A5059981469- Semiconductor materials and devices
- Diamond and Carbon-based Materials Research
- Carbon Nanotubes in Composites
- Electron and X-Ray Spectroscopy Techniques
- Electronic and Structural Properties of Oxides
- Photocathodes and Microchannel Plates
- Semiconductor materials and interfaces
- Gyrotron and Vacuum Electronics Research
- Graphene research and applications
- Integrated Circuits and Semiconductor Failure Analysis
- Advancements in Semiconductor Devices and Circuit Design
- Surface and Thin Film Phenomena
- GaN-based semiconductor devices and materials
- Semiconductor Quantum Structures and Devices
- Mechanical and Optical Resonators
- Chalcogenide Semiconductor Thin Films
- Particle Accelerators and Free-Electron Lasers
- Ion-surface interactions and analysis
- Plasma Diagnostics and Applications
- Electrostatic Discharge in Electronics
- Advanced Semiconductor Detectors and Materials
- Nanowire Synthesis and Applications
- Radiation Effects in Electronics
- Advanced Materials Characterization Techniques
- Nanotechnology research and applications
United States Naval Research Laboratory
2008-2019
Naval Research Laboratory Electronics Science and Technology Division
2016-2018
University of California, Los Angeles
2012
TE Connectivity (United Kingdom)
2008
Dalhousie University
2005-2007
Corning (United States)
2006
National Kidney Foundation
2006
United States Navy
2004
United States Department of the Navy
2004
Manchester Metropolitan University
2002
An analytical formula of the emittance a field emitter is given. In contrast to thermal and photoemission, such contains complexity due multidimensional nature source. A formulation given for one- three-dimensional (3D) emitters. The 3D makes use point charge model unit cell coupled with trajectory analysis follow electrons an evaluation plane where determined. single tip theory extended array resulting predicts Spindt-type square emitters 0.2cm on side producing 2000A∕cm2 23mmmrad. Theory...
An analysis of the microwave ( f≳1 GHz) properties field-emitter arrays (FEAs) and several representative medium power (10–100 W) amplifiers employing FEAs is presented. The FEA limited to parallel-plate structures having discrete pointlike vertical emitter tips gate apertures aligned each tip. A transmission line wave propagation in this structure presented used evaluate geometries materials needed for operation. This investigate performance capabilities requirements both modulated-emission...
We report soft x-ray photoemission studies of metal/molecular-beam epitaxy (MBE)-GaAs(100) interfaces formed at low temperature. Our results indicate that rectifying barrier heights are proportional to the metal work function in accordance with Schottky’s original description metal–semiconductor contacts. These confirm predictions a self-consistent model interfaces, and suggest metal-induced gap states native defect mechanisms not major factors determining Fermi level energy ‘‘ideal’’...
Multiwalled carbon nanotubes were grown using chemical vapor deposition on the tops of blunt vertical silicon posts in cells having a horizontal gate aperture conventional field emitter design. We obtained over 1 mA total emission current from single array, or 0.3 μA per cell at 40 V. In addition to low voltage operation, most distinctive differences arrays include their stability and lack catastrophic arcing without any special sample preparation.
We have used soft x-ray photoemission spectroscopy measurements to demonstrate that metal–GaAs interfaces can exhibit relatively unpinned Fermi level (Ef) movements. For clean GaAs (100) surfaces obtained by molecular-beam epitaxy (MBE) growth and thermal decapping of a protective As overlayer, the metals Au, Al, Cu, In produce 0.6–0.7-eV range Ef stabilization. given metal, this stabilization occurs at same energies for n-type p-type GaAs. Furthermore, movements are metal-dependent evolve...
We have used soft x-ray photoemission and optical emission spectroscopies to observe a broad range of Fermi level stabilization energies at metal interfaces with GaAs(100) surfaces grown by molecular beam epitaxy (MBE). The observed metal- As-related interface cathodoluminescence plus orders-of-magnitude differences in bulk-defect-related photoluminescence between melt- versus MBE-grown GaAs suggest role bulk crystal growth processing controlling Schottky barrier formation.
Germanophosphate (GeO2-P2O5) glasses were studied with neutron diffraction, phosphorus, and oxygen nuclear magnetic resonance, calorimetry, viscosity measurements, first-principles calculations. These data sets combined to propose a structural model of GeO2-P2O5 glasses, which includes tetrahedrally coordinated formation octahedrally germanium as P2O5 content increases, an absence trigonally oxygen, hence rutile-like GeO2 domains. The was then used explanations for both the observed...
This report documents energy distribution measurements of field emission from single-tip Si emitter arrays. The distributions are much broader than clean metal distributions, extending several volts below the Fermi level and often including multiple peak structure. positions typically move to lower as gate voltage is increased, however, history well current and/or can change intensity distributions. Changes in shifts higher occur suddenly spontaneously slowly during emission. These results...
Low-energy cathodoluminescence spectroscopy (CLS) is a powerful new technique for characterizing the electronic structure of semiconductor surfaces and ‘‘buried’’ metal–semiconductor interfaces. This extension more conventional electron microscopy provides information on localized states, deep-level defects, band compounds at interfaces below free solid surface. Specifically, CLS direct identification metal-induced interface states which evolve in energy density with multilayer metal...
Electron bunches for high performance free electron lasers are subject to constraints on charge per bunch and pulse shape. A Diamond secondary emitter used in conjunction with a photocathode drive laser has potential enable brightness, peak current photoinjector by increasing the effective quantum efficiency of photocathode. theoretical characterization so produced been heretofore absent. Using combination Monte Carlo analytical models, shape bunches, their transit time, emission time...
We used optical emission techniques to obtain a direct measure of discrete electronic states at GaAs interfaces. These depend on surface preparation, metallization, and semiconductor material. The energy the found metal/molecular-beam epitaxially grown GaAs(100) interfaces integrated within Schottky formalism provides self-consistent results for interface electrostatics. presence large concentration extrinsic defects causes pinning behavior observed metal/melt-grown GaAs(110) provide first...
We report results of x-ray photoemission and cathodoluminescence spectroscopies studies interface formation at metal–GaAs junctions. The are interpreted by using a microscopic model metal–semiconductor interfaces. Our low-temperature measurements analyses show the validity Schottky’s phenomenological description, thereby suggesting that metal-induced gap states native defect mechanisms not major factors in determining Fermi-level energy formed interface. room-temperature broad range...
Electron emission nonuniformity is a cause of intrinsic emittance from the electron source, and consequence work function variation due to crystal faces coatings such as cesium, field enhancement effects surface structure, temperature. Its investigation using particle-in-cell (PIC) codes MICHELLE hampered lack an model that can treat thermal, field, photoemission particularly in crossover regions where canonical equations, e.g., Fowler-Nordheim, Richardson-Laue-Dushman, Fowler-Dubridge...
We demonstrate field emission from an integrated three-terminal device using a suspended planar graphene edge as the source of vacuum electrons. Energy spectra emitted electrons confirm field-emission mechanism. The energy produced by grown chemical vapor deposition and reduced oxide are compared. drain-source voltage required to produce given drain current increases when negative voltages applied gate, confirming field-effect transistor operation. rises exponentially with inverse over...
We report here on DC and RF measurements of electron field emission current obtained from silicon emitter arrays (FEAs) containing more than 1000 tips. The emitters in these FEAs have the form 4 μm tall cylindrical columns where tops were sharpened into points having radii curvature estimated TEM analysis similar devices to be less 100 Å. With a gate bias voltage about 120 V DC, currents approximately 2 mA been collected at anode. This collector current, corresponding μA per tip, is...
We have used reactive metal interlayers to suppress anion outdiffusion at Au-CdTe junctions and thereby alter the formation of deep interfacial states. Using soft x-ray photoemission luminescence spectroscopies, we report a dramatically reduced p-type band bending demonstrate that levels observed directly interface are responsible for chemically induced electrical behavior.
In situ internal photoemission, current–voltage, and capacitance–voltage measurements of electronic barrier heights at metal/molecular-beam epitaxy GaAs(100) interfaces indicate near-ideal behavior large for Au contacts but nonideal characteristics height inhomogeneity Al contacts. The observed 0.98–1.10 eV are comparable among the three techniques employed relatively uniform across interface. Measurements that laterally inhomogeneous. Analysis photoemission results interface using a model...
We have grown multiwalled carbon nanotubes by chemical-vapor deposition on two types of gated structures, one containing a silicon post, and another having an open aperture. A gate current to anode-current ratio 2.5%, the lowest any nanotube field emitter arrays was measured for aperture configuration. The post structures produced 1-nA emission at voltages below 20V up 1mA 40V (from 0.5-mm2 area). relatively stable compared other destructive arcing not observed. voltage needed produce given...
A thin nitrogen-doped layer less than 4% of the total thickness in diamond film amplifier is shown to reduce losses generated secondaries back contact, by a high energy primary electron beam compared without substitutional nitrogen modification. Simulation indicates that due absorption diffusing electrons contact may be considerably reduced factor 2 (depending on field across film, width layer, and boron doping level), thereby mitigating undesirable effects associated with trace amounts boron.
We present soft x‐ray photoemission spectra (SXPS) of cleaved (110) CdTe interfaces with Au and In measured as a function coverage pulsed laser annealing. These show wide range Fermi‐level positions determined by the degree interdiffusion or reaction at interface. Photoluminescence (PL) surface versus processed Au/CdTe interface reveal that metallization processing produce large increases in luminescence intensity from deep‐level defects. The energies intensified PL transitions correlate...
We have used deep level photoluminescence spectroscopy to investigate the surface electronic quality of molecular beam epitaxy (MBE) grown CdTe layers during ultrahigh vacuum cleaning. Spectra are highly sensitive heat treatment, contamination, and electron exposure. The technique provides a guide growth cleaning MBE films optimal quality, which exhibit intense near-band-edge minimal emission exceed substantially bulk crystals.