 Nonlinear and Quantum Optics Near Nanoparticles
 We study the behavior of electric fields in and around dielectric and metal nanoparticles, and prepare the ground for their applications to a variety of systems viz. photovoltaics, imaging and detection techniques, and molecular spectroscopy. We exploit the property of nanoparticles being able to focus the radiation field into small regions and study some of the interesting nonlinear, and quantum coherence and interference phenomena near them. The traditional approach to study the nonlinear lightmatter interactions involves the use of the slowly varying amplitude approximation (SVAA) as it simplifies the theoretical analysis. However, SVVA cannot be used for systems which are of the order of the wavelength of the light. We use the exact solutions of the Maxwell's equations to obtain the fields created due to metal and dielectric nanoparticles, and study nonlinear and quantum optical phenomena near these nanoparticles. We begin with the theoretical description of the electromagnetic fields created due to the nonlinear wavemixing process, namely, secondorder nonlinearity in an nonlinear sphere. The phasematching condition has been revisited in such particles and we found that it is not satisfied in the sphere. We have suggested a way to obtain optimal conditions for any type and size of material medium. We have also studied the modifications of the electromagnetic fields in a collection of nanoparticles due to strong near field nonlinear interactions using the generalized Mie theory for the case of many particles applicable in photovoltaics (PV). We also consider quantum coherence phenomena such as modification of dark states, stimulated Raman adiabatic passage (STIRAP), optical pumping in $4$level atoms near nanoparticles by using rotating wave approximation to describe the Hamiltonian of the atomic system. We also considered the behavior of atomic and the averaged atomic polarization in $7$level atoms near nanoparticles. This could be used as a prototype to study any $n$level atomic system experimentally in the presence of ensembles of quantum emitters. In the last chapter, we suggested a variant of a pulseshaping technique applicable in stimulated Raman spectroscopy (SRS) for detection of atoms and molecules in multiscattering media. We used discretedipole approximation to obtain the fields created by the nanoparticles. digital.library.unt.edu/ark:/67531/metadc822820/
 Fractional Calculus and Dynamic Approach to Complexity
 Fractional calculus enables the possibility of using real number powers or complex number powers of the differentiation operator. The fundamental connection between fractional calculus and subordination processes is explored and affords a physical interpretation for a fractional trajectory, that being an average over an ensemble of stochastic trajectories. With an ensemble average perspective, the explanation of the behavior of fractional chaotic systems changes dramatically. Before now what has been interpreted as intrinsic friction is actually a form of nonMarkovian dissipation that automatically arises from adopting the fractional calculus, is shown to be a manifestation of decorrelations between trajectories. Nonlinear Langevin equation describes the mean field of a finite size complex network at criticality. Critical phenomena and temporal complexity are two very important issues of modern nonlinear dynamics and the link between them found by the author can significantly improve the understanding behavior of dynamical systems at criticality. The subject of temporal complexity addresses the challenging and especially helpful in addressing fundamental physical science issues beyond the limits of reductionism. digital.library.unt.edu/ark:/67531/metadc822832/
 Variational Calculations of Positronium Scattering with Hydrogen
 Positroniumhydrogen (PsH) scattering is of interest, as it is a fundamental fourbody Coulomb problem. We have investigated lowenergy PsH scattering below the Ps(n=2) excitation threshold using the Kohn variational method and variants of the method with a trial wavefunction that includes highly correlated Hylleraastype shortrange terms. We give an elegant formalism that combines all Kohntype variational methods into a single form. Along with this, we have also developed a general formalism for Kohntype matrix elements that allows us to evaluate arbitrary partial waves with a single codebase. Computational strategies we have developed and use in this work will also be discussed.With these methods, we have computed phase shifts for the first six partial waves for both the singlet and triplet states. The 1S and 1P phase shifts are highly accurate results and could potentially be viewed as benchmark results. Resonance positions and widths for the 1S, 1P, 1D, and 1Fwaves have been calculated.We present elastic integrated, elastic differential, and momentum transfer cross sections using all six partial waves and note interesting features of each. We use multiple effective range theories, including several that explicitly take into account the longrange van der Waals interaction, to investigate scattering lengths for the 1,3S and 1,3P partial waves and effective ranges for the 1,3Swave. digital.library.unt.edu/ark:/67531/metadc822803/
 Complex Numbers in Quantum Theory
 In 1927, Nobel prize winning physicist, E. Schrodinger, in correspondence with Ehrenfest, wrote the following about the new theory: “What is unpleasant here, and indeed directly to be objected to, is the use of complex numbers. Psi is surely fundamentally a real function.” This seemingly simple issue remains unexplained almost ninety years later. In this dissertation I elucidate the physical and theoretical origins of the complex requirement. I identify a freedom/constraint situation encountered by vectors when, employed in accordance with adopted quantum representational methodology, and representing angular momentum states in particular. Complex vectors, quite simply, provide more available adjustable variables than do real vectors. The additional variables relax the constraint situation allowing the theory’s representational program to carry through. This complex number issue, which lies at the deepest foundations of the theory, has implications for important issues located higher in the theory. For example, any unification of the classical and quantum accounts of the settled order of nature, will rest squarely on our ability to account for the introduction of the imaginary unit. digital.library.unt.edu/ark:/67531/metadc804988/
 Synthesis and Characterization of Ion Beam Assisted Silver Nanosystems in Silicon Based Materials for Enhanced Photocurrent Collection Efficiency
 In recent years a great deal of interest has been focused on the synthesis of transitional metal (e.g. Ag, Cu, Fe, Au) nanosystems at the surface to subsurface regions of Si and SiO2 matrices for fundamental understanding of their structures as well as for development of technological applications with enhanced electronic and optical properties. The applications of the metal nanoparticle or nanocluster (NC) systems range from plasmonics, photovoltaic devices, medical, and biosensors. In all of these applications; the size, shape and distribution of the metallic NCs in the silicon matrix play a key role. Low energy ion implantation followed by thermal annealing (in vacuum or gas environment) is one of the most suitable methods for synthesis of NCs at near surfaces to buried layers below the surfaces of the substrates. This technique can provide control over depth and concentration of the implanted ions in the host matrix. The implanted low energy metal ions initially amorphizes the Si substrates while being distributed at a shallow depth near the substrate surface. When subject to thermal annealing, the implanted ions agglomerate to form clusters of different sizes at different depths depending upon the fluence. However, for the heavier ions implanted with high fluences (~1×1016  1×1017 atoms/cm2), there lies challenges for accurately predicting the distribution of the implanted ions due to sputtering of the surface as well as redistribution of the implants within the host matrix. In this dissertation, we report the investigation of the saturation of the concentration of the implanted ion species in the depth profiles with low energies (< 80 keV) metal ions (Ag and Au) in Si (100), while studying the dynamic changes during the ion implantation. Multiple low energies (3080 keV) Ag ions with different fluences were sequentially implanted into commercially available Si wafers in order to facilitate the formation of Ag NCs with a wide ion distributions range. The light absorption profile according to different sizes of NCs at the nearsurface layers in Si were investigated. We have investigated the formation of Ag NCs in the Si matrix as a function of implantation and thermal annealing parameters. The absorbance of light is increased in Ag implanted Si with a significant increase in the current collection in IV (currentvoltage) photo switching measurements. The experimental photovoltaic cells fabricated with the Ag implanted Si samples were optically characterized under AM (air mass) 1.5 solar radiation conditions (~1.0 kW/m2). An enhancement in the charge collection were measured in the annealed samples, where prominent Ag NCs were formed in the Si matrix compared to the asimplanted samples with the amorphous layer. The characterization techniques such as Rutherford Backscattering Spectroscopy, XPSdepth profiling, transmission electron microscopy, optical absorption, and IV (currentvoltage) photo switching measurements were employed to understand the underlying science in the observed properties. The results of these investigations are discussed in this research. digital.library.unt.edu/ark:/67531/metadc799502/
 Interaction of Plasmons and Excitons for LowDimension Semiconductors

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The effects of surface plasmon for InGaN/GaN multiquantum wells and ZnO nanoparticles optical linear and nonlinear emission efficiency had been experimentally studied. Due to the critical design for InGaN MQWs with inverted hexagonal pits based on GaN, both contribution of surface plasmon effect and image charge effect at resonant and off resonant frequencies were experimentally and theoretically investigated. With off resonant condition, the InGaN MQWs emission significantly enhanced by metal nanoparticles. This enhancement was caused by the image charge effect, due to the accumulation of carriers to NPs region. When InGaN emission resonated with metal particles SP modes, surface Plasmon effect dominated the emission process. We also studied the surface plasmon effect for ZnO nanoparticles nonlinear optical processes, SHG and TPE. Defect level emission had more contribution at high incident intensity. Emissions are different for pumping deep into the bulk and near surface. A new assumption to increase the TPE efficiency was studied. We thought by using Au nanorods localized surface plasmon mode to couple the ZnO virtual state, the virtual state’s life time would be longer and experimentally lead the emission enhancement. We studied the TPE phenomena at high and near band gap energy. Both emission intensity and decay time results support our assumption. Theoretically, the carriers dynamic mechanism need further studies. digital.library.unt.edu/ark:/67531/metadc799475/  Electromagnetically Modulated Sonic Structures

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Phononic crystals are structures composed of periodically arranged scatterers in a background medium that affect the transmission of elastic waves. They have garnered much interest in recent years for their macroscale properties that can be modulated by the microscale components. The elastic properties of the composite materials, the contrast in the elastic properties of the composite materials, and the material arrangement all directly affect how an elastic wave will behave as it propagates through the sonic structure. The behavior of an elastic wave in a periodic structure is revealed in its transmission bandstructure, and modification of any the elastic parameters will result in tuning of the band structure. In this dissertation, a phononic crystal with properties that can be modulated using electromagnetic radiation, and more specifically, radiofrequency (RF) light will be presented. digital.library.unt.edu/ark:/67531/metadc799496/  Highly Efficient Single Frequency Blue Laser Generation by Second Harmonic Generation of Infrared Lasers Using Quasi Phase Matching in Periodically Poled Ferroelectric Crystals
 Performance and reliability of solid state laser diodes in the IR region exceeds those in the visible and UV part of the light spectrum. Single frequency visible and UV laser diodes with higher than 500 mW power are not available commercially. However we successfully stabilized a multilongitudinal mode IR laser to 860 mW single frequency. This means high efficiency harmonic generation using this laser can produce visible and UV laser light not available otherwise. In this study we examined three major leading nonlinear crystals: PPMgO:SLN, PPKTP and PPMgO:SLT to generate blue light by second harmonic generation. We achieved record high net conversion efficiencies 81.3% using PPMgO:SLT (~500 mW out), and 81.1% using PPKTP (~700 mW out). In both these cases an external resonance buildup cavity was used. We also studied a less complicated single pass waveguide configuration (guided waist size of ~ 5 um compared to ~60 um) to generate blue. With PPMgO:SLN we obtained net 40.4% and using PPKT net 6.8% (110mW and 10.1 mW respectively). digital.library.unt.edu/ark:/67531/metadc799538/
 Studies of Charged Particle Dynamics for Antihydrogen Synthesis
 Synthesis and capture of antihydrogen in controlled laboratory conditions will enable precise studies of neutral antimatter. The work presented deals with some of the physics pertinent to manipulating charged antiparticles in order to create neutral antimatter, and may be applicable to other scenarios of plasma confinement and charged particle interaction. The topics covered include the electrostatic confinement of a reflecting ion beam and the transverse confinement of an ion beam in a purely electrostatic configuration; the charge sign effect on the Coulomb logarithm for a two component (e.g., antihydrogen) plasma in a Penning trap as well as the collisional scattering for binary Coulomb interactions that are cut off at a distance different than the Debye length; and the formation of magnetobound positronium and protonium. digital.library.unt.edu/ark:/67531/metadc699934/
 Analysis of Biological Materials Using a Nuclear Microprobe
 The use of nuclear microprobe techniques including: Particle induced xray emission (PIXE) and Rutherford backscattering spectrometry (RBS) for elemental analysis and quantitative elemental imaging of biological samples is especially useful in biological and biomedical research because of its high sensitivity for physiologically important trace elements or toxic heavy metals. The nuclear microprobe of the Ion Beam Modification and Analysis Laboratory (IBMAL) has been used to study the enhancement in metal uptake of two different plants. The roots of corn (Zea mays) have been analyzed to study the enhancement of iron uptake by adding Fe (II) or Fe (III) of different concentrations to the germinating medium of the seeds. The Fe uptake enhancement effect produced by lacing the germinating medium with carbon nanotubes has also been investigated. The aim of this investigation is to ensure not only high crop yield but also Ferich food products especially from calcareous soil which covers 30% of world’s agricultural land. The result will help reduce iron deficiency anemia, which has been identified as the leading nutritional disorder especially in developing countries by the World Health Organization. For the second plant, Mexican marigold (Tagetes erecta), the effect of an arbuscular mycorrhizal fungi (Glomus intraradices) for the improvement of leadphytoremediation of lead contaminated soil has been investigated. Phytoremediation provides an environmentally safe technique of removing toxic heavy metals (like lead), which can find their way into human food, from lands contaminated by human activities like mining or by natural disasters like earthquakes. The roots of Mexican marigold have been analyzed to study the role of arbuscular mycorrhizal fungi in enhancement of lead uptake from the contaminated rhizosphere. digital.library.unt.edu/ark:/67531/metadc700099/
 Electrical Conduction Mechanisms in the Disordered Material System Ptype Hydrogenated Amorphous Silicon
 The electrical and optical properties of boron doped hydrogenated amorphous silicon thin films (aSi) were investigated to determine the effect of boron and hydrogen incorporation on carrier transport. The aSi thin films were grown by plasma enhanced chemical vapor deposition (PECVD) at various boron concentrations, hydrogen dilutions, and at differing growth temperatures. The temperature dependent conductivity generally follows the hopping conduction model. Above a critical temperature, the dominant conduction mechanism is Mott variable range hopping conductivity (MVRH), where p = ¼, and the carrier hopping depends on energy. However, at lower temperatures, the coulomb interaction between charge carriers becomes important and EfrosShklosvkii variable hopping (ESVRH) conduction, where p=1/2, must be included to describe the total conductivity. To correlate changes in electrical conductivity to changes in the local crystalline order, the transverse optical (TO) and transverse acoustic (TA) modes of the Raman spectra were studied to relate changes in short and midrange order to the effects of growth temperature, boron, and hydrogen incorporation. With an increase of hydrogen and/or growth temperature, both short and midrange order improve, whereas the addition of boron results in the degradation of short range order. It is seen that there is a direct correlation between the electrical conductivity and changes in the short and midrange order resulting from the passivation of defects by hydrogen and the creation of trap states by boron. This work was done under the ARO grant W911NF1010410, William W. Clark Program Manager. The samples were provided by L3 Communications. digital.library.unt.edu/ark:/67531/metadc700106/
 Sputtering of Bi and Preferential Sputtering of an Inhomogeneous Alloy
 Angular distributions and total yields of atoms sputtered from bismuth targets by normally incident 10 keV 50 keV Ne+ and Ar+ ions have been measured both experimentally and by computer simulation. Polycrystalline Bi targets were used for experimental measurements. The sputtered atoms were collected on high purity aluminum foils under ultrahigh vacuum conditions, and were subsequently analyzed using Rutherford backscattering spectroscopy. The MonteCarlo based SRIM code was employed to simulate angular distributions of sputtered Bi atoms and total sputtering yields of Bi to compare with experiment. The measured sputtering yields were found to increase with increasing projectile energy for normally incident 10 keV  50 keV Ne+ and Ar+ ions. The shapes of the angular distributions of sputtered Bi atoms demonstrated good agreement between experiment and simulation in the present study. The measured and simulated angular distributions of sputtered Bi exhibited an overcosine tendency. The measured value of the degree of this overcosine nature was observed to increase with increasing incident Ne+ ion energy, but was not strongly dependent on incident Ar+ ion energy. The differential angular sputtering yield and partial sputtering yields due to Ar ion bombardment of an inhomogeneous liquid Bi:Ga alloy have been investigated, both experimentally and by computer simulation. Normally incident 25 keV and 50 keV beams of Ar+ were used to sputter a target of 99.8 at% Ga and 0.2 at% Bi held at 40° C in ultrahigh vacuum (UHV), under which conditions the alloy is known to exhibit extreme Gibbsian surface segregation that produces essentially a monolayer of Bi atop the bulk liquid. Angular distributions of sputtered neutrals and partial sputtering yields obtained from the conversion of areal densities of Bi and Ga atoms on collector foils were determined. The MonteCarlo based SRIM code was employed to simulate the experiment and obtain the angular distribution of sputtered components. The angular distribution of sputtered Ga atoms, originating from underneath the surface monolayer, was measured to be sharply peaked in angle about the surface normal direction compared to the Bi atoms originating from surface monolayer. The simulation study produced contradicting results, where the species originating from surface monolayer was strongly peaked around the surface normal compared to the species originating from beneath the surface monolayer. digital.library.unt.edu/ark:/67531/metadc700021/
 Temporal Complexity and Stochastic Central Limit Theorem
 Complex processes whose evolution in time rests on the occurrence of a large and random number of intermittent events are the systems under study. The mean time distance between two consecutive events is infinite, thereby violating the ergodic condition and activating at the same time a stochastic central limit theorem that explains why the MittagLeffler function is a universal property of nature. The time evolution of these complex systems is properly generated by means of fractional differential equations, thus leading to the interpretation of fractional trajectories as the average over many random trajectories, each of which fits the stochastic central limit theorem and the condition for the MittagLeffler universality. Additionally, the effect of noise on the generation of the MittagLeffler function is discussed. Fluctuations of relatively weak intensity can conceal the asymptotic inverse power law behavior of the MittagLeffler function, providing a reason why stretched exponentials are frequently found in nature. These results afford a more unified picture of complexity resting on the MittagLeffler function and encompassing the standard inverse power law definition. digital.library.unt.edu/ark:/67531/metadc700093/
 Enhancement of Mechanical, Thermal Stability, and Tribological Properties by Addition of Functionalized Reduced Graphene Oxide in Epoxy
 The effects of octadecylaminefunctionalized reduced graphene oxide (FRGO) on the frictional and wear properties of diglycidylether of bisphenolA (DGEBA) epoxy are studied using a pinondisk tribometer. It was observed that the addition of FRGO significantly improves the tribological, mechanical, and thermal properties of epoxy matrix. Graphene oxide (GO) was functionalized with octadecylamine (ODA), and then reduction of oxygencontaining functional groups was carried out using hydrazine monohydrate. The Raman and xray photoelectron spectroscopy studies confirm significant reduction in oxygencontaining functional groups and formation of ODA functionalized reduced GO. The nanocomposites are prepared by adding 0.1, 0.2, 0.5 and 1.0 wt % of FRGO to the epoxy. The addition of FRGO increases by more than an order of magnitude the sliding distance during which the dynamic friction is ≤ 0.1. After this distance, the friction sharply increases to the range of 0.4  0.5. We explain the increase in sliding distance during which the friction is low by formation of a transfer film from the nanocomposite to the counterface. The wear rates in the low and high friction regimes are approximately 1.5 x 104 mm3/N·m and 5.5 x 104 mm3/N·m, respectively. The nanocomposites exhibit a 74 % increase in Young’s modulus with 0.5 wt. % of FRGO, and an increase in glass transition and thermal degradation temperatures. digital.library.unt.edu/ark:/67531/metadc699889/
 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/
 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/
 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/
 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/
 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/
 Field Dependence of Optical Properties in Quantum Well Heterostructures Within the Wentzel, Kramers, and Brillouin Approximation
 This dissertation is a theoretical treatment of the electric field dependence of optical properties such as Quantum Confined Stark (QCS) shifts, Photoluminescence Quenching (PLQ), and Excitonic Mixing in quantum well heterostructures. The reduced spatial dimensionality in heterostructures greatly enhances these optical properties, more than in three dimensional semiconductors. Charge presence in the quantum well from doping causes the potential to bend and deviate from the ideal square well potential. A potential bending that varies as the square of distance measured from the heterostructure interfaces is derived selfconsistently. This potential is used to solve the timeindependent Schrodinger equation for bound state energies and wave functions within the framework of the Wentzel, Kramers, and Brillouin (WKB) approximation. The theoretical results obtained from the WKB approximation are limited to wide gap semiconductors with large split off bands such as gallium arsenidegallium aluminum arsenide and indium gallium arsenide—indium phosphide. Quantum wells with finite confinement heights give rise to an energy dependent WKB phase. External electric and magnetic fields are incorporated into the theory for two different geometries. For electric fields applied perpendicular to the heterostructure multilayers, QCS shifts and PLQ are found to be in excellent agreement with the WKB calculations. Orthogonality between electrons and holes gives rise to interband mixing in the presence of an external electric field. On the contrary, intraband mixing between light and heavy holes is not sufficiently accounted for in the WKB approximation. digital.library.unt.edu/ark:/67531/metadc330576/
 Lshell Xray production cross sections of ₂₉Cu, ₃₂Ge, ₃₇Rb, ₃₈Sr, and ₃₉Y and Mshell Xray production cross sections of ₇₉Au, ₈₂Pb, ₈₃Bi, ₉₀Th, and ₉₂U by 70200 keV protons
 Lshell xray production cross sections have been measured for thin targets of 29Cu, 32Ge, 37Rb, 38Sr, and 39Y. Mshell xray production cross sections have been measured for thin targets of 79Au, 82Pb, 83Bi, 90Th, and 92U. All targets were irradiated with a beam of H+ ions with energies in a range from 70 to 200 keV. Experimental cross sections are compared to other measurements at higher energies and to first Born (Plane Wave Born Approximation for direct ionization and OppenheimerBrinkmanKramersNikolaev approximation for electron capture) and the ECPSSR (Energy loss, Coulomb deflection, Perturbed Stationary State calculations with Relativistic effects) theoretical cross sections. digital.library.unt.edu/ark:/67531/metadc330628/
 Detection of the Resonant Vibration of the Cellular Membrane Using Femtosecond Laser Pulses
 An optical detection technique is developed to detect and measure the resonant vibration of the cellular membrane. Biological membranes are active components of living cells and play a complex and dynamic role in life processes. They are believed to have oscillation modes of frequencies in the range of 1 to 1000 GHz. To measure such a highfrequency vibration, a linear laser cavity is designed to produce a train of femtosecond pulses of adjustable repetition rate. The method is then directly applied to liposomes, "artificial membrane", stained with a liphophilic potential sensitive dye. The spectral behavior of a selection of potential sensitive dyes in the membrane is also studied. digital.library.unt.edu/ark:/67531/metadc331235/
 Microwave Spectra of ¹³C Isotopic Species of Methyl Cyanide in the Ground, v₈=1 and v₈=2 Vibrational States
 The problem of the quadrupole interaction occurring in a vibratingrotating C₃v symmetric top molecule has been studied in detail. The quadrupole interaction has been treated as another perturbation term to a general frequency expression accounting for the vibratingrotating interaction of the molecule so that a complete frequency formula is obtained for both interactions, and from which hyperfine spectral components are predicted and measured. The hyperfine transitions in the ground, and v₈=1 and v₈=2 excited vibrational states of the ¹³C isotopes of methyl cyanide have been investigated in the frequency range 1772 GHz, primarily in the low J transitions (0≤J≤3). The study of the ground state of isotope i3CH3i3CN, and the v₈=1, v₈=2 excited vibrational states for all the isotopes have been conducted here for the first time. A substantial perturbation has been discovered and discussed at the ΔJ=3→4 transitions within the Kl=1 sets in the v₈=1 mode for isotopes ¹³CH₃CN and CH₃¹³CN. A total of 716 hyperfine transitions have been assigned from measurements, only 7 of which have been measured previously. A total of 84 molecular constants have been reported; 70 of these constants are derived for the first time from microwave data. digital.library.unt.edu/ark:/67531/metadc332039/
 Nonlinear Absorption Initiated LaserInduced Damage in [Gamma]Irradiated Fused Silica, Fluorozirconate Glass and Cubic Zirconia
 The contributions of nonlinear absorption processes to laserinduced damage of three selected groups of transparent dielectrics were investigated. The studied materials were irradiated and nonirradiated fused silica, doped and undoped fluorozirconate glass and cubic zirconia stabilized with yttria. The laserinduced damage thresholds, prebreakdown transmission, and nonlinear absorption processes were studied for several specimens of each group. Experimental measurements were performed at wavelengths of 1064 nm and 532 nm using nanosecond and picosecond Nd:YAG laser pulses. In the irradiated fused silica and fluorozirconate glasses, we found that there is a correlation between the damage thresholds at wavelength λ and the linear absorption of the studied specimens at λ/2. In other words, the laserinduced breakdown is related to the probability of all possible twophoton transitions. The results are found to be in excellent agreement with a proposed twophotoninitiated electron avalanche breakdown model. In this model, the initial "seed" electrons for the formation of an avalanche are produced by twophoton excitations of E' centers and metallic impurity levels which are located within the bandgaps of irradiated Si02 and fluorozirconate glasses, respectively. Once the initial electrons are liberated in the conduction band, a highly absorbing plasma is formed by avalanche impact ionization. The resultant heating causes optical damage. In cubic zirconia, we present direct experimental evidence that significant energy is deposited in the samples at wavelength 532 nm prior to electron avalanche formation. The mechanism is found to be due to formation of color centers (F+ or F° centers) by the twophoton absorption process. The presence of these centers was directly shown by transmission measurements. The twophoton absorption (2PA) process was independently investigated and 2PA coefficients obtained. The accumulated effects of the induced centers on the nonlinear absorption measurements were also considered and the 2PA coefficients were measured using short pulses where this effect is negligible. At room temperature, the color centers slowly diffuse out of the irradiated region. The density of these centers was monitored as a function of time. The initial distribution of the centers was assumed to have a Gaussian profile. For this model the diffusion equation was solved exactly and the diffusion constant obtained. digital.library.unt.edu/ark:/67531/metadc331327/
 Coherent Resonant Interaction and Harmonic Generation in Atomic Vapors
 This work examines the use of higher order multiphoton resonances in higher harmonic generation together with judicious exploitation of coherent interaction properties to achieve efficient harmonic generation. A detailed experimental study on third harmonic generation in two photon resonant coherent interaction and a theoretical study on four photon resonant coherent interaction have been conducted. Two photon resonant coheren propagation in lithium vapor (2S4S and 2S3D interaction) has been studied in detail as a function of phase and delay of the interacting pulse sequence. Under coherent lossless propagation of 90 phase shifted pulse pair, third harmonic generation is enhanced. A maximum energy conversion efficiency of 1% was measured experimentally. This experiment shows that phase correlated pulse sequence can be used to control multiphoton coherent resonant effects. A larger two photon resonant enhancement does not result in more efficient harmonic generation, in agreement with the theoretical prediction. An accurate (to at least 0.5 A°) measurement of intensity dependent Stark shift has been done with the newly developed "interferometric wavemeter." Stark shifts as big as several pulse bandwidths (of picosecond pulses) result in a poor tuning of multiphoton resonance and become a limiting factor of resonant harmonic generation. A complete theory has been developed for harmonic generation in a four photon resonant coherent interaction. A numerical application of the theory to the Hg atom successfully interprets the experimental observations in terms of the phase dependent stimulated Raman scattering. With the intensity required for four photon resonant transition, the calculation predicts a dramatic Stark shift effect which completely destroys the resonance condition. This model provides a basis for the development of future schemes for efficient higher order coherent upconversion. digital.library.unt.edu/ark:/67531/metadc332243/
 Two Photon Resonant Picosecond Pulse Propagation in Lithium Vapor
 The work of this dissertation has been to prove that the coherence of multiphoton excitation can be studied by an appropriately phased and time delayed sequence of pulses. An application of this fundamental study of coherence has been made for the enhancement of third harmonic generation. The coherent recovery of the energy lost to the two photon absorption process enalled a larger propagation distance for the fundamental than in an interaction which is incoherent or coherent, but not using a 90 degree phase shifted pulse pair. Phase matching over this longer propagation distance gave an enhancement of third harmonic generation. digital.library.unt.edu/ark:/67531/metadc331546/
 Dispersion of the Nonlinear Refractive Index of CS₂ in the Spectral Range of 911 μm
 The nonlinear refractive index (n2) of room temperature liquid CS2 in the wavelength range of 9 to 11 micrometers is measured. A line tunable hybrid C02 TEA laser and amplifier system is used for the experiments. In these measurements the well known photoacoustic method is utilized to observe the onset of whole beam selffocusing. The photoacoustic signal in a CS2 cell, much longer than the confocal parameter, is monitored. The departure of the acoustic signal from linear growth marks the critical power for the onset of nonlinearity. It is experimentally verified that the phenomenon is power dependent as expected from selffocusing theory. The value of n2 is then calculated from the theoretical model of self focusing. Measurements of the onaxis irradiance transmitted through the nonlinear material as well as the measurements of beam distortion are used to verify the validity of the photoacoustic method. In all the measurements the onaxis intensity was smaller than the calculated threshold intensity for stimulated Brillouin scattering. The back reflection was monitored to make sure that stimulated Brillouin scattering was not playing a role in the phenomenon. digital.library.unt.edu/ark:/67531/metadc332448/
 A Comprehensive Model for the Rotational Spectra of Propyne CH₃CCH in the Ground and V₁₀=1,2,3,4,5 Vibrational States
 The energy states of C₃ᵥ symmetric top polyatomic molecules were studied. Both classical and quantum mechanical methods have been used to introduce the energy states of polyatomic molecules. Also, it is shown that the vibrationrotation spectra of polyatomic molecules in the ground and excited vibrational states can be predicted by group theory. A comprehensive model for predicting rotational frequency components in various v₁₀ vibrational levels of propyne was developed by using perturbation theory and those results were compared with other formulas for C₃ᵥ symmetric top molecules. The v₁₀=1,2,3 and ground rotational spectra of propyne in the frequency range 1770 GHz have been reassigned by using the derived comprehensive model. The v₁₀=3 and v₁₀=4 rotational spectra of propyne have been investigated in the 70 GHz, and 17 to 52 GHz regions, respectively, and these spectral components assigned using the comprehensive model. Molecular constants for these vibrationally excited states have been determined from more than 100 observed rotational transitions. From these experimentally observed components and a model based upon first principles for C₃ᵥ symmetry molecules, rotational constants have been expressed in a form which enables one to predict rotational components for vibrational levels for propyne up to v₁₀=5. This comprehensive model also appears to be useful in predicting rotational components in more highly excited vibrational levels but data were not available for comparison with the theory. Several techniques of assignment of rotational spectra for each excited vibrational state are discussed. To get good agreement between theory and experiment, an additional term 0.762(J+1) needed to be added to Kℓ=1 states in v₁₀=3. No satisfactory theoretical explanation of this term has been found. Experimentally measured frequencies for rotational components for J→(J+1)=+1 (0≤J≤3) in each vibration v₁₀=n (0≤n≤4) are presented and compared with those calculated using the results of basic perturbation theory. The v₉=2 rotational spectrum of the propyne molecule was introduced in Appendix A to compare the rotational spectra of the same molecule in different vibrational levels v₉ and v₁₀. digital.library.unt.edu/ark:/67531/metadc332026/
 K, L, and MShell XRay Production Cross Sections for Beryllium, Aluminum and Argon Ions Incident Upon Selected Elements
 Incident 0.5 to 2.5 MeV charged particle beams were used to ionize the innershells of selected targets and study their subsequent emission of characteristic xrays. ⁹Be⁺ ions were used to examine Kshell xray production from thin F, Na, Al, Si, P, Cl, and K targets, Lshell xray production from thin Cu, An, Ge, Br, Zr and Ag targets, and Mshell xray production from thin Pr, Nd, Eu, Dy, Ho, Hf, W, Au, Pb and Bi targets. Lshell xray production cross sections were also measured for ²⁷Al⁺ ions incident upon Ni, Cu, Zn, As, Zr, and Pd targets. Mshell xray production cross sections were measure for ²⁷Al⁺ and ⁴⁰Ar⁺ ions incident upon Pr, Nd, Gd, Dy, Lu, Hf, Au, Pb, Bi, and U targets. These measurements were performed using the 2.5 MV Van de Graaff accelerator at North Texas State University. The xrays were detected with a Si(Li) detector whose efficiency was determined by fitting a theoretical photon absorption curve to experimentally measure values. The xray yields were normalized to the simultaneously measured Rutherford backscattered (RBS) yields which resulted in an xray production cross section per incident ion. The RBS spectrum was obtained using a standard surface barrier detector calibrated for to account for the "pulse height defect." The experimental results are compared to the predictions of both the first Born and ECPSSR theories; each of which is composed of two parts, the direct ionization (DI) of the target electron to the continuum and the capture (EC) of the target electron to the projectile. The first Born describes DI by the PlaneWaveBornApproximation (PWBA) and EC by the OppenheimerBrinkmanKramers treatment of Nikolaev (OBKN). ECPSSR expands upon the first Born by using perturbed (PSS) and relativistic (R) target electron wave functions in addition to considering the energy loss (E) of the projectile in the target and its deviation from straight line trajectory (Coulomb deflection (C)). The measurements presented show that the first Born theories overestimate the measured results rather significantly for all experiments using the ⁹Be beams to examine the inner shell xrays, while the ECPSSR predictions fir the measured data much better. For incident ²⁷Al and ⁴⁰Ar ions, the measured results are not predicted by the theories. The first Born generally overpredicts the data for low target atomic numbers while underpredicting at high atomic numbers. The ECPSSR theory greatly underpredicts the results (factors of 10³ to 10²⁰). Reasons for this behavior are discussed as well as suggestions for future experiments. digital.library.unt.edu/ark:/67531/metadc331170/
 Carbon KShell XRay and AugerElectron Cross Sections and Fluorescence Yields for Selected Molecular Gases by 0.6 To 2 .0 MeV Proton Impact
 Absolute Kshell xray cross sections and Augerelectron cross sections are measured for carbon for 0.6 to 2.0 MeV proton incident on CH₄, nC₄H₁₀ (nButane), iC₄H₁₀ (isobutane), C₆H₆ (Benzene), C₂H₂ (Acetylene), CO and CO₂. Carbon Kshell fluorescence yields are calculated from the measurements of xray and Augerelectron cross sections. Xray cross sections are measured using a variable geometry end window proportional counter. An alternate method is described for the measurement of the transmission of the proportional counter window. Auger electrons are detected by using a constant transmission energy Π/4 parallel pi ate electrostatic analyzer. Absolute carbon Kshell xray cross sections for CH₄ are compared to the known results of Khan et al. (1965). Augerelectron cross sections for proton impact on CH₄ are compared to the known experimental values of RΦdbro et al. (1979), and to the theoretical predictions of the first Born and ECPSSR. The data is in good agreement with both the first Born and ECPSSR, and within our experimental uncertainties with the measurements of RΦdbro et al. The xray cross sections, Augerelectron cross sections and fluorescence yields are plotted as a function of the Pauling charge, and show significant variations. These changes in the xray cross sections are compared to a model based on the number of electrons present in the 2s and 2p sub shells of these carbon based molecules. The changes in the Augerelectron cross sections are compared to the calculations of Matthews and Hopkins. The variation in the fluorescence yield is explained on the basis of the multiconfiguration DiracFock model. digital.library.unt.edu/ark:/67531/metadc331849/
 Linear and Nonlinear Optical Techniques to Characterize Narrow Gap Semicondutors: (Hg /Cd)Te and InSb
 Several methods have been developed and used to characterize the narrow gap semiconductors Hg^_xCdxTe (HgCdTe) (0.20<x<0.32) and InSb both in the presence of CO2 laser radiation and in the dark. The results have allowed the determination of certain band parameters including the fundamental energy bandgap Eg which is directly related to x, the mole fraction of Cd. In the dark, characterization of several different samples of HgCdTe and InSb were carried out by analyzing the temperature dependence of the Hall coefficient and the magnetic field positions of the magnetophonon extrema from which their xvalues were determined. The quality of the magnetophonon spectra is also shown to be related to the inhomogeneity Ax of the HgCdTe samples. Onephoton magnetoabsorption (OPMA) spectra have been obtained for x ~ 0.2 samples of pHgCdTe thin films and nHgCdTe bulk samples. Analysis of the OPMA transition energies allows the xvalue to be determined to within « ±0.001. A method is also discussed which can be used to estimate the sample inhomogeneity Ax. Nonlinear optical properties of semiconductors are not only scientifically interesting to study, but are also proving to be technologically important as various nonlinear optical devices are being developed. One of the most valuable nonlinear optical characterization method uses twophoton absorption (TPA). Two techniques using TPA processes were developed and used to measure the cutoff wavelength of several different samples of HgCdTe (x ~ 0.3) from which xvalues were determined to within «± 0.0005. Intensity and temperature dependent measurements on impurity and TPA processes have also been carried out and the results are compared with rate equations describing the photoexcited carrier dynamics. These results have yielded important information about the optical and material properties of HgCdTe such as the detection of impurity and trapping levels, TPA coefficients, carrier lifetimes, and recombination mechanisms. TPA and impurity absorption studies were also carried out on n— and p—InSb in order to obtain information about impurity levels, carrier lifetimes, and recombination mechanisms. digital.library.unt.edu/ark:/67531/metadc330622/
 Optical Nonlinearities in Semiconductors for Limiting
 I have conducted detailed experimental and theoretical studies of the nonlinear optical properties of semiconductor materials useful for optical limiting. I have constructed optical limiters utilizing twophoton absorption along with photogenerated carrier defocusing as well as the bound electronic nonlinearity using the semiconducting material ZnSe. I have optimized the focusing geometry to achieve a large dynamic range while maintaining a low limiting energy for the device. The ZnSe monolithic optical limiter has achieved a limiting energy as low as 13 nJ (corresponding to 300W peak power) and a dynamic range as large as 105 at 532 nm using psec pulses. Theoretical analysis showed that the ZnSe device has a broadband response covering the wavelength range from 550 nm to 800 nm. Moreover, I found that existing theoretical models (e.g. the Auston model and the bandresonant model using Boltzmann statistics) adequately describe the photogenerated carriers refractive nonlinearity in ZnSe. Material nonlinear optical parameters, such as the twophoton absorption coefficient β_2=5.5cm/GW, the refraction per unit carrier density σ_n=0.8∗10^21cm^3 and the bound electronic refraction n_2=4∗10^11esu, have been measured via timeintegrated beam distortion experiments in the near field. A numerical code has been written to simulate the beam distortion in order to extract the previously mentioned material parameters. In addition, I have performed timeresolved distortion measurements that provide an intuitive picture of the carrier generation process via twophoton absorption. I also characterized the optical nonlinearities in a ZnSe FabryPerot thin film structure (an interference filter). I concluded that the nonlinear absorption alone in the thin film is insufficient to build an effective optical limiter, as it did not show a net change in refraction using psec pulses. An innovative numerical program was developed to simulate the nonlinear beam propagation inside the FabryPerot structure. For comparison, pumpprobe experiments were performed using both thin film and bulk ZnSe. The results showed relatively long carrier lifetimes (>300 psec) in both samples. A numerical code was written to fit the pumpprobe experimental results. The fitting yielded that carrier lifetimes (recombination through traps), radiative decay rate, twophoton absorption coefficient as well as the free carrier absorption coefficient for ZnSe bulk material. digital.library.unt.edu/ark:/67531/metadc331203/
 Anomalous Behavior in the Rotational Spectra of the v₈=2 and the v₈=3 Vibrations for the ¹³C and ¹⁵N Tagged Isotopes of the CH₃CN Molecule in the Frequency Range 1795 GHz
 The rotational microwave spectra of the three isotopes (^13CH_3^12C^15N, ^12CH_3^13C^15N, and ^13CH_3^13C^15N) of the methyl cyanide molecule in the v_8=3, v_8=2, v_7=1 and v_4=1 vibrational energy levels for the rotational components 1£J£5 (for a range of frequency 1795 GHz.) were experimentally and theoretically examined. Rotational components in each vibration were measured to determine the mutual interactions in each vibration between any of the vibrational levels investigated. The method of isotopic substitution was employed for internal tuning of each vibrational level by single and double substitution of ^13C in the two sites of the molecule. It was found that relative frequencies within each vibration with respect to another vibration were shifted in a systematic way. The results given in this work were interpreted on the basis of these energy shifts. Large departure between experimentally measured and theoretically predicted frequency for the quantum sets (J, K=±l, ϑ=±1), Kϑl in the v_8=3 vibrational states for the ^13c and ^15N tagged isotopes of CH_3CN showed anomalous behavior which was explained as being due to Fermi resonance. Accidently strong resonances (ASR) were introduced to account for some departures which were not explained by Fermi resonance. digital.library.unt.edu/ark:/67531/metadc330976/
 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/
 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/