Structure of chemisorbed acetylene on the Si(001)-(2 × 1) surface and the effect of coadsorbed atomic hydrogen

The structure of chemisorbed acetylene on the Si(001)-(2 × 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 SiSi 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 SiSi dimer bonds results in cleavage of the SiSi bond and separation of the two silicon atoms by a distance equal to the second-nearest neighbor distance in bulk crystalline silicon.