What Is Thermionic Emission?

Thermionic emission means that as the temperature of a metal rises, the kinetic energy of the electrons in the metal increases, and the number of electrons whose kinetic energy exceeds the work function increases. When the temperature rises to a certain value, a large number of electrons escape from the metal. This phenomenon is called thermionic emission. Thermionic emission is widely used in radio technology. Various electron tubes and electron ray tubes use thermionic emission to generate electron beams.

Thermionic emission refers to heating under vacuum or filled with inert gas

The magnitude of the hot electron emission current density strongly depends on the properties of the material itself and the heating temperature. The temperature should not be too high during use to prevent excessive evaporation of the material ^[1]

There is a force on the metal surface that prevents the electrons from escaping. The electrons need to overcome the resistance to do work, which is called work of escape. At room temperature, the kinetic energy of only a very small number of electrons exceeds the work function, and very few electrons escape from the metal surface.

Generally, when the temperature of the metal rises above 1000K, the number of electrons whose kinetic energy exceeds the work function increases sharply, and a large number of electrons escape from the metal. This is thermionic emission. Without an external electric field, the escaped hot electrons accumulate near the metal surface and become a space charge, which will prevent the hot electrons from continuing to emit ^[2] .