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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 1,189 records · Page 66
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Grazing-Incidence Texture Tomography and Diffuse Reflectivity Tomography of an Organic Semiconductor Device Array

The use of grazing-incidence scattering methods for the characterization of 2D patterned organic thin films is limited due to the elongated 1D footprint of the X-ray beam on the sample. However, this characteristic feature can be turned into an advantage, when combined with tomographic reconstruction. In this pilot study we show, how the use of a chosen texture reflection and a diffuse reflectivity signal can each provide 2D images of the deposits, simultaneously revealing the organic film's crystal orientation and the location of the metal electrodes in a field-effect transistor structure from a single sequence of diffraction images.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Photoconductive Semiconductor Switches: Materials, Physics, and Applications

Photoconductive semiconductor switching (PCSS) devices have unique characteristics to address the growing need for electrically isolated, optically gated, picosecond-scale jitter devices capable of operating at high voltage, current, and frequency. The state of the art in material selection, doping, triggering, and system integration in PCSSs is presented. The material properties and doping considerations of GaN, GaAs, SiC, diamond, and β-Ga2O3 in the fabrication of PCSS devices are discussed. A review of the current understanding of the physics of the high-gain mode known as lock-on is presented.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Intrinsic (Trap‐Free) Transistors Based on Epitaxial Single‐Crystal Perovskites

Abstract The first experimental realization of the intrinsic (not dominated by defects) charge conduction regime in lead‐halide perovskite field‐effect transistors (FETs) is reported. The advance is enabled by: i) a new vapor‐phase epitaxy technique that results in large‐area single‐crystalline cesium lead bromide (CsPbBr 3 ) films with excellent structural and surface properties, including atomically flat surface morphology, essentially free from defects and traps at the level relevant to device operation; ii) an extensive materials analysis of these films using a variety of thin‐film and surface probes certifying the chemical and structural quality of the material; and iii) the fabrication of nearly ideal (trap‐free) FETs with characteristics superior to any reported to date. These devices allow the investigation of the intrinsic FET and (gated) Hall‐effect carrier mobilities as functions of temperature. The intrinsic mobility is found to increase on cooling from ≈30 cm 2 V −1 s −1 at room temperature to ≈250 cm 2 V −1 s −1 at 50 K, revealing a band transport limited by phonon scattering. Establishing the intrinsic (phonon‐limited) mobility provides a solid test for theoretical descriptions of carrier transport in perovskites, reveals basic limits to the technology, and points to a path for future high‐performance perovskite electronic devices.

36 MATERIALS SCIENCE↗
NASA NTRS1990

In Situ deposition of YBCO high-T(sub c) superconducting thin films by MOCVD and PE-MOCVD

Metalorganic Chemical Vapor Deposition (MOCVD) offers the advantages of a high degree of compositional control, adaptability for large scale production, and the potential for low temperature fabrication. The capability of operating at high oxygen partial pressure is particularly suitable for in situ formation of high temperature superconducting (HTSC) films. Yttrium barium copper oxide (YBCO) thin films having a sharp zero-resistance transition with T( sub c) greater than 90 K and Jc approx. 10 to the 4th power A on YSZ have been prepared, in situ, at a substrate temperature of about 800 C. Moreover, the ability to form oxide films at low temperature is very desirable for device applications of HTSC materials. Such a process would permit the deposition of high quality HTSC films with a smooth surface on a variety of substrates. Highly c-axis oriented, dense, scratch resistant, superconducting YBCO thin films with mirror-like surfaces have been prepared, in situ, at a reduced substrate temperature as low as 570 C by a remote microwave-plasma enhanced metalorganic chemical vapor deposition (PE-MOCVD) process. Nitrous oxide was used as a reactant gas to generate active oxidizing species. This process, for the first time, allows the formation of YBCO thin films with the orthorhombic superconducting phase in the as-deposited state. The as-deposited films grown by PE-MOCVD show attainment of zero resistance at 72 K with a transition width of about 5 K. MOCVD was carried out in a commercial production scale reactor with the capability of uniform deposition over 100 sq cm per growth run. Preliminary results indicate that PE-MOCVD is a very attractive thin film deposition process for superconducting device technology.

Zhao, J.↗
DOE OSTI2021

Metamaterial-Inspired Vacuum Electron Devices and Accelerators

Metamaterials (MTMs) are structured materials with subwavelength features that can be engineered to have some unique properties not found in nature, such as negative refractive index, reversed Doppler effect, and reversed Cherenkov radiation. Based on these novel MTMs, several important research groups have made great attempts to develop novel MTM-inspired vacuum electron devices (VEDs) and accelerators. Just as solid-state power devices are innovated by incessant emerging of new semiconductor materials, VEDs can also be inspired by MTMs to have very remarkable advantages, such as smaller size, higher power, higher efficiency, and/or larger gain relative to conventional VEDs, such as traveling-wave tubes, backward-wave oscillators, and klystrons. Similarly, relative to conventional accelerators, MTM-inspired accelerators have obvious advantages, such as smaller size and higher accelerating gradient. Furthermore, MTM-inspired devices have promising applications in areas such as radar, communication, electronic warfare, microwave heating, and imaging.

43 PARTICLE ACCELERATORS↗
NASA NTRS1991

In-situ deposition of YBCO high-Tc superconducting thin films by MOCVD and PE-MOCVD

Metal-Organic Chemical Vapor Deposition (MOCVD) offers the advantages of a high degree of compositional control, adaptability for large scale production, and the potential for low temperature fabrication. The capability of operating at high oxygen partial pressure is particularly suitable for in situ formation of high temperature superconducting (HTSC) films. Yttrium barium copper oxide (YBCO) thin films having a sharp zero-resistance transition with T(sub c) greater than 90 K and J(sub c) of approximately 10(exp 4) A on YSZ have been prepared, in situ, at a substrate temperature of about 800 C. Moreover, the ability to form oxide films at low temperature is very desirable for device applications of HTSC materials. Such a process would permit the deposition of high quality HTSC films with a smooth surface on a variety of substrates. Highly c-axis oriented, dense, scratch resistant, superconducting YBCO thin films with mirror-like surfaces have been prepared, in situ, at a reduced substrate temperature as low as 570 C by a remote microwave-plasma enhanced metal-organic chemical vapor deposition (PE-MOCVD) process. Nitrous oxide was used as a reactant gas to generate active oxidizing species. This process, for the first time, allows the formation of YBCO thin films with the orthorhombic superconducting phase in the as-deposited state. The as-deposited films grown by PE-MOCVD show attainment of zero resistance at 72 K with a transition width of about 5 K. MOCVD was carried out in a commercial production scale reactor with the capability of uniform deposition over 100 sq cm per growth run. Preliminary results indicate that PE-MOCVD is a very attractive thin film deposition process for superconducting device technology.

Zhao, J.↗
DOE OSTI2020

Quantum coherent devices with reduced energy dissipation

The disclosed technology can be used to increase lifetimes of quantum coherent devices such as qubits including transmons and xmons and to reduce the losses in resonators. Energy stored in superconducting devices can be lost by emission of phonons that couple to the environment. Defects in one or more materials in the quantum coherent device can cause the coupling to phonons. Patterning one or more of the layers creates a phononic bandgap that reduces or eliminates the emission of the phonons to the environment. The energy then couples back to the quantum coherent device.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Mixed halide bulk perovskite triplet sensitizers: Interplay between band alignment, mid-gap traps, and phonons

Photon upconversion, particularly via triplet-triplet annihilation (TTA), could prove beneficial in expanding the efficiencies and overall impacts of optoelectronic devices across a multitude of technologies. The recent development of bulk metal halide perovskites as triplet sensitizers is one potential step toward the industrialization of upconversion-enabled devices. In this work, we investigate the impact of varying additions of bromide into a lead iodide perovskite thin film on the TTA upconversion process in the annihilator molecule rubrene. We find an interplay between the bromide content and the overall device efficiency. In particular, a higher bromide content results in higher internal upconversion efficiencies, enabled by more efficient charge extraction at the interface, likely due to a more favorable band alignment. However, the external upconversion efficiency decreases, as the absorption cross section in the near infrared is reduced. The highest upconversion performance is found in our study for a bromide content of 5%. This result can be traced back to a high absorption cross section in the near infrared and higher photoluminescence quantum yield in comparison to the iodide-only perovskite, as well as an increased driving force for charge transfer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2016

A Computationally-Efficient, Multi-Mechanism Based Framework for the Comprehensive Modeling of the Evolutionary Behavior of Shape Memory Alloys

The report summarizes the accomplishments made during the 4-year duration of the project. Here, the major emphasis is placed on the different tasks performed by the two research teams; i.e., the modeling activities by the University of Akron (UA) team and the experimental and neutron diffraction studies conducted by the University of Central Florida (UCF) team, during this 4-year period. Further technical details are given in the upcoming sections by UA and UCF for each of the milestones/years (together with the corresponding figures and captions).The project majorly involved the development, validation, and application of a general theoretical model that is capable of capturing the nonlinear hysteretic responses, including pseudoelasticity, shape memory effect, rate-dependency, multi-axiality, asymmetry in tension versus compression response of shape memory alloys. Among the targeted goals for the SMA model was its ability to account for the evolutionary character response (including transient and long term behavior under sustained cycles) for both conventional and high temperature (HT) SMAs, as well as being able to simulate some of the devices which exploit these unique material systems. This required extensive (uniaxial and multi-axial) experiments needed to guide us in calibrating and characterizing the model. Moreover, since the model is formulated on the theoretical notion of internal state variables (ISVs), neutron diffraction experiments were needed to establish the linkage between the micromechanical changes and these ISVs. In addition, the design of the model should allow easy implementation in large scale finite element application to study the behavior of devices making use of these SMA materials under different loading controls. Summary of the activities, progress/achievements made during this period is given below in details for the University of Akron and the University (Section 2.0) of Central Florida (Section 3.0).

Alloys↗
NASA NTRS2015

Compliant Electrode and Composite Material for Piezoelectric Wind and Mechanical Energy Conversions

A thin film device for harvesting energy from wind. The thin film device includes one or more layers of a compliant piezoelectric material formed from a composite of a polymer and an inorganic material, such as a ceramic. Electrodes are disposed on a first side and a second side of the piezoelectric material. The electrodes are formed from a compliant material, such as carbon nanotubes or graphene. The thin film device exhibits improved resistance to structural fatigue upon application of large strains and repeated cyclic loadings.

Chen, Bin↗
DOE OSTI2023

Ultra-thin lithium aluminate spinel ferrite films with perpendicular magnetic anisotropy and low damping

Ultra-thin films of low damping ferromagnetic insulators with perpendicular magnetic anisotropy have been identified as critical to advancing spin-based electronics by significantly reducing the threshold for current-induced magnetization switching while enabling new types of hybrid structures or devices. Here, we have developed a new class of ultra-thin spinel structure Li 0.5 Al 1.0 Fe 1.5 O 4 (LAFO) films on MgGa 2 O 4 (MGO) substrates with: 1) perpendicular magnetic anisotropy; 2) low magnetic damping and 3) the absence of degraded or magnetic dead layers. These films have been integrated with epitaxial Pt spin source layers to demonstrate record low magnetization switching currents and high spin-orbit torque efficiencies. These LAFO films on MGO thus combine all of the desirable properties of ferromagnetic insulators with perpendicular magnetic anisotropy, opening new possibilities for spin based electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Manipulation of the magnetic monopole injection for topological transition

Abstract Manipulating the topological properties of spin textures in magnetic materials is of great interest due to the rich physics and promising technological applications of these materials in advanced electronic devices. A spin texture with desired topological properties can be created by magnetic monopole injection, resulting in topological transitions involving changes in the topological charge. Therefore, controlling magnetic monopole injection has paramount importance for obtaining the desired spin textures but has not yet been reported. Here, we report the use of reliably manipulated magnetic monopole injection in the topological transition from stripe domains to skyrmions in an Fe/Gd multilayer. An easily tunable in-plane magnetic field applied to an Fe/Gd multilayer plays a key role in the magnetic monopole injection by modulating the local exchange energy. Our findings facilitate the efficient management of topological transitions by providing an important method for controlling magnetic monopole injection.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Parallel transport modeling of linear divertor simulators with fundamental ion cyclotron heating *

Abstract The Material Plasma Exposure eXperiment (MPEX) is a steady state linear device with the goal to perform plasma material interaction studies at future fusion reactor relevant conditions. A prototype of MPEX referred as ‘Proto-MPEX’ is designed to carry out research and development related to source, heating and transport concepts on the planned full MPEX device. The auxiliary heating schemes in MPEX are based on cyclotron resonance heating with radio frequency (RF) waves. Ion cyclotron heating (ICH) and electron cyclotron heating in MPEX are used to independently heat the ions and electrons and provide fusion divertor conditions ranging from sheath-limited to fully detached divertor regimes at a material target. A hybrid particle-in-cell code- PICOS++ is developed and applied to understand the plasma parallel transport during ICH in MPEX/Proto-MPEX to the target. With this tool, evolution of the distribution function of MPEX/Proto-MPEX ions is modeled in the presence of (a) Coulomb collisions, (b) volumetric particle sources and (c) quasi-linear RF-based ICH. The code is benchmarked against experimental data from Proto-MPEX and simulation data from B2.5 EIRENE. The experimental observation of ‘density-drop’ near the target in Proto-MPEX and MPEX during ICH is demonstrated and explained via physics-based arguments using PICOS++ modeling. In fact, the density drops at the target during ICH in Proto-MPEX/MPEX to conserve the flux and to compensate for the increased flow during ICH. Furthermore, sensitivity scans of various plasma parameters with respect to ICH power are performed for MPEX to investigate its role on plasma transport and particle and energy fluxes at the target.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

A chiral switchable photovoltaic ferroelectric 1D perovskite

Spin and valley degrees of freedom in materials without inversion symmetry promise previously unknown device functionalities, such as spin-valleytronics. Control of material symmetry with electric fields (ferroelectricity), while breaking additional symmetries, including mirror symmetry, could yield phenomena where chirality, spin, valley, and crystal potential are strongly coupled. Here we report the synthesis of a halide perovskite semiconductor that is simultaneously photoferroelectricity switchable and chiral. Spectroscopic and structural analysis, and first-principles calculations, determine the material to be a previously unknown low-dimensional hybrid perovskite (R)-(-)-1-cyclohexylethylammonium/(S)-(+)-1 cyclohexylethylammonium) PbI 3 . Optical and electrical measurements characterize its semiconducting, ferroelectric, switchable pyroelectricity and switchable photoferroelectric properties. Temperature dependent structural, dielectric and transport measurements reveal a ferroelectric-paraelectric phase transition. Circular dichroism spectroscopy confirms its chirality. The development of a material with such a combination of these properties will facilitate the exploration of phenomena such as electric field and chiral enantiomer–dependent Rashba-Dresselhaus splitting and circular photogalvanic effects

36 MATERIALS SCIENCE↗
NASA NTRS1975

Ternary compound thin film solar cells

A group of ternary compound semiconductor (I-III-VI2) thin films for future applications in photovoltaic devices is proposed. The consideration of these materials (CuInSe2, CuInTe2 and especially CuInS2) for long range device development is emphasized. Much of the activity to date has been concerned with the growth and properties of CuInX2 films. X-ray and electron diffraction analyses, Hall mobility and coefficient, resistivity and carrier concentration variations with substrate and film temperature as well as grain size data have been determined. Both p- and n-type films of CuInS2 and CuInSe2 have been produced. Single and double source deposition techniques have been utilized. Some data have been recorded for annealed films.

Kazmerski, L. L.↗
DOE OSTI2025

Opportunities and Challenges of Computational Electromagnetics Methods for Superconducting Circuit Quantum Device Modeling: A Practical Review

High-fidelity numerical methods that model the physical layout of a device are essential for the design of many technologies. For methods that characterize electromagnetic effects, these numerical methods are referred to as computational electromagnetics (CEM) methods. Although the CEM research field is mature, emerging applications can still stress the capabilities of the techniques in use today. The design of superconducting circuit quantum devices falls in this category due to the unconventional material properties and important features of the devices covering nanometer to centimeter scales. Such multiscale devices can stress the fundamental properties of CEM tools which can lead to an increase in simulation times, a loss in accuracy, or even cause no solution to be reliably found. While these challenges are being investigated by CEM researchers, knowledge about them is limited in the broader community of users of these CEM tools. This review is meant to serve as a practical introduction to the fundamental aspects of the major CEM techniques that a researcher may need to choose between to model a device, as well as provide insight into what steps they may take to alleviate some of their challenges. Our focus is on highlighting the main concepts without rigorously deriving all the details, which can be found in many textbooks and articles. After covering the fundamentals, we discuss more advanced topics related to the challenges of modeling multiscale devices with specific examples from superconducting circuit quantum devices. We conclude with a discussion on future research directions that will be valuable for improving the ability to successfully design increasingly more sophisticated superconducting circuit quantum devices. Although our focus and examples are taken from this area, researchers from other fields will still benefit from the details discussed here.

Elkin, Samuel T. [Virginia Tech., Blacksburg]↗
DOE OSTI2022

Control of structure and spin texture in the van der Waals layered magnet CrSBr

Controlling magnetism at nanometer length scales is essential for realizing high-performance spintronic, magneto-electric and topological devices and creating on-demand spin Hamiltonians probing fundamental concepts in physics. Van der Waals (vdW)-bonded layered magnets offer exceptional opportunities for such spin texture engineering. Here, we demonstrate nanoscale structural control in the layered magnet CrSBr with the potential to create spin patterns without the environmental sensitivity that has hindered such manipulations in other vdW magnets. We drive a local phase transformation using an electron beam that moves atoms and exchanges bond directions, effectively creating regions that have vertical vdW layers embedded within the initial horizontally vdW bonded exfoliated flakes. We calculate that the newly formed two-dimensional structure is ferromagnetically ordered in-plane with an energy gap in the visible spectrum, and weak antiferromagnetism between the planes, suggesting possibilities for creating spin textures and quantum magnetic phases.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Foundry-compatible high-resolution patterning of vertically phase-separated semiconducting films for ultraflexible organic electronics

Solution processability of polymer semiconductors becomes an unfavorable factor during the fabrication of pixelated films since the underlying layer is vulnerable to subsequent solvent exposure. A foundry-compatible patterning process must meet requirements including high-throughput and high-resolution patternability, broad generality, ambient processability, environmentally benign solvents, and, minimal device performance degradation. However, known methodologies can only meet very few of these requirements. Here, a facile photolithographic approach is demonstrated for foundry-compatible high-resolution patterning of known p- and n-type semiconducting polymers. This process involves crosslinking a vertically phase-separated blend of the semiconducting polymer and a UV photocurable additive, and enables ambient processable photopatterning at resolutions as high as 0.5 μm in only three steps with environmentally benign solvents. The patterned semiconducting films can be integrated into thin-film transistors having excellent transport characteristics, low off-currents, and high thermal (up to 175 °C) and chemical (24 h immersion in chloroform) stability. Moreover, these patterned organic structures can also be integrated on 1.5 μm-thick parylene substrates to yield highly flexible (1 mm radius) and mechanically robust (5,000 bending cycles) thin-film transistors.

36 MATERIALS SCIENCE↗