Preparation of Ordered Nanohole Arrays by Two-Step Anodization of Austenitic Stainless Steel Substrates.

An anodic oxide film with a regular pore arrangement was formed by the two-step anodization of an austenitic stainless steel (JIS SUS304) substrate. In this study, we determined the anodization conditions under which the pore arrangement in the anodic oxide film became self-organized. After removing the anodic oxide film formed by the first anodization with a mixture containing CrO and HF, the residual substrate was anodized under the same conditions as those in the first anodization. As a result, we found that it was possible to form an anodic oxide film with pores arranged in a regular pattern from the surface to the bottom. This is the first report on the formation of anodic oxide films with ordered nanohole array structures by the two-step anodization of austenitic stainless steel. The interpore distance of the resulting nanohole array structures can be controlled by changing the anodization conditions. By measuring the capacitance of the anodic oxide film, we confirmed that its properties depended on the heat-treatment temperature and pore depth. In addition, no significant decrease in the capacity of anodic oxide films with ordered nanohole array structures was observed, even when the scan rate of the cyclic voltammogram measurement was increased. This is considered to be because the cylindrical pores facilitate ion diffusion to the bottom of the holes. Anodic oxide films obtained by the anodization of austenitic stainless steel substrates can be applied as electrodes for capacitors.