| Zinc oxide (ZnO), with a wide bandgap (3.37eV) and larger exciton binding energy (60meV), is a multifunction II-VI compound semiconductor material. In addition, ZnO is green material with stability and biological compatibility. Due to its unique mechanical, thermal, optical and electrical properties, ZnO can be used for versatile applications in optics, electronics, optoelectronics and so on. Moreover, ZnO has the coupling properties of piezoelectric and semiconducting, which is the foundation for the fabrication of piezoelectric nanodevices. Up to now, lots of one-dimensional (ID) ZnO micro/nanostructures based piezoelectric devices (such as piezoelectric field effect transistors, piezoelectric resonators, piezoelectric strain sensors and nanogenerators) have been fabricated, and show their potential and wide applications in the micro/nano electromechanical system, biomedical medicine medical, micro/nano energy recycling and self-powered micro/nanosystems, which greatly promote the development of nano science and technology.In this paper, focusing on the controllable growth of one-dimensional (1D) ZnO micro/nanostructures, the design and preparation of piezoelectric nanogenerators and piezoelectric strain sensors, we carried out a series of research work, and the main research and results are as follows:(1) ZnO nanorods were synthesized on common paper substrate by low-temperature hydrothermal method. The morphologies, crystal structure and optical properties of samples were characterized by XRD, SEM and PL. The results show that ZnO nanorods with well-crytallized hexagonal wurtzite structure were densely and uniformly distributed on the surfaces of the paper fibers. In addition, the formation mechanism was investigated and the effects of the growth conditions (such as seed layer, precursor concentration, growth time) on nanorods morphology were also studied systematically, which was beneficial to further research on flexible piezoelectric devices.(2) Piezoelectric nanogenerators based on common paper substrates were successfully fabricated, the core part of which was the fiber paper covered by ZnO nanorods. By periodic bending-releasing the nanodevices, the AC-type voltage and current outputs were obtained. The output voltage and current were typically10mV and10nA, respectively. Moreover, the device’s electric output behavior can be optionally changed between four modes simply by controlling the straining rate. The nanogenerator could also be utilized as a self-powered vibration sensor, to not only harvest energy from environmental mechanical energy, but also monitor and alarm some emergency in our daily life.(3) In order to improve the electric output, a novel structure of AC-type piezoelectric nanogenerator based on terylene fabrics was fabricated using two-step hydrothermal process. It was found that the voltage output of the device was200-fold increase compared to that fabricated by one-step hydrothermal process. Furthermore, the device fabricated by two-step hydrothermal process was only sensitive to strain rather than strain rate or frequency. By increasing the strain applied to the nanogenerator, the corresponding output voltage was also increased. The maximum output voltage was measured to be over7V, which is large enough to power common electric device.(4) A novel structure of piezoelectric strain sensor was proposed and realized by using gear-shaped ZnO microwires (GMWs) synthesized by CVD method. The results showed that the cross-sections of the microwires were mainly gear-shaped rather than hexagonal, which were formed by lateral coalescence of ZnO fine wires. In addition, high-quality Schottky devices based on ZnO microwires were also fabricated by using Cu-contained silver paste (CSP) as the contact electrodes of one end of ZnO microwire-based M-S-M structure. The device exhibited a very high rectifying ratio of105at±1V and a very high gauge factor of1123at a strain of1.28%. |
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