Interface evolution during electrochemical oxidation-dissolution

We present results from an experimental study on the roughening of Al thin film during electrochemical oxidation reduction. The surface reaction occurred in two stages. Anodic alumina forms during oxidation of aluminum followed by immediate dissolution of alumina. The surface image using AFM showed randomly oriented grains with lateral feature size 280 nm at early stage (30 s) of oxidation-dissolution (OD). As farther dissolution of alumina (90 s) progressed, oriented rectangular grains were observed with lateral feature size 400 nm, indicating a disordered to ordered transition at the surface. The roughness exponent at the earlier stage found to be 0.44 0.02, consistent with nonlinear KPZ equation. However, for the later case, roughness exponent increased to 0.84 0.03, which is close to the value derived in continuum model. The value of dissolution exponent (growth exponent) b found to be 0.47 0.1. These values are slightly different from the theoretical values but they are consistent with the theoretical models within the experimental error. Shadow instability found to be a dominant feature in this experiment and contributed to the discrepancy. Interface instabilities are discussed in terms of local and non-local effects