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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Emergence of electric-field-tunable interfacial ferromagnetism in 2D antiferromagnet heterostructures

Van der Waals (vdW) magnet heterostructures have emerged as new platforms to explore exotic magnetic orders and quantum phenomena. Here, we study heterostructures of layered antiferromagnets, CrI 3 and CrCl 3 , with perpendicular and in-plane magnetic anisotropy, respectively. Using magneto-optical Kerr effect microscopy, we demonstrate out-of-plane magnetic order in the CrCl 3 layer proximal to CrI 3 , with ferromagnetic interfacial coupling between the two. Such an interlayer exchange field leads to higher critical temperature than that of either CrI 3 or CrCl 3 alone. We further demonstrate significant electric-field control of the coercivity, attributed to the naturally broken structural inversion symmetry of the heterostructure allowing unprecedented direct coupling between electric field and interfacial magnetism. These findings illustrate the opportunity to explore exotic magnetic phases and engineer spintronic devices in vdW heterostructures.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Panoramic Mapping of Phonon Transport from Ultrafast Electron Diffraction and Scientific Machine Learning

Abstract One central challenge in understanding phonon thermal transport is a lack of experimental tools to investigate frequency‐resolved phonon transport. Although recent advances in computation lead to frequency‐resolved information, it is hindered by unknown defects in bulk regions and at interfaces. Here, a framework that can uncover microscopic phonon transport information in heterostructures is presented, integrating state‐of‐the‐art ultrafast electron diffraction (UED) with advanced scientific machine learning (SciML). Taking advantage of the dual temporal and reciprocal‐space resolution in UED, and the ability of SciML to solve inverse problems involving coupled Boltzmann transport equations, the frequency‐dependent interfacial transmittance and frequency‐dependent relaxation times of the heterostructure from the diffraction patterns are reliably recovered. The framework is applied to experimental Au/Si UED data, and a transport pattern beyond the diffuse mismatch model is revealed, which further enables a direct reconstruction of real‐space, real‐time, frequency‐resolved phonon dynamics across the interface. The work provides a new pathway to probe interfacial phonon transport mechanisms with unprecedented details.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Large Dzyaloshinskii-Moriya interaction induced by chemisorbed oxygen on a ferromagnet surface

The Dzyaloshinskii-Moriya interaction (DMI) is an antisymmetric exchange interaction that stabilizes chiral spin textures. It is induced by inversion symmetry breaking in noncentrosymmetric lattices or at interfaces. Recently, interfacial DMI has been found in magnetic layers adjacent to transition metals due to the spin-orbit coupling and at interfaces with graphene due to the Rashba effect. We report direct observation of strong DMI induced by chemisorption of oxygen on a ferromagnetic layer at room temperature. The sign of this DMI and its unexpectedly large magnitude—despite the low atomic number of oxygen—are derived by examining the oxygen coverage–dependent evolution of magnetic chirality. We find that DMI at the oxygen/ferromagnet interface is comparable to those at ferromagnet/transition metal interfaces; it has enabled direct tailoring of skyrmion’s winding number at room temperature via oxygen chemisorption. This result extends the understanding of the DMI, opening up opportunities for the chemisorption-related design of spin-orbitronic devices.

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

Ultrahigh pressure compaction-resistant thin film crosslinked composite reverse osmosis membranes

In this study, we present a class of thin-film crosslinked (TFX) composite reverse osmosis (RO) membranes that resist physical compaction at ultrahigh pressures (up to 200 bar). Since RO membranes experience compaction at virtually all pressure ranges, the ability to resist compaction has widespread implications for RO membrane technology. The process described herein involves crosslinking a phase inverted porous polyimide (PI) support membrane followed by interfacial polymerization of a polyamide layer, thereby forming a fully thermoset composite membrane structure. We explore a range of phase inversion membrane formation parameters such as PI concentration, solvent-cosolvent ratios, coagulation bath composition, and crosslinking methods in addition to interfacial polymerization reaction chemistry and conditions. Overall, TFX membranes exhibit significantly less compaction compared to hand-cast and commercial high-pressure RO membranes, experiencing less than 10% decline in water permeance and maintaining salt rejection over 99% for NaCl solutions up to 180,000 mg/L with 200 bar applied pressure.

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

Tuning interfacial Dzyaloshinskii-Moriya interactions in thin amorphous ferrimagnetic alloys

Skyrmions can be stabilized in magnetic systems with broken inversion symmetry and chiral interactions, such as Dzyaloshinskii-Moriya interactions (DMI). Further, compensation of magnetic moments in ferrimagnetic materials can significantly reduce magnetic dipolar interactions, which tend to favor large skyrmions. Tuning DMI is essential to control skyrmion properties, with symmetry breaking at interfaces offering the greatest flexibility. However, in contrast to the ferromagnet case, few studies have investigated interfacial DMI in ferrimagnets. Here we present a systematic study of DMI in ferrimagnetic CoGd films by Brillouin light scattering. We demonstrate the ability to control DMI by the CoGd cap layer composition, the stack symmetry and the ferrimagnetic layer thickness. The DMI thickness dependence confirms its interfacial nature. In addition, magnetic force microscopy reveals the ability to tune DMI in a range that stabilizes sub-100 nm skyrmions at room temperature in zero field. Our work opens new paths for controlling interfacial DMI in ferrimagnets to nucleate and manipulate skyrmions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Interfacial Spin-Orbit Coupling: A Platform for Superconducting Spintronics

Spin-orbit coupling (SOC) is a key interaction in spintronics, allowing electrical control of spin or magnetization and, vice versa, magnetic control of electrical current. However, recent advances have revealed much broader implications of SOC that is also central to the design of topological states with potential applications from low-energy dissipation and faster magnetization switching to high tolerance of disorder. SOC and the resulting emergent interfacial spin-orbit fields are simply realized in junctions through structural inversion asymmetry, while the anisotropy in magnetoresistance (MR) allows their experimental detection. Surprisingly, we demonstrate that an all-epitaxial ferromagnet/MgO/metal junction with a single ferromagnetic region and only negligible MR anisotropy undergoes a remarkable transformation below the superconducting transition temperature of the metal. The superconducting junction has a MR anisotropy 3 orders of magnitude higher and could enable novel applications in superconducting spintronics. In contrast to common realizations of MR effects that require a finite applied magnetic field, our system is designed to have two stable zero-field states with mutually orthogonal magnetizations: in plane and out of plane. This bistable magnetic anisotropy allows us to rule out orbital and vortex effects due to an applied magnetic field and identify the SOC origin of the observed MR. Such MR reaches approximately 20% without an applied magnetic field and could be further increased for large magnetic fields that support vortices. Our findings call for a revisit of the role of SOC, even when it seems negligible in the normal state, and suggest an alternative platform for superconducting spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Atomic Structural Origin of the High Methanol Selectivity over In 2 O 3 –Metal Interfaces: Metal–Support Interactions and the Formation of a InO x Overlayer in Ru/In 2 O 3 Catalysts during CO 2 Hydrogenation

CO 2 hydrogenation to methanol is of great environmental and economic interest due to its potential to reduce carbon emissions and produce valuable chemicals in one single reaction. Compared with the unmodified traditional Cu/ZnO/Al 2 O 3 catalyst, an indium oxide (In 2 O 3 )-based catalyst can double the methanol selectivity from 30–50 to 60–100%. It is worth noting that over catalysts involving various active metals dispersed on indium oxide (M/In 2 O 3 , M = Pd, Ni, Au, etc.), although the methanol yield is boosted, the selectivity remains similar to that of plain In 2 O 3 despite the distinct chemical properties of the added metals. Here, to investigate the phenomena behind this behavior, we used RuO 2 /In 2 O 3 as a test catalyst. The results of ambient pressure photoelectron spectroscopy, in situ X-ray absorption fine structure, and time-resolved X-ray diffraction indicate that the structure of the RuO 2 /In 2 O 3 catalyst is highly dynamic in the presence of a reactive environment. Specifically, under CO 2 hydrogenation conditions, Ru clusters facilitate the reduction of In 2 O 3 to generate In 2 O 3–x aggregates, which encapsulate the Ru systems in a migration driven by thermodynamics. In this way, the Ru O sites for CH 4 production are blocked while creating RuO x –In 2 O 3–x interfacial sites with tunable metal–oxide interactions for selective methanol production. In an inverse oxide/metal configuration, indium oxide has properties not seen in its bulk phase that are useful for the binding and conversion of CO 2 . This work reveals the dynamic nature of In 2 O 3 -based catalysts, providing insights for a rational design of materials for the selective synthesis of methanol.

36 MATERIALS SCIENCE↗
NASA NTRS1980

The microstructure of MnBi/Bi eutectic alloys

Directionally solidified eutectic alloys of the system MnBi/Bi have been investigated with reference to the dependence of the fiber spacing on the growth rate and the interfacial temperature gradient. It is found that the fiber spacing varies as the inverse square root of the growth rate and does not depend on the temperature gradient in contrast to the claims that all faceted/non-faceted eutectics should show a temperature gradient influence.

Ravishankar, P. S.↗
DOE OSTI2023

Bimetallic-Derived Catalytic Structures for CO 2 -Assisted Ethane Activation

In recent years, the simultaneous upgrading of CO 2 and ethane has emerged as a promising approach for generating valuable gaseous (CO, H 2 , and ethylene) and liquid (aromatics and C 3 oxygenates) chemicals from the greenhouse gas CO 2 and large-reserved shale gas. The key challenges for controlling product selectivity lie in the selective C-H and C-C bond cleavage of ethane with the assistance of CO 2 . Bimetallic-derived catalysts likely undergo alloying or oxygen-induced segregation under reaction conditions, thus providing diverse types of interfacial sites, e.g., metal/support (M/M'O x ) interface and metal oxide/metal (M'O x /M) inverse interface, that are beneficial for selective CO 2 -assisted ethane upgrading. The alloying extent can be initially predicted by cohesive energy and atomic radius (or Wigner-Seitz radius), while the preference for segregation to form the on-top suboxide can be approximated using the work function, electronegativity, and binding strength of adsorbed oxygen. Furthermore, bimetallic-derived catalysts are typically supported on high surface area oxides. Modifying the reducibility and acidity/basicity of the oxide supports and introducing surface defects facilitate CO 2 activation and oxygen supplies for ethane activation. Using in situ synchrotron characterization and density functional theory (DFT) calculations, we found that the electronic properties of oxygen species influence the selective cleavage of C-H/C-C bonds in ethane, with electron-deficient oxygen over the metal (or alloy) surface promoting nonselective bond scission to produce syngas and electron-enriched oxygen over the metal oxide/metal interface enhancing selective C-H scission to yield ethylene. Here, we further demonstrate that the preferred structures of the catalyst surfaces, either alloy surfaces or metal oxide/metal inverse interfaces, can be controlled through the appropriate choice of metal combinations and their atomic ratios. Through a comprehensive comparison of experimental results and DFT calculations, the selectivity of C-C/C-H bond scission is correlated with the thermodynamically favorable bimetallic-derived structures (i.e., alloy surfaces or metal oxide/metal inverse interfaces) under reaction conditions over a wide range of bimetallic catalysts. These findings not only offer structural and mechanistic insights into bimetallic-derived catalysts but also provide design principles for selective catalysts for CO 2 -assisted activation of ethane and other light alkanes. This Account concludes by discussing challenges and opportunities in designing advanced bimetallic-derived catalysts, incorporating new reaction chemistries for other products, employing precise synthesis strategies for well-defined structures with optimized site densities, and leveraging time/spatial/energy-resolved in situ spectroscopy/scattering/microscopy techniques for comprehensive structural analysis. The research methodologies established here are helpful for the investigation of dynamic alloy and interfacial structures and should inspire more efforts toward the simultaneous upgrading of CO 2 and shale gas.

03 NATURAL GAS↗
DOE OSTI2022

Spin orbit torque in ferromagnet/topological-quantum-material heterostructures

The main objective of this proposal was to investigate the spin-orbital driven phenomena in topological insulator (TI)/ferromagnet (FM) or transition metal (TM) heterostructures. In particularly, we tried to utilize the spin-momentum locking properties on the surface of TIs to achieve ideal spin-orbit torques (SOTs). In practice, we found that the surface properties have been greatly modified, resulting in much more complicated magneto-transport behaviors than what is expected in SOT-driven magnetotransport. Through systematic and extended investigations, we start to unravel that the nonlinear magnetotransport properties, which was, in the past, mainly attributed to SOT-driven phenomena, can be used to infer the modification of the electronic band structures of TIs and spin textures in FMs which are closely related with charge-spin interconversion phenomena. Regarding the band structures In TIs, we find under electrostatic perturbations imposed by deposition of nonmagnetic TMs, the quantum well states formed on the surface of TIs develop substantial Rashba spin-splitting, which is detected as a bilinear magnetoresistance (BMR). Under magnetic perturbations, the nonlinear planar Hall effect (NPHE) in the topological surface states is greatly enhanced, possibly reflecting the modified surface band structure due to time-reversal symmetry breaking. In a double HM/FM heterostructure where the magnetic anisotropy can be robustly tuned, we observed second-harmonic Hall voltage responses corresponding to domain wall structures with fixed chirality, stabilized by interfacial Dzyaloshinskii–Moriya interaction (DMI). In addition, in the linear transport regime, we utilized inverse-SHE-induced anomalous Hall effect in Pt to probe the exchange bias on the surface of a doped magnetic insulator Tm 3 Fe 5 O 12 .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Preparing Li-garnet electrodes with engineered structures by phase inversion and high shear compaction processes

We report solid-state lithium batteries are promising for safety and energy density com-pared with traditional lithium-ion batteries. However, the large interfacial resistance between the electrode and electrolyte is a bottleneck to achieving high-performance solid-state batteries. Engineered electrode structures with a porous scaffold of the solid electrolyte material are promising to lower the interfacial resistance and provide a mechanical support for a thin solid electrolyte layer. In this work, two ceramic processing techniques are used to fabricate porous/dense bilayer architectures based on a Li 6.25 Al 0.25 La 3 Zr 2 O 12 (LLZO) Li-garnet material. Finger-like vertically aligned pores are created by the phase inversion (PI) process. A water bath presaturated with Li salt prevents Li loss during the PI solvent exchange step. Pore size and porosity can be optimized by adjusting the bath temperature. The high shear compaction process was used to prepare LLZO tapes with 40, 60, and 80 vol% poreformer. The porosity of the tapes after sintering is 39.5%, 58.4%, and 75.4%, respectively. Microtomography exhibits the porosity, pore shape, and pore distribution of the tapes. A typical cathode material LiNi 0.33 Mn 0.33 Co 0.33 O 2 (NMC) is filled into the pores via vacuum infiltration, and a dense cathode layer is formed within the garnet scaffold.

25 ENERGY STORAGE↗
DOE OSTI2021

Driving magnetic domains at the nanoscale by interfacial strain-induced proximity

Here, we investigate the local nanoscale changes of the magnetic anisotropy of a Ni film subject to an inverse magnetostrictive effect by proximity to a V 2 O 3 layer. Using temperature-dependent photoemission electron microscopy (PEEM) combined with X-ray magnetic circular dichroism (XMCD), direct images of the Ni spin alignment across the first-order structural phase transition (SPT) of V 2 O 3 were obtained. We find an abrupt temperature-driven reorientation of the Ni magnetic domains across the SPT, which is associated with a large increase of the coercive field. Moreover, angular dependent ferromagnetic resonance (FMR) shows a remarkable change in the magnetic anisotropy of the Ni film across the SPT of V 2 O 3 . Micromagnetic simulations based on these results are in quantitative agreement with the PEEM data. Direct measurements of the lateral correlation length of the Ni domains from XMCD images show an increase of almost one order of magnitude at the SPT compared to room temperature, as well as a broad spatial distribution of the local transition temperatures, thus corroborating the phase coexistence of Ni anisotropies caused by the V 2 O 3 SPT. We show that the rearrangement of the Ni domains is due to strain induced by the oxide layers’ structural domains across the SPT. Our results illustrate the use of alternative hybrid systems to manipulate magnetic domains at the nanoscale, which allows for engineering of coercive fields for novel data storage architectures.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Vector potential and surface magnetic field in magnetoelectric antiferromagnetic materials

A general formula for the average vector potential of bulk periodic systems is proposed and shown to set the boundary conditions at magnetic interfaces. Here, for antiferromagnetic materials, the study reveals a unique relation between the macroscopic potential and the orientation-dependent magnetic quadrupole as a result of the different crystalline and magnetic symmetries. In particular, at surfaces and interfaces of a truncated bulk without inversion and time-reversal symmetries, the average vector potential exhibits a discontinuity which results in an interfacial magnetic field. In general, however, due to the surface and interface electronic and atomic relaxations, additional magnetization may result. For the experimentally observed magnetoelectric antiferromagnets, in particular, our symmetry analysis suggests that the relaxation effects could well be a system response to the presence of such a potential discontinuity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Thick graded interfaces increase wear resistance in Ti/TiN nanolayered thin films

Multilayered composites with nanoscale layer thickness incorporating titanium and titanium nitride (Ti/TiN) are used as a model system to study the effects of heterophase interface structure on elastic and plastic deformation, as well as wear behavior. Here, in this work, hardness, modulus, and wear rate under dry reciprocating sliding contact are quantified as a function of Ti-TiN heterophase interfacial nitrogen gradient thickness for Ti/TiN multilayers with 10–80 nm layer thickness. Hardness and modulus are found to be inversely proportional to layer thickness and independent of interface gradient for most specimens. Wear rate is found to be inversely proportional to interface gradient thickness at constant layer thickness, demonstrating that control of nanoscale interface structure is a valid approach to enhancing wear behavior. The materials studied in this work wear comparably or slower than other Ti- and TiN-based composites in the literature, providing a promising avenue for engineering wear-resistant materials for use in industrially relevant applications.

Graded interfaces↗
DOE OSTI2020

Strain-induced majority carrier inversion in ferromagnetic epitaxial LaCo O 3 - δ thin films

Tensile-strained LaCoO 3-δ thin films are ferromagnetic, in sharp contrast to the zero-spin bulk, although no clear consensus has emerged as to the origin of this phenomenon. While magnetism has been heavily studied, relatively little attention has been paid to electronic transport, due to the insulating nature of the strain-stabilized ferromagnetic state. Here, structure, magnetism, and transport are studied in epitaxial LaCoO 3-δ films (10–22-nm thick) on various substrates (from 1.4% compressive to 2.5% tensile strain), using synchrotron x-ray diffraction, scanning probe and transmission electron microscopy, magnetometry, polarized neutron reflectometry, resistivity, and Hall effect. High quality, smooth films are obtained, exhibiting superstructures associated with both oxygen vacancy ordering and periodic in-plane ferroelastic domains. Consistent with prior work, ferromagnetism with an approximately 80–85 K Curie temperature is observed under tension; polarized neutron reflectometry confirms a relatively uniform magnetization depth profile, albeit with interfacial dead layer formation. Electrical transport is found to have similar semiconducting nature to bulk, but with reduced resistivity and activation energy. Hall effect measurements, however, reveal a striking inversion of the majority carrier type, from p-type in the bulk and under compression to n-type under tension. While thus far overlooked, ferromagnetism in epitaxial LaCoO 3-δ films is thus directly correlated with n-type behavior, providing important insight into the ferromagnetic state in this system. Here, aided by density functional theory calculations, these results are interpreted in terms of tensile-strain-induced orbital occupation and band structure changes, including a rapid decrease in effective mass at the e g -derived conduction band minimum, and corresponding increase at the valence band maximum.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The dependence of aluminum lattice orientation on semiconductor lattice parameter in planar InAs/Al hybrid heterostructures

We present a detailed study of 7-nm thick Al layers epitaxially grown on In x Al 1-x As or Al 1-x Ga x Sb y As 1-y (0 0 1) semiconductors using high-resolution transmission electron microscopy (HRTEM) and synchrotron X-ray diffraction (XRD). These techniques provide high spatial and high reciprocal space resolution information about Al lattice orientations and interfacial structure, highlighting the existence of a strong correlation between the surface lattice parameter of the semiconductor and the normal orientation of the aluminum film. The normal orientation of Al layers is found to be [1 1 1] when the in-plane semiconductor surface lattice parameter, a S , is smaller than 5.98 Å, and is [1 1 0] when aS is larger than this value. In the transition between these lattice parameters where one orientation is preferred, both orientations may be observed. Concomitant with the change in normal orientation is an inversion in the strain state of the aluminum film. When the normal orientation is [1 1 1], the Al film is compressively strained; while for [1 1 0] normal orientations, the Al in-plane strain is tensile. An energy balance model, accounting for surface, interfacial, side-face, and strain energy, and the registry of lattice planes across the semiconductor/aluminum interface provide explanations for the observed normal orientation and strain inversion.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Activation and Assembly of Plasmonic-Magnetic Nanosurfactants for Encapsulation and Triggered Release

Multifunctional surfactants hold great potentials in catalysis, separation, and biomedicine. Highly active plasmonic-magnetic nanosurfactants are developed through a novel acid activation treatment of Au–Fe 3 O 4 dumbbell nanocrystals. The activation step significantly boosts nanosurfactant surface energy and enables the strong adsorption at interfaces, which reduces the interfacial energy one order of magnitude. Mediated through the adsorption at the emulsion interfaces, the nanosurfactants are further constructed into free-standing hierarchical structures, including capsules, inverse capsules, and two-dimensional sheets. The nanosurfactant orientation and assembly structures follow the same packing parameter principles of surfactant molecules. Furthermore, nanosurfactants demonstrate the capability to disperse and encapsulate homogeneous nanoparticles and small molecules without adding any molecular surfactants. The assembled structures are responsive to external magnetic field, and triggered release is achieved using an infrared laser by taking advantage of the enhanced surface plasmon resonance of nanosurfactant assemblies. Finally, solvent and pH changes are also utilized to achieve the cargo release.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

On the engulfment of antifreeze proteins by ice

Antifreeze proteins (AFPs) are remarkable biomolecules that suppress ice formation at trace concentrations. To inhibit ice growth, AFPs must not only bind to ice crystals, but also resist engulfment by ice. The highest supercooling, ΔT*, for which AFPs are able to resist engulfment is widely believed to scale as the inverse of the separation, L, between bound AFPs, whereas its dependence on the molecular characteristics of the AFP remains poorly understood. By using specialized molecular simulations and interfacial thermodynamics, here, we show that in contrast with conventional wisdom, ΔT* scales as L –2 and not as L –1 . We further show that ΔT* is proportional to AFP size and that diverse naturally occurring AFPs are optimal at resisting engulfment by ice. By facilitating the development of AFP structure–function relationships, we hope that our findings will pave the way for the rational design of AFPs.

Science & Technology - Other Topics↗