Freestanding, highly flexible, large area, nanoporous alumina membranes with complete through-hole pore morphology

Electrochemical anodic oxidation of aluminium metal sheets leads to the formation of compact and dense, but highly porous alumina surfaces on top of the anode. The alumina surfaces obtained by anodic oxidation can be detached from the bare metal by using a voltage detachment procedure, without employing chemical etching techniques. This procedure leads to large area porous alumina membranes with closed backsides. Prestructuring of the aluminium base metal leads to ordered pore regions at anodisation voltages of 25, 40 and 50 V, resulting in porous alumina membranes with pore diameters of 33, 40 and 72 nm. The careful opening of the backside alumina membranes can be realised by acid treatment leading to highly flexible large area porous alumina membranes with complete through-hole pore morphology. The backside pore-opening process realised by chemical etching is strongly dependent on time and acid concentration and is best monitored routinely by microscopy techniques in order to gain control over the process. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).