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

The dissociative chemisorption of NH3 on the Si(1 1 1)-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(1 1 1)-7×7 surface.