Physics Commons^™

Reactive Quantum Scattering In Two Dimensions, Roy S. Calfas

Theses and Dissertations

In an effort to develop a more efficient time dependent approach for calculating scattering matrix elements, absorbing boundary conditions are combined together with the channel packet method. As an introduction to scattering, scattering matrix elements are presented for a one-dimensional square well and a one-dimensional potential consisting of a Gaussian well with symmetric Gaussian barriers. Next, the combination of the channel packet method together with absorbing boundary conditions yields an order of magnitude savings in the time necessary to compute the correlation function for the collinear H+H

Photoluminescence Study Of Gan Implanted With Erbium And Erbium-Oxygen, Lori R. Everitt

Theses and Dissertations

Erbium emits at 1540 nm, which propagates well through fiber optic cables. This work studies the photoluminescence (PL) from GaN, GaN implanted with Er alone, and GaN implanted with both Er and O as functions of excitation laser energy and sample temperature. When the exciton bound to a neutral donor recombined, a photon was emitted at 3.47 eV. A photon emitted at 3.457 eV may have been evidence of the recombination of an exciton bound to a neutral acceptor. Second, the Er-ion transitions were observed in two groups around 0.805 and 1.25 eV. The PL intensity was measured at four …

Time Resolved Photoluminescence Spectra Of A Mid-Infrared Multiple Quantum Well Semiconductor Laser, Anthony L. Franz

Theses and Dissertations

Recombination mechanisms in mid-IR semiconductor lasers are strongly dependent on the carrier density of the active region. The objective of this research is to improve previous carrier density estimates through the incorporation of spectral information. One hundred photoluminescence (PL) spectra were calculated for a variety of carrier densities. Calculations were made for an InAsSb/InAlAsSb multiple quantum well laser sample assuming parabolic bands. The widths of the calculated spectral profiles were tabulated as a function of carrier density. Actual spectra were measured using the Ultrafast Mid-Infrared Photoluminescence System, which uses upconversion to measure the PL intensity in time steps smaller than …

Collisional Broadening Of Spectral Lines In The X → B System Of O2 And The First Vibrational Band Of No By The Noble Gases, John J. Cornicelli

Theses and Dissertations

Collisional broadening of the rotational spectral lines of the X to b system of O₂ and the first vibrational band of NO by the noble gases is examined by Fourier transform spectroscopy. Peaks of the individual rotational lines are modeled with a Voigt function, from which Lorentzian half widths are extracted. Lorentzian widths are plotted vs. pressure of foreign gas, from which the pressure broadening coefficients and pressure broadening cross sections are calculated. The pressure broadening coefficients are compared to theoretical values determined by past research for O₂. NO coefficients are compared to similar research using N …

Photolithographic Patterning Of Vacuum-Deposited Organic Light Emitting Devices, Peifang Tian, P. E. Burrows, S. E. Forrest

Peifang Tian

We demonstrate a photolithographic technique to fabricate vacuum-deposited organic light emitting devices. Photoresist liftoff combined with vertical deposition of the emissive organic materials and the metal cathode, followed by oblique deposition of a metal cap, avoids the use of high processing temperatures and the exposure of the organic materials to chemical degradation. The unpackaged devices show no sign of deterioration in room ambient when compared with conventional devices fabricated using low-resolution, shadow mask patterning. Furthermore, the devices are resistant to rapid degradation when operated in air for extended periods. This work illustrates a potential foundation for the volume production of …

Hybrid Quantum And Molecular Mechanics Embedded Cluster Models For Chemistry On Silicon And Silicon Carbide Surfaces, James R. Shoemaker

Theses and Dissertations

Fabrication of silicon carbide SiC semiconductor devices are of interest for aerospace applications because of their high-temperature tolerance. Growth of an insulating SiO₂ layer on SiC is a poorly understood process, and sometimes produces interface defects that degrade device performance. Accurate theoretical models of surface chemistry, using quantum mechanics QM, do not exist because of the huge computational cost of solving Schroedingers equation for a molecular cluster large enough to represent a surface. Molecular mechanics MM, which describes a molecule as a collection of atoms interacting through classical potentials, is a fast computational method, good at predicting molecular structure, …

Aspects Of Postcollision Interactions (Pci) Near The Ar L-Shell, James A.R. Samson, Y. Lu, Wayne C. Stolte

Chemistry and Biochemistry Faculty Research

In the present work we are interested in near-threshold photoionization experiments involving postcollision effects related to the Auger decay of a vacancy in the Ar L shell. In particular, we have measured the photoelectron energy spectrum resulting from the above postcollision interaction effects and have observed electrons produced by the process of electron capture and reemission.

Neutron Resonance Spectroscopy Of 107ag, And 109ag, L Y. Lowie, J D. Bowman, Bret E. Crawford, P P J. Delheij, T Haseyama, J N. Knudsen, A Masaike, Y Matsuda, G E. Mitchell, S I. Penttila, H Postma, N R. Roberson, S J. Seestrom, E I. Sharapov, Sharon L. Stephenson, Y-F Yen, V W. Yuan

Physics and Astronomy Faculty Publications

Parity violation has been observed in a number of previously unreported neutron resonances in silver. Analysis of these parity violation data requires improved neutron resonance spectroscopy. The neutron total cross section for natural silver was measured for E_n=10–800 eV with the time-of-flight method at the Los Alamos Neutron Scattering Center. The neutron capture reaction was studied with both a natural silver target and a highly enriched sample (98.29%) of ¹⁰⁷Ag. A total of 38 previously unreported resonances were observed. The combination of the two measurements allowed assignment of the newly observed resonances to ¹⁰⁷Ag or to …

Nondipole Resonant X-Ray-Raman Spectroscopy: Polarized Inelastic Scattering At The K Edge Of Cl2, J. D. Mills, J. A. Sheehy, T. A. Ferrett, S. H. Southworth, R. Mayer, Dennis W. Lindle, P. W. Langhoff

Chemistry and Biochemistry Faculty Research

Experimental and theoretical studies are reported on the inelastic (Raman) scattering of wavelength-selected polarized x rays from the K edge of gas-phase chlorine molecules. The polarized emission spectra exhibit prominent nondipole features consequent of phase variations of the incident and emitted radiation over molecular dimensions, as predicted by the Kramers-Heisenberg scattering formalism. Issues pursuant to the detection of core-hole localization by resonant Raman scattering from homonuclear diatomic molecules are critically examined. [S0031-9007(97)03486-8]

Core Scattering Of Stark Wave Packets, M. L. Naudeau, C. I. Sukenik, P. H. Bucksbaum

Physics Faculty Publications

We investigate the wave packet dynamics of electrons bound in the nonseparable potential of cesium in a static electric field using time-domain Ramsey interferometry. Specially shaped wave packets with low radial dispersion enable us to view the interaction between the wave packet and the atomic core. Experiments in cesium, together with quantum defect calculations of cesium and hydrogen, demonstrate changes in the motion and shape of these wave packets due to core scattering.

Features Of The Photon Statistics Of Two Coupled Electromagnetic Field Modes Under The Conditions Of Strong Mode Coupling, Mikhail E. Veisman, Serguei Y. Kalmykov

Serge Youri Kalmykov

The probabilities of transitions between the Fock states of two electromagnetic field modes under the influence of coupling between modes of finite duration are investigated. It is shown that the transition probability is a strongly oscillating function of the mode numbers of the photons. Under conditions in which the coupling frequency exceeds the geometric mean of the mode frequencies (strong coupling), large numbers of photons are excited in the mode with the lower frequency. The excitation of a two-dimensional radiation field oscillator and the ‘‘red’’ symmetry of the transition probabilities can be attributed to instability of the classical two-dimensional oscillator …

On The Stark Broadening Parameters Of The Two Nii Spectral Lines Of The 3d-4f Transition, Vladimir Milosavljevic, Stevan Djenize

Articles

Stark parameters (width and shift) of two singly ionized nitrogen spectral lines, that belong to 3d-4f transition have been measured in a linear pulsed, low pressure, arc discharge in the nitrogen-oxygen plasma at a 54000 K electron temperature and at a 2.8×10 23 m−3 electron density. The measured values have been compared to the existing experimental and calculated data

A Surface-Emitting Vacuum-Deposited Organic Light Emitting Device, V. Bulovic, Peifang Tian, P. E. Burrows, M. R. Gokhale, S. R. Forrest, M. E. Thompson

Peifang Tian

We demonstrate a vacuum-deposited organic light emitting device which emits from its top surface through a transparent indium-tin-oxide anode. This device employs a novel protective cap layer which prevents damage to the organic layers during sputter deposition of the anode, while also improving hole injection. Mechanisms of current transport and carrier injection from the contacts are investigated. This device configuration allows for integration of organic light emitting devices with n-channel field effect transistors used in display active matrix backplanes.

Breakdown Of The Independent Particle Approximation In High-Energy Photoionization, E. W. B. Dias, H. S. Chakraborty, P. C. Deshmukh, S. T. Manson, Oliver Hemmers, P. Glans, D. Hansen, H. Wang, S. B. Whitfield, Dennis W. Lindle, R. Wehlitz, Jon C. Levin, I. A. Sellin

Environmental Studies Faculty Publications

The independent particle approximation is shown to break down for the photoionization of both inner and outer nℓ (ℓ>0) electrons of all atoms, at high enough energy, owing to interchannel interactions with the nearby ns photoionization channels. The effect is illustrated for Ne 2p in the 1 keV photon energy range through a comparison of theory and experiment. The implications for x-ray photoelectron spectroscopy of molecules and condensed matter are discussed.

Kinetics And Spectroscopy Of Brno, Patrick E. Godfrey

Theses and Dissertations

The infrared spectra and photochemistry of nitrosyl bromide, BrNO, are important to characterizing the performance of a recently demonstrated Br(²P_1/2)-NO(v=2 → v=1) transfer laser pumped by photolysis of iodine molecules. This wavelength agile, mid-infrared laser may be a desirable source for remote sensing and infrared countermeasures missions. Nitrosyl bromide also plays a role in the destruction of stratospheric ozone. The kinetics of BrNO formation and destruction were examined using time-resolved photolysis techniques. The equilibrium constant for the dark reaction Br₂ + 2NO (reversible reaction) 2BrNO was determined as K_eq 168 ± 23 /atm and …

Correlated And Coherent States Of The Two-Dimensional Quantum Oscillator With A Nonstationary Mode Coupling, Mikhail E. Veisman, Serguei Y. Kalmykov

Serge Youri Kalmykov

We investigate the squeezing and correlation phenomena of quantum fluctuations in correlated coherent states of a system of two oscillatory modes with a parametric coupling of the coordinates. In the regime of strong coupling between the modes, we discover an excitation and a strong correlation of the quantum fluctuations. The matrix of dispersions and covariances of the coordinates and momenta is found explicitly with the help of the method of the linear quantum integrals of motion.

Angle-Resolved Study Of Ar 2p₁/₂,₃/₂⁻1Ns,D Resonant Auger Decay, Marc Andrew Humphrey

Honors Theses

Angle-resolved measurements of the Ar 2p_1/2,3/2^-14s,3d,4d and 2p_3/2^-14s,3d,4d resonant Auger transitions have been carried out using photons from an undulator beamline at the Advanced Light Source of Lawrence Berkeley National Laboratory. The intensity distributions and angular distribution anisotropy (β) parameters have been reported for nearly all of the possible 3p⁴nl final ionic states. These results further verify the predictions of the spectator model for the 2p_1/2,3/2^-14s resonances and the subsequent breakdown of this model for the 2p_1/2,3/2^-13d and 2p_1/2,3/2^-14d relative intensities. This work …

Two-Photon Optogalvanic Spectra Of Argon: Odd Parity Rydberg States, Naveed Piracha, M. Baig, S. Khan, B. Suleman

Naveed K. Piracha

Extensive new data on the odd-parity, single-colour, two-photon optogalvanic spectra of argon in the visible region is reported using an excimer-pumped dye laser in conjunction with an argon discharge cell. The experimental technique enables us to record a pure two-photon spectrum in a region which is dominated by one-photon transitions. A large number of two-photon transitions, originating from the two metastable states [...] and [...] to the excited states of configurations [...] (J=0, 2) and [...] (J = 0 - 4) of argon, has been recorded and arranged into 10 Rydberg series. The interchannel interactions among the [...] and the …

Roughening And Preroughening Of Diamond-Cubic {111} Surfaces, Donald L. Woodraska, John A. Jaszczak

Department of Physics Publications

A solid-on-solid model for {111} surfaces of diamond-cubic materials that correctly takes into account the diamond-cubic crystal structure has been developed for Monte Carlo simulation. In addition to a roughening transition at temperature T_R, a distinct preroughening transition at T_PR≈0.43T_R is indicated by divergences in the surface specific heat and order-parameter susceptibility. Preroughening appears to arise naturally in our nearest-neighbor bond model from the entropic freedom available in the nontrivial crystal structure. Preroughening is shown to dramatically lower the nucleation barrier for growth and etching at low driving forces.

Quantum Coherence In Small Antiferromagnets, S. E. Barnes, R. Ballou, B. Barbara, J. Strelen

Physics Articles and Papers

An antiferromagnetic particle with an excess spin j⃗ has 2 degrees of freedom. The one associated with j⃗ is ferromagnetic, while the antiferromagnetic behavior involves Néel vector n⃗. It is shown that the spin-parity effect described by Loss et al. has to do with the ferromagnetic degree of freedom and does not imply the localization of n⃗ for small enough particles for half-integer spin. It is also shown that the tunnel splitting associated with n⃗ is insensitive to applied fields.

Separating K+/- From Pi+/- Using In-Flight Decays To Mu+/- + Nu, Wilfred J. Braithwaite, Edwin S. Braithwaite

Journal of the Arkansas Academy of Science

A method is presented for completely distinguishing between charged kaons and charged pions by using their charged muon (plus neutrino) decays (with neutrinos undetected) for meson laboratory momenta up to 1000 MeV/c. When either a charged kaon or a charged pion decays into a muon and a neutrino, momentum-energy (four-momentum) conservation will be used to provide unique "kinematic trajectories" for distinguishing kaon decays from pion decays when the change in three-momentum of the muon from that of either parent kaon or pion is measured (or simulated). Ina magnetic field, observation of a tracked particle showing a "kink" and/or a change …

Coplanarity Test For Selecting A Pair Of Charged-Particle Tracks Resulting From A Single Neutral-Particle Decay, Edwin S. Braithwaite, Wilfred J. Braithwaite

Journal of the Arkansas Academy of Science

It is hard to determine directly the position of a neutral subatomic particle, but when such a particle decays into a pair of charged particles, it is easy to determine the positions of the charged decay particles and thereby infer the position of the parent particle at the time of its decay. A minimum of two coordinate points for each of the two decay particles is needed to reconstruct the position of the parent vertex. The mathematics of the reconstruction process is inherently interesting, and it can be used to demonstrate to students the utility of some of the most …

Collision-Induced Secondary Electron And Negative Ion Emission From Metallic Surfaces, John Christopher Tucek

Dissertations, Theses, and Masters Projects

Absolute yields of negative ions and secondary electrons resulting from collisions of positive sodium ions (Na{dollar}\sp{lcub}+{rcub}){dollar} with polycrystalline aluminum (Al) and molybdenum (Mo) surfaces and the Mo (100) surface have been measured as a function of the oxygen (O) coverage, from none up to several monolayers, for impact energies, E {dollar}<{dollar} 500 eV. Negative oxygen ions (O{dollar}\sp{lcub}-{rcub}){dollar} are found to be the dominant sputtered negative ions and for the three surfaces at all O coverages and Na{dollar}\sp{lcub}+{rcub}{dollar} impact energies. The O{dollar}\sp{lcub}-{rcub}{dollar} and secondary electron yields share a common impact energy threshold at {dollar}\rm E\sb{lcub}th{rcub}\approx 50{dollar} eV, and both have a strong dependence on the oxygen coverage of the surface.;The kinetic energy distributions of the secondary electrons and sputtered O{dollar}\sp{lcub}-{rcub}{dollar} were determined as functions of O coverages and impact energies. The O{dollar}\sp{lcub}-{rcub}{dollar} distributions are characterized by a narrow, low energy peak (at {dollar}\sim{dollar}1-2 eV) followed by a low level, high energy tail. The secondary electrons have a narrow (FWHM {dollar}\sim{dollar} 1-2 eV) kinetic energy distribution, centered essentially at the same most probable kinetic energy as the ions. The shapes of the respective distributions and the most probable kinetic energies are essentially invariant with the impact energy, O coverage and the metal surface.;The results were analyzed in terms of conventional collision cascade model, but the calculation could not be fitted to the experimental results. An electronic excitation mechanism is proposed to augment the collision cascade and to provide a mechanism for secondary electron emission. In the model, adsorbed O, which resides on the surface essentially as O{dollar}\sp{lcub}-{rcub},{dollar} is collisionally excited into an (MO{dollar}\sp{lcub}-{rcub})\sp*{dollar} repulsive state, and as the O{dollar}\sp{lcub}-{rcub}{dollar} exits the surface along the surface potential energy curve, it can decay by emission of an electron to the metal or to the vacuum, or it can survive as an ion. The parameters of this model can be adjusted such that the calculated kinetic energy distribution, together with that of the collision cascade, can reasonably reproduce the experimental observations for the ions and provide a reasonable fit to the corresponding electron kinetic energy distributions as well.

Characterization Of Iron Oxides And Atmospheric Corrosion Of Steel, Sei Jin Oh

Physics Theses & Dissertations

The study of corrosion behavior was performed using three different analytical techniques, which provided information on the formation, development and layering of iron oxides on the corrosion products as a function of atmospheric conditions, exposure time and type of steel. In particular, the protective layer formed on weathering steel was investigated as a function of different amounts of alloying elements in the steel, atmospheric conditions and exposure times. Combined together, the results provided a better understanding of the atmospheric corrosion behavior of steel, and formed a part of database of the atmospheric corrosion characteristics.

Accurate characterization of the iron oxides …