Electrochemical nucleation and growth of copper and copper alloys.

摘要

This dissertation aims to contribute to a fundamental understanding of the physicochemical processes occurring in electrochemical nucleation and growth. To this end, the effects of various anions (chloride (Cl-), sulfate (SO42-) and sulfamate (NH2SO 3-)) on the electrochemical kinetics and the mechanism of copper reduction, as well as on the microstructure of the resulting films, were studied. On the basis of this work, the deposition of copper alloys (Cu-Ag with positive heat of mixing, Cu-Au with negative heat of mixing) was investigated with the main objective to achieve an insight on the role of solid state thermodynamics on the electrocrystallization process.;Chloride ions cause two competing effects: at low chloride concentration the formation of an adsorbed chloride layer introduces an additional reaction pathway, resulting in an overall depolarization of the reduction process with no significant change of the Tafel slope. At high chloride concentration, complexation phenomena induce a cathodic polarization of the deposition process and a decrease in the Tafel slope. Chlorides cause a decrease in the density and an increased size of copper nuclei. Sulfamate depolarizes copper reduction the most and results in the largest nucleus density.;Chloride promotes the faceting, and dendritic growth of copper deposits along 110> direction by introducing interfacial anisotropy.;Addition of Ag in the solution or in the electrode substrate enhances copper deposition and results in an additional reduction peak. Codeposition of Cu-Ag increases nucleus density and decreases nucleus size. Such enhancement of copper deposition, the increase in nucleus density and the decrease in nucleus size by Ag could be due to the continued formation of a surface alloy of Cu-Ag and the fast interface dynamics of Ag deposition.;Cu can be underpotentially codeposited in the Cu-Au alloy. Homogeneous solid solutions are grown under conditions of underpotential deposition of Cu, while precipitation of Cu-rich films is observed under Cu overpotential conditions. Indirect evidence for the formation of a Au3Cu L12 structure is observed. Nucleus density increases significantly with the addition of small amounts of gold in the solution, due to the negative heat of mixing decreasing the nucleation barrier.