Copper Growth on a Stepped Nickel Surface: Electronic and Geometric Effects on CO Reactivity

Abstract

The deposition of Cu on a stepped Ni(119) surface was investigated by experimental and computational (DFT) methods. At ambient temperature, Cu grows thermodynamically stable in a layer-by-layer mode, occupying 4-fold hollow sites below the step edge. Although CO and Cu adsorption does not appear to be competitive in terms of stable surface sites, Cu was found to alter quantitatively the adsorption of CO. The Cu-Ni interaction is determined by both geometric (higher coordination number) and electronic (perturbation of surface electron density) effects. The latter is supported from the negative binding energy shifts observed for the Cu 2p3/2photoelectron peak combined with the shift of the Cu 3d band center, which reflects a Ni-induced increase in the d-electron population of Cu metal atoms. CO preferably adsorbs on the step edges on the clean and submonolayer Cu-covered Ni(119) where the minimum electron density is observed. These results highlight the importance of geometric and electronic effects in a bimetallic system, which mimics real catalysts, where heteroatoms can electronically alter or selectively block certain surface sites and therefore change dramatically the overall reactivity of the surface.