THE STRUCTURE OF MONOLAYER FILMS OF FEO ON PT(111)

The structure and growth of iron oxide monolayers on Pt(111) has been studied by scanning tunneling microscopy. Atomically resolved images reveal a non-coincidence overlayer lattice where a short overlayer periodicity (approximately 3 angstrom) is modulated by a larger periodicity of approximately 26 angstrom. We explain this result as due to a bilayer of FeO with structure similar to the (111) plane of wustite (cubic FeO with the NaCl structure) overlaying the Pt(111) surface. A small rotational mismatch (0.6-degrees +/- 0.3-degrees) between overlayer and substrate is observed that produces two domains. Measurements of the relative angular rotation of these domains allowed accurate determination of the monolayer Fe-Fe (or 0-0) distances as 3.09 +/- 0.02 angstrom.