Determination of the bonding configuration of the metastable molecular oxygen adsorbed on a Si(111)-(7×7) surface

The initial adsorption stage of oxygen on a $\mathrm{Si}\mathrm{}\left(111\right)\mathrm{}-(7\mathrm{}\times 7)$ surface has been investigated using real time high-resolution core-level measurements at 100 K. Among the six $\mathrm{O}\hspace{0.5em}1s$ components observed on an ${\mathrm{O}}_2$ exposed Si(111) surface, the three components, whose intensities saturate at the same dosage, have the same lifetime. These results lead to a conclusion that three oxygen atoms with different chemical environments compose the metastable species. Based on a comparison with our calculated $\mathrm{O}\hspace{0.5em}1s$ binding energies, we have determined the bonding configuration of the metastable oxygen.