Effects of Anodizing Voltages and Corresponding Current Densities on Self-ordering Process of Nanopores in Porous Anodic Aluminas Anodized in Oxalic and Sulfuric Acids

In the fabrication of ferroelectric nanostructures, the template-based approach using porous anodic alumina (PAA) has been popularly used because the ordering and the dimensions of the nanostructures can be easily controlled by using various kinds of PAA. We report here the effects of anodizing voltage on the pore morphologies of PAA and the corresponding current density variations. Various kinds of PAA were fabricated at different anodizing voltages in two acids, 0.3 M oxalic and 0.3 M sulfuric acids, by the anodization of aluminum. We found that highly ordered arrays of nanopores with a uniform pore diameter could be obtained at a moderate and stable current density for both acids. At a low current density, the size of the nanopores was uniform, but the pores showed a disordered arrangement. At a high and unstable current density, the sizes and the arrangements of the pores were not uniform. These results show that the anodizing voltage and the corresponding current density play an important role in the self-ordering process of nanopores in PAA.