Interaction of CO with Cu/Rh(100), Cu overlayer structures and CO surface diffusion

Abstract

The interaction of CO with ultrathin Cu films on a Rh(100) surface has been studied using infrared reflection–absorption spectroscopy (IRAS). The CO vibrational frequency on Cu/Rh(100) at low Cu coverage [∼0.1 monolayer (ML)] shows a blue shift relative to its gas phase stretching frequency (2143 cm−1 ). This blue shift likely arises from CO adsorbed onto Cu adatoms which are either slightly charged due to charge transfer from Cu to Rh or self‐polarized because of a strong Cu–Rh interaction. It is further shown that disordered Cu islands, well‐ordered Cu pseudomorphic islands, and Cu three‐dimensional clusters are distinctively characterized by CO peaks at 2122, 2093, and 2076 cm−1, respectively. In addition, it is found that CO adsorbed onto ∼0.1 ML Cu/Rh(100) diffuses from Cu to Rh at a sample temperature (Ts) of 150–270 K, and that Cu deposition onto CO‐covered Rh(100) at Ts=90 K causes CO spill over from Rh to Cu, thus forming a CO/Cu/Rh(100) structure.