SnO films and their oxidation to SnO2: Raman scattering, IR reflectivity and X-ray diffraction studies

Polycrystalline SnO films prepared by evaporation were studied by Raman scattering, IR reflection and X-ray diffraction. All the allowed Raman-active and IR-active phonon modes were observed. Subsequently, the SnO films were oxidized in steps to SnO2. After each oxidation step, Raman scattering and X-ray diffraction measurements were performed. New lines appear in both cases with advancing oxidation. Close to complete oxidation to SnO2, however, these lines disappear. Analysing these structures, we conclude that oxidation starts by an internal displacement of oxygen (disproportionation), followed by an incorporation of external oxygen.