| 摘要 |
There is disclosed a field emission electron gun comprising a field emission tip, an extraction electrode for producing an electric field that extracts electrons from the tip, and an accelerating electrode for accelerating the electrons extracted by the extraction electrode. The extraction electrode is inclined to a plane perpendicular to the optical axis of the beam of the electrons and shaped like an inverted cone. The surface of the accelerating electrode which faces the extraction electrode is inclined in the same manner as the extraction electrode. A recess that faces the extraction electrode is formed in the center of the accelerating electrode. The ratio of the voltage V0 applied to the accelerating electrode to the voltage V1 applied to the extraction electrode, i.e., V0/V1, can be varied over a wide range while maintaining the virtual source within the virtual image region.
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