Alumina Nanohoneycombs with Controlled Spatial Ordering of Pore Channels – Fabrication, Theory and Mechanical Properties

Abstract

Large-area nano-porous anodized aluminium oxide (AAO) films with well-controlled pore ordering are highly desirable for making nano-technological devices with consistent performance. We discovered that by carefully conditioning the orientation of the aluminium substrate, the ordering of the AAO pores over mm2-to-cm2 areas can be controlled. AAO films grown on large [001]-oriented aluminium grains in oxalic acid exhibit ideal close-packing typically up to the 10th nearest neighbours, whereas those grown on [101] grains do not show any resemblance to close packing. Computer simulation of the anodization process suggests that the competition between the oxidation and ionization reactions at the metal-oxide interface may be an important factor for the substrate-orientation dependence of the pore ordering. Nanoindentation and micro-pillar compression experiments on such AAO structures revealed that their strength and deformation depend significantly on the pore ordering of the structure. Moreover, deformation in general occurs in a jerky manner, with cascading collapse of layers of the porous structure. This is the first successful method to control the pore ordering of AAO of unprecedented large areas and to assess their mechanical behaviour. This method enables systematic and industrial-scale exploitation of the AAO properties versus pore ordering.