Ultra-slow growth rate: Accurate control of the thickness of porous anodic aluminum oxide films

Abstract

Porous anodic aluminum oxide (PAAO) films have attracted widespread attention because they can be used as porous templates for the preparation of various nanomaterials. However, there are still some challenges. For example, although fine control of the thickness of AAO films is generally quite easy to achieve, it is difficult to control the thickness of extremely thin films (e.g. <1 µm). This is important for practical applications where accurate control of film thickness is necessary. In the present work, PAAO films have been prepared in an electrolyte composed of a mixture of ethanol and oxalic acid under 40–50 V (at −20 to 0 °C), attaining a minimum growth rate (νa) of ~1.4 nm min−1 (at −20 °C). The influence of anodization conditions on νa, the regularity of structural cells, and the interpore distance has been studied in detail. The results show that νa can be reduced effectively by using an extremely low anodization temperature. Ultra-thin PAAO films with precisely controlled thicknesses have been fabricated using this approach.