Nanoporous alumina fomation using multi-step anodization

초록

Introduction In recent years, highly ordered porous aluminum template is the widely researched material due to the fabrication of nanodevices such as electronic, optoelectronic and micromechanical devices. Many researchers have developed two-types fabrication methods such as anodizing and molding for porous aluminum template and showed final images of nanopores with high density and straight channel. Fabrication of anodic porous alumina consists of formation and dissolution of alumina, e.g. electropolishing, first anodization, alumina dissolution and second anodization. Inspite of their efforts, the mechanism for anodic porous alumina is not well established. In this work, we have investigated formation processes of highly ordered anodic porous alumina through the physical and electrochemical characterization. Experimental Section A high purity aluminum plate (Aldrich 99.999%) was used as support for anodic porous alumina and embedded in a Teflon holder with exposed surface area ca. 1.18cm2. During experiments, the electrolyte was rigorously stirred and has a constant temperature by recirculated system. Fabrication process of anodic porous alumina consists of four stages e.g. electropolishing, first anodization, chemical etching and second anodizing. Prior to the first anodization, aluminum substrate was electropolished in a 4:45:1 volume mixture of HClO4:C2H5OH:H2O at 21V for 4min. Porous alumina was grown by first anodization with 0.3M oxalic acid at 40V for 24h. After that, the porous alumina was removed by chemical etching in a mixture of chromic acid and phosphoric acid at 30~40℃ for 24h. After the removal of the porous film by chemical etching, the periodic concave patterns remain on the aluminum plate. Highly ordered porous alumina by second anodization process was obtained with straight pore array due to the concave patterns on the aluminum substrate.