Abstract
The VG Microscopes 100 kV and 300 kV scanning transmission electron
microscopes at Oak Ridge National Laboratory were equipped with Nion aberration
correctors several years ago. This chapter reviews our experience with these correctors,
specifically, the reduction in probe size by more than a factor of two and the associated
benefits for materials research, which extend far beyond improved resolution. A smaller,
brighter probe brings enhanced image contrast and signal to noise ratio, making it
possible to image light atom columns in materials such as oxide perovskites. It vastly
increases the sensitivity to single atoms, both for imaging and electron energy loss
spectroscopy. In addition, aberration correction greatly improves the collection efficiency
for bright field phase contrast imaging, allowing simultaneous, aberration-corrected, Zcontrast
and phase contrast imaging. Finally, the larger probe-forming aperture gives a
reduced depth of field, giving a depth resolution less than the thickness of a typical
specimen. It becomes possible to focus directly on features at different depths in the
specimen, and three-dimensional information can be extracted with single atom
sensitivity. In conjunction with density functional and elasticity theory, these advances
provide a new level of insight into the atomistic origins of materials properties. Several
examples are discussed that illustrate the potential for applications including the detection
of orbital occupation stripes and interface stacking in complex oxides, the mechanism for
improved critical currents in Ca-doped grain boundaries in high-Tc superconductors, the
segregation of rare earth dopants in Si3N4 grain boundaries, the quantitative analysis of
strain-induced growth phenomena in semiconductor quantum wells, the determination of
the three-dimensional distribution of stray Hf atoms in a high dielectric constant device
structure, and the origin of the remarkable catalytic activity of Au nanoparticles
