Oxidation–reduction reactions at as-grown Fe/NiO interface

Fe films 1–10 ML thick were grown in ultrahigh vacuum by thermal deposition on a 10 ML NiO(0 0 1) film pre-deposited on an Ag(0 0 1) substrate. X-ray photoelectron spectroscopy, low energy electron diffraction and scattering-interference of energetic primary electrons were used in order to investigate the chemical and structural modifications of the Fe film and of the Fe/NiO interface. The film morphology has been checked by STM. Room temperature deposition results in a nearly continuous, tetragonally distorted bcc Fe film with Fe(0 0 1)∥NiO(0 0 1) and Fe[1 1 0]∥NiO[1 0 0] orientation. We obtained clear quantitative evidence of NiO reduction at the metal/oxide interface and of Fe overlayer oxidation. The chemical modification involves the NiO film for a thickness of 1–3 ML, depending on the thickness of the deposited Fe film. Post-deposition annealing above the NiO Néel temperature (540 K) increases the overall crystalline quality of the Fe overlayers, but also extends the thickness of the interfacial reduced layer and the amount of Fe oxidation.