Comparative study of the adsorption of C2H4 on the Si(0 0 1) and Ge(0 0 1) 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-σ 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-σ 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-σ model for the ethylene adsorption on IV(0 0 1)-(2×2).