Porous Anodic Aluminum Oxide: Anodization and Templated Synthesis of Functional Nanostructures

Many desirable engineering properties such as excellent hardness, corrosion, and abrasion resistance can be obtained by anodizing aluminum metals in acid electrolytes. In addition, due to its high porosity, the porous oxide films formed on the metals serve as a good adhesion base for electroplating, painting, and semi-permanent decorative coloration. Porous AAO film grown on aluminum is composed of a thin barrier oxide layer in conformal contact with aluminum, and an overlying, relatively thick, porous oxide film containing mutually parallel nanopores extending from the barrier oxide layer to the film surface. Each cylindrical nanopore and its surrounding oxide region constitute a hexagonal cell aligned normal to the metal surface. Under specific electrochemical conditions, the oxide cells self-organize into hexagonal close-packed arrangement, forming a honeycomb-like structure.