Fast fabrication of long-range ordered porous alumina membranes by hard anodization


Nanoporous anodic aluminium oxide has been widely used for the development of various functional nanostructures. So far these self-organized pore structures could only be prepared within narrow processing conditions. Here we report a new oxalic-acid-based anodization process for long-range ordered alumina membranes. This process is a new generation of the so-called ‘hard anodization’ approach that has been widely used in industry for high-speed fabrication of mechanically robust, very thick (>100 μm) and low-porosity alumina films since the 1960s. This hard anodization approach establishes a new self-ordering regime with interpore distances, (Dint)=200–300 nm, which have not been achieved by mild anodization processes so far. It offers substantial advantages over conventional anodization processes in terms of processing time, allowing 2,500–3,500% faster oxide growth with improved ordering of the nanopores. Perfectly ordered alumina membranes with high aspect ratios (>1,000) of uniform nanopores with periodically modulated diameters have been realized.

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Figure 1: Hard anodization versus mild anodization.
Figure 2: The effect of voltage on the self-ordering of AAO.
Figure 3: A new and second regime of self-ordering for oxalic acid anodization.
Figure 4: Long-range ordered alumina membranes with modulated pore diameters.


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We thank F. Müller for helpful discussions, D. Hesse for his comments on the manuscript and W. Gruner at the Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden (IFW-Dresden) for chemical anaysis. We acknowledge financial support from the German Federal Ministry for Education and Research (BMBF, Project No. 03N8701).

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Correspondence to Woo Lee.

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Lee, W., Ji, R., Gösele, U. et al. Fast fabrication of long-range ordered porous alumina membranes by hard anodization. Nature Mater 5, 741–747 (2006).

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