Ultra-narrow 12 nm pore diameter self-ordered anodic alumina templates

• 8–12 nm Porous alumina templates have been obtained by self-organization.
• The electrochemical bath viscosity should be taking into account when studied porous alumina fabrication.
• We found that the highest degree of ordering in a 12 nm template is after 48 h of first anodization.
• The nucleation step may be at the origin of the mismatched multi-domain nanopore ordering in self-ordered alumina.

Ordered anodic aluminum oxide (AAO) templates with pores of 12 nm in diameter and aspect-ratios (length-to-diameter) of >1000 are prepared by a simple two-step anodization process under mild-anodization conditions. Such a low diameter pores are consequence of the reduction of the dielectric constant of the electrolyte together with the effect of increasing the electrolyte viscosity. We show that the temperature has a strong impact on reducing the pore diameter, as provokes the increase of viscosity of the medium and thus the hindering of the diffusion of species involved in the widening of pores. Moreover, we manage to stop the AAO growth process at the pore nucleation stage and we show that 8 nm in diameter pores are originally formed under these conditions. The presented ultra-narrow pore templates may allow for the preparation of ordered arrays of high aspect-ratio ultra-small one dimensional (1D) nanostructures that could be useful to explore quantum phenomena and integrate quantum-devices.

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