Selected Microarea Electron Diffraction Technique in High Voltage Electron Microscopy and Some Metallurgical Applications

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Abstract
In view of the practical uses of the selected microarea electron diffraction technique in high voltage electron microscopy, errors in correspondence between the selected and contributed areas for diffraction have been observed with a 650 kV electron microscope provided with a five‐stage imaging lens system. Under optimum conditions, the observed errors were the same order as the theoretical ones due to the spherical aberration of the objective lens. That is, the contributed areas for diffraction were displaced relative to the selected ones by about 300 Å for diffraction angles the order of 2×10−2 rad which correspond to reflections from the planes of ∼0.6 Å spacing. Thus, it was concluded that a specimen area about 300 Å in diameter can be selected significantly so far as the diffractions of angles larger than 2×10−2 rad are ignored. The technique of selected microarea electron diffraction has been applied to the study of crystallography of small precipitates in 18% Ni maraging steel and the diffraction effects due to a dislocation line in a pure iron.