Research Assistant Professor, Northwestern University
2006-2007
Academic Professional Associate, University of Georgia
2001-2006
Postdoctoral Research Associate, Arizona State University
1999-2001
Humboldt fellowship, Juelich Research Center, Juelich, Germany
1998-1999
Postdoctoral Researcher, Ecole des Mines de Nancy, Nancy, France
1993-1998
Ph.D., Beijing Laboratory of Electron Microscopy, Chinese Academy of Sciences, Beijing, China; and the Department of Materials Science and Engineering, Dalian University of Technology, Dalian, China
Dr. Wu got his Ph.D. in the department of materials science and engineering, Dalian University of Technology, while the most of the experiments were conducted at Beijing Laboratory of Electron Microscope (from 1993-1998, under supervision of Prof. K.H. Kuo). His Ph.D. project was to study structure of quasicrystals and their crystalline approximants by means of transmission electron microscopy. In 1998, He took his first postdoctoral position at the Ecole des Mines de Nancy in France, working with Prof. J.M. Dubois on the deformed surface of quasicrystals. From 1999-2001, he worked at Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (http://www.er-c.org/centre.htm) at Juelich Germany, supported by Homboldt foundation and hosted by Prof. K. Urban. He worked on structure of oxides thin films interfaces by means of high electron microscopy. In 2001, he moved to Arizona State University and joined Prof. John Spence's group working on quantitative electron diffraction, methods to solve phase problem for electron diffraction, convergent electron diffraction and electron diffractive imaging. In 2006-2007, He took an Academic Professional Associate at the university of Georgia with the duties of facility maintenance, users traning, teaching and research. In the summer 2007, he moved to the Northwestern university working with Prof. Dravid. The main research topics are electron diffraction, diffractive imaging and cryo-TEM.
Research Objective(s) and Approach
Diffractive imaging of nanoparticles
Development of new algorithm to solve phase problem of electron diffraction: modified iterative algorithm combined the Oszlnáyi and Süto charge-flipping and Fienup's error-reduction to reconstruct the nano-structure.
Reconstruct ion of the atomic-resolution complex image (exit-face wavefunction) of nano-particles consisting of multiple domains from the combination of their electron microdiffraction patterns and high-resolution electron images. The method has the advantage that the reconstructed exit-face wave function is free of the aberrations of the objective lens normally used in the electron microscope, while resolution is extended to limited only by thermal vibration and noise in recording the diffraction pattern.
Results
Developed a novel algorithm to solve structure of nanocrystals from their powder diffraction pattern.
Reconstruction of electron exit-wave function of nano-particles by combining the HREM images and nano-diffraction patterns.
Future Directions
3-Dimensional electron microscopy at atomic resolution
Cryo-TEM for macromolecular and biological materials.
Solving complex structure by using quantitative electron diffraction and synchrotron X-ray diffraction.
References and Publications
He, Y.P., Wu, J.S. & Zhao Y.P. (2007): Designing catalytic nanomotors by dynamic shadowing growth. Nano Lett. 7, 1369-1375.
Wu, J.S., Leinenweber, K, Spence, J.C.H. & O'Keeffe, M. (2006): Ab initio phasing of X-ray powder diffraction patterns by charge flipping. Nature Materials 5, 647-652.
Wu, J.S. and Spence, J.C.H. (2005): Reconstruction of complex single-particle images using the charge-flipping algorithm. Acta Cryst. A61, 194-200.
Wu, J.S., Weierstall, U., Spence, J.C.H. and Koch, C.T. (2004): Iterative phase retrieval without support. Opt. Lett. 29, 2737-2739.
Wu, J.S. and Spence J.C.H. (2004): Electron diffraction of thin-film pentacene, J. Appl. Cryst., 37, 78-81.
Group Leader
