Aberration-corrected STEM and ultra-high energy resolution EELS
Aberration-corrected STEM and ultra-high energy resolution EELS
- Date: May 6, 2019
- Time: 11:00 AM - 12:00 PM (Local Time Germany)
- Speaker: Dr. Ondrej L. Krivanek
- Nion R&D, 11515 NE 118th St., Kirkland, WA 98034, USA Department of Physics, Arizona State University, Tempe, Arizona, USA
- Location: Max-Planck-Institut für Eisenforschung GmbH
- Room: Large Conference Room No. 203
- Host: Prof. Gerhard Dehm
Electron microscopy has advanced very significantly in the last two decades. Electron-optical correction of aberrations, which we introduced for the scanning transmission electron microscope (STEM) in 1997, has allowed STEMs to reach sub-Å resolution from 2002 on. It has led to new STEM capabilities, such as atomic-resolution elemental mapping, and determining the type of single atoms by electron energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDXS). More recently, we have focused on Ultra-High Energy Resolution EELS (UHERE). We have developed a monochromator and a spectrometer that use multipolar optics similar to the optics of aberration correctors, plus several stabilization methods, and we have reached <5 meV energy resolution at 30 keV primary energy. This has opened up a new field: vibrational spectroscopy in the electron microscope. When collecting large-angle scattering events, vibrational spectroscopy can lead to sub-nm spatial resolution, and when collecting small-angle scattering angle events, it can produce EEL spectra with the electron beam positioned tens of nm away from the probed area. The second geometry has led to a powerful new technique: aloof vibrational analysis of materials, which avoids significant radiation damage. Even more recently, we have focused on combining the analytical techniques with in-situ sample treatment. Our progress includes cooling the sample to liquid N2 temperature in a side-entry holder capable of reaching better than 1 Å resolution. My talk will review these developments, and illustrate them by application examples.