Fabrication of highly ordered porous anodic alumina films in 0.75 M oxalic acid solution without using nanoimprinting

Abstract

Porous anodic alumina (PAA) films have received particular attention due to the ordered hexagonal pore array structure. Under conventional mild anodization conditions, however, a very long period of time is needed to prepare the ordered PAA films. Here, we report a high-field anodization process of aluminum in a highly concentrated (0.75 M) oxalic acid solution, where highly ordered PAA films can be fabricated rapidly. Special attention was given to the effects of the purity of aluminum sheets, aluminum substrate grain orientation, anodization time and electrolyte temperature on the ordering quality of the PAA films. For example, a highly ordered PAA film with a thickness of ∼57 μm was prepared conveniently at 50 V for 50 min at 30 °C. The as-prepared PAA film has a self-ordered pore structure with a typical interpore distance of ∼120 nm and a pore diameter of ∼75 nm, which are particularly useful in many applications.