HEXAGONAL PORE ARRAYS WITH A 50-420 NM INTERPORE DISTANCE FORMED BY SELF-ORGANIZATION IN ANODIC ALUMINA

Self-organized hexagonal pore arrays with a 50-420 nm interpore distan ce in anodic alumina have been obtained by anodizing aluminum in oxali c, sulfuric, and phosphoric acid solutions. Hexagonally ordered pore a rrays with distances as large as 420 nm were obtained under a constant anodic potential in phosphoric acid. By comparison of the ordered por e formation in the three types of electrolyte, it was found that the o rdered pore arrays show a polycrystalline structure of a few micromete rs in size. The interpore distance increases linearly with anodic pote ntial, and the relationship obtained from disordered porous anodic alu mina also fits for periodic pore arrangements. The best ordered period ic 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 previ ously proposed mechanical stress model, i. e., the repulsive forces be tween neighboring pores at the metal/oxide interface promote the forma tion of hexagonally ordered pores during the oxidation process. (C) 19 98 American Institute of Physics. [S0021-8979(98)00423-X]