INTRODUCTION

Compared to other techniques used to obtain structural information of materials, high resolution electron microscopy (HREM) has the great advantage that it yields local information about the atomic arrangements, projected along the direction of electron incidence at a resolution comparable to the interatomic distances. This enables the study of complicated structures, crystal defects, precipitates, etc. down to the atomic level. Furthermore the electronic structure can be probed by electron energy loss spectroscopy (EELS), yielding information on the local environment of the atoms in the illuminated area.

Knowledge of the atomic arrangements of surfaces and interfaces is of vital importance for the understanding of the properties. With the increasing need of the accurate determination of the atomic arrangements at non-periodic structures in materials design and control of microstructures and nanostructures, techniques that provide quantitative structural information at the sub-angstrom level will be indispensable. High-resolution electron microscopy (HREM) is by far the best technique to obtain sub-surface structural information on a local scale. X-ray and neutron diffraction can only give structural information that is averaged over a large area. This is in part because the interaction between electrons and matter is much higher than for X-rays and neutrons (about 10 ⁵ to 10 ⁷ times respectively) and in part because electrons can be focussed very easily by magnetic lenses. The local 3-D information is essential for understanding the...