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Summary of Z.L. Wang’s Accomplishments
http://www.nanoscience.gatech.edu/zlwang
Dr. Z.L. Wang received his Ph.D in Physics from Arizona State University in 1987, and he is a now a Regents’
Professor, COE Distinguished Professor and Director, Center for Nanostructure Characterization (CNC), at
Georgia Tech. 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).
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LEADERSHIP
Under Dr. Wang's leadership and extremely hard work, the Georgia Tech Electron Microscopy Center was
established in 1999. This Center not only links numerous research programs and groups on campus, but also is
becoming a center for education and collaboration. This Center has been extensively developed and expanded to
include 15 major research equipment, and it is now becomes a Center for Nanostructure Characterization and
Fabrication (CNCF). Dr. Wang is the founding Director for the Center on Nanoscience and Nanotechnology at
Georgia Tech, which is playing the most crucial role in organizing GT and other universities for national
competition on nanotechnology initiatives launched by federal government. Dr. Wang is also very active in
initiating and driving the join research, education and degree programs between Georgia Tech and Peking
University (China). He is the Chair of the Department of Advanced Materials and Nanotechnology at Peking
University.
HONOR AND AWARDS
Dr. Wang has received the 1999 Burton Medal from Microscopy Society of America, 1998 NSF CAREER award,
1998 China-NSF Oversea Outstanding Young Scientists Award, 2000 and 2005 Georgia Tech outstanding
research award, 2005 Sigma Xi Sustained Research Award, 2001 S.T. Li prize for outstanding contribution in
nanotechnology, and has also received three best paper awards. His research papers have been cited for over
19,000 times. The h-index of his publications is 67. He is the world’s top 25 most cited authors in nanotechnology
for the last decade (ISI). He has also received research fellowships from Univ. Cambridge, US Department of
Energy and ORISE. He is a member of the editorial boards of over 10 major journals. He is an honorable and
guest professor of over 10 universities. Two symposiums (May 7, 2003; Oct. 12, 2005) organized by the
University of Pierre & Marie Curie (Paris) and sponsored by the L'Institut Universitaire de France (IUF) in the
honor of Prof. Wang for his outstanding contribution in nanotechnology. Dr. Wang is a fellow of APS, fellow of
AAAS, and a fellow of the World Innovation Foundation.
RESEARCH GRANTS AND FUNDING
Dr. Wang is PI or co-PI on numerous proposals. He has received funding from NSF, DOE, DARPA, NASA, China
NSF and industry. The total value of contracts awarded in which he has either been PI, co-PI or an investigator is
$18M over the past 13 years at Georgia Tech.
COMMUNITY SERVICE
Dr. Wang is actively participating in the activities and services in scientific professional societies. He has served
as chair and co-chair for 14 local, national and international conferences organized 10 symposia and chaired
over 15 sessions in national and international conferences. He has served as a member for the review panel for
NSF, NASA and DOE and advisory board for numerous centers on nanotechnology. He is a referee for numerous
prestigious journals, such as Nature, Science, Physical Review Letters, Nature Materials and J. American
Chemical Soc.
RESEARCH
Dr. Wang has filed 15 patents, has authored and co-authored 4 textbooks, edited 20 books/proceedings,
authored 43 book chapters, over 500 peer reviewed publications and 120 other conference proceeding
publications, and has given over 450 invited presentations, keynote speaks, distinguished lectures and seminars,
and 150 contributed presentations at national and international conferences. Dr. Wang's research covers a wide
range of technical interests in materials science ranging from theoretical to experimental research on
fundamental as well as applied problems. He has been invited to give a series of lectures in China, France,
Switzerland, Mexico, Germany, Japan and US. His recent research focuses on nanomaterials for biomedical
applications, nanomaterials for MEMS and NEMS technology and integration of nanotechnology with
biotechnology.His primary research accomplishments are in the following fields.
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1. Invented nanowire piezo-electric generators for self-powered nanodevices (Science, 312, (2006) 242;
Science 316 (2007) 102-104)
Developing novel technologies for wireless nanodevices and nanosystems are of critical importance for in-situ,
real-time and implantable biosensing, biomedical monitoring and biodetection. An implanted wireless biosensor
requires a power source, which may be provided directly or indirectly by charging of a battery. It is highly desired
for wireless devices and even required for implanted biomedical devices to be self-powered without using battery.
Therefore, it is essential to explore innovative nanotechnologies for converting mechanical energy, vibration
energy, and hydraulic energy into electric energy that will be used to power nanodevices without using battery. A
groundbreaking research by Dr. Wang in 2006 is the invention of the Piezo-Electric Generators for Self-Powered
Nanodevices. He demonstrated an innovative approach for converting nano-scale mechanical energy into electric
energy by piezoelectric zinc oxide nanowire (NW) arrays. By deflecting the aligned NWs using a conductive
atomic force microscopy (AFM) tip in contact mode, the energy that was first created by the deflection force and
later converted into electricity by piezoelectric effect has been measured for demonstrating nano-scale power
generator. The operation mechanism of the electric generator relies on the unique coupling of piezoelectric and
semiconducting dual properties of ZnO as well as the elegant rectifying function of the Schottky barrier formed
between the metal tip and the NW. The efficiency of the NW based piezo-electric power generator is ~ 17-30%.
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Wang has also invented the first DC nanogenerators driven by ultrasonic wave (Science 316 (2007) 102-104).
The nanogenerator is composed of aligned ZnO NWs and a zigzag top electrode, which is a novel, adaptable,
mobile and cost-effective approach with a great potential in nanotechnology. The NWs can be grown on solid
substrates or polymer substrates as flexible power generators. The principle and technology demonstrated here
have the potential of converting mechanical movement energy (such as body movement, muscle stretching,
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. The prototype technology established by the DC nanogenerator set a platform
for developing self-powering nanosystems with important applications in implantable in-vivo biosensing, wireless
and remote sensing, nanorobotics, MEMS, sonic wave detection and more.
2. Polar surface induced novel growth processes and mechanism of oxide nanostructures and
electromechanical coupled devices (Science 303 (2004) 1348; Science, 309 (2005) 170)
The wurtzite structure family has a few important members, such as ZnO, GaN, AlN, ZnS and CdSe, which are
important materials for applications in optoelectronics, lasing and piezoelectricity. The two important
characteristics of the wurtzite structure are the non-central symmetry and the polar surfaces. The structure of
ZnO, for example, can be described as a number of alternating planes composed of tetrahedrally coordinated O2and Zn2+ ions, stacked alternatively along the c-axis. The oppositely charged ions produce positively charged
(0001)-Zn and negatively charged (000-1)-O polar surfaces, resulting in a normal dipole moment and
spontaneous polarization along the c-axis. This polar surface gives rise a few interesting growth features.
The breakthroughs by Wang’s group in 2004 is the success of first piezoelectric nanobelts and nanorings
(Science 303 (2004) 1348) for applications as sensors, transducers and actuators in micro- and nanoelectromechanical systems. 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. The mechanism for the
helical growth is suggested for the first time to be a consequence of minimizing the total energy contributed by
spontaneous polarization and elasticity. The nanobelts have widths of 10-60 nanometers and thickness of 5-20
nanometers, and they are free of dislocations. The polar surface dominated ZnO nanobelts and helical
nanosprings are likely to be an ideal system for understanding piezoelectricity and polarization induced
ferroelectricity at nano-scale.
The major discovery made by Wang’s group in 2005 was the discovery of a new rigid helical structure of zinc
oxide consisting of a superlattice-structured nanobelt (Science, 309 (2005) 170), which was formed
spontaneously in a vapor-solid growth process. Starting from a single-crystal stiff-nanoribbon dominated by the
c-plane polar-surfaces, an abrupt structural transformation into the superlattice-structured nanobelt led to the
formation of a uniform nanohelix due to a rigid lattice rotation or twisting. The nanohelix was made of two types of
alternating and periodically distributed long crystal stripes, which were oriented with their c-axes perpendicular to
each other. The nanohelix terminated by transforming into a single-crystal nanobelt dominated by nonpolar
surfaces. The nanohelix could be manipulated, and its elastic properties were measured, which suggests
possible uses in electromechanically-coupled sensors, transducers and resonators.
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3. Nanobelts of semiconducting oxides: from materials, to properties and to devices (Science, 209 (2001)
1947)
Recently a series of binary semiconducting oxide nanobelts (or nanoribbons), such as ZnO, In2O3, Ga2O3, CdO
and PbO2 and SnO2 have been successfully synthesized in Dr. Wang’s laboratory by simply evaporating the
source compound (Science, 209 (2001) 1947). The as-synthesized oxide nanobelts are pure, structurally
uniform, single crystalline and most of them free from defects and dislocations; they have a rectangular-like
cross-section with typical widths of 30-300 nm, width-to-thickness ratios of 5-10 and lengths of up to a few
millimeters. The belt-like morphology appears to be a unique and common structural characteristic for the family
of semiconducting oxides with cations of different valence states and materials of distinct crystallographic
structures. The nanobelts are an ideal system for fully understanding dimensionally confined transport
phenomena in functional oxides and building functional devices along individual nanobelts. This discovery has
been reported by over 20 media and professional society journals. The paper (Science, 209 (2001) 1947) has
been the the second most cited paper in chemistry according to Science Watch (ISI). Dr. Wang’s group has
recently applied the nanobelt materials to make the world’s first field effect transistor, single wire sensors and
nano-size cantilevers for scanning probe microscopy. This invention has been highlighted by Nature as research
news (Nature 423 (2003) 134).
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4. In-situ nanomeasurements on the mechanical, electrical and field emission properties of nanotubes,
nanoblets and nanowires
Characterizing the physical properties of carbon nanotubes is limited not only by the purity of the specimen but
also by the size distribution of the nanotubes. Traditional measurements relies on scanning probe microscopy.
Based on transmission electron microscopy, Dr. Wang and his colleagues have developed a series of unique
techniques for measuring the mechanical, electrical and field emission properties of individual nanotubes. The insitu TEM technique developed by him is not only an imaging tool that allows a direct observation of the crystal
and surface structures of nanocrystals, but also an in-situ apparatus that can be effectively used to carry nanoscale measurements (Science, 283 (1999) 1513). Using a custom-built specimen stage, the quantum
conductance of a carbon nanotube has been observed in-situ in TEM, confirming the ballistic conductance and
no-heat dissipation across a defect-free nanotube first published by de Heer’s group (Science, 280 (1998) 1744).
A nanobalance technique and a novel approach toward nanomechanics have been (Phys. Rev. Letts. 85 (2000)
622). Their discoveries have attracted a great deal attention of the medium and professional community.
5. Dynamics of shape-controlled nanocrystals and nanocrystals self-assembly (Science 272 (1996) 1924;
Science 316 (2007) 732-735; Nature, 420 (2002) 395)
Nanosize colloidal platinum (Pt) particles are potentially important in industrial catalysis. The selectivity and
activities of Pt particles strongly depend on their sizes and shapes. Much effort has been devoted to synthesize
smaller size Pt particles for increasing the surface to volume atom ratio. Searching for techniques which can
produce monoshape Pt particles has attracted a lot of interest because the chemical activities of Pt between
{100} and {111} facets have distinct differences. Dr. Wang's collaboration with Prof. M.A. El-Sayed had led to a
new technique based on colloidal chemistry for controlling the shapes and sizes of Pt particles at room
temperature [Science 272 (1996) 1924]. Following this development, the growth mechanism of shape controlled
Pt nanocrystals was studied using in-situ transmission electron microscopy. The shape transformation and
melting behavior of the Pt nanocrystals were revealed for the first time.
Wang and his collaborators have developed a novel electrochemical approach for successfully synthesizing
tetrahexahedral (THH) Pt nanocrystals at high purity (>90%), which are a very unsual shape as defined by
twenty-four facets of high-index planes ~{730} and vicinity planes such as {210} and {310} with a high density of
surface steps and dangling bonds (Science 316 (2007) 732-735). The THH nanocrystals have demonstrated
much enhanced catalytic performance of up to 400% per unit surface area than that of the Pt nanospheres or
commercial catalyst. The success of synthesizing THH Pt nanocrystals by a square-wave electrochemical
method starting from Pt nanospheres on amorphous carbon substrate presents a new approach for controlling
the stability of nanocrystals defined by high-energy surfaces that have important applications in catalysis and fuel
cells. This study demonstrates a novel approach for designing unusual and well-controlled particle shapes of
noble metals, and it could be extended to other metals such as palladium. This research was selected as the
2007 highlights by ACS.
The physical and chemical functional specificity of nanoparticles suggest that they are ideal building blocks for
two- and three-dimensional cluster self-assembled superlattice structures in which the particles behave as welldefined molecular matter and they are arranged with long-range translational and orientational order. In 1996, Dr.
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Wang collaborating with the research group of Prof. R.L. Whetten obtained concrete experimental results
demonstrating success of forming such superlattice structures using Au nanocrystals. Following this, Dr. Wang
has concentrated on the preparation of size and shape controlled Ag and CoO nanocrystals. His group was the
first to study the role of particle shape in determining the crystallography of 3-D assembling of nanocrystals and
the structural stability and molecular bonding between nanocrystals. Dr. Wang's recent research has been
focused on self-assembly of magnetic nanocrystals for ultrahigh density data storage media. His paper (Phys.
Rev. Lett., 79 (No. 13) (1997) 2570-2573) won the 1998 Georgia Tech Sigma Xi Best Paper Award in a campus
wide competition.
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Dr. Wang and his collaborators at IBM (H. Zeng and S. Sun) and University of Texas Arlington (J.P. Liu) have
developed a process that incorporates FePt and Fe3O4 particles with different mass and radii ratio into binary
assemblies (Nature, 420 (2002) 395-398). Controlled annealing results in metallic composites with magnetically
hard and soft phase exchange coupled. The approach offers precise engineering control on the dimension of the
components and their nanoscale interactions in the composite, rendering isotropic FePt-based nanocomposites
with energy product value of 20 MGOe that exceeds the theoretical limit of 13 MGOe for single phase FePt.
6. Functional materials: structure evolution and structure analysis
Dr. Wang's research in high temperature superconductor and functional materials began in 1991 while he was
working with Dr. D. Kroeger at ORNL. His interests lie in structure-property relationships. His most notable
contribution in this field is a book co-authored with Dr. Z.C. Kang, entitled "Functional and Smart Materials structural evolution and structure analysis" published by Plenum Press, New York, 1998. This book is unique and
is different from the existing books in a way that it emphasizes the intrinsic connection among crystal systems.
"The authors consider the atomic scale crystal structure and chemistry of oxides with physical and chemical
properties that are sensitive to changes in the environment such as temperature, pressure, electric or magnetic
fields, pH, and optical wavelength. They explain relationships among different structures and explore approaches
to characterizing and synthesizing these important components for electronic devices" (Science, Vol. 281 (July
10, 1998) p. 181). "... this book is a unique, cutting-edge text on smart materials ... it is recommended as an
adjunct to device design books used for engineers as well as scientists during the development of smart devices
and structures" (Physics Today , Nov. 1998, p. 70). It "brings together, for the first time, the fundamentals of
atomic scale crystal structure and chemistry.... and it is a cutting-edge text at the forefront of modern materials
evolution", Professor David Williams, Professor and Chair of Materials Science and Engineering at Lehigh
University. This book also " Fills a gap left in the field", and it is "a basic reference in the domain of oxides of
functional and smart materials", Professor C. Boulesteix, Universite Aix-Marseille, France. This book is
"extremely valuable for materials scientists working on functional oxide materials, and it is an interesting textbook
for teaching graduate students", Professor M. Rühle, Director of the Electron Microscopy Lab., Max Planck
Institute for Metallurgy, Germany.
Very recently, Dr. Wang and his collaborator have developed a few systems of Ce, Pr and Tb oxide based
materials for producing hydrogen at low temperatures. An innovative approach has been developed to produce
hydrogen through a two step process using the lattice oxygen released from the oxide and it has three major
advantages in comparison to existing methods: low temperature operation by swing temperature between 300
and 700 oC; no catalyst is required and reduced cost; eliminated catalyst deactivation problem. This could be a
breakthrough for fuel cell technology and hydrogen based green-economy.
7. Dynamic electron diffraction due to thermal diffuse scattering
Electron diffraction theory in a periodically structured crystal is well established, but the theory for inelastic
electron diffraction and scattering from a partially disordered system, such as systems containing point defects, is
not well understood. In this field, Dr. Wang has proposed several theoretical approaches for solving the
problems. Prof. J.M. Cowley and he were the first to show that thermal diffuse scattering is the mechanism of
forming the Z-contrast image in scanning transmission electron microscopy. Subsequently, Dr. Wang has
proposed a dynamic theory that can be applied to quantify electron diffraction data from a partially disordered
systems containing point defects with short-range order. Recently, he has mathematically proven the equivalence
between the quantum mechanical phonon excitation theory and the "frozen" lattice semi-classical model of
electron diffraction, which filled a major gap in the field.
In his text book entitled, "Elastic and Inelastic Scattering in Electron Diffraction and Imaging" (Plenum Press, New
York, 1995), Dr. Wang has critically summarized all the existing theories on electron diffraction and imaging
developed over the past 40 years. This book serves as the fundamental reference book for understanding image
contrast in the energy-filtered TEM and diffraction patterns, a future direction of TEM, and has been praised by
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many prominent scientists. Some quotations from the reviewers include: "a noteworthy achievement and a
valuable contribution to the literature", American Scientist, 1996; "This is an excellent and comprehensive book ...
If you are interested in electron scattering by crystals, in the theory underlying the interpretation of electron
micrographs ... you should buy this book. It is comprehensive and right up to date", J. Microscopy, 1996; "I can
compliment him (Dr. Wang) for the huge effort he has accomplished to make all of them classified and accessible
to us. And I am convinced that this book is quite important for anyone wishing to cleverly use the new TEMs with
energy filtering devices", Professor C. Colliex, Editor-in-Chief, Journal of Microscopy Microanalysis Microstructure
and Director of Atomic Clusters Laboratory, CNRS, France, 1996.
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8. Reflection electron microscopy and reflection electron energy-loss spectroscopy for surface analysis
Dr. Wang's research in Reflection Electron Microscopy (REM) and Reflection Electron Energy-Loss Spectroscopy
(REELS) started when he was a graduate student under the supervision of Prof. J.M. Cowley. He was the first
one to propose and demonstrate the REELS technique. This technique has been used for monitoring layer-bylayer growth in MBE. Dr. Wang thoroughly investigated the resonance phenomenon of electrons in the process of
surface reflection, establishing the basis for understanding the image contrast in REM. He succeeded in
observing the in-situ surface step movement on alumina surfaces at 1400 oC. In recognition of this research, he
was invited by Cambridge University Press to author a book on "Reflected Electron Microscopy And
Spectroscopy For Surface Analysis", Cambridge University Press, 1996. This is the only book on RHEED and
REM. Since RHEED is a widely used technique for monitoring surface growth in molecular beam epitaxy (MBE),
this book serves as the basic text for guiding the readers in interpreting RHEED data. "For those with a TEM
background it (this book) represents, perhaps, the definitive text for reflection methods", Analysis, 1997. "It
contains a lot of illustrations and excellent images and a good balance of theory and experimental techniques... it
is a book that any materials science or physics libraries should be holding", MRS Bulletin, Oct., 1998.
9. Valence-loss excitation spectroscopy for studying of supported small metal particles, carbon tubes
and spheres
In characterizing nanoparticles, it is desirable to measure the electronic property of a single particle, such as a
single carbon sphere or tube. This difficult task can only be achieved using a fine electron probe with a diameter
smaller than 1 nm. Traditionally, all of the theoretical models before 1986 were developed for free particles, which
assume that the particle is a suspended object without any contact with other objects. In practice, nanocrystals
must be supported by a substrate. Thus, a key question is, how is the electronic property of the particle affected
by the substrate? By introducing a semi-embedded particle model, Dr. Wang and Prof. Cowley were the first ones
who solved the problem theoretically and proved experimentally. In 1995, Dr. Wang was invited to write a review
article on the subject, and this is still the most comprehensive paper on the subject. In 1997, he was invited to
give one month special lectures at the Swiss Federal Institute of Technology (EPFL at Lausanne, Switzerland).
During his visit, he also conducted collaborative research on valence excitation of carbon spheres, carbon tubes
and single wall carbon tubes. Several publications resulted from this trip.
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