Correlation between chemical properties and electronic structure of pseudomorphic Cu monolayers on Ni(1 1 1) and Ru(0 0 0 1)

The adsorption of CO and benzene on pseudomorphic Cu monolayers on Ni(1 1 1) and Ru(0 0 0 1) shows pronounced differences: For Cu/Ni(1 1 1) a behavior very similar to that of Cu(1 1 1) is observed, for Cu/Ru(0 0 0 1) the adsorbate substrate bond is significantly strengthened for both molecules, as is deduced from a shift of the desorption temperature to higher values. Based on angle resolved UV photoelectron spectroscopy using synchrotron radiation at BESSY and density functional calculations we have determined the two-dimensional band structure of the pseudomorphic Cu monolayers on Ni(1 1 1) and Ru(0 0 0 1). Our results show that for Cu/Ni(1 1 1) only weak coupling of the Cu 3d states to the Ni substrate states occurs. On the other hand, strong coupling is observed for Cu/Ru(0 0 0 1). This difference is made responsible for the strongly modified chemical properties of Cu/Ru(0 0 0 1) as compared to Cu/Ni(1 1 1).