Understanding and morphology control of pore modulations in nanoporous anodic alumina by discontinuous anodization

Here, we report on an electrochemical approach so-called discontinuous anodization (DA) for controlling the generation of pore modulations in nanoporous anodic alumina (NAA) under self-ordering conditions. In this method, the anodization of aluminium is performed by voltage pulses under mild anodization regime and thermal-acidic conditions. Furthermore, we perform an exhaustive and systematic study about the relationship between the pore modulation morphology and the main anodization parameters (i.e. acid electrolyte temperature and relax time between consecutive voltage pulses). The generation mechanism of the pore modulations is associated with the formation of a gel-like layer under these thermal-acidic conditions and its subsequent detachment during the beginning of each voltage pulse. All this makes it possible to control the pore modulation morphology in NAA at will, what is crucial for developing new nanostructures with accurately controlled geometry for such purposes as nanofluidics, magnetic nanostructures, optical biosensors, templates, selective molecular separators and so forth. A three-dimensional network based on NAA with controlled geometry: The DA by voltage pulses under hydrothermal conditions yields an accurate control over the pore modulation morphology. Therefore, the structure of the resulting 3D-NAA network can be designed at will for later applications. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim