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**Degree Discipline:**Physics

**Collection:**UNT Theses and Dissertations

### The Effect of Average Grain Size on Polycrystalline Diamond Films

**Date:**May 2002

**Creator:**Abbott, Patrick Roland

**Description:**The work function of hydrogen-terminated, 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 x-ray photoelectron spectroscopy to determine elemental composition and the sp2/sp3 carbon fraction. The percentage of (111) diamond was determined by x-ray 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 3-component model in which the work function is controlled by single-crystal (111) diamond at larger grain sizes, graphitic carbon at smaller grain sizes, and by the electron affinity for the intervening grain sizes.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc3164/

### Solutions of the Equations of Radiative Transfer by an Invariant Imbedding Approach

**Date:**January 1969

**Creator:**Adams, Charles N.

**Description:**This thesis is a study of the solutions of the equations of radiative transfer by an invariant imbedding approach.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc131045/

### Perturbation of renewal processes

**Date:**May 2008

**Creator:**Akin, Osman Caglar

**Description:**Renewal theory began development in the early 1940s, as the need for it in the industrial engineering sub-discipline operations research had risen. In time, the theory found applications in many stochastic processes. In this thesis I investigated the effect of seasonal effects on Poisson and non-Poisson renewal processes in the form of perturbations. It was determined that the statistical analysis methods developed at UNT Center for Nonlinear Science can be used to detect the effects of seasonality on the data obtained from Poisson/non-Poisson renewal systems. It is proved that a perturbed Poisson process can serve as a paradigmatic model for a case where seasonality is correlated to the noise and that diffusion entropy method can be utilized in revealing this relation. A renewal model making a connection with the stochastic resonance phenomena is used to analyze a previous neurological experiment, and it was shown that under the effect of a nonlinear perturbation, a non-Poisson system statistics may make a transition and end up in the of Poisson basin of statistics. I determine that nonlinear perturbation of the power index for a complex system will lead to a change in the complexity characteristics of the system, i.e., the system will reach ...

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc6140/

### Structural and Photoelectron Emission Properties of Chemical Vapor Deposition Grown Diamond Films

**Date:**August 1998

**Creator:**Akwani, Ikerionwu Asiegbu

**Description:**The effects of methane (CH4), diborone (B2H6) and nitrogen (N2) concentrations on the structure and photoelectron emission properties of chemical vapor deposition (CVD) polycrystalline diamond films were studied. The diamond films were grown on single-crystal Si substrates using the hot-tungsten filament CVD technique. Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) were used to characterize the different forms of carbon in the films, and the fraction of sp3 carbon to sp3 plus sp2 carbon at the surface of the films, respectively. Scanning electron microscopy (SEM) was used to characterize the surface morphology of the films. The photoelectron emission properties were determined by measuring the energy distributions of photoemitted electrons using ultraviolet photoelectron spectroscopy (UPS), and by measuring the photoelectric current as a function of incident photon energy.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc279053/

### 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 17-95 GHz

**Date:**December 1990

**Creator:**Al-Share, Mohammad A. (Mohammad Abdel)

**Description:**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 17-95 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), Kϑ-l 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.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc330976/

### Synchronous Chaos, Chaotic Walks, and Characterization of Chaotic States by Lyapunov Spectra

**Date:**August 1993

**Creator:**Albert, Gerald (Gerald Lachian)

**Description:**Four aspects of the dynamics of continuous-time 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.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc277794/

### Model for Long-range Correlations in DNA Sequences

**Date:**December 1996

**Creator:**Allegrini, Paolo

**Description:**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 long-range 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 infinite-dimensional 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 a-stable 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 short-range scale, but show up in the long-range one. We denote our prescription to generate statistical sequences as the Copying Mistake Map (CMM). We carry out our analysis of several DNA sequences, ...

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc279189/

### Investigation of the Uniaxial Stress Dependence of the Effective Mass in N-Type InSb Using the Magnetophonon Effect

**Date:**December 1971

**Creator:**Alsup, Dale Lynn

**Description:**The magnetophonon effect was used to investigate the uniaxial stress dependence of the effective mass in n-type InSb (indium antimonide).

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc164537/

### Thermal Properties of a Single Crystal of Bismuth at Liquid-helium Temperatures

**Date:**January 1964

**Creator:**Alsup, Dale Lynn

**Description:**The purpose of this investigation was the determination of the thermal conduction properties of a single crystal of bismuth at liquid-helium temperatures in magnetic fields up to eighteen kilogauss.

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc108252/

### Studying Interactions of Gas Molecules with Nanomaterials Loaded in a Microwave Resonant Cavity

**Date:**August 2007

**Creator:**Anand, Aman

**Description:**A resonant cavity operating in TE011 mode was used to study the adsorption response of single walled carbon nanotubes (SWCNTs) and other nanomaterials for different types of gas molecules. The range of the frequency signal as a probe was chosen as geometry dependent range between 9.1 -9.8 GHz. A highly specific range can be studied for further experiments dependent on the type of molecule being investigated. It was found that for different pressures of gases and for different types of nanomaterials, there was a different response in the shifts of the probe signal for each cycle of gassing and degassing of the cavity. This dissertation suggests that microwave spectroscopy of a complex medium of gases and carbon nanotubes can be used as a highly sensitive technique to determine the complex dielectric response of different polar as well as non-polar gases when subjected to intense electromagnetic fields within the cavity. Also, as part of the experimental work, a range of other micro-porous materials was tested using the residual gas analysis (RGA) technique to determine their intrinsic absorption/adsorption characteristics when under an ultra-high vacuum environment. The scientific results obtained from this investigation, led to the development of a chemical biological sensor prototype. ...

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**Permallink:**digital.library.unt.edu/ark:/67531/metadc4009/