Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “devices”

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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Sub-wavelength waveguide loaded by a complementary electric metamaterial for vacuum electron devices

We report the electromagnetic properties of a waveguide loaded by complementary electric split ring resonators (CeSRRs) and the application of the waveguide in vacuum electronics. The S-parameters of the CeSRRs in free space are calculated using the HFSS code and are used to retrieve the effective permittivity and permeability in an effective medium theory. The dispersion relation of a waveguide loaded with the CeSRRs is calculated by two approaches: by direct calculation with HFSS and by calculation with the effective medium theory; the results are in good agreement. An improved agreement is obtained using a fitting procedure for the permittivity tensor in the effective medium theory. The gain of a backward wave mode of the CeSRR-loaded waveguide interacting with an electron beam is calculated by two methods: by using the HFSS model and traveling wave tube theory; and by using a dispersion relation derived in the effective medium model. Results of the two methods are in very good agreement. The proposed all-metal structure may be useful in miniaturized vacuum electron devices.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Nanoscale pressure sensors realized from suspended graphene membrane devices

We study the transport properties of graphene layers placed over ∼200 nm triangular holes via attached electrodes under applied pressure. We find that the injected current division between counter electrodes depends on pressure and can be used to realize a nanoscale pressure sensor. Estimating various potential contributions to the resistivity change of the deflected graphene membrane including piezoresistivity, changing gate capacitance, and the valley Hall effect due to the pressure-induced synthetic magnetic field, we find that the valley Hall effect yields the largest expected contribution to the longitudinal resistivity modulation for accessible device parameters. Such devices in the ballistic transport regime may enable the realization of tunable valley polarized electron sources.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Development of core ion temperature gradients and edge sheared flows in a helicon plasma device investigated by laser induced fluorescence measurements

We report experimental observation of ion heating and subsequent development of a prominent ion temperature gradient in the core of a linear magnetized plasma device, and the controlled shear de-correlation experiment. Simultaneously, we also observe the development of strong sheared flows at the edge of the device. Both the ion temperature and the azimuthal velocity profiles are quite flat at low magnetic fields. As the magnetic field is increased, the core ion temperature increases, producing centrally peaked ion temperature profiles and therefore strong radial gradients in the ion temperature. Similarly, we observe the development of large azimuthal flows at the edge, with increasing magnetic field, leading to strong radially sheared plasma flows. The ion velocities and temperatures are derived from laser induced fluorescence measurements of Doppler resolved velocity distribution functions of argon ions. These features are consistent with the previous observations of simultaneously existing radially separated multiple plasma instabilities that exhibit complex plasma dynamics in a very simple plasma system. The ion temperature gradients in the core and the radially sheared azimuthal velocities at the edge point to mechanisms that can drive the multiple plasma instabilities, that were reported earlier.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Parallel Reconstruction of Three Dimensional Magnetohydrodynamic Equilibria in Plasma Confinement Devices

Fast, accurate three dimensional reconstructions of plasma equilibria, crucial for physics interpretation of fusion data generated within confinement devices like stellarators/ tokamaks, are computationally very expensive and routinely require days, even weeks, to complete using serial approaches. Here, we present a parallel implementation of the three dimensional plasma reconstruction code, V3FIT. A formal analysis to identify the performance bottlenecks and scalability limits of this new parallel implementation, which combines both task and data parallelism, is presented. The theoretical findings are supported by empirical performance results on several thousands of processor cores of a Cray XC30 supercomputer. Parallel V3FIT is shown to deliver over 40X speedup, enabling fusion scientists to carry out three dimensional plasma equilibrium reconstructions at unprecedented scales in only a few hours (instead of in days/weeks) for the first time.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Modeling DNP3 Traffic Characteristics of Field Devices in SCADA Systems of the Smart Grid

In the generation, transmission, and distribution sectors of the smart grid, intelligence of field devices is realized by programmable logic controllers (PLCs). Many smart-grid subsystems are essentially cyber-physical energy systems (CPES): For instance, the power system process (i.e., the physical part) within a substation is monitored and controlled by a SCADA network with hosts running miscellaneous applications (i.e., the cyber part). To study the interactions between the cyber and physical components of a CPES, several co-simulation platforms have been proposed. However, the network simulators/emulators of these platforms do not include a detailed traffic model that takes into account the impacts of the execution model of PLCs on traffic characteristics. As a result, network traces generated by co-simulation only reveal the impacts of the physical process on the contents of the traffic generated by SCADA hosts, whereas the distinction between PLCs and computing nodes (e.g., a hardened computer running a process visualization application) has been overlooked. To generate realistic network traces using co-simulation for the design and evaluation of applications relying on accurate traffic profiles, it is necessary to establish a traffic model for PLCs. In this work, we propose a parameterized model for PLCs that can be incorporated into existing co-simulation platforms. We focus on the DNP3 subsystem of slave PLCs, which automates the processing of packets from the DNP3 master. To validate our approach, we extract model parameters from both the configuration and network traces of real PLCs. Simulated network traces are generated and compared against those from PLCs. Our evaluation shows that our proposed model captures the essential traffic characteristics of DNP3 slave PLCs, which can be used to extend existing co-simulation platforms and gain further insights into the behaviors of CPES.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2021

CdSexTe1-x/CdTe Devices with Reduced Interface Recombination Through Novel Back Contacts and Group-V Doping

Since excellent carrier lifetimes and front interface electronic quality are now achieved, rear interface recombination can limit V OC in CdSexTe1-x/CdTe solar cells. Several back-contact structures for devices were fabricated using combinations of tellurium, aluminum oxide, amorphous silicon, and indium tin oxide (ITO). Time-resolved photoluminescence was used to characterize such structures. We show increasingly improved interface passivation through the subsequent use of aluminum oxide, amorphous silicon, and ITO. Additionally, we show that arsenic-doped absorbers form a more passive interface with numerous back contact structures.

aluminum oxide↗
DOE OSTI2023

A Novel Spatial-Temporal Variational Quantum Circuit to Enable Deep Learning on NISQ Devices

Quantum computing presents a promising approach for machine learning with its capability for extremely parallel computation in high-dimension through superposition and entanglement. Despite its potential, existing quantum learning algorithms, such as Variational Quantum Circuits (VQCs), face challenges in handling more complex datasets, particularly those that are not linearly separable. What’s more, it encounters the deployability issue, making the learning models suffer a drastic accuracy drop after deploying them to the actual quantum devices. To overcome these limitations, this paper proposes a novel spatial-temporal design, namely “ST-VQC”, to integrate nonlinearity in quantum learning and improve the robustness of the learning model to noise. Specifically, ST-VQC can extract spatial features via a novel block-based encoding quantum sub-circuit coupled with a layer-wise computation quantum sub-circuit to enable temporal-wise deep learning. Additionally, a SWAP-Free physical circuit design is devised to improve robustness. These designs bring a number of hyperparameters. After a systematic analysis of the design space for each design component, an automated optimization framework is proposed to generate the ST-VQC quantum circuit. The proposed ST-VQC has been evaluated on two IBM quantum processors, ibm-cairo with 27 qubits and ibmq-lima with 7 qubits to assess its effectiveness. The results of the evaluation on the standard dataset for binary classification show that ST-VQC can achieve over 30% accuracy improvement compared with existing VQCs on actual quantum computers. Moreover, on a non-linear synthetic dataset, the STVQC outperforms a linear classifier by 27.9%, while the linear classifier using classical computing outperforms the existing VQC by 15.58%.

Li, Jinyang↗
DOE OSTI2017

Analysis of Multilayer Devices for Superconducting Electronics by High-Resolution Scanning Transmission Electron Microscopy and Energy Dispersive Spectroscopy

We used a focused ion beam to obtain cross-sectional specimens from both magnetic multilayer and Nb/Al-AlOx/Nb Josephson junction devices for characterization by scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDX). An automated multivariate statistical analysis of the EDX spectral images produced chemically unique component images of individual layers within the multilayer structures. STEM imaging elucidated distinct variations in film morphology, interface quality, and/or etch artifacts that could be correlated to magnetic and/or electrical properties measured on the same devices.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Investigation of interfacial impurities in m-plane GaN regrown p-n junctions for high-power vertical electronic devices

GaN is an attractive material for high-power electronics due to its wide bandgap and large breakdown field. Verticalgeometry devices are of interest due to their high blocking voltage and small form factor. One challenge for realizing complex vertical devices is the regrowth of low-leakage-current p-n junctions within selectively defined regions of the wafer. Presently, regrown p-n junctions exhibit higher leakage current than continuously grown p-n junctions, possibly due to impurity incorporation at the regrowth interfaces, which consist of c-plane and non-basal planes. Here, we study the interfacial impurity incorporation induced by various growth interruptions and regrowth conditions on m-plane p-n junctions on free-standing GaN substrates. The following interruption types were investigated: (1) sample in the main MOCVD chamber for 10 min, (2) sample in the MOCVD load lock for 10 min, (3) sample outside the MOCVD for 10 min, and (4) sample outside the MOCVD for one week. Regrowth after the interruptions was performed on two different samples under n-GaN and p-GaN growth conditions, respectively. Secondary ion mass spectrometry (SIMS) analysis indicated interfacial silicon spikes with concentrations ranging from 5e16 cm -3 to 2e18 cm -3 for the n-GaN growth conditions and 2e16 cm -3 to 5e18 cm-3 for the p-GaN growth conditions. Oxygen spikes with concentrations ~1e17 cm -3 were observed at the regrowth interfaces. Carbon impurity levels did not spike at the regrowth interfaces under either set of growth conditions. We have correlated the effects of these interfacial impurities with the reverse leakage current and breakdown voltage of regrown m-plane p-n junctions.

42 ENGINEERING↗
DOE OSTI2017

Liquefied gas electrolytes for electrochemical energy storage devices

Electrochemical capacitors and lithium-ion batteries have seen little change in their electrolyte chemistry since their commercialization, which has limited improvements in device performance. Combining superior physical and chemical properties and a high dielectric-fluidity factor, the use of electrolytes based on solvent systems that exclusively use components that are typically gaseous under standard conditions show a wide potential window of stability and excellent performance over an extended temperature range. Electrochemical capacitors using difluoromethane show outstanding performance from –78° to +65°C, with an increased operation voltage. The use of fluoromethane shows a high coulombic efficiency of ~97% for cycling lithium metal anodes, together with good cyclability of a 4-volt lithium cobalt oxide cathode and operation as low as –60°C, with excellent capacity retention.

Science & Technology - Other Topics↗
DOE OSTI2016

Review—Ultra-Wide-Bandgap AlGaN Power Electronic Devices

“Ultra” wide-bandgap semiconductors are an emerging class of materials with bandgaps greater than that of gallium nitride (EG > 3.4 eV) that may ultimately benefit a wide range of applications, including switching power conversion, pulsed power, RF electronics, UV optoelectronics, and quantum information. This paper describes the progress made to date at Sandia National Laboratories to develop one of these materials, aluminum gallium nitride, targeted toward high-power devices. The advantageous material properties of AlGaN are reviewed, questions concerning epitaxial growth and defect physics are covered, and the processing and performance of vertical- and lateral-geometry devices are described. The paper concludes with an assessment of the outlook for AlGaN, including outstanding research opportunities and a brief discussion of other potential applications.

36 MATERIALS SCIENCE↗