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

Abstract

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 ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$(111) multilayer. Moreover, we prepared well-ordered multilayers with \ensuremath{\alpha}-${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$ stoichiometry. Core and valence level photoemission data clearly reveal that the ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ and \ensuremath{\alpha}-${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$ 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\ifmmode\pm\else\textpm\fi{}0.22 \AA{}, which almost corresponds to the bond length in the bulk FeO (2.15 \AA{}). 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.