Rotational magnetization vector measurements on polycrystalline samples of YBa\sb2Cu\sb3O\sb7 (YBCO) and (Ba, K)BiO\sb3 at various fixed fields (H) and temperatures (T) reveal that the vortex flux density (B) in a rotational state consists of a component BR, which rotates rigidl…
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The purpose of this dissertation is to study different properties of the transition metal oxides, especially the high-Tc superconductors. Applying Monte Carlo methods to a Spin-Fermion model, the behavior of the band structure, Fermi surface, pairing correlations, and optical co…
Doping a liquid crystal with an appropriate substance, which may or may not have mesogenic properties, can induce substantial changes in its physical properties. It may change the symmetry of the phase, it may induce new phases, and it may drastically change particular physical …
This thesis is organized in two independent parts, in which I study two different aspects of high Tc superconductivity. The first part begins with an introduction aimed to briefly introduce some relevant experimental and theoretical works performed in recent years, that have hel…
Current-Voltage measurements in the presence of a small magnetic field have been preformed on high quality samples of Y₁₂₃ and Y₁₂₃/(Ag\sb2O)x Hi-Tc superconductors, to study the behaviour of the critical currents, pinning forces and flux flow resistance (FFR) near Tc. The addit…
XRD and residual stress ({\sim}\sin\sp2ψ) measurements were carried out on YBa\sb2Cu\sb3Ox superconductor with varying oxygen stoichiometry x = 6.32 to 7. Using published data for c-axis, Tc and oxygen content it was found that the measured c-axis varies linearly with and is sen…
We have obtained ultraviolet and vacuum ultraviolet electroreflectance spectra of GaN and a series of AlGaN samples. The spectra obtained from them include the fundamental and the next higher energy transitions around the E1 critical point. This is the first report of vacuum ult…
Using a variable temperature scanning tunneling microscope, we have studied several adsorbates on silicon surfaces. We have studied the adsorption characteristics of H\sb2S on Si(111)-(7 × 7). H\sb2S adsorbs dissociatively at sub-monolayer coverage, from 50 to 300 K, with HS bon…
This thesis consists of spectroscopic studies of the electron-doped high temperature cuprate superconductors Pr2−xCe xCuO4−δ (PCCO) and Nd 2−xCexCuO 4−δ (NCCO). Point contact and high barrier tunneling spectroscopies were employed to study the evolution of the superconducting ga…
The main thrust of this thesis is the investigation of a Focused Ion Beam (FIB)-based approach for fabricating p+-n shallow junctions approaching the nanometer scale (15-50 nm) which will be compatible with future generation CMOS technology. Ultra shallow junctions are formed by…
Heterogeneous ferromagnetic-superconducting systems such as a regular array of ferromagnetic nano dots deposited on the top of a superconducting thin film have attracted many research teams both experimental and theoretical. The interest in these systems does not only stem from …
This dissertation is concerned with the interplay of long-range order and anisotropy in the tetragonal RNi2Ge2 (R = rare earth) family of compounds. Microscopic magnetic structures were studied using both neutron and x-ray resonant exchange scattering (XRES) techniques. The magn…
An alternative to the conventional dry cast and spin cast methods of forming films of nanocrystals is electrophoretic deposition. A pair of Au-on-Si electrodes was submerged in a nanocrystal solution (∼3 nm diameter CdSe/TOPO nanocrystals in hexane) and high dc voltage was appli…
Atomic and molecular adsorptions of oxygen and hydrogen on actinide surfaces have been studied within the generalized gradient approximations to density functional theory (GGA-DFT). The primary goal of this work is to understand the details of the adsorption processes, such as c…
The techniques of many body perturbation theory and coupled cluster theory have been used to study the electronic and geometric structures of neutral, cationic, and anionic small silver clusters. Hay-Wadt relativistic effective core potentials replacing the twenty-eight core ele…
ZnO thin films were prepared by using the DC Reactive Magnetron Sputtering technique. The effect of the working pressure, substrate temperature, Fe-doping, and oxygen concentration in the gas ambient on the structural, optical and electrical properties of the grown films were st…
In this thesis we have studied phase transitions in a polymer solution and also in a two dimensional (2D) disordered system. In our study on the polymer system we present a model in an attempt to understand the observed crossover of a stiff polymer chain with side groups in a so…
Nanostructures have become an important field of study in the past few years for their interesting physical characteristics due to features' size and quantum confinement, which have added new potential applications to the scope of electrical and optical devices. Quantum dots (QD…
An alternative method for the growth of crack free, dislocation reduced III-Nitride layers on Silicon substrate has been developed that relies on formation of an ion implanted defective layer in the substrate with implantation taking place in the presence of AlN buffer layer. Th…