Kinetics of the electrodeposition of PbSn alloys part II. At polycrystalline gold electrodes

The electrodeposition of lead, tin and lead-tin alloys on gold has been stu died by cyclic voltammetry and chronoamperometry. The nucleation mechanism was obtained from the potentiostatic I-t transients, while the alloy compos ition was determined by differential pulse anodic stripping voltammetry. St ructural information of the electrodeposited layers was obtained by X-ray d iffraction, and scanning electron microscopy was used to determine the surf ace morphology. The electrodeposition of tin on gold results in the formati on 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 approximat ely 400 A. Electrodeposition of lead on gold results in underpotential depo sition of lead as expected. However, in the presence of tin the gold surfac e 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 surfac e layer and on tin. SEM images show that the microstructure of the electrod eposited 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 grow th mechanism. (C) 2000 Elsevier Science S.A. All rights reserved.