Taper PbZr<sub>0.2</sub>Ti<sub>0.8</sub>O<sub>3</sub> Nanowire Arrays: From Controlled Growth by Pulsed Laser Deposition to Piezopotential Measurements

Single crystalline PbZr<sub>0.2</sub>Ti<sub>0.8</sub> (PZT) nanowires arrays (NWAs) with taper morphology were epitaxially grown on SrTiO<sub>3</sub> (STO) substrate using pulse laser deposition. The taper morphology was attributed to the overcoating of PZT layer <i>via</i> a lateral growth of PZT clusters/adatoms during PZT NW growth. The growth window for PZT film or nanowire was systematically studied at varied temperatures and pressures. The proposed growth mechanism of the taper PZT NWAs was investigated from a layer by layer growth <i>via</i> Frank–Van Der Merwe growth, followed by a formation of three-dimensional islands <i>via</i> Stranski–Krastanow growth, and then axial growth on the lowest energy (001) plane with growth direction of [001] <i>via</i> vapor–solid growth mechanism. However, under certain conditions such as at higher or lower pressure (>400 or <200 mTorr) or substrate temperatures (>850 °C and <725 °C), formation of the PZT NWs is suppressed while the epitaxial PZT thin film <i>via</i> the layer-by-layer growth remains. The controllable growth directions of the PZT NWAs on (001), (110), and (111) STO substrates were demonstrated. The piezopotential of the taper PZT NWAs using a conducting atomic force microscope with the average voltage output of ∼18 mV was measured. The theoretical piezopotential of a PZT NW was calculated to compare with the measured outputs, providing a comprehensively experimental and theoretical understanding of the piezoelectricity for the PZT NW.