Nanogenerators and Piezotronics

Developing wireless nanodevices and nanosystems is of critical importance for sensing, medical science, environmental/infrastructure monitoring, defense technology and even personal electronics. It is highly desirable for wireless devices to be self-powered without using battery. This is a new initiative in today's energy research for mico/nano-systems in searching for sustainable self-sufficient power sources [1]. We have invented an innovative approach for converting nano-scale mechanical energy into electric energy by piezoelectric zinc oxide nanowire arrays [2]. As today, a gentle straining can output 1-3 V from an integrated nanogenerator, using which a self-powered nanosensor has been demonstrated. A commercial LED has been lid up [3-5]. Due to the polarization of ions in a crystal that has non-central symmetry, a piezoelectric potential\textit{ (piezopotential)} is created in the crystal by applying a stress. The effect of piezopotential to the transport behavior of charge carriers is significant due to their multiple functionalities of piezoelectricity, semiconductor and photon excitation. Electronics fabricated by using inner-crystal piezopotential as a ``gate'' voltage to tune/control the charge transport behavior is named \textit{piezotronics [6,7].Piezo-phototronic effect} is a result of three-way coupling among piezoelectricity, photonic excitation and semiconductor transport, which allows tuning and controlling of electro-optical processes by strain induced piezopotential [8]. \\[4pt] [1] Z.L. Wang, \textit{Scientific American}, 298 (2008) 82-87; \\[0pt] [2] Z.L. Wang and J.H. Song, \textit{Science}, 312 (2006) 242-246. \\[0pt] [3] R.S. Yang, Y. Qin, L.M. Dai and Z.L. Wang, \textit{Nature Nanotechnology}, 4 (2009) 34-39. \\[0pt] [4] S. Xu, Y. Qin, C. Xu, Y.G. Wei, R.S. Yang, Z.L. Wang, \textit{Nature Nanotechnology}, 5 (2010) 366. \\[0pt] [5] G. Zhu, R.S. Yang, S.H. Wang, and Z.L. Wang , Nano Letters, 10 (2010) 3151. \\[0pt] [6] Z.L. Wang, \textit{Adv. Mater}., 19 (2007) 889-992. \\[0pt] [7] W.Z. Wu, Y.G. Wei and Zhong Lin Wang , Adv. Materials, DOI: adma.201001925. \\[0pt] [8] Y.F. Hu, Y.L. Chang, P. Fei, R.L. Snyder and Z.L. Wang, \textit{ACS Nano}, $4$ (2010) 1234--1240. \\[0pt] [9] Research supported by DARPA, DOE, NSF, Airforce, NIH, Samsung. For details: http://www.nanoscience.gatech.edu/zlwang/.