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19901999
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Physics
 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/
 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/
 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/
 Characterization and Field Emission Properties of Mo2C and Diamond Thin Films Deposited on Mo Foils and Tips by Electrophoresis
 In this dissertation M02C and diamond films deposited by electrophoresis on flat Mo foils and tips have been studied to determine their suitability as field emission tips. digital.library.unt.edu/ark:/67531/metadc278393/
 Charge State Dependence of LShell XRay Production Cross Sections of ₂₈Ni, ₂₉Cu, ₃₀Zn, ₃₁Ga, and ₃₂Ge by Energetic Oxygen Ions
 Charge state dependence of Lshell xray production cross sections have been measured for 414 MeV ¹⁶O^q (q=3⁺8⁺) ions incident on ultraclean, ultrathin copper, and for 12 MeV ¹⁶O^q (q=3⁺8⁺) on nickel, zinc, gallium and germanium solid foils. Lshell xray production cross section were measured using target foils of thickness ≤0.6 μg/cm² evaporated onto 5 μg/cm² carbon backings. Oxygen ions at MeV energies and charge state q were produced using a 3MV 9SDH2 National Electrostatics Corporation tandem Pelletron accelerator. Different charge states, with and without Kvacancies, were produced using a post acceleration nitrogen striping gas cell or ¹²C stripping foils. Lshell xrays from ultrathin ₂₈Ni, ₂₉Cu,₃₀Zn,₃₁Ga, and ₃₂Ge targets were measured using a Si(Li) xray detector with a FWHM resolution of 135 eV at 5.9 keV. The scattered projectiles were detected simultaneously by means of silicon surface barrier detectors at angle of 45° and 169° with respect to the beam direction. The electron capture (EC) as well as direct ionization (DI) contributions were determined from the projectile charge state dependence of the target xray production cross sections under single collision conditions. The present work was undertaken to expand the measurements of Lshell xray production cross sections upon selected elements with low Lshell binding energies by energetic ¹⁶O^q (q=3⁺,4⁺,5⁺,6⁺,7⁺,8⁺) incident ions. Collision systems chosen for this work have sufficiently large Z₁/Z₂ ratios (0.250.28) so that EC may noticeably contribute to the xray production enhancement. In this region, reliable experimental data are particularly scarce, thus, fundamental work in this area is still necessary. DI and EC cross section measurements were compared with the ECPSSR and the first Born theories over the range of 0.25 <Z₁/Z₂ < 0.29 and 0.38 < v₁/v₂_L <0.72. The ECPSSR theoretical predictions (including DI and EC) are in closer agreement with the data than the first Born's. digital.library.unt.edu/ark:/67531/metadc277981/
 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/
 Charge State Distributions in Molecular Dissociation
 The present work provides charge state fractions that may be used to generate TEAMS relative sensitivity factors for impurities in semiconductor materials. digital.library.unt.edu/ark:/67531/metadc278340/
 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/
 Dielectric Relaxation of Aqueous Solutions at Microwave Frequencies for 335 GHz. Using a Loaded Microwave Cavity Operating in the TM010 Mode
 The frequency dependence and temperature dependence of the complex dielectric constant of water is of great interest. The temperature dependence of the physical properties of water given in the literature, specific heat, thermal conductivity, electric conductivity, pH, etc. are compared to the a. c. (microwave) and d. c. conductivity of water with a variety of concentration of different substances such as HC1, NaCl, HaS04, etc. When each of these properties is plotted versus inverse absolute temperature, it can be seen that each sample shows "transition temperatures". In this work, Slater's perturbation equations for a resonant microwave cavity were used to analyze the experimental results for the microwave data. digital.library.unt.edu/ark:/67531/metadc279039/
 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/
 An Experimental Study of Collision Broadening of some Excited Rotational States of the Bending Vibration of Methyl Cyanide
 A double modulation microwave spectrometer is used to evaluate the linewidth parameters for some excited rotational components in the bending vibration v_8 of 13CH3 13C 15N and 13CH3C15N isotopomers of methyl cyanide. The linewidth parameters for selfbroadening of the ΔJ=2←1 rotational components for the ground v_8 , 1v_8, and the 2v_8 vibrations were determined over a pressure range of 1 to 13 mtorr and at a temperature of 300 K. The double modulation technique is used to explore the high eighth derivative of the line shape profile of the spectral line. This technique proved to give good signaltonoise ratios and enabled the recovery of weak signals. An experimental method is developed to correct for source modulation broadening. The tests of the ratios of the two inner peak's separation of the eighth derivative of the line showed that they were up to 95% similar to those for a Lorentzian line shape function. The line shapes were assumed to be Lorentzian for the theoretical analysis of the derivative profiles and comparisons were made between experiment and theory on this basis. Dipole moments for vibrationally excited states were calculated from linewidth parameters and show systematic decrease with the increase of excitation. Impact parameters were calculated using the "hard sphere" model of the kinetic theory of gases. The results were many times larger than the size of the molecule itself. This suggests that the dominant interaction is a long range dipoledipole force interaction. digital.library.unt.edu/ark:/67531/metadc278369/
 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/
 Expulsion of Carriers from the DoubleBarrier Quantum Well and Investigation of Its Spectral and Transport Consequences
 In this work I investigate the expulsion of carriers from nanostructures using the doublebarrier quantum well (DBQW) as an example and discuss manifestations of this effect in the spectrum of the DBQW in absence of bias, and in the tunneling current in presence of bias. Assuming equality of the Fermi energy in all regions of the considered system, I compute the relative density of carriers localized in the DBQW and conclude that a fraction of carriers is expelled from this nanostructure. digital.library.unt.edu/ark:/67531/metadc277697/
 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/
 The Fractal Stochastic Point Process Model of Molecular Evolution and the Multiplicative Evolution Statistical Hypothesis
 A fractal stochastic point process (FSPP) is used to model molecular evolution in agreement with the relationship between the variance and mean numbers of synonymous and nonsynonymous substitutions in mammals. Like other episodic models such as the doubly stochastic Poisson process, this model accounts for the large variances observed in amino acid substitution rates, but unlike other models, it also accounts for the results of Ohta's (1995) analysis of synonymous and nonsynonymous substitutions in mammalian genes. That analysis yields a powerlaw increase in the index of dispersion and an inverse powerlaw decrease in the coefficient of variation with the mean number of substitutions, as predicted by the FSPP model but not by the doubly stochastic Poisson model. This result is compatible with the selection theory of evolution and the nearlyneutral theory of evolution. digital.library.unt.edu/ark:/67531/metadc277827/
 Linear, Nonlinear Optical and Transport Properties of Quantum Wells Composed of Short Period Strained InAs/GaAs Superlattices
 In this work, ordered allbinary shortperiod strained InAs/GaAs superlattice quantum wells were studied as an alternative to strained ternary alloy InGaAs/GaAs quantum wells. InGaAs quantum wells QWs have been of great interest in recent years due to the great potential applications of these materials in future generations of electronic and optoelectronic devices. The all binary structures are expected to have all the advantages of their ternary counterparts, plus several additional benefits related to growth, to the elimination of alloy disorder scattering and to the presence of a higher average indium content. digital.library.unt.edu/ark:/67531/metadc278855/
 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/
 Microstructural Studies of Dental Amalgams Using Analytical Transmission Electron Microscopy
 Dental amalgams have been used for centuries as major restorative materials for decaying teeth. Amalgams are prepared by mixing alloy particles which contain Ag, Sn, and Cu as the major constituent elements with liquid Hg. The study of microstructure is essential in understanding the setting reactions and improving the properties of amalgams. Until the work reported in this dissertation, optical microscopy (OM), scanning electron microscopy (SEM), and xray diffractometry (XRD) were used commonly to analyze amalgam microstructures. No previous systematic transmission electron microscopy (TEM) study has been performed due to sample preparation difficulties and composite structure of dental amalgams. The goal of this research was to carry out detailed microstructural and compositional studies of dental amalgams. This was accomplished using the enhanced spatial resolution of the TEM and its associated microanalytical techniques, namely, scanning transmission electron microscopy (STEM), xray energy dispersive spectroscopy (XEDS) and micromicrodiffraction (μμD). A new method was developed for thinning amalgam samples to electron transparency using the "wedge technique." Velvalloy, a lowCu amalgam, and Tytin, a highCu amalgam, were the two amalgams characterized. Velvalloy is composed of a Ag₂Hg₃ (γ₁)/HgSn₇₋₉ (γ₂) matrix surrounding unreacted Ag₃Sn (γ) particles. In addition, hitherto uncharacterized reaction layers between Ag₃Sn(γ)/Ag₂Hg₃ (γ₂) and Ag₂Hg₃ (γ₁)/HgSn₇₋₉ (γ₂) were observed and analyzed. An AgHgSn (β₁) phase was clearly identified for the first time. In Tytin, the matrix consists of Ag₂Hg₃ (γ₁) grains. Fine precipitates of Cu₆Sn₅ (η') are embedded inside the γ₁ and at the grain boundaries. These precipitates are responsible for the improved creep resistance of Tytin compared to Velvalloy. The additional Cu has completely eliminated the γ₂ phase which is the weakest component of amalgams. AgHgSn (β₁) and large grains of Cu₆Sn₅ (η') are found adjacent to the unreacted alloy particles. Tytin alloy particles contain Cu₃Sn (ε) precipitates in a matrix of Ag₃Sn (γ) and Ag₄Sn (β). SEM was used to correlate the TEM findings in the context of the general microstructure. The results are in good agreement with those published in the literature. The microstructural details reported here, many of which were not previously available, will help provide insight into the deformation mechanisms of dental amalgams. digital.library.unt.edu/ark:/67531/metadc277884/
 Model for Longrange Correlations in DNA Sequences
 We address the problem of the DNA sequences developing a "dynamical" method based on the assumption that the statistical properties of DNA paths are determined by the joint action of two processes, one deterministic, with longrange correlations, and the other random and delta correlated. The generator of the deterministic evolution is a nonlinear map, belonging to a class of maps recently tailored to mimic the processes of weak chaos responsible for the birth of anomalous diffusion. It is assumed that the deterministic process corresponds to unknown biological rules which determine the DNA path, whereas the noise mimics the influence of an infinitedimensional environment on the biological process under study. We prove that the resulting diffusion process, if the effect of the random process is neglected, is an astable Levy process with 1 < a < 2. We also show that, if the diffusion process is determined by the joint action of the deterministic and the random process, the correlation effects of the "deterministic dynamics" are cancelled on the shortrange scale, but show up in the longrange one. We denote our prescription to generate statistical sequences as the Copying Mistake Map (CMM). We carry out our analysis of several DNA sequences, and of their CMM realizations, with a variety of techniques, and we especially focus on a method of regression to equilibrium, which we call the Onsager Analysis. With these techniques we establish the statistical equivalence of the real DNA sequences with their CMM realizations. We show that longrange correlations are present in exons as well as in introns, but are difficult to detect, since the exon "dynamics" is shown to be determined by theentaglement of three distinct and independent CMM's. Finally we study the validity of the stationary assumption in DNA sequences and we discuss a biological model for the shortrange random process based on a folding mechanism of the nucleic acid in the cell nucleus. digital.library.unt.edu/ark:/67531/metadc279189/
 Nonlinear Dynamics of Semiconductor Device Circuits and Characterization of Deep Energy Levels in HgCdTe by Using MagnetoOptical Spectroscopy
 The nonlinear dynamics of three physical systems has been investigated. Diode resonator systems are experimentally shown to display a period doubling route to chaos, quasiperiodic states, periodic locking states, and Hopf bifurcation to chaos. Particularly, the transition from quasiperiodic states to chaos in linecoupled systems agrees well with the CurryYorke model. The SPICE program has been modified to give realistic models for the diode resonator systems. digital.library.unt.edu/ark:/67531/metadc278165/
 Nonlinear Optical Absorption and Refraction Study of Metallophthalocyanine Dyes
 This dissertation deals with the characterization of the nonlinear absorption and refraction of two representative metallophthalocyanine dyes: chloro aluminum phthalocyanine dissolved in methanol, referred to as CAP, and a silicon naphthalocyanine derivative dissolved in toluene, referred to as SiNc. Using the Zscan technique, the experiments are performed on both the picosecond and nanosecond timescales at a wavelength of 0.532 μm. digital.library.unt.edu/ark:/67531/metadc278287/
 Numerical Investigations of Quantum Effects of Chaos
 The quantum dynamics of minimum uncertainty wave packets in a system described by the surfacestateelectron (SSE) Hamiltonian are studied herein. digital.library.unt.edu/ark:/67531/metadc278488/
 On Chaos and Anomalous Diffusion in Classical and Quantum Mechanical Systems
 The phenomenon of dynamically induced anomalous diffusion is both the classical and quantum kicked rotor is investigated in this dissertation. We discuss the capability of the quantum mechanical version of the system to reproduce for extended periods the corresponding classical chaotic behavior. digital.library.unt.edu/ark:/67531/metadc278244/
 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/
 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/
 Photoelectric Emission Measurements for CVD Grown Polycrystalline Diamond Films
 We examined CVD grown polycrystalline diamond films having different methane concentrations to detect defects and study the possible correlation between the methane concentration used during the growth process and the defect density. SEM and Raman results show that the amorphous and sp2 carbon content of the films increases with methane concentration. Furthermore, photoelectric emission from diamond is confirmed to be a twophoton process, hence the electrons are emitted from normally unoccupied states. We found that the photoelectric yield, for our samples, decreases with the increase in methane concentration. This trend can be accounted for in two different ways: either the types of defects observed in this experiment decrease in density as the methane concentration increases; or, the defect density stays the same or increases, but the increase in methane concentration leads to an increase in the electron affinity, which reduces the overall photoelectric yield. digital.library.unt.edu/ark:/67531/metadc2199/
 The Physics of Gaseous Exposures on Active Field Emission Microcathode Arrays
 The interaction of active molybdenum field emission microcathode arrays with oxygen, water, carbon dioxide, methane, hydrogen and helium gases was studied. Experiments were setup to measure the emission characteristics as a function of gas exposures. The resulting changes in the surface work function of the tips were determined from the FowlerNordheim plots. The kinetics of the FEAgas interaction were studied by observing the ion species originating from the array during and after gas exposures with a high resolution quadrupole mass spectrometer. With the work function data and the mass spectrometry information, the mechanisms responsible for emission degradation and subsequent device recovery after exposures have been determined. The data obtained was used in estimating the device lifetimes under various vacuum environments. Also it was found that the gas exposure effects are similar in dc and pulsed modes of operation of the arrays, thus permitting the use of dc mode testing as an effective acceleration method in establishing the device lifetimes under various vacuum conditions. The vacuum conditions required for the long term emission current stability and reliability of vacuum microelectronic devices employing FEAs are established. Exposure of Mo field emitter arrays to oxygen bearing species like oxygen, water and carbon dioxide resulted in serious emission current degradation. Whereas, exposure to methane and hydrogen caused a significant increase in emission current. The control of residual gases like 02, C02 and H20 in the vacuum envelope is essential for the emission current stability and long term reliability of vacuum microelectronic devices employing field emission microcathode technology. digital.library.unt.edu/ark:/67531/metadc278588/
 Picosecond Dynamics of FreeCarrier Populations, SpaceCharge Fields, and Photorefractive Nonlinearities in Zincblende Semiconductors
 Generally, nonlinear optics studies investigate opticallyinduced changes in refraction or absorption, and their application to spectroscopy or device fabrication. The photorefractive effect is a nonlinear optical effect that occurs in solids, where transport of an opticallyinduced freecarrier population results in an internal spacecharge field, which produces an index change via the linear electrooptic effect. The photorefractive effect has been widely studied for a variety of materials and device applications, mainly because it allows large index changes to be generated with laser beams having only a few milliwatts of average power.Compound semiconductors are important photorefractive materials because they offer a nearinfrared optical response, and because their carrier transport properties allow the index change to be generated quickly and efficiently. While many researchers have attempted to measure the fundamental temporal dynamics of the photorefractive effect in semiconductors using continuouswave, nanosecond and picosecondpulsed laser beams, these investigations have been unsuccessful. However, studies with this goal are of clear relevance because they provide information about the fundamental physical processes that produce this effect, as well as the material's speed and efficiency limitations for device applications.In this dissertation, for the first time, we timeresolve the temporal dynamics of the photorefractive nonlinearities in two zincblende semiconductors, semiinsulating GaAs and undoped CdTe. While CdTe offers a latticematch to the infrared material HgxCd1xTe, semiinsulating GaAs has been widely used in optoelectronic and highspeed electronic applications. We use a novel transientgrating experimental method that allows picosecond temporal resolution and high sensitivity. Our results provide a clear and detailed picture of the picosecond photorefractive response of both materials, showing nonlinearities due to hotcarrier transport and the Dember spacecharge field, and a longlived nonlinearity that is due to the EL2 midgap species in GaAs. We numerically model our experimental results using a general set of equations that describe nonlinear diffraction and carrier transport, and obtain excellent agreement with the experimental results in both materials, for a wide variety of experimental conditions. digital.library.unt.edu/ark:/67531/metadc2202/
 Precision Atomic Spectroscopy with an Integrated Electro Optic Modulator and DBR Diode Laser at 1083nm

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We have explored the use of recently developed high speed integrated electro optic modulators and DBR diode lasers as a tool for precision laser studies of atoms. In particular, we have developed a technique using a high speed modulator as a key element and applied it to the study of the fine structure of the 23P state of atomic helium. This state has been of long standing interest in atomic physics and its study has been the aim of several recent experiments using various precision techniques. We present our method and results, which will describe a new method for determining the fine structure constant, and lead to a precision test of atomic theory. digital.library.unt.edu/ark:/67531/metadc5847/  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/
 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/
 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/
 LShell XRay Production Cross Sections for ₂₀Ca, ₂₆Fe, ₂₈Ni, ₂₉Cu, ₃₀Zn, ₃₁Ga, and ₃₂Ge by Hydrogen, Helium, and Lithium Ions
 Lshell xray production cross sections are presented for Fe, Ni, Cu, Zn, Ga, and Ge by 0.5 to 5.0MeV protons and by 0.5 to 8.0MeV helium ions and Ca, Fe, Ni, Cu, and Ge by 0.75 to 4.5MeV lithium ions. These measurements are compared to the first Born theory and the perturbedstationary state theory with energyloss, Coulomb deflection, and relativistic corrections (ECPSSR). The results are also compared to previous experimental investigations. The high precision xray measurements were performed with a windowless Si(Li) detector. The efficiency of the detector was determined by the use of thin target atomicfield bremsstrahlung produced by 66.5 keV electrons. The measured bremsstrahlung spectra were compared to theoretical bremsstrahlung distributions in order to obtain an efficiency versus energy curve. The targets for the measurement were manufactured by the vacuum evaporation of the target element onto thin foils of carbon. Impurities in the carbon caused interferences inthe Lshell xray peaks. Special cleansing procedures were developed that reduced the impurity concentrations in the carbon foil, making the use of less than 5 μg/cm^2 targets possible. The first Born theory is seen to greatly overpredict the data at low ion energies. The ECPSSR theory matches the data very well at the high energy region. At low energies, while fitting the data much more closely than the first Born theory, the ECPSSR theory does not accurately predict the trend of the data. This is probably due to the onset of molecularorbital effects, a mechanism not accounted for in the ECPSSR theory. digital.library.unt.edu/ark:/67531/metadc277620/
 ShortPeriod Transient Grating Measurement of Perpendicular Transport in GaAs/AlGaAs Multiple Quantum Wells
 In this thesis the author describes the use of transient grating techniques to study the transport of electrons and holes perpendicular to the layers of a GaAs/AlGaAs multiple quantum well (MQW). digital.library.unt.edu/ark:/67531/metadc277907/
 Spatiotemporal Properties of Coupled Nonlinear Oscillators
 Spatiotemporal properties of classical coupled nonlinear oscillators are investigated in this thesis. Chapter 1 gives an introduction to nonlinear lattices and to the concept of breathers, that are spatially localized and temporally periodic excitation in nonlinear lattices. The concept of anticontinuous limit that provides the basic methodology in probing spatiotemporal breather properties is discussed. In Chapter 2, the general approach for finding exact breather solutions from the anticontinuous limit is examined, and the rotating wave approximation(RWA) is applied to probe the spatial structure of static breathers. Numerical evidence reveals that the RWA relates the spatial structure of stable multibreathers to a single breather of the same frequency. Chapter 3 presents linear stability analysis of static breathers and gives a systematic way to construct mobile breathers. Formation and collision properties of this moving breathers are also studied. Chapter 4 discusses dynamics of kinks and antikinks in hydrogenbonded chains in the context of twocomponent soliton model. From molecular dynamics simulations with finite temperature, it is observed that, in a real system (eg. ice), a pair of kink and antikink can evolve into a movingbreatherlike excitation. Chapter 5 is devoted to the understand of the effects of disorder in the Holstein model. The summary is given in Chapter 6. digital.library.unt.edu/ark:/67531/metadc278564/
 The Stopping Power of Amorphous and Channelled Silicon at All Energies as Computed with the Binary Encounter Approximation
 This thesis utilizes the binary encounter approximation to calculate the stopping power of protons penetrating silicon. The main goal of the research was to make predictions of the stopping power of silicon for lowenergy and mediumenergy channelled protons, in the hope that this will motivate experiments to test the theory developed below. In attaining this goal, different stopping power theories were compared and the binary encounter approach was applied to random (nonchannelled) and highenergy channelled protons in silicon, and these results were compared with experimental data. digital.library.unt.edu/ark:/67531/metadc279387/
 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/
 Studies of Classically Chaotic Quantum Systems within the PseudoProbablilty Formalism
 The evolution of classically chaotic quantum systems is analyzed within the formalism of Quantum PseudoProbability Distributions. Due to the deep connections that a quantum system shows with its classical correspondent in this representation, the PseudoProbability formalism appears to be a useful method of investigation in the field of "Quantum Chaos." In the first part of the thesis we generalize this formalism to quantum systems containing spin operators. It is shown that a classicallike equation of motion for the pseudoprobability distribution ρw can be constructed, dρw/dt = (L_CL + L_QGD)ρw, which is rigorously equivalent to the quantum von NeumannLiouville equation. The operator L_CL is undistinguishable from the classical operator that generates the semiclassical equations of motion. In the case of the spinboson system this operator produces semiclassical chaos and is responsible for quantum irreversibility and the fast growth of quantum uncertainty. Carrying out explicit calculations for a spinboson Hamiltonian the joint action of L_CL and L_QGD is illustrated. It is shown that the latter operator, L_QGD makes the spin system 'remember' its quantum nature, and competes with the irreversibility induced by the former operator. In the second part we test the idea of the enhancement of the quantum uncertainty triggered by the classical chaos by investigating the analogous effect of diffusive excitation in periodically kicked quantum systems. The classical correspondents of these quantum systems exhibit, in the chaotic region, diffusive behavior of the unperturbed energy. For the Quantum Kicked Harmonic Oscillator, in the case of quantum resonances, we provide an exact solution of the quantum evolution. This proves the existence of a deterministic drift in the energy increase over time of the system considered. More generally, this "superdiffusive" excitation of the energy is due to coherent quantum mechanical tunnelling between degenerate tori of the classical phase space. In conclusion we find that some of the quantum effects resulting from this fast increase do not have any classical counterpart, they are mainly tunnelling processes. This seems to be the first observation of an effect of this kind. digital.library.unt.edu/ark:/67531/metadc278979/
 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/
 A Study of Nonlinear Dynamics in an Internal Water Wave Field in a Deep Ocean
 The Hamiltonian of a stably stratified incompressible fluid in an internal water wave in a deep ocean is constructed. Studying the ocean internal wave field with its full dynamics is formidable (or unsolvable) so we consider a testwave Hamiltonian to study the dynamical and statistical properties of the internal water wave field in a deep ocean. Chaos is present in the internal testwave dynamics using actual coupling coefficients. Moreover, there exists a certain separatrix net that fills the phase space and is covered by a thin stochastic layer for a twotriad pure resonant interaction. The stochastic web implies the existence of diffusion of the Arnold type for the minimum dimension of a nonintegrable autonomous system. For nonresonant case, stochastic layer is formed where the separatrix from KAM theory is disrupted. However, the stochasticity does not increase monotonically with increasing energy. Also, the problem of relaxation process is studied via microscopic Hamiltonian model of the testwave interacting nonlinearly with ambient waves. Using the Mori projection technique, the projected trajectory of the testwave is transformed to a form which corresponds to a generalized Langevin equation. The mean action of the testwave grows ballistically for a short time regime, and quenches back to the normal diffusion for a intermediate time regime and regresses linearly to a state of statistical equilibrium. Applying the NakajimaZwanzig technique on the testwave system, we get the generalized master equation on the testwave system which is nonMarkovian in nature. From our numerical study, the distribution of the testwave has nonGaussian statistics. digital.library.unt.edu/ark:/67531/metadc278092/
 A Study of Quantum Electron Dynamics in Periodic Superlattices under Electric Fields
 This thesis examines the quantum dynamics of electrons in periodic semiconductor superlattices in the presence of electric fields, especially uniform static fields. Chapter 1 is an introduction to this vast and active field of research, with an analysis and suggested solutions to the fundamental theoretical difficulties. Chapter 2 is a detailed historical review of relevant theories, and Chapter 3 is a historical review of experiments. Chapter 4 is devoted to the timeindependent quantum mechanical study of the electricfieldinduced changes in the transmission properties of ballistic electrons, using the transfer matrix method. In Chapter 5, a new timedependent quantum mechanical model free from the fundamental theoretical difficulties is introduced, with its validity tested at various limiting cases. A simplified method for calculating fieldfree bands of various potential models is designed. In Chapter 6, the general features of "Shifting Periodicity", a distinctive feature of this new model, is discussed, and a "BlochFloquet Theorem" is rigorously proven. Numerical evidences for the existence of WannierStarkLadders are presented, and the conditions for its experimental observability is also discussed. In Chapter 7, an analytical solution is found for Bloch Oscillations and WannierStarkLadders at low electric fields. In Chapter 8, a new quantum mechanical interpretation for Bloch Oscillations and WannierStarkLadders is derived from the analytical result. The extension of this work to the cases of timedependent electric fields is also discussed. digital.library.unt.edu/ark:/67531/metadc277643/
 A Study of Some Biological Effects of NonIonizing Electromagnetic Radiation
 The experimental studies of this work were done using a microwave cavity spectrometer, Escherichia coli (Ecoli) bacteria, and other peripheral equipment. The experiment consists of two steps. First, a general survey of frequencies from 8 GHz to 12 GHz was made. Second, a detailed experiment for specific frequencies selected from the first survey were further studied. Interesting frequency dependent results, such as unusually higher growing or killing rates of Ecoli at some frequencies, were found. It is also concluded that some results are genetic, that is, the 2nd, and 3rd subcultures showed the same growing status as the 1st cultures. digital.library.unt.edu/ark:/67531/metadc278105/
 Synchronous Chaos, Chaotic Walks, and Characterization of Chaotic States by Lyapunov Spectra
 Four aspects of the dynamics of continuoustime dynamical systems are studied in this work. The relationship between the Lyapunov exponents of the original system and the Lyapunov exponents of induced Poincare maps is examined. The behavior of these Poincare maps as discriminators of chaos from noise is explored, and the possible Poissonian statistics generated at rarely visited surfaces are studied. digital.library.unt.edu/ark:/67531/metadc277794/
 Synthesis and Physical Properties of Environmentally Responsive Polymer Gels
 Polymer gels undergo the volume phase transition in response to an infinitesimal environmental change. This remarkable phenomenon results in many potential applications of polymer gels. This dissertation systematically investigates the chemical and physical properties of polymer gels. It is found that infrared radiation laser not only induces a volume phase transition in Nisopropylacrylamide (NIPA) gel, but also causes the gel to bend toward the laser beam. The transmission of visible laser light through a NIPA gel can also be controlled by adjusting the infrared laser power. A new class of environmentally responsive materials based on spatial modulation of the chemical nature of gels has been proposed and demonstrated. Three simple applications based on the modulated gels are presented: a bigel strip, a shape memory gel, and a gel hand. The bending of bigels has been studied as a function of temperature, acetone aqueous solution, and salt solution. As the polymer network concentration increases, the behavior of shear modulus of acrylamide (PAAM) gels deviates significantlyfromthe classical theory. The ionic NIPA gels undergo two sequential volume phase transitions: one occurs in dilute NaCl solution, the other occurs in concentrated NaCl solution. An interpenetrating polymer network (IPN) of PAAMNIPA has also been synthesized using free radical polymerization. It is found that the IPN gels preserve the essential properties of individual components. The volume phase transition of the IPN gels can be triggered by multiple external stimuli including temperature, acetone concentration, and salt concentration. digital.library.unt.edu/ark:/67531/metadc277945/
 Synthesis and Study of Engineered Heterogenous Polymer Gels
 This dissertation studies physical properties and technological applications of engineered heterogenous polymer gels. Such gels are synthesized based on modulation of gel chemical nature in space. The shape memory gels have been developed in this study by using the modulated gel technology. At room temperature, they form a straight line. As the temperature is increased, they spontaneously bend or curl into a predetermined shape such as a letter of the alphabet, a numerical number, a spiral, a square, or a fish. The shape changes are reversible. The heterogenous structures have been also obtained on the gel surface. The central idea is to cover a dehydrated gel surface with a patterned mask, then to sputterdeposit a gold film onto it. After removing the mask, a gold pattern is left on the gel surface. Periodical surface array can serve as gratings to diffract light. The grating constant can be continuously changed by the external environmental stimuli such as temperature and electric field. Several applications of gels with periodic surface arrays as sensors for measuring gel swelling ratio, internal strain under an uniaxial stress, and shear modulus have been demonstrated. The porous NIPA gels have been synthesized by suspension technique. Microstructures of newly synthesized gels are characterized by both SEM and capillary test and are related to their swelling and mechanical properties. The heterogenous porous NIPA gel shrink about 35,000 times faster than its counterpartthe homogeneous NIPA gel. Development of such fast responsive gels can result in sensors and devices applications. A new gel system with builtin anisotropy is studied. This gel system consists of interpenetrated polymer network (IPN) gels of polyacrylamide (PAAM) and Nisopropylacrylamide (NIPA). The swelling property of the anisotropy IPN gels along the prestressing direction is different from that along other directions, in contrast to conventional gels which swell isotropically. It is found that the ratio (L/D) of length (L) and diameter (D) of IPN samples has stepwise changes as the samples are heated from below the volume phase transition temperature to the above. A theoretical model is proposed and is in good agreement with the experimental results. digital.library.unt.edu/ark:/67531/metadc278503/
 Temperature Dependency of Some of the Thermodynamical Properties of Aqueous BinaryMixture Systems
 The temperature dependence of the refractive index and the density of aqueous binary mixtures of water and ethyl alcohol (C₂H₅OH) were measured by using a modified Michelson interferometer and a narrow glass capillary tube over the temperature range of 278≤T≤353 K for solutions of 100, 75,65, 50, 25, 10 and 0 volume percent ethyl alcohol. The temperature was cycled over both increasing and decreasing directions to explore hysteresis in the cycling. The data are discussed and compared with the LorentzLorenz (LL) formula. A more accurate formula which fits the experimental data better than the LL relation was derived. An attempt was made to determine the nature of the solventsolute interaction through any changes that were found in the refractive index for HeNe laser light and IR diode signals and to analyze the refractive index and density results to test the accuracy of the available mixing rules in predicting the refractive index values and the density of binary systems. Conductivity measurements (d. c.) over the temperature range 278≤T≤353 K of aqueous solutions of NaCl at various concentrations were made and used to establish transport properties of ions in solution. The dynamical properties of the electrolytes were used to establish the nature of hydrogen bonding in aqueous binary mixture systems. Rate equations for ion formation and recombination were used to establish the temperature ranges in which hydrogen bonding dominated in forming polymeric species. From experimental data on the binary mixtures with water, a better understanding of water in its different functions and aggregation is possible. The water molecule itself and its response to the environment are understood when suitable studies are made of the forces in the system. In this work, some qualitative aspects of the interactions and dynamics of the water molecule have been investigated. Classical molecular dynamics simulations were tried to explain some of the thermodynamical properties of the water molecule. digital.library.unt.edu/ark:/67531/metadc278376/
 Transport Processes in Synchrotrons
 This thesis examines the evolution of beams in synchrotrons. Following an introduction to accelerator physics in Chapter 1, in Chapter 2 I describe the Fermilab E778 'diffusion' experiment. Families of sextupoles were powered to drive the 2/5 resonance, and a beam was then kicked to populate a nonlinear region of the transverse phase space. The beam was then observed over periods of approximately 30 minutes for a variety of kick amplitudes and physical apertures. In Chapter 3 comments about the analytic treatment of such systems are discussed, including the assumptions inherent in the conventional treatment. I motivate my use of a simplified model in Chapter 4 after examining common computational methods. Deriving the model from the formalism of traditional accelerator physics, I discuss its implementation on a massively parallel computer, the Intel iPSC/860 hypercube, and examine the performance of this algorithm in detail. Using the simple model to perform the numerical experiment equivalent to E778 is the subject of Chapter 5. I derive the parameters needed for the simple model based upon the physical experiment. Both three dimensional cases and cases with reduced dimensionality are run. From power supply ripple data and an electrical model of the magnet string, I compute tune modulation depths, and a subset of these are run. I conclude that tune modulation from power supply ripple is not a significant source of transport for this system. In Chapter 6, the intensities of the beams are used to compare the experimental and numerical runs, using both exponential and algebraic decays, and the algebraic form is seen to provide a better fit. The agreement between numerical and experimental results is best for fully threedimensional runs, but the numerical results show slower decay than the experimental. Individual particles are examined, whose motion consists of stochastic motion interspersed with regular motion, suggestive of a Continuous Time Random Walk process. A pausing time distribution is extracted which is algebraic in time, which is consistent with dispersive transport observed elsewhere. digital.library.unt.edu/ark:/67531/metadc277803/
 TwoFold Role of Randomness: A Source of Both LongRange Correlations and Ordinary Statistical Mechanics
 The role of randomness as a generator of long range correlations and ordinary statistical mechanics is investigated in this Dissertation. The difficulties about the derivation of thermodynamics from mechanics are pointed out and the connection between the ordinary fluctuationdissipation process and possible anomalous properties of statistical systems is highlighted. digital.library.unt.edu/ark:/67531/metadc278012/
 Work Function Study of Iridium Oxide and Molybdenum Using UPS and Simultaneous FowlerNordheim IV Plots with Field Emission Energy Distributions
 The characterization of work functions and field emission stability for molybdenum and iridium oxide coatings was examined. Single emission tips and flat samples of molybdenum and iridium oxide were prepared for characterization. The flat samples were characterized using Xray Photoelectron Spectroscopy and Xray diffraction to determine elemental composition, chemical shift, and crystal structure. Flat coatings of iridium oxide were also scanned by Atomic Force Microscopy to examine topography. Work functions were characterized by Ultraviolet Photoelectron Spectroscopy from the flat samples and by Field Emission Electron Distributions from the field emission tips. Field emission characterization was conducted in a custom build analytical chamber capable of measuring Field Emission Electron Distribution and FowlerNordheim IV plots simultaneously to independently evaluate geometric and work function changes. Scanning Electron Microscope pictures were taken of the emission tips before and after field emission characterization to confirm geometric changes. Measurement of emission stability and work functions were the emphasis of this research. In addition, use of iridium oxide coatings to enhance emission stability was evaluated. Molybdenum and iridium oxide, IrO2, were characterized and found to have a work function of 4.6 eV and 4.2 eV by both characterization techniques, with the molybdenum value in agreement with previous research. The analytic chamber used in the field emission analysis demonstrated the ability to independently determine the value and changes in work function and emitter geometry by simultaneous measurement of the Field Emission Energy Distribution and FowlerNordheim IV plots from single emitters. Iridium oxide coating was found to enhance the stability of molybdenum emission tips with a relatively low work function of 4.2 eV and inhibited the formation of high work function molybdenum oxides. However, the method of deposition of iridium and annealing in oxygen to form iridium oxide on molybdenum emitters left rather severe cracking in the protective oxide coating exposing the molybdenum substrate. digital.library.unt.edu/ark:/67531/metadc2211/
 Z1 Dependence of IonInduced Electron Emission
 Knowledge of the atomic number (Zt) dependence of ioninduced electron emission yields (Y) can be the basis for a general understanding of ionatom interaction phenomena and, in particular, for the design of Zrsensitive detectors that could be useful, for example, in the separation of isobars in accelerator mass spectrometry. The Zx dependence of ioninduced electron emission yields has been investigated using heavy ions of identical velocity (v = 2 v0, with v0 as the Bohr velocity) incident in a normal direction on sputtercleaned carbon foils. Yields measured in this work plotted as a function of the ion's atomic number reveal an oscillatory behavior with pronounced maxima and minima. This nonmonotonic dependence of the yield on Zx will be discussed in the light of existing theories. digital.library.unt.edu/ark:/67531/metadc277977/