Electronic structure of ultrathin ordered iron oxide films grown onto Pt(111)

It has recently been shown that well-ordered iron oxide films can be prepared epitaxially onto Pt(111) surfaces. We have investigated a one-monolayer-thick film with FeO stoichiometry and a Fe3O4(111) multilayer. Moreover, we prepared well-ordered multilayers with alpha-Fe2O3 stoichiometry. Core and valence level photoemission data clearly reveal that the Fe3O4 and alpha-Fe2O3 multilayers on Pt(111) are chemically identical to thick single crystals and polycrystalline powder samples. The x-ray-absorption near-edge structures (XANES) at the O K edge arise from the hybridization between O 2p and Fe 3d states as well as Fe 4sp states, showing that the latter also are important for the bonding interaction of the oxides. Polarization-dependent XANES measurements at the O K edge reveal a FeO bond length in the monolayer of 2.23 +/- 0.22 Angstrom, which almost corresponds to the bond length in the bulk FeO (2.15 Angstrom). The electronic structure of the iron oxides derived from the set of spectra presented will be described in terms of the ligand-field theory taking into consideration the exchange interaction between the iron 3d electrons.