A Dominant Dissociation Mode of cis-Dichloroethylene on Si(100)2 × 1: Adjacent Si Dimer Double Dechlorination

Abstract

The dehalogenation mechanisms of cis-dichloroethylene (cis-DCE) and cis-dibromoethylene (cis-DBE) adsorption on Si(100)2 × 1 are explored by using a first principles method to understand the halogen substitution effects. Instead of the two C−X (X = Cl, Br) bonds cleaved on a single broken Si dimer to produce the vinylene di-σ product, a newly identified adjacent Si dimer didechlorination mode is found to be more favorable. This double dechlorination is a two-step reaction, including the initial cycloaddition and the following didechlorination, with activation barriers of no more than 0.40 eV. The overall reaction yields two new adspecies, named as the intra- and interdimer tetra-σ. The mono-σ adspecies derived from one C−Cl cleavage is a minor product, although it is thermally less favorable than the intra- and interdimer tetra-σ states. With thermal evolution, its conversion to the final product (interdimer tetra-σ) is investigated, which accounts for the C 1s photoelectron peaks shifting from 285.6 to 2...