High oxidation state at the epitaxial interface of γ -Al₂ O₃ thin films grown on Si(111) and Si(001)

High resolution synchrotron radiation x-ray photoelectron spectroscopy allowed us to identify the chemical bonding at the interface between epitaxial γ -Al₂ O₃ and Si substrate. The experiments were performed on 1 nm thick epitaxial γ -Al₂ O₃ layers grown on both Si(111) and Si(001) substrates. In both cases, the Si 2p core level decomposition recorded at photon energy of 160 eV provided evidence for the absence of Si2+ and Si3+ species and the presence of two different Si4+ species. A microscopic model is proposed for the interface obtained with two incomplete SiO₂ planes based on the Si 2 p3/2 line shape.