Thick self-ordered nanoporous Ta₂O₅ films with long-range lateral order

In this work we report the anodic formation of highly ordered nanoporous Ta₂O₅ layers that exhibit a self-ordered alignment of pores uniformly over the anodized surface. These layers are grown by anodization of tantalum in a nonaqueous electrolyte consisting of an optimized glycerol/ethylene glycol mixture with the addition of NH₄ F. To reach an optimized nanoporous structure, several factors [fluoride concentration and content of supporting electrolyte (NH₄)₂SO₄] need to be controlled. Once optimized, the nanopore diameter can be adjusted using the applied voltage in the range of 7-18 nm, and layers with a thickness of more than 10 μm can be grown. As a result, a pore aspect ratio of >1000 can be reached.