Abstract
Electrochemical oxidation of metals, in solutions where the oxide is somewhat soluble, produces anodic oxides with highly regular arrangements of pores. Although porous aluminium and titanium oxides have found extensive use in functional nanostructures, pore initiation and self-ordering are not yet understood. Here we present an analysis that examines the roles of oxide dissolution and ionic conduction in the morphological stability of anodic films. We show that patterns of pores with a minimum spacing are possible only within a narrow range of the oxide formation efficiency (the fraction of oxidized metal atoms retained in the film), which should exist when the metal ion charge exceeds two. Experimentally measured efficiencies, over diverse anodizing conditions on both aluminium and titanium, lie within the different ranges predicted for each metal. On the basis of these results, the relationship between dissolution chemistry and the conditions for pore initiation can now be understood in quantitative terms.
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Change history
09 December 2011
In the version of this Article originally published online, the term Auger electron spectroscopy was incorrectly used; it should have read atomic emission spectroscopy. This error has been corrected in all versions of the Article.
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Acknowledgements
This research was supported financially by the National Science Foundation (CMMI-100748) and the Deutsche Forschungsgemeinschaft (including DFG cluster of excellence EAM). We thank W. Hong (Iowa State University) for helpful discussions.
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K.R.H. carried out linear stability analysis and project planning. S.P.A. and I.P. made measurements of oxide formation efficiency during growth of anodic titania nanotube layers. P.S. contributed to the planning and analysis of these experiments.
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Hebert, K., Albu, S., Paramasivam, I. et al. Morphological instability leading to formation of porous anodic oxide films. Nature Mater 11, 162–166 (2012). https://doi.org/10.1038/nmat3185
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DOI: https://doi.org/10.1038/nmat3185
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