Semiconductor nanowires represent an important class of nanostructure building block for photovoltaics as well as direct solar-to-fuel application, because of their high surface area, tunable bandgap, light-trapping capabilities, and efficient charge transport and collection. The generation of fuels by the direct conversion of solar energy in a fully integrated system is an attractive goal; however, no such system has been demonstrated that shows the required efficiency, is sufficiently durable, or can be manufactured at reasonable cost. It requires major research advancement in the area of semiconductor light absorber and catalyst discovery. One of the most critical issues in solar water splitting is the development of a suitable photoanode with high efficiency and long-term durability in an aqueous and photo-oxidative environment. Nanowires can be readily designed and synthesized to deterministically incorporate heterojunctions with improved light absorption, charge separation, and vectorial charge transport. High surface-area nanowire arrays can serve as photocathodes and photoanodes within an artificial photosynthetic system. Meanwhile, it is also possible to selectively decorate different oxidation or reduction catalysts onto specific segments of the nanowires to mimic the compartmentalized reactions in natural photosynthesis. The bottom-up synthetic approach for the semiconductor nanowires also enables several important principles of sustainability in materials and technology development, namely, using earth-abundant elements and using less energy-intensive processes. In this talk, I will highlight several recent examples from this lab, using semiconductor nanowires and their heterostructures for the purpose of solar-to-electricity and solar-to-chemical energy conversion.

Biography:
Peidong Yang received a BS in chemistry from University of Science and Technology of China (1993) and a PhD in chemistry from Harvard University (1997). He did postdoctoral research at the University of California, Santa Barbara, before joining the Department of Chemistry faculty at the University of California, Berkeley (1999). He is currently a professor in the Department of Chemistry, Materials Science and Engineering, and a senior faculty scientist at the Lawrence Berkeley National Laboratory. Yang is the Department Head/North Site Director of the Joint Center for Artificial Photosynthesis (JCAP) at LBNL. He is the deputy director for the Center of Integrated Nanomechanical Systems. Yang is an associate editor for the Journal of the American Chemical Society and also serves on the editorial advisory boards for a number of journals, including Acct. Chem. Res. and Nano. Lett. The founder of the Nanoscience subdivision within the American Chemical Society (ACS), Yang has also co-founded two startups, Nanosys Inc., and Alphabet Energy, Inc. He is the recipient of the Materials Research Society (MRS) Medal; the Baekeland Medal; the Alfred P. Sloan Research Fellowship; the Arnold and Mabel Beckman, National Science Foundation, and MRS Young Investigator Awards; the Julius Springer Prize for Applied Physics; the ACS Pure Chemistry Award; and the Alan T. Waterman Award. He was recently elected an MRS Fellow. According to ISI (Thomas Reuters), for the past decade, Yang has been ranked number one in materials science and number ten in chemistry based on average citations per paper. His main research interest is in the area of one-dimensional semiconductor nanostructures and their applications in nanophotonics and energy conversion.

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.[1] Z.L. Wang and J.H. Song, Science, 312 (2006) 242-246.[2] X.D. Wang, J.H. Song J. Liu, and Z.L. Wang, Science, 316 (2007) 102-105.[3] Y. Qin, X.D. Wang and Z.L. Wang, Nature, 451 (2008) 809-813.[4] R.S. Yang, Y. Qin, L.M. Dai and Z.L. Wang, Nature Nanotechnology, 4 (2009) 34-39.[5] S. Xu, Y. Qin, C. Xu, Y.G. Wei, R.S. Yang, Z.L. Wang, Nature Nanotechnology, 5 (2010) 366 - 373 [6] Z.L. Wang, Nano Today 5 (2010) 540.[7] W.Z. Wu, Y.G. Wei and Z.L. Wang, Adv. Materials, 22 (2010) 4711.[8] W.Z. Wu and Z.L. Wang, Nano Letters, 11 (2011) 2779[9] Y.F. Hu, Y.L. Chang, P. Fei, R.L. Snyder and Z.L. Wang, ACS Nano, 4 (2010) 1234.[10] Q. Yang, X. Guo, W.H. Wang, Y. Zhang, S. Xu, D.H. Lien, Z.L. Wang, ACS Nano, 4 (2010) 6285.[11] Q. Yang, W.H. Wang, S. Xu, Z.L. Wang, Nano Letters, dx.doi.org/10.1021/nl202619d.[12] for details: www.nanoscience.gatech.edu.

Biography:
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.

The sun, a natural fusion reactor, is located far enough away to safely bring 10,000 times as much energy as we need to the earth. In principle, all the global energy demand could be afforded in the form of electricity by covering 4% of the world’s desert surface with photovoltaic (PV) panels. Although various semiconductors are available for PV, we can deduce that 100 GW annual solar cell production is the minimum requirement for covering > 30% global energy needs and that only Si can clear this hurdle. The serious disadvantage in PV, output power fluctuation depending on the time, climate, and location, could be overcome by global PV networking with a superconducting grid. In addition to the well-recognized two values of vast land and sunshine, the desert has the third value, sand, for its main component, SiO2. The Science Council of Japan (SCJ) proposed the Sahara solar breeder (SSB) plan at the G8+5 Academies’ meeting in Rome in 2009, and appealed for international cooperation to solve the global energy and ecological issues. The SSB plan starts from basic material research on innovative solar Si technology (more than and beyond Siemens processes) and high-Tc superconducting dc transmission. SSB may be presumed to be a quixotic challenge, but it is the universal dream come true if we can say “yes” for the following questions:1)Can PV be superior to conventional energy sources judging from its quality, quantity, cost, and sustainability?2)Is SSB feasible scientifically, technologically, and economically?Biography
Hideomi Koinuma started his research career as a polymer chemist at Tokyo University, where he invented biodegradable polycarbonate by copolymerization of CO₂ and epoxide while pursuing his PhD in 1970. After two years as a postdoc at Kansas University, he returned to Tokyo to continue his polymer research. He also studied solid state electronic thin films of amorphous silicon, as well as transparent conductive oxides, which was extended to high-Tc superconducting thin films. His primary concern is atomic-scale chemical control of surface, interface, and epitaxy of materials. He has founded three international conferences: Workshops of Oxide Electronics (1995) Combinatorial Material Science and Technology (2000) and the first Asia-Arab Sustainable Energy Forum (Aug. 2011). He has served as the director of the Materials Research Laboratory at the Tokyo Institute of Technology, as vice-president of the National Institute for Materials Science, as a funding agency strategy designer, and as chairman of a high-tech venture of advanced materials.