E3D1 was lower than those in B-E1D1 sample. This condition gives the resistance value in A-E3D1 lower than value in B-E1D1. This result is close to the Raman Spectroscopy data measurement which obviously suggests changes on the Raman spectrum due to implantation related to Oxygen excitation from B-E1D1 sample.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Wavelength conversion for single-photon polarization qubits through continuous-variable quantum teleportation

A quantum internet connects remote quantum processors that need to interact and exchange quantum signals over a long distance through photonic channels. However, these quantum nodes operate at the wavelength ranges unsuitable for long-distance transmission. Therefore, quantum wavelength conversion to telecom bands is crucial for long-distance quantum networks based on optical fiber. Here, we propose wavelength conversion devices for single-photon polarization qubits using continuous-variable quantum teleportation that can efficiently convert qubits between near-infrared (780–795 nm suitable for interacting with atomic quantum nodes) and telecom wavelength (1300–1500 nm suitable for long-distance transmission). The teleportation uses entangled photon fields (i.e., nondegenerate two-mode squeezed state) that can be generated by four-wave mixing in a rubidium atomic gas using a diamond configuration of atomic transitions. The entangled fields can be emitted in two orthogonal polarizations with locked relative phase, making them especially suitable for interfacing with single- photon polarization qubits. Furthermore, our work may pave the way for the realization of long-distance quantum networks.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Dislocation content of grain boundary phase junctions and its relation to grain boundary excess properties

In this work, we analyze the dislocation content of grain boundary (GB) phase junctions, i.e., line defects separating two different GB phases coexisting on the same GB plane. While regular GB disconnections have been characterized for a variety of interfaces, GB phase junctions formed by GBs with different structures and different numbers of excess atoms have not been previously studied. We apply a general Burgers circuit analysis to calculate the Burgers vectors b of junctions in two Σ5 Cu boundaries previously simulated with molecular dynamics. The Burgers vectors of these junctions cannot be described by the displacement shift complete (DSC) lattice alone. We show that, in general, the normal component of b is not equal to the difference in the GB excess volumes but contains another contribution from the numbers of GB atoms per unit area ΔN* required to transform one GB phase into another. In the boundaries studied, the latter component dominates and even changes the sign of b. We derive expressions for the normal and tangential components of b in terms of the DSC lattice vectors and the non-DSC part due to ΔN* and additional GB excess properties, including excess volume and shears. These expressions provide a connection between GB phase transformations driven by the GB free energy difference and the motion of GB junctions under applied normal and shear stresses. The proposed analysis quantifies b and therefore makes it possible to calculate the elastic part of the energy of these defects, evaluate their contribution to the nucleation barrier during GB phase transformations, and treat elastic interactions with other defects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Formation of a Nanophase Wetting Layer and Metal Growth on a Semiconductor

Based on the data on the atomic density of a film and degree of its homogeneity during the formation of the interface between 3d transition metals (Cr, Co, Fe, or Cu) and silicon, a new concept of forming a contact between a reactive metal and a semiconductor has been justified. According to this concept, the low-temperature vapor-phase deposition of a metal onto a semiconductor is accompanied by the formation of a two-dimensional nanophase wetting layer of a metal or its mixture with silicon with a thickness of several monolayers, which significantly affects the interface formation and structure. This concept changes a perspective of forming a contact between a metal and a semiconductor substrate: it is necessary to take into account not only the formation of surface phases and clusters and/or the mixing process, but also the effect of elastic wetting of a substrate by the forming phases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

The effect of size and composition on the strength and hardening of Cu–Ni/Nb nanoscale metallic composites

Nanoscale metallic material composites consisting of bilayer and trilayer systems of two and three different metallic alternating layers show significant gains in hardness over monolithic single phase films. One of the main applications of these composites can be as protective coatings to technical components to increase their lifespan acting as a mechanical barrier to the carriers of permanent deformation. In this work, we study the strength of bilayer structures made of alternating layers of niobium (Nb) and copper–nickel (Cu–Ni) alloys. The effect of the layer size and composition on strength and hardening as well as the effect of the metal–alloy interface on the dislocation motion is investigated. The simulations reveal a close relationship between the atomic composition of the alloy and the hardening of the film. The results are also compared with experimental findings on nanopillars made of similar structures, and strong similarities are revealed and discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Experiments Simulations and Diagnostics for Spatial and Temporal Resolution of Liquid Atomization

Progress toward quantitative measurements and simulations of 3D, temporally resolved aerodynamic induced liquid atomization is reported. Columns of water and galinstan (liquid metal at room temperature) are subjected to a step change in relative gas velocity within a shock tube. Breakup morphologies are shown to closely resemble previous observations of spherical drops. The 3D position, size, and velocity of secondary fragments are quantified by a high-speed digital inline holography (DIH) system developed for this measurement campaign. For the first time, breakup dynamics are temporally resolved at 100 kHz close to the atomization zone where secondary drops are highly non-spherical. Experimental results are compared to interface capturing simulations using a combined level set moment of fluid approach (CLSMOF). Initial simulation results show good agreement with observed breakup morphologies and rates of deformation.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Chemical nature of silicon nitride-indium phosphide interface and rapid thermal annealing for InP MISFETs

A rapid thermal annealing (RTA) process in pure N2 or pure H2 was developed for ion-implanted and encapsulated indium phosphide compound semiconductors, and the chemical nature at the silicon nitride-InP interface before and after RTA was examined using XPS. Results obtained from SIMS on the atomic concentration profiles of the implanted silicon in InP before and after RTA are presented, together with electrical characteristics of the annealed implants. Using the RTA process developed, InP metal-insulator semiconductor FETs (MISFETS) were fabricated. The MISFETS prepared had threshold voltages of +1 V, transconductance of 27 mS/mm, peak channel mobility of 1200 sq cm/V per sec, and drain current drift of only 7 percent.

Biedenbender, M. D.↗
NASA NTRS1990

Influence of convection on microstructure

In eutectic growth, as the solid phases grow they reject atoms to the liquid. This results in a variation of melt composition along the solid/liquid interface. In the past, mass transfer in eutectic solidification, in the absence of convection, was considered to be governed only by the diffusion induced by compositional gradients. However, mass transfer can also be generated by a temperature gradient. This is called thermotransport, thermomigration, thermal diffusion or the Soret effect. A theoretical model of the influence of the Soret effect on the growth of eutectic alloys is presented. A differential equation describing the compositional field near the interface during unidirectional solidification of a binary eutectic alloy was formulated by including the contributions of both compositional and thermal gradients in the liquid. A steady-state solution of the differential equation was obtained by applying appropriate boundary conditions and accounting for heat flow in the melt. Following that, the average interfacial composition was converted to a variation of undercooling at the interface, and consequently to microstructural parameters. The results obtained show that thermotransport can, under certain circumstances, be a parameter of paramount importance.

Wilcox, William R.↗
DOE OSTI2020

Low Temperature Activation of Methane on Metal-Oxides and Complex Interfaces: Insights from Surface Science

The abundance of inexpensive, natural gas has transformed the energy landscape, whereby revealing new possibilities for sustainable chemical technologies or impacting those that have relied on traditional fossil fuels. The primary component, methane, is underutilized and wastefully exhausted, leading to anthropogenic global warming. Historically, the manipulation of methane remained “ clavis aurea ,” an insurmountable yet rewarding challenge and thus the focus of intense research. This is primarily due to an inability to dissociate C–H bonds in methane selectively, which requires a high energy penalty and is an essential prerequisite for the direct conversion of methane into a large set of value-added products. The discovery of such processes would promise an energy gainful use of natural gas benefiting several essential chemical processes associated with C1 chemistry. This first C–H bond dissociation step of the methane molecule appears in numerous catalytic mechanisms as the rate-determining step or most essential barrier sequence for all subsequent steps that follow in the production of C–C, C–O, or C x –H y –O z bonds found in value added products. A main goal is to catalytically reduce the energy barrier for the first C–H bond dissociation to be able to achieve the activation of methane at low or moderate temperatures. As such there is great value in understanding the fundamental nature of the active sites responsible for bond breaking or formation and thus be able to facilitate better control of this chemistry, leading to the development of new technologies for fuel production and chemical conversion. Surface science studies offer enhanced perspectives for a careful manipulation of bonds over the last layer atoms of catalyst surfaces, an essential factor for the design of atomically precise catalysts and unravelling of the reaction mechanism. With the advent of new surface imaging, spectroscopy, and in situ tools, it has been possible to decipher the surface chemistry of complex materials systems and further our understanding of atomic active sites on the surfaces of metals, oxides, and carbides or metal–oxide and metal–carbide interfaces. The once considered near impossible step of C–H bond activation is now observed at low temperatures with high propensity over a collection of oxide, metal–oxide, and metal–carbide systems in a conventional or inverse configuration (oxide or carbide on metal). The enabling of C–H activation at low temperature has opened interesting possibilities for the specific production of chemicals such as methanol directly from methane, a step toward facile synthesis of liquid fuels. We highlight the most recent of these results and present the key aspects of active site configurations engineered from surface science studies which enable such a simple reactive event through careful manipulation of the last surface layer of atoms found in the catalyst structure. New concepts which help in the activation and conversion of methane are discussed.

36 MATERIALS SCIENCE↗