Self-ordered anodic porous alumina with inter-hole spacing over 1.5 µm

Ordered anodic porous alumina with an inter-hole spacing of over 1.5 µm was prepared by anodization of Al in a citric acid solution containing an organic solvent and a small amount of phosphoric acid. The hole period of ordered anodic porous alumina could be controlled by adjusting anodizing voltage because the ratio of the inter-hole spacing against the applied voltages was also 2.5 nm V^-1 even under high anodizing voltage conditions. In this study, the largest inter-hole spacing of the sample was 1.8 µm. The formation of ordered anodic porous alumina with an inter-hole spacing of 1.8 µm was performed under a constant anodizing voltage of 700 V. The ordered hole arrangement of the anodic porous alumina could also be observed even by optical microscopy. The obtained ordered anodic porous alumina with a large hole period is expected to be applied in various functional devices that require ordered hole arrangement with large inter-hole spacings and hole sizes.