SCATTERING OF FAST ELECTRONS BY CRYSTALS

Electron diffraction and microscopy are among the most important techniques for studying the structures of solids. This review aims to give a comprehensive introduction to the basic principles of the scattering of fast electrons and to highlight selected applications of importance. It begins by discussing electron scattering by single atoms and describes how single atoms may be imaged. The geometry of diffraction from perfect single crystals is then considered and a simple kinematical theory which yields approximate values for diffracted intensities is given. It is shown how simple principles have been used to image monatomic steps on the surface of crystals. More accurate methods of calculating diffracted intensities are given and particular attention is paid to describing concepts often found to be difficult, for example the dispersion surface. Principles of various recent electron scattering techniques are outlined including high-voltage electron microscopy, scanning electron microscopy, convergent-beam electron diffraction and the critical voltage effect. Applications described range from measuring bonding electron charge densities to the imaging of dislocations. Finally some recent theoretical developments on the problem of imaging imperfect crystals at atomic resolution are discussed.