Comparative study of phenol and thiophenol adsorption on Cu(110)

Adsorption of phenol and thiophenol (benzenethiol) on Cu(110) is investigated by a scanning tunneling microscope and electron energy loss spectroscopy. Phenol adsorbs intact and forms a cyclic trimer at 78 K. It is dehydrogenated to yield a phenoxy (C6H5O) group at 300 K. On the other hand, thiophenol is dehydrogenated to a thiophenoxy (C6H5S) group even at 78 K. Both products are bonded via chalcogen atom to the short-bridge site with the phenyl ring oriented nearly parallel to the surface. The C6H5O and C6H5S groups are preferentially assembled into the chains along the [001] and [112] directions, respectively. Dipole-dipole interaction is responsible for the chain growth, while the chain direction is ruled by the steric repulsion between chalcogen atoms and adjacent phenyl ring. This work demonstrates a crucial role of chalcogen atom of phenol species in their overlayer growth on the surface.