Structural engineering of nanoporous anodic alumina funnels with high aspect ratio

Four types of high aspect ratio nanoporous anodic alumina funnels with one, two, three and four segments are fabricated by following sequentially anodizing and pore widening steps. The length of each segment is controlled by the total current charge passed through the system, and the pore diameter is regulated by the pore widening time length. Both the segment length and its diameter are previously established by corresponding calibration processes, which allow design with high degree of accuracy the resulting nanostructures. The geometric characteristics of the fabricated nanostructures are analyzed in detail through environmental scanning electron microscopy. It is demonstrated that the key factor to control the fabrication process of nanoporous anodic alumina funnels with high aspect ratio under controlled potential conditions is the total current charge passed through the anodization system. It is expected that this nanostructures will have multiple potential applications such as arrays of nanotubes or nanowires with various diameter-modulated segments based on multiple materials (e.g. metals, polymers, ceramics, etc.), optoelectronic devices and so forth. (C) 2011 Elsevier B.V. All rights reserved.