Fabrication of Special-Type Nanoporous Anodic Alumina Templates

Porous anodic alumina (FAA) templates have been used widely and studied extensively due to their excellent mechanical and thermal stabilities, highly-ordered hexagonal nanochannel-array architecture and controllable pore structures. In recent years, significant progress has been made in the field of PAA synthesis and a variety of special type PAA templates have been prepared by precisely adjusting the anodizing conditions. By means of the special templates, many novel functional nanomaterials have been synthesized successfully via physical or chemical processing routes. After a brief introduction to the fabrication methods of conventional PAA templates, this paper presents a comprehensive review on the fabrication approaches of FAA templates with special nanopore arrays (e. g., branched, serrated, bone-shaped or inverted cone nanopores); diamond, triangle or square pore patterns; modulated pore structures with different diameters, lengths, geometries, and periodicity. Several critical factors including the applied electric field, temperature, type and concentration of the electrolyte which determine the pore modulation of FAA are emphasized. Finally, the development trend and future prospects of the special templates are given.