Hexagonal pore arrays with a 50–420 nm interpore distance formed by self-organization in anodic alumina

Abstract

Self-organized hexagonal pore arrays with a 50–420 nm interpore distance in anodic alumina have been obtained by anodizing aluminum in oxalic, sulfuric, and phosphoric acid solutions. Hexagonally ordered pore arrays with distances as large as 420 nm were obtained under a constant anodic potential in phosphoric acid. By comparison of the ordered pore formation in the three types of electrolyte, it was found that the ordered pore arrays show a polycrystalline structure of a few micrometers in size. The interpore distance increases linearly with anodic potential, and the relationship obtained from disordered porous anodic alumina also fits for periodic pore arrangements. The best ordered periodic arrangements are observed when the volume expansion of the aluminum during oxidation is about 1.4 which is independent of the electrolyte. The formation mechanism of ordered arrays is consistent with a previously proposed mechanical stress model, i.e., the repulsive forces between neighboring pores at the metal/oxide interface promote the formation of hexagonally ordered pores during the oxidation process.

Morphology Defects Guided Pore Initiation during the Formation of Porous Anodic Alumina

“…However, smaller defects still remain on polished Al foils, which are sufficient to create electric field inhomogeneity and initial the pore formation under lower voltages. The conventional anodization voltages in sulfuric, 31 oxalic, 31 phosphoric, 31 citric acid, 27 and malonic acid 32 solutions are usually lower than the critical voltages required to form BAA. That could be the reason why we rarely observe BAA under general anodization conditions.…”

Carbon nanotubes prepared by anodic aluminum oxide template method

“…The barrier layer can also be removed to obtain two side open AAO film as shown in Figure 2(c). Chemical etching is often used to dissolve the barrier layer, for example by immersing into a H 3 PO 4 solution, and the opening time depends directly on the barrier layer thickness [61,62]. However, pore-widening often occurs due to the difficulty in precisely control the degree of barrier layer etching.…”

Fabrication of Arrays of Metal and Metal Oxide Nanotubes by Shadow Evaporation

“…Regardless of the irregularity of the arrays formed with the "branched" side of the AAO membrane and the polycarbonate membrane, these experiments suggest that this evaporation technique is capable of replicating templates of almost arbitrarily small dimensions, shape, and composition (including AAO membranes with regular, cylindrical pores as small as 20 nm, which are not commercially available but have been produced using established anodization methods). 3,[27][28][29][30][31] Control of the Heights of the Nanotubes. The heights of the structures depended on the angle of evaporation (␣, the angle between the axis of rotation and a line between the www.acsnano.org source and the AAO membrane).…”