NITRIDE FORMATION AND DANGLING-BOND PASSIVATION ON SI(111)-(7X7) WITHNH3

Thermal nitridation of the Si(111)-(7 x 7) reconstructed surface with ammonia has been investigated using scanning tunneling microscopy (STM ). True nitride formation in the form of ring-like structures as in st oichiometric silicon nitride (Si3N4) was observed at imperfections on the surface, which otherwise preserved the characteristics of the (7 x 7) reconstruction. However, the ratio of reacted adatoms in the recon struction never exceeded similar to 50%, indicative of a frustrated sa turation behavior for the adatom dangling bonds in the Si(111)-(7 x 7) -NH3 reaction system. (C) 1997 Elsevier Science B.V.