Effect of chemical etching on the morphology of anodic aluminum oxides in the two-step anodization process

Morphological features of the anodic aluminum oxide (AAO) templates fabricated by electrochemical oxidation under different chemical etching conditions were investigated. The chemical etching treatment had a paramount impact on the morphological features of the AAO templates produced with the two-step anodization process. Increasing the etching treatment time was found to be favourable, provided that the ratio of the etching treatment time to that of anodization must be at least one half. Etching solutions based merely on H3PO4 fail to remove the aluminum oxides from the first anodization step. The addition of as much as 2% CrO3 offers a marked improvement in the AAO pore features. Increasing the H3PO4 concentration in H3PO4–CrO3 mixtures improves the pore features while an increase in the CrO3 concentration has no effect. The temperature of the etching solution also affects the morphology of AAO pores remarkably. An etching solution temperature of 55 °C is the optimum.