Effect of solvent on the morphology of nickel localized electrochemical deposition

Localized electrochemical deposition (LECD) was performed by microanode-guided electroplating (MAGE) in two different baths to investigate the effect of solvent on the deposit morphology. One of the baths contained an ordinary aqueous solution prepared from distilled water and ionic liquid by mixing choline chloride with ethylene glycol; the other bath contained the same concentration of nickel chloride. A nonuniform micro deposit was obtained in the ionic liquid and it appeared as if it had been directly accumulated with huge nodular nickel particles; a uniform micro pillar was formed in the aqueous solution and this micro pillar exhibited a smooth appearance. The distinct deposit morphology is governed by the nature of the bath, which is characterized by the electrical resistivity and viscosity. The activation energy that arose from the electrical resistivity (E_η) and viscosity (E) in the different baths was estimated. The sum of activation energies (i.e., E _sum E_p E_η) is much higher in the ionic liquid than in the aqueous solution. The higher activation energy in the ionic liquid bath leads to the formation of nodular deposits. The lower activation energy in the aqueous solution bath leads to the formation of a micro pillar with fine uniform particles that have a smooth appearance. Therefore, loosely-packed coarse particles grow in the ionic liquid bath to form nickel nodules whereas tiny dense particles are formed in the aqueous solution bath to form a micro pillar with a smooth surface.