Pulse-plating of copper-cobalt alloys

Pulse-plating of copper-cobalt alloys was studied theoretically and experimentally. The deposits were produced from a citrate electrolyte using a recessed rotating cylinder electrode (rRCE) and an inverted recessed rotating disk electrode (IrRDE), respectively. A mathematical model developed previously by the authors was applied to the prediction of alloy composition as a function of pulse off-time. The displacement reaction between copper and cobalt during the pulse off-time was simulated using step functions for the characterization of the coverage of the surface by a copper layer. Comparison of simulated and measured alloy compositions showed that a displacement reaction occurred even at the longest pulse off-times studied. Potential responses measured during pulse off-time suggest that the displacement reaction leads to incomplete coverage of the alloy surface by copper. Investigation of deposit cross-sections with the scanning electron microscope showed that distinct phases rich in copper and in cobalt form a columnar structure. This is thought to be the reason that a displacement reaction could be observed even at long pulse off-times. (C) 1999 Elsevier Science Ltd. All rights reserved.