Direct observation of overlapping of growth centres in Ni and Co electrocrystallisation using atomic force microscopy

Electrocrystallization of Ni and Co on vitreous carbon and gold substrates from dilute chloride baths was studied by chronoamperometric experiments. The Scharifker and Hills model was used to analyse the current transients. A progressive nucleation mechanism was found to fit the experimental results for both Ni and Co. The calculated values of the rate of nucleation varied from 0.95 to 5.79×105 cm−2 s−1 for Ni and from 1.01 to 18.5×105 cm−2 s−1 for Co. In addition, scanning electron microscopy was used in an attempt to visualise the morphology of the surface, in particular the overlap of the growth centres. This technique failed to show overlap due to the fact that the size of the growth centres at coalescence is much smaller than the scanning electron microscopy resolution. To overcome this limitation, atomic force microscopy was used. With the greater resolution of atomic force microscopy, the growth centres at coalescence were visualised as overlapping hemispheres with several different diameters of the order of 50 nm, below the scanning electron microscopy resolution. Both the geometry and the growth centre overlap are in agreement with the boundary conditions of the Scharifker and Hills model.