Crystalline Orientation of PbTiO 3 Nanorods Grown by MOCVD Using ZnO Nanorods as a Template

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Crystalline Orientation of PbTiO3 Nanorods Grown by MOCVD Using ZnO Nanorods as a Template Hironori Fujisawa1, Masaru Shimizu1, Ryohei Kuri1, Seiji Nakashima1, Yasutoshi Kotaka2 and Koichiro Honda2 1 Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2201, Japan 2 Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0197, Japan ABSTRACT ¯ PbTiO3-covered ZnO nanorods were grown on Al2O3(1120) by metalorganic chemical vapor deposition (MOCVD), and their crystalline orientation was investigated by x-ray diffraction (XRD). Structural analysis by scanning electron microscopy and XRD revealed that ¯ facets. XRD analysis of PbTiO3 thin films on the hexagonal ZnO nanorods had {1010}-side ¯ ¯ ¯ ZnO(1010)/Al 2O3(1010) revealed that PbTiO3 was epitaxially grown on ZnO(1010), showing 6 variants of crystallites with the c-axis tilted either 27o or 69o from the surface normal to the ¯ ZnO(1010) plane. Effective piezoelectric coefficients calculated for the 27o and 69o-crystallites using piezoresponse force microscopy confirm that deformation of nanorods and nanotubes contributed to the large electrically-induced strain along the radial direction.

INTRODUCTION One-dimensional nanorods, nanowires, and nanotubes have recently attracted significant attention from the viewpoint of practical applications as well as for studying the basic physics of ferroelectrics. One-dimensional ferroelectrics with high aspect ratios have potential for practical applications in nanogenerators [1,2], ferroelectric capacitors for use in ferroelectric random access memories (FeRAMs) [3,4], and vertical surrounding gate ferroelectric transistors, in combination with low-dimensional semiconductors. To date, ferroelectric nanorods and nanotubes have been synthesized by solution-based processes with negative templates (e.g., porous Si and Al2O3) [1,5-10] and by vapor phase deposition with positive templates (e.g., Si nanowires, ZnO nanorods, and carbon nanotubes) [3,4,11-13]. For future device applications, a vapor deposition technique is appropriate for the growth of ferroelectric nanowires and nanotubes on a substrate, because it will enable mass production and in addition is compatible with practical semiconductor processes. However, there have been only a few reports on the growth of one-dimensional ferroelectrics by vapor deposition methods using a positive template [3,4,11-13]. For example, Alexe et al. reported the fabrication and electrical characterization of ferroelectric and metal-ferroelectric-metal composite nanotubes using Si and ZnO nanowires as positive templates by pulsed laser deposition (PLD) [3]. Kawasaki et al. demonstrated the possibility of conformally coating carbon nanotubes with Pb-Zr-Ti oxide by liquid source-misted chemical deposition (LSMCD) [4]. In view of its capability of conformal growth on templates with a high aspect ratio, we have developed a fabrication technique for PbTiO3 and Pb(Zr,Ti)O3 (PZT) nanorods by metalorganic chemical vapor deposition (MOCVD) using ZnO nano