Electrocrystallization of distinct Ni nanostructures at the ionic liquid/Au(111) interface: An electrochemical and in-situ STM investigation

Electrocrystallization of Ni nanostructures has been studied at the Au(111)/ionic liquid [AlCl3-[C(4)mim]Cl-+(-) (58:42) + 5 mM Ni(II)] interface by in-situ scanning tunneling microscopy, cyclovoltammetry, and chronoamperometry. In the underpotential deposition (UPD) region, a well-defined superstructure, incommensurate c(p x 2mt;sys rl3rlx mx) structure, of adsorbed AlCl4- layers is observed. It exists over a potential range of more than 0.35 V down to 0.15 V. Below this potential, 2D Ni phase formation sets in and a complete monolayer grows over a period of similar to 800 s. In the overpotential (OPD) range, different morphologies of Ni nanoclusters have been obtained depending on the parameters of the respective electrodeposition procedures. Jumping the potential from above 0.15 V (UPD) to -0.25 V, the peak potential of bulk Ni deposition, large nearly spherical (similar to 10 nm diameter) Ni clusters first nucleate at the step edges of the Au(111) substrate and spread with time all over the surface. In this case, a progressive nucleation and growth mechanism with diffusion control is found. A distinct and interesting morphology is obtained, if first a complete monolayer of Ni is deposited at UPD conditions and then the potential is directly decreased to OPD values near -0.18 V. Elongated Ni clusters with a diameter of similar to 10 nm and an aspect ratio of similar to 2 nucleate and grow instantaneously. Most interestingly, they are all oriented in one direction which is indicative of a magnetic interaction between the Ni clusters.