Highly self-assembled nanotubular aluminum oxide by hard anodization

Anodized aluminum oxide (AAO), well-known hexagonally ordered vertical pore nanostructure, can be altered to form nanotubular AAO arrays potentially having many favorable properties due to its large surface area and unique geometry. We present here a creation of novel nanotubular AAO structure by the hard anodization technique. Because of the guided formation of void channels at triple cell junctions during the course of the controlled anodization process, periodically spaced-apart aluminum oxide nanotubular geometry could be achieved over large areas. Further separation to well-defined individual AAO nanotube arrays was obtained when etched in a mixed CuCl₂/HCl solution during Al substrate removal. Nanotubular geometry AAO with periodic and mechanically robust structure can be useful not only for biomedical applications such as to enhance cell adhesion and viability or drug delivery vehicles, but also as a large-surface-area catalyst support or sensor elements.