The self-ordering behavior of anodic porous alumina that was formed by anodizing in selenic acid electrolyte
(H2SeO4) at various concentrations and voltages was investigated with SEM and AFM imaging.
A high purity aluminum foil was anodized in 0.1-3.0 M selenic acid solutions at 273K and at constant
cell voltages in the range of 37 to 51V. The regularity of the cell arrangement increased with increasing
anodizing voltage and selenic acid concentration under conditions of steady oxide growth without
burning. Anodizing at 42-46V in 3.0 M selenic acid produced highly ordered porous alumina. By selective
dissolution of the anodic porous alumina, highly ordered convex nanostructures of aluminum with
diameters of 20 nm and heights of 40 nm were exposed at the apexes of each hexagonal dimple array.
Highly ordered anodic porous alumina with a cell size of 102 nm from top to bottom can be fabricated
by a two-step selenic acid anodizing process, that includes the first anodizing step, the selective oxide
dissolution, and the second anodizing step.