Oxygen adsorption on hydrogen-preadsorbedSi(111)7 × 7 observed by second harmonic generation (SHG)

Oxygen adsorption was in situ observed by second harmonic generation (SHG) on both clean and hydrogen-preadsorbedSi(111)7 × 7. The sticking probability of molecular oxygen was decreased by monohydride formation, although it was not a completely passivating surface. This is a different effect of monohydride from that onSi(111)1 × 1 for passivation. Hydrogen adsorption at room temperature leading to both monohydride and polyhydride formation showed two different stages of sticking probability: with increasing exposure for hydrogen preadsorption, sticking probability was furthermore decreased with oxygen adsorption. This is expected due to the formation of polyhydride species onSi(111)7 × 7 which was found to be necessary for passivating reconstructedSi(111)7 × 7.