Ferroelectric Micro- and Nanotubes


Tubes of ferroelectric materials

PZT/BTO tubes


Y. Luo, M. Steinhart, R. Ramesh and M. Alexe


Nanotubes exhibiting ferroelectric or piezoelectric behavior are promising components for nano-electromechanical systems (NEMS) since they can act as nano-actuators. We have demonstrated the ferroelectric switching of lead zirconate titanate (PZT, PbZr0.52Ti0.48O3) and barium titanate (BaTiO3) nanotubes by atomic force microscopy in the piezoresponse mode (Y. Luo, I. Szafraniak, V. Nagarjan, R. B. Wehrspohn, M. Steinhart, J. H. Wendorff, N. D. Zakharov, R. Ramesh, M. Alexe, Applied Physics Letters 2003, 83, 440). We obtained a rectangular ferroelectric hysteresis loop of an individual PZT nanotube showing a sharp switching at the coercive voltage of about 2 V. The effective remnant piezoelectric coefficient was about 90 pm/V (Fig. 1).


Fig.1. Ferroelectric hysteresis loop of an individual PZT nanotube


The BaTiO3 and PZT nanotubes were fabricated by wetting of ordered porous templates, such as porous alumina or macroporous silicon, by polymeric precursors. Ferroelectric nanotubes consisting of the perovskite phase were obtained by pyrolysis and annealing. They were straight, smooth and had a very high aspect ratio of about 50 (Fig 2). Depending on the templates, their outer diameter ranges from 50 nm up to several micrometers and their length up to more than 100 microns. Extended ordered arrays of aligned free-standing ferroelectric tubes are accessible by selective etching of the template. Composite systems consisting of ferroelectric oxides and metals can be obtained by consecutive wetting steps.


Fig. 2. Scanning electron micrographs of ferroelectric nanotubes.

A bundle of BaTiO3 nanotubes

Arrays of PZT nanotubes attached to a silicon wafer


We propose several applications based on the piezoelectric properties of the ferroelectric nanotubes (Fig. 3): piezoelectric scanner (a), mass storage device (b) and tunable photonic crystal (c), as shown in the picture below. (M. Alexe, Y. Luo, I. Szafraniak, R. B. Wehrspohn, and M. Steinhart, European Patent Application No. 03000969.0/2002).


Fig 3. Potential applications of ferroelectric nanotubes. (a) piezoelectric scanner,(b) mass storage device (c) and tunable photonic crystal.

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