Driving force and growth mechanism for spontaneous oxide nanowire formation during the thermal oxidation of metals

The spontaneous formation of oxide nanowires (and whiskers) from the oxidation of metals is a well-established phenomenon that has, however, long resisted interpretation. Here we report new fundamental insights into this phenomenon by studying CuO nanowire formation during the thermal oxidation of copper. It is shown that the volume change associated with the solid-state transformation at the CuO/Cu2O interface produces compressive stresses, which stimulate CuO nanowire growth to accompany the interface reaction. A kinetic model based on the stress-driven grain-boundary diffusion followed by rapid surface diffusion of cations on the sidewall of nanowires is developed to account for CuO nanowire growth. The mechanism proposed explains our observations on CuO nanowires and other past observations.