Comparative study of the adsorption of C2H4 on the Si(001) and Ge(001) surfaces

Using a first-principles pseudopotential method we have compared the interaction processes involved in the adsorption of ethylene on the silicon and germanium surfaces. We have found that, at low temperatures, the di-sigma bond configuration is the most stable structure from the energetic point of view. According to our calculations C2H4 adsorbs preferentially on the alternate dimer sites, corresponding to a coverage of 0.5 ML. The di-sigma adsorbed system is characterized by symmetric and slightly elongated Si-Si (Ge-Ge) dimers, and by a symmetric C-C bond close to the single carbon bond length of the ethane molecule. The electronic band structure derived from our calculations suggest that the adsorption of the C2H4 molecule leaves a surface state in the fundamental band gap that is mainly localized around the adsorbate. Finally, our ab initio vibrational spectra further support the di-sigma model for the ethylene adsorption on IV(001)-(2 x 2). (C) 2002 Elsevier Science B.V. All rights reserved.