Structure and composition of thin epitaxial iron oxide films grown onto Pt(111)

Ordered films of several iron oxide phases were grown layer-by-layer onto a Pt(111) substrate by repeatedly depositing iron at room temperature and oxidizing it afterwards at 1000 K under different oxygen partial pressures. Growth, structures and compositions of these films were studied by low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). When iron oxidation is performed at 10(-6) mbar, the first layer forms an expanded FeO-like hexagonal iron-oxygen bilayer containing only Fe2+ species. At one monolayer coverage an abrupt structural change occurs and the film grows in the bulk structure of Fe3O4 containing Fe2+ and Fe3+ species. Multilayer Fe3O4 films form an unreconstructed, strongly relaxed (111) surface termination. Ordered alpha-Fe2O3 multilayer films containing only Fe3+ species were prepared by high-pressure oxidation at 30 mbar. They exhibit a hexagonal LEED pattern characteristic of an unreconstructed alpha-Fe2O3(0001) surface. The preparation parameters of the oxide films were compared to calculated stability ranges of the corresponding iron-oxide bulk phases.