Surface-orientation-dependent growth of SrRuO3 epitaxial thin films
Résumé
The growth of epitaxial transition metal oxide thin films depends on various parameters including the substrate temperature, oxygen partial pressure, kinetics of incoming adatoms, Gibbs free energy, and surface energy. Naturally, the change in the crystallographic surface orientation with a distinctive surface energy also influences the growth rate and growth mode of the epitaxial thin films substantially. Using perovskite SrRuO3 as a model system, we studied the growth characteristics by changing the surface orientation of the SrTiO3 substrate. Employing X-ray diffraction and surface atomic and Kelvin probe force microscopy (KPFM), we observed a systematic decrease in the growth rate and a modification in the growth mode from a two-dimensional growth to a three-dimensional island growth with the change in the surface orientation from (100) to (110) to (111). A spin-polarized density functional theory calculation demonstrated the corresponding difference in the surface energy, which was also confirmed experimentally by the KPFM measurements. The difference in the surface energy could explain the observed change in the growth kinetics, based on the modified classical nucleation theory. A combinatorial method using a polycrystalline epitaxial thin film was employed to generalize our understanding of the crystallographic surface-orientation-dependent thin film growth.