Shrinking Anodized Aluminum Oxide Pores Beyond 10 Nanometers

Anodization of aluminum has piqued research interest because of the self-ordering porous nanostructure created during anodization. This porous structure can be tuned to be a specific diameter and packing density based on macroscopic properties, such as voltage, acid type, and concentration. Recent work has achieved smaller pore sizes with the addition of an organic solvent that enables a reduction of temperature. Another study demonstrated rapid fabrication of 10 nm pores by utilizing selenic acid as the electrolyte. However, no study has successfully fabricated sub-10 nanometer pores through anodization. Shrinking the pore diameter below 10 nanometers is problematic because the driving force for oxidation is insufficient at lower anodization potentials. In this work, we report a novel, self-ordering method that produces sub-10 nanometer pores during anodization in selenic acid/ethylene glycol. The pores fabricated in this method have a mean pore size of five nanometers, half the size of those reported from previous approaches. These sub-10 nm pores have the potential to be used in a variety of applications, including photonics, membranes for gas separations, and as templates for fabricating nanowires.