Adsorption of small hydrocarbon molecules on Si surfaces: Ethylene on Si(001)

The interaction between small unsaturated hydrocarbon molecules of C2H4 with a vicinal silicon (001) surface is studied by means of reflectance anisotropy spectroscopy and analyzed with first principles calculations. Our results confirm that ethylene adsorbs without breaking the silicon dimers. Comparison of theoretical optical spectra with experimental data shows that the C2H4 molecules lay on top of the silicon dimers from low to high coverage. This occurs even though, from a purely energetic point of view, a bridge configuration would be favorable at 1 monolayer coverage.