A facile approach to the formation of the alumina nanostructures from anodic alumina membranes

Alumina nanostructures with different morphologies (half-nanotubes, nanowires and nanopillars) on the surface of the porous anodic alumina membranes (AAMs) have been fabricated via a simple chemical etching process. We fabricated the novel alumina nanostructures with the half-nanotubes for the first time, and alumina nanowires (ANWs) and nanopillars were also found in our experiment. Porous AAMs, fabricated by two-step anodization method in 0.3 M oxalic acid, were used as the matrix. Then the different nanostructures were fabricated via a simple etching method: dipping in 5 wt.% NaOH solution with different etching time. The SEM image of AAMs shows the array of highly ordered hexagonal pore distribution. The formation mechanism of nanostructures may be that the thickness difference between the triple point and the thin walls results in the formation of the alumina structures. Such new nanostructures may be suitable for two dimensional photonic bandgap structural materials.