Epitaxial growth and electrode impedance of copper electrodeposits

Abstract

Copper electrocrystallization in acidified 1.25 M sulfate solution has been investigated by means of impedance measurements on polycrystalline electrodes and on (111), (110) and (100) single crystals. In all cases the Cu 2+ reduction is confirmed to occur in two consecutive charge transfer reactions. The high frequency impedance data show that the two reactions have the same cathodic transfer coefficients in a high purity electrolyte. With the addition of 2 × 10 −4 M KCl, the cathodic transfer coefficient of the second reaction is increased. The low frequency features depend on the growth mode of deposits. The inductive response observed for polycrystalline deposits and also at low current densities for the epitaxial growth on single crystals essentially reflects the activation of the electrode area. A capacitive loop appears only when a regular growth is achieved. The low frequency features are discussed on the basis of a model for the birth and growth of monolayers which propagate over a finite distance.