Growth of electrolytic copper dendrites. I: Current transients and optical observation

The growth of electrolytic copper dendrites between two coplanar copper disc electrodes, 250 μm in diameter, was investigated in oxalic acid medium by a technique based on the coupling of electrochemical measurements and optical in situ observations. The current transients observed when a potential difference was applied between the two microdiscs were recorded. Simultaneously, the length of the dendrite was measured in real time thanks to a microvideo equipment. After some image processing, the growth rate of the dendrite was calculated by considering the increase of its length for a time increment. It was shown that the current transients exhibited a steep increase when the dendrites reach the anode and then formed a short circuit between the two copper discs. Depending on the experimental conditions, two types of dendrite morphology were observed: a filamentary growth and hierarchically branched thick structures. A strong relationship between the current transients, the change of the growth rate with time and the morphology of the dendrites was demonstrated. Low deposition currents are associated with a constant growth rate and filamentary dendrites whereas higher currents are associated with increasing growth rate with respect to time and hierarchical dendritic morphology.