Structure of chemisorbed acetylene on the Si(001)-(2x1) surface and the effect of coadsorbed atomic hydrogen

The structure of chemisorbed acetylene on the Si(001)-(2 x 1) surface is investigated based on ab initio molecular-dynamics simulations according to the Car-Parrinello method and within the local-density approximation (LDA) to density-functional theory. The calculations reveal that the Si-Si dimer bond is stable upon acetylene chemisorption resulting in the formation of a four-member disilacyclobutene ring. Coadsorption of two hydrogen atoms together with the acetylene molecule onto the Si-Si dimer bonds results in cleavage of the Si-Si bond and separation of the two silicon atoms by a distance equal to the second-nearest neighbor distance in bulk crystalline silicon. (C) 1997 Elsevier Science B.V.