Chemisorption of formic acid and CO on Cu particles on the Zn-terminated ZnO (0001) surface

Abstract

The chemisorption of formic acid and CO on ultrathin Cu films vapor-deposited on to the Zn-terminated ZnO(0001)-Zn surface has been studied with temperature programmed desorption (TPD), XPS and low-energy ion scattering spectroscopy (ISS). Previous structural characterization has shown these Cu films to be predominantly in the form of Cu particles supported on the ZnO, with controllable thicknesses from one atomic layer to multilayers. The influence of the thickness of the Cu islands on their chemisorption properties is addressed. The results are also compared to similar measurements on the oxygen-terminated ZnO(0001) surface to see how the underlying oxide's surface structure affects the chemisorption properties of oxide-supported ultrathin metal particles. In both cases, the Cu atoms in two-dimensional Cu islands (i.e. islands that are only one atom thick) resemble the coordinatively unsaturated Cu atoms of Cu(110) in their chemisorption properties. This is not because of a geometric similarity, but because the Cu atoms bond so weakly to the oxide below. Thick, annealed Cu islands resemble Cu(111) both in chemisorption behavior and in structure.