Decay mechanism of double-layer Cu islands on Cu(1 1 1)

A debate on the decay mechanism of copper mounds lasted several years since 1998. We use molecular dynamics to simulate the evolution of a double-layer Cu island on Cu(1 1 1), finding that the top-layer atoms descend to the lower layer mainly undergoing two-atom exchange which occurs most probably at straight steps. The inverse process that an atom just descended into the lower layer returns immediately back to the top layer can also take place but at a relatively low probability. The atoms originally in the lower layer can be ‘dragged’ up to the top layer with considerable probability.