PURPOSE: To observe a diffracted diagram and to measure the intensity of the diffracted spot at the original S/N ratio processed by a signal, by providing a visual field iris capable of being moved on the picture almost vertical to diffracted corpuscular beam and making the area of an opening part variable.
CONSTITUTION: A specimen 3 is irradiated with electron beam 2 from an electron gun 1. A diffracted figure is observed on a fluorescent plate 7 by widening the opening part 5 of a visual field iris 4 to pass a plurality of reflected diffracted electron beams therethrough. When the intensity of a diffracted spot is measured, the opening part 5 of the visual field iris 4 is moved to the position of specific reflected diffracted electron beam and, thereafter, the opening part 5 is throttled to a proper area and the reflected diffracted electron beam 6 is converted to light by the fluorescent plate 7 to be detected by a photomultiplier tube. Therefore, the quantum noise originally posseded by diffracted electron beam becomes the same to the detected one and an S/N ratio is not lowered.
ISU TOSHIRO
WATANABE AKISADA
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