Optical properties and structural characterization of ceramic crystals, pellets, and laser-ablation-deposited thin films

Abstract

This study was divided into two main parts as there were two kind of films studied. The method of deposition, pulsed laser ablation, was common to both SrBi₂Ta₂O₉ and TiO₂ films. The methods of investigations were also the same.

There is an important race for the development of a practical ferroelectric memory. Among ferroelectrics that have attracted attention are the novel compounds with the Aurivillius layered structure. Ferroelectric films of SrBi₂Ta₂O₉, seem to have promising properties, low fatigue and good hysteresis. In this thesis, structure and crystal vibrations in the films were investigated with Raman scattering, infrared absorption, and x-ray diffraction. Similar studies were carried out on powders and crystals of these materials also. The results obtained prove that the films have the orthorhombic SrBi₂Ta₂O₉, structure, and the Raman and IR measurements (the first reported for SBT films) are demonstrated to provide valuable tools for optimizing the deposition process.

TiO₂ is another important material in the domain of thin films. This work was undertaken to study its deposition with laser ablation. The TiO₂ films deposited are very unusual; we discovered that they contain the rare brookite phase. This is the first time that brookite has been obtained in laser-ablation-deposited films. This opens up a new area in thin film development with new potential applications. The absorption edge of brookite was measured, using natural crystals. The optical bandgap was found to be lower than the bandgaps of the rutile and anatase forms of TiO₂, in contradiction of a recent theoretical calculation.