Nucleation and growth of Cu clusters on highly oriented pyrolytic graphite observed with an in situ electrochemical scanning tunneling microscope

Using an electrochemical scanning tunneling microscope (ECSTM), we have observed nucleation and growth of Cu clusters on highly oriented pyrolytic graphite (HOPG). In situ observations were made at different sample potentials. Firstly, preliminary images were obtained at the sample potential where Cu did not precipitate. Then, we obtained images at the sample potential where Cu deposition was observed. We found superperiodic structures on the top graphite layer and Cu clusters of about 2 nm in diameter formed along the step-edge with a constant interval. The interval between clusters had a same periodicity as that of the superperiodic structure. Namely, the superperiodic structure on the top graphite layer induced nucleation of Cu along the step-edge.