Optical and electrical properties of rare earth and transition metal oxide thin films and crystals.

摘要

Optical and electrical properties of rare earth and transition metal oxide thin films and crystals have been studied in this work.; We report the first explanation of the novel switching mechanism in two terminal devices based on the layered material {dollar}rm Vsb2Osb5cdot 1.6Hsb2O{dollar}. The switching is shown to be associated with the existence of a current-induced channel between the contacts. Resistivity data on the channel exhibit a sharp transition at T = 334 K which is also the average sample temperature above which the device was observed to stop switching. We further observed the formation of a conducting filament inside the channel. The metal-insulator transition in the filament is responsible for the switching in these devices. A thermal transport model was developed to explain several crucial characteristics in a thermal switching device which involve the filament formation.; A novel single-target planar magnetron sputtering system was developed to sputter various high T{dollar}sb{lcub}rm c{rcub}{dollar} superconducting thin films. Superconducting transition temperature of the films prepared in this system are 80 K and 81 K for {dollar}rm YBasb2Cusb3Osb{lcub}7-delta{rcub}{dollar} and {dollar}rm HoBasb2Cusb3Osb{lcub}7-delta{rcub}{dollar} films, respectively.; The first optical studies on single crystal samples of {dollar}rm Ndsb{lcub}2-X{rcub}Cesb{lcub}X{rcub}CuOsb{lcub}4-delta{rcub}{dollar} (x = 0, 0.2) over a wide energy range (0.005 to 6 eV) is presented. An unusually broad and strong mid-infrared (IR) absorption band has been observed. The band is "activated" by either annealing in Hc, or by Cc-doping. A shell model was used to analyze the in-plane, infrared (IR) active TO and LO phonon modes in {dollar}rm Ndsb2CuOsb{lcub}4-delta{rcub}{dollar}. A new algorithm was developed to determine the rigorous transverse and longitudinal optical modes (TO and LO) in single crystals.; Photoluminescence, transmission and reflection studies on CaS:Eu{dollar}sp{lcub}2+{rcub}{dollar}:Sm{dollar}sp{lcub}3+{rcub}{dollar} thin films are reported. The as-grown film exhibits very weak luminescence emission, and exhibits a direct energy gap at 4.48 eV. After annealing,the film shows a broad emission band at {dollar}sp{lcub}sim{rcub}{dollar}1.92 eV identified with emission from Eu{dollar}sp{lcub}2+{rcub}{dollar} ions, and a set of sharp peaks corresponding to emission from Sm{dollar}sp{lcub}3+{rcub}{dollar} ions. The unusual decrease of Sm{dollar}sp{lcub}3+{rcub}{dollar} photoluminescence with decreasing temperature suggests the energy transfer between Eu{dollar}sp{lcub}2+{rcub}{dollar} and Sm{dollar}sp{lcub}3+{rcub}{dollar} ions.