An investigation of the Cu/ZnO/Zn system: Evidence for the formation of Cu-Zn alloys by the inward diffusion of Cu

Cu deposited on 5 or 10 Angstrom thick ZnO layers (grown on Zn metal), has been investigated as a function of Cu coverage by employing X-ray photoelectron and Auger electron spectroscopies The 2p core-level binding energy of Cu increases with decreasing metal coverage, the maximum shift observed (with respect to bulk Cu metal) at the smallest coverage being similar to 0.9 eV. Temperature dependent studies show that Cu diffuses through the ZnO layer with the rate of diffusion varying with the substrate temperature as well as the oxide layer thickness. The inward diffusion of Cu results in the formation of Cu-Zn alloys. Diffusion kinetic experiments at different temperatures show that the activation energy for diffusion increases with the increasing oxide layer thickness.