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Physics Faculty Publications

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Articles 1471 - 1500 of 2178

Full-Text Articles in Physical Sciences and Mathematics

Next-To-Leading Order Evolution Of Color Dipoles, Ian Balitsky, Giovanni A. Chirilli Jan 2008

Next-To-Leading Order Evolution Of Color Dipoles, Ian Balitsky, Giovanni A. Chirilli

Physics Faculty Publications

The small-x deep inelastic scattering in the saturation region is governed by the nonlinear evolution of Wilson-line operators. In the leading logarithmic approximation it is given by the Balitsky-Kovchegov equation for the evolution of color dipoles. In the next-to-leading order the Balitsky-Kovchegov equation gets contributions from quark and gluon loops as well as from the tree gluon diagrams with quadratic and cubic nonlinearities. We calculate the gluon contribution to the small-x evolution of Wilson lines (the quark part was obtained earlier).

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Unusual Heavy-Mass Nearly Ferromagnetic State With A Surprisingly Large Wilson Ratio In The Double Layered Ruthenates (Sr1−Xcax)3ru2o7, Zhe Qu, Leonard Spinu, Huiqiu Yuan, Vladimir Dobrosavljevic, Wei Bao, Jeffrey W. Lynn, M. Nicklas, Jin Peng, Tijang Liu, David Fobes, Etienne Flesch, Z. Q. Mao Jan 2008

Unusual Heavy-Mass Nearly Ferromagnetic State With A Surprisingly Large Wilson Ratio In The Double Layered Ruthenates (Sr1−Xcax)3ru2o7, Zhe Qu, Leonard Spinu, Huiqiu Yuan, Vladimir Dobrosavljevic, Wei Bao, Jeffrey W. Lynn, M. Nicklas, Jin Peng, Tijang Liu, David Fobes, Etienne Flesch, Z. Q. Mao

Physics Faculty Publications

We report an unusual nearly ferromagnetic heavy-mass state with a surprisingly large Wilson ratio Rw (e.g., Rw∼700 for x=0.2) in double layered ruthenates (Sr1−xCax)3Ru2O7 with 0.08

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Measurement Of The Critical Curve Of A Synthetic Antiferromagnet, Cosmin Radu, Dorin Cimpoesu, Alexandru Stancu, Leonard Spinu Jan 2008

Measurement Of The Critical Curve Of A Synthetic Antiferromagnet, Cosmin Radu, Dorin Cimpoesu, Alexandru Stancu, Leonard Spinu

Physics Faculty Publications

In this paper, we propose a method for a synthetic antiferromagnet structure’s critical curve determination. The method is based on reversible susceptibility’s singularities detection, as the magnetic field is swept along easy axis, in both positive and negative direction, while a hard axis bias field is also applied. By performing susceptibility measurements with different values of the bias field, the critical curve can be determined. Knowing the critical curve of a synthetic antiferromagnetic structure is essential for devices such as magnetic random access memories.

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Superconductivity Close To Magnetic Instability In Fe(Se1−Xtex)0.82, M H. Fang, H M. Pham, B Qian, T J. Liu, E K. Vehstedt, Y Liu, L Spinu, Z Q. Mao Jan 2008

Superconductivity Close To Magnetic Instability In Fe(Se1−Xtex)0.82, M H. Fang, H M. Pham, B Qian, T J. Liu, E K. Vehstedt, Y Liu, L Spinu, Z Q. Mao

Physics Faculty Publications

We report our study of the evolution of superconductivity and the phase diagram of the ternary Fe(Se1−xTex)0.82 (0≤x≤1.0) system. We discovered a superconducting phase with Tc,max=14 K in the 0.30.82, which exhibits an incommensurate antiferromagnetic order. We discuss the relationship between the superconductivity and magnetism of this material system in terms of recent results from neutron-scattering measurements. Our results and analyses suggest that superconductivity in this class of Fe-based compounds is associated with magnetic fluctuations and therefore may be unconventional in nature.

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High-Frequency Characterization Of Permalloy Nanosized Strips Using Network Analyzer Ferromagnetic Resonance, Bijoy K. Kuanr, Radek Lopusnik, Leszek M. Malkinski, Matt Wenger, Minghui Yu, Donald Scherer Ii, Z Celinski, R E. Camley Jan 2008

High-Frequency Characterization Of Permalloy Nanosized Strips Using Network Analyzer Ferromagnetic Resonance, Bijoy K. Kuanr, Radek Lopusnik, Leszek M. Malkinski, Matt Wenger, Minghui Yu, Donald Scherer Ii, Z Celinski, R E. Camley

Physics Faculty Publications

We report on the dynamic properties of Permalloy nanostrips at gagahertz frequencies. The thickness of the strips is 100 nm, strip width is 300 nm, strip spacing is 1 μm, and length is 0.3–100 μm; aspect ratios are 1:1, 1:2, 1:3, 1:5, 1:10, and 1:333. The dynamic behavior was studied by network analyzer ferromagnetic resonance (FMR) using Permalloy strips on a coplanar waveguide in flip-chip geometry. The FMR mode frequencies (fr) can be controlled by the aspect ratio as well as by the applied magnetic field (H). In longer strips (1:10 and 1:333), …

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Local Structures Surrounding Zr In Nanostructurally Stabilized Cubic Zirconia: Structural Origin Of Phase Stability, Y. L. Soo, P. J. Chen, S. H. Huang, T. J. Shiu, T Y. Tsai, Y. H. Chow, Y. C. Lin, S. C, Weng, S. L. Chang, G. Wang, Chin Li Cheung, Renat F. Sabirianov, Wai-Ning Mei, Fereydoon Namavar, Hani Haider, Kevin L. Garvin, J. F. Lee, H. Y. Lee, P. P. Chu Jan 2008

Local Structures Surrounding Zr In Nanostructurally Stabilized Cubic Zirconia: Structural Origin Of Phase Stability, Y. L. Soo, P. J. Chen, S. H. Huang, T. J. Shiu, T Y. Tsai, Y. H. Chow, Y. C. Lin, S. C, Weng, S. L. Chang, G. Wang, Chin Li Cheung, Renat F. Sabirianov, Wai-Ning Mei, Fereydoon Namavar, Hani Haider, Kevin L. Garvin, J. F. Lee, H. Y. Lee, P. P. Chu

Physics Faculty Publications

Local environment surrounding Zr atoms in the thin films of nanocrystalline zirconia (ZrO2) has been investigated by using the extended x-ray absorption fine structure (EXAFS) technique. These films prepared by the ion beam assisted deposition exhibit long-range structural order of cubic phase and high hardness at room temperature without chemical stabilizers. The local structure around Zr probed by EXAFS indicates a cubic Zr sublattice with O atoms located on the nearest tetragonal sites with respect to the Zr central atoms, as well as highly disordered locations. Similar Zr local structure was also found in a ZrO2 nanocrystal …

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Dynamic And Temperature Effects In Spin-Transfer Switching, Dorin Cimpoesu, Huy Pham, Leonard Spinu, Alexandru Stancu Jan 2008

Dynamic And Temperature Effects In Spin-Transfer Switching, Dorin Cimpoesu, Huy Pham, Leonard Spinu, Alexandru Stancu

Physics Faculty Publications

We have studied the dynamic switching triggered by spin angular momentum transfer in a pulsed current of a spin-valve-type trilayer structure, and its dependence on thermal effects. In order to determine the current pulse parameters, where fast and stable switching can be achieved, we have studied the magnetization’s dynamics properties as a function of applied current pulse amplitude and shape, waiting time, and initial orientation, and also as a function of the Gilbert damping constant. The magnetic layer is assumed to be single domain, ellipsoid shaped. In this paper also we present the thermal fluctuation effects on the switching behavior. …

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The Temperature Dependence Of Hysteretic Processes In Co Nanowires Arrays, I Astefanoaei, I Dumitru, A Diaconu, L Spinu, A Stancu Jan 2008

The Temperature Dependence Of Hysteretic Processes In Co Nanowires Arrays, I Astefanoaei, I Dumitru, A Diaconu, L Spinu, A Stancu

Physics Faculty Publications

In this paper, the temperature dependence of the hysteretic processes of Co nanowires, squarelly ordered in an array prepared by electrodeposition in nanopores of alumina membranes was analyzed. Both the magnetostatic interactions induced in the nanowires arrays and the thermal stresses (radial, azimuthal and axial stresses), which appear during the cooling of the system (nanowire and alumina template) from room temperature to 3 K was evaluated. The analysis of thermal induced stresses provides useful informations concerning the magnetic anisotropy in the Co nanowires. The temperature dependence of the remanent magnetization and coercitive field as an effect of the induced thermal …

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Switching Behavior Of A Stoner–Wohlfarth Particle Subjected To Spin-Torque Effect, Dorin Cimpoesu, Alexandru Stancu, Leonard Spinu, Huy Pham Jan 2008

Switching Behavior Of A Stoner–Wohlfarth Particle Subjected To Spin-Torque Effect, Dorin Cimpoesu, Alexandru Stancu, Leonard Spinu, Huy Pham

Physics Faculty Publications

Recently, the current-induced spin-transfer torque has been proposed as a convenient writing process in high density magnetic random access memory. A spin-polarized current can switch the magnetization of a ferromagnetic layer more efficiently than a current induced magnetic field. Our paper discusses the switching properties of a Stoner–Wohlfarth magnetic particle for the case when spin torques and external field pulses are simultaneously present. The theoretical investigation of precessional motion is described by using Landau–Lifschitz–Gilbert equation with a spin-transfer torque term included. The main goal is to determine the parameters of field pulse for that the fast and stable switching can …

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Cross Sections And Beam Asymmetries For E ⃗ P → Enπ+ In The Nucleon Resonance Region For 1.7 ⩽ Q2 ⩽ 4.5 Gev2, M. J. Amaryan, H. Bagdasaryan, S. Bültmann, K. V. Dharmawardane, G. E. Dodge, G. Gavalian, N. Guler, C. E. Hyde-Wright, N. Kalantarians, A. Klein, A. V. Klimenko, S. E. Kuhn, J. Lachniet, R. A. Niyazov, F. Sabatié, S. Tkachenko, L. B. Weinstein, J. Zhang, Et Al., The Clas Collaboration Jan 2008

Cross Sections And Beam Asymmetries For E ⃗ P → Enπ+ In The Nucleon Resonance Region For 1.7 ⩽ Q2 ⩽ 4.5 Gev2, M. J. Amaryan, H. Bagdasaryan, S. Bültmann, K. V. Dharmawardane, G. E. Dodge, G. Gavalian, N. Guler, C. E. Hyde-Wright, N. Kalantarians, A. Klein, A. V. Klimenko, S. E. Kuhn, J. Lachniet, R. A. Niyazov, F. Sabatié, S. Tkachenko, L. B. Weinstein, J. Zhang, Et Al., The Clas Collaboration

Physics Faculty Publications

The exclusive electroproduction process e ⃗ p → e'nπ+ was measured in the range of the photon virtuality Q2 =1.7-4.5 GeV2, and the invariant mass range for the n π+ system of W=1.15-1.7 GeV using the CEBAF Large Acceptance Spectrometer. For the first time, these kinematics are probed in exclusive π+ production from protons with nearly full coverage in the azimuthal and polar angles of the nπ+ center-of-mass system. The nπ+ channel has particular sensitivity to the isospin 1/2 excited nucleon states, and together with the pπ0 final state will serve …

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G Factor Of The 2+1 State Of 170Hf, A. Wolf, Z. Berant, A. Heinz, V. Werner, E. A. Mccutchan, G. Gurdal, R. Cakirli, Y. Oktem, J. Ai, L. Amon, C. W. Beausang, D. S. Brenner, R. F. Casten, R. J. Casperson, K. Dusling, C. R. Fitzpatrick, A. B. Gransworthy, N. Pietralla, J. Qian, P. H. Regan, N. J. Thompson, E. Williams, R. Winkler Oct 2007

G Factor Of The 2+1 State Of 170Hf, A. Wolf, Z. Berant, A. Heinz, V. Werner, E. A. Mccutchan, G. Gurdal, R. Cakirli, Y. Oktem, J. Ai, L. Amon, C. W. Beausang, D. S. Brenner, R. F. Casten, R. J. Casperson, K. Dusling, C. R. Fitzpatrick, A. B. Gransworthy, N. Pietralla, J. Qian, P. H. Regan, N. J. Thompson, E. Williams, R. Winkler

Physics Faculty Publications

The g factor of the 2+1 state of 170Hf was measured by perturbed γ-γ angular correlation in a static external magnetic field. The result, g(2+1) = 0.28(5), extends the systematics of g factors of even-even Hf isotopes to N = 98 and enables a better test of theoretical models. The g(2+1) experimental values of these isotopes exhibit a remarkable constancy as a function of neutron number. This phenomenon, which was also observed for other isotopic chains in the Gd–W range, is explained in terms of a recently proposed empirical …

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High-Spin States In 191, 193Au And 192Pt: Evidence For Oblate Deformation And Triaxial Shapes, Y. Oktem, D. L. Balabanski, B. Akkus, C. W. Beausang, M. Bostan, R. Cakirli, R. F. Casten, M. Danchev, M. Djongolov, M. N. Erduran, S. Erturk, K. A. Gladniski, G. Gurdal, J. Tm. Goon, D. J. Hartley, A. A. Hecht, R. Krucken, N. Nikolov, J. R. Novak, G. Rainovski, L. L. Riedinger, I. Yigitoglu, N. V. Zamfir, O. Zeidan Oct 2007

High-Spin States In 191, 193Au And 192Pt: Evidence For Oblate Deformation And Triaxial Shapes, Y. Oktem, D. L. Balabanski, B. Akkus, C. W. Beausang, M. Bostan, R. Cakirli, R. F. Casten, M. Danchev, M. Djongolov, M. N. Erduran, S. Erturk, K. A. Gladniski, G. Gurdal, J. Tm. Goon, D. J. Hartley, A. A. Hecht, R. Krucken, N. Nikolov, J. R. Novak, G. Rainovski, L. L. Riedinger, I. Yigitoglu, N. V. Zamfir, O. Zeidan

Physics Faculty Publications

High-spin states of 191, 193Au and 192Pt have been populated in the 186W(11B, xn) and 186W(11B, p4n) reactions, respectively, at a beam energy of 68 MeV and their γ decay was studied using the YRAST Ball detector array at the Wright Nuclear Structure Laboratory at Yale University. The level scheme of 193Au has been extended up to Iπ = 55/2+. New transitions were observed also in 191Au and 192Pt. Particle-plus-Triaxial-Rotor (PTR) and Total Routhian Surface (TRS) calculations were performed to determine the equilibrium deformations of the …

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Passive All-Optical Diode Using Asymmetric Nonlinear Absorption, Reji Philip, M. Anij, Chandra S. Yelleswarapu, D.V.G.L.N. Rao Oct 2007

Passive All-Optical Diode Using Asymmetric Nonlinear Absorption, Reji Philip, M. Anij, Chandra S. Yelleswarapu, D.V.G.L.N. Rao

Physics Faculty Publications

Saturable and reverse saturable absorptions are well-known phenomena, originating from the imaginary component of the third order nonlinear optical susceptibility. We note that structures with an axially asymmetric nonlinear absorption can be easily realized from saturable and reverse saturable absorption materials arranged in tandem. In this paper, the basic transmission behavior of such a structure is worked out. Detailed numerical simulations demonstrate passive all-optical diode behavior, and the results are verified experimentally. The principle will work for all light polarizations, has no phase-matching restrictions, and can be extended to a large number of available nonlinear media for possible applications.

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Btec Thermal Model, Lance J. Irving, P.D.S. Maseberg, Gavin D. Buffington, Clifton D. Clark, Robert J. Thomas, Michael L. Edwards, Jacob Stolarski Oct 2007

Btec Thermal Model, Lance J. Irving, P.D.S. Maseberg, Gavin D. Buffington, Clifton D. Clark, Robert J. Thomas, Michael L. Edwards, Jacob Stolarski

Physics Faculty Publications

AFRL/RHDO has developed a configurable, laser-tissue interaction model that includes components from various areas of Biophysics. The model predicts heat transfer in biological tissue, in either one-dimension or two-dimensional cylindrical coordinates, and is coupled to an Arrhenius damage model. A simulation can be configured as a single run, or a damage-threshold search. Multiple models for describing the laser-tissue interaction are available, including linear absorption (1D, 2D), Monte Carlo scattering (2D) and Beam Propagation Methods using Finite Difference approximations or Hankel Transform methods (2D).

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Introduction And Recovery Of Ga And N Sublattice Defects In Electron-Irradiated Gan, F. Tuomisto, V. Ranki, David C. Look, Gary C. Farlow Oct 2007

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 …

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Effect Of Tip Resonances On Tunnelling Anisotropic Magnetoresistance In Ferromagnetic Break Junctions: A First-Principles Study, J. D. Burton, Renat F. Sabirianov, Julian P. Velev, Oleg N. Mryasov, Evgeny Y. Tsymbal Oct 2007

Effect Of Tip Resonances On Tunnelling Anisotropic Magnetoresistance In Ferromagnetic Break Junctions: A First-Principles Study, J. D. Burton, Renat F. Sabirianov, Julian P. Velev, Oleg N. Mryasov, Evgeny Y. Tsymbal

Physics Faculty Publications

First-principles calculations of electron tunneling transport in nanoscale Ni and Co break-junctions reveal strong dependence of the conductance on the magnetization direction, an effect known as tunneling anisotropic magnetoresistance TAMR. An important aspect of this phenomenon stems from resonant states localized in the electrodes near the junction break. The energy and broadening of these states is strongly affected by the magnetization orientation due to spin-orbit coupling, causing TAMR to be sensitive to bias voltage on a scale of a few millivolts. Our results bear a resemblance to recent experimental data and suggest that TAMR driven by resonant states is a …

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Constraining F(R) Gravity As A Scalar-Tensor Theory, Thomas Faulkner, Max Tegmark, Emory F. Bunn, Yi Mao Sep 2007

Constraining F(R) Gravity As A Scalar-Tensor Theory, Thomas Faulkner, Max Tegmark, Emory F. Bunn, Yi Mao

Physics Faculty Publications

We search for viable f(R) theories of gravity, making use of the equivalence between such theories and scalar-tensor gravity. We find that models can be made consistent with solar system constraints either by giving the scalar a high mass or by exploiting the so-called chameleon effect. However, in both cases, it appears likely that any late-time cosmic acceleration will be observationally indistinguishable from acceleration caused by a cosmological constant. We also explore further observational constraints from, e.g., big bang nucleosynthesis and inflation.

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Gigahertz Optical Spin Transceiver, Patrick Irvin, Petru S. Fodor, Jeremy Levy Sep 2007

Gigahertz Optical Spin Transceiver, Patrick Irvin, Petru S. Fodor, Jeremy Levy

Physics Faculty Publications

We present a time-resolved optical technique to measure electron spin dynamics with GHz dynamical bandwidth, transform-limited spectral selectivity, and phase-sensitive (lock-in) detection. Use of a continuous-wave (CW) laser and fast optical bridge enables greatly improved signal-to-noise characteristics compared to traditional optical sampling (pump-probe) techniques. We demonstrate the technique with a measurement of GHz-spin precession in n-GaAs. This approach may be applicable to other physical systems where stroboscopic techniques cannot be used because of either noise or spectral limitations.

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Near-Terminator Venus Ionosphere: Evidence For A Dawn/Dusk Asymmetry In The Thermosphere, Jane L. Fox, W. T. Kasprzak Sep 2007

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 …

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Near-Terminator Venus Ionosphere: How Chapman-Esque?, Jane L. Fox Sep 2007

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 …

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Thermal Stability Of Nanostructurally Stabilized Zirconium Oxide, Fereydoon Namavar, Gonghua Wang, Chin Li Cheung, Xiao Cheng Zeng, Renat F. Sabirianov, Wai-Ning Mei, Jaeil Bai, Joseph R. Brewer, Hani Haider, Kevin L. Garvin Sep 2007

Thermal Stability Of Nanostructurally Stabilized Zirconium Oxide, Fereydoon Namavar, Gonghua Wang, Chin Li Cheung, Xiao Cheng Zeng, Renat F. Sabirianov, Wai-Ning Mei, Jaeil Bai, Joseph R. Brewer, Hani Haider, Kevin L. Garvin

Physics Faculty Publications

Nanostructurally stabilized zirconium oxide (NSZ) hard transparent films were produced without chemical stabilizers by the ion beam assisted deposition technique (IBAD). A transmission electron microscopy study of the samples produced below 150 °C revealed that these films are composed of zirconium oxide (ZrO2) nanocrystallites of diameters 7.5 ± 2.3 nm. X-ray and selected-area electron diffraction studies suggested that the as-deposited films are consistent with cubic phase ZrO2. Rutherford backscattering spectroscopy (RBS) indicated the formation of stoichiometric ZrO2. The phase identity of these optically transparent NSZ films was in agreement with cubic ZrO2, …

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Observation Of Type-I And Type-Ii Excitons In Strained Si/Sige Quantum-Well Structures, K. Y. Wang, W. P. Huang, H. H. Cheng, Greg Sun, R. A. Soref, R. J. Nicholas, Y. W. Suen Aug 2007

Observation Of Type-I And Type-Ii Excitons In Strained Si/Sige Quantum-Well Structures, K. Y. Wang, W. P. Huang, H. H. Cheng, Greg Sun, R. A. Soref, R. J. Nicholas, Y. W. Suen

Physics Faculty Publications

The authors report photoluminescence (PL) measurement on a series of Si/SiGequantum-well structures that had different internal strain distributions. When each sample was placed in a high magnetic field, the field-dependent energy shift of the relevant PL peaks revealed either type-I or type-II exciton formation depending on the strain distribution. This observation is in agreement with theoretical modeling. The present investigation shows that type-I band alignment—desired for electroluminescent devices—can be achieved by strain engineering.

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Force-Response Considerations In Ciliary Mechanosensation, Andrew Resnick, Ulrich Hopfer Aug 2007

Force-Response Considerations In Ciliary Mechanosensation, Andrew Resnick, Ulrich Hopfer

Physics Faculty Publications

Considerable experimental evidence indicates that the primary, nonmotile cilium is a mechanosensory organelle in several epithelial cell types. As the relationship between cellular responses and nature and magnitude of applied forces is not well understood, we have investigated the effects of exposure of monolayers of renal collecting duct chief cells to orbital shaking and quantified the forces incident on cilia. An exposure of 24 h of these cells to orbital shaking resulted in a decrease of amiloride-sensitive sodium current by ∼60% and ciliary length by ∼30%. The sensitivity of the sodium current to shaking was dependent on intact cilia. The …

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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 Aug 2007

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.

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Absolute And Relative Surrogate Measurements Of The 236U(N,F) Cross Section As A Probe Of Angular Momentum Effects, B. F. Lyles, L. A. Bernstein, J. T. Burke, F. S. Dietrich, J. Escher, I. Thompson, D. L. Bleuel, R. M. Clark, P. Fallon, J. Gibelin, A. O. Macchiavelli, M. A. Mcmahan, L. Phair, E. Rodriguez-Vieitez, M. Wiedeking, C. W. Beausang, S. R. Lesher, B. Darakchieva, M. Evtimova Jul 2007

Absolute And Relative Surrogate Measurements Of The 236U(N,F) Cross Section As A Probe Of Angular Momentum Effects, B. F. Lyles, L. A. Bernstein, J. T. Burke, F. S. Dietrich, J. Escher, I. Thompson, D. L. Bleuel, R. M. Clark, P. Fallon, J. Gibelin, A. O. Macchiavelli, M. A. Mcmahan, L. Phair, E. Rodriguez-Vieitez, M. Wiedeking, C. W. Beausang, S. R. Lesher, B. Darakchieva, M. Evtimova

Physics Faculty Publications

Using both the absolute and relative surrogate techniques, the 236U(n,f) cross section was deduced over an equivalent neutron energy range of 0 to 20 MeV. A 42 MeV 3He beam from the 88 Inch Cyclotron at Lawrence Berkeley National Laboratory was used to perform a (3He,α) pickup reaction on targets of 235U (Jπ=7/2−) and 238U (Jπ = 0+) and the fission decay probabilities were determined. The 235U(3He,αf) and 238U(3He,αf) were surrogates for 233 …

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Directionality In The Wilkinson Microwave Anisotropy Probe Polarization Data, D. Hanson, Douglas Scott, Emory F. Bunn Jul 2007

Directionality In The Wilkinson Microwave Anisotropy Probe Polarization Data, D. Hanson, Douglas Scott, Emory F. Bunn

Physics Faculty Publications

Polarization is the next frontier of cosmic microwave background analysis, but its signal is dominated over much of the sky by foregrounds which must be carefully removed. To determine the efficacy of this cleaning, it is necessary to have sensitive tests for residual foreground contamination in polarization sky maps. The dominant Galactic foregrounds introduce a large-scale anisotropy on to the sky, so it makes sense to use a statistic sensitive to overall directionality for this purpose. Here, we adapt the rapidly computable D statistic of Bunn and Scott to polarization data, and demonstrate its utility as a foreground monitor by …

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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 Jul 2007

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 …

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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 Jul 2007

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 …

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Strain-Free Ge/Gesisn Quantum Cascade Lasers Based On L-Valley Intersubband Transitions, Greg Sun, H. H. Cheng, J. Menéndez, Jacob B. Khurgin, R. A. Soref Jun 2007

Strain-Free Ge/Gesisn Quantum Cascade Lasers Based On L-Valley Intersubband Transitions, Greg Sun, H. H. Cheng, J. Menéndez, Jacob B. Khurgin, R. A. Soref

Physics Faculty Publications

The authors propose a Ge/Ge0.76Si0.19Sn0.05 quantum cascade laser using intersubband transitions at L valleys of the conduction band which has a “clean” offset of150 meV situated below other energy valleys (Γ,X). The entire structure is strain-free because the lattice-matched Ge and Ge0.76Si0.19Sn0.05 layers are to be grown on a relaxed Ge buffer layer on a Si substrate. Longer lifetimes due to the weaker scattering of nonpolar optical phonons reduce the threshold current and potentially lead to room temperature operation.

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Urban Spatial Pattern As Self-Organizing System: An Empirical Evaluation Of Firm Location Decisions In Cleveland–Akron Pmsa, Ohio, Mukesh Kumar, William M. Bowen, Miron Kaufman Jun 2007

Urban Spatial Pattern As Self-Organizing System: An Empirical Evaluation Of Firm Location Decisions In Cleveland–Akron Pmsa, Ohio, Mukesh Kumar, William M. Bowen, Miron Kaufman

Physics Faculty Publications

Economic models of urban spatial patterns have largely ignored complexity as an attribute of urban systems. Complexity theorists on the other hand have not made sufficiently serious and sustained attempts to verify empirically the relevance of complex systems models for urban spatial patterns. This research bridges this gap by simulating the evolution of an urban employment pattern as a self-organizing complex system and seeking its empirical validation. It estimates the model’s parameters by using firm data aggregated to the level of municipalities in Cleveland-Akron Consolidated Metropolitan Statistical Area in Ohio. The interaction among four parameters, forces of attraction and dispersion …

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