Electrochemical Deposition of Copper on a Gold Electrode in Sulfuric Acid: Resolution of the Interfacial Structure

The structure of electrochemically deposited submonolayer Cu on Au(111) in sulfuric acid has been extensively investigated but is still poorly known. We report an x-ray scattering determination of this structure that explains existing data. The Cu adatoms form a honeycomb lattice and are adsorbed on threefold hollow sites, while sulfate anions occupy the honeycomb centers. Three oxygens of each sulfate bond to Cu atoms. This stabilizes the structure and illustrates that anion effects can be important in electrodeposited structures. Our results indicate that previous scanning tunneling and atomic force microscopy measurements imaged the sulfate molecules not the Cu atoms.