Secondary Electron Emission – Definition, Working, Methods, Uses & Applications

Define Secondary electron emission?

What is Secondary electron emission?

Secondary electron emission is the emission of free electrons from the metal surface, which happens when the high speed electrons or primary electrons hit the free electrons or secondary electrons in the metal.

Metals under normal temperature

Under typical temperature, some of the valence electrons gain adequate energy from the heat source and breaks the holding with the parent atom. The valence electrons that break the holding with the parent atom moves freely from one point to the next point inside the metal are called free electrons.

Free electrons have some kinetic energy. But, they don’t have adequate energy to escape from the metal. The attractive force of the nuclei resists the free electrons that attempt to escape from the metal. The free electrons in the metal need adequate energy from the external source to escape from the metal.

Metals bombarded with high speed electrons

At the point when the high-speed electrons strike the metal surface, they move their kinetic energy to the free electrons in the metals. The free electrons that acquires adequate energy will defeats the strong attractive force of the nuclei and escapes from the metal.

The high speed electrons that strike the free electrons in the metal are called primary electrons though the free electrons emitted from the metal surface are called secondary electrons. We are emitting the secondary electrons from the metal surface. Thus, the most common way of emitting the secondary electrons from the metal surface is called secondary emanation.

Note: Secondary electron emission depends on the number of primary electrons and energy of primary electrons

Number of primary electrons

At the point when huge number of fast or high-energy electrons strikes the free electrons in the metal, enormous number of free electrons acquires sufficient energy and bounces into the vacuum. Then again, when modest number of high speed or high-energy electrons strikes the free electrons in the metal, modest number of free electrons acquires sufficient energy and bounces into the vacuum.

Energy of primary electrons

The minimum energy given by the primary electrons to emit the secondary electrons from the metal is called threshold energy.

The secondary electrons are emitted from the metal surface, when they acquires energy that is equivalent to or greater than the threshold energy.

If the energy given by the primary electrons is equivalent to or greater than the threshold energy, metal beginnings emitting the free electrons. Then again, if the energy given by the primary electrons is less than the threshold energy, metal don’t emit the free electrons.

Uses of secondary electron emission

  • Secondary electron emission is used in the image intensifier and photomultiplier tubes.

Secondary electron emissive materials

  • Commonly used electron emissive materials include alkali antimonite, lead oxide, magnesium oxide, and gallium phosphide.

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