Effects of applied voltage on barrier oxide layer in porous AAO fabrication

Anodic aluminum oxide (AAO) with self-aligned nano-pores has fascinated researchers because of its potential application as an excellent template for nanotechnology. However the process to obtain long-range ordered pore structure is somewhat complicated, which hinders the full utilization of AAO. To make well-aligned porous AAO by hard anodizing (HA, ≫100V), one has to study more closely the controlling parameters of the barrier oxide layer thickness. On the basis of experimental results, a model for relation between external voltage and barrier layer thickness is suggested. The model has been derived through 3 steps. (1)The oxide growth rate is acquired from the oxidation current density combined with the ‘high field conduction’ model and the Faraday's law. (2)Equation for dissolution rate of oxide is calculated from the Joule heating effect and heat of formation of Al2O3. (3)The relation between the barrier layer thickness and the voltage at the steady state is obtained by equating the growth and the dissolution rate of porous anodic oxide film. Finally, experimental results are fitted to the model and interpretation of various parameters in the model is given.