Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “multilayers.”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Strain-Modulated Exciton Localization and Enhanced Emission in Multilayer GaSe

Strain engineering is one of the most effective routes for tuning the electrical and optical properties of two-dimensional layered materials. Besides reproducing the results of other groups on the tunability and photoluminescence (PL) enhancement of free and bound excitons under mechanical deformation or thermal effects, we systematically studied the mechanical strain (wrinkle) and local thermal strain (laser heating) effects on the PL lifetime and polarization in GaSe multilayers and their interplay, revealing their coupled impact on excitonic dynamics. Here, the PL intensity of localized excitons in the wrinkle region of GaSe increases superlinearly with the excitation laser power. The polarization effect has been observed for the bound exciton in GaSe under mechanical strain, but not in GaSe under thermal strain. Fluorescence lifetime imaging (FLIM) measurements reveal strain-tunable lifetimes for both free and bound excitons, and the lifetime of the bound exciton is longer than the free exciton in the mechanical strain region, correlating with the enhanced emission of the bound exciton. These results highlight previously uncharacterized optoelectronic tunability in GaSe and broaden the design space for strain (or thermally)-controlled 2D layered devices.

, GaSe, Exciton localization↗
DOE OSTI2020

Thermodynamic Preference for Atom Adsorption on versus Intercalation into Multilayer Graphene

The thermodynamic preference of a foreign atom for adsorption on versus intercalation into a graphitic surface is of fundamental and widespread interest. From an exhaustive first-principles density functional theory investigation for 38 typical elements over the periodic table, we reveal a quasilinear correlation between the Shannon effective ionic radius and the chemical-potential difference for a single atom from adsorption to intercalation at multilayer graphene surfaces. A critical Shannon radius is found to be around 0.10 nm, below (above) which intercalation (adsorption) is more favorable for elements with ionic-like bonding after intercalation. Single atoms with van der Waals-biased bonding show some deviation from the linear relationship, while single atoms for the elements with covalent-like bonding do not favor intercalation relative to adsorption. An energy decomposition analysis indicates that the chemical-potential difference determining the thermodynamic preference of a foreign atom for adsorption versus intercalation results from the competition between the electronic and elastic strain effects.

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

Time-Resolved Observation of Hole Tunneling in van der Waals Multilayer Heterostructures

We reported a time-resolved study of quantum-mechanical tunneling of holes between two MoSe 2 monolayers that are separated by a monolayer WS 2 energy barrier. Four-layer heterostructures of MoSe 2 /WS 2 /MoSe 2 /graphene, as well as control samples, were fabricated by mechanical exfoliation and dry transfer techniques. To time-resolve the hole tunneling process, an ultrashort laser pulse was used to excite electrons and holes in both MoSe 2 layers. Here, by utilization of the graphene layer to eliminate carriers in the third MoSe 2 layer, the first MoSe 2 layer is selectively populated with the holes, which then tunnel to the third MoSe 2 layer. By monitoring decay of the hole population with an ultrashort probe pulse, we measure a hole tunneling time of about 20 ps, which is found to slightly increase with the injected carrier density. Besides the fundamental interests of real-time observation of the quantum-mechanical tunneling effect across a nanometer barrier, these results provide quantitative understanding on tunneling mechanisms of charge transfer in van der Waals heterostructures, which is useful for designing sophisticated van der Waals multilayer heterostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Potential-Controlled Deposition of Multilayer CO 2 Reduction Catalyst Films onto Silicon Photoelectrodes Demonstrates Thickness-Dependent Catalytic Rates

Covalently attaching molecular catalysts to semiconductor surfaces yields promising hybrid photoelectrode architectures for reducing CO 2 to higher-value carbon products. Polymeric molecular catalyst films have higher loading densities than their monolayer counterparts, promising greater rates of solar fuel production. Using photoassisted diazonium electrografting, multilayered films of a Re(apbpy)(CO) 3 Cl CO 2 -reduction catalyst were attached to low-doped p-type Si (pSi). Parallel characterization of the newly formed films with ellipsometry, XPS, and ICP-MS revealed that catalyst loading increased with increasingly negative applied grafting potentials (Vgraft), providing us an experimental test bed to study the effects of film thickness on photocatalytic performance. Controlled-potential electrolysis experiments showed enhanced CO evolution rates on all photoelectrodes with increasingly negative applied potentials (V app ), with thicker films exhibiting the greatest rates of enhancement. Competitive proton reduction reactions at the Si surface were not strongly linked to V app but dependent on film thickness, with thicker films showing increased CO-to-H 2 production ratios.

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

Selective-Area Remote Epitaxy of ZnO Microrods Using Multilayer–Monolayer-Patterned Graphene for Transferable and Flexible Device Fabrications

Here, selective-area remote epitaxy (SA-REpi) is demonstrated for fabricating mechanically releasable position-controlled ZnO microrod (MR) arrays from donor wafers in an arrayed form. Intaglio-patterned graphene, consisting of basal single-layer graphene (SLG) overlayered with multilayer graphene (MLG) patterned with perforated holes, is transferred onto a GaN/Al 2 O 3 wafer on which the hydrothermal synthesis is performed for growing ZnO MRs. The basal SLG area exposed through the MLG pattern yields ZnO MRs, whereas the MLG plateau inhibits the growth. The noncovalent remote epitaxial heterointerface enables the release of the MR overlayer in the arrayed form, and the original source wafer is refurbished for reproducibly repeating the SA-REpi. Density-functional theory calculations suggest that localized surface charge density is induced on the surface of SLG by the underlying GaN across ultrathin SLG, which possibly provides a driving force for precursor adatoms and the following remote epitaxy of ZnO. In contrast, the induction of the charge density redistribution does not clearly occur through MLG; so, that keeps the surface of MLG nearly charge-neutral. The diameter and spacing of ZnO MRs are controlled in a designed way by changing the pattern geometries. High-resolution scanning transmission electron microscopy reveals the remote heteroepitaxial relationship at an atomic level. The remote epitaxy is expected to provide an ideal platform to transfer the addressable spatial arrays of nano- or micro-architecture semiconductor components to arbitrary target surfaces directly after the growth without the assembly procedures.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Multilayered Cu-Carbon Nanotube Composites for Advanced Conductors

Improving the efficiency of electrical components is critical in reducing energy consumption for various industrial and residential applications, ranging from rotating machinery to all electric devices and electric vehicle (EV) components to power grid systems. Substituting Cu wires with reduced resistance conductors that incorporate carbon nanotubes (CNTs) into Cu─ultraconductive Cu (UCC) composites─has recently been considered a promising strategy to improve energy efficiency, power density, and/or performance across various applications. Here, in this study, we created stable material formulations [CNT-containing polyvinylpyrrolidone (PVP) in dimethylformamide (DMF) solution] and utilized commercially viable fabrication approaches (electrospinning and magnetron sputtering) that produced high-performance multilayered tape-based UCC composite architectures. Increasing the CNT volume fraction by sequential layering of the structure with additional Cu-CNT layers showed a nearly stepwise improved performance in electrical and mechanical properties. This study also provides valuable insight into the effectiveness of nitrogen doping in modifying the conductivity of the CNT matrix. Fabricated prototypes demonstrated a >10% increase in current carrying capacity and >10% improvement in mechanical strength compared to those obtained on pure Cu. We believe that the properties demonstrated here, combined with the scalable manufacturing pathway of our approach, pave the way in designing future advanced conductors for diverse energy efficient and high-performance electrical systems and applications.

Carbon nanotubes↗
DOE OSTI2022

Multilayer Chitin–Chitosan–Cellulose Barrier Coatings on Poly(ethylene terephthalate)

Currently, effective barrier properties over a wide range of humidity are achieved by layering multiple plastics, resulting in structures that are nearly impossible to recycle through current systems. There is strong interest in developing barriers that are recyclable, biodegradable, or compostable. Chitin and cellulose nanomaterials are promising alternatives because of their high crystallinity, renewable sourcing, strong electrostatic interactions, and potential for biodegradation or composting. In this paper, we explore the potential to create multilayer materials with effective oxygen and water vapor barrier properties at elevated humidity by combining recyclable poly(ethylene terephthalate) (PET) films with single-layer and bilayer coatings of chitin nanowhiskers (ChNWs), chitosan (CS), and cellulose nanocrystals (CNCs). The addition of CS to the ChNW suspension improved the gas barrier properties of ChNW coatings, likely by filling voids, and short ChNWs (SChNW, 114 nm) performed better than long ChNWs (LChNW, 230 nm). At the optimal mass ratio of 1:1 SChNW/CS, the oxygen permeability (OP) of SChNW/CS-coated PET films was 5.1 cm 3 μm m –2 day –1 kPa –1 versus 15.9 cm 3 μm m –2 day –1 kPa –1 for neat PET. To take advantage of electrostatic attraction and hydrogen bonding, CNC was first coated on the PET, followed by coating with ChNW/CS, resulting in an OP as low as 3.6 cm 3 μm m –2 day –1 kPa –1 at 50% relative humidity (RH), and 6.4 cm 3 μm m –2 day –1 kPa –1 at 80% RH. Furthermore, after thermal treatment (120 °C, 2.5 h), the OP dropped to 2.2 cm 3 μm m –2 day –1 kPa –1 (50% RH) and 4.8 cm 3 μm m –2 day –1 kPa –1 (80% RH). The ChNW/CS and CNC coating can be efficiently removed with alkali treatment enabling possible recycling of the coated PET films.

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

Quantum Emitters Induced by High Pressure and UV Laser Irradiation in Multilayer GaSe

In this work, we report on defect generation in multilayer GaSe through hydrostatic pressure quenching and UV laser irradiation. The Raman line width from the UV 266 nm irradiated sample is much wider than that in pressure-quenched GaSe, corresponding to a wider defect energy distribution range in the former sample than the latter. After quenching from 11.2 GPa, three photoluminescence (PL) peaks from defect states are observed at 657, 681, and 695 nm at a low temperature of 93 K. Defect-related peaks at 649, 694, 750, and 774 nm also appear in low-temperature PL spectra after UV laser irradiation, with a nonmonotonous intensity dependence on irradiation duration. There are common features in defects produced by these two methods: the PL peaks with the lowest energy are sharp, and their PL intensities increase linearly with the excitation laser power and saturate above a certain excitation laser power. These two features are similar to those in defects for single-photon emission (SPE) in other 2D materials at even lower temperatures. Fluorescence lifetime imaging shows distinguished short (2.3 ns) and long (75.6 nm) lifetimes of the 695 nm PL line in pressure-quenched GaSe. The density functional theory predicts defect energy levels related to Se vacancy.

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

Scalable Synthesis and Characterization of Multilayer γ-Graphyne, New Carbon Crystals with a Small Direct Band Gap

γ-Graphyne is the most symmetric sp 2 /sp 1 allotrope of carbon, which can be viewed as graphene uniformly expanded through the insertion of two-carbon acetylenic units between all the aromatic rings. To date, synthesis of bulk γ-graphyne has remained a challenge. In this work, we report the synthesis of multilayer γ-graphyne through crystallization-assisted irreversible cross-coupling polymerization. A comprehensive characterization of this new carbon phase is described, including synchrotron powder X-ray diffraction, electron diffraction, lateral force microscopy, Raman spectroscopy, infrared spectroscopy, and cyclic voltammetry. Experiments indicate that γ-graphyne is a 0.48 eV band gap semiconductor, with a hexagonal a-axis spacing of 6.88 Å and an interlayer spacing of 3.48 Å, which is consistent with theoretical predictions. The observed crystal structure has an aperiodic sheet stacking. The material is thermally stable up to 240 °C but undergoes transformation at higher temperatures. While conventional 2D polymerization and reticular chemistry rely on error correction through reversibility, we demonstrate that a periodic covalent lattice can be synthesized under purely kinetic control. The reported methodology is scalable and inspires extension to other allotropes of the graphyne family.

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

Creation and observation of Hopfions in magnetic multilayer systems

Among topological solitons, magnetic skyrmions are two-dimensional particle-like objects with a continuous winding of the magnetization, and magnetic Hopfions are three-dimensional objects that can be formed from a closed loop of twisted skyrmion strings. Theoretical models suggest that magnetic Hopfions can be stabilized in frustrated or chiral magnetic systems, and target skymions can be transformed into Hopfions by adapting their perpendicular magnetic anisotropy, but their experimental verification has been elusive so far. Here, we present an experimental study of magnetic Hopfions that are created in Ir/Co/Pt multilayers shaped into nanoscale disks, known to host target skyrmions. To characterize three-dimensional spin textures that distinguish Hopfions from target skyrmions magnetic images are recorded with surface-sensitive X-ray photoemission electron microscopy and bulk-sensitive soft X-ray transmission microscopy using element-specific X-ray magnetic circular dichroism effects as magnetic contrast. These results could stimulate further investigations of Hopfions and their potential application in three-dimensional spintronics devices.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Diamagnetic mechanism of critical current non-reciprocity in multilayered superconductors

The suggestion that non-reciprocal critical current (NRC) may be an intrinsic property of non-centrosymmetric superconductors has generated renewed theoretical and experimental interest motivated by an analogy with the non-reciprocal resistivity due to the magnetochiral effect in uniform materials with broken spatial and time-reversal symmetry. Theoretically it has been understood that terms linear in the Cooper pair momentum do not contribute to NRC, although the role of higher-order terms remains unclear. In this work we show that critical current non-reciprocity is a generic property of multilayered superconductor structures in the presence of magnetic field-generated diamagnetic currents. In the regime of an intermediate coupling between the layers, the Josephson vortices are predicted to form at high fields and currents. Experimentally, we report the observation of NRC in nanowires fabricated from InAs/Al heterostructures. The effect is independent of the crystallographic orientation of the wire, ruling out an intrinsic origin of NRC. Non-monotonic NRC evolution with magnetic field is consistent with the generation of diamagnetic currents and formation of the Josephson vortices. This extrinsic NRC mechanism can be used to design novel devices for superconducting circuits.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Ultrastrong magnon-magnon coupling and chiral spin-texture control in a dipolar 3D multilayered artificial spin-vortex ice

Strongly-interacting nanomagnetic arrays are ideal systems for exploring reconfigurable magnonics. They provide huge microstate spaces and integrated solutions for storage and neuromorphic computing alongside GHz functionality. These systems may be broadly assessed by their range of reliably accessible states and the strength of magnon coupling phenomena and nonlinearities. Increasingly, nanomagnetic systems are expanding into three-dimensional architectures. This has enhanced the range of available magnetic microstates and functional behaviours, but engineering control over 3D states and dynamics remains challenging. Here, we introduce a 3D magnonic metamaterial composed from multilayered artificial spin ice nanoarrays. Comprising two magnetic layers separated by a non-magnetic spacer, each nanoisland may assume four macrospin or vortex states per magnetic layer. This creates a system with a rich 16 N microstate space and intense static and dynamic dipolar magnetic coupling. The system exhibits a broad range of emergent phenomena driven by the strong inter-layer dipolar interaction, including ultrastrong magnon-magnon coupling with normalised coupling rates of $\frac{Δf}{v}$ = 0.57, GHz mode shifts in zero applied field and chirality-control of magnetic vortex microstates with corresponding magnonic spectra.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Neuromorphic overparameterisation and few-shot learning in multilayer physical neural networks

Abstract Physical neuromorphic computing, exploiting the complex dynamics of physical systems, has seen rapid advancements in sophistication and performance. Physical reservoir computing, a subset of neuromorphic computing, faces limitations due to its reliance on single systems. This constrains output dimensionality and dynamic range, limiting performance to a narrow range of tasks. Here, we engineer a suite of nanomagnetic array physical reservoirs and interconnect them in parallel and series to create a multilayer neural network architecture. The output of one reservoir is recorded, scaled and virtually fed as input to the next reservoir. This networked approach increases output dimensionality, internal dynamics and computational performance. We demonstrate that a physical neuromorphic system can achieve an overparameterised state, facilitating meta-learning on small training sets and yielding strong performance across a wide range of tasks. Our approach’s efficacy is further demonstrated through few-shot learning, where the system rapidly adapts to new tasks.

Science & Technology - Other Topics↗
DOE OSTI2025

Momentum space AC Josephson effect and intervalley coherence in multilayer graphene

Electron transport driven by the phase coherence and interference of quantum many-body wavefunctions is a fascinating phenomenon with potential technological significance. Superconductivity, for example, enables dissipationless transport through macroscopic phase twisting, while charge-density waves show broadband noise and AC-DC interference once their phase is depinned. We identify an analogous phase-coherent dynamics in the intervalley-coherent (IVC) state frequently observed in rhombohedral multilayer graphene. We show that a static magnetic field drives an oscillating intervalley current, which produces an oscillating orbital magnetization and thereby a detectable AC Hall response. This mechanism is similar to the Josephson effect observed in superconductors but now happening in momentum space. In this analogy, the static magnetic field acts as the DC voltage, while the oscillating intervalley current is the AC Josephson current. We provide microscopic calculations of all the phase-number free-energy parameters in rhombohedral trilayer graphene, establishing this effect as an experimental signature of IVC order.

electronic properties and materials↗
DOE OSTI2026

Tailorable multiferroic tunnel junctions from all-van der Waals multilayer stacking

Multiferroic tunnel junctions (MFTJs) represent a class of multistate, non-volatile spintronic devices, in which electron tunnelling can be manipulated by switching long-range lattice and spin orders. In contrast to conventional oxide-based MFTJs, MFTJs constructed from two-dimensional van der Waals (vdW) crystals promise minimal defect concentration in the constituents and at interfaces, which may allow for probing intrinsic tunnelling physics and the development of high-performance devices. Here, in this study, we construct Fe 3 GeTe 2 /CuInP 2 S 6 /Fe 3 GeTe 2 all-vdW MFTJs by assembling multilayer flakes of ferromagnetic Fe 3 GeTe 2 electrodes and a ferroelectric CuInP 2 S 6 spacer. These MFTJs exhibit four non-volatile resistance states featuring sizable tunnelling magnetoresistance of ∼10 2 % and tunnelling electroresistance of ∼10 4 %. To tune the properties of the vdW MFTJ, we make use of the flexibility in material choice offered by vdW heterostructure devices; we use Fe 3 GeTe 2 /Fe 5 GeTe 2 asymmetric electrodes to boost the tunnelling electroresistance by 10 3 %, we integrate In 2 Se 3 as a ferroelectric with a smaller bandgap to enhance the ON-state current density by 10 4 % to 10 4 A cm −2 and we use Fe 3 GaTe 2 electrodes to demonstrate room temperature operation. Furthermore, when we combine the asymmetric ferromagnetic electrodes with the small-bandgap ferroelectric spacer to construct Fe 3 GeTe 2 /In 2 Se 3 /Fe 5 GeTe 2 MFTJs, we simultaneously realized tunnelling electroresistance of 10 6 % and an ON-state current density of 10 4 A cm −2 , both two orders of magnitude higher than the highest values achieved with conventional oxide-based MFTJs. In the future, our all-vdW MFTJs with the tailorability of all functional layers may make it possible to investigate fundamental aspects of interlayer tunnelling and enable the design of functional magnetoelectric nanodevices.

Xie, Ti [University of Maryland, College Park, MD ↗
DOE OSTI2020

Exploring phase transitions and magnetoelectric coupling of epitaxial asymmetric multilayer heterostructures

Magnetoelectric (ME) heterostructures can exhibit higher magnetic and ferroelectric ordering temperatures along with large ME coupling compared to single-phase multiferroic materials. We synthesized Pb(Fe 0.5 Nb 0.5 )O 3 (PFN)/Ni 0.65 Zn 0.35 Fe 2 O 4 (NZFO)/Pb(Fe 0.5 Nb 0.5 )O 3 (PFN)/Ni 0.65 Zn 0.35 Fe 2 O 4 (NZFO)/Pb(Fe 0.5 Nb 0.5 )O 3 (PFN) multilayer heterostructures having dimensions of 40/10/40/10/40 nm. High quality epitaxial growth of these heterostructures was confirmed via X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns. These nanostructures show well saturated polarization (~52 μC cm -2 ) and magnetization (~62 emu cm -3 ) at room temperature (RT). The magnetic and ferroelectric transitions occur well above RT. These heterostructures exhibit relaxor behavior and undergo 2nd order ferroelectric phase transition. Magnetodielectric measurements show significant coupling between the magnetic and electrical order parameters at RT. These characteristics of the heterostructures make them suitable as potential candidates for ultra-low power memory, spintronics, and different multifunctional (micro)nanoscale device applications.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Sub-nanograin metal based high efficiency multilayer reflective optics for high energies

The present finding illuminates the physics of the formation of interfaces of metal based hetero-structures near layer continuous limit as an approach to develop high-efficiency W/B 4 C multilayer (ML) optics with ML periodicity varying d = 1.86–1.23 nm at a fixed number of layer pairs N = 400. The microstructure of metal layers is tailored near the onset of grain growth to control the surface density of grains resulting in small average sizes of grains to sub-nanometers. This generates concurrently desirable atomically sharp interfaces, high optical contrast, and desirable stress properties over a large number of periods, which have evidence through the developed ML optics. We demonstrate significantly high reflectivities of ML optics measured in the energy range 10–20 keV, except for d = 1.23 nm due to quasi-continuous layers. The reflectivities at soft gamma-rays are predicted.

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

Quantifying the environmental benefits of a solvent-based separation process for multilayer plastic films

Food packaging often appears in the form of multilayer (ML) plastic films, which leverage the functional properties of different polymers to achieve specific food protection goals (e.g., oxygen, water, and temperature barriers). These properties are essential to enable long shelf lives, reduce refrigeration usage, mitigate food waste, and increase food accessibility. However, ML film production processes generate large amounts of plastic waste that cannot be mechanically recycled. Recently, we have proposed a process, called solvent-targeted recovery and precipitation (STRAP), that enables the separation and recycling of the constituent polymers of ML films. This technology uses a series of solvent washes that selectively dissolve and precipitate target polymers. Quantifying the environmental benefits of STRAP over virgin resin production is essential for the commercial deployment of this technology. Further, this work uses life cycle assessment (LCA) methods to evaluate these impacts in terms of carbon footprint, energy use, water use, and toxicity. We analyze three STRAP process variants that use antisolvent and temperature-driven precipitation to treat different ML films. Our analysis reveals that the STRAP-A and STRAP-B process variants can provide environmental benefits over virgin film production. Furthermore, it gives valuable insight into the critical components of ML films (specific polymers) and of the STRAP processes (equipment) that are responsible for the highest impacts. Ultimately, we believe that the proposed analysis framework can lead to the design of more environmentally-friendly ML films and recycling processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗