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Physics Faculty Publications

2009

Articles 1 - 30 of 79

Full-Text Articles in Physical Sciences and Mathematics

Partial Wave Analysis Of The Reaction Γp→Pω And The Search For Nucleon Resonances, M. Williams, Gerard P. Gilfoyle, Et. Al. Dec 2009

Partial Wave Analysis Of The Reaction Γp→Pω And The Search For Nucleon Resonances, M. Williams, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

An event-based partial wave analysis (PWA) of the reaction γp → pω has been performed on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world’s first high-precision spin-density matrix element measurements, available to the event-based PWA through the decay distribution of ω → π +π −π0. The data confirm the dominance of the t-channel π0 exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F15(1680) and …

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Differential Cross Sections And Spin Density Matrix Elements For The Reaction Γp→Pω, M. Williams, Gerard P. Gilfoyle, Et. Al. Dec 2009

Differential Cross Sections And Spin Density Matrix Elements For The Reaction Γp→Pω, M. Williams, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

High-statistics differential cross sections and spin-density matrix elements for the reaction γp → pω have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass (c.m.) energies from threshold up to 2.84 GeV. Results are reported in 112 10-MeV wide c.m. energy bins, each subdivided into cos θωc.m. bins of width 0.1. These are the most precise and extensive ω photoproduction measurements to date. A number of prominent structures are clearly present in the data. Many of these have not previously been observed due to limited statistics in earlier measurements.

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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 …

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Electroexcitation Of Nucleon Resonances From Clas Data On Single Pion Electroproduction, I. G. Aznauryan, Gerard P. Gilfoyle, Et. Al. Nov 2009

Electroexcitation Of Nucleon Resonances From Clas Data On Single Pion Electroproduction, I. G. Aznauryan, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

We present results on the electroexcitation of the low mass resonances ∆(1232)P33, N(1440)P11, N(1520)D13, and N(1535)S11 in a wide range of Q2. The results were obtained in the comprehensive analysis of data from the Continuous Electron Beam Accelerator Facility (CEBAF) large acceptance spectrometer (CLAS) detector at the Thomas Jefferson National Accelerator Facility (JLab) on differential cross sections, longitudinally polarized beam asymmetries, and longitudinal target and beam-target asymmetries for π electroproduction off the proton. The data were analyzed using two conceptually different approaches—fixed-t dispersion …

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G Factor Of The 2+1 State Of 172Hf, Z. Berant, E. Oster, R. J. Casperson, A. Wolf, V. Werner, A. Heinz, R. F. Casten, G. Gurdal, E. A. Mccutchan, D. S. Brenner, J. R. Terry, R. Winkler, E. Williams, J. Qian, A. Schmidt, M. K. Smith, T. Ahn, C. W. Beausang, P. H. Regan, T. J. Ross, M. Bunce, B. Darakchieva, D. A. Meyer, J. Leblanc, K. Dudziak, C. Bauer, G. Henning Nov 2009

G Factor Of The 2+1 State Of 172Hf, Z. Berant, E. Oster, R. J. Casperson, A. Wolf, V. Werner, A. Heinz, R. F. Casten, G. Gurdal, E. A. Mccutchan, D. S. Brenner, J. R. Terry, R. Winkler, E. Williams, J. Qian, A. Schmidt, M. K. Smith, T. Ahn, C. W. Beausang, P. H. Regan, T. J. Ross, M. Bunce, B. Darakchieva, D. A. Meyer, J. Leblanc, K. Dudziak, C. Bauer, G. Henning

Physics Faculty Publications

The g factor of the 2+1 state of 172Hf was measured using the perturbed angular correlation technique in a static external magnetic field. The result, g(2+1) = 0.25(5), is discussed in relation to the systematics of the previously reported g factors in the Hf isotopes and compared with the predictions of several models. An interesting outcome of the analysis presented in this paper is the agreement between the calculated g factors within the interacting boson approximation (IBA) and the results of a large-scale shell model calculation. This agreement supports the emphasis in the …

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The Surface Relaxation And Band Structure Of Mo(112), Ning Wu, Ya. B. Losovyj, Zhaoxian Yu, Renat F. Sabirianov, Wai-Ning Mei, N. Lozova, J. A. Colón Santana, Peter Dowben Nov 2009

The Surface Relaxation And Band Structure Of Mo(112), Ning Wu, Ya. B. Losovyj, Zhaoxian Yu, Renat F. Sabirianov, Wai-Ning Mei, N. Lozova, J. A. Colón Santana, Peter Dowben

Physics Faculty Publications

The experimental and theoretical surface band structures of Mo(112) are compared. This surface band structure mapping is presented with corrections included for the lattice relaxation of the Mo(112) surface. Quantitative low energy electron diffraction (LEED) has been used to determine the details of the Mo(112) surface structure. The first layer contraction is 14.9% by LEED intensity versus voltage analysis and is in general agreement with the 17.6% contraction found from total surface energy optimization. The electronic band structure is mapped out along ¯– ¯ X and ¯–¯Y of the surface Brillouin zone (SBZ). There is strong evidence of electron–phonon coupling …

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Differential Cross Sections For The Reactions Γp→Pη And Γp→Pη', M. Williams, Gerard P. Gilfoyle, Et. Al. Oct 2009

Differential Cross Sections For The Reactions Γp→Pη And Γp→Pη', M. Williams, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

High-statistics differential cross sections for the reactions γp → pη and γp → pη' have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass energies from near threshold up to 2.84 GeV. The η' results are the most precise to date and provide the largest energy and angular coverage. The η measurements extend the energy range of the world’s large-angle results by approximately 300 MeV. These new data, in particular the η' measurements, are likely to help constrain the analyses being performed to search for new baryon resonance states.

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Impact Of High-Order Surface Plasmon Modes Of Metal Nanoparticles On Enhancement Of Optical Emission, Greg Sun, Jacob B. Khurgin, C. C. Yang Oct 2009

Impact Of High-Order Surface Plasmon Modes Of Metal Nanoparticles On Enhancement Of Optical Emission, Greg Sun, Jacob B. Khurgin, C. C. Yang

Physics Faculty Publications

We consider the impact of high-order surface plasmon modes supported by the metal nanoparticles on the efficiency enhancement of optical emission. Using the example of Au nanosphere embedded in the GaN dielectric, we show that for an emitter with certain original radiative efficiency, placing the emitter too close to the metal sphere does not always produce additional enhancement. Thus our model provides analytical treatment of the luminescence quenching and can be used to optimize both nanoparticle size and its separation from the emitter to yield maximum enhancement.

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Photoproduction Of Π​+Π​- Meson Pairs On The Proton, M. Battaglieri, Gerard P. Gilfoyle, Et. Al. Oct 2009

Photoproduction Of Π​+Π​- Meson Pairs On The Proton, M. Battaglieri, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

The exclusive reaction γp → pπ+π- was studied in the photon energy range 3.0–3.8 GeV and the momentum transfer range 0:4 < -t < 1:0 GeV2. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. In this kinematic range, the integrated luminosity was about 20 pb-1. The reaction was isolated by detecting the π+ and proton in CLAS, and reconstructing the π- via the missing-mass technique. Moments of the di-pion decay angular distributions were derived from the experimental data. Differential cross sections for the S, P, and D …

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Photodisintegration Of 4He Into P + T, R. Nasseripour, Gerard P. Gilfoyle, Et. Al. Oct 2009

Photodisintegration Of 4He Into P + T, R. Nasseripour, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

The two-body photodisintegration of 4He into a proton and a triton has been studied using the CEBAF Large-Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Real photons produced with the Hall-B bremsstrahlung-tagging system in the energy range from 0.35 to 1.55 GeV were incident on a liquid 4He target. This is the first measurement of the photodisintegration of 4He above 0.4 GeV. The differential cross sections for the γ 4He → pt reaction were measured as a function of photon-beam energy and proton-scattering angle and are compared with the latest model calculations by J.M. …

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Determining The Gasb/Gaas-(2 × 8) Reconstruction, Jessica E. Bickel, Normand A. Modine, Joanna Mirecki Millunchick Oct 2009

Determining The Gasb/Gaas-(2 × 8) Reconstruction, Jessica E. Bickel, Normand A. Modine, Joanna Mirecki Millunchick

Physics Faculty Publications

Highly strained thin layers of GaSb/GaAs possess a (2 × 4) reconstruction at low Sb overpressures, and a (2 × 8) reconstruction at high Sb overpressures. While the atomic details of the Sb/GaAs-(2 × 4) are well known, the details of the (2 × 8) are not understood. In this paper, we use density functional theory to analyze possible (2 × 8) structures. Comparing scanning tunneling microscope images from both simulation and experiment and examining the relative energies of possible (2 × 8) structures, we show the α(2 × 8) and β(2 × 8) are the thermodynamically stable surface reconstructions …

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Beam Spin Asymmetries In Deeply Virtual Compton Scattering (Dvcs) With Clas At 4.8 Gev, G. Gavalian, Gerard P. Gilfoyle, Et. Al. Sep 2009

Beam Spin Asymmetries In Deeply Virtual Compton Scattering (Dvcs) With Clas At 4.8 Gev, G. Gavalian, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

We report measurements of the beam spin asymmetry in deeply virtual Compton scattering (DVCS) at an electron beam energy of 4.8 GeV using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The DVCS beam spin asymmetry has been measured in a wide range of kinematics, 1.0 < Q2 < 2.8 (GeV/c)2, 0.12 < xB < 0.48, and 0.1 < −t < 0.8 (GeV/c)2, using the reaction ep → e' p X. The number of H(e, e' γ p) and H(e, e'π0p) events are separated in each (Q2, xB, t …

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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 …

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Assessment Of Mixing In Passive Microchannels With Fractal Surface Patterning, Petru S. Fodor, M. Itomlenskis, Miron Kaufman Sep 2009

Assessment Of Mixing In Passive Microchannels With Fractal Surface Patterning, Petru S. Fodor, M. Itomlenskis, Miron Kaufman

Physics Faculty Publications

We explore numerically the feasibility of enhancing the mixing capability of microchannels by employing the Weierstrass fractal function to generate a pattern of V-shaped ridges on the channel floor. Motivated by experimental limitations such as the finite resolution (similar to 10 mu m) associated with rapid prototyping through soft lithography techniques, we study the influence on the quality of mixing of having finite width ridges. The mixing capability of the designs studied is evaluated using an entropic measure and the designs are optimized with respect to: the distances between the ridges and the position range of their tip along the …

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Extended Defects In The Potts-Percolation Model Of A Solid: Renormalization Group And Monte Carlo Analysis, H. T. Diep, Miron Kaufman Sep 2009

Extended Defects In The Potts-Percolation Model Of A Solid: Renormalization Group And Monte Carlo Analysis, H. T. Diep, Miron Kaufman

Physics Faculty Publications

We extend the model of a 2d solid to include a line of defects. Neighboring atoms on the defect line are connected by springs of different strength and different cohesive energy with respect to the rest of the system. Using the Migdal-Kadanoff renormalization group we show that the elastic energy is an irrelevant field at the bulk critical point. For zero elastic energy this model reduces to the Potts model. By using Monte Carlo simulations of the three- and four-state Potts model on a square lattice with a line of defects, we confirm the renormalization-group prediction that for a defect …

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High-K Multi-Quasiparticle States And Rotational Bands In 255103Lr., H. B. Jeppesen, R. M. Clark, K. E. Gregorich, A. V. Afanasjev, M. N. Ali, J. M. Allmond, C. W. Beausang, M. Cromaz, M. A. Deleplanque, I. Dragojevic, J. Dvorak, P. A. Ellison, P. Fallon, M. A. Garcia, J. M. Gates, S. Gros, I. Y. Lee, A. O. Macchiavelli, S. L. Nelson, H. Nitsche, L. Stavsetra, F. S. Stephens, M. Wiedeking Aug 2009

High-K Multi-Quasiparticle States And Rotational Bands In 255103Lr., H. B. Jeppesen, R. M. Clark, K. E. Gregorich, A. V. Afanasjev, M. N. Ali, J. M. Allmond, C. W. Beausang, M. Cromaz, M. A. Deleplanque, I. Dragojevic, J. Dvorak, P. A. Ellison, P. Fallon, M. A. Garcia, J. M. Gates, S. Gros, I. Y. Lee, A. O. Macchiavelli, S. L. Nelson, H. Nitsche, L. Stavsetra, F. S. Stephens, M. Wiedeking

Physics Faculty Publications

Two isomeric states have been identified in 255Lr. The decay of the isomers populates rotational structures. Comparison with macroscopic-microscopic calculations suggests that the lowest observed sequence is built upon the [624]9/2+ Nilsson state. However, microscopic cranked relativistic Hartree-Bogoliubov (CRHB) calculations do not reproduce the moment of inertia within typical accuracy. This is a clear challenge to theories describing the heaviest elements.

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Destruction, Amorphization And Reactivity Of Nano-Bn Under Ball Milling, A. N. Streletskii, D. G. Permenov, B. B. Bokhonov, I. V. Kolbanev, A. V. Leonov, I. V. Berestetskaya, Kiril A. Streletzky Aug 2009

Destruction, Amorphization And Reactivity Of Nano-Bn Under Ball Milling, A. N. Streletskii, D. G. Permenov, B. B. Bokhonov, I. V. Kolbanev, A. V. Leonov, I. V. Berestetskaya, Kiril A. Streletzky

Physics Faculty Publications

The processes of mechanical activation of a hexagonal boron nitride (h-BN) and its reactivity upon interaction with hydrogen and water were investigated using X-ray, TEM, Microdiffraction, Dynamic Light Scattering, FTIR-spectroscopy, adsorption (BET). Initial h-BN samples were monocrystalline plates 70–80 nm thick. Mechanical treatment of h-BN is accompanied by plate splitting and formation of crystallographically oriented “rods.” The rod thickness gradually diminishes to less than 5 nm. Specific surface area of the rods (400 m2/g), is found to be equal to the outer geometrical surface of rods. As nanocrystallites form “c” parameter of h-BN increases. When nanocrystallites are less than several …

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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 …

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Π+ Photoproduction On The Proton For Photon Energies From 0.725 To 2.875 Gev, M. Dugger, Gerard P. Gilfoyle, Et. Al. Jun 2009

Π+ Photoproduction On The Proton For Photon Energies From 0.725 To 2.875 Gev, M. Dugger, Gerard P. Gilfoyle, Et. Al.

Physics Faculty Publications

Differential cross sections for the reaction γp → nπ+ have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged photon beam with energies from 0.725 to 2.875 GeV. Where available, the results obtained here compare well with previously published results for the reaction. Agreement with the SAID andMAID analyses is found below 1 GeV. The present set of cross sections has been incorporated into the SAID database, and exploratory fits have been made up to 2.7 GeV. Resonance couplings have been extracted and compared to previous determinations. With the addition of these cross sections to the …

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Impact Of Disorder On Surface Plasmons In Two-Dimensional Arrays Of Metal Nanoparticles, Jacob B. Khurgin, Greg Sun Jun 2009

Impact Of Disorder On Surface Plasmons In Two-Dimensional Arrays Of Metal Nanoparticles, Jacob B. Khurgin, Greg Sun

Physics Faculty Publications

We study the impact of disorder on the properties of surface plasmons (SP) in metal nanoparticle arrays and develop analytical expressions enabling us to ascertain the degree of localization and mixing between the SP states. We show that it might be advantageous to intentionally introduce a certain degree of disorder in order to engineer the improved sensors and detectors.

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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; …

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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 …

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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 …

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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 …

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Relative 235U(N,Γ) And (N,F) Cross Sections From 235U(D,Pγ) And (D,Pf), J. M. Allmond, L. A. Bernstein, C. W. Beausang, L. Phair, D. L. Bleuel, J. T. Burke, J. Escher, K. E. Evans, B. L. Goldblum, R. Hatarik, H. B. Jeppesen, S. R. Lesher, M. A. Mcmahan, J. O. Rasmussen, N. D. Scielzo, M. Wiedeking May 2009

Relative 235U(N,Γ) And (N,F) Cross Sections From 235U(D,Pγ) And (D,Pf), J. M. Allmond, L. A. Bernstein, C. W. Beausang, L. Phair, D. L. Bleuel, J. T. Burke, J. Escher, K. E. Evans, B. L. Goldblum, R. Hatarik, H. B. Jeppesen, S. R. Lesher, M. A. Mcmahan, J. O. Rasmussen, N. D. Scielzo, M. Wiedeking

Physics Faculty Publications

The internal surrogate ratio method allows for the determination of an unknown cross section, such as (n,γ), relative to a better-known cross section, such as (n,f), by measuring the relative exit-channel probabilities of a surrogate reaction that proceeds through the same compound nucleus. The validity of the internal surrogate ratio method is tested by comparing the relative γ and fission exit-channel probabilities of a 236U∗ compound nucleus, formed in the 235U(d,p) reaction, to the known 235U(n,γ) and (n,f) cross sections. A model-independent method for measuring the …

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Enhancement Of Light Absorption In A Quantum Well By Surface Plasmon Polariton, Jacob B. Khurgin, Greg Sun May 2009

Enhancement Of Light Absorption In A Quantum Well By Surface Plasmon Polariton, Jacob B. Khurgin, Greg Sun

Physics Faculty Publications

We investigate analytically the degree to which the absorption of light in a single quantum well can be enhanced in the proximity of a structured metallic surface and show that the wavelength at which the maximum enhancement of about one order of magnitude is attained depends on metal loss and the initial absorption in a quantum well.

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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 …

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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 …

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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 …

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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 …

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