SIMES Seminar: Byung-Kuk Yoo

Date(s) - May 15 2018
11:00 AM - 12:00 PM

Shasta Room, Bldg. 40, Room 361


Ultrafast Electron Microscopy: From Materials Science to Biology

Dr. Byung-Kuk Yoo

California Institute of Technology

Unlike the conventional transmission electron microscope (TEM), femtosecond time-resolved ultrafast electron microscope (UEM) has a time resolution that is 10 orders of magnitude faster than that of TEM. Instead of using thermionic electrons in TEM, laser-driven single pulses of electrons allow various modes of detection such as imaging, diffraction, and spectroscopy, all with unprecedented spatiotemporal resolution; sub-nanometer and femtosecond. In this presentation, I will discuss the development of 4D UEM and summarize the up-to-date accomplishments that represent its broad capability in chemical, materials, and biological sciences. Among them, I will present the critical role of 4D Ultrafast EM in investigating the crystallization dynamics of matter as a first example. It could observe in space and time the ephemeral nucleation of liquid-to-crystal phase transitions of titanium dioxide by probing the serial electron diffraction snapshots. Interestingly, it was found that the temporal behavior of crystallization exhibits unique two-step dynamics, with a robust plateau that extends over a microsecond. Such behavior reflects the presence of intermediate state(s) that are the precursor of the ordered crystal state. Secondly, I will introduce how this technique provides a dynamic probe for catalytic active site in photocatalytic materials and visualizes the femtosecond atomic movement at the titanium active center in a single-site photocatalyst. These findings contribute fundamental insights for developing advanced photocatalysts and suggest broad ranges of applications.