Observation of metastable O adsorption structure on Si(111)-77 at room temperature by real-time O1s and Si2p XPS using synchrotron radiation

Yoshigoe, Akitaka ; Teraoka, Yuden

Since the numbers of oxygen atoms at the backbond sites have been ambiguous only from O1s XPS, the mechanism of initial oxidation processes has been under debate. In this talk, we report the initial O adsorption processes investigated by real-time Si2p XPS using high resolution synchrotron radiation in addition to O1s one. All experiments were performed at SUREAC2000, BL23SU, in SPring-8. After the thermal process, the oxygen gas was exposed to the clean surface at 300K and the oxidation process was in-situ monitored by real-time XPS for O1s and Si2p alternate measurement using SR. Comparing the chemical shifts of O1s with those of Si2p in photoelectron spectra, we found that the oxidation states corresponding to Si and Si were formed at the observable dosage for the metastable O adsorbate. Thus, it is found that the metastable O species adsorb at the on-top site of Si adatom bonding to an oxygen atom at that backbond, i.e. ins-paul structure.