β-hydride elimination processes on silicon

Abstract

The adsorption and decomposition of ethylbromide on the Si(100) and Si(111) surfaces is investigated. Ethylbromide adsorbs molecularly on Si at surface temperatures below 110 K. Warming the ethylbromide-covered surface above 200 K results in the cleavage of the carbon–bromine bond with the formation of surface ethyl groups and coadsorbed bromine atoms. Further heating of the surface leads to the decomposition of surface ethyl groups which desorb as ethylene leaving hydrogen at the Si surface. The hydrogen atoms recombine at higher surface temperatures (near 800 K) and desorb as molecular hydrogen. Isotopic labeling of the hydrogen within the ethyl group provides greater insight into the mechanism for ethylene formation. A branching reaction is observed between β- and α-hydride elimination within the ethyl group to form ethylene. The ratio of the amount of ethylene produced by β-hydride to α-hydride elimination can be varied by the position of the deuterium label within the ethyl group. The reaction rate for ethylene production is measured and how this rate is influenced by the isotopic substitution is discussed.