Porous Alumina with Shaped Pore Geometries and Complex Pore Architectures Fabricated by Cyclic Anodization**

摘要

The fabrication of three-dimensional (3D) architectures withnanoscale dimensions is still an evolving research area ofnanotechnology. Various methodologies including conven-tional and unconventional fabrications, such as photolitho-graphy, scanning beam lithography, molding, embossing, andimprinting, have been developed in the past decade.r1-21However, the production of 3D structures using thesetechniques is expensive and inherently complex. Electro-chemistry is regarded as a key discipline for nanotechnology,with a view to the development of applications for cost-effective fabrication of nanostructured materials.131 Poroussilicon fabricated by electrochemical etching and porousanodic alumina oxide (AAO) fabricated by anodization aretwo particularly well-known examples.[4.51 Due to theirsimplicity, inexpensive electrochemical fabrication, andattractive properties, they are the most widely used nanoma-terials for numerous nanotechnological applications.16.71 Thestructure of AAO is, ideally, a hexagonally packed array ofself-organized and vertically aligned columnar cells, eachcontaining a central pore with a diameter ranging from 10 to400 nm.18-1°1 In recent years, AAO has attracted considerableinterest for applications in template synthesis, molecularfiltration, catalysis, sensing, electronics, photonics, energystorage, and drug delivery.r11-151 In particular, its applicationas a nanotemplate has been widely explored for the fabricationof nanostructures including nanoparticles, nanowires, nano-tubes, nanorings, and nanocones.[16-21] Three well-studiedgrowth regimes using conventional, so-called mild (or low-field) anodization (MA) in H2SO4, H2C204, and H3PO4 areaccepted as the optimal conditions for fabrication of AAOwith highly ordered pore structures.122-251 To solve theproblem of very slow anodization by MA (1-2 h-1), anew method called hard (or high-field) anodization (HA) hasrecently been introduced to considerably speed up the process(50-100