Initial oxidation of H-terminated Si( 111) surfaces studied by HREELS

We have investigated the initial oxidation process and the local bonding structure of Si-0-Si bonds of H-terminated Si(1 1 1)-l X 1 surfaces using high-resolution electron energy loss spectroscopy (HREELS) below an oxygen coverage of 2.5 ML. Oxygen atoms randomly adsorb on the sites between surface and subsurface Si atoms at room temperature in this oxidation coverage. The vibrational energy of the Si-0-Si asymmetric stretching mode increases monotonously with increasing the number of adsorbed 0 atoms in contrast with the case of Si( 100)~(1 X 1)H. The relaxation of Si-0-Si structures is promoted by the existence of Si-H bonds.