Preparation and structure of 1–8 monolayer thick epitaxial iron oxide films grown on Pt(111)

Well ordered epitaxial iron oxide layers with FeO stoichiometry were grown onto Pt(111) single crystal substrates and characterized afterwards with low-energy electron diffraction (LEED) and Auger electron spectroscopy. They were prepared by first depositing iron from the vapor onto the substrate and then oxidizing it in 10−6 Torr of oxygen. At 1 monolayer coverage, a very stable structure with a hexagonal unit cell 15% larger than the platinum (1×1) substrate unit cell is formed, exhibiting a threefold symmetric LEED pattern. This pattern is consistent with a (8×8) superstructure, as 8 FeO(111)-(1×1) lattice spacings fit onto nine lattice spacings on the Pt(111)-(1×1) substrate surface due to the lattice mismatch. Above 2 monolayer coverage a hexagonal (2×2) structure with respect to the FeO(111)-(1×1) unit cell forms, which shows a sixfold symmetric LEED pattern revealing a lattice constant which is in agreement with that of the sodium chloride structure of bulk FeO. LEED beam intensity spectra as a function of the electron energy of these two LEED structures have been measured and are discussed with respect to their symmetry and their changes as a function of the overlayer thickness. The step structure on the surface of an 8 monolayer thick iron oxide film with a FeO(111)-(2×2) LEED pattern was studied by analyzing the LEED beam profiles. We observe steps one iron–oxygen bilayer high as well as one Pt(111) layer distance high. This indicates that only one type of atom termination exists on the FeO(111)-(2×2) surface.