In-depth study of self-ordered porous alumina in the 140–400 nm pore diameter range

The growth of self-ordered anodic aluminum oxide (AAO) templates with pore diameters in the 140–400 nm range is achieved by anodization in phosphoric acid at low temperatures (−4 °C). The procedure used in this study is able to completely avoid the “burning” of the oxide, highly frequent in anodizations in phosphoric acid solutions at high voltages. The current density measured during the anodizations is rather low, 0.6–0.7 mA/cm2; therefore, low growth rates have been also measured (<2 μm/h). AAO templates present a relatively low porosity value of 8.4%. However, a considerable pore-enlargement-rate (vΔd = 0.636 ± 0.101 nm/h) has been observed as a consequence of the chemical dissolution of the pore walls during the anodization. Thus, the results reported here constitute an exhaustive study on the preparation of large-diameter-pore self-ordered AAO templates that enables both to access to pore diameters up to now inaccessible and to efficiently overcome the difficulties of their fabrication process ascribed to its aggressive reaction conditions.

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► We obtain anodic alumina templates with pores of 140 nm in diameter.
► We reduce 40 nm the hardly-accessible diameter range of self-ordered AAO.
► The procedure completely avoids the “burning”.
► Low porosity and growth rate have been measured.