A THEORETICAL-STUDY OF THE INITIAL-STAGES OF THE HYDROGENATION OF SI(111) 7X7

We have used the periodic extended Huckel method to examine the initia l stages of the hydrogenation of Si(111) 7 x 7. Energies, atomic charg es and reduced overlap populations are considered, and we discuss the inequivalence of the adatoms. The adatom dangling bond (DB) level posi tions with respect to E(F) are also discussed. On the basis of our res ults, we propose the following adsorption sequence: first, saturation of the five occupied adatom DBs, then hydrogenation of the remaining a toms by pairs, the hydrogenation of an adatom being coupled with that of a restatom or that of the comer atom. We also show that the atomic charges of the surface become more uniform when the 19 DBs are saturat ed, and that this modification occurs in discontinuous stages.