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.