Ultra-small nanopores obtained by self-organized anodization of aluminum in oxalic acid at low voltages

A simple method of fabrication of anodic aluminum oxide at low voltages (from 5 to 15 V) in 0.3 M oxalic acid is presented. To overcome the issues concerning the anode's burning, a high velocity stirring was applied. It allowed to achieve nanopores with ultra-small diameters (even 12 nm), interpore distance (even 31 nm) and tremendously high pore densities (up to 980 pores per 1 µm 2 ) with simultaneous high porosity (up to 38%). Moreover, the presented approach (no modifier added to the electrolyte) resulted in the AAO with relatively well arranged ultra-small nanopores.