Filament Growth and Related Instabilites during Adsorbate Suppressed Electrodepositon

Anisotropic electrochemical deposition and whisker growth is shown to be a consequence of operating a bistable active-passive critical system under galvanostatic control. Specifically, whisker growth is examined during galvanostatic Cu electrodeposition from an electrolyte containing suppressor additives. Disruption of the passivating polyether-halide bilayer triggered by metal deposition leads to positive feedback and highly localized deposition. On macroscale electrodes active-passive Turing patterns develop while on micrometer-sized electrodes the bifurcation is frustrated and proceeds as a single active zone reinforced by hemispherical transport fields. Extended electrodeposition leads to symmetry breaking and lateral propagation of a single whisker. An increasing fraction of the applied current supports expansion of the passive sidewall area and eventually results in termination of anisotropic deposition. The dynamic range between passive versus active growth determines the shape and extent of whisker formation. Similar critical behavior may account for reports of whisker growth in certain metal/metal ion battery systems.