The Phoenix-like Noble Metal: Cu

Copper is one of the least reactive metals under atmospheric conditions. By heating copper in air to hundreds Of degrees centigrade, its surface is oxidized to black CuO. Interestingly, the black CuO surface layer peels off automatically when the temperature of the sample is lowered to room temperature. Three-dimensional red self-assembled Cu2O nanostructures are observed in the new exposed surface (this phenomenon is compared to a phoenix reborn from the ashes). A simple extension of the spinodal decomposition to single phase system is proposed to account quantitatively for the,self-assembled behavior of Cu2O nanostructures. The presented analysis is also useful to understand similar behaviors of other single phase systems.