Welcome to the Scanning Transmission Electron Microscopy (STEM) Group

The Scanning Transmission Electron Microscopy (STEM) Group of the Materials Science and Technology Division, ORNL, currently operates four aberration-corrected STEMs, a Nion UltraSTEM (presently operating at 100 kV, to be upgraded with a Nion 200 kV cold field emission source in the future) and three VG Microscopes STEMs, a 300 kV HB603U, a 100 kV HB501UX and a 100 kV HB 601. The UltraSTEM is equipped with a 5th order Nion [link to website] aberration-corrector, the VG microscopes with 3rd order correctors. 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, chemical and nanosciences. 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.

The principal technical contact for discussing potential projects in the STEM Group is Dr. Stephen J. Pennycook, Group Leader; tel. (865) 574-5504, e-mail pennycooksj@ornl.gov.