This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.

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Figure 4555 shows the schematic diagram of an SEM system with a thermionic electron gun. The schematic illustration is a simplistic drawing, but the real electron optics is far more complicated. The purpose of the condenser lens system in the SEM is to deliver electrons from the first crossover to the specimen plane in a small-diameter, high-intensity beam. SEMs with thermionic electron guns have two condenser lenses. The positions of BSE (backscattered electron) and SE (secondary electron) detectors can be different depending on different applications. Refer to BSE and SE detectors.

Figure 4555. Schematic diagram of an SEM system with a thermionic electron gun.