Initial stages of native oxide growth on hydrogen passivated Si(111) surfaces studied by scanning tunneling microscopy

We show by scanning tunneling microscopy (STM) imaging that native oxide growth in moist air on hydrogen terminated Si(111) 1×1 surfaces begins by continuing formation of small oxide nuclei, 10–20 Å in diameter, in the topmost Si layer. Their statistical distribution on the flat terraces points to a homogeneous nucleation process. Oxidation is extremely slow; after about 800 h only one complete monolayer is oxidized. In addition, a small number of three-dimensional oxide nuclei, several layers deep and 50–100 Å in width, are formed at step edges as a minority species, which may be related to surface defects or contaminations.