|Quantitative Electron Microscopy and Spectroscopy at Atomic-Scale |
|K. Andre Mkhoyan, Cornell University|
10:00 AM, CCR 201
Scanning transmission electron microscopes (STEM) equipped with electron energy loss spectrometers (EELS) are powerful experimental tools to study the new phenomena in nano-scale materials with atomic-level precision. With current advances in sub-Å resolution, it is now possible to image local crystal structures of materials where dramatically different atoms are separated from each other at distances of less than 1 Å. In one case, implementation of annular dark field (ADF) imaging in an aberration-corrected STEM allowed direct imaging of atomic columns of light nitrogen atoms in close proximity to columns of aluminum in wurtzite aluminum nitride and, as a result, provided direct determination of the local lattice polarity. In another case, by employing EELS capabilities of STEM an unusual complete recovery of extensive electron-beam-induced damage in CaO-Al2O3-SiO2 glass was discovered. Nano-scale EELS measurements showed that the glass may return to its original compositional and structural state. EELS measurements also provided detail understanding of the atomic processes that taking place during damage and recovery. The combination of ADF imaging and energy loss spectroscopy, in the case of III-V nitride heterostructures, allowed in-depth atomic-scale characterization of the system and, therefore, provided better quantification of the critical electronic properties of these systems.