Immediate Product after Exposing Si(111)-7×7 Surface to O₂ at 300 K

Using real-time O 1s X-ray photoelectron spectroscopy together with Si 2p X-ray photoelectron spectroscopy, the oxygen bonding configurations of oxides shortly after exposing the Si(111)-7×7 surface to O 2 at 300 K are revealed. It is found that the ins structure firstly forms where one oxygen atom sits in the backbond of the silicon adatom. It is confirmed that the chemisorbed molecular oxygen, the so-called paul oxygen, is the adsorbate on top of the ins structure. It is also clarified that the ad–ins structure and the ins–tri structure, where ad means an oxygen atom adsorbed onto top of the silicon adatom and tri means the interstitial oxygen atom, appear after a short time. The results implying the presence of mobile O 2 on the surface were obtained.