Study Of Growth Mechanism And Strain-Modulation Of BST Series Ferroelectric Thin Films

Scientific and technological interest on perovskite-type Ba_xSr_1-xTiO₃(0≤x1) ferroelectric thin films with their particular properties and wide applications in many fields has attracted much attention of physical and material scientist and became the key point in the ferroelectrics. Some studies about the BST films had been carried out. However, toward these complex oxide thin films, their structure and properties are more complex than that of the binary oxide films, as well as the normal semiconductor and metal films. Therefore, there still exits some remained unsolved and neglected problems. Systemic theoretical and experimental studies of the BST films, including the growth dynamics and the control of the surface microstructure are still lacking, especially when the thickness of the films reaches the nanometer level, the unclear problems has become more noticeable, which has prevented the development of the BST ferroelectric films.In this dissertation, based on the BST films by the experimental methods the growth condition, growth dynamic process, growth mechanism, and the control of the surface microstructure of the BST films have been explored and investigated. The basic physical mechanisms of growth issues have been further discussed and analyzed. The main results are as following.1. Study of growth mode control and growth dynamics of BST films (1)BST thin films were grown by laser molecular beam epitaxy. The layer-by-layer, Stranski-Krastanov, and island growth mode were determined by many methods. It was found that the diffusion barrier ES was determined by the growth temperature. The varieties of diffusion barrier and deposition rate determined the change of the growth mode. At high growth temperature and low deposition rate, layer-by-layer growth was dominating, while at low growth temperature and high deposition rate the island growth mode was prevailed. The transition of the two growth modes is the Stranski-Krastanov (layer-by-layer plus island) growth mode. (2) With the optimization of the growth conditions, by in-situ reflective high energy electron diffraction(RHEED), according to the oscillation and patterns of RHEED, the growth mode of the BST films was controlled, and the growth mode map of the films was obtained as a function of substrate temperature for various laser repetition rate...