Electrochemical preparation of overlapped porous layers on anodic alumina.

In this paper, we report the development of a new architecture on porous anodic alumina using the conventional two-step anodization method. The samples prepared in two identical steps using galvanostatic anodization exhibited two porous layers overlapped with distinct pore area distributions. The effects from the first anodization time and temperature on this different morphology were assessed using Factorial Design. The chemical removal time of the oxide formed during the first anodization was not relevant for the overlapped porous structure. The most important factor was the time of the first anodization required for formation of stable patterns on the substrate, which would be reproduced in the second anodization. A pore mismatch appeared because under galvanostatic control the changes in the actual area become important, which is not the case for sample preparation under potentiostatic control where the current density is adjusted according to the new boundary condition. The new architecture with mismatching layers may open the way for further applications of porous alumina as template for nanomaterial.