ATOMIC-STRUCTURE OF THE METASTABLE C(4X4) RECONSTRUCTION OF SI(100)

A c (4 X 4) reconstruction can be formed on the clean Si(100) surface by special surface treatment techniques. We have studied the atomic structure of this metastable phase, which is prepared by hydrogen exposure and annealing, using scanning tunneling microscopy and first-principles total-energy calculations. A new model is derived which has two types of surface dimers oriented parallel and perpendicular to the underlying 2 X 1 dimer rows. Our results are thus in disagreement with the missing dimer model which has earlier been proposed in the literature.