Applications of electronically controlled illumination in the conventional transmission electron microscope.

A device used to produce electronic cone illumination in an analog fashion in the conventional transmission electron microscope has been applied to a number of materials problems which require special diffraction conditions not readily achieved in the microscope's normal operating mode. The device manipulates the primary beam tilt to produce a variety of virtual condenser aperture conditions, and hence electron diffraction patterns can be recorded which reflect the manner in which the direct beam is tilted during the exposure of a micrograph. For single crystalline material, the device provides an improvement over convergent-beam electron diffraction for systematic row reflections and allows direct observation of dynamical beam interactions. It has also been applied to imaging defects in thin crystalline films which would often be obscured under normal microscope conditions. The device allows the imaging of polycrystalline material and the selection of given diffraction orders to determine the orientation of crystallites in a large field of view. It can also modify amorphous patterns to extend the information contained in dark-field images beyond normal tilted-beam dark-field imaging. Control of the incident beam can be accomplished digitally for more varied beam manipulation requirements. A few cases of manipulation of diffraction patterns will be considered.