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 postgrowth 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