Electroconvective and compositional instabilities during electrodeposition of alloys

Electrodeposition of a single metal cation can occur by electromigration and diffusion in a quiescent electrolyte solution at low applied voltages. Increasing the applied potential leads to strong concentration polarization, the formation of an extended space charge layer near the electrode surface, and subsequently an electroconvective flow that degrades the quality of the metal film. In this study, we determine the conditions under which two metal species can be simultaneously deposited by electromigration and diffusion through a quiescent solution to form a solid-solution metal alloy film. The conditions leading to formation of a space charge layer due to depletion of one of the metal cations will be examined. Linear stability analysis will reveal the nature and growth rate of electroconvective instabilities that would lead to compositional as well as morphological variations of the metal film. An interesting question is whether the formation of a space charge layer is a prerequisite for electroconvection during deposition of an alloy as it is for a single metal species.