High‐resolution dark‐field electron microscopy of small metal particles

A technique to study the shape of small metal particles (20 to 200 Å in diameter) is described. This consists in high‐resolution dark‐field electron microscopy using weak beams under diffraction conditions in which a large number of beams are excited. Many‐beam dynamical electron diffraction theory is used to explain the effect. Examples of application of this technique in the study of growth of thin films are presented. It is found that epitaxial gold particles growing on a NaCl substrate have square and rounded pyramids shapes which are very often truncated.