Date of Award

Winter 1998

Project Type

Dissertation

Program or Major

Engineering

Degree Name

Doctor of Philosophy

First Advisor

Dale P Barkey

Abstract

The influence of chloride on the kinetics and morphology of copper electrodeposition on copper single crystal in acidified copper sulfate solution was studied by atomic force microscopy (AFM) and by electro-analytical methods. AFM was employed to image deposits on low-index single crystal copper surface formed under potential control in a fluid electrolyte. The kinetic parameters for cathodic deposition of copper on the same surface from acid sulfate and chloride solution were measured by galvanostatic polarization.

Chloride has a great influence on the morphology of copper deposits Isotropic structures were obtained only in high purity sulfate solution, whereas anisotropic structures emerged when even trace amounts of chloride were present. Chloride ion stabilizes terraces oriented along preferred directions on single crystal surfaces. While deposition in pure sulfate solution is uniform and isotropic, in chloride solution it is source (or nucleation) limited. As a result, step propagation is an important mechanism of growth in chloride solution. Spiral growth in particular was observed only in chloride solution.

Chloride changes the reaction mechanism of copper deposition as well. When chloride is present, the reduction of the intermediate Cu+ to Cu becomes rate limiting. Additional effects of chloride include adsorption, desorption, and CuCl precipitation on the substrate. Three regions in the polarization curve were observed. The appearance of a limiting current in the second region is due to Precipitation of a film of CuCl, which blocks deposition. Charge transfer was not the rate-controlling step in this region. At higher current densities, in the third region, the dissolution of the CuCl film follows the Tafel form in dilute chloride solution. The Tafel slopes are 40 to 120 mV/decade in the Tafel region depending on chloride and cupric ion concentration.

Chloride and oxygen are competitors in the copper cathodic reduction process. Chloride ions stabilize the cuprous ion while oxygen oxidizes the cuprous ions to cupric ion.

Chloride ion greatly influences the degree of kinetic anisotropy. This study supports the conjecture that anisotropy in the interfacial kinetics stabilize dendrite growth, while absence of anisotropy results in tip-splitting.

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