Incident energy dependence of metastable adsorption states in O/Si(111)

Yoshigoe, Akitaka ; Moritani, Kosuke*; Narihiro, Eisuke*; Teraoka, Yuden

The metastable molecularly adsorption state as a precursor state in O/Si(111) at room temeprature is normally observed by many surface analysis method, such as photoelectron spectroscopy. It is known that the adsorption dynamics is changed from trapping-mediated adsorption to direct one at around 0.06eV by means of molecular beam experiment. However, there is no unified adsorption model for those adsorbates. We investigated the incident energy dependence of the metastable moleculary adsorbate by using synchrotron radiation real-time photoelectron spectroscopy. All experiments were performed at SUREAC2000 in SPring-8. The translational kinetic energy was controlled by supersonic molecular beam method up to 2.3eV and real-time photoelectron spectra in 10eV scanning range were measured with the accumulation time of 8s and 22s for O1s and Si2p under molecular beam irradiation. The peak of metastable adsorbate was clearly observed at 0.06eV condition. The peak decreased with incident energy and remained over 0.06eV where the direct adsorption process is dominant. This result suggest that the adsorption pathways are competitive between the trapping-mediated adsorption process via metastable molecularly state and the direct dissociative adsorption one.