N-15 NUCLEAR-REACTION ANALYSIS OF H-1 ON [111]SI SURFACES

Polished [111] Si wafers, exposed to wet-chemical hydrogenation proced ures for monolayer (ML) coverage, were analyzed with the nuclear N-15- reaction technique in order to determine both areal concentration and vibrational properties of H-1. Initial multilayer coverages of up to 4 ML H equivalent were observed to desorb with ion or electron beam irr adiation until rather stable layers of about 1 ML H were reached. The quickly desorbing excess layers are attributed to physisorbed H-bearin g compounds. The remaining 1 ML constitutes chemisorbed H terminating dangling bonds of Si surface atoms. The observed Doppler width lies in between theoretical estimates for an ordered surface layer, perfectly aligned along the [111] direction, and a disordered, randomly oriente d one, so that a partial surface reconstruction cannot be excluded.