Fabrication of AAO films with controllable nanopore size by changing electrolytes and electrolytic parameters

In this paper, we fabricate two kinds of anodic aluminum oxide (AAO) films with controllable nanopore size by changing electrolytes and electrolytic parameters. The first AAO film with a four-layer structure was fabricated by sequential anodization of aluminum in aqueous solution of H₂SO₄, H₂C₂O₄, malonic acid, and tartaric acid at different anodic oxidation voltages. The average pore diameter of the as-prepared AAO film is 25 nm in the first layer, 54 nm in the second layer, 68 nm in the third layer, and 88 nm in the fourth layer, respectively. The pore densities of each layer decrease downwards to Al substrate, which are 300?×?10⁸, 100?×?10⁸, 21?×?10⁸, and 6.9?×?10⁸ cm^?2, respectively. Furthermore, another AAO film with periodically changed pore diameter was fabricated by alternating anodization of aluminum in aqueous solution of H₃PO₄ and tartaric acid under galvanostatic mode. The anodization processes present approximately identical best ordering voltage (195 V) in H₃PO₄ and tartaric acid under galvanostatic mode. The pore diameter with periodic change can be enlarged through a pore-widening treatment. Both AAO films with special nanopore structures can be used not only as templates for preparing nano-array materials whose pore diameter presents periodic change or gradual increase, but also as nanofilters to separate materials in some special media.