Cyanide-free electrolyte for Au/Co-Au nano-multilayer electrodeposition utilising 5,5-dimethylhydantoin as a complexing agent

A novel cyanide-free electrolyte was used in electrodepositing Au/Co-Au nano-multilayers. Firstly, an optimised electrolyte for Au-Co alloy electrodeposition was obtained from orthogonal experiments. The effect of current density and potential values on the deposited composition was investigated. Results showed that low current density and over-potential value promoted Au deposition. A large current density and high over-potential value resulted in high cobalt concentration. The co-deposition of gold and cobalt in this study system was canonical. When the electrode potential was positive (-0.6 V, -0.7 V vs. saturated calomel electrode (SCE)), only gold was deposited; when the potential was negative (-0.8 V vs. SCE), gold and cobalt were co-deposited. Using an optimised cyanide-free electrolyte produced Au/94.07 at% Co-Au multi-layers with a gold layer of approximately 20 nm and a 94.07 at% Co-Au alloy layer of approximately 90 nm in the 5,5-dimethylhydantoin-containing, cyanide-free system.