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Nanoscience Research Group

Dr. Zhong Lin (ZL) Wang is the Hightower Chair in Materials Science and Engineering, Regents'Professor, College of Engineering Distinguished Professor and Director, Center for Nanostructure Characterization, at Georgia Tech. Dr. 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 applications of nanowires in energy sciences, electronics,optoelectronics and biological science. He invented and pioneered the in-situ technique for measuring the mechanical and electrical properties of a single nanotube/nanowire inside a transmission electron microscope (TEM). He is the world leader in ZnO nanostructure research in the last decade. His discovery and breakthroughs in developing nanogenerators establish the principle and technological road map for harvesting mechanical energy from environment and biological systems for powering a personal electronics. The field created by him on self-powered nanosystems inspired the worldwide effort in academia and industry for studying energy for micro-nano-systems, which is now a distinct disciplinary in energy research and future sensor networks. He coined and pioneered the field of piezotronics and piezo-phototronics by introducing piezoelectric potential gated charge transport process in fabricating new electronic and optoelectronic devices, which have potential applications in MEMS/NEMS, nanorobotics, human-electronics interface, sensors, medical diagnosis and photovoltaic.

Our recent research is focused on:

 1. Nanogenerators and self-powered nanosystems (2005 – today)

 2. Piezotronics for smart systems (2006 – today)

 3. Piezo-phototronics for energy science and optoelectronics (2009 – today)

 4. Hybrid cells for energy harvesting (2008 – today)

1. Nanogenerators and self-powered nanosystems (2005 – today).

Ever since the wide range applications of laptop computers and cell phones, seeking of power sources for driving portable electronics is becoming increasingly important. The current technology mainly relies on rechargeable batteries. But for the near future, micro/nano-systems will be widely used in health monitoring, infrastructure and environmental monitoring, internet of things and defense technologies; the traditional batteries may not meet or may not be the choice as power sources for the following reasons. First, with the increasing shrinkage in size, the size of the total micro/nano-systems could be largely dominated by the size of the battery rather than the devices. Second, the number and density of micro/nano-systems to be used for sensor network could be large, thus, replacing batteries for these mobile devices are becoming challenging and even impractical. Lastly, the power needed to drive a micro/nano-system is rather small, in the range of micro- to milli-Watt range. To meet these technological challenges, Wang proposed the self-powering nanotechnology in 2005, aiming at harvesting energy from the environment to power the micro/nano-systems based sensor network. After 6 years of effort, we have extensively developed the science, engineering and technology related to nanogenerator as a sustainable self-sufficient power source for micro/nano-systems by harvesting energy from our body and living environment. We initiated the research for self-powered system in 2005, which is now a very attractive field of research worldwide. Our research aims at solving the power needs for small electronics, with applications in personal/mobile electronics, medical care/sciences, environmental/infrastructure monitoring and other related fields.

2. Piezotronics for smart systems (2006 – today)

     Piezoelectricity, a phenomenon known for centuries, is an effect that is about the production of electrical potential in a substance as the pressure on it changes. The most well-known material that has piezoelectric effect is the perovskite structured Pb(Zr, Ti)O3 (PZT), which has found huge applications in electromechanical sensors, actuators and energy generators. But PZT is an electric insulator and it is less useful for building electronic devices. Wurtzite structures, such as ZnO, GaN, InN and ZnS, also have piezoelectric properties but they are not extensively used as much as PZT in piezoelectric sensors and actuators due to their small piezoelectric coefficients. In fact, due to the polarization of ions in a crystal that has non-central symmetry, a piezoelectric potential (piezopotential) is created in the crystal by applying a stress. For materials such as ZnO, GaN, InN in the wurtzite structure family, the effect of piezopotential to the transport behavior of charge carriers is significant due to their multiple functionalities of piezoelectricity, semiconductor and photon excitation. By utilizing the advantages offered by these properties, a few new fields have been created. Electronics fabricated by using inner-crystal piezopotential as a “gate” voltage to tune/control the charge transport behavior is named piezotronics, which was first coined by Wang in 2006. Devices fabricated using the piezotronic effect are distinctly different from those realized through traditional CMOS technologies in principle, design and applications. Piezotronics will have important applications in human-CMOS interfacing, micro/nano-electromechanical systems, nanorobotics, next generation of sensor and transducers, smart electronics, flexible electronics and many more.

3. Piezo-phototronics for energy science and optoelectronics (2009 – today)

    Due to the polarization of ions in a crystal that has non-central symmetry, a piezoelectric potential (piezopotential) is created in the crystal under stress. Piezopotential can effectively raise the Schottky barrier height at a metal-semiconductor interface or change the transport at a p-n junction, while laser excitation and effectively low the Schottky barrier height. Therefore, we can use the coupling between piezoelectric effect and laser excitation to introduce new optoelectronic devices. Piezo-phototronics 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. The piezo-phototronic effect was first coined by Wang in 2009. Recently, we have applied this effect for fabricating highly sensitive UV sensors, LED with largely enhanced efficiency and high performance solar cells. The development of piezo-phototronics will have great impact to the energy science and optoelectronic devices fabricated using ZnO and GaN materials.

4. Hybrid cells for energy harvesting (2008 – today)

    Our living environment has an abundance of energies in the forms of light, thermal, mechanical (such as vibration, sonic wave, wind and hydraulic), magnetic, chemical and biological. Harvesting these types of energies is of critical importance for long-term energy needs and sustainable development of the world. Over the years, rationally designed materials and technologies have been developed for converting solar and mechanical energies into electricity. Photovoltaic relies on approaches such as inorganic p-n junctions, organic thin films, and organic-inorganic heterojunctions. Mechanical energy generators have been designed based on principles of electromagnetic induction and piezoelectric effect. Innovative approaches have to be developed for conjunctional harvesting of multiple types of energies using an integrated structure/material so that the energy resources can be effectively and complimentarily utilized whenever and wherever one or all of them are available. We have been developing hybrid cells that are designed for simultaneously harvesting solar and mechanical, and chemical and mechanical energies using nanotechnology. The two energy harvesting approaches can work simultaneously or individually, and they can be integrated in parallel and serial for raising the output current and voltage, respectively. This study is to demonstrate an innovative approach for developing integrated technologies for effectively scavenging available energies in our environment around the clock.

 

For more details:

http://www.nanoscience.gatech.edu/


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