INITIAL OXIDATION OF H-TERMINATED SI(111) SURFACES STUDIED BY HREELS

We have investigated the initial oxidation process and the local bondi ng structure of Si-O-Si bonds of H-terminated Si(111)-1 x 1 surfaces u sing high-resolution electron energy loss spectroscopy (HREELS) below an oxygen coverage of 2.5 ML. Oxygen atoms randomly adsorb on the site s between surface and subsurface Si atoms at room temperature in this oxidation coverage. The vibrational energy of the Si-O-Si asymmetric s tretching mode increases monotonously with increasing the number of ad sorbed O atoms in contrast with the case of Si(1CO)-(1 x 1)H. The rela xation of Si-O-Si structures is promoted by the existence of Si-H bond s.