title: Anodization of nanoporous alumina on impurity-induced hemisphere curved surface of aluminum at room temperature.
abstract: Nanoporous alumina which was produced by a conventional direct current anodization [DCA] process at low temperatures has received much attention in various applications such as nanomaterial synthesis, sensors, and photonics. In this article, we employed a newly developed hybrid pulse anodization [HPA] method to fabricate the nanoporous alumina on a flat and curved surface of an aluminum [Al] foil at room temperature [RT]. We fabricate the nanopores to grow on a hemisphere curved surface and characterize their behavior along the normal vectors of the hemisphere curve. In a conventional DCA approach, the structures of branched nanopores were grown on a photolithography-and-etched low-curvature curved surface with large interpore distances. However, a high-curvature hemisphere curved surface can be obtained by the HPA technique. Such a curved surface by HPA is intrinsically induced by the high-resistivity impurities in the aluminum foil and leads to branching and bending of nanopore growth via the electric field mechanism rather than the interpore distance in conventional approaches. It is noted that by the HPA technique, the Joule heat during the RT process has been significantly suppressed globally on the material, and nanopores have been grown along the normal vectors of a hemisphere curve. The curvature is much larger than that in other literatures due to different fabrication methods. In theory, the number of nanopores on the hemisphere surface is two times of the conventional flat plane, which is potentially useful for photocatalyst or other applications.PACS: 81.05.Rm; 81.07.-b; 82.45.Cc.
authors.affiliation: Department of Mechanical Engineering, Center for Micro/Nano Science and Technology, and Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan, Taiwan 701, Republic of China. ckchung@mail.ncku.edu.tw.
authors.forename: Chen-Kuei
authors.initials: CK
authors.lastname: Chung
authors.forename: Ming-Wei
authors.initials: MW
authors.lastname: Liao
authors.forename: Chun-Te
authors.initials: CT
authors.lastname: Lee
authors.forename: Hao-Chin
authors.initials: HC
authors.lastname: Chang
references.citation: Science. 1995 Jun 9;268(5216):1466-8
references.pmid: 17843666
references.citation: Nat Nanotechnol. 2008 Apr;3(4):234-9
references.pmid: 18654508
references.citation: Nanotechnology. 2009 Feb 4;20(5):055301
references.pmid: 19417342
references.citation: Nanotechnology. 2007 Jan 24;18(3):035304
references.pmid: 19636119