Excited electronic state on Si(0Â 0Â 1) surface at initial stage of oxidation studied by two-photon photoemission spectroscopy

► A TR-2PPE study for Si(0 0 1) at the initial oxidation stage has been performed. ► Transient 2PPE intensity from CBM shows maximum at about 1 ps. ► These electrons relax via unoccupied oxide states. ► The lifetime of CBM and oxide states show explicit dependence on oxidation.