Adsorption and thermal behavior of ethylene on Si(100)-(2 × 1)

Abstract

The adsorption of ethylene on Si(100)-(2 × 1) has been studied in ultrahigh vacuum. Chemisorption was found to occur via a mobile precursor mechanism. The activation energy difference for desorption and chemisorption from the precursor ( E d − E r), was found to be 2.9 kcal mol −1. The saturation coverage of ethylene is 1 C 2H 4/Si 2 dimer. Hydrogen-site blocking and thermochemical arguments suggest that C 2H 4 bonds as a di- σ surface complex to dimer sites; upon chemisorption of C 2H 4 the SiSi dimer is cleaved. Chemisorbed ethylene desorbs unimolecularlfrom Si(100) at ∼ 550 K, with approximately 2% of the monolayer undergoing dissociation. The activation energy of C 2H 4 desorption is 38 kcal mol −1, and for the di- σ C 2H 4Si 2 complex, each SiC bond has a strength of ∼ 73 kcal mol −1. The low desorption activation energy allows C 2H 4 to desorb prior to signifi dissociation, preventing the formation of significant coverages of surfaces carbon and hydrogen.