Effect of thiourea on electrocrystallization of Cu-Sn alloys from sulphate electrolytes

In this work, the effect of thiourea on the initial stages of the Cu–Sn electrodeposition in the potential range of the underpotential deposition (UPD) of tin from the sulphate electrolyte was studied by linear sweep voltammetry. The mechanism of Cu–Sn alloy nucleation and growth was proposed based on the results of chronoamperometry, chronopotentiometry, and scanning electron microscopy. Thiourea in the concentrations of 0.001–0.010 g/L showed a significant inhibitory effect on the reduction of copper ions. Analysis of the current-time dependencies revealed that Cu–Sn deposition in the UPD region of tin from thiourea-containing solutions proceeds through 3D diffusion-controlled growth of copper clusters. The nucleation type and the main nucleation parameters were calculated based on the Scharifker and Hills theoretical model. Galvanostatic experiments proved that the UPD of tin occurs on the surface of initially formed copper clusters. Surface characterization of Cu–Sn coatings deposited in the presence of thiourea showed a good correlation with electrochemical experiments.