Initial stages of NH3 adsorption on Si(111) 7 x 7

We present a theoretical study of the first stages of the ammonia chemisorp tion on Si(111)7 x 7. NH3 dissociates on this surface. In a first model, pa rtial dissociation generating two radical species, NH2 and H, that adsorb o n the surface dangling bonds is investigated. Our result shows an adsorptio n mechanism closely similar to that of water on Si(111)7 x 7. Further disso ciation of NH3 is more favorable, A geometry with NI-I in a bridge position between an adatom and one of its backbond atoms seems to be more likely th an the picture with NH saturating an Si dangling bond. (C) 2000 Elsevier Sc ience B.V. All rights reserved.