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Physics Faculty Publications

2007

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Articles 1 - 30 of 56

Full-Text Articles in Physical Sciences and Mathematics

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, Jack Maseberg, Gavin D. Buffington, Clifton D. Clark, Robert J. Thomas, Michael L. Edwards, Jacob Stolarski Oct 2007

Btec Thermal Model, Lance J. Irving, Jack 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: 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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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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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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Local Effective Potential Theory: Nonuniqueness Of Potential And Wave Function, Viraht Sahni, Marlina Slamet, Xiao-Yin Pan May 2007

Local Effective Potential Theory: Nonuniqueness Of Potential And Wave Function, Viraht Sahni, Marlina Slamet, Xiao-Yin Pan

Physics Faculty Publications

In local effective potential energy theories such as the Hohenberg-Kohn-Sham density functional theory (HKS-DFT) and quantal density functional theory (Q-DFT) electronic systems in their ground or excited states are mapped to model systems of noninteracting fermions with equivalent density. From these models, the equivalent total energy and ionization potential are also obtained. This paper concerns the nonuniqueness of the local effective potential energy function of the model system in the mapping from a nondegenerate ground state, the nonuniqueness of the local effective potential energy function in the mapping from a nondegenerate excited state, and in the mapping to a model …

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Systematic Errors In Cosmic Microwave Background Interferometry, Emory F. Bunn Apr 2007

Systematic Errors In Cosmic Microwave Background Interferometry, Emory F. Bunn

Physics Faculty Publications

Cosmic microwave background (CMB) polarization observations will require superb control of systematic errors in order to achieve their full scientific potential, particularly in the case of attempts to detect the B modes that may provide a window on inflation. Interferometry may be a promising way to achieve these goals. This paper presents a formalism for characterizing the effects of a variety of systematic errors on interferometric CMB polarization observations, with particular emphasis on estimates of the B-mode power spectrum. The most severe errors are those that couple the temperature anisotropy signal to polarization; such errors include cross talk within …

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Electron Irradiation Induced Deep Centers In Hydrothermally Grown Zno, Z-Q. Fang, B. Claflin, David C. Look, Gary C. Farlow Apr 2007

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 …

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Spin Dependence Of K Mixing, Strong Configuration Mixing, And Electromagnetic Properties Of 178Hf, A. B. Hayes, D. Cline, C. Y. Wu, H. Ai, H. Amro, C. W. Beausang, R. F. Casten, J. Gerl, A. A. Hecht, A. Heinz, H. Hua, R. O. Hughes, R.V. F. Janssens, C. J. Lister, A. O. Macchiavelli, D. A. Meyer, E. F. Moore, P. Napiorkowski, R. C. Pardo, Ch. Schlegel, D. Seweryniak, M. W. Simon, J. Srebrny, R. Teng, K. Vetter, H. J. Wollersheim Mar 2007

Spin Dependence Of K Mixing, Strong Configuration Mixing, And Electromagnetic Properties Of 178Hf, A. B. Hayes, D. Cline, C. Y. Wu, H. Ai, H. Amro, C. W. Beausang, R. F. Casten, J. Gerl, A. A. Hecht, A. Heinz, H. Hua, R. O. Hughes, R.V. F. Janssens, C. J. Lister, A. O. Macchiavelli, D. A. Meyer, E. F. Moore, P. Napiorkowski, R. C. Pardo, Ch. Schlegel, D. Seweryniak, M. W. Simon, J. Srebrny, R. Teng, K. Vetter, H. J. Wollersheim

Physics Faculty Publications

The combined data of two Coulomb excitation experiments has verified the purely electromagnetic population of the Kπ = 4+, 6+, 8−, and 16+rotational bands in 178Hf via 2≤ν ≤14 K-forbidden transitions, quantifying the breakdown of the K-selection rule with increasing spin in the low-K bands. The γ -, 4+, and 6+bands were extended, and four new states in a rotational band were tentatively assigned to a previously known Kπ = 0+band. The quasiparticle structure of the 6+( …

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Practicable Enhancement Of Spontaneous Emission Using Surface Plasmons, Greg Sun, Jacob B. Khurgin, Richard A. Soref Mar 2007

Practicable Enhancement Of Spontaneous Emission Using Surface Plasmons, Greg Sun, Jacob B. Khurgin, Richard A. Soref

Physics Faculty Publications

The authors develop a rigorous theory of the enhancement of spontaneous emission from a light emitting device via coupling the radiant energy in and out of surface plasmon polaritons (SPPs) on the metal-dielectric interface. Using the GaN/Ag system as an example, the authors show that using SPP pays off only for emitters that have a low luminescence efficiency.

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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 Mar 2007

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 …

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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 Mar 2007

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.

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Correlation Effects And Electronic Structure Of Gd@C60, Renat F. Sabirianov, Wai-Ning Mei, Jing Lu, Yi Gao, Xiao Cheng Zeng, Robert D. Bolskar, P. Jeppson, Ning Wu, A. N. Caruso, Peter Dowben Feb 2007

Correlation Effects And Electronic Structure Of Gd@C60, Renat F. Sabirianov, Wai-Ning Mei, Jing Lu, Yi Gao, Xiao Cheng Zeng, Robert D. Bolskar, P. Jeppson, Ning Wu, A. N. Caruso, Peter Dowben

Physics Faculty Publications

We have investigated the electronic structure of Gd@C60 using ab initio calculations, photoemission and resonant photoemission (constant initial state spectroscopy). In comparing our calculations based on the local spin density approximation and the Hubbard model description with the observed photoemission spectra, we conclude that Gd 4f states exhibit enhanced correlation energies. These correlation energies have values larger than those normally observed in metallic gadolinium and gadolinium compounds. We attributed the enhanced correlation to the diminished screening of the encapsulated Gd. Both calculation and experiment confi rm a strong hybridization between the valence states of Gd and the C 2p states …

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Mosaicking With Cosmic Microwave Background Interferometers, Emory F. Bunn, Martin White Jan 2007

Mosaicking With Cosmic Microwave Background Interferometers, Emory F. Bunn, Martin White

Physics Faculty Publications

Measurements of cosmic microwave background (CMB) anisotropies by interferometers offer several advantages over single-dish observations. The formalism for analyzing interferometer CMB data is well developed in the flat-sky approximation, which is valid for small fields of view. As the area of sky is increased to obtain finer spectral resolution, this approximation needs to be relaxed. We extend the formalism for CMB interferometry, including both temperature and polarization, to mosaics of observations covering arbitrarily large areas of the sky, with each individual pointing lying within the flat-sky approximation. We present a method for computing the correlation between visibilities with arbitrary pointing …

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Isospin Purity Of T=1 States In The A=38 Nuclei Studied Via Lifetime Measurements In K38, F. M. Prados Estevez, A. M. Bruce, M. J. Taylor, H. Amro, C. W. Beausang, R. F. Casten, J. J. Ressler, C. J. Barton, C. Chandler, G. Hammond Jan 2007

Isospin Purity Of T=1 States In The A=38 Nuclei Studied Via Lifetime Measurements In K38, F. M. Prados Estevez, A. M. Bruce, M. J. Taylor, H. Amro, C. W. Beausang, R. F. Casten, J. J. Ressler, C. J. Barton, C. Chandler, G. Hammond

Physics Faculty Publications

The Doppler Shift Attenuation Method was used to measure lifetimes for levels in 38K at excitation energies of 1698, 2404, 2830, 2996, and 3671 keV, populated using the 40Ca(d, α) 38K reaction at a beam energy of 4.5 MeV. Values of 109(29), 95(22), 457(63), 130(40), and 160(50) fs, respectively, were measured and are compared with previous values obtained using different stopping powers. The matrix element for the transition between the Jπ = 2+ T=1 and 0+ T=1 states in this Tz = 0 nucleus is compared with the analogous transition in the other nuclei in the T = 1 triplet, …

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