A5067926751- Laser-Plasma Interactions and Diagnostics
- Laser-induced spectroscopy and plasma
- Plasma Diagnostics and Applications
- Atomic and Molecular Physics
- GaN-based semiconductor devices and materials
- Magnetic confinement fusion research
- Semiconductor materials and devices
- Silicon Carbide Semiconductor Technologies
- Ion-surface interactions and analysis
- Diamond and Carbon-based Materials Research
- Metal and Thin Film Mechanics
- Magnetic properties of thin films
- Semiconductor materials and interfaces
- Laser-Matter Interactions and Applications
- Atomic and Subatomic Physics Research
- Ga2O3 and related materials
- Laser Material Processing Techniques
- Electron and X-Ray Spectroscopy Techniques
- Optical measurement and interference techniques
- Laser Design and Applications
- Electromagnetic Launch and Propulsion Technology
- Advanced Optical Sensing Technologies
- Microwave and Dielectric Measurement Techniques
- Combustion and Detonation Processes
- Pulsed Power Technology Applications
Virginia Tech
2019-2023
NIHR Surgical Reconstruction and Microbiology Research Centre
2012
Hyper Tech Research (United States)
2005
General Electric (United States)
1956
This work demonstrates a novel junction termination extension (JTE) with graded charge profile for vertical GaN p-n diodes. The fabrication of this JTE obviates etch and requires only single-step implantation. A bi-layer photoresist is used to produce an ultra-small bevel angle ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 0.1^{\text {o}}{)}$ </tex-math></inline-formula> at the sidewall dielectric...
In principle, boron (B) as a material has many excellent surface properties, including corrosion resistance, very high hardness, refractory and strong tendency to bond with most substrates. The potential technological benefits of the have not been realized, because it is difficult deposit coatings. B evaporate, does sputter well, cannot be thermally sprayed. this article, first successful deposition results from robust system, based on vacuum (cathodic) arc technology, are reported. Adherent...
Carbon, a compensator in GaN, is an inherent part of the organometallic vapor phase epitaxy (OMVPE) environment due to use sources. In this study, impact growth conditions are explored on incorporation carbon GaN prepared via OMVPE pseudo-bulk wafers (in several cases, identical growths were performed GaN-on-Al2O3 templates for comparison purposes). Growth with different efficiencies but ammonia molar flows, when normalized rate, resulted incorporation. It concluded that only...
Measurements of the components microwave permeability tensor ferrites are usually made on very small specimens, such as spheres, discs, or rods, placed in cavities. Using degenerate modes, one can relate frequency shifts these modes to real parts, and changes Q imaginary components. The technique herein described makes use measurements performed a ferrite rod along axis circular waveguide. Exciting specimen successively with two senses polarization, obtains phase attenuation information for...
Many emerging GaN electronic and optoelectronic devices comprise p-GaN layers buried below n-GaN or AlGaN. The activation of these usually relies on the lateral hydrogen diffusion through etched mesa sidewalls, which is known to induce nonuniform acceptor distributions. However, profile, electric field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}$ </tex-math></inline-formula> -field) blocking...
The current versus voltage (I-V) characteristics of a Ni/GaN Schottky diode are measured from 50 to 400 K and the temperature dependence extracted barrier heights ideality factors is described as consequence lateral inhomogeneity at metal-semiconductor (M-S) interface. It shown that by invoking modified log-normal distribution M-S interface, height can be well explained. Further, it this approach describe revealing for effective values calculated increasingly higher voltages, begins converge...
Filtered cathodic arc deposition of fully ionized boron (B) was used to fill ∼2 μm wide trenches in silicon, having a depth:width ratio up 3:1. Optimal, void-free, infill is achieved with proper balance between and self-sputtering, as controlled by the substrate bias. Previously, this technique similar copper [O. R. Monteiro, J. Vac. Sci. Technol. B 17, 1094 (1999)]. In work, successful extension process found require ten times higher bias voltage (up 1000 V) for sputtering phase benefit...
The spatial profiles of key physical variables such as electron temperature and density are crucial in determining the overall radiating efficiency a Z pinch well emitted photon energy distribution. present work uses spatially resolved x-ray lines from shots taken on 4 MA Double EAGLE generator [C. Deeney et al., Phys. Rev. A 44, 6762 (1991)] at Maxwell Physics International to infer profiles. loads were arrays 15 wires consisting 95% Al, 5% Si, producing nearly 50 kJ K-shell radiation with...
This paper presents a first demonstration of radio-frequency (RF)-excited optical gas analyzer (RF-OGA) designed to quantitatively measure minority species inside the neutralization region ITER fusion experiment divertor. The sensor head, which creates its own plasma excitation and light emission, is operate in strong magnetic field, RF coupling leads bright emission. It also allows for operation at low voltages, avoiding radiation-enhanced breakdowns expected when high voltages are present...
The Doppler broadening of ion line profiles emitted by z-pinch plasma provides information about the thermalization implosion kinetic energy and radiation efficiency pinch. Measurements these are often complicated source in instrument opacity radiation. A high resolution concave crystal spectrometer Johann geometry was used to record time averaged spectra optically thin trace elements load. An imaging slit provided radially resolved but axially spectra. measurements indicate that lower...
This paper discusses the potential use of hydrogen atomic line emission at 656.3 nm (H/sub /spl alpha//) as an effective in-situ sensor for a closed-loop control system to improve reproducibility reactive sputter deposition nano-structured, metal-containing, hydrogenated, diamond-like carbon (Me:DLC:H) coatings. The includes experimental results showing good correlation between H/sub alpha// in process plasma and formation metal-carbide, important component these first attempts actual...
Theoretical studies have predicted that the disruptive role of Rayleigh-Taylor (R-T) instability on current conduction and implosion characteristics annular Z-pinch loads will be mitigated by mass accretion if uniform fill or multiple shell are used. Holographic interferometry was used to study these physical processes during phase puff-on-puff a terawatt accelerator. Both axial (r-z) density perturbation azimuthal (r-/spl theta/) filamentation modes R-T were observed. Significant ionization...
Summary form only given. Large radius implosions of gas-puff Z-pinches are the subject intense investigation. Such needed to achieve high specific energy required excite K-line radiation from high-atomic-number (e.g. Z>26) radiators, for proper matching with high-current (~10 MA and higher) generators, continuum radiator concepts that require heating beyond optimum He/H-like state K-shell emission, utilize more efficiently long-current-rise-time (>100 ns) generators. The key physics issues...
Summary form only given. A multiple reference beam holographic system has been developed to study PRS loads. This diagnostic employs three, spatially distinct beams that are used create three holograms stored on the same film plate. One of records undistorted laser wavefront (reference), while other two record distorted after passage through plasma at different times shot and along path. An optical time delay up 50 ns is implemented using a polarizing beam-splitter, steering mirrors, pair...
This paper presents a first demonstration of an rf-excited optical gas analyzer (RF-OGA) designed to quantitatively measure minority species inside the neutralization region ITER divertor. The sensor head, which creates its own plasma excitation and light emission, is operate in strong magnetic field rf coupling leads emission. It also allows for operation at low voltages, avoiding radiation-enhanced breakdowns expected when high voltages are present environment. Furthermore, preferred head...
Summary form only given. Radially resolved X-ray spectra were recorded with a time Johann spectrometer on Double EAGLE. Four percent Cl was added as an optically thin trace element to the Ar in individual shells of multi shell gas-puff loads study implosion and radiation characteristics these shells. The ratios observed line intensities compared predicted values using CRE codes determine radial distribution electron temperature, T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML"...
Summary form only given. Tailoring the radial density profile of gas loads on radiation simulators is expected to increase X-ray yield by mitigating adverse effects Rayleigh-Taylor instability axial uniformity current carrying sheath during implosion phase load. Multi-shell puff loads, with and without axis jets, have been studied achieve this objective. The role inner shell on-axis jet characteristics pinch assembly an argon load a time resolved Johann spectrometer. distribution K-shell...
Summary form only given. A double exposure, three-reference-beam, holographic interferometer using a pulsed Nd:YAG laser has been developed by HYTech Research for NRL. This was used previously in plasma-filled-rod-pinch diode experiments. In this work, we report on the implementation of, and initial results from, to study effects implosion dynamics pinch stagnation phenomena associated with varying gas density profile of an 8-cm, shell-on-shell ("1234"), long-implosion-time (200 3 ns), neon...
Summary form only given. To improve the reproducibility of metal-containing, hydrogenated diamond-like carbon (Me-DLC:H) coatings deposited by physical vapor deposition (PVD) techniques such as reactive sputtering, various plasma probes have been studied potential in-situ sensors integrated with a closed-loop control system. In series Design-of-Experiment (DoE) test runs on an unbalanced magnetron sputtering setup, were tested for their sensitivity to process input factors and candidates...