Benzene adsorption on Cu(111): Formation of a stable bilayer

Abstract

The structure of benzene deposited on a Cu(111) surface has been investigated by a combination of temperature-programmed desorption (TPD), high-resolution electron energy loss spectroscopy (HREELS), and near-edge x-ray absorption fine structure (NEXAFS) measurements. The results indicate that benzene forms a stable bilayer on Cu(111) at 110 K prior to multilayer formation. The TPD studies show that the second layer benzene desorbs with a peak temperature 5 K higher than that for benzene multilayers. HREELS and NEXAFS results indicate that benzene in the first layer bonds with its π ring parallel to the surface. With increasing coverage, benzene forms a second layer with its π ring significantly tilted away from the surface. The results are consistent with an approximately perpendicular configuration between the first and second layer benzene molecules, which is analogous to the structure of crystalline benzene. Isotope labeling experiments indicate there is almost complete mixing between molecules in different layers during sequential adsorption at 110 K.