Basic Principles of Electron Optics
The electron optical relations summarized in this chapter are essentially oriented toward electron microscopy. The course of the beam in a conventional transmission electron microscope is sketched in Figure 2.1. The electrons emitted from the cathode are first accelerated in a system of electrostatic lenses. The beam then enters the condenser system, which adjusts the illuminated area of the specimen. The specimen is situated somewhat above the center of the objective lens. The magnified image of the specimen is produced by the objective lens. Further magnification is achieved by additional lenses. Contrast, i.e., variation of the intensity of the electron beam image, is accomplished by scattering of the electrons by the atoms of the specimen and/or as a result of the phase shift of the electron waves in the specimen.
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