No description available.

No description available.

An automated ellipsometer was used to study field-induced optical anisotropy in anodic niobium oxide films. The oxide films were found to change from the optically isotropic state to the optically anisotropic state when an electric field was applied normal to the film surface. The anisotropic refractive indices of the oxide films decreased quadratically while the thickness of the films increased quadratically with the applied field. The quadratic electro-optic coefficients were determined. The changes in refractive indices and in thickness of the oxide films were found to be independent of time. Field recrystallization of the anodic niobium oxide films was investigated using a scanning electron microscope. The results are compared with those reported for anodic tantalum oxide films in the published literature. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

For nearly a decade, quasi-one-dimensional conductors have been the subject of intensive study. Theoretically, much attention has been devoted to the development of one-dimensional Fermi gas models, some which may be solved exactly, and to the calculation of their response functions. After a review of this theory, a different approach is adopted in the investigation of two models. The dielectric response theory of the three-dimensional Coulomb gas has been applied to an anisotropic system in which the particles interact with an effective one-dimensional long-range potential. Within the framework of the approximation of Singwi, Tosi, Land, and Sjolander, the dielectric properties of the model are examined in order to determine the conditions under which it is unstable with respect to formation of a charge density wave state. It is found that the positive neutralizing background must be polarizable in order for such an instability to occur. The same approximation method, when applied to a one-dimensional fermion gas with a ʃ-function interaction may be compared with the exact solution of Yang. This solution, which exists in the form of coupled integral equations, has been calculated numerically, and, as predicted by the Lieb-Mattis theorem, the ground state is found to be non-magnetic. The approximation of Singwi et al. proves to give better correlation energies than other inexact methods, particularly at higher densities. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This investigation is a theoretical study of the influence of defects of finite volume on the electrical conductivity in the quantum size effect regime. Correction terms to existing equations are derived, and a physical explanation of the results is given. Many macroscopic properties of films exhibit an oscillatory dependence on thickness when the thickness is comparable to the de Broglie wavelength of an electron at the Fermi surface. This behavior is called the quantum size effect. In very thin films, scattering from surfaces, phonons, and crystal defects plays an increasingly important role. In this investigation the influence of scattering centers (defects) in semimetal films on the electrical conductivity is explored by extending existing work to include scattering centers of finite range. The purpose of this study is to determine the overall change in the conductivity and the alteration of the amplitude of the oscillations. The Boltzmann transport equation is the starting point for the calculation. An equation for the vector mean free path is derived, and a solution is obtained by the iterative process. The relaxation approximation need not be made since the vector mean free path is determined. The sample is a thin slab that is infinite in two dimensions. The assumption is made that the electron wave function is zero at the walls of the sample. It is further assumed that there is a known number of randomly located defects within the slab. The noninteracting electrons are considered free except in the vicinity of the scattering centers. The defects are characterized by a potential that is constant within a small cube and zero outside of it. This approach allows the potential matrix elements to be evaluated by expanding in a power series. The electrical conductivity is calculated for three defect sizes, and a comparison is made to 3-function (infinitely small) scattering centers. An overall decrease in the conductivity is found in each case, and the absolute magnitude of the oscillations is decreased. The percentage of oscillation, however, is increased. The general conductivity decrease is attributed to the increase in the scattering range. The change in the amplitude of the oscillations is explained by analyzing the transition probabilities to available energy states at critical film thicknesses. The oscillations are found to be a result of transitions from states with large energies in the plane of the film to states with small energies in the plane of the film. The number of electrons occupying the various states is determined at critical film thicknesses, and a comparison with the conductivity equation shows excellent agreement.

No description available.

No description available.

Fatigue and electrical degradation including low voltage breakdown of ferroelectric lead zirconate titanate Pb(Zr_xTi₁)O₃ (i.e. PZT) thin films are the major limitations for commercial memory applications of these films. It is noted that the presence of oxygen vacancies and their entrapment at the electrode-ferroelectric interfaces are the sources of the degradation phenomena. Attempts were made in this study to solve these problems: 1) by minimizing oxygen vacancy entrapment at the interfaces by employing RuO₂ electrodes; 2) by lowering the oxygen vacancy concentration in PZT films using donor doping (e.g. La³⁺ at Pb²⁺ site and Nb⁵⁺ at Ti/Zr⁴⁺ site). For this study, PZT thin films were prepared by a sol-gel method and deposited on both Pt/Ti/SiO₂/Si and RuO₂/SiO₂/Si substrates. The microstructure and electrical properties, such as hysteresis properties, fatigue, leakage current, time-dependent dielectric breakdown (TDDB), and retention, were studied with regard to the Zr/Ti ratio, the excess lead, the annealing temperature, the electrode material, and the doping amount. Furthermore, the pyrochlore to perovskite phase transformation of PZT on RuO₂ electrodes was also investigated. It was shown that PZT films (Zr/Ti=50/50) with 10 at.% excess lead annealed at 650°C for 30 min possessed the best electrical properties for ferroelectric memory application. In confirmation with earlier theoretical and experimental results, no polarization loss was observed up to 10¹¹ switching cycles for the PZT films deposited on RuO₂ electrodes. However, the low Schottky barrier at the interfaces between RuO₂ and PZT films resulted in a higher leakage current at a high electric fields. Donor doping of PZT films decreased carrier concentrations in PZT films, and thus, decreased the leakage current to acceptable limits. In addition, it was also noted that the pyrochlore to perovskite phase transformation of PZT on RuO₂ was similar to that of PZT on Pt electrodes. It can be concluded that the combination of RuO₂ electrodes and donor doping produced PZT films with high fatigue endurance and low leakage currents which are suitable for memory applications. / Master of Science

A complex permittivity measurement system composed of a network analyzer and a open-ended coaxial waveguide has been used to evaluate the permittivity of rubber samples. The conductivity of rubber provides an indication of the dispersion of carbon black throughout the rubber matrix. The technique is based on the Deschamps antenna modeling theorem which relates the effective admittance of an antenna in some arbitrary medium to the effective admittance of the same antenna embedded in free space. This technique is well suited for material with loss tangents between 0.1 and 1.0. Only material within a radius on the order of the outer conductor radius of the coaxial waveguide is interrogated. Inferred permittivity measurements for rubber samples are presented. An APC-7 connector is used as the transducer which provides a means for convenient calibration because standard calibration terminations can be used. The amount of pressure from the sample applied to the waveguide affects reflection coefficient measurements, preventing consistent results. / Master of Science

Polyimides are well known for their high thermal stability, chemical inertness, and their high electrical resistance. These properties make them ideal for use in the aerospace and electronics industries. Often polyimides are modified by coating or doping the films with metal species to change the surface or bulk properties of the polyimide. Usually this is done to create an electrically conductive surface layer. Previously, surface layers of metal and/or metal oxide on polyimide films have been made by homogeneously doping a poly(amide acid) solution with a metal complex and then thermally curing to 300°C. However, much of the dopant remains in the bulk of the films. Depending on the nature of the metal salt or complex, it has been postulated that lower polymer decomposition temperatures result if residual dopant remains in the bulk of the polymer. Deposition by infusion of the metal salt or complex was proposed as an alternative method for developing surface layers on polyimide films. The infusion processes attempted and the resulting films will be described and discussed. / Master of Science