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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Surface structure of water from soft X-ray second harmonic generation

The microscopic structure of water’s surface is crucial to many natural and industrial processes, but studying its hydrogen bond (H-bond) network directly remains challenging due to the required interfacial sensitivity of experimental techniques. By leveraging advances in flat liquid sheet microjets and terawatt-scale attosecond soft X-ray pulses from the LCLS X-ray free electron laser, we employed soft X-ray second harmonic generation (SXSHG) spectroscopy to examine the liquid water/vapor interface. SXSHG combines the elemental selectivity of X-ray spectroscopies with the surface selectivity of SHG and gives access to the electronic structure of interfacial species. Here, we show the SXSHG spectrum differs from bulk water’s X-ray absorption, with its peak shifted several eV, indicating a vastly different electronic environment at the interface as compared to the bulk. First-principles electronic structure calculations show the signal is highly sensitive to H-bond interactions, such as water molecules accepting a single H-bond, which are surface abundant.

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

Probing the polar-nonpolar oxide interfaces using resonant x-ray standing wave techniques

Transition metal (TM) oxide heterostructure superlattices have attracted great attention in research communities because of their emergent interfacial phenomena that do not exist in the bulk form. In order to understand the mechanisms that cause these phenomena, it is important to use depth-resolved spectroscopies to study the electronic structure across the buried oxide interfaces. In this review, we focus on the recent applications of standing wave (SW) photoemission (SW-XPS) and resonant inelastic x-ray scattering (SW-RIXS) spectroscopy to study the depth profiles of electronic structure or carriers around the polar-nonpolar oxide interfaces. Here, using the incident photon energies near the TM x-ray absorption resonance, the created SW excitation can enhance the spectral response and certain electronic transitions, providing important insight into the interfacial electronic structure in the energy and real space regimes. Following the background introductions, we describe two SW experiments and demonstrate that the combination of SW-XPS and SW-RIXS has the potential to obtain the depth distribution of electronic/orbital states around the buried interfaces with Angstrom precision.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Electron transfer between sorbed Fe(II) and structural Fe(III) in smectites and its effect on nitrate-dependent iron oxidation by Pseudogulbenkiania sp. strain 2002

Studies have shown interfacial electron transfer (IET) between sorbed Fe(II) and structural Fe(III) in clays, but how such process alters their reactivity has not been investigated. Here we studied nitrate reduction by Fe(II)-sorbed nontronite (NAu-2) and montmorillonite (SWy-2) in the presence of an Fe(II)-oxidizer, Pseudogulbenkiania sp. At pH 6 a similar amount of Fe(II) (~1.4% wt) sorbed onto the basal surface of both clays, but with different extents of IET. For NAu-2, because a large fraction of sorbed Fe(II) remained on unreactive basal surface, its reactivity towards nitrate reduction was low. For SWy-2, IET changed majority of sorbed Fe(II) to structural Fe(II), resulting in a higher reactivity. At pH 8 the amount of edge-sorbed Fe(II) to NAu-2 (2.93%) was lower than that on SWy-2 (4.66%), and IET oxidized the majority of NAu-2 sorbed Fe(II) to Fe(III). The resulting IET-induced structural Fe(II) and the remaining fraction of sorbed-Fe(II) as a “magnetite-like” phase were highly reactive towards nitrate. In contrast, because of isolated Fe(III) atoms within the SWy-2 structure, the extent of IET was limited and the majority of sorbed Fe(II) co-precipitated or was associated with oxidized Fe(III) as mixed Fe(II)-Fe(III) nanoparticles, which was responsible for its highest reactivity towards nitrate reduction.

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

Imaging the Phase Evolution of the Li-N-H Hydrogen Storage System

Complex metal hydrides provide high-density hydrogen storage, which is essential for vehicular applications. However, the utility of these materials has been limited by thermodynamic and kinetic barriers present during the dehydrogenation and rehydrogenation processes as new phases form inside parent phases. Better understanding of the mixed-phase mesostructures and their interfaces may assist in improving cyclability. In this work, the evolution of the phases during hydrogenation of lithium nitride and dehydrogenation of lithium amide with lithium hydride are probed with scanning-transmission X-ray microscopy at the nitrogen K edge. With this technique, intriguing core-shell structures were observed in particles of both partially hydrogenated Li 3 N and partially dehydrogenated LiNH 2 + 2 LiH. The potential contributions of both internal hydrogen mobility and interfacial energies on the generation of these structures are discussed.

08 HYDROGEN↗
NASA NTRS1992

Design for progressive fracture in composite shell structures

The load carrying capability and structural behavior of composite shell structures and stiffened curved panels are investigated to provide accurate early design loads. An integrated computer code is utilized for the computational simulation of composite structural degradation under practical loading for realistic design. Damage initiation, growth, accumulation, and propagation to structural fracture are included in the simulation. Progressive fracture investigations providing design insight for several classes of composite shells are presented. Results demonstrate the significance of local defects, interfacial regions, and stress concentrations on the structural durability of composite shells.

Minnetyan, Levon↗
DOE OSTI2024

Electronic conductivity in metal-graphene composites: the role of disordered carbon structures, defects, and impurities

Abstract This paper explores the transport properties of aluminum-carbon composite material via ab initio methods. Interfacial and electronic dynamics of the aluminum-graphene interface structure were investigated using models of amorphous graphene added to an aluminum matrix. We examine the impact on electronic conduction caused by the presence of nitrogen impurities within the interfacial amorphous graphene layer. We elucidate the conduction mechanisms by using a projection of the electronic conductivity into space.

36 MATERIALS SCIENCE↗
NASA NTRS2005

Pd/CeO2/SiC Chemical Sensors

The incorporation of nanostructured interfacial layers of CeO2 has been proposed to enhance the performances of Pd/SiC Schottky diodes used to sense hydrogen and hydrocarbons at high temperatures. If successful, this development could prove beneficial in numerous applications in which there are requirements to sense hydrogen and hydrocarbons at high temperatures: examples include monitoring of exhaust gases from engines and detecting fires. Sensitivity and thermal stability are major considerations affecting the development of high-temperature chemical sensors. In the case of a metal/SiC Schottky diode for a number of metals, the SiC becomes more chemically active in the presence of the thin metal film on the SiC surface at high temperature. This increase in chemical reactivity causes changes in chemical composition and structure of the metal/SiC interface. The practical effect of the changes is to alter the electronic and other properties of the device in such a manner as to degrade its performance as a chemical sensor. To delay or prevent these changes, it is necessary to limit operation to a temperature <450 C for these sensor structures. The present proposal to incorporate interfacial CeO2 films is based partly on the observation that nanostructured materials in general have potentially useful electrical properties, including an ability to enhance the transfer of electrons. In particular, nanostructured CeO2, that is CeO2 with nanosized grains, has shown promise for incorporation into hightemperature electronic devices. Nanostructured CeO2 films can be formed on SiC and have been shown to exhibit high thermal stability on SiC, characterized by the ability to withstand temperatures somewhat greater than 700 C for limited times. The exchanges of oxygen between CeO2 and SiC prevent the formation of carbon and other chemical species that are unfavorable for operation of a SiC-based Schottky diode as a chemical sensor. Consequently, it is anticipated that in a Pd/CeO2/SiC Schottky diode, the nanostructured interfacial CeO2 layer would contribute to thermal stability and, by contributing to transfer of electrons, would also contribute to sensitivity.

Lu, Weijie↗
DOE OSTI2023

Energy-Resolved Femtosecond Hot Electron Dynamics in Single Plasmonic Nanoparticles

Efficient excitation and harvesting of hot carriers from nanoscale metals is central to many emerging photochemical, photovoltaic, and ultrafast optoelectronic applications. Nevertheless, direct experimental evidence of the energy-dependent femtosecond dynamics in ubiquitous tens-of-nanometer gold structures remains elusive, despite the potentially rich interplay between interfacial and internal plasmonic fields, excitation distributions, and scattering processes. To explore the effects of nanoscale structure on these dynamics, we employ simultaneous time-, angle-, and energy-resolved photoemission spectroscopy of single plasmonic nanoparticles. Photoelectron velocity and electric field distributions reveal bulk-like ballistic hot electron transport in different geometries, lacking any signatures of surface effects. Energy-resolved dynamics are measured in the 1–2 eV range and extrapolated to lower energies via Boltzmann theory, providing a detailed view of hot electron lifetimes within nanoscale gold. Here, we find that particles with relevant dimensions as small as 10 nm serve as exemplary platforms for studying intrinsic metal dynamics.

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

Ambient Ion Trapping and Separations for High Throughput Structurally Selective Material Deposition

While ion mobility coupled to mass spectrometry (IMS/MS) has been increasingly adapted to biological analysis, the structural and molecular specificity offered by IMS/MS has untapped potential for creating novel materials (for energy, catalysis, biomolecular switches etc.) with rationally tailored properties by precisely controlling the chemical structure and composition of these materials. While electrochemical and catalytic properties of the bulk material are understood by mass-selective ion-soft-landing, different structures of one molecule can exhibit distinct properties from the bulk. Many biological phenomenon occur at interfaces and are highly structurally specific. IMS/MS offers means to separate molecules in a sample (which is first ionized and released to gas phase from the condensed phase) based on mass and structure. Species thus separated can potentially be deposited onto surfaces with molecular and structural specificity, to perform fundamental investigations for understanding critical interfacial phenomenon. Key performance metrics for IMS/MS analysis are resolution of separations and sensitivity. Recently developed Structures for Lossless Ion Manipulations (SLIM)4 enabled unprecedented resolution in IMS separations. In addition, high sensitivity was enabled in SLIM due to lossless confinement of ions using radio frequency fields. Thus, SLIM enabled extremely long path length separations (up to 0.1 km thus far) providing efficient separation of molecular ions never before achieved (e.g. isotopologues, D&L amino acids). While SLIM has unprecedented analytical separations power/utility, the use of SLIM platform for depositing mobility and mass selected molecular ions has two specific technological challenges: (a) Pulsed nature of IMS separations and their low duty cycle and (b) the need for a low vacuum of ~4 torr for lossless ion confinement. These limitations lead to long deposition times due to loss of ions generated from the sample. Enabling ion confinement at atmospheric pressure will be path-breaking contribution to the fundamental understanding of ion manipulations and separations and will also enable novel science currently precluded due to the inability of the present technologies to confine ions under ambient conditions. Traditionally used radio frequency fields are ineffective in confining ions at high pressures due to ion/neutral collisions. To address these, we propose to (a) develop methods for confining and manipulating ions for lossless IMS separations at atmospheric pressure enabling high sensitivity and throughput and (b) use the high specificity of IMS/MS and high throughput from ambient ion confinement to perform mobility and mass selective ion deposition at atmospheric pressure. Our goal is to enable the study of the fundamental properties of energy/catalysis materials and biomolecules. This project paves the way for high-throughput, mass and structure selective material deposition for highly specific surface creation/functionalization (discussed in Section 2 of the report). Further, the developments reported continue to push the boundaries of this process to ambient conditions (discussed in Section 3 of the report). We conclude with a list of specific intellectual property and publications which have been the outcome of this funded project.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Evidence for Interfacial Octahedral Coupling as a Route to Enhance Magnetoresistance in Perovskite Oxide Superlattices

Engineering octahedral rotations in oxide heterostructures is a promising route for controlling magnetic properties in perovskites, with recent work focusing on magnetic-ordering temperatures and magnetic anisotropies. Here the effects of interfacial octahedral coupling on magnetoresistance are demonstrated in a series of (La 0.7 Sr 0.3 MnO 3 ) n /(LaFeO 3 ) 10 superlattices grown on (001)- and (111)-oriented SrTiO 3 substrates. The different crystallographic orientations allow for the interfacial octahedral connectivity to be tuned, with weaker interfacial coupling present at the (001)-oriented than the (111)-oriented structures as revealed by density functional theory calculations. In n = 14 superlattices, the effect of orientation on the physical properties is minimal with both (001)- and (111)-oriented samples exhibiting similar magnetoresistance. As the fraction of interfacial volume within the LSMO layers is increased by decreasing n, the magnetoresistive behavior of the samples diverges with significantly larger magnetoresistance magnitudes present in the (111)-oriented superlattices. Furthermore, the results are consistent with octahedral coupling playing a greater role in the functional properties at (111)-heterointerfaces and demonstrate a structure-driven approach to tuning interfacial magnetoresistance in complex-oxide heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Nanometer Scale Imaging to Develop Quantitative Descriptors of Bipolar Membrane Junction Structure

Swings in pH can be achieved by electrically polarizing a bipolar membrane (BPM) to drive water dissociation at the BPM junction for electrochemical conversion and separation processes. BPM junction design is critical to tailor performance for specific applications; however, characterization techniques capable of resolving the nanometer scale physical structure of the junction are limited. We present sample preparation, imaging, and analysis workflows that are adaptable to a variety of BPM junction architectures. Atomic force microscopy produces BPM junction images with nanometer scale lateral resolution for samples with and without a graphene oxide water dissociation catalyst in the junction. Subsequent image segmentation and analysis quantify line edge roughness and catalyst layer thickness as descriptors of junction structure. Comparison of pre- and post-electrodialysis junctions suggests electric field-induced alignment of catalyst particles during electrodialysis. This characterization workflow can inform manufacturing protocols, computational modeling, and failure mode analysis for next-generation BPMs.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Sensitivity of the strength and toughness of concrete to the properties of the interfacial transition zone

We report Civil infrastructure is made primarily of concrete structures or components and therefore understanding durability and fracture behavior of concrete is of utmost importance. Concrete contains an interfacial transition zone (ITZ), a porous region surrounding the aggregates, that is often considered to be the weakest region in the concrete. The ITZ is poorly characterized and property estimates for the ITZ differ considerably. In this simulation study, representative concrete mesostructures are produced by packing coarse aggregates with realistic geometries into a mortar matrix. A meshless numerical method, peridynamics, is utilized to simulate the mechanical response including fracture under uniaxial compression and tension. The sensitivity of the stiffness and fracture toughness of the samples to the ITZ properties is computed, showing strong relationships between the ITZ properties and the effective modulus and effective yield strength of the concrete. These results provides insight into the influence of the poorly characterized ITZ on the stiffness and strength of concrete. This work showcases the applicability of peridynamics to concrete systems, matching experimental strength and modulus values. Additionally, relationships between the ITZ’s mechanical properties and the overall concrete strength and stiffness are presented to enable future design decisions.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Janus skyrmion: Interfacial quasiparticle with two-faced helicity

Janus particles are functional particles with at least two surfaces showing asymmetric properties. Here, we show at the interface between two magnetic regions with different antisymmetric exchange interactions, an alternative species of two-dimensional topological quasiparticles can emerge, in which different helicity structures can coexist. We name such an interfacial quasiparticle a “Janus skyrmion,” in analogy to the Janus particle. As the Janus skyrmion shows helicity asymmetry, its size could vary with both the in-plane and out-of-plane magnetic fields. A vertical spin current could drive the Janus skyrmion into one-dimensional motion along the interface without showing the skyrmion Hall effect, at a speed which depends on both the in-plane spin-polarization direction and current density. Thermal fluctuations could also lead to one-dimensional random walk of a Brownian Janus skyrmion. This work uncovers unique dynamics intrinsic to interfacial quasiparticles with exotic helicity, which may be realized in interface-engineered magnetic layers.

36 MATERIALS SCIENCE↗
DOE OSTI2021

3D Printed, Low Tortuosity Garnet Framework For Beyond 500 Wh/kg Batteries

In this project, we developed LLZO garnet ink recipes and processes for 3D-printing highly ordered ionically conductive garnet porous structures on dense garnet separators. Using this technique, we are able to fabricate controlled architecture LLZO garnet solid-state electrolyte (SSE) trilayers for application in solid-state lithium batteries. The trilayer comprises a thin dense center layer sandwiched between a 3D-printed patterned porous layer and a random porous layer. The dense layer functions as the ionic separator between the anode and cathode. The random porous layer hosts the lithium-metal anode and provides the structural support. The 3D-printed SSE patterned porous layer hosts the cathode, providing continuous, low tortuosity pathways for fast 3D Li+ transport through the cell while increasing the electrode/electrolyte interface area to decrease the interfacial resistance. Compared to the random porous structure, this ordered patterned structure possesses more vacant space for higher cathode loading without sacrificing ionically conducting capability, thus potentially greatly increasing the cell energy density. For demonstration purposes, we developed two patterns for the 3D-printed porous layer: grids and columns, for hosting sulfur and NMC cathode, respectively. The corresponding two types of cells were fabricated and tested, and have demonstrated achievement of theoretical discharge capacity without cathode calendaring. In addition, we developed a fundamental solid-state ionic and electronic transport model to optimize the 3D-printed structures for maximum energy and power density. The model was validated by experiment and provides the critical design criteria for achieving the >500 Wh/kg energy goal as function of C-rate.

25 ENERGY STORAGE↗
NASA NTRS2014

A Coupled Fluid-Structure Interaction Analysis of Solid Rocket Motor with Flexible Inhibitors

A capability to couple NASA production CFD code, Loci/CHEM, with CFDRC's structural finite element code, CoBi, has been developed. This paper summarizes the efforts in applying the installed coupling software to demonstrate/investigate fluid-structure interaction (FSI) between pressure wave and flexible inhibitor inside reusable solid rocket motor (RSRM). First a unified governing equation for both fluid and structure is presented, then an Eulerian-Lagrangian framework is described to satisfy the interfacial continuity requirements. The features of fluid solver, Loci/CHEM and structural solver, CoBi, are discussed before the coupling methodology of the solvers is described. The simulation uses production level CFD LES turbulence model with a grid resolution of 80 million cells. The flexible inhibitor is modeled with full 3D shell elements. Verifications against analytical solutions of structural model under steady uniform pressure condition and under dynamic condition of modal analysis show excellent agreements in terms of displacement distribution and eigen modal frequencies. The preliminary coupled result shows that due to acoustic coupling, the dynamics of one of the more flexible inhibitors shift from its first modal frequency to the first acoustic frequency of the solid rocket motor.

Yang, H. Q.↗
DOE OSTI2023

Characterizing Structure-Dependent TiS 2 /Water Interfaces Using Deep-Neural-Network-Assisted Molecular Dynamics

As a promising layered electrode material, TiS 2 -based capacitive deionization (CDI) devices for water desalination have attracted significant attention. However, TiS 2 /H 2 O interfacial features, potentially important for device optimization, remain unidentified. Using Deep Potential Molecular Dynamics (DPMD), we characterized distinct aqueous interfaces introduced by four TiS 2 terminations expected to be present as water intercalates into TiS 2 , namely, Armchair, Zigzag, Zigzag-L, and Zigzag-R. First, we assessed important representative physical properties of the system to validate the deep potentials (DPs). DPMD simulations agree well with experiments and first-principles simulations, suggesting the DPs are accurate and reliable. Subsequent simulations of these TiS 2 /water interfaces revealed how TiS 2 surface termination influences the structure of interfacial water. This effect is most evident in the first and second water layers close to the TiS 2 surface, and more pronounced when spontaneous dissociative adsorption of water occurs. The extent of water dissociation on each surface was evaluated using enhanced sampling. Zigzag-L is the only interface where proton transfer from adsorbed water to TiS 2 surface S atoms is thermodynamically and kinetically favored. The coexistence of surface four-fold-coordinated Ti (Ti 4c ) and one-fold-coordinated S (S 1c ) is found to be essential to making proton transfer feasible on the Zigzag-L surface. Furthermore, remaining unprotonated S 1c atoms can act as good proton acceptors after water dissociation. Thus, TiS 2 with Zigzag-L termination may be a surface to avoid in CDI device construction, given that pH fluctuations adversely affect performance. Furthermore, this work provides new understanding of TiS 2 /H 2 O interfacial features that could aid future design and optimization of TiS 2 -based CDI devices for water desalination.

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

Ultrafast Switching of Interfacial Thermal Conductance

Dynamical control of thermal transport at the nanoscale provides a time-domain strategy for optimizing thermal management in nanoelectronics, magnetic devices, and thermoelectric devices. However, the rate of change available for thermal switches and regulators is limited to millisecond time scales, calling for a faster modulation speed. Here, in this work, time-resolved X-ray diffraction measurements and thermal transport modeling reveal an ultrafast modulation of the interfacial thermal conductance of an FeRh/MgO heterostructure as a result of a structural phase transition driven by optical excitation. Within 90 ps after optical excitation, the interfacial thermal conductance is reduced by a factor of 5 and lasts for a few nanoseconds, in comparison to the value at the equilibrium FeRh/MgO interface. The experimental results combined with thermal transport calculations suggest that the reduced interfacial thermal conductance results from enhanced phonon scattering at the interface where the lattice experiences transient in-plane biaxial stress due to the structural phase transition of FeRh. Our results suggest that optically driven phase transitions can be utilized for ultrafast nanoscale thermal switches for device application.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Molecularly Mixed Composite Membranes: Challenges and Opportunities

The fabrication of porous molecules, such as metal–organic polyhedra (MOPs), porous organic cages (POCs) and others, has given rise to the potential for creating “solid solutions” of molecular fillers and polymers. Such solid solutions circumvent longstanding interface issues associated with mixed matrix membranes (MMMs), and are referred to as molecularly mixed composite membranes (MMCMs) to distinguish them from traditional two-phase MMMs. Early investigations of MMCMs highlight the advantages of solid solutions over MMMs, including dispersion of the filler, anti-plasticization of the polymer network, and removal of deleterious interfacial issues. However, the exact microscopic structure as well as the transport modality in this new class of membrane are not well understood. Moreover, there are clear engineering challenges that need to be addressed for MMCMs to transition into the field. Finally in this Minireview, the authors outline several scientific and technological challenges associated with the aforementioned questions and their suggestions to tackle them.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗