Ferroelectric Lead Zirconate Titanate and Barium Titanate Nanoshell Tubes
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Ferroelectric Lead Zirconate Titanate and Barium Titanate Nanoshell Tubes Yun Luo1, Izabela Szafraniak1, Valanoor Nagarajan2, Ralf B. Wehrspohn1, Martin Steinhart1,3, Joachim H. Wendorff3, Nicolai D. Zakharov1, Ramamoorthy Ramesh2 and Marin Alexe1 1 Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120 Halle, Germany 2 University of Maryland, College Park, MD 20742, USA 3 Institute of Physical Chemistry, University of Marburg, Hans-Meerwein-Straße, D-35032 Marburg, Germany ABSTRACT Wetting of the pore walls of porous templates is a simple and convenient method to prepare nanoshell tubes. Wafer-scale fabrication of ferroelectric lead zirconate titanate and barium titanate nanoshell tubes was accomplished by wetting porous silicon templates with polymeric precursors. The ferro- and piezoelectric properties of an individual ferroelectric nanoshell tube either of PZT or of BaTiO3 were electrically characterized by measuring the local piezoelectric hysteresis. A sharp switching at the coercive voltage of about 2 V was shown from the hysteresis loop. The corresponding effective remnant piezoelectric coefficient is about 90 pm/V. We have also prepared highly ordered arrays of free-standing ferroelectric nanoshell tubes obtained by partial etching of the silicon template. Such materials might be used as building blocks of miniaturized devices and could have a significant impact in the field of nano-electromechanical systems. INTRODUCTION One-dimensional systems such as nanotubes or nanorods from various materials have attracted great interest in the last decade, because they exhibit different physical properties than their bulk counterparts. The successful preparation of carbon nanotubes by a simple method [1] along with their bouquet of new effects (e.g. the transistor effect [2]) has generated a completely new research field. Various nanotubes made of such materials as metals or semiconductors were also obtained by methods such as the roll-up of thin films deposited onto a sacrificial layer [3], self-assembly [4-8] or template-mediated fabrication [9-15]. However, the preparation of functionalized nanotubes, e.g., from complex oxide ferroelectrics, still remains a challenge in materials science. The broad range of properties of ferroelectric oxides, such as spontaneous polarization, high dielectric permittivity as well as piezo- and pyroelectricity, make ferroelectric nanotubes an extremely interesting materials class for research as well as for applications. Recently, ferroelectric nanorods with diameters as small as 5 to 60 nm and with lengths of more than 10 µm were obtained by solution-phase decomposition of bimetallic alkoxide precursors in the presence of coordinating ligands [16]. By means of electrostatic force microscopy, ferroelectric switching was shown in a 12 nm diameter rod [17]. Here we report on the wafer-scale fabrication of ferroelectric nanoshell tubes or ordered nanoshell tubes arrays via a simple and convenient method: wetting of porous templates. This approach allows tailoring t
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