Synthesis of Arrayed, TiO 2 Needlelike Nanostructures via a Polystyrene-block-poly(4-vinylpyridine) Diblock Copolymer Template Chin-Cheng Weng, Kuo-Feng Hsu, and Kung-Hwa Wei* Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan 30049, Republic of China Received April 19, 2004. Revised Manuscript Received August 10, 2004 Arrayed, needlelike nanostructures of rutile phase crystal TiO 2 were grown on a Si substrate containing TiO 2 seeds prepared through a thin polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymer template. The morphology of the deposited TiO 2 nanostruc- tures was characterized by field-emission scanning electron microscopy, X-ray diffraction, and transmission electron microscopy (TEM). By using TiO 2 seeds prepared from their diblock copolymer PS-b-P4VP template, we fabricated arrayed, needlelike rutile TiO 2 nanostructures with variable spatial positions and densities. The distance between two TiO 2 needle bunches (120 and 160 nm) could be controlled using block copolymer templates with different molecular weights. Introduction Titanium dioxide (TiO 2 ) is a highly versatile material, because of the optical and catalytic properties exhibited by its two common crystal forms: rutile and anatase. The rutile phase of TiO 2 has a high refractive index and is useful for optical devices, such as waveguides. 1 The photocatalytic activity of the anatase phase of TiO 2 is widely applied in many fields, such as microorganism photolysis, 2 medical treatment, 3 environmental purifica- tion, 4 and photovoltaic cells. 5,6 More recently, ordered nanostructures have been prepared using templating techniques. For example, ordered TiO 2 nanotubes were synthesized using porous anodic alumina as tem- plates via a sol-gel process. 7-12 TiO 2 nanowire arrays have also been synthesized using an electrochemical method. 13 On the other hand, the fabrication of periodically ordered two-dimensional nanostructures on the scale of tens to hundreds of nanometers is critically important as electronic, optical, and magnetic devices are continu- ally miniaturized. Attempts have been taken to arrange nanomaterials, such as semiconductor nanocrystals, as well as metal and metal oxide nanoparticles, into ordered structures for device applications. 14-17 A diblock copolymer chain consists of two chemically dissimilar blocks attached through a covalent bond. 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Mater. 2004, 16, 4080-4086 10.1021/cm049367j CCC: $27.50 © 2004 American Chemical Society Published on Web 09/25/2004