Molecular Beam Epitaxy Growth and Scanning Tunneling Microscopy Study of Pyrite CuSe₂ Films on SrTiO₃

We perform molecular beam epitaxy growth and scanning tunneling microscopy study of copper diselenide (CuSe2) films on SrTiO3(001). Using a Se-rich condition, the single-phase pyrite CuSe2 grows in the StranskiKrastanov (layer-plus-island) mode with a preferential orientation of (111). Our careful inspection of both the as-grown and post-annealed CuSe2 films at various temperatures invariably shows a Cu-terminated surface, which, depending on the annealing temperature, reconstructs into two distinct structures 2× 3 and 3×3-R30°. The Cu termination is supported by the depressed density of states near the Fermi level, measured by in-situ low temperature scanning tunneling spectroscopy. Our study helps understand the preparation and surface chemistry of transition metal pyrite dichalcogenides thin films.