Adsorption of benzonitrile on Si (001) -2×1 at 300 K

We have studied the adsorption geometries of benzonitrile (C6 H5 -C N) deposited on Si (001) -2×1 at 300 K, using synchrotron radiation x-ray photoemission spectroscopy and x-ray absorption spectroscopy. The experimental data are interpreted through density functional theory calculations of ground and excited states. It is shown that the molecule chemisorbs under multiple forms. While the literature indicated that adsorption is highly selective at 110 K (bonding via the cyano), at 300 K, cyano bonding is observed concomitantly with other geometries for which the molecule interacts with the surface by the phenyl ring. Among the phenyl-bonded species, the cyano group can remain unreacted or can make a dativelike bond with the substrate via its nitrogen end (the latter species is a minority species at surface saturation). Real-time kinetic studies show that all species are present on the surface with the same distribution from the very beginning of the adsorption process.