First-principles calculations of the adsorption of S on theSi(001)c(4×2)surface

Abstract

The adsorption of S on the Si(001)c(4 x 2) surface is studied by first-principles total-energy calculations. We started with the adsorption of a single atom up to a full-monolayer coverage. The first S atom occupies a bridge site, on top of a Si dimer that becomes completely symmetric. At half-monolayer coverage, all bridge sites are occupied, and all Si dimers become symmetric. The overall periodicity is (2 x 1). The adsorption of an additional S atom results in the breaking of two Si dimers. From this point and up to one monolayer, it is energetically more favorable for the S atoms to be adsorbed along the [{bar 1}10] direction. At full monolayer coverage, all Si dimers are broken, and the Si surface is dereconstructed with all Si atoms near bulk ideal positions.