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UNT Theses and Dissertations
 Synthesis Strategies and a Study of Properties of Narrow and Wide Band Gap Nanowires
 Various techniques to synthesize nanowires and nanotubes as a function of growth temperature and time were investigated. These include growth of nanowires by a chemical vapor deposition (CVD) system using vaporliquidsolid (VLS) growth mechanism and electrochemical synthesis of nanowires and nanotubes. Narrow band gap InSb Eg = 0.17 eV at room temp) nanowires were successively synthesized. Using a phase diagram, the transition of the nanowire from metallic semiconducting semimetallic phase was investigated. A thermodynamic model is developed to show that the occurrence of native defects in InSb nanowires influenced by the nanowire growth kinetics and thermodynamics of defect formation. Wide band gap ZnO (Eg = 3.34 eV) and In2O3 (3.7 eV) were also synthesized. ZnO nanowires and nanotubes were successfully doped with a transition metal Fe, making it a Dilute Magnetic Semiconductor of great technological relevance. Structural and electronic characterizations of nanowires were studied for different semiconducting, metallic and semimetallic nanowires. Electron transport measurements were used to estimate intrinsic material parameters like carrier concentration and mobility. An efficient gas sensing device using a single In2O3 nanowire was studied and which showed sensitivity to reducing gas like NH3 and oxidizing gas like O2 gas at room temperature. The efficiency of the gas sensing device was found to be sensitive to the nature of contacts as well as the presence of surface states on the nanowire. digital.library.unt.edu/ark:/67531/metadc499984/
 Synthesis, Characterization, Structural, and Optical Properties of Zinc Oxide Nanostructures Embedded in Silicon Based Substrates
 Structural and optical properties of ZnO nanostructures synthesized by low energy ion implantation technique were examined. ZnO molecular ions were implanted into Si/SiO2 substrates at room temperature and then furnace annealed under different temperatures and environments. In all asimplanted samples only Zn nanostructures with varying diameters distributed into the Si/SiO2 matrices were observed. No trace of ZnO was found. The distributions of Zn nanostructures in Si/SiO2 closely matched results from Stopping and Range of Ions in Matter (SRIM) simulations. During annealing at 750 oC, Zn diffused both toward and away from the surface of the substrate and combine with oxygen to form ZnO nanostructures. At higher annealing temperatures ZnO bonding started to break down and transfer to zinc silicate (Zn2SiO4), and at 900 oC the ZnO was completely converted into Zn2SiO4. The average sizes of Zn/ZnO nanostructures depended on the ion fluence. If the fluence increased the average sizes of nanostructures also increased and vice versa. For room temperature photoluminescence (RTPL), bandedge emission in the ultraviolet (UV) region was observed from all samples annealed at 700 oC/750 oC and were slightly blue shifted as compare to bulk ZnO. Donorbound exciton (D,X) and acceptorbound exciton (A,X) transitions were observed in low temperature photoluminescence (PL). The lifetime of both donorbound excitonic emission (D, X) and acceptorbound excitonic emission (A, X) were found to be in the picosecond (ps) range. digital.library.unt.edu/ark:/67531/metadc500222/
 The Effects of Residual Gases on the Field Emission Properties of Zno, Gan, Zns Nanostructures, and the Effects of Light on the Resistivity of Graphene
 In this dissertation, I present that at a vacuum of 3×107 Torr, residual O2, CO2, H2 and Ar exposure do not significantly degrade the field emission (FE) properties of ZnO nanorods, but N2 exposure significantly does. I propose that this could be due to the dissociation of N2 into atomic nitrogen species and the reaction of such species with ZnO. I also present the effects of O2, CO2, H2O, N2, H2, and Ar residual gas exposure on the FE properties of GaN and ZnS nanostructure. A brief review of growth of ZnO, GaN and ZnS is provided. In addition, Cs deposition on GaN nanostructures at ultrahigh vacuum results in 30% decrease in turnon voltage and 60% in work function. The improvement in FE properties could be due to a Csinduced spacecharge layer at the surface that reduces the barrier for FE and lowers the work function. I describe a new phenomenon, in which the resistivity of CVDgrown graphene increases to a higher saturated value under light exposure, and depends on the wavelength of the light—the shorter the wavelength, the higher the resistivity. Firstprinciple calculations and theoretical analysis based on density functional theory show that (1) a water molecule close to a graphene defect is easier to be split than that of the case of no defect existing and (2) there are a series of metastable partially disassociated states for an interfacial water molecule. Calculated disassociation energies are from 2.5 eV to 4.6 eV, that match the experimental observation range of light wavelength from visible to 254 nm UV light under which the resistivity of CVDgrown graphene is increased. digital.library.unt.edu/ark:/67531/metadc500202/
 Effects of Quantum Coherence and Interference

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Quantum coherence and interference (QCI) is a phenomenon that takes place in all multilevel atomic systems interacting with multiple lasers. In this work QCI is used to create several interesting effects like lasing without inversion (LWI), controlling group velocity of light to extreme values, controlling the direction of propagation through nonlinear phase matching condition and for controlling the correlations in field fluctuations. Controlling group velocity of light is very interesting because of many novel applications it can offer. One of the unsolved problems in this area is to achieve a slow and fast light which can be tuned continuously as a function of frequency. We describe a method for creation of tunable slow and fast light by controlling intensity of incident laser fields using QCI effects. Lasers are not new to the modern world but an extreme ultraviolet laser or a xray laser is definitely one of the most desirable technologies today. Using QCI, we describe a method to realize lasing at high frequencies by creating lasing without inversion. Role of QCI in creating correlations and anticorrelations, which are generated by vacuum fluctuations, in a three level lambda system coupled to two strong fields is discussed. digital.library.unt.edu/ark:/67531/metadc500094/  How Cooperative Systems Respond to External Forces
 Cooperative interactions permeate through nature, bringing about emergent behavior and complexity. Using a simple cooperative model, I illustrate the mean field dynamics that occur at the critical point of a second order phase transition in the framework of Langevin equations. Through this formalism I discuss the response, both linear and nonlinear, to external forces. Emphasis is placed on how information is transferred from one individual to another in order to facilitate the collective response of the cooperative network to a localized perturbation. The results are relevant to a wide variety of systems, ranging from nematic liquid crystals, to flocks and swarms, social groups, and neural networks. digital.library.unt.edu/ark:/67531/metadc500014/
 An Electro Magnetostatic Field for Confinement of Charged Particle Beams and Plasmas
 A system is presented that is capable of confining an ion beam or plasma within a region that is essentially free of applied fields. An Artificially Structured Boundary (ASB) produces a spatially periodic set of magnetic field cusps that provides charged particle confinement. Electrostatic plugging of the magnetic field cusps enhances confinement. An ASB that has a small spatial period, compared to the dimensions of a confined plasma, generates electro magnetostatic fields with a short range. An ASBlined volume thus constructed creates an effectively field free region near its center. It is assumed that a nonneutral plasma confined within such a volume relaxes to a MaxwellBoltzmann distribution. Space charge based confinement of a second species of charged particles is envisioned, where the second species is confined by the space charge of the first nonneutral plasma species. An electron plasma confined within an ASBlined volume can potentially provide confinement of a positive ion beam or positive ion plasma. Experimental as well as computational results are presented in which a plasma or charged particle beam interact with the electro magnetostatic fields generated by an ASB. A theoretical model is analyzed and solved via selfconsistent computational methods to determine the behavior and equilibrium conditions of a relaxed plasma. The equilibrium conditions of a relaxed two species plasma are also computed. In such a scenario, space charge based electrostatic confinement is predicted to occur where a second plasma species is confined by the space charge of the first plasma species. An experimental apparatus with cylindrical symmetry that has its interior surface lined with an ASB is presented. This system was developed by using a simulation of the electro magnetostatic fields present within the trap to guide mechanical design. The construction of the full experimental apparatus is discussed. Experimental results that show the characteristics of electron beam transmission through the experimental apparatus are presented. A description of the experimental hardware and software used for trapping a charged particle beam or plasma is also presented. digital.library.unt.edu/ark:/67531/metadc500001/
 Novel SemiConductor Material Systems: Molecular Beam Epitaxial Growth and Characterization
 Semiconductor industry relies heavily on silicon (Si). However, Si is not a directband gap semiconductor. Consequently, Si does not possess great versatility for multifunctional applications in comparison with the direct bandgap IIIV semiconductors such as GaAs. To bridge this gap, what is ideally required is a semiconductor material system that is based on silicon, but has significantly greater versatility. While sparsely studied, the semiconducting silicides material systems offer great potential. Thus, I focused on the growth and structural characterization of ruthenium silicide and osmium silicide material systems. I also characterized iron silicon germanide films using extended xray absorption fine structure (EXAFS) to reveal phase, semiconducting behavior, and to calculate nearest neighbor distances. The choice of these silicides material systems was due to their theoretically predicted and/or experimentally reported direct band gaps. However, the challenge was the existence of more than one stable phase/stoichiometric ratio of these materials. In order to possess the greatest control over the growth process, molecular beam epitaxy (MBE) has been employed. Structural and film quality comparisons of asgrown versus annealed films of ruthenium silicide are presented. Structural characterization and film quality of MBE grown ruthenium silicide and osmium silicide films via in situ and ex situ techniques have been done using reflection high energy electron diffraction, scanning tunneling microscopy, atomic force microscopy, crosssectional scanning electron microscopy, xray photoelectron spectroscopy, and micro Raman spectroscopy. This is the first attempt, to the best of our knowledge, to grow osmium silicide thin films on Si(100) via the template method and compare it with the regular MBE growth method. The pros and cons of using the MBE template method for osmium silicide growth are discussed, as well as the structural differences of the asgrown versus annealed films. Future perspectives include further studies on other semiconducting silicides material systems in terms of growth optimization and characterization. digital.library.unt.edu/ark:/67531/metadc490047/
 Cooperationinduced Criticality in Neural Networks
 The human brain is considered to be the most complex and powerful informationprocessing device in the known universe. The fundamental concepts behind the physics of complex systems motivate scientists to investigate the human brain as a collective property emerging from the interaction of thousand agents. In this dissertation, I investigate the emergence of cooperationinduced properties in a system of interacting units. I demonstrate that the neural network of my research generates a series of properties such as avalanche distribution in size and duration coinciding with the experimental results on neural networks both in vivo and in vitro. Focusing attention on temporal complexity and fractal index of the system, I discuss how to define an order parameter and phase transition. Criticality is assumed to correspond to the emergence of temporal complexity, interpreted as a manifestation of nonPoisson renewal dynamics. In addition, I study the transmission of information between two networks to confirm the criticality and discuss how the network topology changes over time in the light of Hebbian learning. digital.library.unt.edu/ark:/67531/metadc283813/
 Electron Density and Collision Frequency Studies Using a Resonant Microwave Cavity as a Probe
 Electron densities and collision frequencies were obtained on a number of gases in a dc discharge at low pressures (0.702mm of Hg). These measurements were performed by microwave probing of a filament of the dc discharge placed coaxially in a resonant cavity operating in a TM₀₁₀ mode. The equipment and techniques for making the microwave measurements employing the resonant cavity are described. One of the main features of this investigation is the technique of differentiating the resonance signal of the loaded cavity in order to make accurate measurements of the resonant frequency and halfpower point frequencies. digital.library.unt.edu/ark:/67531/metadc279091/
 Magnetomorphic Oscillations in Zinc
 In making this study it is important to search for ways to enhance and, if possible, make detection of MMO signals simpler in order that this technique for obtaining FS measurements may be extended to other materials. This attempt to improve measurement techniques has resulted in a significant discovery: the eddycurrent techniques described in detail in a later section which should allow MMO to be observed and sensitively measured in many additional solids. The second major thrust of the study has been to use the newly discovered eddycurrent technique in obtaining the first indisputable observation of MMO in zinc. digital.library.unt.edu/ark:/67531/metadc279266/
 QuantumConfined CdS Nanoparticles on DNA Templates
 As electronic devices became smaller, interest in quantumconfined semiconductor nanostructures increased. Selfassembled mesoscale semiconductor structures of IIVI 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 quantumconfined 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. digital.library.unt.edu/ark:/67531/metadc279352/
 Structural and Photoelectron Emission Properties of Chemical Vapor Deposition Grown Diamond Films
 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 singlecrystal Si substrates using the hottungsten filament CVD technique. Raman spectroscopy and xray 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. digital.library.unt.edu/ark:/67531/metadc279053/
 On Delocalization Effects in Multidimensional Lattices
 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 nonstationary second moments (correlations and dispersions) of their distribution are studied in a connection with the other evidences of transport in a onedimensional 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 nonAnderson disorder of a specific type. More precisely, this type of a disorder in the onedimensional case would result in a positive localization threshold. A specific type of such nonAnderson 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 onedimensional tightbinding 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 onedimensional lattices, when the noise intensity is below the nonzero critical value. This work is an important step towards isolating the general properties of a nonAnderson noise. This gives a basis for understanding of the insulator to metal transition in a linear crystal with a subcritical noise. digital.library.unt.edu/ark:/67531/metadc278868/
 Scanning Tunneling Microscopy of Epitaxial Diamond (110) and (111) Films and Field Emission Properties of Diamond Coated Molybdenum Microtips
 The growth mechanism of chemical vapor deposition (CVD) grown homoepitaxial 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. digital.library.unt.edu/ark:/67531/metadc279160/
 Scaling Behaviors and Mechanical Properties of Polymer Gels
 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 Nisopropyacrylamide (NIPA) and polyacrylamide (PAAM) gels has been studied. digital.library.unt.edu/ark:/67531/metadc279278/
 Accelerator Mass Spectrometry Studies of Highly Charged Molecular Ions
 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. digital.library.unt.edu/ark:/67531/metadc279004/
 Experimental Synchronization of Chaotic Attractors Using Control
 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. digital.library.unt.edu/ark:/67531/metadc278971/
 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
 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. digital.library.unt.edu/ark:/67531/metadc279039/
 Charge State Dependence of MShell XRay Production in 67Ho by 212 MeV Carbon Ions
 The charge state dependence of Mshell xray production cross sections of 67HO bombarded by 212 MeV carbon ions with and without Kvacancies are reported. The experiment was performed using an NEC 9SDH2 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 postaccelerator stripping gas cell. Ultraclean holmium targets were used in ionatom collision to generate Mshell x rays at energies from 1.05 to 1.58 keV. The xray measurements were made with a windowless Si(Li) xray detector that was calibrated using radiative sources, particle induced xray emission (PIXE), and the atomic field bremsstrahlung (AFB) techniques. digital.library.unt.edu/ark:/67531/metadc278725/
 Deterministic Brownian Motion
 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 FokkerPlanck 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 FokkerPlanck 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 longstanding 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 firstorder 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 FokkerPlanck equation and Brownian motion, possible. digital.library.unt.edu/ark:/67531/metadc279262/
 MagnetoOptical and Chaotic Electrical Properties of nInSb
 This thesis investigation concerns the optical and nonlinear electrical properties of nInSb. Two specific areas have been studied. First is the magnetooptical study of magnetodonors, and second is the nonlinear dynamic study of nonlinear and chaotic oscillations in InSb. The magnetooptical study of InSb provides a physical picture of the magnetodonor 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. digital.library.unt.edu/ark:/67531/metadc279131/
 Studies of Particles and Wave Propagation in Periodic and Quasiperiodic Nonlinear Media
 This thesis examines the properties of transmission and transport of light and charged particles in periodic or quasiperiodic systems of solid state and optics, especially the nonlinear and external field effects and the dynamic properties of these systems. digital.library.unt.edu/ark:/67531/metadc278708/
 Angular Dependence of the Stopping Processes and the Yields of Ioninduced Electron Emission from Channeled MEV Protons in <100> Silicon Foils
 The present work reports the experimental evidence of anomalous energy loss, energy straggling, and the corresponding ioninduced electron emission yields of channeled protons in silicon. digital.library.unt.edu/ark:/67531/metadc279025/
 Studies of Classically Chaotic Quantum Systems within the PseudoProbablilty Formalism
 The evolution of classically chaotic quantum systems is analyzed within the formalism of Quantum PseudoProbability Distributions. Due to the deep connections that a quantum system shows with its classical correspondent in this representation, the PseudoProbability formalism appears to be a useful method of investigation in the field of "Quantum Chaos." In the first part of the thesis we generalize this formalism to quantum systems containing spin operators. It is shown that a classicallike equation of motion for the pseudoprobability distribution ρw can be constructed, dρw/dt = (L_CL + L_QGD)ρw, which is rigorously equivalent to the quantum von NeumannLiouville equation. The operator L_CL is undistinguishable from the classical operator that generates the semiclassical equations of motion. In the case of the spinboson system this operator produces semiclassical chaos and is responsible for quantum irreversibility and the fast growth of quantum uncertainty. Carrying out explicit calculations for a spinboson Hamiltonian the joint action of L_CL and L_QGD is illustrated. It is shown that the latter operator, L_QGD makes the spin system 'remember' its quantum nature, and competes with the irreversibility induced by the former operator. In the second part we test the idea of the enhancement of the quantum uncertainty triggered by the classical chaos by investigating the analogous effect of diffusive excitation in periodically kicked quantum systems. The classical correspondents of these quantum systems exhibit, in the chaotic region, diffusive behavior of the unperturbed energy. For the Quantum Kicked Harmonic Oscillator, in the case of quantum resonances, we provide an exact solution of the quantum evolution. This proves the existence of a deterministic drift in the energy increase over time of the system considered. More generally, this "superdiffusive" excitation of the energy is due to coherent quantum mechanical tunnelling between degenerate tori of the classical phase space. In conclusion we find that some of the quantum effects resulting from this fast increase do not have any classical counterpart, they are mainly tunnelling processes. This seems to be the first observation of an effect of this kind. digital.library.unt.edu/ark:/67531/metadc278979/
 On Chaos and Anomalous Diffusion in Classical and Quantum Mechanical Systems
 The phenomenon of dynamically induced anomalous diffusion is both the classical and quantum kicked rotor is investigated in this dissertation. We discuss the capability of the quantum mechanical version of the system to reproduce for extended periods the corresponding classical chaotic behavior. digital.library.unt.edu/ark:/67531/metadc278244/
 Steadystate and Dynamic Probe Characteristics in a Lowdensity Plasma
 The problem with which this investigation is concerned is that of determining the steadystate and dynamic characteristics of the admittance of a metallic probe immersed in a laboratory plasma which has the low electron densities and low electron temperatures characteristic of the ionospheric plasma. The problem is separated into three related topics: the design and production of the laboratory plasma, the measurement of the steadystate properties of dc and very low frequency probe admittance, and the study of transient ion sheath effects on radio frequency probe admittance. digital.library.unt.edu/ark:/67531/metadc278232/
 Evolution of Vacancy Supersaturations in MeV Si Implanted Silicon
 Highenergy Si implantation into silicon creates a net defect distribution that is characterized by an excess of interstitials near the projected range and a simultaneous excess of vacancies closer to the surface. This defect distribution is due to the spatial separation between the distributions of interstitials and vacancies created by the forward momentum transferred from the implanted ion to the lattice atom. This dissertation investigates the evolution of the nearsurface vacancy excess in MeV Siimplanted silicon both during implantation and postimplant annealing. Although previous investigations have identified a vacancy excess in MeVimplanted silicon, the investigations presented in this dissertation are unique in that they are designed to correlate the freevacancy supersaturation with the vacancies in clusters. Freevacancy (and interstitial) supersaturations were measured with Sb (B) dopant diffusion markers. Vacancies in clusters were profiled by Au labeling; a new technique based on the observation that Au atoms trap in the presence of openvolume defects. The experiments described in this dissertation are also unique in that they were designed to isolate the deep interstitial excess from interacting with the much shallower vacancy excess during postimplant thermal processing. digital.library.unt.edu/ark:/67531/metadc277663/
 Distribution of Nighttime Fregion Molecular Ion Concentrations and 6300 Å Nightglow Morphology
 The purpose of this study is twofold. The first is to determine the dependence of the molecular ion profiles on the various ionospheric and atmospheric parameters that affect their distributions. The second is to demonstrate the correlation of specific ionospheric parameters with 6300 Å nightglow intensity during periods of magnetically quiet and disturbed conditions. digital.library.unt.edu/ark:/67531/metadc278620/
 Charge State Distributions in Molecular Dissociation
 The present work provides charge state fractions that may be used to generate TEAMS relative sensitivity factors for impurities in semiconductor materials. digital.library.unt.edu/ark:/67531/metadc278340/
 Anisotropic Relaxation Time for Solids with Ellipsoidal Fermi Surfaces
 Many solids have Fermi surfaces which are approximated as ellipsoids. A comprehensive solution for the magnetoconductivity of an ellipsoid is obtained which proves the existence of a relaxation time tensor which can be anisotropic and which is a function of energy only. digital.library.unt.edu/ark:/67531/metadc278322/
 Fluorine Adsorption and Diffusion in Polycrystalline Silica
 The measurement of fluorine penetration into archeological flint artifacts using Nuclear Reaction Analysis (NRA) has been reported to be a potential dating method. However, the mechanism of how fluorine is incorporated into the flint surface, and finally transported into the bulk is not well understood. This research focuses on the study of the fluorine uptake phenomenon of flint mineral in aqueous fluoride solutions. Both theoretical and experimental approaches have been carried out. In a theoretical approach, a pipediffusion model was used to simulate the complicated fluorine transportation problem in flint, in which several diffusion mechanisms may be involved. digital.library.unt.edu/ark:/67531/metadc277986/
 TwoFold Role of Randomness: A Source of Both LongRange Correlations and Ordinary Statistical Mechanics
 The role of randomness as a generator of long range correlations and ordinary statistical mechanics is investigated in this Dissertation. The difficulties about the derivation of thermodynamics from mechanics are pointed out and the connection between the ordinary fluctuationdissipation process and possible anomalous properties of statistical systems is highlighted. digital.library.unt.edu/ark:/67531/metadc278012/
 Synthesis and Study of Engineered Heterogenous Polymer Gels
 This dissertation studies physical properties and technological applications of engineered heterogenous polymer gels. Such gels are synthesized based on modulation of gel chemical nature in space. The shape memory gels have been developed in this study by using the modulated gel technology. At room temperature, they form a straight line. As the temperature is increased, they spontaneously bend or curl into a predetermined shape such as a letter of the alphabet, a numerical number, a spiral, a square, or a fish. The shape changes are reversible. The heterogenous structures have been also obtained on the gel surface. The central idea is to cover a dehydrated gel surface with a patterned mask, then to sputterdeposit a gold film onto it. After removing the mask, a gold pattern is left on the gel surface. Periodical surface array can serve as gratings to diffract light. The grating constant can be continuously changed by the external environmental stimuli such as temperature and electric field. Several applications of gels with periodic surface arrays as sensors for measuring gel swelling ratio, internal strain under an uniaxial stress, and shear modulus have been demonstrated. The porous NIPA gels have been synthesized by suspension technique. Microstructures of newly synthesized gels are characterized by both SEM and capillary test and are related to their swelling and mechanical properties. The heterogenous porous NIPA gel shrink about 35,000 times faster than its counterpartthe homogeneous NIPA gel. Development of such fast responsive gels can result in sensors and devices applications. A new gel system with builtin anisotropy is studied. This gel system consists of interpenetrated polymer network (IPN) gels of polyacrylamide (PAAM) and Nisopropylacrylamide (NIPA). The swelling property of the anisotropy IPN gels along the prestressing direction is different from that along other directions, in contrast to conventional gels which swell isotropically. It is found that the ratio (L/D) of length (L) and diameter (D) of IPN samples has stepwise changes as the samples are heated from below the volume phase transition temperature to the above. A theoretical model is proposed and is in good agreement with the experimental results. digital.library.unt.edu/ark:/67531/metadc278503/
 Numerical Investigations of Quantum Effects of Chaos
 The quantum dynamics of minimum uncertainty wave packets in a system described by the surfacestateelectron (SSE) Hamiltonian are studied herein. digital.library.unt.edu/ark:/67531/metadc278488/
 Characterization and Field Emission Properties of Mo2C and Diamond Thin Films Deposited on Mo Foils and Tips by Electrophoresis
 In this dissertation M02C and diamond films deposited by electrophoresis on flat Mo foils and tips have been studied to determine their suitability as field emission tips. digital.library.unt.edu/ark:/67531/metadc278393/
 Z1 Dependence of IonInduced Electron Emission
 Knowledge of the atomic number (Zt) dependence of ioninduced electron emission yields (Y) can be the basis for a general understanding of ionatom interaction phenomena and, in particular, for the design of Zrsensitive detectors that could be useful, for example, in the separation of isobars in accelerator mass spectrometry. The Zx dependence of ioninduced electron emission yields has been investigated using heavy ions of identical velocity (v = 2 v0, with v0 as the Bohr velocity) incident in a normal direction on sputtercleaned carbon foils. Yields measured in this work plotted as a function of the ion's atomic number reveal an oscillatory behavior with pronounced maxima and minima. This nonmonotonic dependence of the yield on Zx will be discussed in the light of existing theories. digital.library.unt.edu/ark:/67531/metadc277977/
 Expulsion of Carriers from the DoubleBarrier Quantum Well and Investigation of Its Spectral and Transport Consequences
 In this work I investigate the expulsion of carriers from nanostructures using the doublebarrier quantum well (DBQW) as an example and discuss manifestations of this effect in the spectrum of the DBQW in absence of bias, and in the tunneling current in presence of bias. Assuming equality of the Fermi energy in all regions of the considered system, I compute the relative density of carriers localized in the DBQW and conclude that a fraction of carriers is expelled from this nanostructure. digital.library.unt.edu/ark:/67531/metadc277697/
 LShell XRay Production Cross Sections for ₂₀Ca, ₂₆Fe, ₂₈Ni, ₂₉Cu, ₃₀Zn, ₃₁Ga, and ₃₂Ge by Hydrogen, Helium, and Lithium Ions
 Lshell xray production cross sections are presented for Fe, Ni, Cu, Zn, Ga, and Ge by 0.5 to 5.0MeV protons and by 0.5 to 8.0MeV helium ions and Ca, Fe, Ni, Cu, and Ge by 0.75 to 4.5MeV lithium ions. These measurements are compared to the first Born theory and the perturbedstationary state theory with energyloss, Coulomb deflection, and relativistic corrections (ECPSSR). The results are also compared to previous experimental investigations. The high precision xray measurements were performed with a windowless Si(Li) detector. The efficiency of the detector was determined by the use of thin target atomicfield bremsstrahlung produced by 66.5 keV electrons. The measured bremsstrahlung spectra were compared to theoretical bremsstrahlung distributions in order to obtain an efficiency versus energy curve. The targets for the measurement were manufactured by the vacuum evaporation of the target element onto thin foils of carbon. Impurities in the carbon caused interferences inthe Lshell xray peaks. Special cleansing procedures were developed that reduced the impurity concentrations in the carbon foil, making the use of less than 5 μg/cm^2 targets possible. The first Born theory is seen to greatly overpredict the data at low ion energies. The ECPSSR theory matches the data very well at the high energy region. At low energies, while fitting the data much more closely than the first Born theory, the ECPSSR theory does not accurately predict the trend of the data. This is probably due to the onset of molecularorbital effects, a mechanism not accounted for in the ECPSSR theory. digital.library.unt.edu/ark:/67531/metadc277620/
 Synchronous Chaos, Chaotic Walks, and Characterization of Chaotic States by Lyapunov Spectra
 Four aspects of the dynamics of continuoustime dynamical systems are studied in this work. The relationship between the Lyapunov exponents of the original system and the Lyapunov exponents of induced Poincare maps is examined. The behavior of these Poincare maps as discriminators of chaos from noise is explored, and the possible Poissonian statistics generated at rarely visited surfaces are studied. digital.library.unt.edu/ark:/67531/metadc277794/
 An Experimental Study of Collision Broadening of some Excited Rotational States of the Bending Vibration of Methyl Cyanide
 A double modulation microwave spectrometer is used to evaluate the linewidth parameters for some excited rotational components in the bending vibration v_8 of 13CH3 13C 15N and 13CH3C15N isotopomers of methyl cyanide. The linewidth parameters for selfbroadening of the ΔJ=2←1 rotational components for the ground v_8 , 1v_8, and the 2v_8 vibrations were determined over a pressure range of 1 to 13 mtorr and at a temperature of 300 K. The double modulation technique is used to explore the high eighth derivative of the line shape profile of the spectral line. This technique proved to give good signaltonoise ratios and enabled the recovery of weak signals. An experimental method is developed to correct for source modulation broadening. The tests of the ratios of the two inner peak's separation of the eighth derivative of the line showed that they were up to 95% similar to those for a Lorentzian line shape function. The line shapes were assumed to be Lorentzian for the theoretical analysis of the derivative profiles and comparisons were made between experiment and theory on this basis. Dipole moments for vibrationally excited states were calculated from linewidth parameters and show systematic decrease with the increase of excitation. Impact parameters were calculated using the "hard sphere" model of the kinetic theory of gases. The results were many times larger than the size of the molecule itself. This suggests that the dominant interaction is a long range dipoledipole force interaction. digital.library.unt.edu/ark:/67531/metadc278369/
 ShortPeriod Transient Grating Measurement of Perpendicular Transport in GaAs/AlGaAs Multiple Quantum Wells
 In this thesis the author describes the use of transient grating techniques to study the transport of electrons and holes perpendicular to the layers of a GaAs/AlGaAs multiple quantum well (MQW). digital.library.unt.edu/ark:/67531/metadc277907/
 Diffusion Kinetics and Microstructure of Eutectic and Composite Solder/Copper Joints
 Sn/Pb solders are widely used by the electronics industry to provide both mechanical and electrical interconnections between electronic components and printed circuit boards. Solders with enhanced mechanical properties are required for high reliability for Surface Mount Technology (SMT) applications. One approach to improve the mechanical properties of solder is to add metallic or intermetallic particles to eutectic 63Sn/37Pb solder to form composite solders. Cu6Sn5 and Cu3Sn form and grow at the solder/copper substrate interface. The formation and growth of these intermetallics have been proposed as controlling mechanisms for solderability and reliability of solder/copper joints. The goal of this study was to investigate the diffusion kinetics and microstructures of six types of composite solder/copper joints. digital.library.unt.edu/ark:/67531/metadc278545/
 Nonlinear Dynamics of Semiconductor Device Circuits and Characterization of Deep Energy Levels in HgCdTe by Using MagnetoOptical Spectroscopy
 The nonlinear dynamics of three physical systems has been investigated. Diode resonator systems are experimentally shown to display a period doubling route to chaos, quasiperiodic states, periodic locking states, and Hopf bifurcation to chaos. Particularly, the transition from quasiperiodic states to chaos in linecoupled systems agrees well with the CurryYorke model. The SPICE program has been modified to give realistic models for the diode resonator systems. digital.library.unt.edu/ark:/67531/metadc278165/
 Transport Processes in Synchrotrons
 This thesis examines the evolution of beams in synchrotrons. Following an introduction to accelerator physics in Chapter 1, in Chapter 2 I describe the Fermilab E778 'diffusion' experiment. Families of sextupoles were powered to drive the 2/5 resonance, and a beam was then kicked to populate a nonlinear region of the transverse phase space. The beam was then observed over periods of approximately 30 minutes for a variety of kick amplitudes and physical apertures. In Chapter 3 comments about the analytic treatment of such systems are discussed, including the assumptions inherent in the conventional treatment. I motivate my use of a simplified model in Chapter 4 after examining common computational methods. Deriving the model from the formalism of traditional accelerator physics, I discuss its implementation on a massively parallel computer, the Intel iPSC/860 hypercube, and examine the performance of this algorithm in detail. Using the simple model to perform the numerical experiment equivalent to E778 is the subject of Chapter 5. I derive the parameters needed for the simple model based upon the physical experiment. Both three dimensional cases and cases with reduced dimensionality are run. From power supply ripple data and an electrical model of the magnet string, I compute tune modulation depths, and a subset of these are run. I conclude that tune modulation from power supply ripple is not a significant source of transport for this system. In Chapter 6, the intensities of the beams are used to compare the experimental and numerical runs, using both exponential and algebraic decays, and the algebraic form is seen to provide a better fit. The agreement between numerical and experimental results is best for fully threedimensional runs, but the numerical results show slower decay than the experimental. Individual particles are examined, whose motion consists of stochastic motion interspersed with regular motion, suggestive of a Continuous Time Random Walk process. A pausing time distribution is extracted which is algebraic in time, which is consistent with dispersive transport observed elsewhere. digital.library.unt.edu/ark:/67531/metadc277803/
 Nonlinear Optical Absorption and Refraction Study of Metallophthalocyanine Dyes
 This dissertation deals with the characterization of the nonlinear absorption and refraction of two representative metallophthalocyanine dyes: chloro aluminum phthalocyanine dissolved in methanol, referred to as CAP, and a silicon naphthalocyanine derivative dissolved in toluene, referred to as SiNc. Using the Zscan technique, the experiments are performed on both the picosecond and nanosecond timescales at a wavelength of 0.532 μm. digital.library.unt.edu/ark:/67531/metadc278287/
 A New Approach for Transition Metal Free Magnetic Sic: Defect Induced Magnetism After Selfion Implantation
 SiC has become an attractive wide bandgap semiconductor due to its unique physical and electronic properties and is widely used in high temperature, high frequency, high power and radiation resistant applications. SiC has been used as an alternative to Si in harsh environments such as in the oil industry, nuclear power systems, aeronautical, and space applications. SiC is also known for its polytypism and among them 3CSiC, 4HSiC and 6HSiC are the most common polytypes used for research purposes. Among these polytypes 4HSiC is gaining importance due to its easy commercial availability with a large bandgap of 3.26 eV at room temperature. Controlled creation of defects in materials is an approach to modify the electronic properties in a way that new functionality may result. SiC is a promising candidate for defectinduced magnetism on which spintronic devices could be developed. The defects considered are of room temperature stable vacancy types, eliminating the need for magnetic impurities, which easily diffuse at room temperature. Impurity free vacancy type defects can be created by implanting the host atoms of silicon or carbon. The implantation fluence determines the defect density, which is a critical parameter for defect induced magnetism. Therefore, we have studied the influence of low fluence low energy silicon and carbon implantation on the creation of defects in ntype 4HSiC. The characterization of the defects in these implanted samples was performed using the techniques, RBSchanneling and Raman spectroscopy. We have also utilized these characterization techniques to analyze defects created in much deeper layers of the SiC due to implantation of high energy nitrogen ions. The experimentally determined depths of the Si damage peaks due to low energy (60 keV) Si and C ions with low fluences (< 1015 cm2) are consistent with the SRIM2011 simulations. From RBSC Si sublattice measurements for different fluences (1.1×1014 cm2 to 3.2×1014 cm2) of Si implantation in 4HSiC, the Si vacancy density is estimated to range from 1.29×1022 cm3 to 4.57×1022 cm2, corresponding to average vacancy distances of 4.26 Å to 2.79 Å at the damage peak (50±5 nm). Similarly, for C implanted fluences (1.85×1014 cm2 to 1×1015 cm2), the Si vacancy density varies from 1.37×1022 cm3 to 4.22×1022 cm3 with the average vacancy distances from 4.17 Å to 2.87 Å at the damage peak (110±10 nm). From the Raman spectroscopy, the implantationinduced lattice disorders calculated along the caxis (LO mode) and perpendicular to caxis (TO mode) in 4HSiC are found to be similar. Furthermore, the results obtained from SQUID measurements in C implanted ntype 4HSiC sample with fluences ranging from 1×1012 to 1.7×1016 ions/cm2 have been discussed. The implanted samples showed diamagnetism similar to the unimplanted sample. To date, to our best of knowledge, no experimental work has been reported on investigating defect induced magnetism for selfion implantation in ntype 4HSiC. These first reports of experimental results can provide useful information in future studies for a better understanding of selfion implantation in SiCbased DMS. digital.library.unt.edu/ark:/67531/metadc271849/
 Zinc Oxide Nanoparticles for Nonlinear Bioimaging, Cell Detection and Selective Cell Destruction

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Light matter interactions have led to a great part of our current understanding of the universe. When light interacts with matter it affects the properties of both the light and the matter. Visible light, being in the region that the human eye can "see," was one of the first natural phenomenon we used to learn about our universe. The application of fundamental physics research has spilled over into other fields that were traditionally separated from physics, being considered two different sciences. Current physics research has applications in all scientific fields. By taking a more physical approach to problems in fields such as chemistry and biology, we have furthered our knowledge of both. Nanocrystals have many interesting optical properties. Furthermore, the size and properties of nanocrystals has given them applications in materials ranging from solar cells to sunscreens. By understanding and controlling their interactions with systems we can utilize them to increase our knowledge in other fields of science, such as biology. Nanocrystals exhibit optical properties superior to currently used fluorescent dyes. By replacing molecular dyes with nanoparticles we can reduce toxicity, increase resolution and have better cellular targeting abilities. They have also shown to have toxicity to cancer and antibacterial properties. With the understanding of how to target specific cells in vitro as well as in vivo, nanoparticles have the potential to be used as highly cell specific nanodrugs that can aid in the fight against cancer and the more recent fight against antibiotic resistant bacteria. This dissertation includes our work on bioimaging as well as our novel drug delivery system. An explanation of toxicity associated with ZnO nanoparticles and how we can use it and the nonlinear optical properties of ZnO for nanodrugs and nanoprobes is presented. digital.library.unt.edu/ark:/67531/metadc271908/  Criticality in Cooperative Systems
 Cooperative behavior arises from the interactions of single units that globally produce a complex dynamics in which the system acts as a whole. As an archetype I refer to a flock of birds. As a result of cooperation the whole flock gets special abilities that the single individuals would not have if they were alone. This research work led to the discovery that the function of a flock, and more in general, that of cooperative systems, surprisingly rests on the occurrence of organizational collapses. In this study, I used cooperative systems based on selfpropelled particle models (the flock models) which have been proved to be virtually equivalent to sociological network models mimicking the decision making processes (the decision making model). The critical region is an intermediate condition between a highly disordered state and a strong ordered one. At criticality the waiting times distribution density between two consecutive collapses shows an inverse power law form with an anomalous statistical behavior. The scientific evidences are based on measures of information theory, correlation in time and space, and fluctuation statistical analysis. In order to prove the benefit for a system to live at criticality, I made a flock system interact with another similar system, and then observe the information transmission for different disturbance values. I proved that at criticality the transfer of information gets the maximal efficiency. As last step, the flock model has been shown that, despite its simplicity, is sufficiently a realistic model as proved via the use of 3D simulations and computer animations. digital.library.unt.edu/ark:/67531/metadc271910/
 Theoretical and Experimental Investigations of Peg Based Thermo Sensitive Hydro Microgel
 Poly ethylene glycol (PEG) based microgels were synthesized and investigated. The PEG microgel has the same phase transition as the traditional poly Nisopropylacrylamide (PNIPAM). As a good substitute of PNIPAM, PEG microgel exhibits many advantages: it is easier to control the lower critical solution temperature (LCST) of the microgel by changing the component of copolymers; it has a more solid spherical coreshell structure to have a double thermo sensitivity; it is straightforward to add other sensitivities such as pH, magnetic field or organic functional groups; it readily forms a photonic crystal structure exhibiting Bragg diffraction; and, most importantly, the PEG microgel is biocompatible with human body and has been approved by FDA while PNIPAM has not. PEG microgels with coreshell structure are synthesized with a twostep free radical polymerization and characterized with DLS, SLS and UV–Vis. The dynamic mechanics of melting and recrystallizing of the PEG coreshell microgel are presented and discussed. Photonic crystals of PEG microgels were synthesized and characterized. The crystal can be isolated in a thin film or a bulk column. The phase transition of PEG microgel was simulated with the mean field theory. The enthalpy and entropy of phase transition can be estimated from the best fit to theoretical calculation with experimental data. digital.library.unt.edu/ark:/67531/metadc177187/
 Investigation of the Uniaxial Stress Dependence of the Effective Mass in NType InSb Using the Magnetophonon Effect
 The magnetophonon effect was used to investigate the uniaxial stress dependence of the effective mass in ntype InSb (indium antimonide). digital.library.unt.edu/ark:/67531/metadc164537/