The Scanning Transmission Electron Microscopy (STEM) Group of the Materials Science and Technology Division, ORNL, currently operates four aberration-corrected STEMs, a Nion UltraSTEM200, operating at 200 kV, and three VG Microscopes STEMs, a 300 kV HB603U, a 100 kV HB501UX and a 100 kV HB601. The UltraSTEM is equipped with a 5th order Nion aberration-corrector, and a Gatan Enfinium dual EELS system, the VG microscopes with 3rd order Nion correctors, Gatan Enfina EELS systems. The HB601 is also equipped with a cathodoluminescence system.
Research goals are now possible that were unthinkable just a few years ago: 3-D images of individual nanostructures, imaging and lattice location of individual impurity atoms within materials and on their surfaces, identification of single atoms and determination of their chemical valence. This program aims to push STEM imaging and spectroscopy to the ultimate spatial and spectral resolution and sensitivity, and to provide theoretical underpinning in the physics of image formation, elastic and inelastic contrast mechanisms, quantum-mechanical resolution limits, and inversion methods for image and spectral data. We apply these techniques to solve key issues in condensed matter, materials, chemistry and nanoscience. First-principles density functional theory is used extensively to complement microscopic data and has successfully bridged atomic structure to macroscopic properties in a number of cases.