Behavior of thin copper oxide on silver as an analogue for copper nanoparticles

The behavior of a thin copper oxide (CuOx) layer deposited on silver (Ag) was examined in order to clarify the process by which an interface is formed when Cu nanoparticles bond to an Ag adhesive. The results of X-ray photoelectron spectroscopy and atomic force microscopy revealed that an active interfacial reaction occurs between CuOx and Ag when annealed in a reductive atmosphere at temperatures above 523 K. This reaction involves the migration of Ag atoms toward the surface, which is accompanied by the reduction of CuOx to metallic Cu and the growth of newly generated elongated grains. As this reaction was limited in an inert atmosphere, it is concluded that annealing causes phase separation into Ag and Cu, which is then followed by the formation of an AgCu solid solution. This suggests that interfaces are created through inter-diffusion between the Ag layer and a metastable metallic Cu surface layer formed on the surface of Cu nanoparticles by annealing in a reductive atmosphere.