Cleavage surfaces of the BaFe2−xCoxAs2 and FeySe1−xTex superconductors: A combined STM plus LEED study

We elucidate the termination surface of cleaved single crystals of the BaFe2−xCoxAs2 and FeySe1−xTex families of the high-temperature iron-based superconductors. By combining scanning tunneling microscopic data with low-energy electron diffraction we prove that the termination layer of the BaFe2As2 systems is a remnant of the Ba layer, which exhibits a complex diversity of ordered and disordered structures. The observed surface topographies and their accompanying superstructure reflections in electron diffraction depend on the cleavage temperature. In stark contrast, FeySe1−xTex possesses only a single termination structure—that of the tetragonally ordered Se1−xTex layer.