INFLUENCE OF CHEMICAL PERTURBATIONS ON THE SURFACE ROUGHNESS OF THIN LAYER ELECTRODEPOSITS
Alexander Kuhn, Françoise Argoul · Fractals · 1993
We have studied the origin of macroscopic and microscopic changes of the morphology of metal electrodeposits in thin layer cells. We concentrate on zinc electrodeposition to show that a part of the variety of growth patterns reported in the literature (dense radial, stringy, dendritic and DLA-like fractal morphologies) is probably due to pollution of the electrolyte. One common pollution in these experiments is molecular oxygen, which is dissolved in the electrolyte during its preparation and conservation in contact with air. Its cathodic reduction can seriously perturb the metallic host lattice by formation and intercalation of metal oxide. Other perturbations with equal dramatic effects on the morphology and the roughness of the deposit are alkali cations. By well-controlled addition of one of these ions or molecules, we are able to generate a wide variety of morphologies, from highly ordered dendritic growth to completely disordered growth. Other metals such as copper or tin are shown to be also highly sensitive towards impurities. Based on this sensitivity upon chemical perturbation, we finally propose a new explanation for the morphological changes, called Hecker effect, which can occur during the growth process.