Ellipsometry of the Growth and Dissolution of Anodic Oxide Films on Aluminum in Alkaline Solution

Abstract

Ellipsometry has been used to study the growth of anodic films on superpure aluminum in sodium hydroxide of concentration range 0.1–4M. The ellipsometer used was a self‐nulling type, and all experiments were performed in situ at a constant wavelength of 632.8 nm. The results are explained by the growth and dissolution of anodic films that are duplex in nature. During the dissolution process, at certain potentials, a highly reproducible transient effect in the optical signal is seen. This effect has been related to roughening of the underlying aluminum substrate, followed by subsequent smoothing upon completion of the dissolution process. The latter is indicated by the optical signal returning close to its initial value prior to film growth.