IBS-CMSD Colloquium_Dr. Byung-Kuk Yoo(California Institute of Technology)(Oct. 25)
IBS Center for Molecular Spectroscopy and Dynamics
COLLOQUIUM |
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SPEAKER
Dr. Byung-Kuk Yoo (California
Institute of Technology)
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TITLE
Ultrafast electron microscopy: applications in
chemical and materials sciences
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ABSTRACT
Unlike
the conventional transmission electron microscope (TEM), 4D ultrafast electron
microscopy (4D UEM) has a time resolution that is 10 orders of magnitude better
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-do-date accomplishments that
represent its broad capability in materials and related fields. First, I will
demonstrate the critical role of 4D UEM in investigating the crystallization
dynamics of matter. It could observe in space and time the ephemeral nucleation
of liquid-to-crystal phase transitions of titanium dioxide by probing the
transient electron diffraction intensities. Interestingly, it is 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 structure(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.
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DATE AND VENUE
October 25, 2017
(Wednesday, 5:00 - 6:00 pm)
Seminar Room 116, KU R&D Center
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LANGUAGE
Korean
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INVITED BY
Prof. Kyungwon Kwak
* If you want to have a dinner with Dr. Byung-Kuk Yo, please contact to Prof. Kyungwon Kwak (kkwak@korea.ac.kr).