A novel gold electroplating system : Gold(I)-iodide-thiosulfate

The electrodeposition of gold from a new electroplating system for gold that contains iodide and thiosulfate has been studied using rotating disk voltammetry. The cathodic electron transfer is slow, with a transfer coefficient of alpha =0.76plus/minus0.02, and is coupled with a preceding chemical reaction, the formation of the complex ion Au(S sub 2 O sub 2 ) sub 2 exp 3- . The magnitude of the current contribution from the chemical step can be made negligible by using high concentrations of thiosulfate and by the proper choice of supporting electrolyte. High quality gold deposits with a very high aspect ratio have been obtained through a photoresist mask from this plating bath under optimized conditions. The choice of univalent salt as supporting electrolyte affects markedly the electroreduction of Au(I).