In situ scanning tunneling microscopy study of the anodic oxidation of Cu(111) in 0.1 M NaOH

In situ electrochemical scanning tunneling microscopy (STM) measurements of the anodic oxidation of Cu(lll) in 0.1 M NaOH are reported. Anodic oxidation is preceded, in the underpotential rang e by adsorption of an ordered layer assigned to OH species. This ordered adlayer is a precursor of the oxide growing at higher potential with the copper surface reordering to mimic the structural arrangement of a (111) oriented Cu2O oxide. In the potential range of Cu(I) oxidation, a Cu2O(lll) oxide film is formed with a faceted, and most likely hydroxylated, surface. The nucleation, growth, and crystallization of this Cu(I) oxide depend on the overpotential of oxidation. At low overpotential, poorly crystallized and one-monolayer thick islands partially covering the substrate are formed after preferential nucleation at step edges. At higher overpotential, well crystallized and several-monolayer-thick films are formed, and the step edges are not preferential sites of nucleation. In the potential range of Cu(II) oxidation, a crystalline Cu2O/CuO,Cu(OH)(2) duplex film is formed. The cathodic reduction of these anodic brides rebuilds the original extended and flat terraces of the substrate for oxides of monolayer thickness but produces a faceted Cu surface when a thicker bride film is reduced.