Pattern organization on Cu(1 1 1) in perchlorate solutions

The first in situ scanning tunneling microscopy (STM) study of Pb underpotential deposition (upd) on Cu(1 1 1) in perchlorate solutions is presented. High resolution STM shows a (4 × 4) Moiré structure of a full density close-packed lead monolayer that is identical to that observed in ultrahigh vacuum. Interestingly, the STM experiments revealed nano-organization morphologies of the topmost Cu(1 1 1) layer following stripping of the lead monolayer in naturally aerated solutions. The length-scale and nature of the ordered structures was found to depend on solution pH. A Moiré structure indicative of an anion adsorption-induced reconstruction was observed in pH 2 and a star-pattern type of dislocation network structure was observed in pH < 2. Experiments performed in deaerated lead-free solutions show the formation of identically ordered structures (pH dependent) suggesting a dominant role of perchlorate adsorption in the surface organization process. No surface ordering was detected in naturally aerated lead-free solutions in which surface oxidation processes dominate owing to an increase of the interfacial pH resulting from oxygen reduction. We suggest that the role of the Pb upd layer and its subsequent removal in the ordering process is simply kinetic, i.e., stripping of the layer yields a bare copper surface allowing perchlorate adsorption to occur prior to the requisite pH increase necessary for the initiation of surface oxidation processes. This is the first report demonstrating that perchlorate adsorption results in the formation of an ordered adlayer which induces a surface reconstruction.