Fabrication of ideally ordered TiO₂ through-hole membrane s by two-layer anodization

Ideally ordered TiO₂ through-hole membranes were obtained by a combination of Ti substrate prepatterning and two-layer anodization. Each concave formed by prepatterning acted as an initiation site for hole development during anodization, and ideally ordered anodic porous TiO₂ was produced by anodization. Two-layered anodic porous TiO₂ samples with different solubilities were formed by heat treatment for the crystallization of the first anodized oxide layer and a subsequent second anodization. The selective dissolution of the lower part of the two-layered porous TiO₂ produced an ideally ordered TiO₂ through-hole membrane. Using present process, the repeated preparation of ideally ordered TiO₂ membranes can be conducted because the ideally ordered concave array, which corresponds to the hole arrangement at the bottom of the detached TiO₂ membrane, is maintained even after detaching the membrane.