A comparison between self-ordering of nanopores in aluminium oxide films achieved by two- and three-step anodic oxidation

We report on the enhancement of naturally-occurred self-ordering of nanopores in anodic aluminium oxide (AAO) membrane by performing three step anodic oxidation. Two and three step anodic oxidation methods were used to achieve self ordering of nanopores and the ordering of nanopores obtained by the methods were compared. The current–time curves, recorded during anodization, elucidate an almost similar features for all three steps in both methods. Scanning electron micrographs (SEM) show hexagonally arranged nanopores in a way which forms highly ordered areas or ordered domains. Domains are placed beside each other like a polycrystalline structure after two and three step anodizing, while larger ones are clearly observed over the surface after three step anodizing. More uniform nanopores with narrower size distribution are observed for AAO films of three step anodic oxidation.