Department of Physics and Astronomy
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 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 the 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 the 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 photophysical 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 the 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 of reactions.
The recent progress of ultrafast electron crystallography (UEC) takes advantage 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 chemical and biological processes employing MEMS-based environmental cells. 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 perception.
UED on gas-phase chemical dynamics
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).
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).
UED on surfaces
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), 974 (2004).
UED on nanoparticles
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).
R. K. Raman, R. A. Murdick, R. J. Worhatch, Y. Murooka, S. D. Mahanti, T-R. T. Han, and C-Y. Ruan, Electronically driven fragmentation of silver nanocrystals revealed by ultrafast electron crystallography, Phys. Rev. Lett. 104, 123401 (2010)
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 article). Micros. Microanal. 15, 323 (2009).
Metastable and hidden states
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).
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).
Z. Tao, F. Zhou, T.–R. T. Han, D. Torres, T. Wang, N. Sepulveda, K. Chang, M. Young R. R. Lunt, C.-Y. Ruan, The nature of photoinduced phase transition and metastable states in vanadium dioxide, Scientific Reports 6, 38514 (2016).
Charge-density wave systems
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).
F. Zhou, J. Williams, S. Sun, S.D. Malliakas, M.G. Kanatzidis, A.F. Kemper, C.-Y. Ruan. Nonequilibrium dynamics of spontaneous symmetry breaking into a hidden state of charge-density wave. Nature communications 12, 566 (2021).
Development of ultrafast electron diffraction and microscopy
F. Zhou, J. Williams, C.-Y. Ruan, Femtosecond electron spectroscopy in an electron microscope with high-brightness beams. Chem. Phys. Lett. 683, 488 (2017).
J. Williams, F. Zhou, T. Sun, Z. Tao, K. Chang, K. Makino, M. Berz, P.M. Duxbury, and C.-Y. Ruan, Active control of bright electron beams with RF optics for femtosecond microscopy, Struc. Dyn. 4 (A tribute to Ahmed Zewail), 044035 (2017).
S. Sun, X. Sun, D. Bartles, E. Wozniak, J. Williams, P. Zhang, C.-Y. Ruan. Direct imaging of plasma waves using ultrafast electron microscopy. Struc. Dyn. 7, 064301 (2020)
X. Sun, S. Sun, and C.-Y. Ruan. Toward nonthermal control of excited quantum materials: Framework and investigations by ultrafast electron scattering and imaging (Review). Comptes Rendus. Physique, Online first (2021), pp. 1-59 (2021).
Recent Group Invited Presentations
- Ultrafast Dynamics and Metastability and Ultrafast Bandgap Photonics Symposium, Crete, Greece, 2022. (Postponed due to Covid-19)
- 10TH Nonequilibrium Quantum Workshop, Krvavec, Slovenia, December 12 - 16, 2021,
- Hosting the 7th International Conference on Photoinduced Phase Transitions and Cooperative Phenomena (PIPT7), Nov. 8-18, 2021. Online: https://pipt7.org.
- KITP Conference: Non-Equilibrium Universality in Many-Body Physics, Santa Barbara, California, Sep. 27-30, 2021,
- Microscopy and Microanalysis (M&M 2020) Meeting, Milwaukee, Wisconsin, August 2-6, 2020.
- Gordon Research Conference on Ultrafast Phenomena in Cooperative Systems, Lucca (Barga), Italy, February 2-7, 2020.
- “Advances in femtosecond electron imaging and spectroscopy with high-brightness beams”, Fudan University Physics Colloquium, Dec 17, 2019.
- “Advances in femtosecond electron imaging and spectroscopy with high-brightness beams”, Center for bright beams, UCLA, November 13, 2019.
- 14th Femtochemistry Conference (FEMTO 14) - Dynamics of the Complexity in Chemistry, Biology, and Physics, Shanghai, China, July 28 to August 2, 2019.
- 5th ICUSD (International Conference on Ultrafast Structural Dynamics), Daejeon, South Korea, June 25-28, 2019.
- 4th International Conference on Femtosecond Electron Imaging and Spectroscopy, Lincoln, Nebraska, May 12-16, 2019.
- Ultrafast Electron Microscopy Workshop, Argonne National Laboratory, April 25-26, 2019.
- The conferences of ultrafast Metastabilities 2019 and Ultrafast Bandgap Photonics 2019, Georgetown, April 15-17, 2019.
- “Imaging thermal and quantum phase transition with femtosecond coherent electron beams”, Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Jan 17, 2019.
- Conference in Memory of the Nobel Laureate Ahmed H. Zewail, Institute of Advanced Studies in Nanyang Technological University, Singapore, May 20-24, 2018.
- “Advances in femtosecond electron imaging and spectroscopy with high-brightness beams: From molecular photochemistry to nanocale material transformations”, Seminar at Physical Measurement Laboratory Division, NIST-Maryland. Nov. 16, 2018.
- “Advances in femtosecond electron imaging and spectroscopy with high-brightness beams: From molecular photochemistry to nanocale material transformations”, Condensed Matter and Optics Seminar, Vanderbilt, Oct. 5, 2018.
- “Imaging macroscopic thermal and quantum phase transitions with femtosecond coherent electron beams”, Vanderbilt Physics Colloquium, Oct 4, 2018.
- “Building the next generation ultrafast electron microscope”, Photon Science Seminar, SLAC, Jan. 17, 2018.
- 2018 SPIE Defense and Commercial Sensing Conference, Orlando, Florida, April 14-19, 2018.
- "Probing the hidden and metastable states in complex materials using femtosecond coherent electron pulses", International Workshop on Ultrafast Dynamics and Metastability, Georgetown, Nov. 12-15, 2017.
- "Femtosecond electron imaging and spectroscopy: From molecular photochemistry to nanocale material transformations", Physical Chemistry Seminar, Waynes State University, Detroit, Oct. 11, 2017.
- "Advances in femtosecond imaging and spectroscopy with high-brightness beams", 16th Frontiers of Electron Microscopy in Materials Science International Conference, Johannesburg, South Africa, September 10 - 15, 2017.
- "Visualization of photoinduced phase transitions: From molecular systems to many-body problems", Femto 13, Cancun, Mexico, Aug. 12-17, 2017.
- "Imaging dynamical scaling responses of photoinduced phase transitions by femtosecond coherent electron beams", 6th International Conference on Photoinduced Phase Transition (PIPT6), Sendai, Japan, June 4-9, 2017.
- "Advances in femtosecond imaging and spectroscopy with high-brightness beams", 3rd International Conference on Femtosecond Electron Imaging and Spectroscopy, Shanghai, China, June 12-14, 2017.
- " Imaging Hidden Orders in Phase Transitions", Baffalo University, Physics Colloquium, May 4, 2017.
- "In situ imaging of complex phase transitions in functional transition metal compounds at ultrafast timescales", 2017 MRS Spring Meeting, Phoenix, April 17-21, 2017.
- "Ultrafast imaging beyond "Uncertainty Principle": Unveiling hidden orders in phase transitions", MSU Physics Colloquium, Sep. 29, 2016.
- "Photoinduced phase transitions and metastable states from the perspectives of nonequilibrium dynamics", International Research School: Electronic States and Phases Induced by Electric or Optical Impacts IMPACT 2016, Cargese, France, Aug. 23-Sep. 2, 2016.
- “Imaging light-induced metastable phases and hidden states in complex electronic materials with femtosecond coherent electron beams”, Institute of Atomic Aand Molecular Sciences, Tapei, Taiwan, March 8, 2016.
- "Principles and applications of ultrafast electron imaging with high-brightness beams", Workshop on Imaging with Femtosecond Electron and X-ray Pulses (IFEXS), Trieste, Italy Feb. 1-3, 2016.
- "Imaging with photons and electrons", The United Nation International Year of Light Symposium, Lansing, Oct. 26, 2015.
- "High-brightness beams for ultrafast microdiffraction and imaging", Femtosecond Electron Imaging and Spectroscopy II, Lansing, May 6-9, 2015.
- “Making molecular movies: Development of high-brightness ultrafast electron microscope”, Center for Complex Quantum Systems, The University of Texas at Austin, April 10, 2015.
- “Exploration and manipulation of interaction-driven phase transitions in correlated electron crystals using femtosecond optical doping”, Center for Complex Quantum Systems, The University of Texas at Austin, April 9, 2015.