Time resolved photoemission spectroscopy on Si(0 0 1)-2 × 1 surface during oxidation controlled by translational kinetic energy of O2 at room temperature

We have experimentally studied the dissociative adsorption of O2 on a clean Si(0 0 1)-2 × 1 surface at room temperature from the viewpoint of time resolved photoemission spectroscopy for surface chemical reactions induced by the O2 incident energy. Combining the high-resolution and intense synchrotron radiation with the supersonic molecular beams technique, we have succeeded in the analysis of the time evolution of Si oxidation states (Si1+, Si2+, Si3+ and Si4+) induced by the translational kinetic energy of O2 (EtO2=0.04, 0.6, 2.0 and 3.0 eV). Furthermore, we proposed that the oxidation on a clean Si(0 0 1)-2 × 1 surface progressed in the mechanism of almost consecutive Si oxidation in the low translational kinetic energy region. It was found that the translational kinetic energy of O2 induced the adsorption of oxygen atom at the bridge site between the Si dimer and at the backbonds of the Si dimers and the subsurface.