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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Epitaxial Metal Electrodeposition Controlled by Graphene Layer Thickness

Control over material structure and morphology during electrodeposition is necessary for material synthesis and energy applications. One approach to guide crystallite formation is to take advantage of epitaxy on a current collector to facilitate crystallographic control. Single-layer graphene on metal foils can promote “remote epitaxy” during Cu and Zn electrodeposition, resulting in growth of metal that is crystallographically aligned to the substrate beneath graphene. However, the substrate–graphene–deposit interactions that allow for epitaxial electrodeposition are not well understood. Here, we investigate how different graphene layer thicknesses (monolayer, bilayer, trilayer, and graphite) influence the electrodeposition of Zn and Cu. Scanning transmission electron microscopy and electron backscatter diffraction are leveraged to understand metal morphology and structure, demonstrating that remote epitaxy occurs on mono- and bilayer graphene but not trilayer or thicker. Density functional theory (DFT) simulations reveal the spatial electronic interactions through thin graphene that promote remote epitaxy. This work advances our understanding of electrochemical remote epitaxy and provides strategies for improving control over electrodeposition.

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

Enantioselective Allenoate-Claisen Rearrangement Using Chiral Phosphate Catalysts

Herein we report the first highly enantioselective allenoate-Claisen rearrangement using doubly axially chiral phosphate sodium salts as catalysts. This synthetic method provides access to β-amino acid derivatives with vicinal stereocenters in up to 95% ee. We also investigated the mechanism of enantioinduction by transition state (TS) computations with DFT as well as statistical modeling of the relationship between selectivity and the molecular features of both the catalyst and substrate. The mutual interactions of charge-separated regions in both the zwitterionic intermediate generated by reaction of an amine to the allenoate and the Na + -salt of the chiral phosphate leads to an orientation of the TS in the catalytic pocket that maximizes favorable noncovalent interactions. Crucial arene-arene interactions at the periphery of the catalyst lead to a differentiation of the TS diastereomers. Finally, these interactions were interrogated using DFT calculations and validated through statistical modeling of parameters describing noncovalent interactions.

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

Adjusting the Criteria for Hydrogen Evolution by Single-Atom Catalysts

Downsizing noble metal catalysts is essential for improving atomic efficiency in sustainable energy applications. Typically, strategies focus on anchoring atomically scaled catalysts onto heteroatom-rich substrates, but these interactions can unintentionally alter the electronic structure of the catalyst, complicating the hydrogen evolution reaction (HER) mechanism. This study focuses on elucidating the interfacial mechanism of HER using structurally well-defined platinum single-atom (Pt SA) electrocatalysts. Unlike chemically reduced SAs, electrochemically deposited Pt SA catalysts do not rely on strong support interactions. As a result, these isolated Pt atoms can potentially achieve the theoretical maximum hydrogen production efficiency. This work introduces electrocatalysts composed solely of true SA sites, clarifying previous ambiguities surrounding the concept of SA electrocatalysis.

adsorption↗
DOE OSTI2018

Structures of chaperone-substrate complexes docked onto the export gate in a type III secretion system

The flagellum and the injectisome enable bacterial locomotion and pathogenesis, respectively. These nanomachines assemble and function using a type III secretion system (T3SS). Exported proteins are delivered to the export apparatus by dedicated cytoplasmic chaperones for their transport through the membrane. The structural and mechanistic basis of this process is poorly understood. Here we report the structures of two ternary complexes among flagellar chaperones (FliT and FliS), protein substrates (the filament-capping FliD and flagellin FliC), and the export gate platform protein FlhA. The substrates do not interact directly with FlhA; however, they are required to induce a binding-competent conformation to the chaperone that exposes the recognition motif featuring a highly conserved sequence recognized by FlhA. The structural data reveal the recognition signal in a class of T3SS proteins and provide new insight into the assembly of key protein complexes at the export gate.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Hydrogen bonding structure of confined water templated by a metal-organic framework with open metal sites

Abstract Water in confinement exhibits properties significantly different from bulk water due to frustration in the hydrogen-bond network induced by interactions with the substrate. Here, we combine infrared spectroscopy and many-body molecular dynamics simulations to probe the structure and dynamics of confined water as a function of relative humidity within a metal-organic framework containing cylindrical pores lined with ordered cobalt open coordination sites. Building upon the agreement between experimental and theoretical spectra, we demonstrate that water at low relative humidity binds initially to open metal sites and subsequently forms disconnected one-dimensional chains of hydrogen-bonded water molecules bridging between cobalt atoms. With increasing relative humidity, these water chains nucleate pore filling, and water molecules occupy the entire pore interior before the relative humidity reaches 30%. Systematic analysis of rotational and translational dynamics indicates heterogeneity in this pore-confined water, with water molecules displaying variable mobility as a function of distance from the interface.

Science & Technology - Other Topics↗
DOE OSTI2023

Selective hydrogenation via precise hydrogen bond interactions on catalytic scaffolds

Abstract The active site environment in enzymes has been known to affect catalyst performance through weak interactions with a substrate, but precise synthetic control of enzyme inspired heterogeneous catalysts remains challenging. Here, we synthesize hyper-crosslinked porous polymer (HCPs) with solely -OH or -CH 3 groups on the polymer scaffold to tune the environment of active sites. Reaction rate measurements, spectroscopic techniques, along with DFT calculations show that HCP-OH catalysts enhance the hydrogenation rate of H-acceptor substrates containing carbonyl groups whereas hydrophobic HCP- CH 3 ones promote non-H bond substrate activation. The functional groups go beyond enhancing substrate adsorption to partially activate the C = O bond and tune the catalytic sites. They also expose selectivity control in the hydrogenation of multifunctional substrates through preferential substrate functional group adsorption. The proposed synthetic strategy opens a new class of porous polymers for selective catalysis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Solution epitaxy of polarization-gradient ferroelectric oxide films with colossal photovoltaic current

Solution growth of single-crystal ferroelectric oxide films has long been pursued for the low-cost development of high-performance electronic and optoelectronic devices. However, the established principles of vapor-phase epitaxy cannot be directly applied to solution epitaxy, as the interactions between the substrates and the grown materials in solution are quite different. Here, we report the successful epitaxy of single-domain ferroelectric oxide films on Nb-doped SrTiO 3 single-crystal substrates by solution reaction at a low temperature of ~200 o C. The epitaxy is mainly driven by an electronic polarization screening effect at the interface between the substrates and the as-grown ferroelectric oxide films, which is realized by the electrons from the doped substrates. Atomic-level characterization reveals a nontrivial polarization gradient throughout the films in a long range up to ~500 nm because of a possible structural transition from the monoclinic phase to the tetragonal phase. This polarization gradient generates an extremely high photovoltaic short-circuit current density of ~2.153 mA/cm 2 and open-circuit voltage of ~1.15 V under 375 nm light illumination with power intensity of 500 mW/cm 2 , corresponding to the highest photoresponsivity of ~4.306×10 -3 A/W among all known ferroelectrics. Our results establish a general low-temperature solution route to produce single-crystal gradient films of ferroelectric oxides and thus open the avenue for their broad applications in self-powered photo-detectors, photovoltaic and optoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Chiral molecules and the electron spin

The electron’s spin is necessary to the stability of matter, and control over the spin opens up avenues for manipulating the properties of molecules and materials. The Pauli exclusion principle requires that two electrons in a single spatial eigenstate have opposite spins, and this fact dictates basic features of atomic states and chemical bond formation. The energy associated with interacting electron clouds changes with their relative spin orientation, and by manipulating the spin directions, one can guide chemical transformations. However, controlling the relative spin orientation of electrons located on two reactants (atoms, molecules or surfaces) has proved challenging. Recent developments based on the chiral-induced spin selectivity (CISS) effect show that the spin orientation is linked to molecular symmetry and can be controlled in ways not previously imagined. For example, the combination of chiral molecules and electron spin opens up a new approach to (enantio)selective chemistry. Our Review describes the theoretical concepts underlying the CISS effect and illustrates its importance by discussing some of its manifestations in chemistry, biology and physics. Specifically, we discuss how the CISS effect allows for efficient long-range electron transfer in chiral molecules and how it affects biorecognition processes. Several applications of the effect are presented, and the importance of controlling relative spin orientations in multi-electron processes, such as electrochemical water splitting, is emphasized. We describe the enantiospecific interaction between ferromagnetic substrates and chiral molecules and how it enables the separation of enantiomers with ferromagnets. Lastly, we discuss the relevance of CISS effects to biological electron transfer, enantioselectivity and CISS-based spintronics applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Operando investigations of the solid electrolyte interphase in the lithium mediated nitrogen reduction reaction

The lithium-mediated nitrogen reduction reaction (Li-NRR) represents a promising approach for electrochemical nitrogen activation, in which the solid electrolyte interphase (SEI) layer formed on the electrochemically plated lithium plays a key role. Herein, we used time-resolved, operando, grazing incidence wide-angle X-ray scattering (GI WAXS) to identify SEI species and reaction intermediates in the Li-NRR, comparing LiBF 4 and LiClO 4 as electrolyte salts. In this study, we demonstrated how the SEI composition influences the Li-NRR performance by regulating proton transport to the plated Li. When LiBF 4 is used as the electrolyte salt, the formation of LiF and lithium ethoxide (LiEtO) is observed. Reaction intermediates such as LiH and LiN x H y species were found and provide insight into reaction pathways towards undesired and desired products, respectively. Observed restructuring of the Cu (111) single crystal substrate also indicates interaction with plated Li that could possibly influence the Li-NRR performance. Together, these experiments give molecular insight into how to design Li-NRR systems and their SEI layers for optimal performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

2D materials-assisted heterogeneous integration of semiconductor membranes toward functional devices

Heterogeneous integration techniques allow the coupling of highly lattice-mismatched solid-state membranes, including semiconductors, oxides, and two-dimensional materials, to synergistically fuse the functionalities. The formation of heterostructures generally requires two processes: the combination of crystalline growth and a non-destructive lift-off/transfer process enables the formation of high-quality heterostructures. Although direct atomic interaction between the substrate and the target membrane ensures high-quality growth, the strong atomic bonds at the substrate/epitaxial film interface hinder the non-destructive separation of the target membrane from the substrate. Alternatively, a 2D material-coated compound semiconductor substrate can transfer the weakened (but still effective) surface potential field of the surface through the 2D material, allowing both high-quality epitaxial growth and non-destructive lift-off of the grown film. This Perspective reviews 2D/3D heterogeneous integration techniques, along with applications of III–V compound semiconductors and oxides. Here, the advanced heterogeneous integration methods offer an effective method to produce various freestanding membranes for stackable heterostructures with unique functionalities that can be applied to novel electrical, optoelectronic, neuromorphic, and bioelectronic systems.

2D materials↗
DOE OSTI2019

Tailoring the growth and electronic structures of organic molecular thin films

In the rapidly developing electronics industry, it has become increasingly necessary to explore materials that are cheap, flexible and versatile which have led to significant research efforts towards organic molecular thin films. Organic molecules are unique compared to their inorganic atomic counterparts as their properties can be tuned drastically through chemical functionalization, offering versatility, though their extended shape and weak intermolecular interactions bring significant challenges to the control of both the growth and the electronic structures of molecular thin films. Herein, we will review the self-assembly process and how to establish long-range ordered organic molecular thin films. We will also discuss how the electronic structures of thin films are impacted by the molecule’s local electrostatic environment and its interaction with the substrate, within the context of controlling interfacial energy level alignment between organic semiconductors and electrodes in electronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2025

First Limits on Light Dark Matter Interactions in a Low Threshold Two-Channel Athermal Phonon Detector from the TESSERACT Collaboration

We present results of a search for spin-independent dark matter-nucleus interactions in a 1 cm 2 by 1 mm thick (0.233 g) high-resolution silicon athermal phonon detector operated above ground. For interactions in the substrate, this detector achieves an rms baseline energy resolution of 361.5⁢(4) m⁢ eV (statistical error), the best for any athermal phonon detector to date. With an exposure of 0.233 g ×12 hours, we place the most stringent constraints on dark matter masses between 44 and 87 M⁢ eV/c 2 , with the lowest unexplored cross section of 4⁢ × 10 −32 c⁢m 2 at 87 M⁢ eV/c 2 . We employ a conservative salting technique to reach the lowest dark matter mass ever probed via direct detection experiment. This constraint is enabled by two-channel rejection of low energy backgrounds that are coupled to individual sensors.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Interfacial triferroicity in monolayer chromium dihalide

Couplings between different ferroics in two-dimensional (2D) materials, with atomic thickness and van der Waals surface, have been long sought but not yet realized. We show the first-principles evidence of unique triferroic couplings in recently synthesized CrI 2 monolayer. Its ferroelasticity with a low switching barrier stems from the Jahn-Teller effect. When coupled with the interaction of a substrate, a type of interfacial ferroelectricity with direction determined by the ferroelastic states can emerge which can be switched following the same low-barrier pathway of ferroelastic switching. The direction of its striped antiferromagnetism is also governed by its ferroelastic states, leading to a coupling of ferroelasticity, ferroelectricity, and magnetism. Such mechanism of multiferroic couplings, denoted as interfacial Jahn-Teller triferroicity, can be applied to other 2D materials such as CuC l2 and their Janus monolayers, enabling electrical manipulation of spintronics for efficient nonvolatile random-access memories.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Highly selective Si 3 N 4 /SiO 2 etching using an NF 3 /N 2 /O 2 /H 2 remote plasma. I. Plasma source and critical fluxes

Highly selective plasma etching of silicon nitride (Si 3 N 4 ), while not etching silicon dioxide (SiO 2 ), is a critical step in the fabrication of microelectronics devices. In many applications, this etching must be damage-free and isotropic, which then motivates the use of remote plasmas where the reactants interacting with the substrate are dominantly neutral species. In this paper and Paper II, mechanisms for highly selective Si 3 N 4 etching in remote plasmas are discussed based on results from experiments and simulations. It has been shown experimentally that high Si 3 N 4 /SiO 2 etch selectivity (≈380) can be achieved in the downstream effluent of an NF 3 /N 2 /O 2 /H 2 plasma. The authors found that H2 plays a principal role in the reaction mechanism as Si 3 N 4 /SiO 2 selectivity shows a sharp maximum as a function of the H2 flow rate. Based on this observation, and measured densities of F-atoms and H2 in the process chamber, a mechanism of selective Si 3 N 4 /SiO 2 etching is proposed in which HF molecules in vibrationally excited states accelerate etching reactions. A reaction mechanism for NF 3 /N 2 /O 2 /H 2 plasmas and its afterglow was developed to computationally determine the species densities and fluxes on the wafer level, validated by comparing with experimentally measured F-atom and H 2 densities. The calculated species densities and fluxes were used as input to an analytical model of Si 3 N 4 and SiO 2 etching based on the results of quantum chemistry simulations. This paper presents experimental results (etching data and species densities), the reaction mechanism for NF 3 /N 2 /O 2 /H 2 plasmas, and the results of simulations of gas phase chemistry. Quantum chemistry simulations of elementary etching reactions, description of the analytical model of Si 3 N 4 and SiO 2 etching, calculations of the etch rates, and Si 3 N 4 and SiO 2 selectivity with this model are presented in Paper II.

42 ENGINEERING↗
DOE OSTI2017

Thermal stability of Pt nanoclusters interacting to carbon sublattice

The catalytic activity of Pt clusters is dependent not only on the nanoparticle size and its composition, but also on its internal structure. To determine the real structure of the nanoparticles used in catalysis, the boundaries of the thermal structure stability of Pt clusters to 8.0 nm in diameter interacting with carbon substrates of two types: a fixed α-graphite plane and a mobile substrate with the diamond structure. The effect of a substrate on the processes melting of Pt nanoclusters is estimated. The role of the cooling rate in the formation of the internal structure of Pt clusters during crystallization is studied. The regularities obtained in the case of “free” Pt clusters and Pt clusters on a substrate are compared. It is concluded that platinum nanoparticles with diameter D ≤ 4.0 nm disposed on a carbon substrate conserve the initial fcc structure during cooling.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Perspective–The Elusive Quantum Anomalous Hall Effect in MnBi 2 Te 4 : Materials

Observation of the quantum anomalous Hall effect (QAHE) in MnBi 2 Te 4 flakes is one of the most exciting results in the study of the intrinsic magnetic topological insulator MnBi 2 Te 4 and related compounds. However, reproducing this fascinating result has been found to be challenging. The quality of starting MnBi 2 Te 4 single crystals is believed to be the key factor. An interesting and important question to address is what is the right quality to enable the QAHE. In this perspective, we present possible approaches to tuning the magnetic and topological properties of MnBi 2 Te 4 by using lattice imperfections, strain, stacking sequence, and interactions between the substrate and flakes/films. It is of critical importance to eventually identify the factor(s) responsible for the realization of QAHE. This paper is part of the JES/JSS Joint Focus Issue In Honor of John Goodenough: A Centenarian Milestone.

36 MATERIALS SCIENCE↗
DOE OSTI2024

maranasgroup/yeastsMFA

The parameterization of kinetic models requires measurement of fluxes and/or metabolite levels for a base strain and a few genetic perturbations thereof. Unlike stoichiometric models that are mostly invariant to the specific strain, it remains unclear whether kinetic models constructed for different strains of the same species have similar or significantly different kinetic parameters. This important question underpins the applicability range and prediction limits of kinetic reconstructions. To this end, herein we parameterize two separate large-scale kinetic models using K-FIT with genome-wide coverage corresponding to two distinct strains of Saccharomyces cerevisiae: CEN.PK 113-7D strain (model k-sacce306-CENPK), and growth-deficient BY4741 (isogenic to S288c; model k-sacce306-BY4741). The metabolic network for each model contains 306 reactions, 230 metabolites, and 119 substrate-level regulatory interactions. The two models (for CEN.PK and BY4741) recapitulate, within one standard deviation, 77% and 75% of the fitted dataset fluxes, respectively, determined by 13C metabolic flux analysis for wild-type and eight single-gene knockout mutants of each strain. Strain-specific kinetic parameterization results indicate that key enzymes in the TCA cycle, glycolysis, and arginine and proline metabolism drive the metabolic differences between these two strains of S. cerevisiae. Our results suggest that although kinetic models cannot be readily used across strains as stoichiometric models, they can capture species-specific information through the kinetic parameterization process.

Dinh, Hoang↗