Porous Tantalum Oxide Prepared by Electrochemical Anodic Oxidation

It has recently been demonstrated [ I. Sieber , B. Kannan , and P. Schmuki , Electrochem. Solid-State Lett. , 8 , J10 (2005) ] that Ta can be porosified by anodic oxidation in diluted HF electrolytes. Pore morphology strongly depends on the HF concentration in the electrolyte and anodization time. In the present article, we investigate various factors that affected the process of self-assembled porous formation. The parameters studied are the HF concentration, the oxidation time, the anodization potential, and the potential scan rate. By optimizing the parameters, the porous tantalum oxide could be obtained that consists of highly regular pore arrays with single pore diameters of about 20 nm and pore spacing of about 15 nm. A steady-state porous film formation/film dissolution mechanism controls the time scale of the development of the porosity, the ordering effects, and the thickness of the formed oxide layer, which are similar to those operative for Ti and Nb.