High charge flexibility of the surface dangling bonds on the Si(1 1 1)- 7 x 7 surface and NH₃ chemisorption: A DFT study

The dissociative chemisorption of NH₃ on the Si(111)-7×7 surface has been investigated by means of hybrid density functional (B3LYP) cluster model calculations. It is shown that the dissociation of NH₃ occurs readily on either the restatom site or the adatom site via a molecular precursor, giving rise to NH₂ and H adspecies. Elaborate NBO (natural bond orbital) analyses reveal quite facile and unexpectedly significant charge transfer between the DBs (dangling bonds) of the restatom-adatom pair site even at a very large H₃N-Si distance (e.g., 3.4 Å), evidencing the high charge flexibility of the DB states on the Si(111)-7×7 surface.