Selective dissolution of copper from Au-rich Cu-Au alloys: an electro chemical STM study

The selective dissolution of Cu from CuAu3 alloys has been studied by STM imaging in situ as a function of anodic polarization. The experiments were performed on (111) oriented films grown on mica that exhibit large terraces separated by steps. Dissolution of Cu in the subcritical region produces vacancies that aggregate to form two-dimensional voids in the terraces. The voids are one atom deep and grow in size as a function of dealloying time. Voids are not formed in the exposed second layer. The layer-by-layer removal of material becomes three-dimensional with profuse surface roughening above the critical potential. A model for the dealloying based on these results is proposed. © 1993.