3. Instrument

A scanning electron microscope consists of the following components (figure 1 ):

• an electron column, comprising an electron gun, a number of electromagnetic lenses ("condensers"), a number of electrical alignment and adjustment coils, and an electron beam scanning device. This column is maintained under vacuum at a minimum level of 10 ^–3 Pa. In conventional microscopes (SEM-W), the necessary vacuum is obtained by a primary pump (vane or scroll) coupled with a secondary pumping system (oil diffusion pump, or more frequently turbo-molecular pump). More powerful FEG-SEMs require ion pumping at the electron gun;

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