Molecular beam epitaxy growth and post-growth annealing of FeSe films on SrTiO3: a scanning tunneling microscopy study.

Low temperature scanning tunneling microscopy and spectroscopy are used to investigate the atomic and electronic structure evolution of FeSe films grown on SrTiO3 as a function of post-growth annealing. Single unit cell FeSe films are found to bond strongly with the underlying substrate, and become superconductive with diminishing chemical bond disorders at the interface via post-annealing. For thicker FeSe films, post-annealing removes excess Se in the films and leads to a transition from semiconductor into metallic behaviors. In double and multilayer films, strain-induced complex textures are observed and suggested to be the main cause for the absent superconductivity.