Understanding Electrodeposition Instabilities

Electrodeposition is a common process via which metal ions are reduced at a cathode as a thin film. However, under certain conditions the deposited film on the cathode exhibits a unique interfacial pattern that is dependent on the applied voltage, the concentration, and the distance between electrodes. Although these morphological instabilities have been observed in the past, it still remains difficult to predict the formation and dimensions of these interfacial patterns. In an electrolytic cell, the reduction runs faster than oxidation. This is apparent when there is a small crest, as a disturbance, on the surface of cathode or a small trough on the surface of anode. These disturbances alter the rate and uniformity of metal deposition and initiate the growth of an interfacial pattern. Here we develop a model that describes the electrodeposition instabilities that lead to interfacial patterns. Transport and kinetic reactions described by Butler-Volmer equations are used to calculate and predict the electric current and growth characteristics of the film. A Cu-Cu electrodeposition system is then investigated to observe the instabilities. The pattern on the cathode is observed with or without the presence of disturbances on the anode. The roughness, periodicity, and thickness of the pattern can also be correlated to specific operating conditions.