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Electron Optics of a Scanning Electron Microscope

  • Ludwig Reimer
Chapter
Part of the Springer Series in Optical Sciences book series (SSOS, volume 45)

Abstract

The purpose of the electron optics of a SEM is to produce a small electron probe at the specimen by demagnifying the crossover, the smallest cross-section of the electron beam near the cathode. For the practical application of a SEM, it must be possible to vary the electron-probe size, aperture and current but this cannot, however, be done independently because these quantities are related by the gun brightness. A geometric optical theory of electron-probe formation can be employed when using a thermionic cathode but for a field-emission gun a wave-optical theory is necessary. Electron-beam deflection by transverse electrostatic and magnetic fields is incorporated for scanning the electron probe across the specimen, for tilting the direction of the incident electron beam for stereo-viewing and for recording electron channelling patterns. Deflection systems are further used for the blanking or chopping of the electron beam up to gigahertz frequencies for stroboscopic modes and time-resolved signals. Due to the large depth of focus, focusing of SEM images raises no problems but the resolution is limited by the electron-probe size and the compensation of the final lens astigmatism.

Keywords

Deflection Angle Electron Optic Spherical Aberration Probe Diameter Condenser Lens 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 1985

Authors and Affiliations

  • Ludwig Reimer
    • 1
  1. 1.Physikalisches InstitutWestfätlische Wilhelms-Univeraität MünsterMünsterFed. Rep. of Germany

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