Simultaneous observation of zone-axis pattern and ±g dark-field pattern in convergent-beam electron diffraction

A convergent-beam electron diffraction (CBED) technique to take the four patterns (whole pattern, bright-field, dark-field and ±G dark-field patterns) which are needed for crystal-point-group determination simultaneously on a film is described with ray path diagrams and obtained results. The technique enables us to obtain these patterns from a 100-nm diameter specimen area with less contamination and to set the exact Bragg angles at the centers of reflection disks. The present method Is compared with other techniques, especially with one previous technique EM. Terauchl and M. Tanaka: J. Electron Microsc., 34, 128 (1985)]. Some application results of the present technique to real crystals are demonstrated.