Si(111) surface oxidation: O 1s core level study using synchrotron radiation

We report new synchrotron radiation results for adsorption of oxygen at room temperature on Si(111) - 7x7 surfaces in the 1 L - 104 L exposure range. Core level Si 2p spectra measured at 150 eV are confronted to O 1s spectra measured at 590 eV with high surface sensitivity and high energy resolution. The main finding is the presence, within the whole adsorption range, of two O 1s components separated by 1.5 eV with an intensity ratio of about 1: 4. The main component at lower binding energy is identified with bridging oxygen atoms whereas the component with smaller intensity is related to surface atomic non bridging oxygen atoms which are converted into bridging oxygen atoms upon heating. These results show that chemisorbed oxygen and oxide-like bridging oxygen coexist and that oxidation dominates at coverages as low as 0.2 monolayer