Wetting Pattern on TiO 2 Nanostructure Films and its Application as a Template for Selective Materials Growth
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Wetting Pattern on TiO2 Nanostructure Films and its Application as a Template for Selective Materials Growth Y. K. Lai1,2, Y. Yang2, Y. X. Huang2, Z. Q. Lin2, Y. X. Tang1, D. G. Gong1, C. J. Lin2 and Z. Chen1 1 School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore. 2 State Key Laboratory of Physical Chemistry of Solid Surfaces, and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China. [email protected]; [email protected] ABSTRACT The present paper describes an unconventional approach to fabricate superhydrophilicsuperhydrophobic template on the TiO2 nanotube structured film by a combination of electrochemical anodization and photocatalytic lithography. Based on template with extreme wetting contrast, various functional nanostructures micropattern with high resolution have been successfully fabricated. The resultant micropattern has been characterized with scanning electron microscopy, optical microscopy, X-ray photoelectron spectroscopy. It is shown that functional nanostructures can be selectively grown at superhydrophilic areas which are confined by the hydrophobic regions, indicating that the combined process of electrochemically self-assembly and photocatalytic lithography is a very promising approach for constructing well-defined templates for various functional materials growth. INTRODUCTION Wettability is an important property governed by not only chemical composition, but also geometrical structure as well [1-3]. Two extremely cases, superhydrophobicity with a water contact angle (CA) above 150° and superhydrophilicity with CA below 5°, have attracted much interest due to their importance in both theoretical research and practical application [4-7]. Micropatterns with different physical or chemical properties have frequently been acted as microtemplates for fabricating various functional materials. Micropatterns can be formed by printing self-assembled monolayers (SAMs) using soft lithography [8], or by decomposing SAMs through electron beams [9], photocatalytic lithography [10], atomic force microscopy [11] and so on. Among these methods, photocatalytic lithography is one of the most practical techniques because it able to accurately transfer an entire photomask pattern to a sample substrate at a single exposure time. Till now, only a few reports on the fabrication of superhydrophilic-superhydrophobic micropatterns have been reported [12-14]. Upon UV irradiation, the electron-hole pairs in TiO2 can be generated and migrated to its surface, where the hole reacts with OH- or adsorbed water to produce highly reactive hydroxyl radicals [15,16]. These hydroxyl radicals can further oxidize and decompose most organic compounds. Recently, we found that the pollutant solution can be rapidly decomposed on a nanotube array TiO2 film with UV irradiation [17,18]. Considering its effectiveness for the photocatalytic decomposition of organic compounds, the photocatalysis of such TiO2 nanotube film can be a promising way to decompose the
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