Real time scanning tunneling microscopy of anodic dissolution of copper

Changes in surface topography of anodically dissolving surfaces have been examined by scanning tunneling microscopy (STM). Since aqueous solutions present the possibility of faradaic reactions during the STM examination, their effects on the tunneling current are discussed. When copper is anodically dissolved in the Tafel region, the initial mechanically polished surface (0.05 mm Al₂O₃) is known to roughen and to form large scale (mm) facets of low index hkl planes. Real time STM shows, in addition, that the crystalline faces of the facet actually smoothen on a finer scale (10 and 100 nm) while the facets are forming. When Cu is selectively dissolved from Cu-Au alloy, pits (10 to 100² nm diameter) and eventual porosity form. The spacing and diameter of the pits obtained by STM are in good agreement with scanning electron microscopy results. As expected, however. STM under estimates the depth of the pits except at the very initial stages of surface roughening.