Nanotubes patterned thin films of barium-strontium titanate
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A novel, low-temperature synthesis method for producing BaxSr(1−x)TiO3 (BST) thin films patterned in the form of nanotubes (“honeycomb”) on Ti substrates is reported. In this two-step method, the Ti substrate is first anodized to produce a surface layer (∼300 nm thickness) of amorphous titanium oxide nanotube (∼100 nm diameter) arrays. In the second step, the anodized substrate is subjected to hydrothermal treatment in aqueous Ba(OH)2 + Sr(OH)2 at 200 °C, where the nanotube arrays serve as templates for their topotactic (shape-preserving) hydrothermal conversion to polycrystalline BST nanotubes. A simple geometrical model is proposed to elucidate the mechanism of the hydrothermal growth of BST nanotubes. This opens the possibility of tailoring the titanium oxide nanotube arrays and of using various precursor solutions and their combinations in the hydrothermal bath to produce ordered, patterned thin-film structures of various Ti-containing ceramics. These could find use not only in a variety of electronic, optoelectronic, and sensor device applications but also in biomedical and catalysis applications, where patterned thin films are desirable. I. INTRODUCTION
Device applications such as memory cells, capacitors, sensors, actuators, and microelectromechanical systems (MEMS) require patterned electroceramic thin films.1–5 Furthermore, some types of patterned electroceramic thin films (e.g., ferroelectric) have improved electrical properties over their continuous counterparts, primarily because patterning relaxes the substrate-induced in-plane constraint.4,6,7 Modern patterning methods such as photolithography,8 focused ion beam,7,9,10 self-assembled monolayers,11,12 or channel stamping13 have been used in conjunction with high-temperature deposition methods (vapor-phase or sol-gel)1,2 to create patterned electroceramics thin films. However, there is a need for lowcost methods that can produce patterned thin films over large areas at low temperatures. In this context, we demonstrated recently that the hydrothermal method can be combined with the selforganized patterning method of anodization to create, on Ti metal substrates, nanotube-patterned thin films of
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Address all correspondence to this author. e-mail: [email protected] Present address: Department of Materials Science and Engineering, Ohio State University, Columbus, OH 43210-1178. This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs .org/publications/jmr/policy.html. DOI: 10.1557/JMR.2005.0264 2140
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J. Mater. Res., Vol. 20, No. 8, Aug 2005 Downloaded: 03 May 2015
BaTiO3 (BT) at 200 °C.14 In the present study, we have created nanotube-patterned thin films of BaxSr(1−x)TiO3 solid-solutions or barium-strontium titanate (BST), a widely used thin-film electroceramic. Furthermore, we present the detailed structure of the BST nanotubes using transmission electron microscopy (TEM), supporting th
