Adsorption of benzene on a Mo(112)-c(2x2)-[SiO4] surface

The orientation and growth of benzene and pyridine on a well-ordered Mo(112)-c(2 x 2)-[SiO4] have been investigated with high-resolution electron energy loss spectroscopy (HREELS), Auger spectroscopy (AES) and low-energy electron diffraction (LEED). Benzene on the c(2 x 2)-[SiO4] surface is bound with its molecular plane parallel to the surface plane at submonolayer coverages. At intermediate coverages (1-3 ML), in contrast to benzene adsorption on metal surfaces, a layer-by-layer growth mode is observed with the benzene molecules bonded parallel to the surface. Pyridine on the c(2 x 2)-[SiO4] surface, on the other hand, undergoes a phase transition from a parallel to a tilted configuration. This is the first reported observation of benzene multilayer growth in which the benzene molecules bond exclusively parallel to the surface plane. The origin for this unusual adsorption behavior of benzene is discussed.