In Situ Scanning Tunneling Microscopy of Corrosion of Silver-Gold Alloys

An in situ scanning tunneling microscope (STM) was used to observe the morphological changes accompanying the selective dissolution of Ag from low-Ag content Ag-Au alloys in dilute perchloric acid. This study was undertaken to explore the role of surface diffusion in alloy corrosion processes. These results are interpreted within the framework of the kink-ledge-terrace model of a crystal surface and a recent model of alloy corrosion based on a variant of percolation theory. The corrosion process leads to roughening of the surface by dissolution of Ag atoms from terrace sites. Annealing or smoothening of the surface occurs by vacancy migration through clusters and the subsequent annihilation of clusters at terrace ledges.