Overpotential-Controlled Nucleation of Ni Island Arrays on Reconstructed Au(111) Electrode Surfaces

In situ scanning tunneling microscopy observations on Ni electrodeposition on reconstructed Au(111) electrodes are presented, which reveal that Ni nucleation proceeds in three distinct, potential-dependent steps: place exchange of Ni with Au atoms at the elbows of the herringbone reconstruction (overpotential $\eta \ge 0\mathrm{mV}$), nucleation of Ni islands on top of these substitutional Ni atoms ( $\eta \ge 80\mathrm{mV}$), and nucleation at the step edges of the Au substrate ( $\eta \ge 100\mathrm{mV}$). This allows one to selectively control the growth via the potential and, in particular, to create nanostructures composed of regularly spaced Ni islands.