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 oxidati on is preceded, in the underpotential rang e by adsorption of an ordered la yer assigned to OH species. This ordered adlayer is a precursor of the oxid e growing at higher potential with the copper surface reordering to mimic t he 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 crystall ization of this Cu(I) oxide depend on the overpotential of oxidation. At lo w overpotential, poorly crystallized and one-monolayer thick islands partia lly covering the substrate are formed after preferential nucleation at step edges. At higher overpotential, well crystallized and several-monolayer-th ick films are formed, and the step edges are not preferential sites of nucl eation. 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 bri des rebuilds the original extended and flat terraces of the substrate for o xides of monolayer thickness but produces a faceted Cu surface when a thick er bride film is reduced.