Latest content added for UNT Digital Library Partner: UNT Librarieshttp://digital.library.unt.edu/explore/partners/UNT/browse/?fq=str_degree_discipline:Physics&fq=untl_collection:UNTETD&fq=untl_decade:1990-19992014-03-26T09:30:20-05:00UNT LibrariesThis is a custom feed for browsing UNT Digital Library Partner: UNT LibrariesQuantum-Confined CdS Nanoparticles on DNA Templates2014-03-26T09:30:20-05:00http://digital.library.unt.edu/ark:/67531/metadc279352/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc279352/"><img alt="Quantum-Confined CdS Nanoparticles on DNA Templates" title="Quantum-Confined CdS Nanoparticles on DNA Templates" src="http://digital.library.unt.edu/ark:/67531/metadc279352/thumbnail/"/></a></p><p>As electronic devices became smaller, interest in quantum-confined semiconductor nanostructures increased. Self-assembled mesoscale semiconductor structures of II-VI nanocrystals are an especially exciting subject because of their controllable band gap and unique photophysical properties. Several preparative methods to synthesize and control the sizes of the individual nanocrystallites and the electronic and optical properties have been intensively studied. Fabrication of patterned nanostructures composed of quantum-confined nanoparticles is the next step toward practical applications. We have developed an innovative method to fabricate diverse nanostructures which relies on the size and a shape of a chosen deoxyribonucleic acid (DNA) template.</p>Structural 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>Dielectric Relaxation of Aqueous Solutions at Microwave Frequencies for 3[less than or equal to]f[less than or equal to]35 GHz. Using a Loaded Microwave Cavity Operating in the TM010 Mode2014-03-26T09:30:20-05:00http://digital.library.unt.edu/ark:/67531/metadc279039/<p><a href="http://digital.library.unt.edu/ark:/67531/metadc279039/"><img alt="Dielectric Relaxation of Aqueous Solutions at Microwave Frequencies for 3[less than or equal to]f[less than or equal to]35 GHz. Using a Loaded Microwave Cavity Operating in the TM010 Mode" title="Dielectric Relaxation of Aqueous Solutions at Microwave Frequencies for 3[less than or equal to]f[less than or equal to]35 GHz. Using a Loaded Microwave Cavity Operating in the TM010 Mode" src="http://digital.library.unt.edu/ark:/67531/metadc279039/thumbnail/"/></a></p><p>The frequency dependence and temperature dependence of the complex dielectric constant of water is of great interest. The temperature dependence of the physical properties of water given in the literature, specific heat, thermal conductivity, electric conductivity, pH, etc. are compared to the a. c. (microwave) and d. c. conductivity of water with a variety of concentration of different substances such as HC1, NaCl, HaS04, etc. When each of these properties is plotted versus inverse absolute temperature, it can be seen that each sample shows "transition temperatures". In this work, Slater's perturbation equations for a resonant microwave cavity were used to analyze the experimental results for the microwave data.</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>