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Figure 18.1: The Electron gun

1.2. Electron–specimen interaction

The individual incident electrons of an electron beam interact with the atoms in a sample, to undergo two types of scattering-elastic and inelastic. During elastic scattering, only the trajectory changes, and the kinetic energy and velocity remain constant. However, in inelastic scattering, some incident electrons will actually ram with and displace electrons from their orbits (shells) around nuclei of atoms comprising the sample. This interaction places the atom in an excited and unstable state. This specimen interaction is what makes electron microscopy possible.