Preparation of self-ordered nanoporous anodic aluminum oxide membranes by combination of hard anodization and mild anodization

Abstract Anodic aluminum oxide (AAO) is one of the most important templates for fabrication of nano-materials. In this paper, we present a fast two-step anodization method to prepare self-ordered AAO films. The first step is hard anodization (HA) in H 2 SO 4 and the second step is mild anodization (MA) in H 2 C 2 O 4 . HA in H 2 SO 4 at a wide range of anodization voltage provided a fast formation of ordered arrays of pits on Al sheet, and in the second step, arrays of pits on Al substrate affected nucleation initially, and the anodization voltage of H 2 C 2 O 4 MA determined the degree of AAO later. Then the best anodization voltage of H 2 C 2 O 4 MA was validated to be around 40 V. The improved combination of HA and MA not only shortens the time of the first anodization step compared to conventional two-step anodization which was reported by Masuda and Fukuda (1995), but also keeps a highly ordered AAO within large area. Moreover, the relationship between the size of arrays of pits formed in H 2 SO 4 HA and degree of order of AAO formed in H 2 C 2 O 4 MA was investigated in detail.