ИСТИНА

Porous anodic aluminium oxide with long-range ordered structure is of high practical importance in modern materials science and nanotechnology owing to its wide applications as membranes or templates for various nanostructures. However, the fundamental reason of self-organized growth of honeycomb-like porous anodic alumina films solely within a narrow region of processing conditions remains unknown. Here, the nature of self-ordering regimes of AAO growth under both mild and hard anodization conditions has been discovered. It is found that the formation of the long-range ordered porous structure occurs only when anodization rate is limited by migration in barrier layer, which separates metal and electrolyte, or by diffusion in pores, whereas the mixed control of anodic oxidation process leads to disordered porous structures. These regimes of anodization for the wide range of compositions and concentrations of electrolytes can be easily distinguished by the comparison of linear voltammograms recorded on bare Al and on the substrate with thick porous oxide layer. To the best of our knowledge, this is the first explanation of narrow processing conditions leading to the creation of porous anodic alumina films with highly ordered honeycomb-like structure. The universality and the predictive power of the suggested model were experimentally confirmed for oxalic and sulfuric acid electrolytes. In 0.3 M and 2 M sulfuric acid solutions, novel hard anodization regimes at 40–60 V, resulting in the extremely fast formation of AAO with highly ordered structure with interpore distance Dint = 75–110 nm, are established. Moreover, self-organized growth of honeycomb-like porous structure with ultra-small interpore distance of ca. 50 nm is predicted and then experimentally shown in 2 M sulfuric acid electrolyte.