Kinetics of the electrodeposition of PbSn alloys

Abstract

The electrodeposition of lead, tin and lead–tin alloys on gold has been studied by cyclic voltammetry and chronoamperometry. The nucleation mechanism was obtained from the potentiostatic I – t transients, while the alloy composition was determined by differential pulse anodic stripping voltammetry. Structural information of the electrodeposited layers was obtained by X-ray diffraction, and scanning electron microscopy was used to determine the surface morphology. The electrodeposition of tin on gold results in the formation of an AuSn intermetallic phase as demonstrated by X-ray diffraction. The charge corresponding to the oxidation of tin from the intermetallic phase approaches a limiting value of 5 mC cm −2 , which corresponds to approximately 400 Å. Electrodeposition of lead on gold results in underpotential deposition of lead as expected. However, in the presence of tin the gold surface is blocked preventing the formation of upd lead. Thus, bulk deposition of lead in the presence of tin takes place on top of the reconstructed surface layer and on tin. SEM images show that the microstructure of the electrodeposited tin is dendrite-like, while deposited lead has a rounded structure. The microstructure of the alloy changes with increasing lead content, and it is evident that lead inhibits the deposition of tin on tin and prevents the formation of dendrites. The bulk deposition of lead, tin and lead–tin alloys on a gold substrate is a diffusion-controlled process with a 3D growth mechanism.