KINETIC STABILITY OF MISSING-DIMER AND SINGLE-ATOM DEFECTS ON SI(100)

Scanning tunneling microscopy shows that the Si(100) surface has a lar ge number of missing-dimer vacancies and almost no missing-atom vacanc ies. In this paper we provide a kinetic explanation for these observat ions. We use the Stillinger-Weber potential to calculate the energy ba rriers opposing various atomic and dimer displacements along the surfa ce. These calculations indicate that vacancy formation by thermal fluc tuations is a very slow process. If a single-atom vacancy is formed th e atom that used to be dimerized with the missing atom will leave the dimer row rapidly; the missing-atom vacancy is thus transformed into a missing-dimer vacancy. The chance that two adsorbed atoms will fill a missing-dimer vacancy is very low: the first atom that fills the vaca ncy leaves it quickly and its lifetime at the vacancy site is shorter than the time in which the second atom joins it; moreover, vacancy fil ling competes for adsorbed single atoms with capture by steps and isla nds and with dimer formation on top of the surface.