Local piezoelectric and ferroelectric responses in nanotube-patterned thin films of BaTiO 3 synthesized hydrothermally a
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Nitin P. Padtureb),c) Department of Materials Science and Engineering, The Ohio State University, Columbus, Ohio 43210 (Received 12 October 2005; accepted 2 December 2005)
Piezoresponse atomic-force microscopy (PFM) has been used to characterize the local piezoelectric properties of a novel, nanotube-patterned (“honeycomb”) thin film of BaTiO3 on Ti substrate synthesized hydrothermally at 200 °C. PFM amplitude and phase images, prior to the application of any direct current (dc) field, show ring-shaped piezoelectric regions that correspond to the nanostructure of this film. These results show clearly that the as-synthesized nanotube-patterned BaTiO3 thin film is piezoelectric, with a net spontaneous polarization perpendicular to the film–substrate interface. In addition, polarization switching and hysteresis were observed as a function of applied dc field, confirming that this novel fabrication procedure results in unique configurations of BaTiO3 film that are also ferroelectric.
There has been growing interest in piezoelectric nanostructures (nanorods, nanowires, nanotubes, patterned thin films), which are promising candidates for use in miniaturized devices such as sensors, actuators, capacitors, and microelectromechanical systems (MEMS).1–4 There is also growing interest in fundamental studies of these nanostructures because they exhibit size-dependent piezoelectric behavior4–6 and enhanced ferroelectric and piezoelectric properties in cases such as nanopatterned thin films.7 Because of the small sizes and intricate geometries of these nanostructures, piezoresponse atomic force microscopy (PFM) has been shown to be a powerful, and sometimes indispensable, tool for measuring piezoelectric properties of these nanostructures.4,7–12 Recently, we have used a low-temperature (200 °C), 2-step anodization-hydrothermal method to synthesize novel, nanotube-patterned (“honeycomb”) thin films of BaxSr(1−x)TiO3 on Ti substrates.13,14 Figure 1(a) is a scanning electron microscope (SEM) plan-view image
a)
Present address: Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210. b) Address all correspondence to this author. e-mail: [email protected] c) 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.2006.0069 J. Mater. Res., Vol. 21, No. 3, Mar 2006
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of one such BaTiO3 film showing the honeycomb structure. 13 Figures 1(b) and 1(c) are transmission electron microscope (TEM) bright-field images showing plan and cross-sectional views, respectively, of a similar Ba0.66Sr0.44TiO3 film.14 The inner diameter of the nanotubes ranges from 70 to 100 nm, and their height ranges from 200 to 300 nm (film thickness). Although the nanotube structures are polycrystalline, the nanograins within a certain region (∼1 m2), which encompasses several tens of na
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