Characterization of copper nucleation and growth from aqueous solution on aluminum: A transmission electron microscopy study of copper cementation

Abstract

A novel technique was developed for the direct observation of copper precipitate nuclei forming on aluminium surfaces by cementation. This technique involves the preparation of thin electron-transparent aluminum films by vapor deposition in vacuum onto cleaved NaCl crystal blanks. Following aqueous CuSO 4 solution contact of an exposed aluminum film surface area, the films with attached copper nuclei were examined by transmision and scanning electron microscopy. For conditions which promoted optimum deposit growth kinetics, the initial faceted polyhedral nuclei developed microdendritic precipatates which led to the growth of massive dendritic deposits. The details of microdendrite arm structures were directly observed in the transmission electron microscope. By systematically varying the residual grain structure of the aluminum films, it was demonstrated that grain size and grain structure do not affect the disposition and morphology of the initial precipitates. Furthermore, in single-crystal aluminum films containing dislocations it was not possible to show any consistent association of nucleation or nuclei with the emergence sites of individual dislocations. The principal feature of the substrate which influences precipitation as a result of the electrochemical cementation reaction seems to be crystallographic orientation, and this is consistent with observations of the growth and structure of conventional electrodeposits.