Decoupling two-step anodization in anodic aluminum oxide

It is well known that ordered anodic aluminum oxide (AAO) can be fabricated by a two-step anodization process, but in the current approach, pore size and interpore spacing are coupled because the ordering mechanism is expected to be the same in both steps. Here, we demonstrate that, by using a different approach during the second anodization step, we can vary the pore size independently (either shrunk or enlarged), while preserving the ordering of AAO inherited from the first step. This approach is based on changing the electrolyte in the second step, while applying the same voltage as the first step. These results imply that ordering in AAO is strongly dependent on the coupled effect of electrolyte and voltage in the first step, whereas ordering in the second step is only affected by the voltage, quite independent of the electrolyte used. With this decoupling, AAO template processing should become more versatile. (C) 2009 American Institute of Physics. [doi:10.1063/1.3257261]