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Thermionic emission is the liberation of charged particles from a hot electrode whose thermal energy gives some particles enough kinetic energy to escape the material's surface. The particles, sometimes called thermions in early literature, are now known to be ions or electrons .
The Schottky effect or field enhanced thermionic emission is a phenomenon in condensed matter physics named after Walter H. Schottky. In electron emission devices, especially electron guns , the thermionic electron emitter will be biased negative relative to its surroundings.
Notably, the effect can be either heating or cooling of the surface emitting the electrons, depending upon the energy at which they are supplied. [4] Above the Nottingham inversion temperature, the emission energy exceeds the Fermi energy of the electron supply and the emitted electron carries more energy away from the surface than is returned by the supply of a replacement electron, and the ...
This gives the barrier a high resistance when small voltage biases are applied to it. Under large voltage bias, the electric current flowing through the barrier is essentially governed by the laws of thermionic emission, combined with the fact that the Schottky barrier is fixed relative to the metal's Fermi level. [6]
From a physical electronic viewpoint, thermionic energy conversion is the direct production of electric power from heat by thermionic electron emission. From a thermodynamic viewpoint, [1] it is the use of electron vapor as the working fluid in a power-producing cycle.
Thermionic emission In thermionic electron guns , the work function and temperature of the hot cathode are critical parameters in determining the amount of current that can be emitted. Tungsten , the common choice for vacuum tube filaments, can survive to high temperatures but its emission is somewhat limited due to its relatively high work ...
The filament is a coil of tungsten of a specified size (usual large and small). When current passes through the wire, heat is produced and causes the filament to release or burn off electrons. This is known as thermionic emission. The electrons are then compressed or focused by the focusing cup into a cloud known as a space charge.
Walter Hans Schottky (23 July 1886 – 4 March 1976) was a German physicist who played a major early role in developing the theory of electron and ion emission phenomena, [2] invented the screen-grid vacuum tube in 1915 while working at Siemens, [3] co-invented the ribbon microphone and ribbon loudspeaker along with Dr. Erwin Gerlach in 1924 [4] and later made many significant contributions in ...