Room-temperature chemisorption of chloroethylenes on Si(1 1 1)7 × 7: formation of surface vinyl, vinylidene and their chlorinated derivatives

Abstract

Chemisorption of a family of six chloroethylenes (C 2H 3Cl, 1,1-C 2H 2Cl 2, cis-1,2-C 2H 2Cl 2, trans-1,2-C 2H 2Cl 2, C 2HCl 3, and C 2Cl 4) on Si(1 1 1)7 × 7 at room temperature (RT) has been investigated by vibrational electron energy loss spectroscopy (EELS). The characteristic vibrational EELS features have been used to identify the prominent surface species upon RT adsorption. Like ethylene, C 2H 3Cl has been found to predominantly adsorb in a di-σ bonding geometry to the Si surface, while 1,1-C 2H 2Cl 2, cis- and trans-1,2-C 2H 2Cl 2, C 2HCl 3 and, to a lesser extent, C 2Cl 4 appear to undergo dechlorination upon adsorption to form chlorinated vinyl adspecies involving single-σ bonding structures. Evidence of vinylidene (>CCH 2) has been obtained for the first time on a semiconductor surface for the adsorption of 1,1-C 2H 2Cl 2. The present work illustrates that the molecular structure and the Cl content of chloroethylenes play a crucial role in controlling not only the adsorption geometry but also the extent of dechlorination and the resulting adspecies upon RT adsorption on Si(1 1 1).