Oxidation of Zn in UHV environment at low temperature

Thermal oxidation of polycrystalline Zn foils at 5 × 10⁻⁷ Torr oxygen pressure and at room temperature, 50 °C, 70 °C, 90 °C and 110 °C was studied. In situ photoemission spectroscopy using synchrotron light with photon energy of 57 eV was used to monitor the formation of ZnO and to determine the thickness of the oxide overlayer. At the initial oxidation, the oxidation rate follows a two-stage logarithmic equation and later trends to saturate at a certain thickness depending on the oxidation temperature. The saturated thickness was found to increase with the oxidation temperature. The two-stage oxidation process may be governed by two kinds of space charge presumably formed in the thin oxide overlayer.