Ab initio study of atomic oxygen adsorption on the Si(111)7 x 7 surface

We study the initial steps of oxidation of the Si(1 1 1)-7 x 7 surface through modeling of different chemisorption sites for atomic O: adatom backbonds in faulted and unfaulted halves of the surface cell, and surface dimer bonds. We use ab initio calculations within local density approximation, and realistic simulation unit cells (4 x 2 and 6 x 3). Our results show the faulted adatom backbond to be favored over the unfaulted adatom backbond, and in-dimer insertion to be the stable adsorption site. We also use our results to interpret scanning tunneling microscopy results, and suggest that adatom adsorption is responsible for bright spots in unoccupied states images, while in-dimer adsorption could be related to dark sites, (C) 2001 Elsevier Science B.V. All rights reserved.