Carbon Monoxide Adsorption on a Cu₃Pt(111) Single Crystal Alloy

Abstract

The adsorption of CO on CU₃Pt(111) was investigated by low energy He⁺ ion scattering. The alloy surface was characterised by low energy electron diffraction (LEED) and work function change (Δφ) measurements. No surface ordering of the alloy was evidenced by LEED. The CO induced work function changes were small. Under normal incidence of the beam, only the scattered He⁺ ions from 0, Cu and Pt were detected, indicating the orientation of the CO molecule with 0 facing away from the surface. In the initial stages of CO adsorption at 200 K, the Pt intensity in a Cu-rich surface was not detectable at an exposure of ~5 L CO, indicating that all the Pt atoms were covered by CO. At a saturation coverage of CO, the Pt intensity in a Pt-rich surface, however, fell to ~12% of its clean surface intensity. This observation strongly suggested that not all the Pt sites were covered by the CO molecules. These results are discussed in relation with the structure and composition of the surface and compared to data for CO adsorption on Pt(111).