Abstract
Piezoelectric materials capable of converting between mechanical and electrical energy have a great range of potential applications in micro- and nano-scale smart devices; however, their performance tends to be greatly degraded when reduced to a thin film due to the large clamping force by the substrate and surrounding materials. Herein, we report an effective method for synthesizing isolated piezoelectric nano-materials as means to relax the clamping force and recover original piezoelectric properties of the materials. Using this, environmentally friendly single-crystalline NaxK1-xNbO3 (NKN) piezoelectric nano-rod arrays were successfully synthesized by conventional pulsed-laser deposition and demonstrated to have a remarkably enhanced piezoelectric performance. The shape of the nano-structure was also found to be easily manipulated by varying the energy conditions of the physical vapor. We anticipate that this work will provide a way to produce piezoelectric micro- and nano-devices suitable for practical application, and in doing so, open a new path for the development of complex metal-oxide nano-structures.
Highlights
Volatility of alkali elements means that the synthesis of fine NKN ceramics is still quite difficult[21]
The out-of plane lattice parameter of the epitaxial NKN thin film and NKN nano-rods were calculated as 4.027 Å which is notably smaller than the lattice parameter of the Nb-doped SrTiO3 (Nb):STO substrate
Given that the crystal structure of NKN with a morphotropic phase boundary (MPB) represents an orthorhombic symmetry[28], any residual in-plane compressive strain in the epitaxial NKN thin film is expected to be produced by a lattice mismatch in the in-plane spacing of the NKN thin film and Nb:STO substrate
Summary
NKN nano-rods were grown on a 5 wt% Nb-doped SrTiO3 (Nb:STO) single-crystal substrate (100) using a conventional pulsed laser deposition (PLD) system with a KrF excimer laser (wavelength = 248 nm). The crystal quality of the NKN nano-rods was examined by X-ray diffraction (XRD: Rint/Dmax 2500, Rigaku Co., Japan) over a 2θ range of 20° to 60° using Cu-Kα radiation. The surface and cross-sectional microstructure of the nano-rods were observed using an environmental scanning electron microscope (ESEM: Philips FEI XL-30 FEG).To determine the growth orientation and crystal structure of the NKN nano-rods, bright field (BF) and high-resolution (HR) images were obtained by high-resolution transmission electron microscopy (HRTEM: FEI,Tecnai F20 G2).The effective piezoelectric coefficient (d33eff) of the NKN nano-rods was measured using a piezoelectric force microscope (PFM, Dimension 3100, Veeco Instruments, USA), with a lock-in amplifier (SR830, Stanford Research) utilized to simultaneously obtain the piezoresponse. A piezoelectric response signal was collected from the top of the nano-rods and the surface of the thin film in each sample, from which piezoelectric responses curves depicting the phase, amplitude and piezoresponse were plotted using an average of values obtained from 9 nano-rods and 9 points on the film surface
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