ZnO nanomaterials with their unique semiconducting and piezoelectric coupled properties have become promising materials for applications in piezotronic devices including nanogenerators, piezoelectric field effect transistors, and diodes. This article will mainly introduce the research progress on piezotronic properties of ZnO nanomaterials investigated by scanning probe microscopy (SPM) and ZnO-based prototype piezotronic nanodevices built in virtue of SPM, including piezoelectric field effect transistors, piezoelectric diodes, and strain sensors. Additionally, nanodamage and nanofailure of ZnO materials and their relevant piezotronic nanodevices will be critically discussed in their safe service in future nanoelectromechanical system (NEMS) engineering.

Three-dimensional ZnO micro/nanorod networks were synthesized through the direct evaporation of metal zinc and graphite powders in Ar and O 2 at 910 °C without any catalyst. The micro/nanorod networks of as-synthesized ZnO were characterized by using scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray diffraction. The branches within one network show very regular cross orientation. The nanorods follow a growth direction [0001]. Mircrowave absorption properties of the ZnO netlike structures have been investigated in detail. The reflection loss (RL) of the netlike structures and nanotetrapod-shaped ZnO were calculated by using the relative complex permeability and permittivity. And the value of minimum RL for the composite with 50 vol % ZnO netlike structures is -37 dB at 6.2 GHz with a thickness of 4.0 mm. These results provide a wide insight for the netlike structure ZnO as desirable materials for the fabrication of micro/nanoscale functional electromagnetic shield devices.

The mechanical properties of individual zinc oxide (ZnO) nanowires, grown by a solid–vapour phase thermal sublimation process, were studied in situ by transmission electron microscopy (TEM) using a home-made TEM specimen holder. The mechanical resonance is electrically induced by applying an oscillating voltage, and in situ imaging has been achieved simultaneously. The results indicate that the elastic bending modulus of individual ZnO nanowires were measured to be ∼58 GPa and the damping time constant of the resonance in a vacuum of 10−8 Torr was ∼14 ms. A nanobalance was built and the mass of the nanoparticle attached at the tip of a nanowire was measured. The ZnO nanowires are promising in potential applications as nanocantilevers and nanoresonators.

In-doped ZnO nanowires were successfully fabricated by thermal evaporation of a powder mixture of Zn, In2O3, and graphite. Field emission of individual In-doped and pure ZnO nanowire was observed in situ by a transmission electron microscopy. The results show that In-doped ZnO nanowires showed an enhanced field emission properties. First-principle density functional calculations were performed to calculate the electronic structure of the In-doped and pure ZnO in order to explain the observed field emission properties. A two-band field emission mechanics was proposed to explain the enhanced field emission from n-type doping.

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The fatigue behavior of ZnO nanowires (NWs) and microwires was systematically investigated with in situ transmission electron microscopy electromechanical resonance method. The elastic modulus and mechanical quality factors of ZnO wires were obtained. No damage or failure was found in the intact ZnO wires after resonance for about 10(8)-10(9) cycles, while the damaged ZnO NW under electron beam (e-beam) irradiation fractured after resonance for seconds. The research results will provide a useful guide for designing, fabricating, and optimizing electromechanical nanodevices based on ZnO nanomaterials, as well as future applications.

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