Influence of noncoherent nucleation on the formation of the polycrystalline structure of metals electrodeposited in the presence of surface-active agents

The formation of the polycrystalline structure of metals electrodeposited in the presence of surface-adsorbed foreign particles was theoretically simulated according to the model of noncoherent nucleation when the substrate does not influence the process any more. Performing a thermodynamic-statistical analysis, it was possible to relate quantitatively the structural parameters of the deposits (average grain size and dislocation density) to the relative decrease of the linear free energy of the nucleus boundary due to surface adsorption of foreign particles. The theoretical results were discussed in connection with our experimental findings on potentiostatic copper electrodeposition in the presence of thiourea. In agreement with theory, by increasing the surface-active agent concentration in the electrolyte, the average grain size decreased while the dislocation density strongly increased. Moreover, the microstructure of the deposit cross-section gradually changed from the columnar to the homogeneous type, becoming completely homogeneous for a thiourea concentration higher than 10 mg l−1 . Furthermore, the density of the twin boundaries gradually decreased, as may be expected on the basis of an increased selective adsorption of thiourea molecules on the twinning planes of the deposits.