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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.
In condensed matter physics, the Nottingham effect is a surface cooling and heating mechanism that occurs during field and thermionic electron emission. The effect is named after physicist Wayne B. Nottingham who explained it in a commentary to 1940 experiments by Gertrude M. Fleming and Joseph E. Henderson. [1] [2] [3]
The scientific aspects of thermionic energy conversion primarily concern the fields of surface physics and plasma physics. The electrode surface properties determine the magnitude of electron emission current and electric potential at the electrode surfaces, and the plasma properties determine the transport of electron current from the emitter ...
Energy level diagrams for thermionic diode in forward bias configuration, used to extract all hot electrons coming out from the emitter's surface. The barrier is the vacuum near emitter surface. In order to move from the hot emitter to the vacuum, an electron's energy must exceed the emitter Fermi level by an amount
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]
Tunneling and thermionic emission are typically observed when the barrier height is low. Thermally-assisted tunneling is a "hybrid" mechanism that attempts to describe a range of simultaneous behaviours, from tunneling to thermionic emission. [10] [11]
This is called thermionic emission. The resulting cloud is negatively charged, and can be attracted to any nearby positively charged object, thus producing an electric current which passes through the vacuum. Space charge can result from a range of phenomena, but the most important are: