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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Exploring few and single layer CrPS 4 with near-field infrared spectroscopy

Abstract We combine synchrotron-based near-field infrared spectroscopy and first principles lattice dynamics calculations to explore the vibrational response of CrPS 4 in bulk, few-, and single-layer form. Analysis of the mode pattern reveals a C 2 polar + chiral space group, no symmetry crossover as a function of layer number, and a series of non-monotonic frequency shifts in which modes with significant intralayer character harden on approach to the ultra-thin limit whereas those containing interlayer motion or more complicated displacement patterns soften and show inflection points or steps. This is different from MnPS 3 where phonons shift as 1/size 2 and are sensitive to the three-fold rotation about the metal center that drives the symmetry crossover. We discuss these differences as well as implications for properties such as electric polarization in terms of presence or absence of the P–P dimer and other aspects of local structure, sheet density, and size of the van der Waals gap.

36 MATERIALS SCIENCE↗
NASA NTRS2008

Fabricating Large-Area Sheets of Single-Layer Graphene by CVD

This innovation consists of a set of methodologies for preparing large area (greater than 1 cm(exp 2)) domains of single-atomic-layer graphite, also called graphene, in single (two-dimensional) crystal form. To fabricate a single graphene layer using chemical vapor deposition (CVD), the process begins with an atomically flat surface of an appropriate substrate and an appropriate precursor molecule containing carbon atoms attached to substituent atoms or groups. These molecules will be brought into contact with the substrate surface by being flowed over, or sprayed onto, the substrate, under CVD conditions of low pressure and elevated temperature. Upon contact with the surface, the precursor molecules will decompose. The substituent groups detach from the carbon atoms and form gas-phase species, leaving the unfunctionalized carbon atoms attached to the substrate surface. These carbon atoms will diffuse upon this surface and encounter and bond to other carbon atoms. If conditions are chosen carefully, the surface carbon atoms will arrange to form the lowest energy single-layer structure available, which is the graphene lattice that is sought. Another method for creating the graphene lattice includes metal-catalyzed CVD, in which the decomposition of the precursor molecules is initiated by the catalytic action of a catalytic metal upon the substrate surface. Another type of metal-catalyzed CVD has the entire substrate composed of catalytic metal, or other material, either as a bulk crystal or as a think layer of catalyst deposited upon another surface. In this case, the precursor molecules decompose directly upon contact with the substrate, releasing their atoms and forming the graphene sheet. Atomic layer deposition (ALD) can also be used. In this method, a substrate surface at low temperature is covered with exactly one monolayer of precursor molecules (which may be of more than one type). This is heated up so that the precursor molecules decompose and form one monolayer of the target material.

Bronikowski, Michael↗
DOE OSTI2022

Domain state exchange bias in a single layer FeRh thin film formed via low energy ion implantation

Modern spintronics relies heavily on the exchange bias effect to pin the orientation of ferromagnetic layers in magnetic tunnel junctions. The current implementations of exchange bias in magnetic tunnel junctions employ pristine interfaces between antiferromagnetic and ferromagnetic layers. Here we reveal an interfacial exchange bias introduced by a single-step, low-energy ion implantation process in a single layer FeRh thin film. Both 1 keV He + ions and 5 keV Fe + were investigated, their energy selected to ensure the ions would stop within the FeRh film. The ions reduce the metamagnetic transition temperature through defect generation to form a surface layer with ferromagnetic ordering. Temperature dependent magnetism measurements reveal a room temperature exchange bias between the ferromagnetic surface and the antiferromagnetic bulk of ~41 Oe in 5 keV Fe + implanted samples and ~36 Oe for 1 keV He + implanted samples. We directly scrutinize this exchange bias effect in magnetic depth profiles obtained by polarized neutron reflectometry which clearly show a pinned ferromagnetic layer adjacent to the disordered layer created by low energy Fe + ion implantation. These results reveal a novel method to implement exchange bias in an antiferromagnetic layer that can have direct application in the field of spintronics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1998

Single layer, multi-channel band-gear system for rotary joint

A multi-channel band-gear system for a rotary joint has a ring gear assembly with a conducting ring band in electrical contact with corresponding conducting bands of a set of intermediary planetary gears, which in turn are in electrical contact with a conducting sun band of a sun gear assembly. The ring band is formed with a plurality of conducting segments which are electrically insulated from each other and positioned angularly in a circumferential direction of the ring gear, such that separate electrical power/signal channels are formed across the rotary joint. In a preferred embodiment having continuously connected channels, the ring band has four conducting segments at 90.degree. intervals, the sun band has two conducting segments at 180.degree. intervals, and three planetary bands are in rolling electrical contact at 120.degree. intervals between the ring band segments and the sun band segments, forming two continuously connected channels in a single layer of the band-gear system. Multiple sets of ring gear, planetary gear, and sun gear assemblies may be used in a stacked configuration in a single axial layer to further increase the number of channels provided through the band-gear system.

Kong, Kin Yuen↗
DOE OSTI2021

Electronic properties of single-layer CoO 2 /Au(111)

Here we report direct measurements via angle-resolved photoemission spectroscopy (ARPES) of the electronic dispersion of single-layer (SL) CoO 2 . The Fermi contour consists of a large hole pocket centered at the $\overline{\Gamma}$ point. To interpret the ARPES results, we use density functional theory (DFT) in combination with the multi-orbital Gutzwiller Approximation (DFT+GA), basing our calculations on crystalline structure parameters derived from x-ray photoelectron diffraction and low-energy electron diffraction. Our calculations are in good agreement with the measured dispersion. We conclude that the material is a moderately correlated metal. We also discuss substrate effects, and the influence of hydroxylation on the CoO 2 SL electronic structure.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Correlations between electronic order and structural distortions and their ultrafast dynamics in the single-layer manganite P r 0.5 C a 1.5 Mn O 4

Time-resolved x-ray diffraction experiments on the half-doped single-layered manganite Pr 0.5 Ca 1.5 Mn O 4 are used to monitor the ultrafast photoinduced dynamics of the structural distortion associated with the charge and orbital ordering (CO/OO). As in the nonlayered three-dimensional counterpart, the ordered phase melts in less than 100 fs after 800-nm photoexcitation and subsequently partially recovers due to thermal equilibration of electronic and vibrational systems. Photoexciting Pr 0.5 Ca 1.5 Mn O 4 below the transition temperature of a second structural phase transition that occurs around 146 K (deep inside the CO/OO phase) releases this structural transition, but progresses on a much slower timescale. Finally, this additional reduction of crystal symmetry, which we ascribe to a further tilt of the oxygen octahedra, can thus be considered to be only weakly coupled to CO/OO. Furthermore, static hard-x-ray and resonant soft-x-ray diffraction at the Mn L 2,3 edges experiments identify correlations between structural distortions and electronic order in thermal equilibrium.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Single-Layer Dititanium Oxide Ti 2 O MOene: Multifunctional Promises for Electride, Anode Materials, and Superconductor

Using the first-principles calculations, we report the existence of the single-layer (SL) dititanium oxide Ti 2 O (labeled as MOene) that constructs a novel family of MXene based on transition-metal oxides. This MOene material strongly contrasts the conventional ones consisting of transition-metal carbides and/or nitrides. SL Ti 2 O has high thermal and dynamical stabilities because of the strong Ti–O ionic bonding interactions. Moreover, this material is an intrinsic electride and exhibits extremely low diffusion barriers of ~12.0 and 6.3 meV for Li and Na diffusion, respectively. When applied as anode materials in lithium-ion batteries and sodium-ion batteries, it possesses a high energy storage capacity (960.23 mAhg –1 ), surpassing the traditional MXenes-based anodes. The superb electrochemical performance stems from the existing anionic electron on Ti 2 O surface. Astonishingly, SL Ti 2 O is also determined to be a superconductor with a superconducting transition temperature (T c ) of ~9.8 K, which originates from the soft-mode of the first acoustic phonon branch and enhanced electron–phonon coupling in the low-frequency region. Furthermore, this soft-mode behaves much softer upon applying a compressive strain of 2%, leading to a higher T c of 11.9 K. Furthermore, our finding broadens the family of MXenes and could facilitate more experimental efforts toward future nanodevices.

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

Pt Atomic Single-Layer Catalyst Embedded in Defect-Enriched Ceria for Efficient CO Oxidation

The local coordination structure of metal sites essentially determines the performance of supported metal catalysts. Here, using a surface defect enrichment strategy, we successfully fabricated Pt atomic single-layer (Pt ASL ) structures with 100% metal dispersion and precisely controlled local coordination environment (embedded vs adsorbed) derived from Pt single-atoms (Pt 1 ) on ceria-alumina supports. The local coordination environment of Pt 1 not only governs its catalytic activity but also determines the Pt 1 structure evolution upon reduction activation. For CO oxidation, the highest turnover frequency can be achieved on the embedded Pt ASL in the CeO 2 lattice, which is 3.5 times of that on the adsorbed Pt ASL on the CeO 2 surface and 10–70 times of that on Pt1. The favorable CO adsorption on embedded Pt ASL and improved activation/reactivity of lattice oxygen within CeO 2 effectively facilitate the CO oxidation. This work provides new insights for the precise control of the local coordination structure of active metal sites for achieving 100% atomic utilization efficiency and optimal intrinsic catalytic activity for targeted reactions simultaneously.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Landscape of coexisting excitonic states in the insulating single-layer cuprates and nickelates

We present an ab initio study of the excitonic states of a prototypical high-temperature superconductor La 2 CuO 4 and compare them to the isostructural single-layer nickelate La 2 NiO 4 . A key difference in the low-energy electronic structure leads to very different excitonic behavior. Excitons in La 2 CuO 4 are delocalized and can freely move in the CuO 2 plane without disturbing the antiferromagnetic order. In contrast, in La 2 NiO 4 , we find the low-lying excitonic states to be extremely localized, producing a nearly flat dispersion. The theoretically obtained excitonic dispersion and behavior are in excellent agreement with RIXS observations. To classify the excitons, we project the electron-hole coupling onto each atomic site including the full manifold of atomic orbitals. We find the excitons to be composed of a linear combination of exciton classes, including Mott-Hubbard, d-d, and charge-transfer. The implication of these excitations to the high-T c pairing mechanism is also discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Permeability of Single–Layer–Free–Standing Meshes at Varying Capillary Pressure via a Novel Method

The permeability of mesh wicks is important for various applications, including two–phase heat transfer. However, the understanding of the permeability of single–layer, free–standing mesh wicks, with liquid–gas interfaces on both sides, is limited. A novel and simpler method is presented to determine the permeability of a free–standing wick and apply it to a representative mesh. This method involves modifying the capillary pressure via elevation and simultaneously measuring the permeability to determine the permeability–capillary pressure relationship. When applied to a copper mesh with plain weave having undergone surface cleaning, the permeability is found to decrease as capillary pressure for deionized water increases. A dimensional analysis is presented to generalize this data for other mesh sizes with similar weaves and fluids. The behavior of mesh in application is modeled, based on the integration of Darcy's law with an analytic function fit to measured data, and parametric studies are conducted to investigate the superficial velocity of liquids through the mesh under varying driving pressures, transport lengths, and liquid viscosity, based on the obtained capillary pressure–permeability relationship. This study provides valuable insights into the transport properties of mesh wicks, with potential applications in fields such as electronics cooling, electrochemical devices, and fluid purification technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Single-Layer Magnet Phase in Intrinsic Magnetic Topological Insulators, [MnTe][Bi 2 Te 3 ] n , Far beyond the Thermodynamic Limit

The intrinsic magnetic topological insulator (IMTI) family [MnTe][Bi 2 Te 3 ]n has demonstrated magneto-topological properties dependent on n, making it a promising platform for advanced electronics and spintronics. However, due to technical barriers in sample synthesis, their properties in the large n limit remain unknown. To overcome this, we utilized the atomic layer-by-layer molecular beam epitaxy (ALL-MBE) technique and achieved IMTIs with n as large as 15, far beyond that previously reported in bulk crystals or thin films. Then, we discover that the “single-layer magnet (SLM)” phase, primarily determined by intralayer ferromagnetic coupling, emerges for n > ∼4 and remains little affected up to n = 15. Nonetheless, still, nonzero, interlayer ferromagnetic coupling is necessary to stabilize the SLM phase, suggesting that the SLM phase eventually disappears in the n → ∞ limit. This study uncovers the secrets of IMTIs beyond the thermodynamic limit and opens a door to diverse magneto-topological applications.

2D ferromagnets↗
DOE OSTI2022

Evidence for a spinon Kondo effect in cobalt atoms on single-layer 1T-TaSe 2

Quantum spin liquids are highly entangled, disordered magnetic states that are expected to arise in frustrated Mott insulators and to exhibit exotic fractional excitations such as spinons and chargons. Despite being electrical insulators, some quantum spin liquids are predicted to exhibit gapless itinerant spinons that yield metallic behaviour in the charge-neutral spin channel. For this study, we deposited isolated magnetic atoms onto single-layer 1T-TaSe 2 , a candidate gapless spin liquid, to probe how itinerant spinons couple to impurity spin centres. Using scanning tunnelling spectroscopy, we observe the emergence of new, impurity-induced resonance peaks at the 1T-TaSe 2 Hubbard band edges when cobalt adatoms are positioned to have maximal spatial overlap with the local charge distribution. These resonance peaks disappear when the spatial overlap is reduced or when the magnetic impurities are replaced with nonmagnetic impurities. Theoretical simulations of a modified Anderson impurity model show that the observed peaks are consistent with a Kondo resonance induced by spinons combined with spin-charge binding effects that arise due to fluctuations of an emergent gauge field.

36 MATERIALS SCIENCE↗
DOE OSTI2021

High temperature fracture toughness of single-layer CrAlN and CrAlSiN hard coatings

Hardness and toughness are among of the most important physical properties of hard coatings and it is important to analyze them at temperatures present during coating applications. CrAlN and CrAlSiN are hard coating materials frequently used in high temperature applications. Here, while both possess high oxidation resistance and thermal stability, they differ in their microstructure. In this work, the fracture toughness of magnetron-sputtered single-layer CrAlN and CrAlSiN hard coatings was determined up to 700 °C by in-situ scanning electron microscopy micro-cantilever deflection tests. The results show a decreasing trend of the fracture toughness with increasing temperature. While both coatings' fracture toughness trends are similar up to 400 °C, they diverge at higher temperatures. In general, the evolution of the fracture toughness with increasing temperature shows similarities to the observed changes in hardness in the same temperature range.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Template‐Directed Growth of Palladium Nanoparticles in Holey Single‐Layer Graphene for High‐Performance Room‐Temperature Hydrogen Sensing

Holey graphene (HG), formed by introducing nanoscale perforations into graphene sheets, combines the structural advantages of continuous sp 2 conjugation with the beneficial effects of high surface area and enhanced chemical reactivity associated with nanoscopic holes. Conventional HG fabrication methods often rely on harsh oxidative treatments that compromise graphene's intrinsic electronic properties by disrupting its sp 2 conjugation. A new approach is introduced to fabricate HG directly from single-layer graphene (SLG), using two-dimensional covalent organic frameworks (COFs) as a template followed by controlled oxygen plasma etching. This method preserves the integrity of the SLG's sp 2 network while producing well-defined holes with an average diameter of 2.7 nm. These hole edges act as reactive sites that facilitate the confined, autoreductive growth of palladium nanoparticles (PdNPs) without external reducing agents. The confined hole geometry prevents NP agglomeration and ensures a uniform size distribution. The resulting Pd@HG hybrid exhibits exceptional chemiresistive hydrogen sensing characteristics, including ultrahigh sensitivity, low detection limits, rapid response and recovery, and long-term stability under both dry and humid conditions. Mechanistic investigations reveal a two-step sensing process involving surface redox interactions and hydrogen absorption into the PdNP lattices. This strategy presents a scalable platform for integrating metal NPs within conductive carbon frameworks for advanced sensing applications.

chemical vapor deposition↗
DOE OSTI2025

Selective mass scaling for single-layer thick shell elements in DYNA3D

Hexahedral elements can be adapted to model thin and moderately thick structures by neglecting the coupling of through-thickness stress, resulting in a fully three-dimensional, but simplified, state of stress. These specialized elements, often referred to as “thick” or “solid” shells, are generally employed to model thin-walled structures using continuum mechanics-based material models. In explicit dynamics simulations, where computational speed is important, these elements are integrated with a single quadrature point and a set of anti-hourglassing (stabilizing) forces. Thick shells, by definition, have a thickness dimension smaller than their in-plane dimensions, and this small thickness often determines the stable time step size in simulations, despite the mechanics being approximated. To alleviate this limitation while retaining the relevant dynamics of thin-walled structures, selective mass scaling (SMS), or selective mass “augmentation,” has been proposed in the literature. In this technical report, we explore the application of SMS to single-layer thick shells in the simulation software DYNA3D.

42 ENGINEERING↗
DOE OSTI2020

Strong correlations and orbital texture in single-layer 1T-TaSe2

© 2020, The Author(s), under exclusive licence to Springer Nature Limited. Strong electron correlation can induce Mott insulating behaviour and produce intriguing states of matter such as unconventional superconductivity and quantum spin liquids. Recent advances in van der Waals material synthesis enable the exploration of Mott systems in the two-dimensional limit. Here we report characterization of the local electronic properties of single- and few-layer 1T-TaSe2 via spatial- and momentum-resolved spectroscopy involving scanning tunnelling microscopy and angle-resolved photoemission. Our results indicate that electron correlation induces a robust Mott insulator state in single-layer 1T-TaSe2 that is accompanied by unusual orbital texture. Interlayer coupling weakens the insulating phase, as shown by reduction of the energy gap and quenching of the correlation-driven orbital texture in bilayer and trilayer 1T-TaSe2. This establishes single-layer 1T-TaSe2 as a useful platform for investigating strong correlation physics in two dimensions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

On-Chip Single-Layer Integration of Diamond Spins with Microwave and Plasmonic Channels

On-chip scalable integration represents a major challenge for practical quantum devices. One particular challenge is to implement on-chip optical readout of spins in diamond. This readout requires simultaneous application of optical and microwave fields along with the efficient collection of fluorescence. These requirements are typically met using bulk optical components and dedicated microwave lines. Here, we experimentally demonstrate an on-chip integrated interface for diamond nitrogen vacancy (NV) spin-state preparation and readout, implemented in a planar single layer with only one patterning step. A nanodiamond with NV centers is positioned inside a v-groove waveguide milled in a thick gold film. The gold film carries the microwave control signal, while the v-groove acts as a fluorescence collector and, potentially, as an integrated pump filter. Hence, the device dimensions and fabrication complexity are substantially reduced. Our approach fosters further development of ultracompact nanoscale quantum sensors and quantum information processing devices on a monolithic platform.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗