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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Electric field control of magnetism using BiFeO{sub 3}-based heterostructures

Conventional CMOS based logic and magnetic based data storage devices require the shuttling of electrons for data processing and storage. As these devices are scaled to increasingly smaller dimensions in the pursuit of speed and storage density, significant energy dissipation in the form of heat has become a center stage issue for the microelectronics industry. By taking advantage of the strong correlations between ferroic orders in multiferroics, specifically the coupling between ferroelectric and magnetic orders (magnetoelectricity), new device functionalities with ultra-low energy consumption can be envisioned. In this article, we review the advances and highlight challenges toward this goal with a particular focus on the room temperature magnetoelectric multiferroic, BiFeO{sub 3}, exchange coupled to a ferromagnet. We summarize our understanding of the nature of exchange coupling and the mechanisms of the voltage control of ferromagnetism observed in these heterostructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Anisotropic MagnetoMemristance

Abstract In the last decade, nanoscale resistive devices with memory have been the subject of intense study because of their possible use in brain-inspired computing. However, operational endurance is one of the limiting factors in the adoption of such technology. For this reason, we discuss the emergence of current-induced memristance in magnetic materials, known for their durability. We show analytically and numerically that a single ferromagnetic layer can possess GHz memristance, due to a combination of two factors: a current-induced transfer of angular momentum (Zhang-Li torque) and the anisotropic magnetoresistance (AMR). We term the resulting effect the anisotropic magneto-memristance (AMM). We connect the AMM to the topology of the magnetization state, within a simple model of a one-dimensional annulus-shaped magnetic layer, confirming the analytical results with micromagnetic simulations for permalloy. Our results open a new path towards the realization of single-layer magnetic memristive devices operating at GHz frequencies.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Ab initio study of molecular and atomic oxygen on GeTe(111) surfaces

Oxidation of the phase-change material germanium telluride (GeTe) is an atomic-scale process of fundamental importance, as it is detrimental to the stability of GeTe-based data-storage devices. Here, we present comprehensive density-functional theory simulations of molecular and atomic oxygen in contact with GeTe(111) surfaces. Molecular O{sub 2} is predicted to readily adsorb on the Ge-terminated (111) surface; the pristine Te-terminated counterpart, by contrast, appears quite inert. The coverage-dependent adsorption of O atoms is then investigated, and based on these data, a surface phase diagram for GeTe(111)/O is constructed. These results afford a detailed, atom-resolved picture of the initial surface oxidation of GeTe, and they harmonize well with a previous X-ray photoelectron spectroscopy study on this very topic.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Carbon doping in GeTe drives differences in local structure and properties

Advances in low-power, energy-efficient information storage and computing require understanding and controlling the atomic and nanoscale structures of functional materials, such as phase-change materials. Phase-change memory technology enables nonvolatile, low-power memory in devices by storing information through reversible changes in a phase-change material's atomic structure (i.e., transformations between amorphous and crystalline phases) that have corresponding changes in properties, including electronic resistivity and optical reflectivity. Here, we apply complementary X-ray absorption spectroscopy and X-ray pair distribution function analyses to experimentally identify the local- and medium-range atomic structure differences of GeTe and C-doped GeTe thin films. Upon controlled heating, composition- and temperature-dependent atomic structure evolution in GeTe and C-doped GeTe films shows differences in bonding behavior and local structure that directly influence crystallization onset temperature. We find that the introduction of C interrupts Ge–Ge bonds in amorphous GeTe, altering the as-deposited structure to be more similar to the distorted rocksalt structure of crystalline α–GeTe. The change alters the response of the amorphous atomic structure to heating and also lowers the crystallization onset temperature, from 230 °C in GeTe to 220 °C in the C-doped film. The combined insights from both X-ray techniques provide understanding of structural transformations that enables the development and optimization of next-generation memory and computing materials.

36 MATERIALS SCIENCE↗
DOE OSTI2014

EqualChance: Addressing Intra-set Write Variation to Increase Lifetime of Non-volatile Caches

To address the limitations of SRAM such as high-leakage and low-density, researchers have explored use of non-volatile memory (NVM) devices, such as ReRAM (resistive RAM) and STT-RAM (spin transfer torque RAM) for designing on-chip caches. A crucial limitation of NVMs, however, is that their write endurance is low and the large intra-set write variation introduced by existing cache management policies may further exacerbate this problem, thereby reducing the cache lifetime significantly. We present EqualChance, a technique to increase cache lifetime by reducing intra-set write variation. EqualChance works by periodically changing the physical cache-block location of a write-intensive data item within a set to achieve wear-leveling. Simulations using workloads from SPEC CPU2006 suite and HPC (high-performance computing) field show that EqualChance improves the cache lifetime by 4.29X. Also, its implementation overhead is small, and it incurs very small performance and energy loss.

cache lifetime↗
NASA NTRS1980

Investigation of multilayer magnetic domain lattice file

The feasibility of the self structured multilayered bubble domain memory as a mass memory medium for satellite applications is examined. Theoretical considerations of multilayer bubble supporting materials are presented, in addition to the experimental evaluation of current accessed circuitry for various memory functions. The design, fabrication, and test of four device designs is described, and a recommended memory storage area configuration is presented. Memory functions which were demonstrated include the current accessed propagation of bubble domains and stripe domains, pinning of stripe domain ends, generation of single and double bubbles, generation of arrays of coexisting strip and bubble domains in a single garnet layer, and demonstration of different values of the strip out field for single and double bubbles indicating adequate margins for data detection. All functions necessary to develop a multilayer self structured bubble memory device were demonstrated in individual experiments.

Torok, E. J.↗
DOE OSTI2014

Humidity effects on tip-induced polarization switching in lithium niobate

In the last several decades, ferroelectrics have attracted much attention as perspective materials for nonlinear optics and data storage devices. Scanning probe microscopy (SPM) has emerged as a powerful tool both for studies of domain structures with nanoscale spatial resolution and for writing the isolated nanodomains by local application of the electric field. Quantitative analysis of the observed behavior requires understanding the role of environmental factors on imaging and switching process. Here, we study the influence of the relative humidity in the SPM chamber on tip-induced polarization switching. The observed effects are attributed to existence of a water meniscus between the tip and the sample surface in humid atmosphere. These results are important for a deeper understanding of complex investigations of ferroelectric materials and their applications and suggest the necessity for fundamental studies of electrocapillary phenomena at the tip-surface junction and their interplay with bias-induced materials responses.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Nanoimaging of Organic Charge Retention Effects: Implications for Nonvolatile Memory, Neuromorphic Computing, and High Dielectric Breakdown Devices

While a large variety of organic and molecular materials have been found to exhibit charge memory effects, the underlying mechanism is not well-understood, which hinders rational device design. Here, we study the charge retention mechanism of a nanoscale memory system, an organic monolayer on a silicon substrate, with Au nanoparticles on top serving as the electrical contact. Combining scanning probe imaging/manipulation and density functional simulations, we observe stable charge retention effects in the system and attributed it to polaron effects at the amine functional groups. Finally, our findings can pave the way for applications in nonvolatile memory, neuromorphic computing, and high dielectric breakdown devices.

36 MATERIALS SCIENCE↗
NASA NTRS2000

Evaluation of Data Retention and Imprint Characteristics of FRAMs Under Environmental Stresses for NASA Applications

A major reliability issue for all advanced nonvolatile memory (NVM) technology devices including FRAMs (Ferroelectric random access memories) is the data retention characteristics over extended period of time, under environmental stresses and exposure to total ionizing dose (TID) radiation effects. For this testing, 256 Kb FRAMs in 28-pin plastic DIPS, rated for industrial grade temperature range of -40 C to +85 C, were procured. These are two-transistor, two-capacitor (2T-2C) design FRAMs. In addition to data retention characteristics, the parts were also evaluated for imprint failures, which are defined as the failure of cells to change from a "preferred" state, where it has been for a significant period of time to an opposite state (e.g., from 1 to 0, or 0 to 1). These 256 K FRAMs were subjected to scanning acoustic microscopy (C-SAM); 1,000 temperature cycles from -65 C to +150 C; high temperature aging at 150 C, 175 C, and 200 C for 1,000 hours; highly accelerated stress test (HAST) for 500 hours; 1,000 hours of operational life test at 125 C; and total ionizing dose radiation testing. As a preconditioning, 10 K read/write cycles were performed on all devices. Interim electrical measurements were performed throughout this characterization, including special imprint testing and final electrical testing. Some failures were observed during high temperature aging test at 200 C, during HAST testing, and during 1,000 hours of operational life at 125 C. The parts passed 10 Krad exposure, but began showing power supply current increases during the dose increment from 10 Krad to 30 Krad, and at 40 Krad severe data retention and parametric failures were observed. Failures from various environmental group testing are currently being analyzed.

Sharma, Ashok K.↗
DOE OSTI2018

Experimental and Theoretical Investigations of Magnetic Properties of Co Ferrite/Polyvinyl Alcohol Nanocomposites

Cobalt ferrite nanoparticles (NPs) have been synthesized by the modified co-precipitation technique in the presence of the polyvinyl alcohol (PVA) matrix. The structural and magnetic properties of NPs are tunable by means of interaction between the polymer and the surface of NPs. Magnetic properties of NPs were simulated using the accurate Monte Carlo (MC) method. In addition, the magnetic anisotropy constant has been obtained by means of the law of approach to saturation magnetization (LAS). The experimental and theoretical results are in good agreement with each other and show that the as-synthesized NPs are single domain and approximately non-interacting. The anisotropy constant and size of the NPs increase by increasing the concentration of precursors in the reaction medium. Nanocomposites have been characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Hysteresis loops were investigated at room temperature using a vibrating sample magnetometer (VSM). The crystallite size of single-domain NPs is lower than 20 nm, and the obtained results from FT-IR confirmed the interaction between PVA and the surface of the particles. These approximately non-interacting NPs are useful for magnetic data storage.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Three Dimensional Dynamics and Fluctuations of DNA-Nanogold Dimers by Individual-Particle Electron Tomography

Over time, organic-inorganic hybridized nanocrystals have been proven as an important additional tool for addressing many emerging challenges biological and material sciences. Nanogold and quantum dot conjugates have been used extensively as biomolecular markers, while DNA base pairing has directed the self-assembly of discrete groupings and arrays of organic and inorganic nanocrystals in formation of a network solid for electronic devices and memory components. The control of DNA-mediated assembly depends crucially upon the ability to exposure three-dimensional (3D) structure of DNA-nanocrystals hybridized building blocks. Current techniques limit in structure determination of flexible and heterogeneous sample. Here, we employed the electron tomography and negative-staining techniques to investigate the 3D structure of DNA-nanogold dimers that were self-assembled from a mixture of an 84-base-pair double-stranded DNA (dsDNA) conjugated with two 5-nm nanogold particles. We reconstructed a total of 14 electron density maps at a resolution of ~2 nm from each individual dsDNA-nanogold particle using the individual-particle electron tomography (IPET) reconstruction method. Using these 3D density maps as constrain, we projected a standard flexible DNA model onto the observed EM density maps and derived 14 conformations of dsDNA by molecular dynamics simulations. By aligning these structures from one distal end nanogold, the distribution showed the DNA fluctuation and flexibility between nanogolds, which providing a blueprint research for studying of DNA-mediated assembly of complex inorganic nanostructures.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Effect of La{sub 2}O{sub 3}-treatment on textural and solid-solid interactions in ferric/cobaltic oxides system

Pure and La{sub 2}O{sub 3}-containing (0.75-3.0 mol%) Fe{sub 2}O{sub 3}/Co{sub 3}O{sub 4} solids were prepared by thermal treatment of their carbonates at 500-700 Degree-Sign C. The produced solids were characterized using XRD, HRTEM, EDX and nitrogen adsorption at -196 Degree-Sign C. The results revealed that pure solids calcined at 600 and 700 Degree-Sign C consisted of nanosized CoFe{sub 2}O{sub 4} phase, while pure mixed solids calcined at 500 Degree-Sign C consisted of trace amount of CoFe{sub 2}O{sub 4} and unreacted Fe{sub 2}O{sub 3}, Co{sub 3}O{sub 4} phases. The presence of 0.75 mol% La{sub 2}O{sub 3} enhanced solid-solid interaction between Fe{sub 2}O{sub 3} and Co{sub 3}O{sub 4} at 500 Degree-Sign C yielding CoFe{sub 2}O{sub 4}. The ferrite phase existed also in all mixed oxides upon treated with La{sub 2}O{sub 3} besides LaCoO{sub 3} phase. LaCoO{sub 3} existed as a major phase in all mixed oxides treated with 3 mol% La{sub 2}O{sub 3}. La{sub 2}O{sub 3}-treatment modified the crystallite size of all phases present to an extent dependent on calcination temperature and amount of La{sub 2}O{sub 3} content. This treatment decreased effectively the S{sub BET} of all mixed solids. - Graphical Abstract: TEM photographs of pure mixed oxides calcined at 500 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer Cobalt ferrite exhibit chemical stability, low electric loss and high coercivity. Black-Right-Pointing-Pointer Cobalt ferrite is used in microwave devices, computer memories and magnetic storage. Black-Right-Pointing-Pointer Solid-solid interactions in ferric/cobaltic oxides system were investigated. Black-Right-Pointing-Pointer La{sub 2}O{sub 3}-treatment modified surface compositions of the system investigated. Black-Right-Pointing-Pointer All phases present in various solids existed as nanosized solids.

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

Electronic and thermal properties of the phase-change memory material, Ge 2 Sb 2 Te 5 , and results from spatially resolved transport calculations

Here, we report new insights into the electronic, structural, and transport (heat and charge) properties of the phase-change memory material amorphous Ge 2 Sb 2 Te 5 . Using realistic structural models of Konstantinou et al., (2019), we analyze the topology, electronic states, and lattice dynamics with density functional methods, including hybrid-functional calculations and machine-learned interatomic potentials. The Kohn–Sham orbitals near the Fermi level display a strong electron–phonon coupling, and exhibit large energy fluctuations at room temperature. The conduction tail states exhibit larger phonon-induced fluctuations than the valence tail states. To resolve transport at the atomic scale, we employ space-projected electronic conductivity and site-projected thermal conductivity methods. Local analysis of heat transport highlights the role of filamentary networks dominated by Te, with Sb and Ge making progressively smaller contributions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

3D Nanomagnetism in Low Density Interconnected Nanowire Networks

Free-standing, interconnected metallic nanowire networks with densities as low as 40 mg/cm 3 have been achieved over centimeter-scale areas, using electrodeposition into polycarbonate membranes that have been ion-tracked at multiple angles. Networks of interconnected magnetic nanowires further provide an exciting platform to explore 3-dimensional nanomagnetism, where their structure, topology, and frustration may be used as additional degrees of freedom to tailor the materials properties. New magnetization reversal mechanisms in cobalt networks are captured by the first-order reversal curve method, which demonstrate the evolution from strong demagnetizing dipolar interactions to intersection-mediated domain wall pinning and propagation, and eventually to shape-anisotropy dominated magnetization reversal. These findings open up new possibilities for 3-dimensional integrated magnetic devices for memory, complex computation, and neuromorphics.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Dynamic Manipulation in Piezoresponse Force Microscopy: Creating Nonequilibrium Phases with Large Electromechanical Response

We discuss how domain walls and topological defects in ferroelectric materials have emerged as a powerful tool for functional electronic devices including memory and logic. Similarly, wall interactions and dynamics underpin a broad range of mesoscale phenomena ranging from giant electromechanical responses to memory effects. Exploring the functionalities of individual domain walls, their interactions, and controlled modifications of the domain structures is crucial for applications and fundamental physical studies. However, the dynamic nature of these features severely limits studies of their local physics since application of local biases or pressures in piezoresponse force microscopy induce wall displacement as a primary response. Here, we introduce an approach for the control and modification of domain structures based on automated experimentation, whereby real-space image-based feedback is used to control the tip bias during ferroelectric switching, allowing for modification routes conditioned on domain states under the tip. This automated experiment approach is demonstrated for the exploration of domain wall dynamics and creation of metastable phases with large electromechanical response.

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

Lead-free epitaxial ferroelectric material integration on semiconducting (100) Nb-doped SrTiO3 for low-power non-volatile memory and efficient ultraviolet ray detection

We report lead-free ferroelectric based resistive switching non-volatile memory (NVM) devices with epitaxial (1-x)BaTiO3-xBiFeO3 (x = 0.725) (BT-BFO) film integrated on semiconducting (100) Nb (0.7%) doped SrTiO3 (Nb:STO) substrates. The piezoelectric force microscopy (PFM) measurement at room temperature demonstrated ferroelectricity in the BT-BFO thin film. PFM results also reveal the repeatable polarization inversion by poling, manifesting its potential for read-write operation in NVM devices. The electroforming-free and ferroelectric polarization coupled electrical behaviour demonstrated excellent resistive switching with high retention time, cyclic endurance and low set/reset voltages. X-ray photoelectron spectroscopy was utilized to determine the band alignment at the BT-BFO and Nb:STO heterojunction and it exhibited staggered band alignment. This heterojunction is found to behave as an efficient ultraviolet photo-detector with low rise and fall time. The architecture also demonstrates half-wave rectification under low and high input signal frequencies, where the output distortion is minimal. The results provide avenue for an electrical switch that can regulate the pixels in low or high frequency images. Combined this work paves the pathway towards designing future generation low-power ferroelectric based microelectronic devices by merging both electrical and photovoltaic properties of BT-BFO materials.

Science & Technology - Other Topics↗
DOE OSTI2024

Recent advancements in chiral spintronics: from molecular-level insights to device applications. A prospect based on the interplay between physical and chemical properties of chiral systems

This review discusses recent advancements in chiral-based spin-electronic devices achieved using suitable combinations of organic, inorganic and hybrid materials. The focus is on how chirality can be effectively used to control spin in practical applications, particularly in spintronic sensors and consumer devices. Interestingly, the underlying mechanism for this control is the chiral-induced spin selectivity (CISS) effect, which links the structural chirality of a material to its spin-selective electronic transport properties. The CISS effect arises from the observation that charge transmission in chiral systems is spin selective. Experimental evidence suggests a relationship between electron spin and the structural handedness of the material. In conclusion, this unique structure-transport relationship can be exploited to design a wide range of spintronics devices, including memory, transistors, logic gates and molecular q-bits.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Process Performance of Optima XEx Single Wafer High Energy Implanter

To meet the process requirements for well formation in future CMOS memory production, high energy implanters require more robust angle, dose, and energy control while maintaining high productivity. The Optima XEx high energy implanter meets these requirements by integrating a traditional LINAC beamline with a robust single wafer handling system. To achieve beam angle control, Optima XEx can control both the horizontal and vertical beam angles to within 0.1 degrees using advanced beam angle measurement and correction. Accurate energy calibration and energy trim functions accelerate process matching by eliminating energy calibration errors. The large volume process chamber and UDC (upstream dose control) using faraday cups outside of the process chamber precisely control implant dose regardless of any chamber pressure increase due to PR (photoresist) outgassing. An optimized RF LINAC accelerator improves reliability and enables singly charged phosphorus and boron energies up to 1200 keV and 1500 keV respectively with higher beam currents. A new single wafer endstation combined with increased beam performance leads to overall increased productivity. We report on the advanced performance of Optima XEx observed during tool installation and volume production at an advanced memory fab.

43 PARTICLE ACCELERATORS↗