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Electrocrystallization of Distinct Ni Nanostructures at the Ionic Liquid/Au(111) Interface:  An Electrochemical and in-Situ STM Investigation

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journal contribution
posted on 12.07.2007, 00:00 by Olivier Mann, Werner Freyland
Electrocrystallization of Ni nanostructures has been studied at the Au(111)/ionic liquid [AlCl3−[C4mim]+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 × 2 ) 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 ∼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 (∼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 ∼10 nm and an aspect ratio of ∼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.