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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 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Frequency and energy characteristics of a Cu – Ne laser at different durations of the leading edge of the excitation pulse

The lasing characteristics of a copper vapour laser in a tube with forced heating, having a length of 50 cm and a diameter of 2 cm, excited by a train of pulses are investigated. Comparative studies of the frequency and energy characteristics of the laser are performed with a leading edge duration of the excitation pulse of ∼25 ns (when the capacitance discharges through a thyratron and a magnetic compression line) and ∼3 and 1 ns (using circuits with a high-speed switch – kivotron). It is shown that a decrease in the leading edge duration gives rise to an increase in the optimal pulse repetition rate up to ∼30 kHz, the generation efficiency up to 3.2 % and the generation power per unit length over 100 W m{sup −1}. The results obtained confirm the concept of limiting the frequency and energy characteristics of a copper vapour laser due to the insufficient rate of energy input into the plasma at high prepulse electron concentrations. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Effects of macroparticle weighting in axisymmetric particle-in-cell Monte Carlo collision simulations

In this paper, the effects of macroparticle (MP) weighting on the plasma discharge, particularly near the centerline, are investigated using a two-dimensional axisymmetric particle-in-cell Monte Carlo collision (PIC/MCC) model. A variable MP weight according to the radial position of the MPs is employed to maintain sufficient number of MPs near the centerline of the plasma source. Finally, the plasma density obtained from the PIC/MCC simulations for low-pressure (25–100 mTorr) capacitively coupled plasmas is found to be artificially large when the MP weight near the centerline is not well resolved, demonstrating the need for particle convergence studies for axisymmetric PIC/MCC simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Dielectric Relaxation by Quantum Critical Magnons

We report the experimental observation of dielectric relaxation by quantum critical magnons. Complex capacitance measurements reveal a dissipative feature with a temperature-dependent amplitude due to low-energy lattice excitations and an activation behavior of the relaxation time. The activation energy softens close to a field-tuned magnetic quantum critical point at H = H c and follows single-magnon energy for H > H c , showing its magnetic origin. Furthermore, our study demonstrates the electrical activity of coupled low-energy spin and lattice excitations, an example of quantum multiferroic behavior.

1-dimensional spin chains↗
DOE OSTI2018

Spread Spectrum Time Domain Reflectometry for Complex Impedances: Application to PV Arrays

Spread spectrum time domain reflectometry (SSTDR) has previously been used for detection and location of intermittent faults on live electrical wiring. These intermittent faults can be open circuits, short circuits, or resistive changes, all of which preserve the original shape of the SSTDR correlated waveform. But things are very different when SSTDR encounters a complex impedance discontinuity such as a capacitor or inductor. In this case, the reflection is a function of frequency, changing the shape of the SSTDR signature. In this paper, we will show the SSTDR response to single capacitors and inductors. We will also explore how SSTDR responds to arrays of PV panels (which are capacitive) connected by wires. We will show both simulations and measurements. In some configurations, it is relatively easy to see faults, although algorithms are still under development. In other configurations, little change occurs, which makes it very difficult to create a system for testing for these faults.

14 SOLAR ENERGY↗
DOE OSTI2017

A Pixel Pitch-Matched Ultrasound Receiver for 3-D Photoacoustic Imaging With Integrated Delta-Sigma Beamformer in 28-nm UTBB FD-SOI

This study presents a pixel pitch-matched readout chip for 3-D photoacoustic (PA) imaging, featuring a dedicated signal conditioning and delta-sigma modulation integrated within a pixel area of 250 μm by 250 μm. The proof-of-concept receiver was implemented in an STMicroelectronics's 28-nm Fully Depleted Silicon On Insulator technology, and interfaces to a 4 × 4 subarray of capacitive micromachined ultrasound transducers (CMUTs). The front-end signal conditioning in each pixel employs a coarse/fine gain tuning architecture to fulfill the 90-dB dynamic range requirement of the application. The employed delta-sigma beamforming architecture obviates the need for area-consuming Nyquist ADCs and thereby enables an efficient in-pixel A/D conversion. The per-pixel switched-capacitor ΔΣ modulator leverages slewing-dominated and area-optimized inverter-based amplifiers. It occupies only 1/4th of the pixel, and its area compares favorably with state-of-the-art designs that offer the same SNR and bandwidth. The modulator's measured peak signal-to-noise-and-distortion ratio is 59.9 dB for a 10-MHz input bandwidth, and it consumes 6.65 mW from a 1V supply. The overall subarray beamforming approach improves the area per channel by 7.4 times and the single-channel SNR by 8 dB compared to prior art with similar delay resolution and power dissipation. Finally, the functionality of the designed chip was evaluated within a PA imaging experiment, employing a flip-chip bonded 2-D CMUT array.

3-D photoacoustic (PA) imaging↗
DOE OSTI2025

Understanding Reliability Trade-Offs in 1T-nC and 2T-nC FeRAM Designs

Ferroelectric random access memory (FeRAM) is a promising candidate for energy-efficient nonvolatile memory, particularly for logic-in-memory and compute-in-memory (CIM) applications. Among the available cell architectures, One-Transistor–n-Capacitor (1T-nC) and two-transistor–n-capacitor (2T-nC) FeRAMs each offer distinct trade-offs in density, scalability, and reliability. In this work, we present a comparative study of these two architectures under both dimensional scaling ( XY/Z shrinkage) and vertical integration (increasing stacked capacitors per cell). Using technology computer-aided design (TCAD) and circuit-level simulations, we analyze how scaling impacts ferroelectric capacitance, parasitic coupling, and floating-node (FN) dynamics, which together dictate sense margin (SM) and read stability. A key mitigation strategy—floating unselected capacitors—is applied to both architectures, effectively decoupling the SM from the number of stacked capacitors and enabling tractable analysis across scaling regimes. Results show that 1T-nC suffers more from charge sharing with the bitline (BL), while 2T-nC benefits from transistor isolation and stronger low-voltage sensing at the cost of increased area. By systematically evaluating these behaviors across scaling directions, this work establishes the reliability trade-offs of 1T-nC and 2T-nC cells and provides design guidelines for high-density, vertically integrated FeRAM systems.

1T-nC↗
DOE OSTI2018

Nanometer-Scale Carrier Imaging of Potential-Induced Degradation in c-Si Solar Cells

We report on nm-resolution imaging of chargecarrier distribution around local potential-induced degradation (PID) defects using scanning capacitance microscopy. We imaged cross sections of heavily field-degraded module areas as cored out and selected by mm-scale photoluminescence imaging. Localized areas with abnormal carrier behavior or junction damage were found: the apparent n-type carrier extends vertically into the absorber to ~1-2 um from the cell surface, and laterally in similar lengths; in defect-free areas, the n-type carrier extends ~0.5 um, which is consistent with the junction depth. For comparison, we also investigated areas of the same module exhibiting less PID stress, and did not find any such heavily damaged junction area. Instead, we found slightly abnormal carrier behavior, where the carrier-type inversion in the absorber did not occur, but the p-type carrier concentration changed slightly in a much smaller lateral length of ~300 nm. These nanoelectrical findings suggest that the existing extended defects, which may not be significantly harmful to cell performance, were changed by PID to heavily damaged junction areas.

14 SOLAR ENERGY↗
DOE OSTI2019

Evaluation of Carrier Trapping in SiNx Towards Ion Migration Measurements

Sodium ion migration has been implicated in potential induced degradation of the shunting type. The kinetics of sodium migration in silicon nitride can be investigated using a simple capacitance-voltage characterization technique. However, we show that the charge trapping strongly affects the measurement and must be taken into consideration in the experimental approach. Furthermore, we perform a systematic analysis of charge carrier trapping in silicon nitride, allowing us to correct trapping effects that otherwise prevent sodium signal detection. We extract trapping and detrapping time constants both on the order of several hours. This shows that trapping cannot be ignored as it occurs relatively quickly and is constantly evolving in time. Accurate determination of sodium behavior in dielectric layers will facilitate robust co-optimization of these layers for optical, passivation, and barrier properties.

42 ENGINEERING↗
DOE OSTI2018

Electrical Properties of p-NiO/n-Si Heterostructures Based on Nanostructured Silicon

Silicon nanowires are formed on n-Si substrates by chemical etching. p-NiO/n-Si heterostructures are fabricated by reactive magnetron sputtering. The energy diagram of anisotype p-NiO/n-Si heterostructures is constructed according to the Anderson model. The current–voltage and capacitance–voltage characteristics are measured and analyzed. The main current-transport mechanisms through the p-NiO/n-Si heterojunction under forward and reverse biases are established.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Features of MIS Structures with Samarium Fluoride on Silicon and Germanium Substrates

The electrophysical characteristics of silicon and germanium MIS structures with an SmF{sub 3} insulator film, as well as their degradation due to the effect of electric fields, although similar, have a number of specific features. The current-transmission mechanism in all studied structures is described by the power dependence. Interface traps form the charge of electrically active traps, which varies during capacitance–voltage measurements, and the charge of inactive traps, which remains invariable. This charge is negative on the n-Ge surface, and the corresponding charge on the n-type and p-type silicon surface is positive. The trap charge density in the bulk of samarium fluoride lies in the range from –0.2 × 10{sup –8} to 0.6 × 10{sup –8} C/cm{sup 2} and is negligibly small when compared with the charge of interface traps in most cases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Electrical Characterization of Hybrid Halide Perovskites Based Heterojunction Device

Herein, we have measured the mobility of Hole’s for the configuration FTO/TiO{sub 2}/CH{sub 3}NH{sub 3}PbBr{sub 3}/PEDOT:PSS/Al by the SCLC regime. The current–voltage (I–V) characteristics of the CH{sub 3}NH{sub 3}PbBr{sub 3} perovskite based device shows the rectifying behavior as Schottky diode. Different parameters of the proposed device such as saturation current, ideality factor, barrier height have been taken out from I–V characteristics. The highest Hole’s mobility from TiO{sub 2} thin film through the perovskite and PEDOT:PSS film to the top aluminum electrode has of order 1.59 × 10{sup –4} cm{sup 2} V{sup –1} s{sup –1}. Moreover, the proposed device shows the TFSCLC regime at lower voltage while, at higher voltages it shows the TCLC regime. In addition to this, some important parameters like junction resistance, capacitance and carrier lifetime of device can be measured by the spectroscopy analysis of impedance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Low-Temperature Annealing of Lightly Doped n-4H-SiC Layers after Irradiation with Fast Electrons

The effect of low-temperature (up to 600°C) isothermal and isochronous annealing on the electrical characteristics of irradiated n-4H-SiC JBS Schottky diodes is studied. Irradiation is performed with 0.9-MeV electrons at a dose of 1 × 10{sup 16} cm{sup –2}. It is shown that the forward current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the irradiated diodes are mainly restored at annealing temperatures of up to 300°C. As the annealing temperature is raised to 500°C, nearly 90% of the defects introduced by irradiation with fast electrons are annealed out. The possible recommended mode of stabilizing annealing to be used in radiation-defect engineering (RDE) is 500°C, 30 min.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Electrical Conductivity and Barrier Properties of Lithium Niobate Thin Films

The thin-film structures made of LiNbO{sub 3} and obtained via laser ablation and magnetron sputtering are studied with volt-farad and volt-ampere characteristics. A potential barrier on the Si–LiNbO{sub 3} interface was found for both types of the films with the capacitance-voltage characteristics. The current-voltage characteristics showed that there are several conduction mechanisms in the structures studied. The Poole–Frenkel effect and the currents limited by a space charge mainly contribute to the electrical conductivity in the LiNbO{sub 3} film produced with the laser ablation method. The currents limited by a space charge contribute to the main mechanism in the film heterostructure obtained with the magnetron sputtering method.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Weak Coupling Effect on the Magnetic Freedericksz Transition in a Ferronematic Liquid Crystal

The magnetic Freedericksz transition in a ferronematic representing a diluted suspension of magnetic nanoparticles in an N-(4-methoxybenzylidene)-4-butylaniline (MBBA) nematic liquid crystal was experimentally studied. The transition point was determined by means of dielectric capacitance measurements in cells of different thickness for samples with various volume fractions of ferroparticles. The effect of weak coupling between the magnetic and liquid-crystal subsystems was studied. Low concentrations of quasispherical magnetic particles were shown to decrease the magnetic Freedericksz transition threshold in comparison with a pure liquid crystal. The obtained results were theoretically substantiated. The phase diagram of the suspension was plotted, and the method of estimating the energy of coupling between magnetic particles and a liquid-crystal matrix was proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Thermostable ferroelectric capacitors based on graded films of barium strontium titanate

The influence of the pressure of working gas during the ion–plasma sputtering on properties of deposited ferroelectric barium strontium titanate coatings has been experimentally studied. Variations in the of pressure of the working gas during deposition allows the component composition of the deposited layer to be changed, which leads to the diffusion of the phase transition and the improvement of temperature stability of properties of ferroelectric film. The gradation of layers has an impact on the temperature of the dielectric permittivity maximum, the shape of the dependence of the capacity on temperature, and the capacitance–voltage characteristics of the capacitor structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Two Modes of the Self-Similar Evolution of Charged Plasma

Two self-similar modes of evolution of charged particles’ high-current beam are described analytically. The situation being considered falls within the field of nonneutral plasma electrodynamics. The process is considered in terms of the nonlinear 1D evolution of the charge density w(x, t) in the channel of a longdistance transmission line with nonlinearly distributed resistance R, capacitance C, and inductance L: R = R(w), C = C(w), and L = 0. It is shown that initially the front of w(x, t) accelerates and then slows down. The description of the process in the channel is based on the charge conservation law. An idealized “kinematic” approach is used according to which an equation in two unknowns (charge density and current density in the channel) can be reduced to an equation in one unknown w(x, t). A strongly nonlinear wave process is studied. A discontinuous solution w(x, t) is constructed with a zero boundary condition at infinity. Such a model description can apply only for revealing the main qualitative features of a complex process. Analytical expressions for the variation in the evolution of the front velocity and perturbed area length are derived. An interrelation between the nonlinearity parameter of the process and the amount of charge in the interelectrode gap is suggested based on the experimental data for the evolution of streamers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Analysis of an Electromagnetic Wave with Circular Electron Beam Interaction in a Slow-Wave System of “Ribbed-Metal-Rod” Type

The interaction of an electromagnetic wave and external annular electron beam in a slow-wave system (SWS) of ribbed-metal-rod type was analyzed and expressions for the equivalent parameters of inductance and capacitance of the structure were found. A dispersion equation describing the excitation of axisymmetric electric waves in the SWS was derived in the impedance approximation. The dispersion characteristics and coupling coefficient have been modeled depending on the geometry of the rod and dielectric permittivity of the material filling the grooves in the SWS structure.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

The Effect of the Fin Shape and Thickness of the Buried Oxide on the DIBL Effect in an SOI FinFET

In this paper, we simulated the dependence of the effect of reducing the drain-induced barrier lowering on the thickness of a buried oxide layer in a finned (vertical) metal-oxide-semiconductor field effect transistor (FinFET) based on silicon-on-insulator technology. Three shapes of the fin with the rectangle, trapezoid, and triangle cross sections were considered. The drain-induced barrier lowering effect significantly depends on both the fin shape and the thickness of the buried oxide layer. The smallest drain-induced barrier lowering effect occurs when the thickness of the buried oxide layer is small for the fin of a triangular shape. This behavior of the drain-induced barrier lowering effect is strongly correlated with the behavior of the parasitic capacitance between a gate and a source.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗