Lead titanate nano- and microtubes
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Jian Yu Materials and Structures Laboratory, Tokyo Institute of Technology, Midori-ku, Yokohama 226-8503, Japan
Ulrich Gösele Max-Planck-Institute of Microstructure Physics, Weinberg 2, 06120 Halle/S, Germany (Received 24 June 2005; accepted 30 November 2005)
Lead titanate (PbTiO3) nano- and microtubes were fabricated by wetting ordered porous alumina and macroporous silicon with precursor oligomers coupled with templated thermolysis. The diameters of the PbTiO3 tubes range from a few tens of nanometers up to one micron. The proper selection of the template allowed for a precise adjustment of their size over two orders of magnitude. Electron microscopy and x-ray diffraction revealed that the tube walls were polycrystalline. The generic approach presented here can be adapted for the fabrication of tubes and rods from a multitude of functional inorganic oxides.
I. INTRODUCTION
Ferroelectric oxides are used for dynamic random access memories, non-volatile memories, electro-optic switches, pyroelectric detectors, waveguides, and optical memory devices.1 Because of their excellent piezoelectricity, nano- and microstructures consisting of these materials are promising building blocks for nanoand microelectronics, sensor technology, and actuators. In particular, one-dimensional (1D) objects such as tubes may play a key role as components of microelectromechanical systems (MEMS). Because the feature size of ferroelectric MEMS is currently approaching sub-micron dimensions, their local properties may deviate from those of the bulk materials because of confinement effects and surface inhomogeneities. A deeper understanding of these phenomena is a prerequisite for the development of miniaturized electronic devices. Much effort has been devoted to the fabrication of highquality ferroelectric nanostructures to understand how the size effects influence their ferroelectric behavior.2,3 Template-based methods provide a straightforward access to 1D nano- and microstructures.4–9 This simple and versatile approach to ordered arrays of tubes or rods with sharp diameter distribution has been studied intensely. Examples include PbZrxTi1−xO3 and BaTiO3 nanorods,10 LiNbO3,11,12 Sr0.8Bi2.2Ta2O9+y,13 PbTiO3,14,15 PbZrxTi1−xO3 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0078 J. Mater. Res., Vol. 21, No. 3, Mar 2006
and BaTiO3 tubes,16,17 as well as BaTiO3 and SrTiO3 nanowires.18,19 In this paper, we report on the fabrication of PbTiO3 nano- and microtubes with adjustable diameter by wetting self-ordered porous alumina20–23 and macroporous silicon templates24,25 with precursor oligomers, followed by a templated thermolysis. The currently accessible pore diameters Dp of porous alumina range from 25 to 400 nm, those of macroporous silicon from 370 nm up to a few microns. Both template systems contain highly ordered arrays of straight pores with sharp diameter distribution and uniform depth. Their pore walls have a high surface energy,26 as required to conduct the wetting (Si is covered by
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