Effect of inter-electrode separation in the fabrication of nanoporous alumina by anodization

The effect of the separation between electrodes on the main output parameters of the anodic aluminum oxide structure, namely the pore size, the cell size, the thickness and the regularity ratio was investigated. Pure aluminum foils were anodized in 0.3 M oxalic acid at different combinations of electrode separations (1.5, 3 and 6 cm), anodization voltages (30, 45 and 60 V) and temperatures (10, 20 and 30 °C). Whereas cell size and thickness appeared to be independent on the electrode separation, minor effects emerged for the pore size and significant effects emerged for the regularity ratio. The latter decreased with electrode separation at the lowest anodization voltage, but increased for the other voltages, especially at intermediate value of 45 V. For the temperature series, the regularity ratio decreased with separation at highest and, mostly, lowest temperature, while increased at intermediate temperature. Therefore, in addition to the major fabrication parameters of anodization voltage, current density, temperature and electrolyte concentration, it appears that the electrode separation may also cause relevant effects on the pattern quality, which should be taken into account for careful control of this nanofabrication process.