Publication

1. Piezoelectric effect of zinc oxide nanowires studied by in-situ TEM method SF1 Group 王立芬、杨是赜、许智、王文龙、白雪冬* *Tel: 82648032; E-mail: xdbai@iphy.ac.cn Abstract Piezoelectric effect in nanoscale structures has attracted much attention for the fundamental research and potential applications. Here, the piezoelectric effect of zinc oxide (ZnO) nanowires, including the response of the electrical transport and photoconducting behaviors on the nanowire bending, has been investigated by in-situ transmission electron microscopy (TEM), where the crystal structure of ZnO nanowires were simultaneously imaged. Serials of consecutively recorded current-voltage (I-V) curves along with an increase of nanowire bending show the striking effect of bending on their electrical behavior. With increasing the nanowire bending, the photocurrent of ZnO nanowire under ultraviolet illumination (UV) drops dramatically and the photoconducting response time becomes much shorter. In addition, the dynamic nanomechanics of ZnO nanowires were studied inside TEM. These phenomena could be attributed to the piezoelectric effect of ZnO nanowires, and they are significant for their potential applications on nanoelectronics devices, sensors, and cantilevers. c (g) Fig. 1 (a-d) Sequential TEM images of the four typical bending cases of the ZnOnanowire. (e) Electron diffraction pattern of the framed area in (a), indicating the nanowire has a wurzite structure with [ ] growth direction. (f) The corresponding high-resolution TEM image of the framed area in (a), showing the high-quality single crystal. (g)Serials of representative I-V curves of the ZnOnanowire, corresponding to the bending cases in (a-d). Fig. 2 Setup for in-situ TEM photoelectric measurements. The individual ZnOnanowire is clamped between two electrodes, one is piezo-driven metal tip. An LED chip is fixed on the frame of the specimen holder. Fig. 4 (Left) The decay tails are fitted by exponential time dependency I = I0exp(-t/τ). The decay time τ becomes shorter with the increase of bending, τ are 17.0 s, 5.9 s and 2.7 s, corresponding to the bending cases in Figure 3(b), (d), and (d), respectively. (Right) Schematic diagrams of the proposed mechanism for the change of the photocurrent and the photo response speed after bending. Piezoelectric field is built in zinc oxide nanowire when the nanowire is bent, which lowers the surface recombination barrier of electrons and holes, so shorten the photoconductingresponse time. (a) (b) (c) Fig. 3 (a) TEM image showing a stationary ZnOnanowire before contacting, (b)-(d) Three typical bending cases of the ZnOnanowire from a sequential bending process. (e) Corresponding I-V characteristics of the ZnOnanowire for the three different bending cases. Both the dark current and photocurrent decrease with the increase of bending. Fig. 5 (a) Scheme of setup for in-situ TEM nanomechanics measurements. (b) A selected stationary ZnO nanowires and its electromechanical resonances with increasing amplitudes. (c) Dependence of vibration amplitude on the applied frequency for the 4 resonance peaks with increasing resonance amplitudes of 1.478, 3.512, 3.879, and 4.682 μm, respectively. The mechanical quality factor decreases as large as ~80% with bending increase from the curves (c), due to the piezoelectric effect. Publication • Lifen Wang, Xuezeng Tian, Shize Yang, Zhi Xu, Wenlong Wang, and Xuedong Bai, “Dynamic nanomechanics of zinc oxide nanowires”, APL 2012, 100, 163110. • Shize Yang, Lifen Wang, Xuezeng Tian, Zhi Xu, Wenlong Wang, Xuedong Bai and Enge Wang, “Piezotronic effect of zinc oxide nanowires studied by in-situ TEM method”, Adv. Mater., 2012, 24, 4676-4682. SF1组联系人: 白雪冬，Tel: 82648032; E-mail: xdbai@iphy.ac.cn