Zhong Lin 'ZL' Wang
Professor and Director, Center for Nanoscience and Nanotechnology;
Director of Electron Microscopy Center
Office: 163 Love Manufacturing Building
Mailing Address:
Materials Science and Engineering
Georgia Institute of Technology
Atlanta, GA 30332-0245
Phone: 404-894-8008
Fax: 404-894-9140
E-mail: zhong.wang@mse.gatech.edu

B.S.- Northwest Telecommunication Engineering Institute (currently Xidian University), China, 1982; Ph.D - Arizona State University, 1987.

Dr. Wang was elected a member of European Academy of Science in 2002, has received the 2001 S.T. Li prize for Outstanding Contribution in Nanoscience and Nanotechnology, the 2000 Georgia Tech Faculty Research Award, the 1999 Burton Medal from Microscopy Society of America, 1998 US NSF CAREER award, 1998 China-NSF Oversea Outstanding Young Scientists Award, and received two best paper awards. Dr. Wang received research fellowships from Univ. Cambridge, US Department of Energy and ORISE.

Research Interests

In-situ nanomeasurements on the mechanical, electrical and field emission properties of carbon nanotubes (1997 - present). 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 in-situ 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 nano-scale 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 (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.

Nanowire and nanobelts of semiconducting oxides: from materials, to properties and to devices (2000 - present). 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. Dr. Wang’s group has recently applied the nanobelt materials to make the world’s first field effect transistor and single wire sensors.

Dynamics of shape-controlled nanocrystals and nanocrystals self-assembly (1995 - present). 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 (June 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.

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 well-defined molecular matter and they are arranged with long-range translational and orientational order. In 1996, Dr. 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.

Very recently, Dr. Wang and his collaborators at IBM have developed a process that incorporates FePt and Fe3O4 particles with different mass and radii ratio into binary assemblies. 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. This paper is being published by Nature.

Functional materials: structure evolution and structure analysis (1991 - present). 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. An US patent has filed and a paper has been submitted to Nature.

Dynamic electron diffraction due to thermal diffuse scattering (1985 - present). 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 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.

Reflection electron microscopy and reflection electron energy-loss spectroscopy for surface analysis (1984-1996). 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-by-layer 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.

Valence-loss excitation spectroscopy for studying of supported small metal particles, carbon tubes and spheres (1983-present). 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.

 
Selected Recent Publications

Hao Zeng, Jing Li, J.-P. Liu, Zhong L. Wang, Shouheng Sun, "Exchange-coupled nanocomposites magnets by nanoparticle self-assembly," Nature 2002, 420, 395-398.

Z. W. Pan, Z. R. Dai and Z. L. Wang, "Nanobelts of semiconducting oxides," Science 2001, 291 1947-1949.

P. Poncharal, Z. L. Wang, D. Ugarte and W. A. De Heer, "Electrostatic deflections and electromechanical resonances of carbon nanotubes," Science 1999, 283 1513-1516.

S. Frank, P. Poncharal, Z. L. Wang, and W. A. De Heer, "Carbon nanotube quantum resistors," Science, 1998, 280 1744-1746.

T. S. Ahmadi, Z. L. Wang, T. C. Green, A. Henglein and M. A. El-Sayed, "Shape-controlled synthesis of colloidal platinum nanoparticles," Science 1996, 28 1924-1926.

R. P. Gao, Z. L. Wang, Z. G. Bai, W. de Heer, L. Dai and M. Gao, "Nanomechanics of aligned carbon nanotube arrays," Phys. Rev. Letts., 2000, 85 622-655.

J. S. Yin and Z. L. Wang, "Ordered self-assembling of tetrahedral oxide nanocrystals," Phys. Rev. Lett., 1997, 79 (No. 13), 2570-2573.

Z. L. Wang, "Transmission electron microscopy of shape-controlled nanocrystals and their assemblies" (Invited review article), J. Phys. Chem. B, 2000, 104(6), 1153-1175.

Z. L. Wang, "Structural analysis of self-Assembling nanocrystal superlattices," Adv. Mater. 1998, 10 13-30.