Initial stages of oxidation of hydrogen-terminated Si surface stored in air

We have investigated the oxidation of hydrogen-terminated Si(111) and (100) surfaces stored in air, using synchrotron radiation photoemission spectroscopy and infrared absorption spectroscopy in the multiple internal reflection geometry. We demonstrate that water present in air is predominantly involved in the oxidation of the topmost layer of the hydrogen-terminated surface. We find that native oxide starts to grow when the surface hydrogen coverage diminishes. This trend is interpreted in terms of a kinetic model of oxidation in which it is assumed that native oxide formation preferentially takes place on the portion of the surface where surface Si atoms having Si-H bonds are oxidized.