Fabrication of Micrometer-Scale Self-Organized Pore Arrays in Anodic Alumina

We demonstrate the fabrication of self-organized ordered porous anodic alumina (PAA) with pore spacing in the micrometer range using a solution of citric acid. More specifically, we have fabricated PAA samples with regular pore spacings of 970 nm, 1070 nm, 1260 nm and 1420 nm, respectively. While pore spacing is expected to be proportional to the anodization voltage, the proportionality factor observed here (1.94 nm/V) is slightly lower than that reported in the literature (similar to 2.5 nm/V). These results were obtained following a careful characterization of the burning voltages of aluminum for various concentrations of citric acid. Voltage limits of 300 V, 370 V and 425 V for concentrations of 4%, 2% and 0,5%, respectively, have been established. We also established that the maximum anodization voltage in pure citric acid at very low concentration (0.05%) is in the range of 540 V. Beyond this voltage, breakdown of the alumina barrier occurs. We discuss the phenomenon of aluminum burning, which occurs when anodizing at voltages too high for a given acid concentration. We also show that high voltage anodization produces less compact PAA than lower voltage ones, and that it is increasingly difficult to obtain a thick PAA as the anodization voltage increases. (C) 2014 The Electrochemical Society. All rights reserved.