Medalist Talk: From Nanogenerators to Piezotronics -- A Decade Study of ZnO Nanostructures.
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, without which most of the sensor network may be impossible. The piezoelectric nanogenerators developed by us have the potential to serve as self-sufficient power sources for mico/nano-systems. For Wurtzite structures that have non-central symmetry, such as ZnO, GaN and InN, a piezoelectric potential (piezopotential) is created in the crystal by applying a strain. The nanogenerator is invented by using the piezopotential as the driving force for electrons to flow in responding to a dynamic straining of piezoelectric nanowires [1-5]. A gentle straining can produce an output voltage of up to 20-40 V from an integrated nanogenerator. Furthermore, piezopotential in the wurtzite structure can serve as a “gate” voltage that can effectively tune/control the charge transport across an interface/junction; electronics fabricated based on such a mechanism is coined as piezotronicsI [6-8], with applications in force/pressure triggered/controlled electronic devices, sensors, logic units and memory. By using the piezotronic effect, we show that the optoelectronc devices fabricated using wurtzite materials can have superior performance as solar cell, photon detector and light emitting diode [9-11]. Piezotronic is likely to serve as a “mediator” for directly interfacing biomechanical action with silicon based technology. Z.L. Wang and J.H. Song, Science, 312 (2006) 242-246. X.D. Wang, J.H. Song J. Liu, and Z.L. Wang, Science, 316 (2007) 102-105. Y. Qin, X.D. Wang and Z.L. Wang, Nature, 451 (2008) 809-813. R.S. Yang, Y. Qin, L.M. Dai and Z.L. Wang, Nature Nanotechnology, 4 (2009) 34-39. S. Xu, Y. Qin, C. Xu, Y.G. Wei, R.S. Yang, Z.L. Wang, Nature Nanotechnology, 5 (2010) 366 - 373  Z.L. Wang, Nano Today 5 (2010) 540. W.Z. Wu, Y.G. Wei and Z.L. Wang, Adv. Materials, 22 (2010) 4711. W.Z. Wu and Z.L. Wang, Nano Letters, 11 (2011) 2779 Y.F. Hu, Y.L. Chang, P. Fei, R.L. Snyder and Z.L. Wang, ACS Nano, 4 (2010) 1234. Q. Yang, X. Guo, W.H. Wang, Y. Zhang, S. Xu, D.H. Lien, Z.L. Wang, ACS Nano, 4 (2010) 6285. Q. Yang, W.H. Wang, S. Xu, Z.L. Wang, Nano Letters, dx.doi.org/10.1021/nl202619d. for details: www.nanoscience.gatech.edu.
Dr. Zhong Lin (Z.L.) Wang received his PhD from Arizona State University in 1987. He holds the Hightower Chair in Materials Science and Engineering at George Tech, where he is also the Regents' Professor, Engineering Distinguished Professor, and director of the Center for Nanostructure Characterization. Wang is a foreign member of the Chinese Academy of Sciences; he is a fellow of the American Physical Society, the American Association for the Advancement of Science (AAAS), the Microscopy Society of America, and the Materials Research Society. Wang has made original and innovative contributions to the synthesis, discovery, characterization, and understanding of fundamental physical properties of oxide nanobelts and nanowires, as well as to applications of nanowires in energy sciences, electronics, optoelectronics, and biological science.He is a world leader in the study of ZnO nanostructures. His discovery and breakthroughs in developing nanogenerators established the principle and technological roadmap for harvesting mechanical energy from environmental and biological systems for powering personal electronics. His research on self-powered nanosystems has inspired worldwide efforts on the part of academia and industry to study energy for micro- and nanosystems. He pioneered the field of piezotronics and piezo-phototronics by introducing the piezoelectric potential gated charge-transport process in the fabrication of new electronic and optoelectronic devices.This breakthrough by redesigned CMOS transistor has important applications in smart MEMS/NEMS, nanorobotics, human-electronics interface, and sensors. Wang’s publications have been cited over 44,000 times. The H-index of his citations is 101. Details can be found at: http://www.nanoscience.gatech.edu.