Secondary Electron Emission

When the surface of a solid is bombarded with charged particles of sufficient kinetic energy, emission of electrons by the solid may be observed. This phenomenon of secondary electron emission was discovered by Austin and Starke in 1902 in a study of the reflection of electrons by metals; they observed that under certain circumstances more electrons were emitted than were incident, indicating that the bombarding primary electrons liberate electrons from the solid.1 Unless otherwise stated, it will be assumed in the present chapter that the bombarding particles are electrons. However, emission of electrons may also result from bombardment with heavy charged particles such as ions.2 The theory of secondary emission under electron bombardment is completely different from that under ion bombardment. The reason is that in the former case the bombarding particles penetrate into the solid, thus producing a bulk effect; in the latter case, however, one deals essentially with a surface effect. For a survey of the field of secondary emission we refer to the bibliography at the end of this chapter. Some of the basic principles involved in the secondary emission process will now be discussed.

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