Surface evolution of strained SrRuO3 films deposited at various temperatures on SrTiO3 (001) substrates

Surface evolution was studied for strained SrRuO3 films with a nominal 75 nm thickness deposited at various substrate temperatures (650-850 degrees C). Epitaxial growth of the films was achieved on single TiO2-terminated SrTiO3 (001) substrates by using ion-beam sputtering. The surface morphology of the deposited films was investigated by scanning tunneling microscopy in ambient conditions, and their microstructure was characterized by transmission electron microscopy. The self-organized step-terrace structure was observed for the films deposited at lower than 800 degrees C, suggesting that the epitaxial growth proceeded by step-flow growth. In particular, each film showed characteristic surface evolutions pertinent to the misfit strain relaxation stage, mostly influenced by the moving segment of misfit dislocations threading up to the surface: surface undulations for the film at the initial stage of relaxation (deposited at 650 degrees C), circular growth spirals during the relaxation stage (700 degrees C), and well-ordered step-terrace structure after almost full development of misfit dislocations (750 and 800 degrees C).