The reduction and oxidation of Fe2O3(0001) surface investigated by scanning tunneling microscopy

By using scanning tunneling microscopy (STM), we study the structure of the (0001) surface of hematite (α-Fe2O3) pre.pared by ultra-high vacuum treatment. The surface is reduced into a Fe3O4(111) phase by Ar ion sputtering followed by annealing in vacuum, while it is oxidized to a honeycomb superstructure by annealing in O2. High-resolution STM images reveal that the O-terminated FeO(111), Fe- and O-terminated Fe2O3(0001) domains coexist with each other in the superstructure. Unlike the reduction of Fe2O3(0001) whose depth increases with repeated annealing in vacuum, the oxidation of Fe3O4(111) occurs only partially on the top layers by annealing in O2.