Adsorption of O2 and CO2 on the Si(111)-7 × 7 surfaces

The interaction of O2 and CO2 with the Si(111)-7 × 7 surface has been studied with X-ray photoelectron spectroscopy (XPS). It was found that both O2 and CO2 molecules can readily oxidize the Si(111)-7 × 7 surface to form thin oxide films. Two oxygen species were identified in the oxide film: oxygen atoms binding to on-top sites of adatom/rest atoms with an O 1s binding energy of ~ 533 eV as well as to bridge sites of adatom/rest atom backbonds at ~ 532 eV. These two oxygen species can be interconverted thermally during the annealing process. Due to the low oxidation capability, the silicon oxide film formed by CO2 has a lower O/Si ratio than that of O2.