The formation of vacancies and their diffusion on the 7 x 7 (111) surfaces, in the initial stages of oxidation, were studied by using  in situ  ultra-high vacuum reflection electron microscopy. During O exposure experiments at low pressures, vacancies were formed on the surfaces, due to the formation and sublimation of SiO, and coalesced into hollows in the central parts of the terraces between successive surface atomic steps when the Si surface temperature was greater than 500C. The distribution of hollows on the surface terraces, and their growth kinetics, were studied. Analysis showed that the activation energy for surface diffusion of the vacancies was about 1.4eV. The reaction rate required to form 2 vacancies by the impingement of an O molecule on the surface was estimated to be about 0.23 at 630C.

N.Shimizu, Y.Tanishiro, K.Takayanagi, K.Yagi: Surface Science, 1987, 191[1-2], 28-44