Adsorption properties of a mixed surface studied by high resolution core level photoemission : CO/0.5 ML Pd/Rh(111)

The coverage-dependent adsorption properties of a laterally heterogeneous bimetallic surface have been investigated by high resolution core level photoemission and low energy electron diffraction. The specific system under study was CO adsorbed on a Rh(111) surface onto which 2D Pd islands (coverage 0.5 ML) were formed by vapor deposition. The CO adsorption properties of the heterogeneous surface were compared with CO adsorption on a Rh(111) surface covered with a full Pd monolayer and with previous results for the CO/Rh(111) system. For low exposures CO is only found on the Rh(111) patches which can be explained by diffusion of CO from the Pd islands onto Rh parts in the adsorption process. At higher exposures CO diffusion from Rh to Pd is indicated. The origin of the diffusion processes can be found in the different coverage-dependent CO adsorption energies on the two surface parts