Electrochemical Cu deposition on thiol covered Au(111) surfaces

The electrochemical deposition of Cu on Au(111) surfaces covered by self-assembled thiol monolayers has been followed in situ by electrochemical STM. Monolayers formed by thiols of different chain length have been chemisorbed on gold electrodes. The thiol molecules are organized in a quasi-crystalline structure characterized by a multi-domain ordering. The presence of the organic layer strongly influences the Cu deposition process. Cyclovoltammetry shows the absence of the underpotential deposition peaks observed on bare gold as well as a decrease of the electrochemical current in the overpotential regime. Independently of the chain length, in the UPD region we observe the formation of Cu nanoparticles 2-5 nm in diameter, one Cu atomic layer in height, uniformly distributed at the surface. The Cu cluster density reaches its maximum in the UPD regime. In the OPD region a chain length dependent behaviour is observed. Long thiol monolayers prevent any further growth of already existing clusters while on short thiol covered surfaces an almost 2D growth of Cu is observed.