Initial oxidation processes of H-terminated Si(100) surfaces studied by high-resolution electron energy loss spectroscopy

The initial oxidation processes of H-terminated Si(100)-1 x 1 surfaces have been investigated using high-resolution electron energy loss spectroscopy at room temperature and 300 degrees C. It has been found that oxygen atoms adsorb on one of the two back-bond sites of a surface Si atom until the oxygen coverage is 0.4 and in the sequential oxidation process, other adsorption sites such as the other back-bond sites and/or Si-Si dimer-bond sites, become occupied by oxygen atoms. The structural relaxation in Si-O-Si bonds is observed when a surface Si atom has two Si-O bonds, and is considered to originate from the change in the force constant of Si-O bonds.