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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Spin Frustration and Unconventional Surface Spin Canting State in Van der Waals Ferromagnet/Antiferromagnet Heterostructures

Atomically flat surfaces of van der Waals (vdW) materials pave an avenue for addressing a long-standing fundamental issue of how a compensated antiferromagnet (AFM) surface frustrates a ferromagnetic (FM) overlayer in FM/AFM heterostructures. We investigate Fe5GeTe2/NiPS3 vdW heterostructures by characterizing AFM and FM spins separately. We find that in-plane zig-zag AFM NiPS3 develops three equivalent AFM domains, which are robust against external magnetic field and magnetic coupling with Fe5GeTe2. Moreover, evidence is provided of in-plane-AFM-induced perpendicular magnetic anisotropy (PMA) in adjacent Fe5GeTe2, and an unconventional out-of-plane surface spin canting state with the Fe5GeTe2 spins spatially turn from out-of-plane direction near the interface to in-plane direction away from the interface in Fe5GeTe2/NiPS3. The out-of-plane surface spin canting is a unique property of spin frustration in vdW magnetic heterostructures.

Wang, Tianye↗
DOE OSTI2017

Effects of Interlayer Coupling on Hot-Carrier Dynamics in Graphene-Derived van der Waals Heterostructures

Graphene exhibits promise as a plasmonic material with high mode confinement that could enable efficient hot carrier extraction. The lifetimes and mean free paths of energetic carriers have been investigated in free-standing graphene, graphite, and a heterostructure consisting of alternating graphene and hexagonal boron nitride layers using ab initio calculations of electron–electron and electron–phonon scattering in these materials. It is found that the extremely high lifetimes (3 ps) of low-energy carriers near the Dirac point in graphene, which are a 100 times larger than that in noble metals, are reduced by an order of magnitude due to interlayer coupling in graphite, but enhanced in the heterostructure due to phonon mode clamping. However, these lifetimes drop precipitously with increasing carrier energy and are smaller than those in noble metals at energies exceeding 0.5 eV. By analyzing the contribution of different scattering mechanisms and interlayer interactions, desirable spacer layer characteristics—high dielectric constant and heavy atoms—that could pave the way for plasmonic heterostructures with improved hot carrier transport have been identified.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Chemically Tunable, All-Inorganic-Based White-Light Emitting 0D-1D Heterostructures

In this study, we initially created one-dimensional (1D) Mn2+-doped ZnS (ZnS: Mn) nanowires (NWs) with a unique optical signature. Specifically, these nanostructures coupled (i) ZnS defect-related self-activated emission spanning from wavelengths of 400 nm to 500 nm with (ii) Mn2+ dopant-induced emission centered at ~580 nm. These doped ZnS nanostructures were initially fabricated for the first time via a template-based co-precipitation approach followed by a post-synthesis annealing process. We subsequently formed novel 1D - zero-dimensional (0D) heterostructures incorporating ZnS: Mn NWs and AET (2-amino-ethanethiol) - CdSe quantum dots (QDs) by assembling annealed ZnS: Mn NWs with AET- capped CdSe QDs as building blocks via a simple technique, involving physical sonication and stirring. Optical analyses of our heterostructures were consistent with charge (hole) and energy transfer-induced quenching of ZnS self-activated emission coupled with hole transfer-related quenching of Mn2+ emission by the QDs. The CdSe QD emission itself was impacted by competing charge (electron) and energy transfer processes occurring between the underlying ZnS host and the immobilized CdSe QDs. Chromaticity analysis revealed the significance of controlling both QD coverage density and Mn2+ dopant ratios in predictably influencing the observed color of our all-inorganic heterostructures. For example, white-light emitting behavior was especially prominent in composites, simultaneously characterized by (i) a 2.22% Mn2+ doping level and (ii) a molar compositional ratio of [ZnS: Mn2+]: [AET-capped CdSe QDs]) of 1: 1.5. Moreover, using these independent chemical ‘knobs’, we have been able to reliably tune for a significant shift within our composites from ‘cold-white’ (9604 K) to ‘warm-white’ (4383 K) light emission.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

High‐Temperature Single‐Photon Emission From Covalently Functionalized van der Waals Heterostructures

Two-dimensional (2D) transition metal dichalcogenides (TMDs) such as tungsten diselenide (WSe 2 ) are attractive nanomaterials for quantum information applications due to single-photon emission (SPE) from intrinsic atomic defects. Defect and strain engineering techniques have been developed to produce high purity, deterministically placed SPE in WSe 2 . However, a major challenge in the application of these techniques is the low temperature required to observe defect-bound TMD exciton emission, typically limiting SPE to T < 30 K. SPE at higher temperatures either loses purity or requires integration into complex devices such as optical cavities. Here, 2D heterostructure engineering and molecular functionalization are combined to achieve high purity (>90%) SPE in strained WSe 2 persisting to over T = 90 K. Covalent diazonium functionalization of graphite in layered WSe 2 /graphite heterostructures maintains high purity up to T = 90 K and single-photon source integrity up to T = 115 K. This method preserves the best qualities of SPE from WSe 2 while increasing working temperature to more than three times the typical range. This work demonstrates the versatility of surface functionalization and heterostructure design to synergistically improve the properties of quantum emission and offers new insights into the phenomenon of SPE from 2D materials.

2D materials↗
DOE OSTI2015

Ultrafast Photoluminescence from the Core and the Shell in CdSe/CdS Dot‐in‐Rod Heterostructures

Abstract With an ultrafast time‐resolved photoluminescence system utilizing a Kerr gate, the time‐resolved photoluminescence of core and shell constituents within CdSe/CdS dot‐in‐rod heterostructures is studied as a function of heterostructure size. Measurements performed at low excitation fluence generating, on average, less than one exciton per nanorod, reveal photoluminescence from direct recombination of carriers in the CdS heterostructure rod with lifetime generally increasing from 0.4 ps to 1.3 ps as the rod length increases. Decay of the CdS rod photoluminescence is accompanied by an increase in emission from the CdSe core on comparable time scales, also trending towards larger values as the rod length increases. The observed kinetics can be explained without invoking a non‐radiative trapping mechanism. We also present alloying as a mechanism for enhancing electron confinement and reducing fluorescence lifetime at nanosecond time scales.

Diroll, Benjamin T.↗
DOE OSTI2021

Contribution of the Sub-Surface to Electrocatalytic Activity in Atomically Precise La 0.7 Sr 0.3 MnO 3 Heterostructures

Electrocatalytic reactions are known to take place at the catalyst/electrolyte interface. Whereas recent studies of size-dependent activity in nanoparticles and thickness-dependent activity of thin films imply that the sub-surface layers of a catalyst can contribute to the catalytic activity as well, most of these studies consider actual modification of the surfaces. Here, in this study, the role of catalytically active sub-surface layers was investigated by employing atomic-scale thickness control of the La 0.7 Sr 0.3 MnO 3 (LSMO) films and heterostructures, without altering the catalyst/electrolyte interface. The activity toward the oxygen evolution reaction (OER) shows a non-monotonic thickness dependence in the LSMO films and a continuous screening effect in LSMO/SrRuO 3 heterostructures. The observation leads to the definition of an “electrochemically-relevant depth” on the order of 10 unit cells. This study on the electrocatalytic activity of epitaxial heterostructures provides new insight in designing efficient electrocatalytic nanomaterials and core-shell architectures.

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

Super‐Hydrophilic Microporous Ni(OH) x /Ni 3 S 2 Heterostructure Electrocatalyst for Large‐Current‐Density Hydrogen Evolution

Abstract Exploiting active and stable non‐precious metal electrocatalysts for alkaline hydrogen evolution reaction (HER) at large current density plays a key role in realizing large‐scale industrial hydrogen generation. Herein, a self‐supported microporous Ni(OH) x /Ni 3 S 2 heterostructure electrocatalyst on nickel foam (Ni(OH) x /Ni 3 S 2 /NF) that possesses super‐hydrophilic property through an electrochemical process is rationally designed and fabricated. Benefiting from the super‐hydrophilic property, microporous feature, and self‐supported structure, the electrocatalyst exhibits an exceptional HER performance at large current density in 1.0 M KOH, only requiring low overpotential of 126, 193, and 238 mV to reach a current density of 100, 500, and 1000 mA cm −2 , respectively, and displaying a long‐term durability up to 1000 h, which is among the state‐of‐the‐art non‐precious metal electrocatalysts. Combining hard X‐rays absorption spectroscopy and first‐principles calculation, it also reveals that the strong electronic coupling at the interface of the heterostructure facilitates the dissociation of H 2 O molecular, accelerating the HER kinetics in alkaline electrolyte. This work sheds a light on developing advanced non‐precious metal electrocatalysts for industrial hydrogen production by means of constructing a super‐hydrophilic microporous heterostructure.

Chemistry↗
DOE OSTI2018

Tunable Magnetic Interaction of Mn-Doped MoS{sub 2}/SiC van der Waals Heterostructures Under Normal Strain

The magnetic properties of Mn-doped MoS{sub 2}/SiC van der Waals (vdW) heterostructures under the influence of normal strain have been investigated by the first-principles method. The interlayer interaction between (Mo,Mn)S{sub 2} and (Si,Mn)C monolayers is antiferromagnetic (AFM) at the equilibrium state. Our results reveal that the compressive strain has much influence on the interlayer interaction of the vdW heterostructures and the interlayer interaction switched from AFM to ferromagnetic (FM). By contrast, under a tensile strain, the interlayer interaction between (Mo,Mn)S{sub 2} and (Si,Mn)C monolayers is always AFM. The results show that the interaction between (Mo,Mn)S{sub 2} and (Si,Mn)C monolayers changes from AFM to FM, which could be explained by the superexchange and the p − d exchange, respectively Moreover, according to the magnetic anisotropy energy (MAE), the easy axis of the magnetization is parallel to the a-axis in current vdW heterostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Strain-Induced Tunable Magnetic Interaction in (Mo,Co)S{sub 2}/(Si,Co)C Heterostructure

Using the first-principles method, we reported tunable magnetic interaction in Co-doped MoS{sub 2}/SiC van der Waals (vdW) heterostructures under normal strain. The interlayer interaction between (Mo,Co)S{sub 2} and (Si,Co)C monolayers is antiferromagnetic (AFM) at the equilibrium state. Our results reveal that the compressive strain has much influence on the interlayer interaction of the vdW heterostructures and the interlayer interaction switched from AFM to ferromagnetic (FM). By contrast, under a tensile strain, the interlayer interaction between (Mo,Co)S{sub 2} and (Si,Co)C monolayers is always AFM. The results show that the interaction between (Mo,Co)S{sub 2} and (Si,Co)C monolayers changes from AFM to FM, which could be explained by the superexchange and the p − d exchange, respectively. Moreover, according to the magnetic anisotropy energy (MAE), the easy axis of the magnetization is parallel to the a-axis in current vdW heterostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Resistance Anomalies at Superconducting Transition in Multilayer N/S/F/S/N Heterostructures

We have prepared lateral N/S/F/S/N heterostructures from perovskite bilayer YBa{sub 2}Cu{sub 3}O{sub 7−x} (YBCO (70 nm), as superconductor S) and La{sub 1−x}Sr{sub x}MnO{sub 3} (LSMO (30 nm), as ferromagnet F) covered ex situ by Au layer (normal metal N, 50 nm) and Ti layer (50 nm). Whereas the Ti layer serves as a mask at Ar{sup +} ion beam etching, the gold layer protects the properties of bilayer LSMO/YBCO during the fabrication process mainly during Ga{sup +} focused ion beam etching. In many cases, the resistance vs. temperature (R(T)) dependences of the heterostructures exhibited some peculiarities (resistance peaks and dips) at superconducting transition. To explain these anomalies, we used transport effects emerging between resistances of individual layers and resistances of their interfaces. Our simulations fit very well the experimental R(T) dependences of N/S/F/S/N heterostructures and show that transport effects can play an important role in multilayer structures which can be used in spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

In-situ construction of ceria-metal/titanate heterostructure with controllable architectures for efficient fuel electrochemical conversion

Construction of ceria-metal/titanate heterostructure via exsolution is a promising strategy to improve the catalytic activity of titanate perovskites and broaden their applications in various energy conversion scenarios. However, the species exsolved after reduction are limited to reducible metal cations, such as Ni, Co, Fe, and precious metals. Herein, we report a modified exsolution approach for co-exsolving active oxides and metal nanoparticles from a titanate perovskite, La 0.8 Ce 0.1 Ni 0.4 Ti 0.6 O 3-δ (LCeNT). We highlight strained facet-specific CeO 2 cubes can be grown on the support after an air-annealing process with their morphology tunable by varying annealing temperature, whilst exsolution of Ni nanoparticles form subsequently following chemical/electrical reduction. An electrolyte-supported SOFC utilizing CeO 2 -Ni@LCeNT anode achieves maximum power density of 642 mW cm -2 at 900 °C in H 2 (~3% H 2 O). Exceptional robustness of the heterostructure is illustrated after running the cell in CH 4 (~3% H 2 O) for 20 h. Here this work demonstrates an intriguing pathway to constructing stable and active ceria-metal/titanate heterostructure for energy applications.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Highly insulating ferromagnetic cobaltite heterostructures

Ferromagnetic insulators are rather rare but possess great technological potential in, for example, spintronics. Individual control of ferromagnetic properties and electronic transport provides a useful design concept of multifunctional oxide heterostructures. We studied the close correlation among the magnetism, atomic structure, and electronic structure of oxide heterostructures composed of the ferromagnetic perovskite LaCoO 3 and the antiferromagnetic brownmillerite SrCoO 2.5 epitaxial thin film layers. By reversing the stacking sequence of the two layers, we could individually modify the electric resistance and saturation magnetic moment. Lastly, the ferromagnetic insulating behavior in the heterostructures was understood in terms of the electronic reconstruction at the oxide surface/interfaces and crystalline quality of the constituent layers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The growth and assembly of organic molecules and inorganic 2D materials on graphene for van der Waals heterostructures

The unique properties of graphene have made it a promising material for integration in future electronic applications. The idealized surface of graphene, atomically-flat and without dangling bonds, offers the opportunity to understand the assembly of organic and inorganic molecules to form a wide range of ordered architectures and functional graphene-based heterostructures. In this review, we summarize recent progress in the growth of hierarchical nanostructures on graphene. The self-assembly of organic molecules and inorganic two-dimensional (2D) layers on graphene for the construction of various types of heterostructures are highlighted. Van der Waals interactions between the assembled molecules and graphene are shown to allow the formation of highly-ordered structures with preferred molecular orientations and stacking configurations that circumvent the strict lattice-matching requirements in traditional epitaxial growth. Lastly, we briefly discuss representative applications of graphene-based heterostructures in electronic and optoelectronics.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Novel spin-orbit coupling driven emergent states in iridate-based heterostructures

Recent years have seen many examples of how the strong spin-orbit coupling present in iridates can stabilize new emergent states that are difficult or impossible to realize in more conventional materials. In this review we outline a representative set of studies detailing how heterostructures based on Ruddlesden-Popper (RP) iridates can be used to access yet more novel physics. Beginning with a short synopsis of iridate thin film growth, the effects of the heterostructure morphology on the RP iridates including Sr 2 IrO 4 and SrIrO 3 are discussed. Example studies explore the effects of epitaxial strain, laser-excitation to access transient states, topological semimetallicity in SrIrO 3 , 2D magnetism in artificial RP iridates, and interfacial magnetic coupling between iridate and neighboring layers. Taken together, these works show the fantastic potential for controlled engineering of novel quantum phenomena in iridate heterostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Pb{sub 5}Bi{sub 24}Se{sub 41}: A new member of the homologous series forming topological insulator heterostructures

We have synthesized Pb{sub 5}Bi{sub 24}Se{sub 41}, which is a new member of the (PbSe){sub 5}(Bi{sub 2}Se{sub 3}){sub 3m} homologous series with m=4. This series of compounds consist of alternating layers of the topological insulator Bi{sub 2}Se{sub 3} and the ordinary insulator PbSe. Such a naturally-formed heterostructure has recently been elucidated to give rise to peculiar quasi-two-dimensional topological states throughout the bulk, and the discovery of Pb{sub 5}Bi{sub 24}Se{sub 41} expands the tunability of the topological states in this interesting homologous series. The trend in the resistivity anisotropy in this homologous series suggests an important role of hybridization of the topological states in the out-of-plane transport. - Graphical abstract: X-ray diffraction profiles taken on cleaved surfaces of single-crystal samples of the (PbSe){sub 5}(Bi{sub 2}Se{sub 3}){sub 3m} homologous series with various m values up to 4, which realizes topological insulator heterostructures. Schematic crystal structure of the new phase, m=4, is also shown. - Highlights: • We have synthesized a new member of the homologous series related to topological insulators. • In this compound, a heterostructure of topological and ordinary insulators naturally forms. • Resistivity anisotropy suggests an important role of hybridization of the topological states. • This compound expands the tunability of the topological states via chemical means.

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

Eco-friendly and effective strategy to synthesize ZnO/Ag{sub 2}O heterostructures and its excellent photocatalytic property under visible light

Highlights: • ZnO/Ag{sub 2}O photocatalysts with heterostructures were synthesized via a facile mechanochemical method. • The synthetic process does not involve any organic solvents and the reaction matrix can be recycled easily. • The synthetic method is gram-scale, and we can easily and routinely scale up this process to produce grams of the heterostructure nanomaterials. • The as-prepared samples without post-calcination show a high degree of crystallinity. - Abstract: ZnO/Ag{sub 2}O photocatalysts with heterostructure were synthesized by a green and effective mechanochemical method. The preparation process was taken in solid state at room temperature with a short grinding time. The as-made products showed a high degree of crystallinity without post-calcination treatment. Such synthetic method does not involve any organic solvents and the reaction matrix can be recycled. The as-prepared ZnO/Ag{sub 2}O samples show excellent photocatalytic activity and photostability for degradation of different organic dyes under visible light. The content of Ag{sub 2}O plays an important role in the photocatalytic activity, which can be tuned by the precursor AgNO{sub 3}. The photodegradation rate constant (k) of the optimal ZnO/Ag{sub 2}O sample under visible light is nearly 0.1004 min{sup −1} for methylene blue (MB), 0.063 min{sup −1} for rhodamine B (RHB) and 0.07 min{sup −1} for methyl orange (MO), which are much better than the pure ZnO (0.0075 min{sup −1}). The enhancement of the visible light photocatalytic activity could be attributed to the heterojunction interfaces induced by the match of crystal lattice and energy band between the Ag{sub 2}O and ZnO. The Ag{sub 2}O generates the excited-state electrons under visible light irradiation. The excited electrons on Ag{sub 2}O could directly transfer to the conduction band (CB) of ZnO, making ZnO/Ag{sub 2}O present remarkable visible light photocatalytic activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Building novel Ag/CeO{sub 2} heterostructure for enhancing photocatalytic activity

Highlights: • Ag nanoparticle is designed to building Schottky heterojunction on CeO{sub 2} nanocube. • The photocatalytic activity of Ag/CeO{sub 2} heterostructure is much enhanced. • 95.33% of MB can be effectively degraded within half an hour. • Ag as acceptor of photoelectrons blocks the recombination of electron–hole pairs. - Abstract: Stable and recyclable photocatalysts with high efficiency to degrade organic contamination are important and widely demanded under the threat of the environment pollution. Ag/CeO{sub 2} heterostructure is designed as a photocatalyst to degrade organic dye under the simulated sunlight. The catalytic activity of CeO{sub 2} nanocubes (NCs) to degrade methylene blue (MB) is obviously enhanced when Ag nanoparticles (NPs) are deposited on the surface of them. The weight ratio of Ag and CeO{sub 2} in forming high efficiency catalyst, the amount of Ag/CeO{sub 2} catalyst used in degradation process, and the dye concentration and pH value of the initial MB solution are examined systematically. 95.33% of MB can be effectively degraded within half an hour when 50 mg of Ag/CeO{sub 2} catalyst in an optimal weight ratio of 1:3, is added to the 100 mL of MB solution (c{sub 0} = 1 × 10{sup −5} mol L{sup −1}, pH 6.2). The mechanism of the enhanced catalytic activity of Ag/CeO{sub 2} heterostructure is discussed. The photocatalytic degradation rate is found to obey pseudo-first-order kinetics equations according to Langmuir–Hinshelwood model. The intermediate products in different stages during the degradation of MB are analyzed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Modulating domain structures in Al2O3-based oxide heterostructures

Highlights: • The trigonal-structure Al{sub 2}O{sub 3} nanotubes and orthorhombic-structure Al{sub 2}O{sub 3} nanosheets are successfully synthesized under high temperature and analyzed based on the electron microscopy. • More importantly, the unexpected Mg-Al-O/Al{sub 2}O{sub 3} heterostructures nucleate, whereas the orthorhombic-structure Al{sub 2}O{sub 3} can effectively modulate the occurrence of monoclinic domains in Mg-Al-O. • This work may provide a meaningful insight for growing specific epitaxial films with suitable alumina substrate. - Abstract: Metal oxide has been the focus of research for decades. In this work, besides the trigonal-structure Al{sub 2}O{sub 3} nanotubes and orthorhombic-structure Al{sub 2}O{sub 3} nanosheets, novel Mg-Al-O/Al{sub 2}O{sub 3} heterostructure nanowires were successfully synthesized at high temperature. The structural characteristics of these oxides were investigated based on electron microscopy and group theory analysis. More importantly, it was found that incorporating the orthorhombic-structure Al{sub 2}O{sub 3} could effectively modulate the occurrence of monoclinic domains and thus the related properties of Mg-Al-O/Al{sub 2}O{sub 3} heterostructures. This work provides a reference for understanding and modulating the complex structures with multiple domain variants in Mg-Al-O oxides.

77 NANOSCIENCE AND NANOTECHNOLOGY↗