Dr. Zhong Lin (Z.L.) Wang (US citizen) received his Ph.D in Physics from Arizona State University in 1987. He served as a Visiting Lecturer in SUNY (1987-1988), Stony Brook, as a research fellow at the Cavendish Laboratory in Cambridge (England) (1988-1989), Oak Ridge National Laboratory (1989-1993) and at National Institute of Standards and Technology (1993-1995) before joining Georgia Tech as a faculty in 1995. He was the Hightower Chair in Materials Science and Engineering and Regents' Professor at Georgia Tech. He served as the director of the Georgia Tech Center for Nanostructure Characterization form 1995-2016.

Summary: Dr. Wang most important contributions in science are: Pioneered the field of nanogenerators and self-powered sensors; Coined piezotronics and piezo-phototronics for the third generation semiconductors.

Wang’s discovery and breakthroughs in developing nanogenerators establish the principle and technological road map for harvesting mechanical energy from environment and biological systems for powering mobile sensors. He first showed that the nanogenerator is originated from the Maxwell’s displacement current, revived the applications of Maxwell’s equations in energy and sensors, which is 155 years later after the invention of electromagnetic wave based on displacement current. His research on self-powered nanosystems has inspired the worldwide effort in academia and industry for harvesting ambient energy for micro-nano-systems, which is now a distinct disciplinary in energy science for future sensor networks and internet of things. He coined and pioneered the fields of piezotronics and piezo-phototronics by introducing piezoelectric potential gated charge transport process in fabricating strain-gated transistors for new electronics, optoelectronics, sensors and energy sciences. The piezotronic transistors have important applications in smart MEMS/NEMS, nanorobotics, human-electronics interface and sensors. Wang also 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).

Dr. Wang is a pioneer and world leader in nanoscience and nanotechnology for his outstanding creativity and productivity. He has authored and co-authored 6 scientific reference and textbooks and over 2000 peer reviewed journal articles (83 in Nature, Science and their family journals), 45 review papers and book chapters, edited and co-edited 14 volumes of books on nanotechnology, and held over 60 US and foreign patents. Wang’s Google scholar gives a citation is over 287,000 with an h-index of 259 [http://scholar.google.com/citations?user=HeHFFW8AAAAJ&hl=en]. Dr. Wang is ranked #1 among 100,000 scientists worldwide across all fields in 2019, as #5 in the entire career scientific impacts! The ranking was made based on six citation metrics (total citations; Hirsch h-index; coauthorship-adjusted Schreiber hm-index; number of citations to papers as single author; number of citations to papers as single or first author; and number of citations to papers as single, first, or last author) (https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3000384; https://data.mendeley.com/datasets/btchxktzyw/2 ). Microsoft Academic: https://academic.microsoft.com/authors/192562407  over 1M scientists published in the Materials Science field in the world; of those 1M, Wang is #1 in Salience, #1 in Citations and #1 in H index. Wang is ranked #14 in Google scholar public profiles across all fields (http://www.webometrics.info/en/hlargerthan100).

He has delivered over 1000 plenaries, keynotes, invited and seminar talks at international and national conferences as well as universities and research institutes worldwide.

Student training. He has supervised over 160 postdoctoral fellows and visiting scientists, 53 PhD students and 10 MS student. These young scientists trained by him are now working in government, industry and academia. Among those he has supervised, 10 of them are faculty in US research universities, 10 are faculty in Taiwan, and over 80 are faculty in China, 4 in Korea and 1 in Canada, and 4 in Europe. His students have received over 40 awards from Georgia Tech and professional societies in the U.S., for best paper/poster presentation and other academic achievements.

Honors and awards: Dr. Wang has received numerous international honors and awards. They include: 2020 Celsius Lecture Laureate, Uppsala University, Sweden; 2019 Albert Einstein World Award of Science; 2019 Diels-Planck lecture award; 2018 ENI award in Energy Frontiers (the “Nobel prize” for energy); American Chemical Soc. Publication most prolific author (2017); Global Nanoenergy Prize (2017), The NANOSMAT Society, UK (2017); Distinguished Research Award, Pan Wen Yuan foundation (2017); Outstanding Achievement in Research Innovation award, Georgia Tech (2016); Distinguished Scientist Award from (US) Southeastern Universities Research Association (2016); Thomas Router Citation Laureate in Physics (2015); World Technology Award (Materials) (2014); Distinguished Professor Award (Highest faculty honor at Georgia Tech) (2014); NANOSMAT prize (United Kingdom) (2014); China International Science and Technology Collaboration Award, China, (2014); The James C. McGroddy Prize in New Materials from American Physical Society (2014); ACS Nano Lectureship (2013); Edward Orton Memorial Lecture Award, American Ceramic Society (2012); MRS Medal from Materials Research Soci. (2011); Dow Lecture, Northwestern University (2011); Hubei Province Bianzhong award (2009); Purdy award, American Ceramic Society (2009); John M. Cowley Distinguished Lecture, Arizona State University (2012); Lee Hsun Lecture Award, Institute of Metal Research, China (2006); NanoTech Briefs, Top50 award (2005); Sigma Xi sustain research awards, Georgia Tech (2005); Georgia Tech faculty outstanding research author award (2004); S.T. Li Prize for Distinguished Achievement in Science and Technology (2001); Outstanding Research Author Award, Georgia Tech (2000); Burton Medal, Microscopy Soc. of America (1999); Outstanding Oversea Young Scientists award from NSF China (1998); NSF CAREER (1998).

Dr. Wang was elected as a foreign member of the Chinese Academy of Sciences in 2009, member of European Academy of Sciences in 2002, academician of Academia of Sinica (Taiwan) 2018; International fellow of Canadian Academy of Engineering 2019; fellow of American Physical Society in 2005, fellow of AAAS in 2006, fellow of Materials Research Society in 2008, fellow of Microscopy Society of America in 2010, fellow of the World Innovation Foundation in 2002, fellow of Royal Society of Chemistry, and fellow of World Technology Network 2014. He is an honorable professor of over 10 universities in China and Europe.

Dr. Wang is the founding editor and chief editor of an international journal Nano Energy, which now has an impact factor of 16.6.

Dr. Wang’s breakthrough researches in the last 15 years have been featured by over 50 media world wide including CNN, BBC, FOX News, New York Times, Washington Post, Reuters, NPR radio, Time Magazine, National Geography Magazine, Discovery Magazine, New Scientists, and Scientific America. Dr. Wang is the #25 in the list of the world’s greatest scientists (http://superstarsofscience.com/scientists). Recent news reports are:

• Wang interviewed by CNN for his research in self-charging power pack being among the top 10 breakthroughs in 2012 by Physics World: http://www.cnn.com/video/#/video/tech/2012/12/29/intv-clancy-battery-breakthrough.cnn
• Reuters: http://news.yahoo.com/video/researchers-tap-power-motion-energy-013803650.html
• Georgia Tech: http://www.news.gatech.edu/2013/12/07/harvesting-electricity-triboelectric-generators-capture-wasted-power

Video lectures on nanogenerators and piezotroncis (6 lectures in English):

• https://www.youtube.com/playlist?list=PLTuWsF3h2oXgDpK5DTDSrtuFin6ALExe6

Video Lecture on the physics origin of nanogenerators – starting from Maxwell’s displacement current

• https://www.youtube.com/watch?v=6snAYTROUa4

Video lectures on nanogenerators and piezotroncis (7 lectures in Chinese):

• i.youku.com/nanogenerator
• https://www.youtube.com/playlist?list=PLtSxO1llzi4odq6ulrneFzCQ1S90CN9uh

Scientific contributions:

Pioneered the field of nanogenrators and self-powered sensors

1. Wang invented the piezoelectric nanogenerators and initiated the field of nanoenergy. Developing novel technologies for wireless nanodevices and nanosystems are of critical importance for in-situ, real-time and implantable biosensors, environmental science, personal electronics and national security. It is highly desired for wireless devices to be self-powered without using battery; otherwise 90% of internet of things would be impossible. A groundbreaking research by Wang in 2006 is the invention of the piezoelectric nanogenerators for self-powered nanodevices (Science, 312, (2006) 242; >3800 citation). He demonstrated an innovative approach for effectively converting mechanical energy into electric energy by piezoelectric zinc oxide nanowire arrays. This research opens up the area of nanoenergy, a field that uses nanomaterials and nanodevices for high efficient harvesting of energy from ambient environment, which is now a focal area of research for applications in sensor networks, mobile electronics and internet of things. This research was chosen as the world top 10 most outstanding discovery in science by the Chinese Academy of Sciences. Wang was featured by Science Watch in Dec. 2008 issue for his pioneer work in nanogenerator.

2. Wang pioneered the original idea of self-powered systems. Wang developed the first microfiber-nanowire hybrid nanogenerator (Science 316 (2007) 102, citation 850; Nature 451 (2008) 809-813, >510 citation; Nature Nanotechnology 4 (2009) 34), establishing the basis of using textile fibers for harvesting mechanical energy. The principle and technology demonstrated converts mechanical movement energy (such as body movement, muscle contractions, blood pressure), vibration energy (such as acoustic/ultrasonic wave), and hydraulic energy (such as flow of body fluid, blood flow, contraction of blood vessel) into electric energy that may be sufficient for self-powering nanodevices and nanosystems. Wang has made ground-breaking progress in scale up the output of the nanogenerators through three-dimensional integration (Nano Letters, 10 (2010) 5025; Nano Letters, 10 (2010) 3151), clearly demonstrating its outstanding potential for powering sensors and personal electronics. The prototype technology established by the nanogenerator sets a platform for developing self-powering nanosystems with important applications in implantable in-vivo biosensors, wireless and remote sensors, nanorobotics, MEMS and sonic wave detection (Scientific American, January issue (2008) 82). The nanogenerator is selected by New Scientist as the top 10 most potential technologies in the coming 30 years, which will be as important as the invention of cell phone, is among the top 20 featured nanotechnologies by Discovery Magazine in 2010, and is the top 10 scientific discoveries by Physics World in 2012. The fiber based nanogenerator was selected as the top 10 most important emerging technologies in 2008 by the British Physics World, MIT Technology Review, and Beijing Daily newspaper.

3. Wang invented triboelectric nanogenerator for internet of things. The principle of electromagnetic generator (EMG) that coverts mechanical energy into electricity was first introduced by Faraday in 1831, which is most efficiently at high frequency (>10-60 Hz). As for low frequency mechanical triggering (<1-5 Hz) in our living environment with random amplitude, EMG is inapplicable for harvesting such energy owing to extreme low output. Therefore, our energy system was established only by using high-quality, regulated energy that has a high operation frequency, because EMG is the only technology available for converting mechanical energy in the last 180 years. However, as the world is advancing into the era of internet of things and artificial intelligence, distributed power sources are desperately needed. In 2011, Wang has made a discovery of utilizing the conjunction of triboelectrification effect and electrostatic induction for electricity generation using organic thin film materials. The triboelectric nanogenerator (TENG) is a simple, low cost and effective approach for power generation using human motion, which is fabricated by stacking two polymer sheets made of materials having distinctly different triboelectric characteristics, with metal films deposited on the top and bottom of the assembled structure. Later, Wang has systematically invented the modes and theories for the TENG to meet a variety of needs. TENG has been demonstrated to exhibit an unprecedented conversion efficiency of 50-85%, an area power density of 500 W/m² (Nature Communication, 5 (2014) 3456; Nano Letters, 12 (2012) 3109; Nano Letters, 12 (2012) 4960; Nano Letters, 12 (2012) 6339; Nano Letters, 13 (2013) 847; Adv. Mater. 26 (2014) 3788). TENGs have the revolutionary applications for harvesting energy from human activities, rotating tires, mechanical vibration and more, with great applications in self-powered systems for personal electronics, environmental monitoring, medical science and even large-scale power. Therefore, he is referred to as the father of nanogenerator. US based IDTechEx predited that TENG will have multi-billion $ of marked in a broad range of fields (https://www.idtechex.com/en/research-report/triboelectric-energy-harvesting-and-sensing-teng-2020-2040/720 )

4. Wang developed triboelectric nanogenerator as a new energy technology for potentially large-scale blue energy. Wang invented the four working modes of the TENG, using which it becomes technologically feasible to harvest energy from the tide and waves in ocean, which is unrealistic using the traditional generators. By constructing a unit of TENG in the size of a baseball that gives an output power of 1-10 mW as driven by water wave energy, connecting and integrating many such units into a “fishing net” structure (Faraday Discussions, 176 (2014) 447). His prediction shows that using the size of state of Georgia (60,000 mi²) and 10 m of depth of water, the energy harvested by TENG grid could be enough to power the world (16 TW). This type of energy is stable and has less dependence on day or night, good weather vs poor weather in comparison to solar energy, so that it has the potential to be integrated with major power grid. This research opens a new chapter in exploring the blue energy to meet the needs of large-scale power (Nature, 542 (2017) 159).

5. Wang expanded and reformulated the Maxwell’s equations as the first principle theory of nanogenerators (Materials Today, 2017). In the Maxwell’s displacement current, the main term  given by Maxwell in 1861 gave the birth of electromagnetic wave in 1886, which is the foundation of wireless communication, radar and later the information technology. Wang’s study indicates that the second term added by him in the Maxwell’s displacement current is directly related to the output electric current of the nanogenerator if the surface polarization is introduced, meaning that the nanogenerators are the applications of Maxwell’s displacement current in energy and sensors (Fig. 2), lighting the applications of Maxwell’s equation in energy and sensors (2006-). He showed that the classical electromagnetic generator is the result of time variation of magnetic field B; while the nanogenerator is the result of time variation of the surface polarization density . (Nano Energy, https://doi.org/10.1016/j.nanoen.2019.104272). More importantly, he has found that the nanogenerator has a killer application at low triggering frequency (< 5 Hz), so that it is the choice for harvesting irregular energy from our living environment, which, however, cannot be accomplished using electromagnetic generator.

6. Wang proposed the mechanism of contact-electrification for nanogenerators. Triboelectrification is the scientific base for nanogenerators. Although the contact electrification (triboelecrification) (CE) has been documented since 2600 years ago, its scientific understanding remains inconclusive, unclear and un-unified. As for solid-solid cases, Wang found that electron transfer is the dominant mechanism for CE between solid-solid pairs (Adv. Mater. 30 (2018) 1706790; Adv. Mater. 30 (2018) 1803968). Electron transfer occurs only when the interatomic distance between the two materials is shorter than the normal bonding length (typically ~0.2 nm) in the region of repulsive forces. A strong electron cloud overlap (or wave function overlap) between the two atoms/molecules in the repulsive region leads to electron transition between the atoms/molecules, owing to the reduced interatomic potential barrier. The role played by contact/friction force is to induce strong overlap between the electron clouds (or wave function in physics, bonding in chemistry). The electrostatic charges on the surfaces can be released from the surface by electron thermionic emission and/or photon excitation, so these electrostatic charges may not remain on the surface if sample temperature is higher than ~300-400 ⁰C. Wang’s study solves a science problem that has been around for 2600 years (Materials Today, 30 (2019) 34-51), and it will have huge impact on the materials design for TENG.

7. Wang revised the mechanism about the formation of the electric double layer at liquid-solid interface based on contact-electrification effect. The electron transfer model for contact-electrification could be extended to liquid-solid, liquid-gas and even liquid-liquid cases (Materials Today, 30 (2019) 34-51). As for the liquid-solid case, molecules in the liquid would have electron cloud overlap with the atoms on the solid surface at the very first contact with a virginal solid surface, and electron transfer is required in order to create the first layer of electrostatic charges on the solid surface. This step only occurs for the very first contact of the liquid with the solid. Then, ion adsorption is the second step on surface, followed by a redistribution of the ions in solution considering electrostatic interactions with the charged solid surface. The ration of electron-transfer to ion-transfer at liquid-solid interface depends on materials (Nature Commun, 2020; Adv. Mater. 2019, 1905696). In general, electron transfer due to the overlapping electron cloud under mechanical force/pressure is proposed as the dominant mechanism for initiating CE between solids, liquids and gases. Wang provides not only the first systematic understanding about the physics of CE, but also demonstrates that the triboelectric nanogenerator (TENG) is an effective method for studying the nature of CE between any materials. This newly proposed electric double layer (EDL) model at the liquid-solid interface can largely impact the interface science in chemical, electrochemistry, chemical engineering, particle separation and even cellular-level biological processes due to electron-ion interaction at liquid-solid interfaces.

Coined piezotronics and piezo-phototronics for third generation semiconductors

1. Wang first discovered the piezotronic effect and coined the field of piezotronics. Owing to the polarization of ions in a crystal that has non-central symmetry, a piezoelectric potential (piezopotential) is created in the material by applying a stress. This internal field created inside of a ZnO nanowire can effectively tune the Schottky barrier height between the nanowire and its metal contact, which can effectively tune and gate the charge carrier transport process across the interface. This is the piezotronic effect first proposed by Wang in 2007 (Advanced Materials, 19 (2007) 889), based on which piezoelectric field effect transistor, piezoelectric diode and strain gated logic operations have been developed by Wang. The electronics fabricated by using the piezopotential as a gate voltage is coined piezotronics (Science, 340 (2013) 952). The design of piezotronics fundamentally changes the design of traditional CMOS transistor in three ways: the gate electrode is eliminated so that the piezotronic transistor only has two leads; the externally applied gate voltage is replaced by an internally created piezopotential so that the device is controlled by the strain applied to the semiconductor nanowire rather than gate voltage; the transport of the charges is controlled by the contact at the drain (source)-nanowire interface rather than the channel width. Wang is also the first who demonstrated the piezotronic effect in 2D materials (Nature, 514 (2014) 470). Piezotronics has applications in human-computer interfacing, smart MEMS, nanorobotics and sensors. Piezotronics was chosen as the top 10 emerging technology in 2009 by the MIT Technology Review.

2. Wang first discovered the piezo-photonic effect, which is about the piezoelectric field induced photon emission from a semiconductor material under mechanical straining (Adv. Funct. Mater. 2008, 18 , 3553; Nano Today 2010, 5 , 540). Wang demonstrated the first mechanoluminescent ZnS:Mn nanoparticles based, self-powered pressure sensor matrix for securer signature collections by recording both the handwritten signatures and the force/pressure applied by the signees at each pixel during signing, leading to an invention of high security electronic signature system (Adv. Mater. DOI: 10.1002/adma.201405826). This large-area, flexible sensor matrix can in-situ map two-dimensional pressure distributions ranging from 0.6~50 MPa either statically or dynamically within 10 ms, with a spatial resolution of 100m (254 dpi). Utilizing strain-induced piezoelectric polarization charges to tune the band structure and facilitate the detrapping of electrons within ZnS:Mn nanoparticles. This device is applicable to real-time pressure mapping, smart sensor networks, high-level security systems, human-machine interfaces and artificial skins.

3. Wang first discovered the piezo-phototronic effect. 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. The presence of polarization charges at an interface can largely tune the local band structure as well as shift the charge depletion zone at a pn junction, which can be effectively used to enhance the separation or recombination of charge carriers at the junction as excited by photon. This is the piezo-phototronic effect first introduced by Wang in 2009 for tuning and controlling optoelectronic processes by strain induced piezopotential. Using this effect, his team has demonstrated individual-nanowire light-emitting-diode (NW-LED) based pressure/force sensor arrays for mapping strain at an unprecedented resolution of 2.7 μm and density of 6350 dpi (Nature Photonics, 7 (2013) 752-758), high sensitive UV sensors (Adv. Mater., 24 (2012) 1410), largely enhancing LED efficiency (Nano Letters, 11 (2011) 4012; Nano Letters, 13 (2013) 607), and high performance solar cells (Nano Letters, 12 (2012) 3302). Piezo-phototronic effect is a newly found physics effect, which has a broad range of applications in optimizing the performance of optoelectronic devices.

4. Wang discovered oxide nanobelts (Science, 209 (2001) 1947; > 5000 citation). The nanobelts are a new class of one-dimensional nanostructures denoting a wide range of semiconducting oxides with cations of different valence states and materials of distinct crystallographic structures. This landmark paper is among the list of the top 30 most influential papers published in Science in the last 10 years, the top 10 most cited paper in materials science in last decade. The rational approach outlined in this work has subsequently served to nucleate a large body of studies by other researchers worldwide. As a result, ZnO is the most exciting type of one-dimensional nanostructures for oxides that holds equal importance to Si nanowires and carbon nanotubes. Wang has been the world leader in studying of ZnO nanostructures.

5. Wang first proposed the growth processes of novel oxide nanostructures. Owing to the positive and negative ionic charges on the zinc- and oxygen-terminated ZnO basal planes, respectively, a spontaneous polarization normal to the nanobelt surface is induced. As a result, helical nanosprings/nanocoils are formed by rolling up single crystalline nanobelts and nanorings (Science, 303 (2004) 1348; > 1000 citation; Science, 309 (2005) 1700; >550 citation). These are the first papers that described the spontaneous polarization-induced novel nanostructures and they open a new direction of research for studying piezoelectric properties at nano-scale.