Measurement of vibrational spectrum of liquid using monochromated scanning transmission electron microscopy-electron energy loss spectroscopy.

Authors:
Tomohiro Miyata
Tomohiro Miyata
The University of Tokyo
Japan
Mao Fukuyama
Mao Fukuyama
Tokyo Institute of Technology
Akihide Hibara
Akihide Hibara
School of Engineering
Medford | United States
Eiji Okunishi
Eiji Okunishi
⊥EM Business Unit
Masaki Mukai
Masaki Mukai
JEOL Ltd.
Teruyasu Mizoguchi
Teruyasu Mizoguchi
The University of Tokyo
Japan

Microscopy (Oxf) 2014 Oct 11;63(5):377-82. Epub 2014 Jul 11.

Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan

Investigations on the dynamic behavior of molecules in liquids at high spatial resolution are greatly desired because localized regions, such as solid-liquid interfaces or sites of reacting molecules, have assumed increasing importance with respect to improving material performance. In application to liquids, electron energy loss spectroscopy (EELS) observed with transmission electron microscopy (TEM) is a promising analytical technique with the appropriate resolutions. In this study, we obtained EELS spectra from an ionic liquid, 1-ethyl-3-methylimidazolium bis (trifluoromethyl-sulfonyl) imide (C2mim-TFSI), chosen as the sampled liquid, using monochromated scanning TEM (STEM). The molecular vibrational spectrum and the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap of the liquid were investigated. The HOMO-LUMO gap measurement coincided with that obtained from the ultraviolet-visible spectrum. A shoulder in the spectrum observed ∼0.4 eV is believed to originate from the molecular vibration. From a separately performed infrared observation and first-principles calculations, we found that this shoulder coincided with the vibrational peak attributed to the C-H stretching vibration of the [C2mim(+)] cation. This study demonstrates that a vibrational peak for a liquid can be observed using monochromated STEM-EELS, and leads one to expect observations of chemical reactions or aids in the analysis of the dynamic behavior of molecules in liquid.

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http://dx.doi.org/10.1093/jmicro/dfu023DOI Listing
October 2014
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