Page 177 - Science at the nanoscale

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June 5, 2009
8.2. Electron Microscopy
Schematic of the magnetic field profile generated by a typical
Figure 8.7.
electromagnet used in a SEM and the focusing effect of the magnetic field
on the electron beam.
Figure 8.8. Spiral trajectory of an electron passing through the electro- 167 ch08
magnetic lens in a SEM.
spirals down the column as it passes through the electromagnetic
lens as shown in Fig. 8.8. The resultant effect is that the electron
beam becomes finely focused and can be scanned over the sample
for imaging purposes.
There are usually two such electromagnetic lenses in the SEM
system, the condenser lens and the objective lens. The condenser
lens provides the first focusing effect and guides the electrons