Preparation and formation mechanism of alumina nanowires

Abstract

The highly ordered anodic aluminum oxide (AAO) film, was prepared with electrochemical anodization method. The as-synthesized AAO film was amorphous as seen from XRD result. Amorphous alumina nanowires were successfully and easily obtained with high yield by etching AAO films in a mixture of H 3PO4 and H2CrO4, NaOH, HCl, or H3PO4 solutions. The AAO film annealed at 800°C for 4 h turned to γ-Al2O3. γ-Al2O 3 alumina nanowires were also obtained with high yield by etching γ-Al2O3 AAO film. Effects of the type of etching solutions, the etching time and the crystalline structure of AAO film on the preparation of alumina nanowire were carefully investigated. And the morphology and structure of alumina nanowires were studied by SEM, TEM and XRD. The results showed that in many kinds of solutions the alumina nanowire could be fabricated by etching method. The length (L) of the nanowire would increase and the diameter (D) would decrease when the etching time became longer, but the ratio of L /D would increase. The crystalline structure of the alumina nanowire was in accordance with that of the AAO film. Furthermore, the morphology of the AAO film was characterized by atomic force microscope (AFM) and SEM in detail. On the basis of AFM and SEM observations, a possible formation mechanism of the alumina nanowire was discussed, and the plum bloom-shape microstructure of the AAO film was considered to be the essential factor deciding the formation of the alumina nanowire.