March 1, 2:30pm
Tracy C. Lovejoy
|Recent Developments in Aberration-Corrected STEM|
Tracy C. Lovejoy
Recent Developments in Aberration-Corrected STEM
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). These tools are now widely applied to diverse fields including semiconductors and catalysis.
We have developed a monochromator and spectrometer that can reach <5 meV energy resolution at 30 keV primary energy. This has opened up a new field: vibrational spectroscopy in the electron microscope. Depending on the scattering geometry, this can give sub-nm spatial resolution, or produce vibrational EEL spectra with the electron beam positioned tens of nm away from the probed area, avoiding significant radiation damage.
Other recent developments include: combining 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; driving the microscope and data analysis with powerful open-source software to foster scientific transparency and collaboration; providing 4D-STEM capabilities as a standard feature; and imaging and analysis with 1 Å spatial resolution at low primary energies down to 30 kV.
This talk will review our recent developments, and illustrate them by application examples.
Dr. Tracy Lovejoy is Chief Operating Officer at Nion Co., a developer of state-of-the-art scanning transmission electron microscopes (STEMs). He earned a Ph.D. from the University of Washington in 2010 studying exotic semiconductors with STM, XPS, and various synchrotron-based spectroscopies. His main activity at Nion is pushing the limits of STEM technology, especially monochromated electron energy loss spectroscopy (EELS).