Physics Commons^™

Nonlinear Magneto-Optic Polarization Rotation With Intense Laser Fields, Paul S. Hsu, Anil K. Patnaik, George R. Welch

Physics Faculty Publications

We have studied the nonlinear Faraday effect with intense linear polarized light in an optically thick atomic rubidium vapor. We demonstrate that the polarization rotation rate (rotation angle per unit magnetic field, in the limit of low field) has a maximum value as the intensity and density are increased. We also show that the optimal sensitivity of an optical magnetometer based on this system reaches a saturation value as the intensity and density are increased.

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

Physics Faculty Publications

The nightside ionosphere of Venus is formed mostly by day-to-night transport of ions below the ionopause, with a small contribution from precipitation of energetic electrons from the wake. This nightward flux of ions should result in dayside ionospheres that are characterized by smaller electron density scale heights at high altitudes than those that are characteristic of diffusive equilibrium. In order to determine both the maximum possible values of the upward fluxes and the upward fluxes implied by comparison of our computed ion and electron density profiles to measurements, we have constructed more than 60 models of the high solar activity …

Metal Modulation Epitaxy Growth For Extremely High Hole Concentrations Above 10(19) Cm(-3) In Gan, Gon Namkoong, Elaissa Trybus, Kyung Kuen Lee, Michael Moseley, W. Alan Doolittle, David C. Look

Physics Faculty Publications

The free hole carriers in GaN have been limited to concentrations in the low 10¹⁸ cm⁻³ range due to the deep activation energy, lower solubility, and compensation from defects, therefore, limiting doping efficiency to about 1%. Herein, we report an enhanced doping efficiency up to ∼ 10% in GaN by a periodic doping, metal modulation epitaxy growth technique. The hole concentrations grown by periodically modulating Ga atoms and Mg dopants were over ∼ 1.5×10¹⁹ cm⁻³.

Variation Of The Martian Ionospheric Electron Density From Mars Express Radar Soundings, D. D. Morgan, D. A. Gurnett, D. L. Kirchner, Jane L. Fox, E. Nielsen, J. J. Plaut

Physics Faculty Publications

The Mars Advanced Radar for Subsurface and Ionospheric Sounding aboard Mars Express has been in operation for over 2 years. Between 14 August 2005 and 31 July 2007, we obtain 34,492 ionospheric traces, of which 14,060 yield electron density profiles and 12,291 yield acceptable fits to the Chapman ionospheric model. These results are used to study the Martian ionosphere under changing conditions: the presence or absence of solar energetic particles, solar EUV flux, season, solar zenith angle, and latitude. The 2-year average subsolar maximum electron density n ₀ is 1.62 × 10⁵ cm⁻³, the average subsolar electron …

Surface Traps In Vapor-Phase-Grown Bulk Zno Studied By Deep Level Transient Spectroscopy, Z-Q. Fang, B. Claflin, David C. Look, Y. F. Dong, H. L. Mosbacker, L. J. Brillson

Physics Faculty Publications

Deep level transient spectroscopy, current-voltage, and capacitance-voltage measurements are used to study interface traps in metal-on-bulk-ZnO Schottky barrier diodes (SBDs). c-axis-oriented ZnO samples were cut from two different vapor-phase-grown crystals, and Au- and Pd-SBDs were formed on their (0001) surfaces after remote oxygen-plasma treatment. As compared to Au-SBDs, the Pd-SBDs demonstrated higher reverse-bias leakage current and forward-bias current evidently due to higher carrier concentrations, which might have been caused by hydrogen in-diffusion through the thin Pd metal. The dominant traps included the well-known bulk traps E₃ (0.27 eV) and E₄ (0.49 eV). In addition, a surface-related trap, …

Two-Layer Hall-Effect Model With Arbitrary Surface-Donor Profiles: Application To Zno, David C. Look

Physics Faculty Publications

A complete two-layer Hall-effect model, allowing arbitrary donor and acceptor profiles, is presented and applied to the problem of conductive surface layers in ZnO. Temperature-dependent mobility and carrier concentration data in the temperature range of 20–320 K are fitted with an efficient algorithm easily implemented in commercial mathematics programs such as MATHCAD. The model is applied to two ZnO samples, grown by the melt (MLT) and hydrothermal (HYD) processes, respectively. Under the assumption of a “square” surface-donor profile, the fitted surface-layer thicknesses are 48 and 2.5 nm, respectively, for the MLT and HYD samples. The surface-donor concentrations are 7.6×10^{17 …}

Active And Passive Imaging In The Thz Spectral Region: Phenomenology, Dynamic Range, Modes, And Illumination, Douglas T. Petkie, Corey Casto, Frank C. De Lucia, Steven R. Murrill, Brian Redman, Richard L. Espinola, Charmaine C. Franck, Eddie L. Jacobs, Steven T. Griffin, Carl E. Halford, Joe Reynolds, Sean O'Brien, David Tofsted

Physics Faculty Publications

The useful compromise between resolution and penetration power of the submillimeter or terahertz (THz) spectral region has long made it attractive for a variety of imaging applications. However, many of the demonstrations of imaging in this spectral region have used strategically oriented targets, especially favorable concealment materials, proximate imaging geometries, etc. This paper reports the results of studies aimed at better understanding the phenomenology of targets, the impact of this phenomenology on various active and passive imaging strategies, and most importantly, the development of imaging strategies that do not require the aforementioned special circumstances. Particular attention is paid to the …

Zn- And O-Face Polarity Effects At Zno Surfaces And Metal Interfaces, Yufeng Dong, Z-Q. Fang, David C. Look, G. Cantwell, J. Zhang, J. J. Song, L. J. Brillson

Physics Faculty Publications

Depth-resolved cathodoluminescence spectroscopy, current-voltage, capacitance-voltage, and deep level transient spectroscopy of ZnO (0001) Zn- and (000) O-polar surfaces and metal interfaces show systematically higher Zn-face near band edge emission and lower near-surface defect emission. Even with remote plasma decreases of the 2.5 eV near-surface defect emission, (0001)-Zn face emission quality still exceeds that of (000)-O face. Ultrahigh vacuum-deposited Au and Pd diodes on as-received and O₂/He plasma-cleaned surfaces display a strong polarity dependence that correlates with defect emissions, traps, and interface chemistry. A comprehensive model accounts for the polarity-dependent transport properties and their correlations with carrier concentration profiles.

Very High Channel Conductivity In Low-Defect Aln/Gan High Electron Mobility Transistor Structures, A. M. Dabiran, A. M. Wowchak, A. Osinsky, J. Xie, Brian Hertzog, David C. Look, P. P. Chow

Physics Faculty Publications

Low defect AlN/GaN high electron mobility transistor (HEMT) structures, with very high values of electron mobility (>1800 cm²/V s) and sheet charge density (>3×10¹³ cm⁻²), were grown by rf plasma-assisted molecular beam epitaxy (MBE) on sapphire and SiC, resulting in sheet resistivity values down to ∼ 100 Ω/◻ at room temperature. Fabricated 1.2 μm gate devices showed excellent current-voltage characteristics, including a zero gate saturation current density of ∼ 1.3 A/mm and a peak transconductance of ∼ 260 mS/mm. Here, an all MBE growth of optimized AlN/GaN HEMT structures plus the results …

Reproducible Increased Mg Incorporation And Large Hole Concentration In Gan Using Metal Modulated Epitaxy, Shawn D. Burnham, Gon Namkoong, David C. Look, Bruce Claflin, W. Alan Doolittle

Physics Faculty Publications

The metal modulated epitaxy (MME) growth technique is reported as a reliable approach to obtain reproducible large hole concentrations in Mg-doped GaN grown by plasma-assisted molecular-beam epitaxy on c-plane sapphire substrates. An extremely Ga-rich flux was used, and modulated with the Mg source according to the MME growth technique. The shutter modulation approach of the MME technique allows optimal Mg surface coverage to build between MME cycles and Mg to incorporate at efficient levels in GaN films. The maximum sustained concentration of Mg obtained in GaN films using the MME technique was above 7×10²⁰ cm⁻³, leading …

The Rotational Spectrum Of Chlorine Nitrate (Ciono2): V6 And The V5/V6V9 Dyad, Zbigniew Kisiel, Ewa Bialkowska-Jaworska, Rebecca A. H. Butler, Douglas T. Petkie, Paul Helminger, Frank C. De Lucia

Physics Faculty Publications

No abstract provided.

Infrared Simulations Derived From Submillimeter Wave Analyses, Douglas T. Petkie, Rebecca A. H. Butler, Paul Helminger, Zbigniew Kisiel, Kenneth W. Jucks, Brenda P. Winnewisser, Manfred Winnewisser, Frank C. De Lucia

Physics Faculty Publications

No abstract provided.

Effects Of Annealing In N(2) Ambient On Traps And Persistent Conduction In Hydrothermally Grown Zno, Z-Q. Fang, B. Claflin, David C. Look

Physics Faculty Publications

Thermally stimulated current (TSC) spectroscopy and temperature–dependent dark current (DC) measurements have been applied to study traps and photoinduced persistent surface conduction in two hydrothermally grown bulk ZnO samples, as-grown, and annealed at 600 °C in N₂ ambient for 30 min, respectively. The as-grown sample had a room-temperature (RT) resistivity of 1.6×10³ Ω cm, mobility of 2.1×10² cm²/V s, and carrier concentration of 1.8×10¹³ cm⁻³, while the annealed sample was highly resistive, with RT resistivity of 3.6×10⁶ Ω cm, mobility of 4.4 cm²/V s, and carrier concentration of 3.9×10 …

Terahertz Imaging System Performance Model For Concealed-Weapon Identification, Steven R. Murrill, Eddie L. Jacobs, Steven K. Moyer, Carl E. Halford, Steven T. Griffin, Frank C. De Lucia, Douglas T. Petkie, Charmaine C. Franck

Physics Faculty Publications

The U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) and the U.S. Army Research Laboratory have developed a terahertz (THz) -band imaging system performance model for detection and identification of concealed weaponry. The MATLAB-based model accounts for the effects of all critical sensor and display components and for the effects of atmospheric attenuation, concealment material attenuation, and active illumination. The model is based on recent U.S. Army NVESD sensor performance modeling technology that couples system design parameters to observer–sensor field performance by using the acquire methodology for weapon identification performance predictions. This THz model has been developed in support …

Characterization Of Inert Gas Rf Plasma-Treated Indium Tin Oxide Thin Films Deposited Via Pulsed Dc Magnetron Sputtering, Amber Nicole Reed

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In this work, the effects of a post-deposition RF plasma treatment on indium tin oxide (ITO) thin films prepared with pulsed DC magnetron sputtering in argon were investigated. The parameters of the post-deposition were studied to determine what RF power and gas pressure resulted in the greatest reduction in resistivity in the films while producing the smallest increase in substrate temperature for treatments with both argon and oxygen plasmas. The as-deposited (untreated) films and the treated films were characterized using Raman spectroscopy and X-ray diffraction to determine the effects of the post-deposition treatment on the degree of film crystallization. XPS …

Evanescent Microwave Microscopy Of Porcine Skin Tissue, Richard A. Kleismit

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This thesis describes the application of a custom designed λ/4 resonant coaxial probe to measurements of the complex permittivity of in vitro freshly excised porcine skin tissue. The dielectric properties of the organic material within the near field of the tip of the probe frustrates the electric field and measurably changes the resonant frequency and quality factor Q of the coaxial sensor, where the change in resonant frequency and quality factor of a tuned resonance is measured as a function of tip-sample separation. The design of the probe enables better spatial resolution than previously developed probes. The following studies were …

Comparison Of Two Methods Of External Scatter Dose Contributions To The Contralateral Breast, James Cutlip

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The treatment outcomes of many forms of breast cancer have become very favorable. The usual standard of successful treatment of five years without a recurrence is not adequate any longer for breast cancer. Many patients live well beyond this time interval only to have a second malignancy develop in the contralateral breast ten or twenty years later. Boice et al (1992) found that there was a correlation between the amount of dose to the contralateral breast and the likelihood of a secondary malignancy forming.

The normal practice today is to use multi-leaf collimators (MLC) to modulate the photon beam in …