Physics Commons^™

Removal Versus Ablation In Krf Dry Laser Cleaning Of Polystyrene Particles From Silicon, Sergey I. Kudryashov, Susan D. Allen

Mechanical Engineering - Daytona Beach

Direct absorption and melting of 0.2, 0.5 and 1.1 μm polystyrene particles on a Si substrate irradiated by 248 nm excimer laser radiation was found to contribute to their dry laser removal via a "hopping" mechanism at cleaning thresholds of 0.05, 0.1, and 0.16 J/cm ², respectively. Ablation of these particles, which starts near the beginning of substrate deceleration at fluences above 0.4-0.5 J/cm ², suppresses particle removal due to ablative recoil momentum. At fluences above a second cleaning threshold of 0.7 J/cm ² particles are completely evaporated without any visible surface damage of the Si substrate.

© …

Effects Of Light Scalar Mesons In Η\To 3Π Decay, Joseph Schechter, Abdou Abdel-Rehim, Deirdre Black, Amir H. Fariborz

Physics - All Scholarship

We study the role of a possible nonet of light scalar mesons in the still interesting \eta \to 3\pi decay process, with the primary motivation of learning more about the scalars themselves. The framework is a conventional non-linear chiral Lagrangian of pseudoscalars and vectors, extended to include the scalars. The parameters involving the scalars were previously obtained to fit the s-wave \pi\pi and \piK scatterings in the region up to about 1 GeV as well as the strong decay \eta' \to \eta \pi\pi. At first, one might expect a large enhancement from diagrams including a light \sigma(560). However there is …

Femtosecond Pump-Probe Reflectivity Study Of Silicon Carrier Dynamics, A. J. Sabbah, D. Mark Riffe

All Physics Faculty Publications

We have studied the ultrafast optical response of native-oxide terminated Si(001) with pump-probe reflectivity using 800 nm, 28 fs pulses at an excitation density of (5.5±0.3)×10¹⁸cm^-3. Time-dependent reflectivity changes comprise third-order-response coherent-transient variations arising from anisotropic state filling and linear-response variations arising from excited free carriers, state filling, and lattice heating. A time constant of 32±5fs associated with momentum relaxation is extracted from the coherent-transient variations. The state-filling and free-carrier responses are sensitive to carrier temperature, allowing an electron-phonon energy relaxation time of 260±30fs to be measured. The recovery of the reflectivity signal back towards its …

Search For R-Parity Violating Supersymmetry In Two-Muon And Four-Jet Topologies, V. M. Abazov, Gregory R. Snow, D0 Collaboration

Gregory Snow Publications

We present results of a search for R-parity-violating decay of the neutralino Χ̅₁⁰, taken as the lightest supersymmetric particle, to a muon and two jets. The decay proceeds through a lepton-number violating coupling λ_2jk¹ (j =1, 2; k = 1; 2, 3), with R-parity conservation in all other production and decay processes. In the absence of candidate events from 77.5 ± 3.9 pb^-1 of data collected by the D0 experiment at the Fermilab Tevatron in pp̅ collisions at√s =1.8 TeV, and with an expected background of 0.18 ± 0.03 …

The Core Structure Of Presolar Graphite Onions, P. Fraundorf, Martin Wackenhut

Physics Faculty Works

Of the “presolar particles” extracted from carbonaceous meteorite dissolution residues, i.e., of those particles that show isotopic evidence of formation in the neighborhood of other stars prior to the origin of our solar system, a subset of the onion-like graphite spheres has an interesting concentric graphene core–graphite rim structure. We show here that single graphene sheet defects in the onion cores (e.g., cyclopentane loops) may be observable edge-on by high-resolution electron microscopy. This could allow a better evaluation of models for their formation and in particular could strengthen the possibility that growth of these assemblages proceeds atom by atom with …

Plateau Effects In The Spectra Of Electrons Scattered From Atoms In A Strong Laser Field, N. L. Manakov, Anthony F. Starace, A. V. Flegel, M. V. Frolov

Anthony F. Starace Publications

An exact quantum solution of the problem of electron scattering from a short-range potential in the presence of a strong elliptically polarized laser field is obtained. The differential scattering cross section as a function of the number of absorbed (or emitted) photons exhibits a plateau caused by the rescattering of electrons from the scattering center. Numerical results for a linearly polarized laser field are presented, and it is shown that the plateau boundaries agree well with classical estimates.

Crystalline Order On A Sphere And The Generalized Thomson Problem, Mark Bowick, Angelo Cacciuto, David R. Nelson, A. Travesset

Physics - All Scholarship

We attack generalized Thomson problems with a continuum formalism which exploits a universal long range interaction between defects depending on the Young modulus of the underlying lattice. Our predictions for the ground state energy agree with simulations of long range power law interactions of the form 1/r^{gamma} (0 < gamma < 2) to four significant digits. The regime of grain boundaries is studied in the context of tilted crystalline order and the generality of our approach is illustrated with new results for square tilings on the sphere.

Ion Contribution To The Astrophysical Important 447.15, 587.56 And 667.82 Nm He I Spectral Lines Broadening, Vladimir Milosavljevic, Stevan Djenize

Articles

Characteristics of the astrophysical important Stark broadened 447.15 nm, 587.56 nm and 667.82 nm spectral line profiles have been measured at electron densities between 0.3 10 and 8.2 10 m and electron temperatures between 8000 and 33 000 K in plasmas created in five various discharge conditions using a linear, low-pressure, pulsed arc as an optically thin plasma source operated in a helium-nitrogen-oxygen gas mixture. On the basis of the observed asymmetry of the line profiles we have obtained their ion broadening parameters ( A) caused by influence of the ion microfield on the line broadening mechanism and also …

University Of Nevada, Las Vegas Advanced Accelerator Applications University Participation Program: Quarterly Report, First Quarter Year 2 (March 2002 To May 2002), Anthony Hechanova

Transmutation Research Program Reports (TRP)

This Quarterly Report is a primary deliverable from the University of Nevada, Las Vegas (UNLV) Advanced Accelerator Applications (AAA) University Participation Program (UPP) Director to the U.S. Department of Energy (DOE) as described in the UNLV AAA proposal, and Statement of Work for the First Quarter Year 2 and AAA FY02 Work Package.

The UNLV AAA UPP Director implements the program’s administration using staff from the Harry Reid Center for Environmental Studies (HRC) to ensure that work conducted under the UNLV AAA UPP meets program objectives. The UNLV AAA program consists of four components: Program Support, Research Infrastructure Augmentation, International …

Apparent Tricritical Behavior At A Nearly Second-Order Nematic-Isotropic Phase Transition Of A Cyclic Liquid Crystalline Trimer, Ishtiaque M. Syed, Virgil Percec, Rolfe G. Petschek, Charles Rosenblatt

Faculty Scholarship

An investigation on the cyclic liquid crystalline trimer TPB-(c)9(3) was performed. The optical retardation and Fréedericksz techniques within a few tens of millikelvins of the superheating limit of the nearly second-order nematic isotropic phase transition were used for the investigation purpose. It was found that both the Fréedericksz bend threshold voltage and optical retardation were in good agreement with tricritical behaviour for the transition.

University Of Nevada, Las Vegas Advanced Accelerator Applications University Participation Program: Quarterly Report, Third Quarter Year 2 (Sept. 2002 To Nov. 2002), Anthony Hechanova

Transmutation Research Program Reports (TRP)

This Quarterly Report is a primary deliverable from the University of Nevada, Las Vegas (UNLV) Advanced Accelerator Applications (AAA) University Participation Program (UPP) Director to the U.S. Department of Energy (DOE) as described in the UNLV AAA proposal and Statement of Work for the Fourth Quarter.

The UNLV AAA UPP Director implements the program’s administration using staff from the Harry Reid Center for Environmental Studies (HRC) to ensure that work conducted under the UNLV AAA UPP meets program objectives. The UNLV AAA program consists of three components: Program Support, Research Infrastructure Augmentation, and Student Research.

Measurement Of Diffractive Production Of D*±(2010) Mesons In Deep-Inelastic Scattering At Hera, S. Chekanov, D. Krakauer, S. Magill, B. Musgrave, J. Repond, R. Yoshida, Margarita C. K. Mattingly, P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherini, A. Bruni, G. Bruni, G. Cara Romeo, L. Cifarelli, F. Cindolo, A. Contin, M. Corradi, S. De Pasquale, P. Giusti, G. Iacobucci, A. Margotti, R. Nania, F. Palmonari, A. Pesci, G. Sartorelli, A. Zichichi, G. Aghuzumtsyan, D. Bartsch, I. Brock

Faculty Publications

Diffractive production of D*±(2010) mesons in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 44.3 pb-1. Diffractive charm production is identified by the presence of a large rapidity gap in the final state of events in which a D*±(2010) meson is reconstructed in the decay channel D*+ → (D0 → K-π+)πs+ (+ charge conjugate). Differential cross sections when compared with theoretical predictions indicate the importance of gluons in such diffractive interactions. © 2002 Elsevier Science B.V. All rights reserved.

Degeneracy In Density Functional Theory: Topology In The V And N Spaces, Carsten A. Ullrich, W. Kohn

Physics Faculty Research & Creative Works

The problem of v-representability had cast a shadow of uncertainty over density functional theory (DFT). Building on CCR, the topology of the v(r)-n(r) mapping is clarified. The Be series and a lattice model are used for rl, to a continuous variable, r, does not appear to offer difficulties.

H2o–D2o Condensation In A Supersonic Nozzle, Christopher H. Heath, Kiril A. Streletzky, Barbara E. Wyslouzil, Judith Woelk, Reinhard Strey

Physics Faculty Publications

We examined the condensation of H2O, D2O, and four intermediate mixtures (20, 40, 60, and 80 mol % D2O) in a supersonic nozzle. Because the physical and chemical properties of protonated and deuterated water are so similar, this system is ideal for studying the change in condensation behavior as a function of condensible composition. In our experiments dilute mixtures of condensible vapor in N2 are expanded from three different stagnation temperatures resulting in a broad range of onset temperatures (190–238 K) and pressures (27–787 kPa). For a fixed stagnation temperature, the partial pressure required to maintain the onset of condensation …

Phase Dependence Of Thomson Scattering In An Ultraintense Laser Field, Fei He, Y. Y. Lau, Donald P. Umstadter, Trevor Strickler

Donald Umstadter Publications

The Thomson scattering spectra of an electron by an ultraintense laser field are computed. It is found that the electron orbit, and therefore its nonlinear Thomson scattering spectra, depend critically on the amplitude of the ultraintense laser field and on the phase at which the electron sees the laser electric field. Contrary to some customary notions, the Thomson scattering spectra, in general, do not occur at integer multiples of the laser frequency and the maximum frequency is proportional to the first instead of the third power of the electric field strength for the case of an ultraintense laser. The implications …

Dephasing Model For Spatially Extended Atomic States In Cyclotronlike Resonances, R E. Wagner, S Radovich, J Gillespie, Q Su, Rainer Grobe

Faculty publications – Physics

In recent work, the formation of ring-shaped electron distributions for hydrogen atoms in resonant static magnetic-laser fields has exclusively been associated with the impact of relativity. In this note we will generalize this statement and show that the nonlinearity associated with the nuclear binding force can trigger similarly shaped steady-state charge clouds in atoms under suitable conditions. The dephasing model, based on modeling the quantum-mechanical state by a classical ensemble of quasiparticles evolving with slightly different cyclotron periods, can recover features, in the two lowest-order resonances as well as the Coulomb-field-induced charge distributions.

Thermoelectric Effect Spectroscopy Of Deep Levels In Semi-Insulating Gan, U. V. Desnica, M. Pavlovic, Z-Q. Fang, David C. Look

Physics Faculty Publications

The report of thermoelectric effect spectroscopy (TEES) applied on semi-insulating GaN was presented. The type of TEES setup, especially suitable for film-on-substrate samples, was devised. TEES enabled determination of sign of observed deep traps. Using TEES and thermally stimulated current spectroscopy measurements in combination with the simultaneous multiple peak analysis formalism all important trap parameters were determined. The shallowest identified electron and hole traps had activation energies E_c−0.09 eV and E_v+0.167 eV, respectively. Results indicate that both these traps, oppositely charged are present in the studied material in relatively high concentrations causing the electrical compensation and …

Adiabatic Invariance With First Integrals Of Motion, Artur D. Adib

Dartmouth Scholarship

The construction of a microthermodynamic formalism for isolated systems based on the concept of adiabatic invariance is an old but seldom appreciated effort in the literature, dating back at least to P. Hertz [Ann. Phys. (Leipzig) 33, 225 (1910)]. An apparently independent extension of such formalism for systems bearing additional first integrals of motion was recently proposed by Hans H. Rugh [Phys. Rev. E 64, 055101 (2001)], establishing the concept of adiabatic invariance even in such singular cases. After some remarks in connection with the formalism pioneered by Hertz, it will be suggested that such an extension can …

Compact Focusing Von Hamos Spectrometer For Quantitative X-Ray Spectroscopy, Larry V. Knight, A. P. Shevelko, Yu S. Kasyanov, O. F. Yakushev

Faculty Publications

A compact focusing crystal spectrometer based on the von Hamos scheme is described. Cylindrically curved mica and graphite crystals with a radius of curvature of R = 20 mm are used in the spectrometer. A front illuminated charge-coupled device (CCD) linear array detector makes this spectrometer useful for real-time spectroscopy of laser-produced plasma x-ray sources within the wavelength range of lambda= 1.8-10 Angstroms. Calibration of crystals and the CCD linear array makes it possible to measure absolute photon fluxes. X-ray spectra in an absolute intensity scale were obtained from Mg, Ti, and Fe laser-produced plasmas, with a spectral resolution lambda/delta …

Physica Junior!: The Newsletter Of Utep’S Department Of Physics, Utep Department Of Physics

The Department of Physics

Electronic newsletter for high school students interested in physics, Fall 2002.

Training Of The Exchange-Bias Effect In Nio-Fe Heterostructures, A. Hochstrat, Christian Binek, Wolfgang Kleemann

Christian Binek Publications

The training effect of a NiO(001)/Fe(110) heterostructure is studied from magnetic hysteresis loops measured by superconducting quantum interference device magnetometry. Consecutive hysteresis loops exhibit a decreasing exchange bias effect. This behavior is known as the training effect, which reflects the dependence of the exchange bias field on the antiferromagnetic interface magnetization. In order to evidence this dependence, we study the decrease of the total saturation magnetization of the heterostructure for an increasing number of hysteresis cycles. Assuming proportionality between the interface magnetization and the total saturation magnetization, the description of the data is consistent within the phenomenological Meiklejohn Bean approach.

Coupling Of Coamps And Wavetech With Improved Wave Physics, Shahrdad Sajjadi, Pat Fitzpatrick, Gueorgui Mostovoi, Yongzuo Li, Matt Bettencourt

Publications

The Model Coupling Executable Library (MCEL), developed at the University of Southern Mississippi's Center of Higher Learning, has been successfully used to couple the Coupled Ocean/Atmospheric Mesoscale Prediction System (COAMPS) and the ocean wave model WAVEWATCH. An example of its application is shown for Hurricane Gordon, showing that two-way coupling results affects boundary layer physics differently than one-way coupling --- in this case, resulting in larger o z and, consequently, larger surface fluxes and a more intense hurricane. However, since analyzing MCEL is difficult because the wave physics is inaccurate, improvements to the wave algorithms are also part of the …

Caustics In Tachyon Matter And Other Born-Infeld Scalars, Gary Felder, Lev Kofman, Alexei Starobinsky

Physics: Faculty Publications

We consider scalar Born-Infeld type theories with arbitrary potentials V(T) of a scalar field T. We find that for models with runaway potentials V(T) the generic inhomogeneous solutions after a short transient stage can be very well approximated by the solutions of a Hamilton-Jacobi equation that describes free streaming wave front propagation. The analytic solution for this wave propagation shows the formation of caustics with multi-valued regions beyond them. We verified that these caustics appear in numerical solutions of the original scalar BI non-linear equations. Our results include the scalar BI model with …

Domain Wall Relaxation, Creep, Sliding, And Switching In Superferromagnetic Discontinuous Co80Fe20/Al2O3 Multilayers, X. Chen, O. Sichelschmidt, Wolfgang Kleemann, Christian Binek, J.B. Sousa, Susana Cardoso De Freitas, P.P. Freitas

Christian Binek Publications

The ac susceptibility of a superferromagnetic discontinuous multilayer [Co₈₀Fe₂₀(1.4   nm)/ Al₂O₃(3   nm)]10 is measured as a function of temperature, frequency, and field amplitude and compared to static and dynamic hysteresis loops. Its properties are successfully mapped onto the predicted [T. Nattermann, V. Pokrovsky, and V. M. Vinokur, Phys. Rev. Lett. 87, 197005 (2001).] dynamical phase transitions, which link the relaxation, creep, sliding, and switching regimes of pinned domain walls.

Experimental Observation Of Energetic Ions Accelerated By Three-Dimensional Magnetic Reconnection In A Laboratory Plasma, Michael R. Brown, C. D. Cothran, Matthew Joseph Landreman , '03, David J. Schlossberg , '01, W. H. Matthaeus

Physics & Astronomy Faculty Works

Magnetic reconnection is widely believed responsible for heating the solar corona as well as for generating X-rays and energetic particles in solar flares. On astrophysical scales, reconnection in the intergalactic plasma is a prime candidate for a local source (Mpc) of cosmic rays exceeding the Greisen-Zatsepin-Kuzmin cutoff (&SIM;10(19) eV). In a laboratory astrophysics experiment, we have made the first observation of particles accelerated by magnetic reconnection events to energies significantly above both the thermal and the characteristic magnetohydrodynamic energies. These particles are correlated temporally and spatially with the formation of three-dimensional magnetic structures in the reconnection region.

Development Of A Hybrid Photo-Diode And Its Front-End Electronics For The Btev Experiment, Raymond Mountain

Physics - All Scholarship

This paper describes the development of a 163-channel Hybrid Photo-Diode (HPD) to be used in the RICH Detector for the BTEV Experiment. This is a joint development project with DEP, Netherlands. It also reports on the development of associated front-end readout electronics based on the va_btev ASIC, undertaken with IDEAS, Norway. Results from bench tests of the first prototypes are presented.

Monte Carlo Simulation On The Indirect Exchange Interactions Of Co-Doped Zno Film, Abraham F. Jalbout, Hanning Chen, Scott L. Whittenburg

Chemistry and Biochemistry Faculty Publications

Monte Carlo simulations using a three-dimensional lattice model studied the Ruderman–Kittel–Kasuya–Yosida (RKKY) indirect exchange interaction of doped magnetic Co ions in ZnOfilms. The results of the calculations show that the RKKY interaction in Co-doped ZnO is long ranged and its magnitude is proportional to (inverse of the distance from a central ion). The sign oscillates with a frequency that depends on the concentration of the carrier. The long-distance sum of the RKKY indirect exchange energies is positive indicating that these materials are ferromagnetic, in direct correlation with previously reported results.

Construction, Pattern Recognition And Performance Of The Cleo Iii Lif-Tea Rich Detector, Raymond Mountain, R. Ayad, Konstantin Vladimirovich Bukin, A. Efimov

Physics - All Scholarship

We briefly describe the design, construction and performance of the LiF-Tea RICH detector built to identify charged particles in the CLEO III experiment. Excellent pion/kaon separation is demonstrated.

Density And Conformation With Relaxed Substrate, Bulk, And Interface In Electrophoretic Deposition Of Polymer Chains, F.W. Bentrem, J. Xie, Ras B. Pandey

Faculty Publications

Characteristics of relaxed density profile and conformation of polymer chains are studied by a Monte Carlo simulation on a discrete lattice in three dimensions using different segmental (kink-jump (K), crank-shaft (C), reptation (R)) dynamics. Three distinct density regimes, substrate, bulk, and interface, are identified. With the KC segmental dynamics, we find that the substrate coverage grows with a power law, d_s∝t^γ with a field (E) dependent non-universal exponent γ=0.23+0.7E. The bulk volume fraction d_b and the substrate polymer density (d_s) increases with the field with power-laws (d_{b …}

Oxidation Of Metals At The Chromium Oxide Interface, Ruihua Cheng, C.N. Borca, N. Pilet, Bo Xu, Lu Yuan, Bernard Doudin, Sy_Hwang Liou, Peter A. Dowben

Peter Dowben Publications

Metal thin-film deposition, over the Cr₂O₃ surface of CrO₂ thin-film substrates, exhibits a redox reaction at the interface. The transition metal forms an oxide in combination with the reduction of the near-surface chromium oxide to Cr₂O₃ . The insulating barrier layer Cr₂O₃ increases with the formation of Pb₃ O₄ in Pb/Cr₂O₃ /CrO₂ and CoO in Co/Cr₂O₃ /CrO₂ junctions, respectively.