Growth of electrodeposited gold on glassy carbon from a thiosulphate-sulphite electrolyte

Abstract

A solution containing thiosulphate and sulphite has been developed specially for microelectronics applications to replace the conventional cyanide-based bath for long-term sustainability of gold electroplating. However, at the end of the electrodeposition process, the spent electrolyte can contain a significant amount of gold in solution. Investigations have been done to study the feasibility of gold recovery from the spent thiosulphate-sulphite electrolyte. In a previous work, flat plate glassy carbon was used to study the initial nucleation mechanism of gold deposition. However, in that study the growth of nuclei or their eventual formation into a gold film was not examined. Here, we present the microscopy observations of crystal growth of gold on glassy carbon at longer deposition times as a function of deposition potentials. It was found that the initial deposition of gold at low-cathodic potential corresponds to an electrochemical diffusion controlled gold discharge from which spherical nuclei are obtained. After a certain time the initial growing nuclei become unstable and the thin gold deposit begins to develop tips, which eventually grow larger and produce dendrites. The dendritic growth is controlled by surface-diffusion limitations of gold. Copyright © 2008 John Wiley & Sons, Ltd.