Etching the oxide barrier of micrometer-scale self-organized porous anodic alumina membranes

We develop a quantitative model to calculate the optimal experimental conditions for the etching of the oxide barrier of porous anodic alumina (PAA) membranes. The method is applied to a membrane fabricated at 370 V in a solution of 2% citric acid. The process creates a network of small pores at the bottom of the larger pores, which accelerates the oxide barrier etching relatively to the pore walls of the PAA membranes, when etched in a solution of phosphoric acid. The oxide barrier etching is confirmed by observation of PAA membranes using scanning electron microscopy, revealing the formation of the small pores and the preferential etching of the bottom of the pores rather than the pore walls. The proposed method, which leads to a better control over the fabrication of nanoporous templates, can be adapted to oxide barriers of different PAA membranes formed at different voltages and in different acids.