Titanium oxide nanotube arrays prepared by anodic oxidation
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Titanium oxide nanotube arrays prepared by anodic oxidation Dawei Gong, Craig A. Grimes,a) and Oomman K. Varghese Department of Electrical Engineering and Materials Research Institute, 208 Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802
Wenchong Hu, R.S. Singh, and Zhi Chen Departments of Material Science and Engineering, and Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802
Elizabeth C. Dickey Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received 11 May 2001; accepted 12 September 2001)
Titanium oxide nanotubes were fabricated by anodic oxidation of a pure titanium sheet in an aqueous solution containing 0.5 to 3.5 wt% hydrofluoric acid. These tubes are well aligned and organized into high-density uniform arrays. While the tops of the tubes are open, the bottoms of the tubes are closed, forming a barrier layer structure similar to that of porous alumina. The average tube diameter, ranging in size from 25 to 65 nm, was found to increase with increasing anodizing voltage, while the length of the tube was found independent of anodization time. A possible growth mechanism is presented.
Titanium oxide is a useful catalytic1 and gas-sensing2 material. Titanium oxide thin films with nanoporous structures are desirable for these applications due to their large surface areas and high reactivities. Nanoporous titanium oxide films have been fabricated by anodizing titanium sheets in hydrofluoric acid containing solutions.3,4 The anodizing approach is able to build a porous titanium oxide film of controllable pore size, good uniformity, and conformability over large areas at low cost.5 Moreover, as dependent upon the titanium alloy used, metal impurities can be readily introduced. Despite these advantages, there is a dearth of literature on anodization of titanium and titanium-based alloys. Our work is aimed toward better understanding of the anodizing mechanism, as well as the fabrication of new nanodimensional structures for possible application in catalytic, biotemplating,6,7 gas-sensing8 and electronic applications. In this work, we examine the morphology of porous titanium oxide thin films fabricated by anodizing pure titanium sheets under variable conditions. It has been found that the anodized titanium films have more complicated morphologies than anodized aluminum.9 In a)
e-mail: [email protected] J. Mater. Res., Vol. 16, No. 12, Dec 2001
addition to porous films, such as those reported earlier,3 well-aligned nanotubelike structures composed of titanium oxide were obtained. In contrast to the continuous pore structures achieved with aluminum anodization, discrete titanium oxide nanotubes are found to grow from the discontinuous nanoporous titanium oxide film. The high-purity (99.99%) titanium foils used in this work were obtained from Alfa Aesar (Ward Hill, MA).10 All anodization experiments were conducted at room temperature (18 °C) wit
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