Cu2O island shape transition during Cu-Au alloy oxidation.

In situ transmission electron microscopy observations of the oxidation of (001) Cu-Au alloys indicate that the Cu2O islands that form undergo a remarkable transformation from an initially compact morphology to a dendritic structure as growth proceeds. Correspondingly, the surface composition becomes nonuniform and the fractal dimension associated with the islands evolves from 2.0 to a stable value of 1.87, indicating a transition in the rate-limiting mechanism of oxidation from oxygen surface diffusion to diffusion of copper through the increasingly gold-rich regions adjacent to the islands.