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Tin exposed to dry oxygen (104–106 L) at 100°C has been studied by ESCA. The ESCA shift for the tin 3d5/2 line was 1.65 eV and the separation between this line and the oxygen 1s line was 43.90 eV. The oxide was identified by comparing its ESCA spectra with those of SnO and SnO2 samples carefully prepared in vacuum. Clean SnO samples were prepared in vacuum by decomposing SnO2 crystallites at high temperature and depositing the vapor product on a gold substrate. The resulting films were identified to be red SnO by ion back-scattering and by Mössbauer experiments. Clean SnO2 samples were prepared by diamond-filing bulk SnO2 crystals in vacuum. Both of these oxides were found to have the same separation between the oxygen 1s and the tin oxide 3d5/2 lines and hence, the same chemical shift. For this reason, the oxidized tin was identified by comparing its valence band and O/Sn ratio, rather than its chemical shift, with those of the SnO and SnO2 samples. The oxidized tin was found to consist of both SnO and SnO2.
Lau et al. (Wed,) studied this question.