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

► Etching treatment impacts the morphological features of the AAO templates. ► Etching treatment time must at least one half that of the anodization treatment. ► H3PO4-based etching solutions fail to remove the aluminum oxides from the first anodization step. ► Addition of 2% CrO3 offers a marked improvement in the AAO pore features. ► An etching solution temperature of 55 °C produces the best pore features.