A5063382303- Semiconductor materials and devices
- Silicon Carbide Semiconductor Technologies
- GaN-based semiconductor devices and materials
- Graphene research and applications
- Semiconductor Quantum Structures and Devices
- Ga2O3 and related materials
- Semiconductor materials and interfaces
- Advancements in Semiconductor Devices and Circuit Design
- ZnO doping and properties
- Diamond and Carbon-based Materials Research
- Carbon Nanotubes in Composites
- Advanced ceramic materials synthesis
- Thin-Film Transistor Technologies
- Metal and Thin Film Mechanics
- Acoustic Wave Resonator Technologies
- Copper Interconnects and Reliability
- Quantum and electron transport phenomena
- Silicon Nanostructures and Photoluminescence
- Advanced Energy Technologies and Civil Engineering Innovations
- Photonic and Optical Devices
- Nanowire Synthesis and Applications
- Boron and Carbon Nanomaterials Research
- Silicon and Solar Cell Technologies
- 2D Materials and Applications
- Molecular Junctions and Nanostructures
Cornell University
2014-2023
Morgan State University
2017-2023
Joint Special Operations University
2023
University of Surrey
2018-2022
University of Guelph
2022
Simon Fraser University
2019
TRIUMF
2018
Abbott Northwestern Hospital
2017
Brock University
2012-2015
Ithaca College
2014
Microporous covalent organic frameworks, which usually form as insoluble powders, grow crystalline films on graphene.
Using ultrafast optical pump-probe spectroscopy, we have measured carrier relaxation times in epitaxial graphene layers grown on SiC wafers. We find two distinct time scales associated with the of nonequilibrium photogenerated carriers. An initial fast transient 70–120fs range is followed by a slower process 0.4–1.7ps range. The found to be inversely proportional degree crystalline disorder as Raman spectroscopy. relate and slow constants carrier-carrier carrier-phonon intraband interband...
The ultrafast relaxation and recombination dynamics of photogenerated electrons holes in epitaxial graphene are studied using optical-pump Terahertz-probe spectroscopy. conductivity at Terahertz frequencies depends on the carrier concentration as well distribution energy. Time-resolved studies can therefore be used to probe associated with intraband interband recombination. We report electron-hole times for first time. Our results show that cooling occurs sub-picosecond time scales density dependent.
We present experimental results on the optical absorption spectra of epitaxial graphene from visible to terahertz frequency range. In range, is dominated by intraband processes with a dependence similar Drude model. near-IR due interband and measured conductivity close theoretical value e2/4ℏ. extract values for carrier densities, number carbon atom layers, scattering times measurements.
ZnO thin films have been grown heteroepitaxially on epi-GaN/sapphire (0001) substrates. Rutherford backscattering spectroscopy, ion channeling, and high resolution transmission electron microscopy studies revealed high-quality epitaxial growth of GaN with an atomically sharp interface. The x-ray diffraction channeling measurements indicate near perfect alignment the epilayers as compared to those directly sapphire (0001). Low-temperature cathodoluminescence also optical quality these...
We investigate the distribution and temperature-dependent optical properties of sharp, zero-phonon emission from defect-based single photon sources in multilayer hexagonal boron nitride (h-BN) flakes. observe sharp lines optically active defects distributed across an energy range that exceeds 500 meV. Spectrally-resolved photon-correlation measurements verify emission, even when multiple are simultaneously excited within same h-BN flake. also present a detailed study linewidth, spectral...
van der Waals epitaxial growth of graphene on c-plane (0001) sapphire by CVD without a metal catalyst is presented. The effects CH(4) partial pressure, temperature, and H(2)/CH(4) ratio were investigated conditions optimized. formation monolayer was shown Raman spectroscopy, optical transmission, grazing incidence X-ray diffraction (GIXRD), low voltage transmission electron microscopy (LVTEM). Electrical analysis revealed that room temperature Hall mobility above 2000 cm(2)/V·s achieved, the...
Understanding the rules of life is one most important scientific endeavours and has revolutionised both biology biotechnology. Remarkable advances in observation techniques allow us to investigate a broad range complex dynamic biological processes which living systems could exploit quantum behaviour enhance regulate functions. Recent evidence suggests that these non-trivial mechanical effects may play crucial role maintaining non-equilibrium state biomolecular systems. Quantum study such...
Electron-hole generation and recombination rates for intravalley intervalley phonon scattering in graphene are presented. The transverse the longitudinal optical modes (${E}_{2g}$ modes) near zone center ($\ensuremath{\Gamma}$ point) contribute to interband carrier scattering. At edge [$K({K}^{\ensuremath{'}})$ point], only mode (${A}_{1}^{\ensuremath{'}}$ mode) contributes significantly with faster than those due zone-center phonons. calculated times range from less a picosecond more...
Very slow drain current and surface potential transients have been observed in AlGaN/GaN heterostructure field effect transistors that are subjected to high bias stress. Simultaneous measurements of indicate large change after stress is responsible for the reduction these devices. Measurements profile from gate edge toward as a function time changes occur mostly near gate. It proposed caused by electrons which tunnel under get trapped at states Passivation with SiN/sub x/ reduces transient...
We report on a method to produce free-standing graphene sheets from epitaxial silicon carbide (SiC) substrate. Doubly clamped nanomechanical resonators with lengths up 20 μm were patterned using this technique and their resonant motion was actuated detected optically. Resonance frequencies of the order tens megahertz measured for most devices, indicating that are much stiffer than expected beams under no tension. Raman spectroscopy suggests is not chemically modified during release...
Using ultrafast optical pump-probe spectroscopy, we study the relaxation dynamics of hot phonons in few-layer and multi-layer graphene films grown by epitaxy on silicon carbide substrates chemical vapor deposition nickel substrates. In first few hundred femtoseconds after photoexcitation, carriers lose most their energy to generation which then present main bottleneck subsequent carrier cooling. Optical phonon cooling short time scales is found be independent growth technique, number layers,...
The electrical properties of multilayer MoS2/graphene heterojunction transistors are investigated. Temperature-dependent I–V measurements indicate the concentration unintentional donors in exfoliated MoS2 to be 3.57 × 1011 cm–2, while ionized donor is determined as 3.61 1010 cm–2. temperature-dependent also reveal two dominant levels, one at 0.27 eV below conduction band and another located 0.05 band. characteristics asymmetric with drain bias voltage dependent on junction used for source or...
Using optical-pump terahertz-probe spectroscopy, we study the relaxation dynamics of photoexcited carriers in graphene at different temperatures. We find that lower temperatures tail transients as measured by differential probe transmission becomes slower, extending beyond several hundred picoseconds below 50K. interpret observed resulting from cooling via phonon emission. The slow low is attributed to bulk electron and hole energy distributions moving close enough Dirac point such both...
Two-dimensional hexagonal boron nitride (h-BN) is a wide bandgap material which has promising mechanical and optical properties. Here we report the realization of an initial nucleation density h-BN <1 per mm2 using low-pressure chemical vapor deposition (CVD) on polycrystalline copper. This enabled wafer-scale CVD growth single-crystal monolayer with lateral size up to ∼300 μm, bilayer ∼60 trilayer ∼35 μm. Based large domain, sizes as-grown bi- grains are 2 orders magnitude larger than...
The literature on direct conversion of radioisotope energy to electricity is reviewed. Considerations the choice radioisotope, converter, and device design are discussed. Recommendations for maximum specific power, energy, lifetime based available radioisotopes made. It found that nuclear batteries have potential achieve powers 1–50 mW/g. Devices utilize beta emitter titanium tritide (TiT2) as isotope most in short term meet combined performance objectives. TiT2 devices a power 0.83 Higher...
A betavoltaic cell in 4H SiC is demonstrated. p-n diode structure was used to collect the charge from a 1mCi Ni-63 source. An open circuit voltage of 0.72V and short current density 16.8nA∕cm2 were measured single junction. 6% lower bound on power conversion efficiency obtained. simple photovoltaic-type model explain results. Fill factor backscattering effects included calculation. The performance device limited by edge recombination.
Surface potentials on GaN epilayers and Al0.35Ga0.65N/GaN heterostructures have been studied by scanning Kelvin probe microscopy (SKPM) in conjunction with noncontact atomic force microscopy. The dependence of the surface potential doping films, as well variation Al0.35Ga0.65N barrier layer thickness has investigated. bare height (BSBH), measured SKPM, is observed to decrease from ∼1. 40±0.1 eV ∼0.60±0.1 increasing epilayers. Schottky calculated measurements BSBH n-GaN agrees very results...
Bare surface barrier heights (BSBHs) of AlGaN∕GaN heterostructures, with varying AlGaN layer thickness and ∼35% Al alloy composition, have been measured using UV laser induced transients. The BSBH has observed to vary thickness, before it saturates beyond a critical the variation found be very similar that two-dimensional electron gas (2DEG) density at interface. Such trend can explained by considering presence donor states distributed in band gap. calculated from 2DEG density, almost...
Electrical tunability of molecular doping graphene has been investigated using back-gated field effect transistors. Variation the gate voltage from positive to negative values resulted in reduced p-type by NO2, which decreased below detection limit at −45 V. A reverse trend was observed for NH3, where its n-type increased with more voltage, becoming undetectable 5 Our results indicate that adsorption induced could not be detected when Fermi level coincides defect states, yields NO2 acceptor...
The answer to the compelling question of whether nanomaterials are new or not is debated by leading scientists.
In this work, we study electron transport across the heterojunction interface of epitaxial few-layer graphene grown on silicon carbide and underlying substrate. The observed Schottky barrier is characterized using current-voltage, capacitance-voltage photocurrent spectroscopy techniques. It found that graphene/SiC cannot be by a single unique height because lateral inhomogeneities. A Gaussian distribution heights with mean φBm=1.06eV standard deviation σ=137±11meV explains experimental data...