X-ray photoelectron spectroscopic study of the formation of Cu/Ni interface mediated by oxide phase

•We report the interfacial reactions between Cu2O and Ni by the annealing.•The solid solution of Cu2O interacted with the surface oxide of Ni were observed.•The valence of Cu transformed from monovalent state to bivalent state.•The interfacial reactions promote the reduction of Cu2O.•The reduction of Cu2O led to the Cu/Ni metallic interface formation.

Chemical properties of CuOx thin films deposited on Ni were investigated by X-ray photoelectron spectroscopy to understand the mechanism of interface formation between Cu nanoparticles and Ni layer. On annealing, the valence state of Cu transformed from a monovalent oxide state to a metallic state in a reducing atmosphere and to bivalent oxide state in an inert atmosphere. Additionally, Ni migrated toward the surface. However, CuOx thin films deposited on Cu scarcely showed such transformations in the valence state of Cu. These results suggest that the surface oxide of Ni layer mediates the reduction of the surface oxide of Cu nanoparticles.