 A dynamic and thermodynamic approach to complexity.
 The problem of establishing the correct approach to complexity is a very hot and crucial issue to which this dissertation gives some contributions. This dissertation considers two main possibilities, one, advocated by Tsallis and coworkers, setting the foundation of complexity on a generalized, nonextensive , form of thermodynamics, and another, proposed by the UNT Center for Nonlinear Science, on complexity as a new condition that, for physical systems, would be equivalent to a state of matter intermediate between dynamics and thermodynamics. In the first part of this dissertation, the concept of KolmogorovSinai entropy is introduced. The Pesin theorem is generalized in the formalism of Tsallis nonextensive thermodynamics. This generalized form of Pesin theorem is used in the study of two major classes of problems, whose prototypes are given by the Manneville and the logistic map respectively. The results of these studies convince us that the approach to complexity must be made along lines different from those of the nonextensive thermodynamics. We have been convinced that the Lévy walk can be used as a prototype model of complexity, as a condition of balance between order and randomness that yields new phenomena such as aging, and multifractality. We reach the conclusions that these properties must be studied within a dynamic rather than thermodynamic perspective. The second part focuses on the study of the heart beating problem using a dynamic model, the socalled memory beyond memory, based on the Lévy walker model. It is proved that the memory beyond memory effect is more obvious in the healthy heart beating sequence. The concepts of fractal, multifractal, wavelet transformation and wavelet transform maximum modulus (WTMM) method are introduced. Artificial time sequences are generated by the memory beyond memory model to mimic the heart beating sequence. Using WTMM method, the multifratal singular spectrums of the sequences are calculated. It is clear that the sequence with strong memory beyond memory effect has broader singular spectrum.200308 digital.library.unt.edu/ark:/67531/metadc4276/
 The dynamic foundation of fractal operators.
 The fractal operators discussed in this dissertation are introduced in the form originally proposed in an earlier book of the candidate, which proves to be very convenient for physicists, due to its heuristic and intuitive nature. This dissertation proves that these fractal operators are the most convenient tools to address a number of problems in condensed matter, in accordance with the point of view of many other authors, and with the earlier book of the candidate. The microscopic foundation of the fractal calculus on the basis of either classical or quantum mechanics is still unknown, and the second part of this dissertation aims at this important task. This dissertation proves that the adoption of a master equation approach, and so of probabilistic as well as dynamical argument yields a satisfactory solution of the problem, as shown in a work by the candidate already published. At the same time, this dissertation shows that the foundation of Levy statistics is compatible with ordinary statistical mechanics and thermodynamics. The problem of the connection with the KolmogorovSinai entropy is a delicate problem that, however, can be successfully solved. The derivation from a microscopic Liouvillelike approach based on densities, however, is shown to be impossible. This dissertation, in fact, establishes the existence of a striking conflict between densities and trajectories. The third part of this dissertation is devoted to establishing the consequences of the conflict between trajectories and densities in quantum mechanics, and triggers a search for the experimental assessment of spontaneous wavefunction collapses. The research work of this dissertation has been the object of several papers and two books. digital.library.unt.edu/ark:/67531/metadc4235/
 Dynamical Friction Coefficients for Plasmas Exhibiting NonSpherical Electron Velocity Distributions
 This investigation is designed to find the net rate of decrease in the component of velocity parallel to the original direction of motion of a proton moving through an electron gas exhibiting a nonspherical velocity distribution. digital.library.unt.edu/ark:/67531/metadc130480/
 EEG, Alpha Waves and Coherence
 This thesis addresses some theoretical issues generated by the results of recent analysis of EEG time series proving the brain dynamics are driven by abrupt changes making them depart from the ordinary Poisson condition. These changes are renewal, unpredictable and nonergodic. We refer to them as crucial events. How is it possible that this form of randomness be compatible with the generation of waves, for instance alpha waves, whose observation seems to suggest the opposite view the brain is characterized by surprisingly extended coherence? To shed light into this apparently irretrievable contradiction we propose a model based on a generalized form of Langevin equation under the influence of a periodic stimulus. We assume that there exist two different forms of time, a subjective form compatible with Poisson statistical physical and an objective form that is accessible to experimental observation. The transition from the former to the latter form is determined by the brain dynamics interpreted as emerging from the cooperative interaction among many units that, in the absence of cooperation would generate Poisson fluctuations. We call natural time the brain internal time and we make the assumption that in the natural time representation the time evolution of the EEG variable y(t) is determined by a Langevin equation perturbed by a periodic process that in this time representation is hardly distinguishable from an erratic process. We show that the representation of this random process in the experimental time scale is characterized by a surprisingly extended coherence. We show that this model generates a sequence of damped oscillations with a time behavior that is remarkably similar to that derived from the analysis of real EEG's. The main result of this research work is that the existence of crucial events is not incompatible with the alpha wave coherence. In addition to this important result, we find another result that may help our group, or any other research group working on the analysis of brain's dynamics, to prove or to disprove the existence of crucial events. We study the diffusion process generated by fluctuations emerging from the same model after filtering out the alpha coherence, and we study the recursion to the origin. We study the survival probability of this process, namely the probability that up to a given time no recrossing of the origin occurs. We find that this is an inverse power law with a power that depends on whether or not crucial events exist. digital.library.unt.edu/ark:/67531/metadc28389/
 The Effect of Average Grain Size on Polycrystalline Diamond Films
 The work function of hydrogenterminated, polycrystalline diamond was studied using ultraviolet photoelectron spectroscopy. Polycrystalline diamond films were deposited onto molybdenum substrates by electrophoresis for grain sizes ranging from 0.3 to 108 microns. The work function and electron affinity were measured using 21.2 eV photons from a helium plasma source. The films were characterized by xray photoelectron spectroscopy to determine elemental composition and the sp2/sp3 carbon fraction. The percentage of (111) diamond was determined by xray diffraction, and scanning electron microscopy was performed to determine average grain size. The measured work function has a maximum of 5.1 eV at 0.3 microns, and decreases to 3.2 eV at approximately 4 microns. Then the work function increases with increasing grain size to 4.0 eV at 15 microns and then asymptotically approaches the 4.8 eV work function of single crystal diamond at 108 microns. These results are consistent with a 3component model in which the work function is controlled by singlecrystal (111) diamond at larger grain sizes, graphitic carbon at smaller grain sizes, and by the electron affinity for the intervening grain sizes. digital.library.unt.edu/ark:/67531/metadc3164/
 Effect of Sample Geometry on Magnetomorphic Oscillations in the Hall Effect in Cadium at LiquidHelium Temperatures
 This thesis presents observations on sizeeffect oscillations in the Hall effect in an oriented single crystal of highly pure cadmium at liquidhelium temperatures. All measurements were made in transverse magnetic field. digital.library.unt.edu/ark:/67531/metadc130799/
 The Effects of Cesium Deposition and Gas Exposure on the Field Emission Properties of Single Wall and Multiwall Carbon Nanotubes
 The effects of Cs deposition on the field emission (FE) properties of singlewalled carbon nanotube (SWNT) bundles were studied. In addition, a comparative study was made on the effects of O2, Ar and H2 gases on the field emission properties of SWNT bundles and multiwall carbon nanotubes (MWNTs). We observed that Cs deposition decreases the turnon field for FE by a factor of 2.1  2.9 and increases the FE current by 6 orders of magnitude. After Cs deposition, the FE current versus voltage (IV) curves showed nonFowlerNordheim behavior at large currents consistent with tunneling from adsorbate states. At lower currents, the ratio of the slope of the FE IV curves before and after Cs deposition was approximately 2.1. Exposure to N2 does not decrease the FE current, while exposure to O2 decreases the FE current. Our results show that cesiated SWNT bundles have great potential as economical and reliable vacuum electron sources. We find that H2 and Ar gases do not significantly affect the FE properties of SWNTs or MWNTs. O2 temporarily reduces the FE current and increases the turnon voltage of SWNTs. Full recovery of these properties occurred after operation in UHV. The higher operating voltages in an O2 environment caused a permanent decrease of FE current and increase in turnon field of MWNTs. The ratios of the slopes before and after O2 exposure were approximately 1.04 and 0.82 for SWNTs and MWNTs, respectively. SWNTs compared to MWNTs would appear to make more economical and reliable vacuum electron sources. digital.library.unt.edu/ark:/67531/metadc3110/
 Effects of Dissipation on Propagation of Surface Electromagnetic and Acoustic Waves
 With the recent emergence of the field of metamaterials, the study of subwavelength propagation of plane waves and the dissipation of their energy either in the form of Joule losses in the case of electomagnetic waves or in the form of viscous dissipation in the case of acoustic waves in different interfaced media assumes great importance. with this motivation, I have worked on problems in two different areas, viz., plasmonics and surface acoustics. the first part (chapters 2 & 3) of the dissertation deals with the emerging field of plasmonics. Researchers have come up with various designs in an efort to fabricate efficient plasmonic waveguides capable of guiding plasmonic signals. However, the inherent dissipation in the form of Joule losses limits efficient usage of surface plasmon signal. a dielectricmetal¬dielectric planar structure is one of the most practical plasmonic structures that can serve as an efficient waveguide to guide electromagnetic waves along the metaldielectric boundary. I present here a theoretical study of propagation of surface plasmons along a symmetric dielectricmetaldielectric structure and show how proper orientation of the optical axis of the anisotropic substrate enhances the propagation length. an equation for propagation length is derived in a wide range of frequencies. I also show how the frequency of coupled surface plasmons can be modulated by changing the thickness of the metal film. I propose a KronigPenny model for the plasmonic crystal, which in the long wavelength limit, may serve as a homogeneous dielectric substrate with high anisotropy which do not exist for natural optical crystals. in the second part (chapters 4 & 5) of the dissertation, I discuss an interesting effect of extraordinary absorption of acoustic energy due to resonant excitation of Rayleigh waves in a narrow water channel clad between two metal plates. Starting from the elastic properties of the metal plates, I derive a dispersion equation that gives resonant frequencies, which coincide with those observed in the experiment that was performed by Wave Phenomena Group at Polytechnic University of Valencia, Spain. Two eigenmodes with different polarizations and phase velocities are obtained from the dispersion equation. at certain critical aperture of the channel, an interesting cutoff effect, which is unusual for an acoustic wave, is observed for one of the eigenmodes with symmetric distribution of the pressure field. the theoretical prediction of the coupling and synchronization of Rayleigh waves strongly supports the experimentally measured shift of the resonant frequencies in the transmission spectra with channel aperture. the observed high level of absorption may find applications in designing metamaterial acoustic absorbers. digital.library.unt.edu/ark:/67531/metadc115126/
 The Effects of Lead Placement and Sample Shape in the Measurement of Electrical Resistivity
 This thesis is a study of the effects of lead placement and sample shape in the measurement of electrical resistivity. digital.library.unt.edu/ark:/67531/metadc131303/
 Electrical Conductivity in Thin Films
 This thesis deals with electrical conductivity in thin films. Classical and quantum size effects in conductivity are discussed including some experimental evidence of quantum size effects. The component conductivity along the applied electric field of a thin film in a transverse magnetic field is developed in a density matrix method. digital.library.unt.edu/ark:/67531/metadc164055/
 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/
 Electron Spin Resonance Absorption in Benzophenone Phenylhydrazone Negative Ion
 This thesis reports an electron spin resonance absorption study of the hyperfine interaction between nuclei and a single "nearlyfree" electron in dilute solutions of the benzophenone phenylhydrazone free radical in tetrahydrofuran. digital.library.unt.edu/ark:/67531/metadc131161/
 Electron Transport in Bismuth at Liquid Helium Tempratures
 To obtain information on the band structure of bismuth, galvanomagnetic potentials were measured in a single crystal at liquidhelium and liquidnitrogen temperatures. These measurements were analyzed for information on the different carriers, particularly for the existence of a highmobility band of holes. digital.library.unt.edu/ark:/67531/metadc130512/
 Electrostatic Effects in IIIV Semiconductor Based Metaloptical Nanostructures

Access: Use of this item is restricted to the UNT Community.
The modification of the band edge or emission energy of semiconductor quantum well light emitters due to image charge induced phenomenon is an emerging field of study. This effect observed in quantum well light emitters is critical for all metaloptics based light emitters including plasmonics, or nanometallic electrode based light emitters. This dissertation presents, for the first time, a systematic study of the image charge effect on semiconductor–metal systems. the necessity of introducing the image charge interactions is demonstrated by experiments and mathematical methods for semiconductormetal image charge interactions are introduced and developed. digital.library.unt.edu/ark:/67531/metadc115090/  Electrostatic Mechanism of Emission Enhancement in Hybrid Metalsemiconductor Lightemitting Heterostructures
 IIIV nitrides have been put to use in a variety of applications including laser diodes for modern DVD devices and for solidstate white lighting. Plasmonics has come to the foreground over the past decade as a means for increasing the internal quantum efficiency (IQE) of devices through resonant interaction with surface plasmons which exist at metal/dielectric interfaces. Increases in emission intensity of an order of magnitude have been previously reported using silver thinfilms on InGaN/GaN MQWs. the dependence on resonant interaction between the plasmons and the light emitter limits the applications of plasmonics for light emission. This dissertation presents a new nonresonant mechanism based on electrostatic interaction of carriers with induced image charges in a nearby metallic nanoparticle. Enhancement similar in strength to that of plasmonics is observed, without the restrictions imposed upon resonant interactions. in this work we demonstrate several key features of this new interaction, including intensitydependent saturation, increase in the radiative recombination lifetime, and strongly inhomogeneous light emission. We also present a model for the interaction based on the aforementioned image charge interactions. Also discussed are results of work done in the course of this research resulting in the development of a novel technique for strain measurement in lightemitting structures. This technique makes use of a spectral fitting model to extract information about electronphonon interactions in the sample which can then be related to strain using theoretical modeling. digital.library.unt.edu/ark:/67531/metadc115113/
 Emergence of Complexity from Synchronization and Cooperation
 The dynamical origin of complexity is an object of intense debate and, up to moment of writing this manuscript, no unified approach exists as to how it should be properly addressed. This research work adopts the perspective of complexity as characterized by the emergence of nonPoisson renewal processes. In particular I introduce two new complex system models, namely the twostate stochastic clocks and the integrateandfire stochastic neurons, and investigate its coupled dynamics in different network topologies. Based on the foundations of renewal theory, I show how complexity, as manifested by the occurrence of nonexponential distribution of events, emerges from the interaction of the units of the system. Conclusion is made on the work's applicability to explaining the dynamics of blinking nanocrystals, neuron interaction in the human brain, and synchronization processes in complex networks. digital.library.unt.edu/ark:/67531/metadc6107/
 Energy Distribution of Sputtered Neutral Atoms from a Multilayer Target
 Energy distribution measurements of sputtered neutral particles contribute to the general knowledge of sputtering, a common technique for surface analysis. In this work emphasis was placed on the measurement of energy distribution of sputtered neutral atoms from different depths. The liquid GaIn eutectic alloy as a sample target for this study was ideal due to an extreme concentration ratio gradient between the top two monolayers. In pursuing this study, the method of sputterinitiated resonance ionization spectroscopy (SIRIS) was utilized. SIRIS employs a pulsed ion beam to initiate sputtering and tunable dye lasers for resonance ionization. Observation of the energy distribution was achieved with a positionsensitive detector. The principle behind the detector's energy resolution is time of flight (TOF) spectroscopy. For this specific detector, programmed time intervals between the sputtering pulse at the target and the ionizing laser pulse provided information leading to the energy distribution of the secondary neutral particles. This experiment contributes data for energy distributions of sputtered neutral particles to the experimental database, required by theoretical models and computer simulations for the sputtering phenomenon. digital.library.unt.edu/ark:/67531/metadc2657/
 Energy Losses of Protons Projected through a Plasma Due to Collisions with Electrons of the Plasma for a Variety of NonMaxwellian Electron Velocity Distributions
 The purpose of this thesis is to study energy losses suffered by protons in traversing a plasma through collision with the electrons of the plasma. For these electrons a variety of nonMaxwellian velocity distributions are assumed. digital.library.unt.edu/ark:/67531/metadc130468/
 An entropic approach to the analysis of time series.
 Statistical analysis of time series. With compelling arguments we show that the Diffusion Entropy Analysis (DEA) is the only method of the literature of the Science of Complexity that correctly determines the scaling hidden within a time series reflecting a Complex Process. The time series is thought of as a source of fluctuations, and the DEA is based on the Shannon entropy of the diffusion process generated by these fluctuations. All traditional methods of scaling analysis, instead, are based on the variance of this diffusion process. The variance methods detect the real scaling only if the Gaussian assumption holds true. We call H the scaling exponent detected by the variance methods and d the real scaling exponent. If the time series is characterized by Fractional Brownian Motion, we have H¹d and the scaling can be safely determined, in this case, by using the variance methods. If, on the contrary, the time series is characterized, for example, by Lévy statistics, H ¹ d and the variance methods cannot be used to detect the true scaling. Lévy walk yields the relation d=1/(32H). In the case of Lévy flights, the variance diverges and the exponent H cannot be determined, whereas the scaling d exists and can be established by using the DEA. Therefore, only the joint use of two different scaling analysis methods, the variance scaling analysis and the DEA, can assess the real nature, Gauss or Lévy or something else, of a time series. Moreover, the DEA determines the information content, under the form of Shannon entropy, or of any other convenient entopic indicator, at each time step of the process that, given a sufficiently large number of data, is expected to become diffusion with scaling. This makes it possible to study the regime of transition from dynamics to thermodynamics, nonstationary regimes, and the saturation regime as well. First of all, the efficiency of the DEA is proved with theoretical arguments and with numerical work on artificial sequences. Then we apply the DEA to three different sets of real data, Genome sequences, hard xray solar flare waiting times and sequences of sociological interest. In all these cases the DEA makes new properties, overlooked by the standard method of analysis, emerge. digital.library.unt.edu/ark:/67531/metadc3033/
 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/
 Experimental Determination of the Scattering Crosssection of Ogives and Prolate Spheroids at Microwave Frequencies
 Because of the great difficulty of obtaining exact numerical values of crosssection, and because of the inherent uncertainties in interpreting and evaluating the approximate methods, accurate experimental crosssection data would be extremely useful to the radar engineer. It was with this purpose in mind that the present longrange research program in microwave scattering was undertaken. Of immediate interest were the scattering properties of the prolate spheroid, the ogive (formed by rotating the minor segment of a circle around the chord), and, for comparison, the long cylinder. digital.library.unt.edu/ark:/67531/metadc107875/
 Exploration of hierarchical leadership and connectivity in neural networks in vitro.
 Living neural networks are capable of processing information much faster than a modern computer, despite running at significantly lower clock speeds. Therefore, understanding the mechanisms neural networks utilize is an issue of substantial importance. Neuronal interaction dynamics were studied using histiotypic networks growing on microelectrode arrays in vitro. Hierarchical relationships were explored using bursting (when many neurons fire in a short time frame) dynamics, pairwise neuronal activation, and information theoretic measures. Together, these methods reveal that global network activity results from ignition by a small group of burst leader neurons, which form a primary circuit that is responsible for initiating most networkwide burst events. Phase delays between leaders and followers reveal information about the nature of the connection between the two. Physical distance from a burst leader appears to be an important factor in follower response dynamics. Information theory reveals that mutual information between neuronal pairs is also a function of physical distance. Activation relationships in developing networks were studied and plating density was found to play an important role in network connectivity development. These measures provide unique views of network connectivity and hierarchical relationship in vitro which should be included in biologically meaningful models of neural networks. digital.library.unt.edu/ark:/67531/metadc9775/
 Extinguishment of a Lowpressure Argon Discharge by a Magnetic Field
 The experiment in this study involves the extinguishment of a lowpressure argon discharge by a magnetic field. digital.library.unt.edu/ark:/67531/metadc108257/
 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/
 Foil Depression Factors for Discshaped Detectors
 The generalized data which are presented in this thesis are the culmination of the determination of the foil depression factor using oblate spheroidal coordinates. digital.library.unt.edu/ark:/67531/metadc130367/
 Fractional Brownian motion and dynamic approach to complexity.
 The dynamic approach to fractional Brownian motion (FBM) establishes a link between nonPoisson renewal process with abrupt jumps resetting to zero the system's memory and correlated dynamic processes, whose individual trajectories keep a nonvanishing memory of their past time evolution. It is well known that the recrossing times of the origin by an ordinary 1D diffusion trajectory generates a distribution of time distances between two consecutive origin recrossing times with an inverse power law with index m=1.5. However, with theoretical and numerical arguments, it is proved that this is the special case of a more general condition, insofar as the recrossing times produced by the dynamic FBM generates process with m=2H. Later, the model of ballistic deposition is studied, which is as a simple way to establish cooperation among the columns of a growing surface, to show that cooperation generates memory properties and, at same time, nonPoisson renewal events. Finally, the connection between trajectory and density memory is discussed, showing that the trajectory memory does not necessarily yields density memory, and density memory might be compatible with the existence of abrupt jumps resetting to zero the system's memory. digital.library.unt.edu/ark:/67531/metadc3992/
 Galvanomagnetic Determination of Energy Bands in Arsenic
 A study of the transport properties of a substance requires the determination of a set of transport coefficients by experiment. From these coefficients, the elements of the electrical conductivity tensor, thermoelectric tensor, et cetera can be determined. In this experiment, measurements and analyses of galvanomagnetic effects in a single crystal of arsenic were performed. The measurements were made at liquidhelium temperatures in magnetic fields ranging to 25 kilogauss. The gross isothermal, electrical conductivities have been analyzed to determine various parameters characterizing the energy bands in arsenic. digital.library.unt.edu/ark:/67531/metadc130903/
 Galvanomagnetic Phenomena in Arsenic at Liquid Helium Temperatures
 The purpose of this investigation was to study some of the transport effects in a single crystal of arsenic at liquid helium temperatures in a magnetic field up to twentyfour kilogauss. The experimental coefficients determined were the isothermal magnetoresistivity and the isothermal Hall resistivity. digital.library.unt.edu/ark:/67531/metadc130697/
 Gamma Ray Distribution from Neutron Excitation in Cesium
 The purpose of this investigation was to analyze the gamma rays resulting from excitation of Cs133 by the inelastic scattering of 14 MeV neutrons and to determine the relative intensity of each gamma ray. digital.library.unt.edu/ark:/67531/metadc163933/
 Gamma Ray Response of a CsI(T1) Crystal to 14 Mev Neutrons
 The purpose of this paper is to study the possible excited states in the nucleus of Cs133. At North Texas State College a 100Kev CockcroftWalton accelerator has been constructed for use as a neutron source for exciting various nuclei and for studying the gamma spectra obtained to determine their energy levels. digital.library.unt.edu/ark:/67531/metadc108020/
 Gamma Rays from Cs¹³³ by Inelastic Scattering of Neutrons
 The purpose of this investigation was to observe the excited states of the Cs¹³³ nucleus when neutrons are inelastically scattered from the nucleus. digital.library.unt.edu/ark:/67531/metadc108105/
 Gamma Rays from Neutron Excitation of Cs133
 This thesis explores gamma rays from neutron excitation of Cs133. digital.library.unt.edu/ark:/67531/metadc108026/
 Gamma Rays Resulting from Neutron Scattering in Cesium
 The purpose of this investigation was to attempt to resolve the energy levels of Cs133 that can be excited by inelastic scattering of 14 Mev neutrons. digital.library.unt.edu/ark:/67531/metadc163901/
 Growing carbon nanotubes by chemical vapor deposition technique.

Access: Use of this item is restricted to the UNT Community.
Carbon nanotubes were synthesized in the laboratory using chemical vapor deposition at different methane concentration. I found that a methane concentration of 4 sccm was ideal for well recognizable carbon nanotubes. A higher concentration led to fewer nanotube growth and silicon carbide structure. Coating the sample first with Fe(NO3)3 created a catalyst base on the substrate for the nanotube to adhere and grow on. digital.library.unt.edu/ark:/67531/metadc2454/  Growth and Characterization of βIron Disilicide, βIron Silicon Germanide, and Osmium Silicides
 The semiconducting silicides offer significant potential for use in optoelectronic devices. Full implementation of the materials, however, requires the ability to tailor the energy gap and band structure to permit the synthesis of heterojunctions. One promising approach is to alloy the silicides with Ge. As part of an investigation into the synthesis of semiconducting silicide heterostructures, a series of βFe(Si1−xGex)2 epilayer samples, with nominal alloy content in the range 0 < x < 0.15, have been prepared by molecular beam epitaxy on Si(100). I present results of the epitaxial and crystalline quality of the films, as determined by reflection highenergy electron diffraction, Rutherford backscattering spectroscopy, and double crystal xray diffraction, and of the band gap dependence on the alloy composition, as determined by Fourier transform infrared spectroscopy. A reduction in band gap was observed with increasing Ge content, in agreement with previous theoretical predictions. However Ge segregation was also observed in βFe(Si1−xGex)2 epilayers when x > 0.04. Osmium silicide films have been grown by molecular beam epitaxy on Si(100). The silicides have been grown using ebeam evaporation sources for both Os and Si onto Si(100) substrates at varying growth rates and temperatures ranging from 600700ºC. The resulting films have been analyzed using reflection highenergy electron diffraction, Raman spectroscopy, reflectivity measurements, inplane and out of plane Xray diffraction and temperature dependent magnetotransport. A change in crystalline quality is observed with an increase in Si overpressure. For a lower silicon to osmium flux ration (JSi/JOs=1.5) both OsSi2 and Os2Si3 occur, whereas with a much larger Si overpressure (JSi/JOs>4), crystalline quality is greatly increased and only a single phase, Os2Si3, is present. The outofplane Xray diffraction data show that the film grows along its [4 0 2] direction, with a good crystal quality as evidenced by the small FWHM in the rocking curve. The inplane Xray diffraction data show growth twins with perpendicular orientation to each other. digital.library.unt.edu/ark:/67531/metadc12107/
 Gurevich Magnetomorphic Oscillations in Single Crystals of Aluminum at Helium Temperatures
 The Sondheimer theory was tested by looking for oscillatory phenomena in a group of single crystals representing a range in dimensions from matchbox geometry to thinfilm geometry. The single crystals were identical with respect to impurity content, strain, orientation, surface condition, and probe placement. digital.library.unt.edu/ark:/67531/metadc130866/
 High Efficiency High Power Blue Laser by Resonant Doubling in PPKTP
 I developed a high power blue laser for use in scientific and technical applications (eg. precision spectroscopy, semiconductor inspection, flow cytometry, etc). It is linearly polarized, single longitudinal and single transverse mode, and a convenient fiber coupled continuous wave (cw) laser source. My technique employs external cavity frequency doubling and provides better power and beam quality than commercially available blue diode lasers. I use a fiber Bragg grating (FBG) stabilized infrared (IR) semiconductor laser source with a polarization maintaining (PM) fiber coupled output. Using a custom made optical and mechanical design this output is coupled with a mode matching efficiency of 96% into the doubling cavity. With this carefully designed and optimized cavity, measurements were carried out at various fundamental input powers. A net efficie ncy of 81 % with an output power of 680 mW at 486 nm was obtained using 840 mW of IR input. Also I report an 87.5 % net efficiency in coupling of blue light from servo locked cavity into a single mode PM fiber. Thus I have demonstrated a total fiber to fiber efficiency of 71% can be achieved in our approach using periodically poled potassium titanyl phosphate (PPKTP). To obtain these results, all losses in the system were carefully studied and minimized. digital.library.unt.edu/ark:/67531/metadc103306/
 Homogeneous Canonical Formalism and Relativistic Wave Equations
 This thesis presents a development of classical canonical formalism and the usual transition schema to quantum dynamics. The question of transition from relativistic mechanics to relativistic quantum dynamics is answered by developing a homogeneous formalism which is relativistically invariant. Using this formalism the KleinGordon equation is derived as the relativistic analog of the Schroedinger equation. Using this formalism further, a method of generating other relativistic equations (with spin) is presented. digital.library.unt.edu/ark:/67531/metadc130781/
 The Interactions of Plasma with Lowk Dielectrics: Fundamental Damage and Protection Mechanisms
 Nanoporous lowk dielectrics are used for integrated circuit interconnects to reduce the propagation delays, and cross talk noise between metal wires as an alternative material for SiO2. These materials, typically organosilicate glass (OSG) films, are exposed to oxygen plasmas during photoresist stripping and related processes which substantially damage the film by abstracting carbon, incorporating O and OH, eventually leading to significantly increased k values. Systematic studies have been performed to understand the oxygen plasmainduced damage mechanisms on different lowk OSG films of various porosity and pore interconnectedness. Fourier transform infrared spectroscopy, xray photoelectron spectroscopy and atomic force microscopy are used to understand the damage kinetics of O radicals, ultraviolet photons and charged species, and possible ways to control the carbon loss from the film. FTIR results demonstrate that O radical present in the plasma is primarily responsible for carbon abstraction and this is governed by diffusion mechanism involving interconnected film nanopores. The loss of carbon from the film can be controlled by closing the pore interconnections, He plasma pretreatment is an effective way to control the damage at longer exposure by closing the connections between the pores. digital.library.unt.edu/ark:/67531/metadc84175/
 An Investigation for Gamma Rays Resulting from the Bombardment of As75 with 14 Mev Neutrons
 It is the purpose of this paper to set forth the method and results of studying the gamma rays resulting from the bombardment of As75 with approximately 14 Mev neutrons. The source of these neutrons was the H3(d,n)He4 reaction. The deuterons of 325 Kev energy were obtained from a Van de Graff electrostatic accelerator. A NaI scintillation spectrometer was used to determine the gammaray energies. digital.library.unt.edu/ark:/67531/metadc107961/
 Investigation of Selected OpticallyActive Nanosystems Fashioned using Ion Implantation
 Optoelectronic semiconductor technology continues to grow at an accelerated pace, as the industry seeks to perfect devices such as light emitting diodes for purposes of optical processing and communication. A strive for greater efficiency with shrinking device dimensions, continually pushes the technology from both a design and materials aspect. Nanosystems such a quantum dots, also face new material engineering challenges as they enter the realm of quantum mechanics, with each system and material having markedly different electronic properties. Traditionally, the semiconductor industry has focused on materials such Group IIVI and IIIV compounds as the basis material for future optoelectronic needs. Unfortunately, these material systems can be expensive and have difficulties integrating into current Sibased technology. The industry is reluctant to leave silicon due in part to silicon's high quality oxide, and the enormous amount of research invested into silicon based circuit fabrication. Although recently materials such as GaN are starting to dominate the electrooptical industry since a Sibased substitute has not been found. The purpose of the dissertation was to examine several promising systems that could be easily integrated into current Sibased technology and also be produced using simple inexpensive fabrication techniques such ion implantation. The development of optically active nanosized precipitates in silica to form the active layer of an optoelectronic device was achieved with ion implantation and thermal annealing. Three material systems were investigated. These systems consisted of carbon, silicon and metal silicide based nanocrystals. The physical morphology and electronic properties were monitored using a variety of material characterization techniques. Rutherford backscattering/channeling were used to monitor elemental concentrations, photoluminescence was used to monitor the optoelectronic properties and transmission electron microscopy was used to study the intricate morphology of individual precipitates. The electronic properties and the morphology were studied as a function of implant dose, anneal times and anneal temperatures. digital.library.unt.edu/ark:/67531/metadc5259/
 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/
 Ion Beam Synthesis of Carbon Assisted Nanosystems in Silicon Based Substrates
 The systematic study of the formation of βSiC formed by low energy carbon ion (C)implantation into Si followed by high temperature annealing is presented. The research is performed to explore the optimal annealing conditions. The formation of crystalline βSiC is clearly observed in the sample annealed at 1100 °C for a period of 1 hr. Quantitative analysis is performed in the formation of βSiC by the process of implantation of different carbon ion fluences of 1×1017, 2×1017, 5×1017, and 8×1017 atoms /cm2 at an ion energy of 65 keV into Si. It is observed that the average size of βSiC crystals decreased and the amount of βSiC crystals increased with the increase in the implanted fluences when the samples were annealed at 1100°C for 1 hr. However, it is observed that the amount of βSiC linearly increased with the implanted fluences up to 5×1017 atoms /cm2. Above this fluence the amount of βSiC appears to saturate. The stability of graphitic CC bonds at 1100°C limits the growth of SiC precipitates in the sample implanted at a fluence of 8×1017 atoms /cm2 which results in the saturation behavior of SiC formation in the present study. Secondly, the carbon cluster formation process in silica and the characterization of formed clusters is presented. Silicon dioxide layers ~500 nm thick are thermally grown on a Si (100) wafer. The SiO2 layers are then implanted with 70 keV carbon ions at a fluence of 5×1017 atoms/cm2. The implanted samples are annealed 1100 °C for different time periods of 10 min., 30 min., 60 min., 90 min., and 120 min., in the mixture of argon and hydrogen gas (96 % Ar + 4% hydrogen). Photoluminescence spectroscopy reveals UV to visible emission from the samples. A detail mechanism of the photoluminescence and its possible origin is discussed by correlating the structural and optical properties of the samples. Raman spectroscopy, Xray photoelectron spectroscopy, Xray diffraction, spectroscopy, photoluminescence spectroscopy, and transmission electron microscopy are used to characterize the samples. digital.library.unt.edu/ark:/67531/metadc68033/
 IonInduced Damage In Si: A Fundamental Study of Basic Mechanisms over a Wide Range of Implantation Conditions
 A new understanding of the damage formation mechanisms in Si is developed and investigated over an extended range of ion energy, dose, and irradiation temperature. A simple model for dealing with ioninduced damage is proposed, which is shown to be applicable over the range of implantation conditions. In particular the concept of defect "excesses" will be discussed. An excess exists in the lattice when there is a local surplus of one particular type of defect, such as an interstitial, over its complimentary defect (i.e., a vacancy). Mechanisms for producing such excesses by implantation will be discussed. The basis of this model specifies that accumulation of stable lattice damage during implantation depends upon the excess defects and not the total number of defects. The excess defect model is validated by fundamental damage studies involving ion implantation over a range of conditions. Confirmation of the model is provided by comparing damage profiles after implantation with computer simulation results. It will be shown that transport of ions in matter (TRIM) can be used effectively to model the ioninduced damage profile, i.e. excess defect distributions, by a simple subtraction process in which the spatially correlated defects are removed, thereby simulating recombination. Classic defect studies illuminate defect interactions from concomitant implantation of high and mediumenergy Si+self ions. Also, the predictive quality of the excess defect model was tested by applying the model to develop several experiments to engineer excess defect concentrations to substantially change the nature and distribution of the defects. Not only are the excess defects shown to play a dominant role in defectrelated processing issues, but their manipulation is demonstrated to be a powerful tool in tailoring the implantation process to achieve design goals. Preamorphization and dual implantation of different energetic ions are two primary investigative tools used in this work. Various analyses, including XTEM, RBS/channeling, PAS, and SIMS, provided experimental verification of the excess defect model disseminated within this dissertation. digital.library.unt.edu/ark:/67531/metadc5248/
 Magnetic Resonance of Protons in the Earth's Magnetic Field
 The purpose of the work reported here was to determine the feasibility of applying the nuclear induction technique of Bloch to the direct observation of nuclear magnetic resonance in the very weak magnetic field of the earth. digital.library.unt.edu/ark:/67531/metadc108047/
 Magnetic Susceptibility of a Crystalline Free Radical
 The entirety of the investigation discussed in this paper was confined to a study of the spin resonance properties of unpaired electrons of an organic free radical. In the remainder of the paper the theory of electron spin resonance, the apparatus used in the investigation, and the experimental results obtained are discussed in that order. digital.library.unt.edu/ark:/67531/metadc108146/
 Magnetically Driven Instabilities in Gas Discharges
 In the present experiment a gas discharge plasma generator was designed and constructed and a search was made for evidence of a plasma instability due to the influence of an externally applied magnetic field. The evidence for such an unstable mode of operation is too indirect to make a possible conclusion, but an approach to more certain identification will be indicated. digital.library.unt.edu/ark:/67531/metadc108219/
 Magnetomorphic Oscillations in Cadmium Cylinders
 The work presented here is an experimental investigation of the effect of cylindrical geometry on electrical conductivity, in which singlecrystal samples of cadmium at the temperature of liquid helium are used, with the diameter on the order of the electron mean free path. digital.library.unt.edu/ark:/67531/metadc131138/
 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/
 Magnetotransport Properties of AlxIn1xAsySb1y/GaSb and Optical Properties of GaAs1xSbx
 Multilayer structures of AlxIn1xAsySb1y/GaSb (0.37 £ x £ 0.43, 0.50 £ y £ 0.52), grown by molecular beam epitaxy on GaSb (100) substrates were characterized using variable temperature Hall and Shubnikovde Haas techniques. For nominally undoped structures both p and ntype conductivity was observed. The mobilities obtained were lower than those predicted by an interpolation method using the binary alloys; therefore, a detailed analysis of mobility versus temperature data was performed to extract the appropriate scattering mechanisms. For ptype samples, the dominant mechanism was ionized impurity scattering at low temperatures and polar optical phonon scattering at higher temperatures. For ntype samples, ionized impurity scattering was predominant at low temperatures, and electronhole scattering dominated for both the intermediate and high temperature range. Analyses of the Shubnikovde Haas data indicate the presence of 2D carrier confinement consistent with energy subbands in GaAszSb1z potential wells. Epilayers of GaAs1xSbx (0.19<x<0.71), grown by MBE on semiinsulating GaAs with various substrate orientations, were studied by absorption measurements over the temperature range of 4300 K. The various substrate orientations were chosen to induce different degrees of spontaneous atomic ordering. The temperature dependence of the energy gap (Eg) for each of these samples was modeled using three semiempirical relationships. The resulting coefficients for each model describe not only the temperature dependence of Eg for each of the alloy compositions investigated, but also for all published results for this alloy system. The effect of ordering in these samples was manifested by a deviation of the value of Eg from the value of the random alloy. The presence of CuPtB type atomic ordering was verified by transmission electron diffraction measurements, and the order parameter was estimated for all the samples investigated and found to be larger for the samples grown on the (111) A offcut orientations. This result strongly suggests that it is the A steps that contribute to the formation of the CuPtB type ordering in the GaAs1xSbx alloy system. digital.library.unt.edu/ark:/67531/metadc5522/