Self-ordered porous alumina membranes with large lattice constant fabricated by hard anodization

We report on the fabrication of self-ordered porous alumina with long interpore distance. The samples were prepared in an oxalic acid solution using hard anodization process. In contrast to the common two-step anodization process, this technique only consists of a single step, where a much higher voltage is applied. The as-produced samples were examined and analysed in detail by scanning electron microscopy. The results show that the porous structures produced by hard anodization have larger interpore distance of 310 nm as compared with the conventional two-step anodization, where this distance can vary between 90 nm and 120 nm. Moreover, the porous-layer growth rate is about 10 times faster. Then the qualitative analysis of Fast Fourier transform was applied on high-resolution SEM surface images. The results confirm a good hexagonal pore ordering. The pore diameter distribution revealed the fact that pores have uniform size of 170 nm with standard deviation of 7 nm.