My research interest lies in understanding the roles of various static and the dynamic forms of matters that lead to key functionalities in the interdisciplinary areas between physics, chemistry, and materials science. I regard the methodology development as a necessary part to advance these scientific goals and have dedicated a significant part of my research career in developing new tools, specifically molecular imaging techniques 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
on 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 redistribution 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
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.
The new development made at MSU includes an ultrafast electron nanocrystallography
system for studying interfaces and nano-materials, and more recently
an rf-enabled high-brightness electron microscope for studying complex
materials and nano-film solution phase chemical and biological
processes. With a proximity-coupled electron optical system,
dynamical pulse compression, femtosecond laser pulse shaping, and nanoscaled sample manipulation and preparation,
enhanced versatility and resolutions are being implemented to examine
complex dynamical patterns of atoms and charges, triggered by ultrafast optical, thermal and electronic initiations. The ongoing efforts include studying phase
transitions, collective phenomena and correlation effects in complex
solids, hot electron dynamics at interfaces, and
processes that are extremely far-from-equilibrium. 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
can be 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
Recent Invited Talks
- "Quantum phase transitions and hidden states visualized by femtosecond optical doping and femtosecond electron imaging and spectroscopy", The Non-Equilibrium Quantum Dynamics in Complex Materials Workshop, Ames Lab, Dec. 11-12, 2014.
- “Bottom-Up View from an Ultrafast Electron Microscope: Thinking and Building Science Cases from Molecular Perspectives”, Oakland University, Colloquium, November 6, 2014.
- “Bottom-Up View from an Ultrafast Electron Microscope: Thinking and Building Science Cases from Molecular Perspectives”, MSU Colloquium , October 29, 2014.
- "The perspectives of femtosecond imaging and spectroscopy of complex materials using electrons", The Ultrafast Nonlinear Imaging and Spectroscopy II Conference, San Diego, CA, August 17 – 21, 2014.
- "Optical exploration of hidden phases in correlated electron materials visualized by femtosecond electron crystallography ", The 5th International Conference on Photoinduced Phase Transitions and Cooperative Phenomena PIPT5, Bled, Slovenia, June 8 - 13, 2014.
- "Ultrafast structural dynamics of materials and macromolecules: the interplay between photons, electrons, and ions ", The Workshop on Applications of Highly Charged Ions (HCI App), NSCL, East Lansing, May 22-23, 2014.
- "Ultrafast insulator-metal switching in strongly correlated transition metal compounds", The Physics at the Falls: Structural and Electronic Instabilities in Oxide Nanostructures Workshop, Buffalo, NY, May 20-23, 2014.
- "Ultrafast Science: Capability Overview", DOE: Future of Electron Scattering & Diffraction Workshop, Rockville, Maryland, Feb. 25-26, 2014.
- “Metal-to-insulator transitions from the perspectives of ultrafast pump-probe techniques”, MSU CMP Seminar, October 14, 2013.
- "Development of ultrafast electron diffraction and microscopy for physical, chemical, and functional imaging of nanomaterials", The Symposium on Chemistry at the Space-Time Limit in 246th National Meeting of the American Chemical Society, Indianapolis, Sep. 11, 2013.
- "Nanoparticle dynamics studied by ultrafast electron crystallography", The Symposium on Nanoscale Materials Modification by Photon, Ion and Electron beams II, JSAP-MRS Joint Symposia, Kyoto, Japan, Sep. 19, 2013.
- “How electrons dance with the ionic lattice to engage insulator-metal transition in correlated solids ?”, CMP Seminar, National High Magnetic Field Laboratory, Aug. 22, 2013.
- "Material transformations induced by intensive laser pulse irradiation investigated by ultrafast electron diffraction", The 1st Workshop on Materials in Extreme Environments – MatX, MSU, May 13, 2013.
- “Probing nonequilibrium electron-phonon dynamics in Mott insulator and charge-density waves using ultrafast electron crystallography”, Physics Colloquium, Waynes State University, Detroit, Jan. 31, 2013.
- "Ultrafast meets ultrasmall: The prospects of nanoscale researches with ultrafast crystallography and microscopy using bright femotosecond electron source", SLAC Accelerator Seminar, SLAC, Menlo Park, Jan 24, 2013.
- "Applications of ultrafast electron diffraction: Ultrafast meets ultrasmall?", Workshop on Ultrafast Electron Sources for Diffraction and Microscopy Applications, UCLA, Dec. 12, 2012.
- "Four dimensional ultrafast electron nanocrystallography", International Conference of Ultrafast Structural Dynamics, Research in Optical Sciences Congress, Berlin, Germany, March 19, 2012.
Recent Selected Publications
T-R.T. Han, F. Zhou, C.D. Malliakas, P.M. Duxbury, S.D. Mahanti, M.G. Kanatzidis, and C-Y. Ruan, Exploration of metastability and hidden phases in correlated electron crystals visualized by femtosecond optical doping and electron crystallography, Science Advances 1, e1400173 (2015).
J. Portman, H. Zhang, Z. Tao, K. Makino, M. Berz, P.M. Duxbury, and C.-Y. Ruan, Computational and experimental characterizations of high-brightness beams for femtosecond electron imaging and spectroscopy, Appl. Phys. Lett.
103, 253115 (2013).
Z. Tao, T.-R. T. Han, S.D. Mahanti, P.M. Duxbury, F. Yuan,
C.-Y. Ruan, K. Wang, J. Wu, Decoupling of Structural and Electronic Phase Transitions in VO2. Phys. Rev. Lett. 109, 166406 (2012).
T.-R. T. Han, Z. Tao, S.D. Mahanti, K. Chang, C.-Y. Ruan, C.D. Malliakas, M. G. Kanatzidis, Structural dynamics of two-dimensional charge-density waves in CeTe3 investigated by ultrafast electron crystallography, Phys. Rev. B 86, 075145 (2012).
K. Chang, R.A. Murdick, Z. Tao, T.-R. T. Han, C.-Y. Ruan, Ultrafast electron diffractive voltammetry: General formalism and applications. (Review)
Mod. Phys. Lett. B 25, 2099 (2011).
C.-Y. Ruan, Y. Murooka, R.K. Raman, R.A. Murdick, R.
J. Worhatch, A. Pell, The development and applications of
ultrafast electron nanocrystallography". (Review)Micros. Microanal. 15,
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).
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).
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).
C.-Y. Ruan, V.A. Lobastov, V. Franco, S. Chen, A.H. Zewail, Ultrafast electron crystallography of Interfacial Water. Science (304), 5667 (2004).
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.
(Review) Helvetica Chimica Acta (86) 1763 (2003).
Physical Review Focus, "Diamonds
J.M. Thomas, Ultrafast electron crystallography: The dawn of a new era,
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 43, 2606 (2004).
Y. Zubavicus, M. Grunze, New insights into the structure of water with ultrafast probes,
SCIENCE 304, 5673 (2004).