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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 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Enhanced neutron detector and electron amplifier structure and a method of fabricating the enhanced neutron detector and electron amplifier structure

An enhanced electron amplifier structure includes a substrate configured to amplify a signal of an incident particle by causing a cascade of secondary electron emissions and an enhancement layer configured to increase a sensitivity of the substrate to the incident particle. The enhancement layer is provided on an upper surface of the substrate.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Single-Shot Diagnostics of Microbunched Electrons in Laser-Driven Plasma Accelerators and Free-Electron Lasers

In general, the inherent statistical variances in the laser-driven plasma accelerators (LPAs) and self-amplified spontaneous emission (SASE) free electron lasers (FELs) motivate the use of single-shot diagnostics. In addition, the microbunching phenomenon in each is also variable, so coherent optical transition radiation (COTR) techniques also warrant single-shot evaluations. In both cases, the enhancements of the signals enable optical beam splitters to be used to direct light to the different measuring devices for electron beam size, divergence, spectral content, and/or bunch length as appropriate. COTR Interferometry (COTRI) modelling results for the pre-buncher case at 266 nm and for the LPA case at 633 nm are presented. In addition, examples of few-micron beam size and sub-mrad beam divergence measurements from a single shot of an LPA are reported.

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Flexible and stretchable electronic systems for epidermal electronics

Provided herein are skin-mounted biomedical devices and methods of making and using biomedical devices for sensing and actuation applications. For example, flexible and/or stretchable biomedical devices are provided, including electronic devices useful for establishing conformal contact with the skin of a subject. Devices disclosed herein can comprise a plurality of sensing and/or actuating devices provided as part of a skin-mounted flexible or stretchable electronic circuit.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Enhanced electron amplifier structure and method of fabricating the enhanced electron amplifier structure

An enhanced electron amplifier structure includes a microporous substrate having a front surface and a rear surface, the microporous substrate including at least one channel extending substantially through the substrate between the front surface and the rear surface, an ion diffusion layer formed on a surface of the channel, the ion diffusion layer comprising a metal oxide, a resistive coating layer formed on the first ion diffusion layer, an emissive coating layer formed on the resistive coating layer, and an optional ion feedback layer formed on the front surface of the structure. The emissive coating produces a secondary electron emission responsive to an interaction with a particle received by the channel. The ion diffusion layer, the resistive coating layer, the emissive coating layer, and the ion feedback layer are independently deposited via chemical vapor deposition or atomic layer deposition.

Mane, Anil U.↗
DOE OSTI2015

Polarized Electron - Polarized Deuteron Deep-Inelastic Scattering in Electron-Ion Collider with Tagging

For the past several years there have been an intensive research and development for the possible electron-ion collider that will be able to probe deep inelastic processes at unprecedentedly high energies in eA channel. One of the important advantages of the collider kinematics in DIS processes is the possibility for an unambiguous separation of hadrons emerging from DIS and hadrons fragmenting from the target nucleus. This creates a unique possibility for tagging the interacting nucleon with the recoil slow fragments in the DIS process. The situation is most clean for the deuteron target in which case the recoil particle is a nucleon. In addition, the possibility of having polarized deuteron beams will create unprecedented opportunities in probing polarization degrees of freedom for parton distributions in the interacting bound nucleon. In this work we develop a theoretical framework for the polarized electron-polarized deuteron deep inelastic scattering in which the recoil nucleon is detected in the target fragmentation region. Two main contributions for which theoretical models are developed are the plane-wave impulse approximation, in which no reinteractions are taking place between the final state products of DIS and the recoil nucleon.

Sargsian, Misak↗
DOE OSTI2013

Numerical investigation of electron self-injection in the nonlinear bubble regime

The process of electron self-injection in the nonlinear bubble wake generated by a short and intense laser pulse propagating in a uniform underdense plasma is studied by means of fully self-consistent particle-in-cell simulations and test-particle simulations. We consider a wake generated by a non-evolving laser driver traveling with a prescribed velocity, which then sets the structure and the velocity of the wake, so the injection dynamics is decoupled from driver evolution, but a realistic structure for the wakefield is retained. We show that a threshold for self-injection into a non-evolving bubble wake exists, and we characterize the dependence of the self-injection threshold on laser intensity, wake velocity, and plasma temperature for a range of parameters of interest for current and future laser-plasma accelerators.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Scattering due to Schottky barrier height spatial fluctuation on two dimensional electron gas in AlGaN/GaN high electron mobility transistors

A scattering mechanism related to the Schottky barrier height (SBH) spatial fluctuation of the two dimensional electron gas (2DEG) in AlGaN/GaN heterostructures is presented. We find that the low field mobility is on the order of 10{sup 4}–10{sup 6} cm{sup 2}/Vs. The 2DEG transport properties are found to be influenced by both the mobility and 2DEG density variations caused by the SBH fluctuation. Our results indicate that a uniform Schottky contact is highly desired to minimize the influence of SBH inhomogeneity on the device performance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Multiple species beam production on laser ion source for electron beam ion source in Brookhaven National Laboratory

Extracted ion beams from the test laser ion source (LIS) were transported through a test beam transport line which is almost identical to the actual primary beam transport in the current electron beam ion source apparatus. The tested species were C, Al, Si, Cr, Fe, Cu, Ag, Ta, and Au. The all measured beam currents fulfilled the requirements. However, in the case of light mass ions, the recorded emittance shapes have larger aberrations and the RMS values are higher than 0.06 π mm mrad, which is the design goal. Since we have margin to enhance the beam current, if we then allow some beam losses at the injection point, the number of the single charged ions within the acceptance can be supplied. For heaver ions like Ag, Ta, and Au, the LIS showed very good performance.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

High precision two-dimensional strain mapping in semiconductor devices using nanobeam electron diffraction in the transmission electron microscope

A classical method used to characterize the strain in modern semiconductor devices is nanobeam diffraction (NBD) in the transmission electron microscope. One challenge for this method lies in the fact that the smaller the beam becomes, the more difficult it becomes to analyze the resulting diffraction spot pattern. We show that a carefully designed fitting algorithm enables us to reduce the sampling area for the diffraction patterns on the camera chip dramatically (∼1/16) compared to traditional settings without significant loss of precision. The resulting lower magnification of the spot pattern permits the presence of an annular dark field detector, which in turn makes the recording of images for drift correction during NBD acquisition possible. Thus, the reduced sampling size allows acquisition of drift corrected NBD 2D strain maps of up to 3000 pixels while maintaining a precision of better than 0.07%. As an example, we show NBD strain maps of a modern field effect transistor (FET) device. A special filtering feature used in the analysis makes it is possible to measure strain in silicon devices even in the presence of other crystalline materials covering the probed area, which is important for the characterization of the next generation of devices (Fin-FETs).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Precessed electron beam electron energy loss spectroscopy of graphene: Beyond channelling effects

The effects of beam precession on the Electron Energy Loss Spectroscopy (EELS) signal of the carbon K edge in a 2 monolayer graphene sheet are studied. In a previous work, we demonstrated the use of precession to compensate for the channeling-induced reduction of EELS signal when in zone axis. In the case of graphene, no enhancement of EELS signal is found in the usual experimental conditions, as graphene is not thick enough to present channeling effects. Interestingly, though it is found that precession makes it possible to increase the collection angle, and, thus, the overall signal, without a loss of signal-to-background ratio.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Comprehensive magnetotransport characterization of two dimensional electron gas in AlGaN/GaN high electron mobility transistor structures leading to the assessment of interface roughness

Magnetotransport in two distinct AlGaN/GaN HEMT structures grown by Molecular Beam Epitaxy (MBE) on Fe-doped templates is investigated using Shubnikov de-Haas Oscillations in the temperature range of 1.8–6 K and multicarrier fitting in the temperature range of 1.8–300 K. The temperature dependence of the two dimensional electron gas mobility is extracted from simultaneous multicarrier fitting of transverse and longitudinal resistivity as a function of magnetic field and the data is utilized to estimate contribution of interface roughness to the mobility and the corresponding transport lifetime. The quantum scattering time obtained from the analysis of Shubnikov de Haas Oscillations in transverse magnetoresistance along with the transport lifetime time were used to estimate interface roughness amplitude and lateral correlation length. The results indicate that the insertion of AlN over layer deposited prior to the growth of GaN base layer on Fe doped GaN templates for forming HEMT structures reduced the parallel conduction but resulted in an increase in interface roughness.

36 MATERIALS SCIENCE↗
DOE OSTI2014

In situ transmission electron microscopy investigation of the interfacial reaction between Ni and Al during rapid heating in a nanocalorimeter

The Al/Ni formation reaction is highly exothermic and of both scientific and technological significance. In this report, we study the evolution of intermetallic phases in this reaction at a heating rate of 830 K/s. 100-nm-thick Al/Ni bilayers were deposited onto nanocalorimeter sensors that enable the measurement of temperature and heat flow during rapid heating. Time-resolved transmission electron diffraction patterns captured simultaneously with thermal measurements allow us to identify the intermetallic phases present and reconstruct the phase transformation sequence as a function of time and temperature. The results show a mostly unaltered phase transformation sequence compared to lower heating rates.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Electronic band structure of ZnO-rich highly mismatched ZnO{sub 1−x}Te{sub x} alloys

We synthesized ZnO{sub 1−x}Te{sub x} alloys with Te composition x < 0.23 by using pulsed laser deposition. Alloys with x < 0.06 are crystalline with a columnar growth structure while samples with higher Te content are polycrystalline with random grain orientation. Electron microscopy images show a random distribution of Te atoms with no observable clustering. We found that the incorporation of a small concentration of Te (x ∼ 0.003) redshifts the ZnO optical absorption edge by more than 1 eV. The minimum band gap obtained in this work is 1.8 eV for x = 0.23. The optical properties of the alloys are explained by the modification of the valence band of ZnO, due to the anticrossing interactions of the localized Te states with the ZnO valence band extended states. Hence, the observed large band gap reduction is primarily originating from the upward shift of the valence band edge. We show that the optical data can be explained by the band anticrossing model with the localized level of Te located at 0.95 eV above the ZnO valence band and the band anticrossing coupling constant of 1.35 eV. These parameters allow the prediction of the compositional dependence of the band gap as well as the conduction and the valence band offsets in the full composition range of ZnO{sub 1−x}Te{sub x} alloys.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

The complex mixed Wentzel–Kramers–Brillouin-full-wave approach and its application to the two dimensional mode structure analysis of ion temperature gradient/collisionless trapped electron mode drift waves

The complex mixed Wentzel–Kramers–Brillouin (WKB)-full-wave approach is applied to the 2D mode structure analysis of ion temperature gradient/collisionless trapped electron mode drift waves in tokamak plasmas. The parallel mode structure is calculated with the full-wave approach, while the radial envelope is calculated with the complex WKB method. The tilting of the global mode structure along radius is demonstrated analytically. The effects of the phase and amplitude variation of the radial envelope on the parallel mode structure are included in terms of a complex radial wave vector in the parallel mode equation. It is shown that the radial equilibrium non-uniformity leads to the asymmetry of the parallel mode structure not only in configuration space but also in spectrum space. The mixed approach provides a practical way to analyze the asymmetric component of the global mode structure due to radial equilibrium non-uniformity.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Unraveling irradiation induced grain growth with in situ transmission electron microscopy and coordinated modeling

Nanostructuring has been proposed as a method to enhance radiation tolerance, but many metallic systems are rejected due to significant concerns regarding long term grain boundary and interface stability. This work utilized recent advancements in transmission electron microscopy (TEM) to quantitatively characterize the grain size, texture, and individual grain boundary character in a nanocrystalline gold model system before and after in situ TEM ion irradiation with 10 MeV Si. The initial experimental measurements were fed into a mesoscale phase field model, which incorporates the role of irradiation-induced thermal events on boundary properties, to directly compare the observed and simulated grain growth with varied parameters. The observed microstructure evolution deviated subtly from previously reported normal grain growth in which some boundaries remained essentially static. In broader terms, the combined experimental and modeling techniques presented herein provide future avenues to enhance quantification and prediction of the thermal, mechanical, or radiation stability of grain boundaries in nanostructured crystalline systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

High-speed nanoscale characterization of dewetting via dynamic transmission electron microscopy

The dewetting of thin films can occur in either the solid or the liquid state for which different mass transport mechanisms are expected to control morphological changes. Traditionally, dewetting dynamics have been examined on time scales between several seconds to hours, and length scales ranging between nanometers and millimeters. The determination of mass transport mechanisms on the nanoscale, however, requires nanoscale spatial resolution and much shorter time scales. This study reports the high-speed observation of dewetting phenomena for kinetically constrained Ni thin films on crystalline SrTiO{sub 3} substrates. Movie-mode Dynamic Transmission Electron Microscopy (DTEM) was used for high-speed image acquisition during thin film dewetting at different temperatures. DTEM imaging confirmed that the initial stages of film agglomeration include edge retraction, hole formation, and growth. Finite element modeling was used to simulate temperature distributions within the DTEM samples after laser irradiation with different energies. For pulsed laser irradiation at 18 μJ, experimentally observed hole growth suggests that Marangoni flow dominates hole formation in the liquid nickel film. After irradiation with 13.8 μJ, however, the observations suggest that dewetting was initiated by nucleation of voids followed by hole growth through solid-state surface diffusion.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

ELECTRON–MUON IDENTIFICATION BY ATMOSPHERIC SHOWER AND ELECTRON BEAM IN A NEW EAS DETECTOR CONCEPT

We present results demonstrating the time resolution and μ/e separation capabilities of a new concept for an EAS detector capable of measuring cosmic rays arriving with large zenith angles. This kind of detector has been designed to be part of a large area (several square kilometer) surface array designed to measure ultra high energy (10–200 PeV) τ neutrinos using the Earth-skimming technique. A criterion to identify electron-gammas is also shown and the particle identification capability is tested by measurements in coincidence with the KASKADE-GRANDE experiment in Karlsruhe, Germany.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗