Latest content added for UNT Digital Library Partner: UNT Librarieshttp://digital.library.unt.edu/explore/partners/UNT/browse/?fq=str_degree_discipline:Physics&start=402014-03-26T09:30:20-05:00UNT LibrariesThis is a custom feed for browsing UNT Digital Library Partner: UNT LibrariesStructural and Photoelectron Emission Properties of Chemical Vapor Deposition Grown Diamond Films2014-03-26T09:30:20-05:00http://digital.library.unt.edu/ark:/67531/metadc279053/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc279053/"><img alt="Structural and Photoelectron Emission Properties of Chemical Vapor Deposition Grown Diamond Films" title="Structural and Photoelectron Emission Properties of Chemical Vapor Deposition Grown Diamond Films" src="http://digital.library.unt.edu/ark:/67531/metadc279053/thumbnail/"/></a></p><p>The effects of methane (CH4), diborone (B2H6) and nitrogen (N2) concentrations on the structure and photoelectron emission properties of chemical vapor deposition (CVD) polycrystalline diamond films were studied. The diamond films were grown on single-crystal Si substrates using the hot-tungsten filament CVD technique. Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) were used to characterize the different forms of carbon in the films, and the fraction of sp3 carbon to sp3 plus sp2 carbon at the surface of the films, respectively. Scanning electron microscopy (SEM) was used to characterize the surface morphology of the films. The photoelectron emission properties were determined by measuring the energy distributions of photoemitted electrons using ultraviolet photoelectron spectroscopy (UPS), and by measuring the photoelectric current as a function of incident photon energy.</p>On Delocalization Effects in Multidimensional Lattices2014-03-26T09:30:20-05:00http://digital.library.unt.edu/ark:/67531/metadc278868/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc278868/"><img alt="On Delocalization Effects in Multidimensional Lattices" title="On Delocalization Effects in Multidimensional Lattices" src="http://digital.library.unt.edu/ark:/67531/metadc278868/thumbnail/"/></a></p><p>A cubic lattice with random parameters is reduced to a linear chain by the means of the projection technique. The continued fraction expansion (c.f.e.) approach is herein applied to the density of states. Coefficients of the c.f.e. are obtained numerically by the recursion procedure. Properties of the non-stationary second moments (correlations and dispersions) of their distribution are studied in a connection with the other evidences of transport in a one-dimensional Mori chain. The second moments and the spectral density are computed for the various degrees of disorder in the prototype lattice. The possible directions of the further development are outlined. The physical problem that is addressed in the dissertation is the possibility of the existence of a non-Anderson disorder of a specific type. More precisely, this type of a disorder in the one-dimensional case would result in a positive localization threshold. A specific type of such non-Anderson disorder was obtained by adopting a transformation procedure which assigns to the matrix expressing the physics of the multidimensional crystal a tridiagonal Hamiltonian. This Hamiltonian is then assigned to an equivalent one-dimensional tight-binding model. One of the benefits of this approach is that we are guaranteed to obtain a linear crystal with a positive localization threshold. The reason for this is the existence of a threshold in a prototype sample. The resulting linear model is found to be characterized by a correlated and a nonstationary disorder. The existence of such special disorder is associated with the absence of Anderson localization in specially constructed one-dimensional lattices, when the noise intensity is below the non-zero critical value. This work is an important step towards isolating the general properties of a non-Anderson noise. This gives a basis for understanding of the insulator to metal transition in a linear crystal with a subcritical noise.</p>Scanning Tunneling Microscopy of Epitaxial Diamond (110) and (111) Films and Field Emission Properties of Diamond Coated Molybdenum Microtips2014-03-26T09:30:20-05:00http://digital.library.unt.edu/ark:/67531/metadc279160/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc279160/"><img alt="Scanning Tunneling Microscopy of Epitaxial Diamond (110) and (111) Films and Field Emission Properties of Diamond Coated Molybdenum Microtips" title="Scanning Tunneling Microscopy of Epitaxial Diamond (110) and (111) Films and Field Emission Properties of Diamond Coated Molybdenum Microtips" src="http://digital.library.unt.edu/ark:/67531/metadc279160/thumbnail/"/></a></p><p>The growth mechanism of chemical vapor deposition (CVD) grown homo-epitaxial diamond (110) and (111) films was studied using ultrahigh vacuum (UHV) scanning tunneling microscopy (STM). In addition, the field emission properties of diamond coated molybdenum microtips were studied as a function of exposure to different gases.</p>Scaling Behaviors and Mechanical Properties of Polymer Gels2014-03-26T09:30:20-05:00http://digital.library.unt.edu/ark:/67531/metadc279278/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc279278/"><img alt="Scaling Behaviors and Mechanical Properties of Polymer Gels" title="Scaling Behaviors and Mechanical Properties of Polymer Gels" src="http://digital.library.unt.edu/ark:/67531/metadc279278/thumbnail/"/></a></p><p>Polymer gels undergo a volume phase transition in solvent in response to an infinitesimal environmental change. This remarkable phenomenon has resulted in many potential applications of polymer gels. The understanding of its mechanical properties has both scientific and technological importance. For this purpose, we have developed a novel method for measuring Poisson's ratio, which is one of the most important parameters determining the mechanical property of gels. Using this method, Poisson's ratio in N-isopropyacrylamide (NIPA) and polyacrylamide (PAAM) gels has been studied.</p>Accelerator Mass Spectrometry Studies of Highly Charged Molecular Ions2014-03-26T09:30:20-05:00http://digital.library.unt.edu/ark:/67531/metadc279004/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc279004/"><img alt="Accelerator Mass Spectrometry Studies of Highly Charged Molecular Ions" title="Accelerator Mass Spectrometry Studies of Highly Charged Molecular Ions" src="http://digital.library.unt.edu/ark:/67531/metadc279004/thumbnail/"/></a></p><p>The existence of singly, doubly, and triply charged diatomic molecular ions was observed by using an Accelerator Mass Spectrometry (AMS) technique. The mean lifetimes of 3 MeV boron diatomic molecular ions were measured. No isotopic effects on the mean lifetimes of boron diatomic molecules were observed for charge state 3+. Also, the mean lifetime of SiF^3+ was measured.</p>Experimental Synchronization of Chaotic Attractors Using Control2014-03-26T09:30:20-05:00http://digital.library.unt.edu/ark:/67531/metadc278971/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc278971/"><img alt="Experimental Synchronization of Chaotic Attractors Using Control" title="Experimental Synchronization of Chaotic Attractors Using Control" src="http://digital.library.unt.edu/ark:/67531/metadc278971/thumbnail/"/></a></p><p>The focus of this thesis is to theoretically and experimentally investigate two new schemes of synchronizing chaotic attractors using chaotically operating diode resonators. The first method, called synchronization using control, is shown for the first time to experimentally synchronize dynamical systems. This method is an economical scheme which can be viably applied to low dimensional dynamical systems. The other, unidirectional coupling, is a straightforward means of synchronization which can be implemented in fast dynamical systems where timing is critical. Techniques developed in this work are of fundamental importance for future problems regarding high dimensional chaotic dynamical systems or arrays of mutually linked chaotically operating elements.</p>Charge State Dependence of M-Shell X-Ray Production in 67Ho by 2-12 MeV Carbon Ions2014-03-26T09:30:20-05:00http://digital.library.unt.edu/ark:/67531/metadc278725/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc278725/"><img alt="Charge State Dependence of M-Shell X-Ray Production in 67Ho by 2-12 MeV Carbon Ions" title="Charge State Dependence of M-Shell X-Ray Production in 67Ho by 2-12 MeV Carbon Ions" src="http://digital.library.unt.edu/ark:/67531/metadc278725/thumbnail/"/></a></p><p>The charge state dependence of M-shell x-ray production cross sections of 67HO bombarded by 2-12 MeV carbon ions with and without K-vacancies are reported. The experiment was performed using an NEC 9SDH-2 tandem accelerator at the Ion Beam Modification and Analysis Laboratory of the University of North Texas. The high charge state carbon ions were produced by a post-accelerator stripping gas cell. Ultra-clean holmium targets were used in ion-atom collision to generate M-shell x rays at energies from 1.05 to 1.58 keV. The x-ray measurements were made with a windowless Si(Li) x-ray detector that was calibrated using radiative sources, particle induced x-ray emission (PIXE), and the atomic field bremsstrahlung (AFB) techniques.</p>Deterministic Brownian Motion2014-03-26T09:30:20-05:00http://digital.library.unt.edu/ark:/67531/metadc279262/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc279262/"><img alt="Deterministic Brownian Motion" title="Deterministic Brownian Motion" src="http://digital.library.unt.edu/ark:/67531/metadc279262/thumbnail/"/></a></p><p>The goal of this thesis is to contribute to the ambitious program of the foundation of developing statistical physics using chaos. We build a deterministic model of Brownian motion and provide a microscpoic derivation of the Fokker-Planck equation. Since the Brownian motion of a particle is the result of the competing processes of diffusion and dissipation, we create a model where both diffusion and dissipation originate from the same deterministic mechanism - the deterministic interaction of that particle with its environment. We show that standard diffusion which is the basis of the Fokker-Planck equation rests on the Central Limit Theorem, and, consequently, on the possibility of deriving it from a deterministic process with a quickly decaying correlation function. The sensitive dependence on initial conditions, one of the defining properties of chaos insures this rapid decay. We carefully address the problem of deriving dissipation from the interaction of a particle with a fully deterministic nonlinear bath, that we term the booster. We show that the solution of this problem essentially rests on the linear response of a booster to an external perturbation. This raises a long-standing problem concerned with Kubo's Linear Response Theory and the strong criticism against it by van Kampen. Kubo's theory is based on a perturbation treatment of the Liouville equation, which, in turn, is expected to be totally equivalent to a first-order perturbation treatment of single trajectories. Since the boosters are chaotic, and chaos is essential to generate diffusion, the single trajectories are highly unstable and do not respond linearly to weak external perturbation. We adopt chaotic maps as boosters of a Brownian particle, and therefore address the problem of the response of a chaotic booster to an external perturbation. We notice that a fully chaotic map is characterized by an invariant measure which is a continuous function of the control parameters of the map. Consequently if the external perturbation is made to act on a control parameter of the map, we show that the booster distribution undergoes slight modifications as an effect of the weak external perturbation, thereby leading to a linear response of the mean value of the perturbed variable of the booster. This approach to linear response completely bypasses the criticism of van Kampen. The joint use of these two phenomena, diffusion and friction stemming from the interaction of the Brownian particle with the same booster, makes the microscopic derivation of a Fokker-Planck equation and Brownian motion, possible.</p>Linear, Nonlinear Optical and Transport Properties of Quantum Wells Composed of Short Period Strained InAs/GaAs Superlattices2014-03-26T09:30:20-05:00http://digital.library.unt.edu/ark:/67531/metadc278855/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc278855/"><img alt="Linear, Nonlinear Optical and Transport Properties of Quantum Wells Composed of Short Period Strained InAs/GaAs Superlattices" title="Linear, Nonlinear Optical and Transport Properties of Quantum Wells Composed of Short Period Strained InAs/GaAs Superlattices" src="http://digital.library.unt.edu/ark:/67531/metadc278855/thumbnail/"/></a></p><p>In this work, ordered all-binary short-period strained InAs/GaAs superlattice quantum wells were studied as an alternative to strained ternary alloy InGaAs/GaAs quantum wells. InGaAs quantum wells QWs have been of great interest in recent years due to the great potential applications of these materials in future generations of electronic and optoelectronic devices. The all binary structures are expected to have all the advantages of their ternary counterparts, plus several additional benefits related to growth, to the elimination of alloy disorder scattering and to the presence of a higher average indium content.</p>Magneto-Optical and Chaotic Electrical Properties of n-InSb2014-03-26T09:30:20-05:00http://digital.library.unt.edu/ark:/67531/metadc279131/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc279131/"><img alt="Magneto-Optical and Chaotic Electrical Properties of n-InSb" title="Magneto-Optical and Chaotic Electrical Properties of n-InSb" src="http://digital.library.unt.edu/ark:/67531/metadc279131/thumbnail/"/></a></p><p>This thesis investigation concerns the optical and nonlinear electrical properties of n-InSb. Two specific areas have been studied. First is the magneto-optical study of magneto-donors, and second is the nonlinear dynamic study of nonlinear and chaotic oscillations in InSb. The magneto-optical study of InSb provides a physical picture of the magneto-donor levels, which has an important impact on the physical model of nonlinear and chaotic oscillations. Thus, the subjects discussed in this thesis connect the discipline of semiconductor physics with the field of nonlinear dynamics.</p>