Anodization of nanoimprinted titanium:: a comparison with formation of porous alumina

Electrochemically prepared ordered porous alumina has become one of the most important nanotemplate materials to date. Naturally the questions arises whether other valve metals such as Ti, Ta, Nb, V, Hf or W can also be used for fabricating ordered pore arrays. We investigate in detail the electrochemical anodization of titanium in different electrolytes and its potential and temperature dependence. It turns out that due to the semiconducting properties of titania, a mirror image of the behaviour of the electrically insulating porous alumina seems to be impossible. So-called porous titania in literature corresponds to the pitting regime of aluminum where pores are created due to dielectric breakdown of titania or alumina, respectively. Below the breakdown potential of titania, only thick barrier layers can be obtained. However, by nanoimprint of titanium and successive anodization below the breakdown potential, monodomain porous titanium oxide with a pore depth of 60 nm on a cm(2) -scale can be prepared. We discuss in detail the growth mechanism of porous Structures of titanium and compare it with that of porous alumina. (C) 2004 Elsevier Ltd. All rights reserved.