Study On One-Dimensional ZnO Nanostructures Based Piezoelectric Nanogenerator

The piezoelectric nanogenerator is an important landmark in the development period of nanotechnology. The piezoelectric nanogenerator, conventing mechanical energy to electrical energy in nanoscale, relies on the coupling of piezoelectric and semiconducting properties of nanomaterials. This approach offers a potential solution for harvesting energy from the environment for self-powered nanotechnology. This nanotechnology can not only reduce the size and weight of the electrical source, but also enlarges the range of the scavenged energy from the environments.Piezoelectric nanogenerating devices based on one-dimensional ZnO nanostructures as piezoelectric materials were studied as follows in this paper. Mathematical models were established to calculate the the piezoelectric potential distribution in a bent ZnO nanorod considering the influence of free charge carriers. Based on the ZnO nanorod arrays prepared by low-temperature hydrothermal method, AFM studys of the electromechanically coupled discharging process of piezoelectric nanogenerator were carried out. The conceptions of heterojunction DC piezoelectric nanogenerating device and parallel nanorod arrays based AC piezoelectric nanogenerating device were proposed and realized in experiment.ZnO nanorod arrays were synthesized on ITO-coated glass substrate using low-temperature aqueous solution method. After dip-coating a ZnO seed film on the substarte using a sol-gel prepared ZnO seed solution, the substrate was dipped into the mixed solution of Zn(NO3)2 and HTMA for epitaxial growth of ZnO nanorod arrays. Characterization results show that densely and uniformly grown ZnO nanorods are well aligned vertically and indicate that each ZnO nanorod is a well-crytallized hexagonal single crystal growing along the c axis.A continuum model of piezoelectric potential generated in a bent ZnO nanorod cantilever was presented by means of the first piezoelectric effect approximation. The analytical solution of the model shows that the piezoelectric potential distribution in the nanorod is proportional to lateral force but is independent along the longitudinal direction, and the electric potential in the stretched area (positive potential) and that of compressed area (negative potential) are antisymmetric in cross section of the nanorod. The influence of free charge carriers on the piezoelectric potential in a bent ZnO nanorod was investigated using the finite difference method. The distributions of carriers and the electrical potential in the nanorod considering different parameters were obtained. The results show that the positive piezoelectric potential in stretched side of the bent nanorod is significantly screened by the carriers and the negative potential in compressed side is well preserved when considering a moderate carrier concentration of 1 ?101 7 cm-3. The mechanism of Pt/ ZnO Schottky junction piezoelectric generator based on the ZnO nanorod arrays was studied in detail with AFM system, by comparing the relationships between the topography of the ZnO nanorod and the detected current signal, as well as piezoelectric potential distribution and rectifying effect of Pt/ ZnO Schottky-junction. A high performance heterojunction piezoelectric nanogenerator was demonstrated by scanning a conductive diamond tip on ZnO nanorod arrays in contact-mode AFM system. About 95% ZnO nanorods generated piezoelectric current due to the excellent mechanical and electrical properties of the tip. Partial rectifying heterojunction was formed when the nitrogen-doped diamond tip contacting with the ZnO nanorod, which played an important role in accumulating and releasing piezoelectric potential of the piezoelectric nanogenerator.Experimental studies of Au/ ZnO Schottky junction DC piezoelectric nanogenerating device were carried out, including the I-V characteristics, current output properties and parallel connection behaviors of such devices. A novel DC piezoelectric nanogenerator with a structure of p-Si/ n-ZnO heterojunction was demonstrated. A low resistance p-type silicon chip dealt with metal-catalyzed chemical etching technique was utilized as the top electrode, forming a p-Si/ n-ZnO heterojunction piezoelectric nanogenerating device. Piezoelectric current with an average signal about 1 nA was generated when the device was drived by ultrasonic waves. Reverse connection and parallel connection experimental results verified the current generated from the device, and eliminated the effects from measurement system errors.A novel structure of AC piezoelectric nanogenerating device to improve the electric output was proposed and realized, by integrating a large number of AC nanogenerating units. Ultra-long ZnO nanorods synthesized by CVD method were transferred to flexible Kapton film using dry contact printing method. The AC piezoelectric nanogenerating device was obtained after depositing Ag electrode arrays on this Kapton film and then packaged. By periodic bent-release movement applied to the device, a forward and reverse short circuit current up to 2.5 nA was output, which was a great improvement relative to former devices.