Robust optimization of the output voltage of nanogenerators by statistical design of experiments

Abstract

Nanogenerators were first demonstrated by deflecting aligned ZnO nanowires using a conductive atomic force microscopy (AFM) tip. The output of a nanogenerator is affected by three parameters: tip normal force, tip scanning speed, and tip abrasion. In this work, systematic experimental studies have been carried out to examine the combined effects of these three parameters on the output, using statistical design of experiments. A statistical model has been built to analyze the data and predict the optimal parameter settings. For an AFM tip of cone angle 70° coated with Pt, and ZnO nanowires with a diameter of 50 nm and lengths of 600 nm to 1 µm, the optimized parameters for the nanogenerator were found to be a normal force of 137 nN and scanning speed of 40 µm/s, rather than the conventional settings of 120 nN for the normal force and 30 μm/s for the scanning speed. A nanogenerator with the optimized settings has three times the average output voltage of one with the conventional settings. KEYWORDSZnO nanowire arrays, robust parameter design, nanogenerator, piezoelectric properties Nanogenerators, developed by Wang's group, constitute a new field in nanotechnology and energy harvesting with promising applications in building self-powered nanosystems [1][2][3][4]. The nanogenerator was discovered in 2006 by manipulating n-type ZnO nanowire arrays using a conductive atomic force microscope (AFM). Stimulated by this work [1], a prototype direct-current nanogenerator driven by ultrasonic waves without using an AFM was fabricated in 2007 [3]. Nanogenerators composed of single ZnO fine wire [5], nanowire and micro-fiber hybrid structure energy harvesting devices [6] and layer-by-layer stacked-up direct current generators [7] have all been demonstrated. Research on nanogenerators is now a new field in energy science [8]. A challenging issue affecting potential applications of nanogenerators is their low power output. In an attempt to obtain higher power output, p-type ZnO nanowire arrays, ZnS nanowires and other materials have all been used to fabricate nanogenerators [9][10][11][12], using a variety of different physical designs. However, a systematic study is still required in order to examine the influence of key parameters-such as the input mechanical force and electrode abrasion-on the output of a nanogenerator.Nano Res. 2010, 3(9): 613-619 ISSN 1998.1007/s12274-010-0029-1 CN 11-5974/O4 Research Article § These authors contributed equally to the work. Address correspondence to Zhong Lin Wang, zhong.wang@mse.gatech.edu; C. F. Jeff Wu, jeffwu@isye.gatech.edu Nano Res. 2010, 3(9): 613-619 614 In this paper, we report a systematic experimental study of the effects of varying different parameters on the output of a nanogenerator, using our first nanogenerator based on conductive AFM scanning of n-type ZnO nanowire arrays. The experimental results were analyzed by statistical modeling, as a result of which the optimum choice of experimental parameters was identified. Experiments using the optimized parameters...

One-dimensional ZnO nanostructures: Solution growth and functional properties

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