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 X 1 surfaces begins by continuing formation of small oxide nuclei, 10-20 angstrom 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 angstrom in width, are formed at step edges as a minority species, which may be related to surface defects or contaminations.