Self-organized formation of hexagonal pore arrays in anodic alumina

TLDR

The study investigated the conditions for self‑organized formation of ordered hexagonal structures in anodic alumina using oxalic and sulfuric acid electrolytes. The authors correlated voltage‑dependent volume expansion and current efficiency of aluminum oxidation with mechanical stress at the metal/oxide interface, proposing that repulsive forces between pores drive the formation of ordered hexagonal arrays. Highly ordered pore arrays were achieved in both oxalic and sulfuric acid, with domain size strongly dependent on anodizing voltage.

Abstract

The conditions for the self-organized formation of ordered hexagonal structures in anodic alumina were investigated for both oxalic and sulfuric acid as an electrolyte. Highly ordered pore arrays were obtained for oxidation in both acids. The size of the ordered domains depends strongly on the anodizing voltage. This effect is correlated with a voltage dependence of the volume expansion of the aluminum during oxidation and the current efficiency for oxide formation. The resulting mechanical stress at the metal/oxide interface is proposed to cause repulsive forces between the neighboring pores which promote the formation of ordered hexagonal pore arrays.