Fabrication of porous anodic aluminum oxide by hybrid pulse anodization at relatively high potential

Anodic aluminum oxide (AAO) containing high-aspect ratio pore channels has been widely used as a template for fabricating nanowires or other 1D nanostructures. For AAO prepared in oxalic acid, the anodizing potential is set as 40 V in order to balance the oxidation and dissolution rates. In practice, a higher potential is beneficial in increasing the pore size. However, a higher potential increases the local electrolyte temperature and therefore damages the pore structure. In this article, this problem is resolved by means of a high-potential hybrid pulse anodization (HPA) technique, in which a period of small negative potential is applied to suppress the Joule heating effect during the AAO preparation process. The scanning electron microscope results showed that HPA with an anodizing potential of 60 V resulted in an intact pore structure on the AAO surface. By contrast, the AAO formed using conventional direct current anodization with the same anodizing potential contained many small irregular pores around each original pore. The present results suggest that HPA has significant potential for the fabrication of high-quality nanowires with various diameters for such applications as magnetic recording, super capacitors or field emission devices.