Synthesis and piezoelectric properties of well-aligned ZnO nanowire arrays via a simple solution-phase approach

An effective, low cost and catalyst-free solution-phase approach was demonstrated for achieving a tailored length and controlled surface-to-volume ratio of aligned ZnO nanowire (NW) arrays. By a slight variation of the solution concentration and growth time, significant changes in length and surface-to-volume ratio of the obtained ZnO NW arrays have been controlled, respectively. The morphology and microstructure of the synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Also the growth mechanism was discussed. For the study of the piezoelectric property of aligned ZnO NW arrays, some measuring models of nanogenerators (NGs) were fabricated with two pieces of grown ZnO NW array structures stacking together and penetrating into each other. One of the pieces was coated with Au film as the conductive nanotip (NTP) array. The NG was driven by an ultrasonic wave. The piezoelectric output current was gained and characteristic curves have been illustrated for different measuring results. The curves show that increasing the length and surface-to-volume ratios of ZnO NW arrays can enhance the output power of the NGs, respectively. It can be seen that the NGs fabricated with size-controlled ZnO NW arrays provide a feasible technology for building high-power output or power-controlled NGs for applications where a smaller size or appointed power output NGs are required. However, no relationship was found between the piezoelectric current output and the driving frequency of ultrasonic waves from 10 to 50 kHz.