Fabrication and characterization of PZT nanofibers and their composites

The Young's modulus measurement of individual electrospun lead zirconate titanate (PZT) nanofibers using in situ scanning electron microscopy (SEM) equipped with a nanomanipulator is presented. The PZT nanofibers were fabricated by an electrospinning process and collected on a silicon substrate. The Young's modulus was calculated as ∼ 70 GPa from the resonant frequency excited by an oscillating electric field applied through a nanomanipulator. A method to adjust the stiffness of individual piezoelectric nanofibers by electron beam induced polarization is discovered. The stiffness can be adjusted up to 76 % by induced polarization under the exposure of an electron beam to control the domain boundaries in single PZT nanofibers. Splitting effect of the resonant frequencies was observed due to anisotropic stiffness in polarized PZT nanofibers. This method of electron beam induced polarization provides a way to tune the mechanical properties of piezoelectric nanostructures before employing them in devices and other applications.;Direct piezoelectric potential measurement of single PZT nanofiber under bending using a nanomanipulator inside a SEM chamber is presented. The PZT nanofibers, with the diameter and length around 100 nm and 70∼100 microm respectively, were aligned across trenches on a silicon substrate with a thermally grown oxide diffusion barrier and evaporated gold electrodes. A potential of ∼0.4 mV was generated when a bending moment was applied to a PZT nanofiber with an effective length of 4 microm by a tungsten tip of the nanomanipulator. The piezoelectric voltage constant g33 was estimated to be 0.079 Vm/N which was in agreement with the value obtained from measurement based on AFM method. The experiment demonstrated the feasibility of using these PZT nanofibers for nanoscale sensing, actuation and energy harvesting.;A new piezoelectric nanogenerator based on PZT nanofiber composites (NFC) is demonstrated. The PZT nanofibers, with a diameter and length of approximately 60 nm and 500 microm, were aligned on interdigitated electrodes of platinum fine wires and packaged using a soft polymer on a silicon substrate. The measured output voltage and power under periodic stress application to the soft polymer was 1.63V and 0.03 microW, respectively. The piezoelectric voltage constant and dielectric constant of PZT nanofibers were much higher than other semiconductor piezoelectric nanowires and nanofibers, making this material ideal for nanogenerator or nanobattery applications. The flexible PZT nanofibers were embedded in soft polydimethylsiloxane (PDMS) polymer matrix, which helped prevent the PZT nanofibers from being damaged, thereby extending the life cycle of the nanogenerator. The simple fabrication and assembly process would allow for the facile mass production of this type of nanogenerator.;A concept that utilizes the PZT NFC to sense the acoustic emission (AE) for structural health monitoring (SHM) is reported. Both rigid and flexible PZT NFCs, which consists of nano scale PZT fibers with interdigitated electrodes, were developed for demonstrating the AE detection by mounting on surfaces and embedding into structures. The three point bending test showed the spontaneous polarization of un-poled PZT nano structures. A 3.7 times larger electromechanical coupling effect was observed after 90 minutes of polarization under an external electric field of ∼3 V/microm. AE detection was demonstrated by mounting the PZT nanofiber sensor on the surface of a carbon fiber composite plate. The signal attenuation maps showed anisotropic sensitivity, which can reduce the number of sensors required to identify the location of an AE source in practical applications. The small size, flexibility, self-powered sensing and high sensitivity allows the possibility of monitoring structures by following curved surfaces or integrating into composite. The flexible PZT NFC AE sensor can open up new applications in monitoring civil structures and even living cells.;A new concept of PZT NFC actuator, which can demonstrate the electromechanical coupling of electrospun PZT nanofibers, was presented. The mathematical model that describes the displacement of the designed PZT NFC actuator is developed. The PZT NFC actuators were fabricated and packaged in a flexible polymer structure with a thickness of ∼5 microm. The electromechanical coupling of electrospun PZT nanofibers was demonstrated by applying a driven voltage on the PZT NFC actuator. A maximum displacement of 120 microm was observed when an electric field of 3 V/microm was applied. Meanwhile, the motion of the PZT NFC actuator was simulated by using the developed model and compared with the experimental data. Smaller amplitude of the experimental results may due to the non-perfect alignment of PZT nanofibers and structure defects in the actuator.