THE WATER-ADSORPTION ON THE SI(111)7X7 SURFACE - A THEORETICAL-STUDY

We present a theoretical study of the initial steps of the water adsor ption on Si(111)7x7. Water dissociates on the surface. In a first step , partial dissociation generates the radical species H-. and HO. which are adsorbed on the dangling bonds of the surface. The first sites to be saturated are those of adatoms from the faulted half of the Si(111 )7x7 unit cell. When three molecules per unit cell are adsorbed, one r est-atom site is involved together with adatom sites and the adsorptio n implies an electron transfer from one unit cell to another. For the subsequent adsorptions, a rest-atom site is involved simultaneously wi th an adatom site. The OH. goes on the rest-atom site since H-., which is more selective, goes preferentially on the adatom site. Complete d issociation of H2O seems to be even more favorable. Water adsorption c an displace the adsorbed hydrogen atoms, initiating an oxidative proce ss. (C) 1997 Elsevier Science B.V.