| 摘要 |
An electron source (1) for an electron microscope is provided with a needle-shaped electron emitter (20) and a membrane-like, completely closed extraction-electrode (22) which is arranged at a small distance from the tip (21) of the needle-shaped emitter (20), an electric voltage being applied between the emitter (20) and th extraction-electrode (22). The thickness of the extraction-electrode (22) is such that a practical fraction of the electrons incident on the membrane under the influence of the electric voltage traverses the membrane to its other side with a negligibly small loss of energy. It is thus achieved that the source can be readily aligned and that the energy spread of the emitted beam can be controlled to an arbitrarily small value by variation of the voltage. Since no high voltage is present within the emissive part of the electron source, a very compact electron source can be realised.
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