Comparative study of the adsorption of oxygen and hydrogen on Si(111)7 x 7by surface differential reflectance spectroscopy

A comparative study of the hydrogenation and oxygenation of the Si(111)7 x 7 surface has been realised by means of surface differential reflectance sp ectroscopy. The experiments were performed for doses below 6000 L (Langmuir ) and at room temperature. The knowledge of the intrinsic optical response of the surface obtained from the hydrogenation allowed us to gain some info rmation about the oxygenation process. The optical results show two differe nt regimes. For doses below 300 L the adsorption of oxygen, in contrast to hydrogen, involves the adatom dangling bonds and backbonds simultaneously. The optical real-time measurements also show the same kinetics for the reac tion of oxygen with both kinds of bonds. For higher doses between 300 and 6 000 L, oxygen and hydrogen react mainly with the adatom backbonds, which ar e less reactive with oxygen compared to hydrogen.