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…
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Hartree-Fock calculations have been performed for linear, three-dimensional and ring-shaped ionized carbon clusters. Magic numbers have been identified and compared with other theoretical and experimental numbers. Stabilities of fairly large carbon clusters have been discussed f…
The characteristics of a pulsed laser ion source have been studied. A pulse from a heating laser (Nd: YAG laser) desorbs the neutral atoms from the surface of a metal target and then a second pulse or pulses from excimer or dye lasers selectively ionize the desorbed neutrals usi…
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…
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…
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 …
A study of the temperature dependence of the photoluminescence spectra from Zn₁₋xMnxS (x = 0.01, 0.03, 0.05, 0.10, 0.20, 0.25, 0.30, 0.35 and 0.50) with different excitation energies (514.5, 488.0, 457.9, 405.5 and 365.9 nm) is given. A new band is reported in addition to the fo…
Zn₁₋xMnxSe is a ternary alloy belonging to a class of materials known as Diluted Magnetic Semiconductors (DMS's). Single-crystal samples of this material possesses a cubic (zinc-blende) structure for x<0.30 and a hexagonal (wurtzite) structure for 0.30<x<0.57. Photoluminescence …
Zinc tungstate (ZnWO\sb4) is promising as a scintillator and laser host material. However, the presence of color centers limit its applications. It has been found that special annealing techniques or doping with metallic elements such as Nb or Sb can bleach the samples (Zhou et …
In low field applications (transport), we employed the time-dependent Schrodinger equation with improved boundary conditions to model resonant tunneling diode (RTD) devices. I will present and discuss a number of features which are characteristics of this device. One of these fe…
In this dissertation I have used photoluminescence (PL) spectrometric analysis to measure the temperature dependence of the spectral features of the direct band gap semiconductor CdxZn1−xSe , for two nominal concentrations x = 0.25, 0.50, in the temperature range 25–300 K. The e…
In this thesis, we investigate the scaling of the critical current density (Jc) and the pinning force (PF) in Y1− xGdxBa 2Cu3O7−δ high-Tc superconductors and La1.45Nd0.40Sr0.15CuO 4 stripe phase superconductor. The main objective is to study the effect of paramagnetic contributi…
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 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…