The effects of electrolyte concentration on film composition and homogeneity in electrodeposition

We have investigated the effects of electrolyte concentration on the composition and homogeneity of thin films of the ternary alloy CoNiCu grown by single-bath electrodeposition techniques. The material was chosen owing to its academic and industrial applications but our results are more generic and will apply to other alloys grown this way. We compare weak (low species concentrations) and strong (high species concentrations) electrolyte solutions using identical electrolyte ratios. By choosing the concentration of the more noble species, in this case Cu, to be 25 times less than that of the other species, we controlled alloy composition as a function of potential. Films grown from the strong electrolyte solution were largely invariant in composition, whereas the weak solution produced highly potential sensitive alloy compositions. We found a trade-off between the accessible alloying range and thickness homogeneity across the film. This was shown to be due to the convective evolution of the diffusion layer using schlieren imaging.

► Strong and weak electrolyte solutions are used to grow alloys and compared ► Weak electrolyte solutions produce films with large scale thickness inhomogeneities ► Weak electrolyte solutions allow large alloy composition variation ► Strong electrolyte solutions have limited compositions of achievable alloy growth ► Simple scaling up in concentration of electrolyte species ratios does not work