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Physics Faculty Publications

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Articles 1711 - 1740 of 2178

Full-Text Articles in Physical Sciences and Mathematics

Characterization Of Homoepitaxial P-Type Zno Grown By Molecular Beam Epitaxy, David C. Look, D. C. Reynolds, C. W. Litton, R. L. Jones, D. B. Eason, G. Cantwell Sep 2002

Characterization Of Homoepitaxial P-Type Zno Grown By Molecular Beam Epitaxy, David C. Look, D. C. Reynolds, C. W. Litton, R. L. Jones, D. B. Eason, G. Cantwell

Physics Faculty Publications

An N-doped, p-type ZnO layer has been grown by molecular beam epitaxy on an Li-diffused, bulk, semi-insulating ZnO substrate. Hall-effect and conductivity measurements on the layer give: resistivity = 4×101 Ω cm; hole mobility = 2 cm2/V s; and hole concentration = 9×1016 cm−3. Photoluminescence measurements in this N-doped layer show a much stronger peak near 3.32 eV (probably due to neutral acceptor bound excitons), than at 3.36 eV (neutral donor bound excitons), whereas the opposite is true in undoped ZnO. Calibrated, secondary-ion mass spectroscopy measurements show an N surface concentration of about …

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Representation Of A Quantum Ensemble As A Minimal Set Of Pure States, Thomas E. Skinner, Steffen J. Glaser Sep 2002

Representation Of A Quantum Ensemble As A Minimal Set Of Pure States, Thomas E. Skinner, Steffen J. Glaser

Physics Faculty Publications

The density matrix ρ for an n-level system is decomposed into the minimum number of pure states necessary to calculate physical observables. The corresponding physical system is first represented by a set B of n pure states |βi〉, together with their statistical weights. The time evolution of the system is therefore calculated as B(t)=UB(t0), with the propagator U operating on each member of the set, in contrast to the more laborious ρ(t)=Uρ(t0)U†. At least one of the states can be eliminated from the set by reducing its weight to zero via a …

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Investigation Of The Magnetic Properties In Strontium–Borate Vanadate Glasses, Manford Chinkhota, Petru S. Fodor, G. D. Khattak, Lowell E. Wenger May 2002

Investigation Of The Magnetic Properties In Strontium–Borate Vanadate Glasses, Manford Chinkhota, Petru S. Fodor, G. D. Khattak, Lowell E. Wenger

Physics Faculty Publications

To further elucidate the nature of the valence state of V ions in vanadate glasses,magnetic susceptibility measurements in the temperature range of 5 to 300 K have been performed on a series of vanadium–strontium–borate (V2O5+SrO+B2O3) oxide glasses with V2O5 concentrations greater than 50 mol %. The magnetic susceptibility for these oxide glasses is found to consist of a temperature-independentparamagnetic contribution arising from V2O5 and a Curie–Weiss temperature-dependent contribution associated with magnetic V4+ ions being present in concentrations between 2% and 10% of the total V concentration. The negative Curie–Weiss temperatures in the range of 0 to −2.8 K indicate a …

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Fabrication And Characterization Of Co1−Xfex Alloy Nanowires, Petru S. Fodor, Georgy M. Tsoi, Lowell E. Wenger May 2002

Fabrication And Characterization Of Co1−Xfex Alloy Nanowires, Petru S. Fodor, Georgy M. Tsoi, Lowell E. Wenger

Physics Faculty Publications

Co1−xFex alloy nanowires with 40 nm diam and x=0–1.0 were fabricated by electrodeposition in nanopores of alumina templates. The crystalline structure of the nanowires is concentration dependent and shows a transition from the cobalt hexagonal-closed-packed structure (hcp) to a face-centered-cubic structure (fcc) in the concentration range 0

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Residential Radon Exposure And Lung Cancer: Variation In Risk Estimates Using Alternative Exposure Scenarios, R. William Field, Brian J. Smith, Daniel J. Steck, Charles F. Lynch May 2002

Residential Radon Exposure And Lung Cancer: Variation In Risk Estimates Using Alternative Exposure Scenarios, R. William Field, Brian J. Smith, Daniel J. Steck, Charles F. Lynch

Physics Faculty Publications

The most direct way to derive risk estimates for residential radon progeny exposure is through epidemiologic studies that examine the association between residential radon exposure and lung cancer. However, the National Research Council concluded that the inconsistency among prior residential radon case-control studies was largely a consequence of errors in radon dosimetry. This paper examines the impact of applying various epidemiologic dosimetry models for radon exposure assessment using a common data set from the Iowa Radon Lung Cancer Study (IRLCS). The IRLCS uniquely combined enhanced dosimetric techniques, individual mobility assessment, and expert histologic review to examine the relationship between cumulative …

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Deep Hole Traps In N-Gan Films Grown By Hydride Vapor Phase Epitaxy, A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, Z-Q. Fang, David C. Look, Richard J. Molnar, A. V. Osinsky May 2002

Deep Hole Traps In N-Gan Films Grown By Hydride Vapor Phase Epitaxy, A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, Z-Q. Fang, David C. Look, Richard J. Molnar, A. V. Osinsky

Physics Faculty Publications

Concentrations of deep hole traps were measured in a set of hydride vapor phase epitaxy grown samples with thicknesses varying from 2.6 to 68 μm. Results were obtained from low temperature capacitance–voltage measurements before and after illumination and from deep level transient spectroscopy measurements with optical injection (ODLTS). The former revealed the presence of high densities (∼1015 to 1016 cm−3) of hole traps whose concentration decreased with sample thickness in a manner similar to that found for the dislocation density. Capacitance versus temperature measurements in the dark and after illumination suggested that these traps form a …

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Depth-Dependent Investigation Of Defects And Impurity Doping In Gan/Sapphire Using Scanning Electron Microscopy And Cathodoluminescence Spectroscopy, X. L. Sun, S. H. Goss, L. J. Brillson, David C. Look, Richard J. Molnar May 2002

Depth-Dependent Investigation Of Defects And Impurity Doping In Gan/Sapphire Using Scanning Electron Microscopy And Cathodoluminescence Spectroscopy, X. L. Sun, S. H. Goss, L. J. Brillson, David C. Look, Richard J. Molnar

Physics Faculty Publications

Cathodoluminescence (CL) imaging and temperature-dependent cathodoluminescence spectroscopy (CLS) have been used to probe the spatial distribution and energies of electronic defects near GaN/Al2O3 interfaces grown by hydride vapor phase epitaxy (HVPE). Cross sectional secondary electron microscopy imaging, CLS, and CL imaging show systematic variations in defect emissions with a wide range of HVPE GaN/sapphire electronic properties. These data, along with electrochemical capacitance–voltage profiling and secondary ion mass spectrometry provide a consistent picture of near-interface doping by O out-diffusion from Al2O3 into GaN over hundreds of nanometers. Low-temperature CL spectra exhibit a new donor level …

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Correlated Alternative Side Chain Conformations In The Rna-Recognition Motif Of Heterogeneous Nuclear Ribonucleoprotein A1, Jacqueline Vitali, Jianzhong Ding, Jianzhong Jiang, Ying Zhang, Adrian R. Krainer, Rui-Ming Xu Apr 2002

Correlated Alternative Side Chain Conformations In The Rna-Recognition Motif Of Heterogeneous Nuclear Ribonucleoprotein A1, Jacqueline Vitali, Jianzhong Ding, Jianzhong Jiang, Ying Zhang, Adrian R. Krainer, Rui-Ming Xu

Physics Faculty Publications

The RNA-recognition motif (RRM) is a common and evolutionarily conserved RNA-binding module. Crystallographic and solution structural studies have shown that RRMs adopt a compact α/β structure, in which four antiparallel β-strands form the major RNA—binding surface. Conserved aromatic residues in the RRM are located on the surface of the β-sheet and are important for RNA binding. To further our understanding of the structural basis of RRM—nucleic acid interaction, we carried out a high resolution analysis of UP1, the N-terminal, two-RRM domain of heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1), whose structure was previously solved at 1.75–1.9 Å …

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Controlling Nucleation And Growth Of Nanodroplets In Supersonic Nozzles, Kiril A. Streletzky, Yury Zvinevich, Barbara E. Wyslouzil, Reinhard Strey Mar 2002

Controlling Nucleation And Growth Of Nanodroplets In Supersonic Nozzles, Kiril A. Streletzky, Yury Zvinevich, Barbara E. Wyslouzil, Reinhard Strey

Physics Faculty Publications

We present the first results for a new supersonic nozzle that decouples nucleation and droplet growth, and closely controls the supersaturation and temperature during nucleation. We characterize the expansions using pressure trace measurements, and the aerosol properties using light scattering and small angle neutron scattering. We show that when nucleation and droplet growth are separated, the aerosol number density decreases, the average particle size increases, and the aerosol can be more monodisperse than that formed in a conventional nozzle. Under these conditions, we can estimate the nucleation rate J as a function of supersaturation S and temperature T directly from …

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Polymorphous Transformations In Alkaline-Earth Silicates, Jianjun Liu, Chun-Gang Duan, Wai-Ning Mei, Robert W. Smith, John R. Hardy Mar 2002

Polymorphous Transformations In Alkaline-Earth Silicates, Jianjun Liu, Chun-Gang Duan, Wai-Ning Mei, Robert W. Smith, John R. Hardy

Physics Faculty Publications

Structural phase transitions in Ca2SiO4 and Sr2SiO4 are investigated by molecular dynamics simulations. The simulations are based on the potentials calculated from the Gordon–Kim modified electron gas formalism extended to molecular ions. We successfully reproduced the transition γ -α’H and β-α’L - α’H - α in Ca2SiO4, and the transition β-α’ in Sr2SiO4. We find that the α’L phase of Ca2SiO4 is an ax3b x c superstructure of the α’H phase, while the α’H phase …

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Production Of Nitrogen Acceptors In Zno By Thermal Annealing, N. Y. Garces, N. C. Giles, L. E. Halliburton, G. Cantwell, D. B. Eason, D. C. Reynolds, David C. Look Feb 2002

Production Of Nitrogen Acceptors In Zno By Thermal Annealing, N. Y. Garces, N. C. Giles, L. E. Halliburton, G. Cantwell, D. B. Eason, D. C. Reynolds, David C. Look

Physics Faculty Publications

Nitrogen acceptors are formed when undoped single crystals of zinc oxide (ZnO) grown by the chemical-vapor transport method are annealed in air or nitrogen atmosphere at temperatures between 600 and 900 °C. After an anneal, an induced near-edge absorption band causes the crystals to appear yellow. Also, the concentration of neutral shallow donors, as monitored by electron paramagnetic resonance (EPR), is significantly reduced. A photoinduced EPR signal due to neutral nitrogen acceptors is observed when the annealed crystals are exposed to laser light (e.g., 364, 442, 458, or 514 nm) at low temperature. The nitrogens are initially in the nonparamagnetic …

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Electrical Characterization Of Vapor-Phase-Grown Single-Crystal Zno, F. D. Auret, S. A. Goodman, M. J. Legodi, W. E. Meyer, David C. Look Feb 2002

Electrical Characterization Of Vapor-Phase-Grown Single-Crystal Zno, F. D. Auret, S. A. Goodman, M. J. Legodi, W. E. Meyer, David C. Look

Physics Faculty Publications

Gold Schottky-barrier diodes (SBDs) were fabricated on vapor-phase-grown single-crystal ZnO. Deep-level transient spectroscopy, using these SBDs, revealed the presence of four electron traps, the major two having levels at 0.12 eV and 0.57 below the conduction band. Comparison with temperature-dependent Hall measurements suggests that the 0.12 eV level has a temperature activated capture cross section with a capture barrier of about 0.06 eV and that it may significantly contribute to the free-carrier density. Based on the concentrations of defects other than this shallow donor, we conclude that the quality of the vapor-phase-grown ZnO studied here supercedes that of other single-crystal …

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A Rf Discharge Cell For Saturated Absorption Spectroscopy Of Metastable Argon, C. I. Sukenik, H. C. Busch Feb 2002

A Rf Discharge Cell For Saturated Absorption Spectroscopy Of Metastable Argon, C. I. Sukenik, H. C. Busch

Physics Faculty Publications

We have produced a rf discharge in 40Ar and used saturated absorption spectroscopy to offset lock a Ti:Sapphire laser to the absorption peak of the 43P243D3 cooling transition at 811 nm. We describe the procedure for fabrication of the cell and production of the discharge.

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Small-Angle Neutron Scattering Of Soot Formed In Laminar Premixed Ethylene Flames, Hai Wang, Bin Zhao, Barbara E. Wyslouzil, Kiril A. Streletzky Jan 2002

Small-Angle Neutron Scattering Of Soot Formed In Laminar Premixed Ethylene Flames, Hai Wang, Bin Zhao, Barbara E. Wyslouzil, Kiril A. Streletzky

Physics Faculty Publications

We used small-angle neutron scattering (SANS) to measure soot development in one-dimensional, laminarpremixed flames. Scattering spectra were collected for two sooting ethylene/oxygen/argon flames at six positions above the burner surface. A detailed analysis of the scattering signals yielded the basic properties of the soot size distributions as a function of position. The experiments demonstrate that SANS can be used to extract spatially resolved, quantitative information about incipient soot formation and growth with better particle size resolution than light scattering and extinction.

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Thermal Hysteresis In The Charge-Density-Wave Transition Of Lu5rh4si10, C. S. Lue, Y. K. Kuo, F. H. Hsu, H. H. Li, H. D. Yang, Petru S. Fodor, Lowell E. Wenger Jan 2002

Thermal Hysteresis In The Charge-Density-Wave Transition Of Lu5rh4si10, C. S. Lue, Y. K. Kuo, F. H. Hsu, H. H. Li, H. D. Yang, Petru S. Fodor, Lowell E. Wenger

Physics Faculty Publications

We report the detailed studies of resistivity, magnetic susceptibility, heat capacity, thermal conductivity, and thermoelectric power on the charge-density-wave (CDW) material Lu5Rh4Si10 in the vicinity of its transition temperature T0 ∼ 147 K. Pronounced thermal hystereses loops between heating and cooling cycles have been observed in all measured quantities, making this system very unique as compared to other isostructural compounds such as Lu5Ir4Si10. The thermal hysteresis features in Lu5Rh4Si10 are attributed to the presence of metastable states arising from pinning of the CDW phase to impurities. In addition, the measured physical quantities are magnetic field independent up to 8 T, …

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Determination Of Magnetic Exchange Stiffness And Surface Anisotropy Constants In Epitaxial Ni_ {1-X} Co_ {X}(001) Films, P. Talagala, Petru S. Fodor, Haddad R. Naik, Lowell E. Wenger, P. P. Vaishnava, V. M. Naik Jan 2002

Determination Of Magnetic Exchange Stiffness And Surface Anisotropy Constants In Epitaxial Ni_ {1-X} Co_ {X}(001) Films, P. Talagala, Petru S. Fodor, Haddad R. Naik, Lowell E. Wenger, P. P. Vaishnava, V. M. Naik

Physics Faculty Publications

Magnetic characteristics of epitaxial Ni1-xCox(001) (x=0, 0.16, and 0.50) films with nominal 200 nm thickness on Cu(001)/Si(100) substrates have been investigated by magnetization and ferromagnetic resonance measurements in order to better clarify the rationale for the large variation in the magnetic exchange stiffness constant A, previously determined from different measurements. The exchange constant as well as the saturation magnetization, effective demagnetizing field, fourth-order magnetocrystalline, and second-order perpendicular uniaxial magnetic anisotropy fields has been determined. The analyses of low-temperature saturation magnetization data on these films yield A values that increase from 0.82×10-6erg/cm for a pure Ni film to 2.27×10-6erg/cm for the …

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A Simple Demonstration Of Mie Scattering Using An Overhead Projector, Charles L. Adler, James A. Lock Jan 2002

A Simple Demonstration Of Mie Scattering Using An Overhead Projector, Charles L. Adler, James A. Lock

Physics Faculty Publications

No abstract provided.

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Donor And Acceptor Concentrations In Degenerate Inn, David C. Look, H. Lu, William J. Schaff, J. Jasinski, Z. Liliental-Weber Jan 2002

Donor And Acceptor Concentrations In Degenerate Inn, David C. Look, H. Lu, William J. Schaff, J. Jasinski, Z. Liliental-Weber

Physics Faculty Publications

A formalism is presented to determine donor (ND) and acceptor (NA) concentrations in wurtzitic InN characterized by degenerate carrier concentration (n) and mobility (μ). The theory includes scattering not only by charged point defects and impurities, but also by charged threading dislocations, of concentration Ndis. For a 0.45-μm-thick InN layer grown on Al2O3 by molecular beam epitaxy, having Ndis = 5×1010 cm−2, determined by transmission electron microscopy, n(20 K) = 3.5×1018 cm−3 and μ(20 K) = 1055 cm2 …

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High Spatial Resolution Thermal Conductivity Of Bulk Zno (0001), Diana I. Florescu, L. G. Mourokh, Fred H. Pollak, David C. Look, G. Cantwell, X. Li Jan 2002

High Spatial Resolution Thermal Conductivity Of Bulk Zno (0001), Diana I. Florescu, L. G. Mourokh, Fred H. Pollak, David C. Look, G. Cantwell, X. Li

Physics Faculty Publications

We measured high spatial/depth resolution 300 K thermal conductivity κ of the Zn and O surfaces of two bulk n-type ZnO (0001) samples, grown by a vapor-phase transport method, using scanning thermal microscopy (SThM). The thermal investigation was performed in both point-by-point (∼2 μm resolution) and area-scan modes. On the first sample κ=1.16±0.08 (Zn face)/1.10±0.09 (O face) W/cm K while for the second material κ=1.02±0.07 (Zn face)/0.98±0.08 (O face) W/cm K. These are the highest κ values reported on ZnO. A correlation between SThM area-scan readings and surface topography was established by simultaneously performing atomic force microscopy scans. The …

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Cooling Atoms In An Optical Trap By Selective Parametric Excitation, Nicola Poli, Robert J. Brecha, Giacomo Roati, Giovanni Modugno Jan 2002

Cooling Atoms In An Optical Trap By Selective Parametric Excitation, Nicola Poli, Robert J. Brecha, Giacomo Roati, Giovanni Modugno

Physics Faculty Publications

We demonstrate the possibility of energy-selective removal of cold atoms from a tight optical trap by means of parametric excitation of the trap vibrational modes. Taking advantage of the anharmonicity of the trap potential, we either selectively remove the most energetic trapped atoms or excite those at the bottom of the trap by tuning the parametric modulation frequency. This process, which had been previously identified as a possible source of heating, also appears to be a robust way for forcing evaporative cooling in anharmonic traps.

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Negative-Parity Baryon Masses Using An O(A)-Improved Fermion Action, M. Göckeler, R. Horsley, D. Pleiter, P. E. L. Rakow, G. Schierholz, C. M. Maynard, D. G. Richards Jan 2002

Negative-Parity Baryon Masses Using An O(A)-Improved Fermion Action, M. Göckeler, R. Horsley, D. Pleiter, P. E. L. Rakow, G. Schierholz, C. M. Maynard, D. G. Richards

Physics Faculty Publications

We present a calculation of the mass of the lowest-lying negative-parity J=1/2− state in quenched QCD. Results are obtained using a non-perturbatively O(a)-improved clover fermion action, and a splitting is found between the mass of the nucleon, and its parity partner. The calculation is performed on two lattice volumes and at three lattice spacings, enabling a study of both finite-volume and finite lattice-spacing uncertainties. A comparison is made with results obtained using the unimproved Wilson fermion action.

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Η Photoproduction On The Proton For Photon Energies From 0.75 To 1.95 Gev, M. Bektasoglu, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, S. Stepanyan, J. Yun, Et Al., Clas Collaboration Jan 2002

Η Photoproduction On The Proton For Photon Energies From 0.75 To 1.95 Gev, M. Bektasoglu, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, S. Stepanyan, J. Yun, Et Al., Clas Collaboration

Physics Faculty Publications

Differential cross sections for γp→ηp have been measured with tagged real photons for incident photon energies from 0.75 to 1.95 GeV. Mesons were identified by missing mass reconstruction using kinematical information for protons scattered in the production process. The data provide the first extensive angular distribution measurements for the process above W = 1.75  GeV. Comparison with preliminary results from a constituent quark model support the suggestion that a third S11 resonance with mass ∼1.8  GeV couples to the ηN channel.

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Publisher's Note: Η Photoproduction On The Proton For Photon Energies From 0.75 To 1.95 Gev [Phys. Rev. Lett. 89, 222002 (2002)], M. Bektasoglu, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, R. A. Niyazov, S. Stepanyan, L. B. Weinstein, Et Al., Clas Collaboration Jan 2002

Publisher's Note: Η Photoproduction On The Proton For Photon Energies From 0.75 To 1.95 Gev [Phys. Rev. Lett. 89, 222002 (2002)], M. Bektasoglu, K. V. Dharmawardane, G. E. Dodge, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, R. A. Niyazov, S. Stepanyan, L. B. Weinstein, Et Al., Clas Collaboration

Physics Faculty Publications

No abstract provided.

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First Measurement Of The Double Spin Asymmetry In →E→P → E ‘Π⁺ In The Resonance Region, G. E. Dodge, K. V. Dharmawardane, T. A. Forest, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, R. A. Niyazov, L. B. Weinstein, J. Yun, Et. Al., Clas Collaboration Jan 2002

First Measurement Of The Double Spin Asymmetry In →E→P → E ‘Π⁺ In The Resonance Region, G. E. Dodge, K. V. Dharmawardane, T. A. Forest, C. E. Hyde-Wright, A. Klein, S. E. Kuhn, R. A. Niyazov, L. B. Weinstein, J. Yun, Et. Al., Clas Collaboration

Physics Faculty Publications

The double spin asymmetry in the →e→p → e' π+n reaction has been measured for the first time in the resonance region for four-momentum transfer Q2 = 0.35-1.5 GeV2. Data were taken at Jefferson Lab with the CLAS detector using a 2.6 GeV polarized electron beam incident on a polarized solid NH3 target. Comparison with predictions of phenomenological models shows strong sensitivity to resonance contributions. Helicity-1/2 transitions are found to be dominant in the second and third resonance regions. The measured asymmetry is consistent with a faster rise with Q2 …

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Application Of Plasma Resonance Condition For Prediction Of Large Kerr Effects, A. De, A. Puri Jan 2002

Application Of Plasma Resonance Condition For Prediction Of Large Kerr Effects, A. De, A. Puri

Physics Faculty Publications

Resonance like enhancement of magneto-optic Kerr effects (MOKEs) have been attributed to numerous effects, one of them being plasma resonance of free charge carriers, which is analytically and numerically investigated here. Analytical expressions for frequency dependent enhancement of MOKE are obtained in the general framework of the Drude model, which are then applied to well known expressions describing MOKE. The derived expressions are numerically tested for various optical constants. It is known that for certain materials, the resonance like enhancements in the Kerr spectrum occur in the near vicinity of Re[εxx]=1, which is generally near the …

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Cyclotron Frequency Coupled Enhancement Of Kerr Rotation In Low Refractive Index-Dielectric/Magneto-Optic Bilayer Thin-Film Structures, A. De, A. Puri Jan 2002

Cyclotron Frequency Coupled Enhancement Of Kerr Rotation In Low Refractive Index-Dielectric/Magneto-Optic Bilayer Thin-Film Structures, A. De, A. Puri

Physics Faculty Publications

We investigate the enhancement of magneto-optic polar Kerr rotation over a broad range of optical frequencies. The Drude model for the dielectric tensor is considered. Resonance-like peaks in the Kerr rotation and ellipticity caused in the vicinity of a plasma edge is extended throughout the visible spectrum by deriving an expression for the cyclotron frequency such that Re(ϵxx)∼1 at any given incident photon energy and plasma frequency of the material. The Kerr rotation obtained by use of this expression was studied for the case of InSb and further enhancement of Kerr rotation was achieved in the …

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Synthesis And Magnetic Properties Of Copt–Poly(Methylmethacrylate) Nanostructured Composite Material, Jiye Fang, Kevin L. Stokes, Jibao He, Weillie L. Zhou, Charles J. O'Connor, Daniela Caruntu Jan 2002

Synthesis And Magnetic Properties Of Copt–Poly(Methylmethacrylate) Nanostructured Composite Material, Jiye Fang, Kevin L. Stokes, Jibao He, Weillie L. Zhou, Charles J. O'Connor, Daniela Caruntu

Physics Faculty Publications

We have prepared nanometer-sized CoPt particles dispersed in a poly~methyl methacrylate~PMMA!matrix, as a novel nanostructured magnetic plastic, through a soft chemical processing route. In this work, CoPt nanoparticles were successfully synthesized from a solution phase reduction system in the presence of capping ligands and stabilizing agents at high temperature. The CoPt nanoparticles were annealed at 400 °C for 3 h, and were subsequently re-dispersed inmethylmethacrylate~monomer! . The polymerization was induced by a UV source and the hardness of final product was adjusted by varying the amount of monomeric cross-link agent. Annealed bare CoPt nanoparticles as a ‘‘core’’ material and CoPt–PMMA …

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Thermoelectric Properties Of Bi2sr2co2o9 Whiskers Under Hydrostatic Pressure, F Chen, Kevin L. Stokes, Ryozi Funahashi Jan 2002

Thermoelectric Properties Of Bi2sr2co2o9 Whiskers Under Hydrostatic Pressure, F Chen, Kevin L. Stokes, Ryozi Funahashi

Physics Faculty Publications

We report the temperature dependence of thermopower (S) in the ab plane of Bi2Sr2Co2O9 {BC-222} single crystalline whiskers under high pressure up to 1.2 GPa. Special modifications were made to our high-pressure transport measurement system to improve the measurement accuracy of S for whiskers with high resistance. Pressure improved the contact resistance dramatically. We observed a slight decrease of  S and four-wire electrical conductivity (sigma) under high pressure. As a result, the power factor (S2sigma) was decreased less than 20% by pressure. From the temperature dependence of sigma, the band gap of BC-222 whiskers increase very slightly …

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Energy Flow And Fluorescence Near A Small Metal Particle, Purna C. Das, Ashok Puri Jan 2002

Energy Flow And Fluorescence Near A Small Metal Particle, Purna C. Das, Ashok Puri

Physics Faculty Publications

We examine the classical energy-balance equation for a fluorescing system consisting of a molecule near a small, spherical metal particle capable of sustaining electromagnetic resonances and irradiated with laser light. From the energy-flow distribution in the entire system, we obtain the enhancement factor for the fluorescence emission of the adsorbed molecule. Numerical results demonstrate that the electromagnetic interactions of the molecule and the surface can be understood in terms of energy flow through the entire system and applied to investigate spectroscopic properties of adsorbates in similar systems. Absorption and emission rates of the adsorbed molecule are determined considering the energy-flow …

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Effect Of Cr3+ And So42- On The Structure Of Rust Layer Formed On Steels By Atmospheric Corrosion, Masato Yamashita, Hitoshi Uchida,, Desmond C. Cook . Jan 2002

Effect Of Cr3+ And So42- On The Structure Of Rust Layer Formed On Steels By Atmospheric Corrosion, Masato Yamashita, Hitoshi Uchida,, Desmond C. Cook .

Physics Faculty Publications

The effect of chromium ion (Cr3+) and sulfate ion (SO42-) on the structure of the rust layer formed by thin electrolyte-film corrosion of low-alloy steels has been examined. By using X-ray diffraction spectroscopy, it was found that coexistence of Cr3+ and SO42- in the electrolyte film covering the steel surface quickly forms the Cr-goethite (α-(Fe 1-X, CrX)OOH) layer which has been known as the final protective rust layer. Scanning vibrating electrode measurements showed that the rust layer formed under the electrolyte film containing Cr3+ and SO42- …

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