Highly piezoelectric BaTiO₃ nanorod bundle arrays using epitaxially grown TiO₂ nanomaterials

Low-dimensional piezoelectric nanostructures such as nanoparticles, nanotubes, nanowires, nanoribbons and nanosheets have been developed for potential applications as energy harvesters, tunable sensors, functional transducers and low-power actuators. In this study, lead-free BaTiO ₃ nanorod bundle arrays (NBA) with highly piezoelectric properties were successfully synthesized on fluorine-doped tin oxide (FTO) substrate via a two-step process consisting of TiO₂ epitaxial growth and BaTiO₃ conversion. Through the TiO₂ epitaxial growth on FTO substrate, (001) oriented TiO₂ nanostructures formed vertically-aligned NBA with a bundle diameter of 80 nm and an aspect ratio of six. In particular, chemical etching of the TiO₂ NBA was conducted to enlarge the surface area for effective Ba²⁺ ion diffusion during the perovskite conversion process from TiO₂ to BaTiO₃. The final structure of perovskite BaTiO₃ NBA was found to exhibit a feasible piezoelectric response of 3.56 nm with a clear phase change of 180° from the single BaTiO₃ bundle, by point piezoelectric forced microscopy (PFM) analysis. Consequently, highly piezoelectric NBA could be a promising nanostructure for various nanoscale electronic devices.