Bi-Cu film deposition in aqueous solutions

The relatively uniform bismuth-copper film was electrode posited between -15 and -20 mV in the sulfate electrolyte containing 4 mmol/L bismuth ion and 2 mmol/L copper ion. Only copper was electrodeposited at -5 mV. The dendritic bismuth-copper film was electrodeposited under -20 mV. The cathodic current became constant between -20 and -400 mV. Therefore, bismuth-copper electrodeposition changes from charge transfer controlling to diffusion controlling at -20 mV. On the other hand, the uniform bismuth-copper film was electrodeposited between -5 and -35 mV in the methanesulfonate electrolyte containing 4 mmol/L bismuth ion and 2 mmol/L copper ion. The dendritic bismuth-copper film was electrodeposited under -35 mV. The potential region for good electrodepositon in methanesulfonate electrolyte is wider than that in sulfate electrolyte. Therefore, it is easy to control electrodeposition conditions by using methanesulfonate electrolyte.