Open Access. Powered by Scholars. Published by Universities.®

Physical Sciences and Mathematics Commons™

Open Access. Powered by Scholars. Published by Universities.®

PDF

Wright State University

Physics Faculty Publications

Series

2009

Articles 1 - 13 of 13

Full-Text Articles in Physical Sciences and Mathematics

Morphology Of The Dayside Ionosphere Of Mars: Implications For Ion Outflows, Jane L. Fox Dec 2009

Morphology Of The Dayside Ionosphere Of Mars: Implications For Ion Outflows, Jane L. Fox

Physics Faculty Publications

Significant fluxes of tailward streaming ions have been detected in the Martian wake by instruments on spacecraft. Imposing outward fluxes at the top of a model will produce dayside ion density profiles that are characterized by smaller scale heights than those of diffusive equilibrium. We determine the maximum outward fluxes of ions, and those implied by radio occultation data, by constructing ∼180 models, with upward velocity boundary conditions in the range from 0 to (7–8) × 105 cm s−1 in small increments. As the upward velocity is increased, the topside ion or electron densities decrease until eventually the …

Go to article

Electric Field Enhancement Of Electron Emission Rates From Z(1/2) Centers In 4h-Sic, A. O. Evwaraye, S. R. Smith, William C. Mitchel, Gary C. Farlow Sep 2009

Electric Field Enhancement Of Electron Emission Rates From Z(1/2) Centers In 4h-Sic, A. O. Evwaraye, S. R. Smith, William C. Mitchel, Gary C. Farlow

Physics Faculty Publications

Z1/2 defect centers were produced by irradiating 4H-SiC bulk samples with 1 MeV electrons at room temperature. The emission rate dependence on the electric field in the depletion region was measured using deep level transient spectroscopy and double-correlation deep level transient spectroscopy. It is found that the Z1/2 defect level shows a strong electric field dependence with activation energy decreasing from Ec−0.72 eV at zero field to Ec−0.47 eV at 6.91×105 V/cm. The phonon assisted tunneling model of Karpus and Perel [Sov. Phys. JETP 64, 1376 (1986) ] completely describes the …

Go to article

Persistent Photoconductivity Studies In Nanostructured Zno Uv Sensors, Shiva Sullavarad, Nilima Hullavarad, David C. Look, Bruce Claflin Aug 2009

Persistent Photoconductivity Studies In Nanostructured Zno Uv Sensors, Shiva Sullavarad, Nilima Hullavarad, David C. Look, Bruce Claflin

Physics Faculty Publications

The phenomenon of persistent photoconductivity is elusive and has not been addressed to an extent to attract attention both in micro and nanoscale devices due to unavailability of clear material systems and device configurations capable of providing comprehensive information. In this work, we have employed a nanostructured (nanowire diameter 30–65 nm and 5 μm in length) ZnO-based metal–semiconductor–metal photoconductor device in order to study the origin of persistent photoconductivity. The current–voltage measurements were carried with and without UV illumination under different oxygen levels. The photoresponse measurements indicated a persistent conductivity trend for depleted oxygen conditions. The persistent conductivity phenomenon is …

Go to article

Effects Of Electron-Irradiation On Electrical Properties Of Algan/Gan Schottky Barrier Diodes, Z-Q. Fang, Gary C. Farlow, B. Claflin, David C. Look, D. S. Green Jun 2009

Effects Of Electron-Irradiation On Electrical Properties Of Algan/Gan Schottky Barrier Diodes, Z-Q. Fang, Gary C. Farlow, B. Claflin, David C. Look, D. S. Green

Physics Faculty Publications

Effects of 1 MeV electron-irradiation at room temperature on the electrical properties of AlGaN/GaN heterostructures, including leakage currents, threshold voltages, and electron traps, have been investigated using Schottky barrier diodes (SBDs) fabricated on the AlGaN. The SBDs, before and after the irradiation with a dose of 5×1015 cm−2, were characterized by temperature dependent current-voltage and capacitance-voltage measurements and deep level transient spectroscopy. It is found that the irradiation causes (i) significant increase in leakage currents, dominated by tunneling conduction, at both reverse and low-forward biases; (ii) a clear negative shift in threshold voltage in the pinch-off region; …

Go to article

Effects Of Collisions On Electronic-Resonance-Enhanced Coherent Anti-Stokes Raman Scattering Of Nitric Oxide, Anil K. Patnaik, Sukesh Roy, James R. Gord, Robert P. Lucht, Thomas B. Settersten Jun 2009

Effects Of Collisions On Electronic-Resonance-Enhanced Coherent Anti-Stokes Raman Scattering Of Nitric Oxide, Anil K. Patnaik, Sukesh Roy, James R. Gord, Robert P. Lucht, Thomas B. Settersten

Physics Faculty Publications

A six-level model is developed and used to study the effects of collisional energy transfer and dephasing on electronic-resonance-enhanced coherent anti-Stokes Raman scattering (ERE-CARS) in nitric oxide. The model includes the three levels that are coherently coupled by the three applied lasers as well as three additional bath levels that enable inclusion of the effects of electronic quenching and rotational energy transfer. The density-matrix equations that describe the evolution of the relevant populations and coherences are presented. The parametric dependencies of the ERE-CARS signal on collisional energy transfer and dephasing processes are described in terms of both a steady-state analytical …

Go to article

Stochastic Simulation And Analysis Of Biomolecular Reaction Networks, John M. Frazier, Yaroslov Chushak, Brent Foy Jun 2009

Stochastic Simulation And Analysis Of Biomolecular Reaction Networks, John M. Frazier, Yaroslov Chushak, Brent Foy

Physics Faculty Publications

Background: In recent years, several stochastic simulation algorithms have been developed to generate Monte Carlo trajectories that describe the time evolution of the behavior of biomolecular reaction networks. However, the effects of various stochastic simulation and data analysis conditions on the observed dynamics of complex biomolecular reaction networks have not recieved much attention. In order to investigate these issues, we employed a a software package developed in out group, called Biomolecular Network Simulator (BNS), to simulate and analyze the behavior of such systems. The behavior of a hypothetical two gene in vitro transcription-translation reaction network is investigated using the Gillespie …

Go to article

Spontaneously Generated Atomic Entanglement In Free Space Reinforced By Incoherent Pumping, Ling Zhou, Gou Hui Yang, Anil K. Patnaik Jun 2009

Spontaneously Generated Atomic Entanglement In Free Space Reinforced By Incoherent Pumping, Ling Zhou, Gou Hui Yang, Anil K. Patnaik

Physics Faculty Publications

We study spontaneously generated entanglement (SGE) between two identical multilevel atoms in free space via vacuum-induced radiative coupling. We show that the SGE in two-atom systems may initially increase with time but eventually vanishes in the time scale determined by the excited-state lifetime and radiative coupling strength between the two atoms. We demonstrate that steady-state SGE can be established by incoherently pumping the atoms to their excited states. We have shown that an appropriate rate of incoherent pump can help in producing optimal steady-state SGE. The multilevel systems offer us more channels to establish entanglement. The system under consideration can …

Go to article

Metal Contacts On Bulk Zno Crystal Treated With Remote Oxygen Plasma, Z-Q. Fang, B. Claflin, David C. Look, Y. F. Dong, L. Brillson May 2009

Metal Contacts On Bulk Zno Crystal Treated With Remote Oxygen Plasma, Z-Q. Fang, B. Claflin, David C. Look, Y. F. Dong, L. Brillson

Physics Faculty Publications

To study the quality of thin metal/ZnO Schottky contacts (SCs), temperature-dependent current-voltage (I-V), capacitance-voltage, deep level transient spectroscopy, and photoluminescence measurements were performed using bulk, vapor-phase ZnO, treated by remote oxygen plasma (ROP). Au/ZnO and Pd/ZnO contacts on both O and Zn faces are compared as a function of the ROP processing sequence and duration. We find that (i) as the duration of ROP treatment increases from 2 to 4 h, Au/ZnO contacts on the Zn face, deposited before ROP treatment, become rectifying, while those on the O face remain Ohmic; (ii) with long-term ROP …

Go to article

Uv Light-Induced Changes To The Surface Conduction In Hydrothermal Zno, B. Claflin, David C. Look May 2009

Uv Light-Induced Changes To The Surface Conduction In Hydrothermal Zno, B. Claflin, David C. Look

Physics Faculty Publications

High quality, bulk ZnO crystals grown by Tokyo Denpa using the hydrothermal process typically exhibit a room temperature carrier concentration in the 1013–1014 cm−3 range and a low mobility, conductive surface layer, observed at low temperature, with a sheet concentration on the order of 1012–1013 cm−2. In the sample discussed here, bulk conduction is controlled by two donor levels at 50 and 400 meV with concentrations of 1.2×1016 and 1.5×1016 cm−3, respectively. Temperature-dependent photo-Hall-effect measurements, using blue/UV light, in vacuum show an increase in the surface sheet …

Go to article

Polarity-Related Asymetry At Zno Surfaces And Metal Interfaces, Y. F. Dong, Z-Q. Fang, David C. Look, Daniel R. Doutt, M. J. Hetzer, L. J. Brillson May 2009

Polarity-Related Asymetry At Zno Surfaces And Metal Interfaces, Y. F. Dong, Z-Q. Fang, David C. Look, Daniel R. Doutt, M. J. Hetzer, L. J. Brillson

Physics Faculty Publications

Clean ZnO (0001) Zn- and (000(/1)) O-polar surfaces and metal interfaces have been systematically studied by depth-resolved cathodoluminescence spectroscopy, photoluminescence, current-voltage and capacitance-voltage measurements, and deep level transient spectroscopy. Zn-face shows higher near band edge emission and lower near surface defect emission. Even with remote plasma decreases of the 2.5 eV near surface defect emission, (0001)-Zn face emission quality still exceeds that of (000(/1))-O face. The two polar surfaces and corresponding metal interfaces also present very different luminescence evolution under low-energy electron beam irradiation. Ultrahigh vacuum-deposited Au and Pd diodes on as-received and O2/He plasma-cleaned surfaces display not …

Go to article

Strain Waves, Earthquakes, Slow Earthquakes, And Afterslip In The Framework Of The Frenkel-Kontorova Model, Naum I. Gershenzon, V. G. Bykov, Gust Bambakidis May 2009

Strain Waves, Earthquakes, Slow Earthquakes, And Afterslip In The Framework Of The Frenkel-Kontorova Model, Naum I. Gershenzon, V. G. Bykov, Gust Bambakidis

Physics Faculty Publications

The one-dimensional Frenkel-Kontorova (FK) model, well known from the theory of dislocations in crystal materials, is applied to the simulation of the process of nonelastic stress propagation along transform faults. Dynamic parameters of plate boundary earthquakes as well as slow earthquakes and afterslip are quantitatively described, including propagation velocity along the strike, plate boundary velocity during and after the strike, stress drop, displacement, extent of the rupture zone, and spatiotemporal distribution of stress and strain. The three fundamental speeds of plate movement, earthquake migration, and seismic waves are shown to be connected in framework of the continuum FK model. The …

Go to article

In-Implanted Zno: Controlled Degenerate Surface Layer, David C. Look, Gary C. Farlow, F. Yaqoob, L. H. Vanamurthy, M. Huang May 2009

In-Implanted Zno: Controlled Degenerate Surface Layer, David C. Look, Gary C. Farlow, F. Yaqoob, L. H. Vanamurthy, M. Huang

Physics Faculty Publications

In was implanted into bulk ZnO creating a square profile with a thickness of about 100 nm and an In concentration of about 1×1020 cm-3. The layer was analyzed with Rutherford backscattering, temperature-dependent Hall effect, and low-temperature photoluminescence measurements. The implantation created a nearly degenerate carrier concentration n of about 2×1019 cm-3, but with a very low mobility μ, increasing from about 0.06 cm2/V s at 20 K to about 2 cm2/V s at 300 K. However, after annealing at 600 °C for 30 min, n increased to about 5×10 …

Go to article

Ga-Related Photoluminescence Lines In Ga-Doped Zno Grown By Plasma-Assisted Molecular-Beam Epitaxy, Z. Yang, David C. Look, J. L. Liu Feb 2009

Ga-Related Photoluminescence Lines In Ga-Doped Zno Grown By Plasma-Assisted Molecular-Beam Epitaxy, Z. Yang, David C. Look, J. L. Liu

Physics Faculty Publications

Low-temperature photoluminescence (PL) and temperature-dependent Hall-effect (T-Hall) measurements were carried out in undoped and Ga-doped ZnO thin films grown by molecular-beam epitaxy. As the carrier concentration increases from 1.8×1018 to 1.8×1020 cm−3, the dominant PL line at 9 K changes from I1 (3.368–3.371 eV) to IDA (3.317–3.321 eV), and finally to I8 (3.359 eV). The dominance of I1, due to ionized-donor bound excitons, is unexpected in n-type samples but is shown to be consistent with the T-Hall results. We also show that IDA has characteristics of …

Go to article