The effect of L (-) cysteine and thiourea on the kinetics of copper electrocrystallization from aqueous sulphate solutions

The production and characterization of nano-crystalline metallic coatings has been a subject of intensive research due to their fundamental and commercial significance. For instance, thin films of copper are used in electronic industry for the fabrication of interconnect for printed circuit boards, integrated chips and multilayer sandwiches. Organic substances such as thiourea (TU), gelatine, polyethylene glycol, and benzotriazole are usually added to electrodeposition bath in low concentrations for beneficial effects such as brightening and levelling of the deposit. Despite the perceived benefits of additives, there is limited fundamental understanding of their mode of action and impact on electrocrystallization kinetics. In this study, the effect of thiourea and L (-) Cysteine (CYS) on mechanisms and kinetics of copper electrodeposition from an aqueous solution at pH 1 and 25 degreesC was studied using Linear Scan Voltammetry (LSV) and Atomic Force Microscopy (AFM). The current density measurements, estimated kinetic parameters and ex situ AFM visual observation indicated that both TU and CYS have a significant inhibition and morphological effects on the electroreduction of Cu(II), resulting in fine-grained deposits. These additives were found to influence the electron and mass transfer at electrode/electrolyte interface and lead to the formation of a crystalline deposit whose structure and morphological analysis indicate S-based impurity incorporation effects