Hydrogenation of acetylene on Si(100)-(2x1) with atomic hydrogen: evidence for quasi Eley-Rideal chemistry

The adsorption of atomic hydrogen on the Si(100)-(2 x 1) surface with pre-adsorbed acetylene has been studied. For exposures of atomic hydrogen less than 2 L, the clean Si dimers without coadsorbed acetylene react to form Si monohydride. With an exposure of 5 to 10 L of atomic hydrogen, acetylene-occupied Si dimers as well as the acetylene itself also react to form Si monohydride and ethylene, respectively. At much higher exposures the formation of ethyl and Si dihydride is observed. This sequence of reaction events is discussed within the context of a quasi Eley-Rideal reaction of atomic hydrogen with the surface species, i.e. the radical atomic hydrogen has a finite diffusion length on the surface prior to reaction or desorption. A modified Kisliuk adsorption model has been employed successfully to describe the rates of Si monohydride and ethylene formation at a surface temperature of 150 K as a function of both the initial acetylene coverage and the post-exposure of atomic hydrogen. (C) 1998 Published by Elsevier Science B.V. All rights reserved.