The Effect of Duration of First and Second Anodization Steps on the Ordering of Nanopores in Anodic Aluminum Oxide Templates Achieved by Three Step Anodic Oxidation Process

Nano-porous templates have a variety of potential applications for fabrication of nano-scale materials [1].Among frequently used templates, Anodic aluminum oxide (AAO) has attracted considerable interest as a nanofabrication template, due mainly to the self-organized formation of extremely well-aligned cylindrical pores introduced by Masuda Fukuda in 1995 [2]. On the other hand, in AAO membranes the interpore distance, pore diameter and channel length can be controlled by tuning anodization parameters such as voltage, electrolyte solution composition, temperature and anodization time. Porous AAO structures aretypically obtained by anodizing of aluminum metal in solutions of sulfuric, oxalic, or phosphoric acid. Aluminum anodizing has been shown to be an easy and inexpensive way of template fabrication. Moreover, it is scalable in both feature sizes (diameter, length and period) and field size [3]. The typical construction of an ideal AAO film consists of a thin non-porous barrier oxide layer which lies adjacent to the substrate and a porous layer on the top. The later contains an array of hexagonally close-packed cylindrical cells at the center of which a straight hole is located. Formation of the porous structure results from the effect of a dynamic mechanical equilibrium between the film growth at the aluminum–oxide interface and the fieldassisted oxide dissolution at the oxide–electrolyte interface [4, 5]. The self-organized arrangement of neighboring pores in hexagonal arrays can be explained by any repulsive interaction between the neighboring pores, which is a result of volume expansion during formation of oxide layer [6].Most of the previous researchers were focused on two step anodic oxidation, in order to obtain highly ordered AAOtemplates [1-6]. In this paper we aim to demonstrate the effect of three-step anodizing of aluminum and how qualitatively it can affect the ordering of the nanopores in AAO template. Furthermore, the influence of duration of first and second steps on the ordering of nanopores was investigated