Sustainable Energy Technologies Department
"Advances in Ultra-High Energy Resolution STEM-EELS"
Presented by Tracy C. Lovejoy, Nion R&D
Wednesday, September 26, 2018, 2:00 pm — Bldg. 734, Room 201
The capabilities of scanning transmission electron microscopes (STEMs) have advanced very significantly in the last two decades. The first major advance was the successful implementation of electron-optical aberration correction, which allowed the STEMs to reach direct sub-angstrom resolution in 2002 . This improvement made the imaging and spectroscopy of single atoms straightforward. A very recent major development has been the improvement of energy resolution of EELS due to the introduction of a new generation of monochromators and ultra-stable electron spectrometers. The Ultra-High Energy Resolution Monochromated EELS-STEM (U-HERMES™) system developed by Nion combines a dispersing-undispersing ground-potential monochromator , a bright cold-field-emission gun, an advanced aberration corrector, and a new EEL spectrometer. The latest version of the system allows 5 meV energy resolution EELS and has achieved 1.07 Å spatial resolution at the sample at 30kV when monochromating, and it greatly extends the capabilities of vibrational spectroscopy in the EM, introduced 4 years ago . U-HERMES™ has so far been used for: damage-free identification of different bonds including hydrogen bonds in guanine ; probing atomic vibrations at surfaces and edges of nano-objects with nm-level spatial resolution ; achieving sub-nm spatial resolution in images obtained with dark-field EELS vibrational signals ; nanoscale mapping of phonon dispersion curves ; nanoscale temperature determination by electron energy gain spectroscopy ; identification of different isotopes by vibrational spectroscopy in the EM ; vibrational spectroscopy of ice; and vibrational fingerprinting of biological molecules.
Hosted by: Feng Wang
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