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 initial stages of the hydrogenation of Si(111) 7 x 7. Energies, atomic charges and reduced overlap populations are considered, and we discuss the inequivalence of the adatoms. The adatom dangling bond (DB) level positions with respect to E(F) are also discussed. On the basis of our results, we propose the following adsorption sequence: first, saturation of the five occupied adatom DBs, then hydrogenation of the remaining atoms 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 saturated, and that this modification occurs in discontinuous stages.