Ethylene adsorption on Si(100)2X1: A high-resolution photoemission study

The adsorption of ethylene on Si(100)2 x 1 has been investigated at room te mperature by high-resolution synchrotron radiation photoemission in the exp osure range: 1-1000 L. A consistent picture in favor of molecularly di-a bo nded ethylene is obtained from the analysis of the photoemission spectral f eatures, which shows the progressive decreasing of the surface states in th e valence band and the Si 2p features related to the surface dimers upon ad sorption. By careful fitting of the Si 2p complex envelope, the appearance of a component in the Si 2p core-level spectrum is evidenced already after 1 L exposure to ethylene. This component, which grows with exposure, is ass igned to the formation of two Si-C bonds per dimer as a result of ethylene adsorption. The line-shape analysis by model functions permits us to follow the symmetrization of Si-Si dimers, which are known to be asymmetric on th e clean surface, and the growth of a Si-C related spectral component upon a dsorption. Relative quantitative analysis of the various peak components su ggests that the intensity increase of the new component almost completely p arallels the progressive decrease of the surface dimer components. No evide nce for carbide formation has been found from the C 1s spectrum.