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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Giant orbital magnetoelectric effect and current-induced magnetization switching in twisted bilayer graphene

Recently, quantum anomalous Hall effect with spontaneous ferromagnetism was observed in twisted bilayer graphenes (TBG) near 3/4 filling. Importantly, it was observed that an extremely small current can switch the direction of the magnetization. This offers the prospect of realizing low energy dissipation magnetic memories. However, the mechanism of the current-driven magnetization switching is poorly understood as the charge currents in graphenes are generally believed to be non-magnetic. In this work, we demonstrate that in TBG, the twisting and substrate induced symmetry breaking allow an out of plane orbital magnetization to be generated by a charge current. Moreover, the large Berry curvatures of the flat bands give the Bloch electrons large orbital magnetic moments so that a small current can generate a large orbital magnetization. We further demonstrate how the charge current can switch the magnetization of the ferromagnetic TBG near 3/4 filling as observed in the experiments.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Dynamic conformational switching underlies TFIIH function in transcription and DNA repair and impacts genetic diseases

Transcription factor IIH (TFIIH) is a protein assembly essential for transcription initiation and nucleotide excision repair (NER). Yet, understanding of the conformational switching underpinning these diverse TFIIH functions remains fragmentary. TFIIH mechanisms critically depend on two translocase subunits, XPB and XPD. To unravel their functions and regulation, we build cryo-EM based TFIIH models in transcription- and NER-competent states. Using simulations and graph-theoretical analysis methods, we reveal TFIIH’s global motions, define TFIIH partitioning into dynamic communities and show how TFIIH reshapes itself and self-regulates depending on functional context. Our study uncovers an internal regulatory mechanism that switches XPB and XPD activities making them mutually exclusive between NER and transcription initiation. By sequentially coordinating the XPB and XPD DNA-unwinding activities, the switch ensures precise DNA incision in NER. Mapping TFIIH disease mutations onto network models reveals clustering into distinct mechanistic classes, affecting translocase functions, protein interactions and interface dynamics.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Extreme fast charging of commercial Li-ion batteries via combined thermal switching and self-heating approaches

Abstract The mass adoption of electric vehicles is hindered by the inadequate extreme fast charging (XFC) performance (i.e., less than 15 min charging time to reach 80% state of charge) of commercial high-specific-energy (i.e., >200 Wh/kg) lithium-ion batteries (LIBs). Here, to enable the XFC of commercial LIBs, we propose the regulation of the battery’s self-generated heat via active thermal switching. We demonstrate that retaining the heat during XFC with the switch OFF boosts the cell’s kinetics while dissipating the heat after XFC with the switch ON reduces detrimental reactions in the battery. Without modifying cell materials or structures, the proposed XFC approach enables reliable battery operation by applying <15 min of charge and 1 h of discharge. These results are almost identical regarding operativity for the same battery type tested applying a 1 h of charge and 1 h of discharge, thus, meeting the XFC targets set by the United States Department of Energy. Finally, we also demonstrate the feasibility of integrating the XFC approach in a commercial battery thermal management system.

25 ENERGY STORAGE↗
DOE OSTI2024

Switching the spin cycloid in BiFeO3 with an electric field

Abstract Bismuth ferrite (BiFeO 3 ) is a multiferroic material that exhibits both ferroelectricity and canted antiferromagnetism at room temperature, making it a unique candidate in the development of electric-field controllable magnetic devices. The magnetic moments in BiFeO 3 are arranged into a spin cycloid, resulting in unique magnetic properties which are tied to the ferroelectric order. Previous understanding of this coupling has relied on average, mesoscale measurements. Using nitrogen vacancy-based diamond magnetometry, we observe the magnetic spin cycloid structure of BiFeO 3 in real space. This structure is magnetoelectrically coupled through symmetry to the ferroelectric polarization and this relationship is maintained through electric field switching. Through a combination of in-plane and out-of-plane electrical switching, coupled with ab initio studies, we have discovered that the epitaxy from the substrate imposes a magnetoelastic anisotropy on the spin cycloid, which establishes preferred cycloid propagation directions. The energy landscape of the cycloid is shaped by both the ferroelectric degree of freedom and strain-induced anisotropy, restricting the spin spiral propagation vector to changes to specific switching events.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Ferroelectrically switched valley-dependent transmission in SnTe-PbTe-SnTe monolayer lateral heterostructures

A special class of valleytronic two-dimensional (2D) semiconductors possesses carrier pockets (i.e., valleys) along certain directions in the first Brillouin zone, which can be applied as a new degree of freedom for information storage and processing. Here we show that members of this family that are ferroelectric allow the location of these valleys to be switched by rotating the ferroelectric polarization. This makes possible the control of electronic state transmission probability through an energy barrier by ferroelectrically switching the polarization direction, thereby creating or eliminating valley matching in reciprocal space. We apply molecular beam epitaxy to grow lateral sandwich heterostructures with monolayer-thick ferroelectric SnTe separated by nanometer-wide paraelectric PbTe as the barriers. Using scanning tunneling microscopy, we show that the transmission probability of the 2D hole states at the valence band maximum of SnTe monolayer strongly relies on the relative orientation between the polarization directions of the two SnTe electrodes. The transmission can be switched from a suppressed state to a permitted state by rotating the ferroelectric polarization of one SnTe electrode by 90 degrees. Our work demonstrates the electric-field-control of valley locations and its potential for tunnel junction valleytronic devices.

electronic devices↗
DOE OSTI2019

Electrical switching in a magnetically intercalated transition metal dichalcogenide

Advances in controlling the correlated behaviour of transition metal dichalcogenides have opened a new frontier of many-body physics in two dimensions. A field where these materials have yet to make a deep impact is antiferromagnetic spintronics-a relatively new research direction promising technologies with fast switching times, insensitivity to magnetic perturbations and reduced cross-talk. Here, we present measurements on the intercalated transition metal dichalcogenide Fe 1/3 NbS 2 that exhibits antiferromagnetic ordering below 42 K. We find that remarkably low current densities of the order of 10 4 A cm -2 can reorient the magnetic order, which can be detected through changes in the sample resistance, demonstrating its use as an electronically accessible antiferromagnetic switch. Finally, Fe 1/3 NbS 2 is part of a larger family of magnetically intercalated transition metal dichalcogenides, some of which may exhibit switching at room temperature, forming a platform from which to build tuneable antiferromagnetic spintronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

An ultrafast symmetry switch in a Weyl semimetal

Topological quantum materials exhibit fascinating properties with important applications for dissipationless electronics and fault-tolerant quantum computers. Manipulating the topological invariants in these materials would allow the development of topological switching applications analogous to switching of transistors. Lattice strain provides the most natural means of tuning these topological invariants because it directly modifies the electron–ion interactions and potentially alters the underlying crystalline symmetry on which the topological properties depend. However, conventional means of applying strain through heteroepitaxial lattice mismatch and dislocations are not extendable to controllable time-varying protocols, which are required in transistors. Integration into a functional device requires the ability to go beyond the robust, topologically protected properties of materials and to manipulate the topology at high speeds. Here in this paper we use crystallographic measurements by relativistic electron diffraction to demonstrate that terahertz light pulses can be used to induce terahertz-frequency interlayer shear strain with large strain amplitude in the Weyl semimetal WTe 2 , leading to a topologically distinct metastable phase. Separate nonlinear optical measurements indicate that this transition is associated with a symmetry change to a centrosymmetric, topologically trivial phase. We further show that such shear strain provides an ultrafast, energy-efficient way of inducing robust, well separated Weyl points or of annihilating all Weyl points of opposite chirality. This work demonstrates possibilities for ultrafast manipulation of the topological properties of solids and for the development of a topological switch operating at terahertz frequencies.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Field-free Magnetization Switching by Utilizing the Spin Hall Effect and Interlayer Exchange Coupling of Iridium

Magnetization switching by spin-orbit torque (SOT) via spin Hall effect represents as a competitive alternative to that by spin-transfer torque (STT) used for magnetoresistive random access memory (MRAM), as it doesn’t require high-density current to go through the tunnel junction. For perpendicular MRAM, however, SOT driven switching of the free layer requires an external in-plane field, which poses limitation for viability in practical applications. Here we demonstrate field-free magnetization switching of a perpendicular magnet by utilizing an Iridium (Ir) layer. The Ir layer not only provides SOTs via spin Hall effect, but also induce interlayer exchange coupling with an in-plane magnetic layer that eliminates the need for the external field. Such dual functions of the Ir layer allows future build-up of magnetoresistive stacks for memory and logic applications. Experimental observations show that the SOT driven field-free magnetization reversal is characterized as domain nucleation and expansion. Micromagnetic modeling is carried out to provide in-depth understanding of the perpendicular magnetization reversal process in the presence of an in-plane exchange coupling field.

Science & Technology - Other Topics↗
DOE OSTI2023

Chromophore carbonyl twisting in fluorescent biosensors encodes direct readout of protein conformations with multicolor switching

Fluorescent labeling of proteins is a powerful tool for probing structure-function relationships with many biosensing applications. Structure-based rules for systematically designing fluorescent biosensors require understanding ligand-mediated fluorescent response mechanisms which can be challenging to establish. We installed thiol-reactive derivatives of the naphthalene-based fluorophore Prodan into bacterial periplasmic glucose-binding proteins. Glucose binding elicited paired color exchanges in the excited and ground states of these conjugates. X-ray structures and mutagenesis studies established that glucose-mediated color switching arises from steric interactions that couple protein conformational changes to twisting of the Prodan carbonyl relative to its naphthalene plane. Mutations of residues contacting the carbonyl can optimize color switching by altering fluorophore conformational equilibria in the apo and glucose-bound proteins. A commonly accepted view is that Prodan derivatives report on protein conformations via solvatochromic effects due to changes in the dielectric of their local environment. Here we show that instead Prodan carbonyl twisting controls color switching. These insights enable structure-based biosensor design by coupling ligand-mediated protein conformational changes to internal chromophore twists through specific steric interactions between fluorophore and protein.

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

Ion manipulations in structures for lossless ion manipulations (SLIM): computational evaluation of a 90° turn and a switch

The process of redirecting ions through 90° turns and ‘tee’ switches utilizing Structures for Lossless Ion Manipulations (SLIM) was evaluated using theoretical and simulation methods at 4 Torr pressure. SIMION simulations were used to optimize and evaluate conditions for performing turns without loss of signal intensity or ion mobility resolving power. Fundamental considerations indicated that the “race track” effect during ion turns may incur only small losses to the ion mobility resolving power at 4 Torr pressure for the typical plume widths predicted in an optimized SLIM ‘tee’ switch design. The dynamic switching of ions into orthogonal channels was also evaluated using SIMION ion trajectory simulations, and achieved similar performance. Simulation results were in close agreement with experimental results and were used to refine SLIM designs and applied potentials for their use.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Localised nanoscale resistive switching in GaP thin films with low power consumption

Nanoscale localisation of the electroforming-free resistive switching (RS) behaviour in polycrystalline GaP thin films has been observed for the first time. A combination of conductive atomic force microscopy and first-order reversal curve current–voltage measurements indicated that the grain boundaries are the preferred sites for the formation of the conductive switching filaments. It is proposed, based on TEM and XPS results, that local electrochemical migration of Ga ions along the grain boundaries plays a critical role in the switching mechanism. In the low-resistance (ON) state, the conduction mechanism was found to be the space-charge-limited current mechanism, while the high-resistance (OFF) state was governed by the Frenkel–Poole mechanism. Here, a high OFF/ON resistance ratio (~10 4 ) and lower power consumption than current RS devices, in addition to the easy integration of GaP with silicon substrates, make these GaP films promising for future applications in future non-volatile resistive random access memory (RRAM).

36 MATERIALS SCIENCE↗
DOE OSTI2019

A Separation Voltage Polarity Switching Method for Higher Sample Loading Capacity and Better Separation Resolution in Transient Capillary Isotachophoresis Separation

A separation voltage polarity switching transient capillary isotachophoresis (PS-tCITP) was developed to overcome a major sample loading volume limitation in transient capillary isotachophoresis (tCITP). The fundamental idea of PS-tCITP is to let sample ions move back and forth in the separation capillary during their initial isotachophoresis focusing stage by switching the polarity of separation voltage, in order to both increase the sample loading volume and improve the separation efficiency as compared to the conventional tCITP method. The experimental evaluation of the novel PS-tCITP method by using two peptide standards at 2 µM concentration showed that the maximum sample loading volume could be increased from 45% of the total separation capillary volume in tCITP to 70% in PS-tCITP, which resulted in a more than 1.5 fold increases in the peptide peak intensity at a given length/volume of the separation capillary. Due to the consecutive focusing of sample volume from each polarity switching of separation voltage, the separation time window at a given sample loading volume was also increased significantly in PS-tCITP as compared to tCITP. Experiment comparison between tCITP and PS-tCITP at 45% sample loading volume using the same setup showed that the migration time difference between the two peptide peaks increased from 0.3 min in tCITP to 0.363 min in PS-tCITP with similar peak widths and heights, resulting in roughly a 21% improvement in separation resolution. The performance advantages of PS-tCITP separation over tCITP separation was further verified by using a mixture of six peptide standards.

Wu, Huanming↗
DOE OSTI2018

Silicon compatible Sn-based resistive switching memory

Large banks of cheap, fast, non-volatile, energy efficient, scalable solid-state memories are an increasingly essential component for today's data intensive computing. Conductive-bridge random access memory (CBRAM) – which involves voltage driven formation and dissolution of Cu or Ag filaments in a Cu (or Ag) anode/dielectric (HfO 2 or Al 2 O 3 )/inert cathode device – possesses the necessary attributes to fit the requirements. Cu and Ag are, however, fast diffusers and known contaminants in silicon microelectronics. In this paper, employing a criterion for electrode metal selection applicable to cationic filamentary devices and using first principles calculations for estimating diffusion barriers in HfO 2 , we identify tin (Sn) as a rational, silicon CMOS compatible replacement for Cu and Ag anodes in CBRAM devices. We then experimentally fabricate Sn based CBRAM devices and demonstrate very fast, steep-slope memory switching as well as threshold switching, comparable to Cu or Ag based devices. Furthermore, time evolution of the cationic filament formation along with the switching mechanism is discussed based on time domain measurements (I vs. t) carried out under constant voltage stress. Finally, the time to threshold is shown to be a function of both the voltage stress (V stress ) as well as the initial leakage current (I 0 ) through the device.

42 ENGINEERING↗
DOE OSTI2021

A chemical switch enabled autonomous two-stage crosslinking polymeric binder for high performance silicon anodes

Silicon (Si) is a promising high-capacity anode material for high-energy-density lithium-ion batteries. However, the drastic volumetric changes of Si upon lithiation/delithiation hinder the practical use of Si anodes. Although adhesive polymeric binders, such as poly(acrylic acid) (PAA), mitigate this issue, the cycling performance of the fabricated Si anodes is still far from meeting the criteria of practical applications. In this study, we present a novel polymeric binder system for Si anodes consisting of PAA, a chemical switch (ammonia, NH 3 ), and a crosslinker (branched polyethylenimine, PEI). The crosslinking between PAA and PEI is switched off in the slurry, which can then be turned on during electrode drying. Interestingly, the crosslinking reaction consists of two stages: ionic cross-linking (PAA-PEI-i) and covalent crosslinking (PAA-PEI-c) at a higher temperature (e.g., 130 °C). In half-cells, Si anodes fabricated using the PAA-PEI-c binder show a 67% increase in capacity retention compared to PAA anodes over 150 cycles at C/3 rate. The PAA-PEI-c binder also outperforms PAA in full cells. In addition, the chemical switch controlled crosslinking binder system also facilitates the slurry making process by avoiding early crosslinking. This system requires no additional steps compared to the conventional electrode lamination process, showing enormous potential for direct adoption in large-scale manufacturing.

25 ENERGY STORAGE↗
DOE OSTI2024

Revealing the structure and electronic characteristics of Te-rich threshold switching materials for high-density integration

Ovonic threshold switching (OTS) selectors play an important role in the integration of advanced three-dimensional memory. Selectors based on tellurium (Te)-containing materials exhibit significant promise due to their low threshold voltages and superior consistency. Here we have theoretically studied the structure and electronic properties of a typical OTS material, amorphous GeTe 6 , to explore the switching mechanisms using ab initio molecular dynamics simulations. The results indicate that Ge atoms tend to bond with Te atoms, forming stable chemical bonds. The Te-centered clusters are predominantly in the form of distorted octahedrons, while the Ge-centered clusters are in the form of both octahedrons and tetrahedrons. Notably, the proportion of tetrahedrons within the 4-coordinated Ge-centered clusters reaches an impressive 66.9%. These tetrahedrons are randomly dispersed throughout the simulated cell, leading to a stable amorphous configuration. The mid-gap state observed in the mobility bandgap originates from the atomic chain composed of both over-coordinated Ge and Te atoms. It is the inherent stability of the chemical environment within amorphous GeTe 6 that enables it to maintain its amorphous phase under a repeated threshold voltage, a characteristic that distinguishes it from non-OTS materials, such as amorphous tellurium. Furthermore, our findings provide an in-depth understanding of the structure and electronic characteristics of amorphous GeTe 6 , which can promote the design and application of the Te-rich threshold switching materials.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Bimodal switching field distributions in all-perpendicular spin-valve nanopillars

Switching field measurements of the free layer element of 75 nm diameter spin-valve nanopillars reveal a bimodal distribution of switching fields at low temperatures (below 100 K). This result is inconsistent with a model of thermal activation over a single perpendicular anisotropy barrier. The correlation between antiparallel to parallel and parallel to antiparallel switching fields increases to nearly 50% at low temperatures. This reflects random fluctuation of the shift of the free layer hysteresis loop between two different magnitudes, which may originate from changes in the dipole field from the polarizing layer. The magnitude of the loop shift changes by 25% and is correlated to transitions of the spin-valve into an antiparallel configuration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Critical analysis and remedy of switching failures in straintronic logic using Bennett clocking in the presence of thermal fluctuations

Straintronic logic is a promising platform for beyond Moore's law computing. Using Bennett clocking mechanism, information can propagate through an array of strain-mediated multiferroic nanomagnets, exploiting the dipolar coupling between the magnets without having to physically interconnect them. Here, we perform a critical analysis of switching failures, i.e., error in information propagation due to thermal fluctuations through a chain of such straintronic devices. We solved stochastic Landau-Lifshitz-Gilbert equation considering room-temperature thermal perturbations and show that magnetization switching may fail due to inherent magnetization dynamics accompanied by thermally broadened switching delay distribution. Avenues available to circumvent such issue are proposed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Electrical switching in a Fe-thiacrown molecular device

First-principles calculations are performed to inspect the electronic and transport properties of a Fe-thiacrown molecular device, namely, a Au-Fe(9S{sub 3}){sub 2}-Au junction. It is found that the junction has a low-spin (LS) ground state and a high-spin (HS) metastable state. Further study shows that the HS state is a conducting state while the LS state is a nearly insulating one, which means that a switch between these two spin configurations results in a good electrical switching behavior and can serve as an ON/OFF state for a logic unit. Thus, it may find applications as switches or memories in molecular electronic circuits.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗