Adsorption dynamics for oxygen molecule on Si(111)-77 at room temperature investigated by means of real-time synchrotron radiation photoelectron spectroscopy; Translational kinetic energy dependence for initial sticking probability and oxygen amount at saturation coverage

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

We report the translational kinetic energy dependence on initial sticking probability and oxygen amount at saturation coverages for O/Si(111)-77 system investigated by real-time synchrotron radiation photoelectron spectroscopy. All experiments were performed at surface reaction analysis appratus at BL23SU in SPring-8. The time evolution and feature of O1s photoelectron spectra dramatically changed with increasing the incident energies. We found that the oxygen uptake curves are almost explained by 2nd-order Langmuir adsorption kinetics and we evaluated the initial sticking probability and saturation coverages from curve fitting procedure. In the incident energy ranges from 0.03 to 0.07eV, the trapping-mediated adsorption dynamics is dominat because the initial sticking probability drastically decreased with increasing incident energy in those energy ranges. On the other hand, the initial sticking probability increases with increasing incident energies, thus we concluded that the direct adsorption becomes a dominat process over 0.07eV energy regions where the contribution of the trapping-mediated adsorption is small. The saturation coverage is almost constant upto 0.4eV, however the saturation coverage increases approximately twice times with increasing the incident energy from 0.4 to about 1.7eV. This result indicates that the dissociative adsorption which is never realized at room temperature, progresses due to overcoming the potential energy barrier by incident energy.