Unravelling transient phases during thermal oxidation of copper for dense CuO nanowire growth

Direct evidence of cupric ion outdiffusion through grain boundaries during thermal oxidation of high purity Cu is obtained using Raman spectroscopy. This diffusion feeds the growth of CuO nanowires on the surface while forming a Cu1+xO phase in the grain boundaries of the underlying Cu2O film. On complete Cu consumption, counter indiffusion of O2- ions converts the entire structure to a CuO film, while viable CuO nanowires still remain on the surface.