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Articles 1 - 19 of 19
Full-Text Articles in Physics
Introduction And Recovery Of Ga And N Sublattice Defects In Electron-Irradiated Gan, F. Tuomisto, V. Ranki, David C. Look, Gary C. Farlow
Introduction And Recovery Of Ga And N Sublattice Defects In Electron-Irradiated Gan, F. Tuomisto, V. Ranki, David C. Look, Gary C. Farlow
Physics Faculty Publications
We have used positron annihilation spectroscopy to study the introduction and recovery of point defects introduced by 0.45 and 2 MeV electron irradiation at room temperature in n-type GaN. Isochronal annealings were performed up to 1220 K. We observe vacancy defects with specific lifetime of τV=190±15 ps that we tentatively identify as N vacancies or related complexes in the neutral charge state in the samples irradiated with 0.45 MeV electrons. The N vacancies are produced at a rate ΣN0.45≃0.25 cm−1. The irradiation with 2 MeV electrons produces negatively charged Ga vacancies and negative …
Near-Terminator Venus Ionosphere: How Chapman-Esque?, Jane L. Fox
Near-Terminator Venus Ionosphere: How Chapman-Esque?, Jane L. Fox
Physics Faculty Publications
We have modeled the near-terminator ionosphere of Venus for solar zenith angles χ between 60 and 85° in 5° increments, and from 86 to 90° in 1° increments. The most important neutral densities of the background thermospheres have been adopted from the VTS3 model of Hedin et al. (1983), which is based on densities from the Pioneer Venus (PV) Orbiter Neutral Mass Spectrometer (e.g., Niemann et al., 1980) that are normalized to the PV Orbiter Atmospheric Drag data (e.g., Keating et al., 1980). We compare the ion density profiles to those of a Chapman layer and to those obtained from …
Near-Terminator Venus Ionosphere: Evidence For A Dawn/Dusk Asymmetry In The Thermosphere, Jane L. Fox, W. T. Kasprzak
Near-Terminator Venus Ionosphere: Evidence For A Dawn/Dusk Asymmetry In The Thermosphere, Jane L. Fox, W. T. Kasprzak
Physics Faculty Publications
Recent models of the near-terminator ionosphere of Venus constructed using neutral density profiles from the VTS3 model of Hedin et al. (1983) have shown that altitudes of the electron density peaks are in agreement with those measured by Pioneer Venus (PV) Orbiter Radio Occultation (ORO) and other radio occultation profiles in the solar zenith angle (SZA) range 60 to 70°, where they are near 140 km (Fox, 2007). The model peaks in the 75–85° range, however, do not decrease in altitude to near 135 km, as do the PV ORO electron density peaks shown in the study of Cravens et …
Thermally Driven Defect Formation And Blocking Layers At Metal-Zno Interfaces, H. L. Mosbacker, C. Zgrabik, M. J. Hetzer, A. Swain, David C. Look, G. Cantwell, J. Zhang, J. J. Song, L. J. Brillson
Thermally Driven Defect Formation And Blocking Layers At Metal-Zno Interfaces, H. L. Mosbacker, C. Zgrabik, M. J. Hetzer, A. Swain, David C. Look, G. Cantwell, J. Zhang, J. J. Song, L. J. Brillson
Physics Faculty Publications
The authors used depth-resolved cathodoluminescence spectroscopy and current-voltage measurements to probe the temperature-dependent formation of native point defects and reaction layers at metal-ZnO interfaces and their effect on transport properties. These results identify characteristic defect emissions corresponding to metal-Zn alloy versus oxide formation. Au alloys with Zn above its eutectic temperature, while Ta forms oxide blocking layers that reduce current by orders of magnitude at intermediate temperatures. Defects generated at higher temperatures and/or with higher initial defect densities for all interfaces produce Ohmic contacts. These reactions and defect formation with annealing reveal a thermodynamic control of blocking versus Ohmic contacts.
Role Of Subsurface Defects In Metal-Zno(0001) Schottky Barrier Formation, H. L. Mosbacker, S. El Hage, M. Gonzalez, S. A. Ringel, M. J. Hetzer, David C. Look, G. Cantwell, J. Zhang, J. J. Song, L. J. Brillson
Role Of Subsurface Defects In Metal-Zno(0001) Schottky Barrier Formation, H. L. Mosbacker, S. El Hage, M. Gonzalez, S. A. Ringel, M. J. Hetzer, David C. Look, G. Cantwell, J. Zhang, J. J. Song, L. J. Brillson
Physics Faculty Publications
The authors fabricated diodes of Au, Al, Ni, Pt, Pd, Mo, Ta, and Ir on single crystal ZnO(0001) surfaces from different vendors and measured their Schottky barriers, idealities, and reverse currents on as-received and remote oxygen (20% O2/80%He) plasma-treated surfaces. Using low temperature nanoscale depth-resolved cathodoluminescence spectroscopy (DRCLS) under the metal, the authors identified the presence of defect transitions at 2.1, 2.5, and 3.0 eV that change dramatically depending on the process steps and choice of metal. I-V measurements exhibited transitions from Ohmic to Schottky and lower idealities for Pt, Au, Ir, and Pd with plasma treatment. ZnO …
Electron And Hole Traps In N-Doped Zno Grown On P-Type Si By Metalorganic Chemical Vapor Deposition, Z-Q. Fang, B. Claflin, David C. Look, Lei L. Kerr, Xiaonan Li
Electron And Hole Traps In N-Doped Zno Grown On P-Type Si By Metalorganic Chemical Vapor Deposition, Z-Q. Fang, B. Claflin, David C. Look, Lei L. Kerr, Xiaonan Li
Physics Faculty Publications
Electron and hole traps in N-doped ZnO were investigated using a structure of n+-ZnO:Al/i-ZnO/ZnO:N grown on a p-Si substrate by metalorganic chemical vapor deposition (for growth of the ZnO:N layer) and sputtering deposition (for growth of the i-ZnO and n+-ZnO:Al layers). Current-voltage and capacitance-voltage characteristics measured at temperatures from 200 to 400 K show that the structure is an abrupt n+−p diode with very low leakage currents. By using deep level transient spectroscopy, two hole traps, H3 (0.35 eV) and H4 (0.48 eV), are found in the p-Si …
Electron Irradiation Induced Deep Centers In Hydrothermally Grown Zno, Z-Q. Fang, B. Claflin, David C. Look, Gary C. Farlow
Electron Irradiation Induced Deep Centers In Hydrothermally Grown Zno, Z-Q. Fang, B. Claflin, David C. Look, Gary C. Farlow
Physics Faculty Publications
An n-type hydrothermally grown ZnO sample becomes semi-insulating (ρ~108 Ω cm) after 1-MeV electron-irradiation. Deep traps produced by the irradiation were studied by thermally stimulated current spectroscopy. The dominant trap in the as-grown sample has an activation energy of 0.24 eV and is possibly related to LiZn acceptors. However, the electron irradiation introduces a new trap with an activation energy of 0.15 eV, and other traps of energy 0.30 and 0.80 eV, respectively. From a comparison of these results with positron annihilation experiments and density functional theory, we conclude that the 0.15-eV trap may be …
The Effect Of Si Doping On The Electrical Properties Of B12as2 Thin Films On (0001) 6h-Sic Substrates, Zhou Xu, J. H. Edgar, David C. Look, S. Baumann, R. J. Bleiler, S. H. Wang, S. E. Mohney
The Effect Of Si Doping On The Electrical Properties Of B12as2 Thin Films On (0001) 6h-Sic Substrates, Zhou Xu, J. H. Edgar, David C. Look, S. Baumann, R. J. Bleiler, S. H. Wang, S. E. Mohney
Physics Faculty Publications
The ability to control the resistivity of the wide band gap semiconductor B12As2 by doping with silicon was verified. The electrical properties of nominally undoped and Si-doped rhombohedral B12As2 thin films on semi-insulating 6H-SiC (0001) substrates prepared by chemical vapor deposition were subjected to Hall effect measurements. Varying the Si concentration in the B12As2 thin films from 7×1018 to 7×1021 at./cm3 (as measured by secondary ion mass spectrometry) decreased the resistivities of the p-type B12As2 films from 2×105 to 10 Ω …
Dominant Effect Of Near-Interface Native Point Defects On Zno Schottky Barriers, L. J. Brillson, H. L. Mosbacker, M. J. Hetzer, Y. Strzhemechny, David C. Look, G. Cantwell, J. Zhang, J. J. Song
Dominant Effect Of Near-Interface Native Point Defects On Zno Schottky Barriers, L. J. Brillson, H. L. Mosbacker, M. J. Hetzer, Y. Strzhemechny, David C. Look, G. Cantwell, J. Zhang, J. J. Song
Physics Faculty Publications
The authors used depth-resolved cathodoluminescence spectroscopy and current-voltage measurements to probe metal-ZnO diodes as a function of native defect concentration, oxygen plasma processing, and metallization. The results show that resident native defects in ZnO single crystals and native defects created by the metallization process dominate metal-ZnO Schottky barrier heights and ideality factors. Results for ZnO(0001) faces processed with room temperature remote oxygen plasmas to remove surface adsorbates and reduce subsurface native defects demonstrate the pivotal importance of crystal growth quality and metal-ZnO reactivity in forming near-interface states that control Schottky barrier properties.
Electron And Hole Traps In N-Doped Zno Grown On P-Type Si Substrate By Mocvd, Zhaoqiang Fang, Bruce B. Claflin, David C. Look, Lei L. Kerr, Xiaonan Li
Electron And Hole Traps In N-Doped Zno Grown On P-Type Si Substrate By Mocvd, Zhaoqiang Fang, Bruce B. Claflin, David C. Look, Lei L. Kerr, Xiaonan Li
Physics Faculty Publications
Electron and hole traps in N-doped ZnO were investigated using a structure of n+-ZnO:Al/i-ZnO/ZnO:N grown on a p-Si substrate by metalorganic chemical vapor deposition (for growth of the ZnO:N layer) and sputtering deposition (for growth of the i-ZnO and n+-ZnO:Al layers). Current-voltage and capacitance-voltage characteristics measured at temperatures from 200 to 400 K show that the structure is an abrupt n+−p diode with very low leakage currents. By using deep level transient spectroscopy, two hole traps, H3 (0.35 eV) and H4 (0.48 eV), are found in the p-Si …
The Metal-Insulator Transition In Vo2 Studied Using Terahertz Apertureless Near-Field Microscopy, Hui Zhan, Victoria Astley, Michael Hvasta, Jason A. Deibel, Daniel M. Mittleman, Yong-Sik Lim
The Metal-Insulator Transition In Vo2 Studied Using Terahertz Apertureless Near-Field Microscopy, Hui Zhan, Victoria Astley, Michael Hvasta, Jason A. Deibel, Daniel M. Mittleman, Yong-Sik Lim
Physics Faculty Publications
We have studied the metal-insulator transition in a vanadium dioxide (VO2) thin film using terahertz apertureless near-field optical microscopy. We observe a variation of the terahertz amplitude due to the phase transition induced by an applied voltage across the sample. The change of the terahertz signal is related to the abrupt change of the conductivity of the VO2 film at the metal-insulator transition. The subwavelength spatial resolution of this near-field microscopy makes it possible to detect signatures of micron-scale metallic domains in inhomogeneous VO2 thin films.
Temperature Dependence Of Terahertz Emission From Inmnas, Hui Zhan, Jason A. Deibel, Jonathan Laib, Chanjuan Sun, Junichiro Kono, Daniel M. Mittleman, Hiro Munekata
Temperature Dependence Of Terahertz Emission From Inmnas, Hui Zhan, Jason A. Deibel, Jonathan Laib, Chanjuan Sun, Junichiro Kono, Daniel M. Mittleman, Hiro Munekata
Physics Faculty Publications
No abstract provided.
Students’ Use Of Symmetry With Gauss’S Law, Adrienne L. Traxler, Katrina E. Black, John R. Thompson
Students’ Use Of Symmetry With Gauss’S Law, Adrienne L. Traxler, Katrina E. Black, John R. Thompson
Physics Faculty Publications
To study introductory student difficulties with electrostatics, we compared student techniques when finding the electric field for spherically symmetric and non-spherically symmetric charged conductors. We used short interviews to design a free-response and multiple-choice-multiple-response survey that was administered to students in introductory calculus-based courses. We present the survey results and discuss them in light of Singh's results for Gauss's Law, Collins and Ferguson's epistemic forms and games, and Tuminaro's extension of games and frames.
Investigation Of The Reflective Properties Of A Left-Handed Metamaterial, Amanda Durham
Investigation Of The Reflective Properties Of A Left-Handed Metamaterial, Amanda Durham
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The purpose of this project is to investigate the reflective properties of a left-handed metamaterial (LHM) through the use of a finite element analysis software called FEMLAB. In the 1960's, V. Veselago theorized that a material with negative permeability and negative permittivity has a negative index of refraction. In 2000, such a metamaterial was built and demonstrated at microwave frequencies. Previous work had focused on the transmission properties of the metamaterial. In our work, the reflected wave was examined for a LHM subject to an incident transverse electric wave. The different generalizations, first proposed by Veselago, of the Fresnel and …
Fabrication And Study Of Zno Micro- And Nanostructures, Monica Morales-Masis
Fabrication And Study Of Zno Micro- And Nanostructures, Monica Morales-Masis
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ZnO micro-structures and nano-structures have been grown on two types of substrate by reacting condensed Zn vapor with oxygen. The source material was either pure zinc powder or zinc acetate which was either evaporated or decomposed. This was done in the temperature range 500 C to 650 C, in a flowing Ar plus oxygen ambient at atmospheric pressure. Variations in the carrier gas composition, gas flow rate and the position of the substrate in the furnace were found to control the formation and the morphology of the nanostructures. Scanning electron microscopy images of samples grown from a Zn powder source …
Evanescent Microwave Characterization Of Carbon Nanotube Films Grown On Silicon Carbide Substrate, Kineshma Munbodh
Evanescent Microwave Characterization Of Carbon Nanotube Films Grown On Silicon Carbide Substrate, Kineshma Munbodh
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The electromagnetic characterization of carbon nanotube films (CNT) grown by the surface decomposition of silicon carbide (SiC) has been performed. The CNT films formed on the carbon and silicon terminated face of the SiC substrate were uncapped by an annealing process at a temperature of 4000 C with dwelling time up to 60 minutes in oxygen or carbon dioxide atmosphere. X-Y scans of the quality factor were used to deduce the local conductive properties of the films measured by evanescent microwave microscopy. Real and imaginary permittivity values, as determined by these electromagnetic measurements, provided valuable information for future field emission …
Comparative Investigation Of Dosimetric Tools In Imrt, Aaron Nicholas Garcia
Comparative Investigation Of Dosimetric Tools In Imrt, Aaron Nicholas Garcia
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Verification of the isodose distribution delivered to the planned tumor volume is required for quality assurance in the clinic. Verification in this context means ensuring that the actual dose delivered to a volume matches the dose that a computerized planning system intended that volume to receive. The computerized planning is performed by a Computerized Medical Systems (CMS) Intensity Modulated Radiation Therapy (IMRT) plan. Two methods of measuring the delivered dose are film dosimetry and diode dosimetry. This project will compare the relative isodose distribution profiles of film dosimetry and MapCheck (Sun Nuclear Corporation, a diode-based dosimetry system) to the relative …
Fabrication Of Silver Nanoparticles By Solution Phase Method And Physical Characterization Of Their Arrays, Jaesung Oh
Fabrication Of Silver Nanoparticles By Solution Phase Method And Physical Characterization Of Their Arrays, Jaesung Oh
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Synthesis of silver nanostructures has been an active research area for many decades because of their importance in biological sensing, imaging, electronics, optoelectronics and catalysis. In particular, much effort has been devoted to the controlled synthesis of silver nanowires because of their potential use as interconnects or active components in fabricating nanoscale devices. The solution phase method is used here to form Ag nanoparticles by reducing silver nitrate with ethylene glycol heated to 160°C. The additional presence of polyvinyl pyrrolidone plays a role of stabilizer to prevent an agglomeration and/or a capping agent to produce highly anisotropic nanowires. Silver nanoparticles …
Polarization Reversal In Potassium Titanyl Phosphate, William D. Mitchell
Polarization Reversal In Potassium Titanyl Phosphate, William D. Mitchell
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Polarization reversal in both hydrothermal and flux grown potassium titanyl phosphate was studied using square pulses at room temperature from 1600 V/mm to 5000 V/mm. Maximum switching current and inverse switching time data is compared to the ferroelectric polarization reversal model developed by Fatuzzo and Merz in the last century. Room temperature calculation of spontaneous polarization is reported and compared to that of potassium titanyl phosphate in the literature.