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My research emphasizes on developing new tools for real-time molecular imaging applied to the studies of complex molecules and nanometer scale materials. Atomic scale resolution in structures of complex materials has been achieved in the late 20th century through modern diffraction and microscopy. The question remains on whether we can obtain temporal resolution required to characterize the molecular motions. This is critical for the understanding of mechanisms and functions in the mesoscopic scales, particularly for those associated with complex materials and macromolecules. The electron diffractions are very useful tools in the studies of molecules, surfaces and nano-meter scale materials because of the large cross-section of electron scattering with matters (5-6 orders larger than that of X-ray). Taking advantage of this high sensitivity, my earlier work with Professor Zewail at Caltech involved combining the spatial resolution of electron diffraction with the temporal resolutions of femtosecond laser to probe the real-time dynamics of complex molecules. This so-called ultrafast electron diffraction (UED) technique employs the “pump-probe” scheme to make movies for molecular reactions. Photo-chemical and photo-physical processes such as the breaking and reforming of chemical bonds and the internal energy redistributes in complex potential energy landscape were captured by electron diffraction in ultrashort time window. The ability to determine the short-lived transition state structure on an excited energy landscape is an important step towards quantum control for reactions.
The recent progress of ultrafast electron crystallography (UEC) takes advantages of the rapidly developing atomic scale preparations of functionalized nanocrystals and assemblies on surfaces, in line with the developments for molecular scale electronics and materials for sensing and catalysis. By interfacing the UED with ultrahigh vacuum and precision sample manipulations and preparations, it is now possible to isolate the structures and dynamics of the surfaces and adsorbates from those of the lattices. This ability allows one to visualize the patterns of energy flow from lattices to the surfaces and adsorbates or vice versa. It also enables the atomic scale studies of the hydrophobic and hydrophilic interactions of interfacial water on chemically modified surfaces, as well as the phase transitions on the nanometer scale.
A new ultrafast electron nanocrystallography system is recently setup at MSU, for studying interfaces and nano-materials. With a proximity-coupled electron optical system and nanoscaled sample manipulation and preparation, we have obtained enhanced versatility in examining nanostructures and their functional transformations triggered by ultrafast optical, thermal and electronic initiations. The ongoing efforts include studying phase transformations, nanotubes and nanocavities, nanocatalysis, molecular transport and photovoltaics. To the extent necessitated by the sciences, we continue to develop techniques that enhance resolutions and enable new sciences. These efforts include
producing brighter, faster electron pulses, combining spectroscopy, local probe and diffraction to correlate structure, dynamics and property. At the bottom of the length scale for material investigations everything looks like a big molecule, and they are in many ways viewed as complex entities with unusual capabilities. In the laboratory as well as from modern sophisticated molecular dynamics simulations, we now begin to have access to the multi-scaled world of matters with atoms and molecules gradually zoomed in for our perceptions.
Publications
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R.K. Raman, Z. Tao, T-R. Han, C-Y. Ruan, "Ultrafast
imaging of photoelectron packets generated from graphite surafce",
Appl. Phys. Lett. 95, 181108 (2009).
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C-Y. Ruan, Y. Murooka, R.K. Raman, R.A. Murdick, R.
J. Worhatch, A.Pell, "The development and applications of
ultrafast electron nanocrystallography", Micros. Microanal. 15,
323 (2009). (Review)
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R.K. Raman, Y. Murooka, C-Y. Ruan, T. Yang, S. Berber, D. Tomanek, “Direct observation of optically induced transient structures in graphite using ultrafast electron crystallography”,
Phys. Rev. Lett. 101, 077401 (2008).
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R.A. Murdick, R.K. Raman, Y. Murooka, C.-Y. Ruan, “Photovoltage dynamics of the hydroxylated Si(111) surface investigated by ultrafast electron diffraction”,
Phys. Rev. B 77, 245329 (2008).
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C.-Y. Ruan, Y. Murooka, R.K. Raman, R.A. Murdick, “Dynamics of Size-Selected Gold Nanoparticles Studied by Ultrafast Electron Nanocrystallography”, Nano Lett. 7, 1290 (2007).
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C-Y. Ruan, Y. Murooka, R.K. Raman, R. Murdick, and M.A. Khasawneh, “Towards ultrafast diffraction and spectroscopy of interfaces and nanomaterials using femtosecond focused electron pulses”, Microscopy and Microanalysis 12 (Suppl.2), 150 (2006).
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C.-Y. Ruan, S.-S. Yang, A.H. Zewail, “Structures and Dynamics of Self-Assembled Surface Monolayers Observed by Ultrafast Electron Crystallography”,
JACS (2004).
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C.-Y. Ruan, V.A. Lobastov, V. Franco, S. Chen, A.H. Zewail, “Ultrafast electron crystallography of Interfacial Water”, Science (304), 974 (2004).
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V. Franco, S. Chen, C.-Y. Ruan, V.A. Lobastov, A.H. Zewail, “Ultrafast electron crystallography of surface structural dynamics with atomic-scale resolution”, Angewandte Chemie Intl. (43), 2705 (2004).
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C.-Y. Ruan, V. Franco, V.A. Lobastov, S. Chen, A.H. Zewail, “Ultrafast electron crystallography : transient structures of molecules, surfaces and phase transitions”, Proc. Natl. Acad. Sci. U.S.A. (101), 1123 (2004).
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B.M. Goodson, C.-Y. Ruan, V.A. Lobastov, R. Srinivasan, A.H. Zewail, “Ultrafast electron diffraction: complex landscapes of molecular structures in thermal and light-mediated reactions”, Chem. Phys. Lett. (374), 417 (2003).
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R. Srinivasan, V.A. Lobastov, C.-Y. Ruan, A.H. Zewail, “Ultrafast electron diffraction (UED) - A new development for the 4D determination of transient molecular structures”, HELVETICA CHIMICA ACTA (86) 1763 (2003).
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V.A. Lobastov, R. Srinivasan, F. Vigliotti, C.-Y. Ruan, J. Feenstra, S. Chen, S.T. Park, S. Xu, and A. H. Zewail, Springer Series in Ultrafast Optics IV, Eds. F. Krausz, G. Korn, P. Corkum, and I. Walmsley, 413 (2003).
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V.A. Lobastov, R. Srinivasan, B.M. Goodson, C.-Y. Ruan, J.S. Feenstra, A.H. Zewail, “Ultrafast diffraction of transient molecular structures in radiationless transitions”, J. Phys. Chem. A (105), 11159 (2001).
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H. Ihee, V. A. Lobastov, U. Gomez, B. M. Goodson, R. Srinivasan, C.-Y. Ruan, A. H. Zewail, “Direct Imaging of Transient Molecular Structures with Ultrafast Diffraction”, Science (291), 458 (2001).
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C.-Y. Ruan, V.A. Lobastov, R. Srinivasan, B.M. Goodson, H. Ihee, A.H. Zewail, “Ultrafast diffraction and structural dynamics: The nature of complex molecules far from equilibrium”, Proc. Natl. Acad. Sci. U.S.A. (98), 7117 (2001).
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C.-Y. Ruan and M. Fink, “Plasma-modulated fast electron pulsing and bunching”, J. App. Phys. (89), 654 (2001).
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V. Mastryukov, C.-Y. Ruan, and M. Fink, Zhiqiang Wang, and Ruth Pachter, “Electron diffraction studies of metal phthalocyanines, MPc, where M = Ni and Cu”, J. Mol. Struct. Sp. Iss. (556), 225 (2000).
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C.-Y. Ruan, V. Mastryukov and M. Fink, “Electron diffraction studies of metal Phthalocyanines, MPc, where M = Sn, Mg and Zn (reinvestigation)”, J. Chem. Phys. (11), 3035(1999).
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C.-Y. Ruan, and M. Fink, “Emission optics of the Steigerwald type electron gun”, Rev. Sci. Instr. (70), 4207(1999).
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C.-Y. Ruan, S. Nguyen, and M. Fink, “Optimization of spherical analyzer with finite size effects”, Rev. Sci. Instr. (70), 4213(1999).
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