The Study on Ferroelectric Domain Patterns Controlled by Twin Stuctures of the Substrate

Abstract

This thesis is mainly consisted of two research topics: One is the film growth mechanism by PLD (Pulsed Laser Deposition) in terms of target-laser interaction and another is new ferroelectric domain patterns on highly elongated BiFeO3 film. Firstly, representative film growth conditions in PLD are temperature, gas partial pressure, and laser intensity. In addition, hidden growing parameter was discovered for LuFe2O4 film growth. The newly suggested growth condition is the process named as 'laser preconditioning', which is certainly necessary to be offered the proper target with component ratio of Lu and Fe closing that of original one. Dealing with the process, we have successfully fabricated epitaxial LuFe2O4 thin films of single phase on sapphire substrates from a stoichiometric target using PLD. This research reminds us of the fundamental principle of PLD in terms of the variation of the component ratio given by different volatility in elements of a target during a growth. Secondly, the strain field affects on the properties of ferroelectric which also regards as ferroelastic. Thin film form offers the strained environment to a ferroelectric bulk. The biaxial strain in between a film and a substrate is very common, here we suggest the newly type of strain on films. We demonstrate the effect of inhomogeneous strain by the buckling in highly elongated BiFeO3 film on LaAlO3 (001) substrate. In particular, the effect gives rise to huge and uniform ferroelectric domain patterns with a high regularity in contrast on those in typical FE films. The driving force for the pattern is thought to be generated from the twin structures of rhombohderal-LAO substrate. Our findings are considered as the very marvelous phenomenon showing the microscopic effect of twins of a substrate on ferroelectric film.