Formation mechanism of alumina nanotubes and nanowires from highly ordered porous anodic alumina template

Alumina nanotube (ANT) and nanowire (ANW) arrays were produced from highly ordered porous anodic alumina (PAA) by etching in phosphoric acid and subsequent thermal treatment. The domain structures that have small sizes provide more boundaries and break the hexagonal symmetry of the PAA template, thereby inducing star-like splitting modes. Using very thin PAA films, ANTs and their arrays are fabricated, whereas ANWs and their arrays are produced when using thick films. This is due to the thin wall between nanopores. Our results provide some mechanistic and fundamental information pertaining to the fabrication of nanostructures via a PAA template.