Model for porous alumina template formation

Anodized alumina templates have emerged as an important material system for the low cost fabrication of semiconductor and metal nanostructure arrays. This material system utilizes natural self-organization for the creation of periodic arrays of nanoscale structures. The underlying principle is that when aluminum is anodized in a suitable acidic electrolyte under controlled conditions, it oxidizes to form a hydrated aluminum oxide (alumina) containing a two dimensional hexagonal array of cylindrical pores. Due to the excellent periodicity of the pores, and the ability to control the pore diameters, such anodized alumina films can be used as templates for the fabrication of periodic arrays of nanostructures. A process-model based on underlying physics and chemistry of the anodization process is developed. The model developed unravels the interplay of various physical and chemical processes and their dependence on the process parameters such as the electrolyte, temperature, current and voltages and yields, an analytical solution relating the voltage (in constant current anodization) and current (in constant voltage anodization) to time. The predicted time behavior agrees fairly well with experimental observations for sulfuric and oxalic acids. Thus, it is believed that the model is general enough and can be used for any anodization system with changes in appropriate model parameters.