Ethylene adsorption onSi(100)2×1: A high-resolution photoemission study

The adsorption of ethylene on $\mathrm{Si}\mathrm{}\left(100\right)2\times 1$ has been investigated at room temperature by high-resolution synchrotron radiation photoemission in the exposure range: 1–1000 L. A consistent picture in favor of molecularly di-σ bonded ethylene is obtained from the analysis of the photoemission spectral features, which shows the progressive decreasing of the surface states in the valence band and the Si $2p$ features related to the surface dimers upon adsorption. 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 assigned 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 the clean surface, and the growth of a Si-C related spectral component upon adsorption. Relative quantitative analysis of the various peak components suggests that the intensity increase of the new component almost completely parallels the progressive decrease of the surface dimer components. No evidence for carbide formation has been found from the C $1s$ spectrum.