Formation and microstructures of unique nanoporous AAO films fabricated by high voltage anodization

Abstract

Nanoporous anodic aluminium oxide (AAO) films with a large-range tunable interpore distance (D_int) and unique microstructures have been fabricated by high voltage anodization (140–400 V) in 0.3 M oxalic acid electrolyte. The influences of anodization conditions (e.g., anodization voltage (U_a) and current density (i_a)) on the microstructures of AAO films have been investigated in detail. Experimental results show that there is a linear relationship between U_a and D_int under relatively low U_a. With the increase of U_a, the influences of i_a and dehydration of aluminium hydroxide on the D_int may not be ignored, thus resulting in a nonlinear relationship between U_a and D_int. When the anodization is performed at an excessively high U_a of 400 V, an interesting competitive growth of nanochannels inside the AAO film tends to occur, thus forming an AAO film with unique nano/micro morphology at the barrier layer side.