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In this regime, the combined effects of field-enhanced thermionic and field emission can be modeled by the Murphy-Good equation for thermo-field (T-F) emission. [35] At even higher fields, FN tunneling becomes the dominant electron emission mechanism, and the emitter operates in the so-called "cold field electron emission (CFE)" regime.
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. This creates an electric field of magnitude F at the
Field emission was explained by quantum tunneling of electrons in the late 1920s. This was one of the triumphs of the nascent quantum mechanics. The theory of field emission from bulk metals was proposed by Ralph H. Fowler and Lothar Wolfgang Nordheim. [1] A family of approximate equations, Fowler–Nordheim equations, is named after them.
Schottky-emitter electron source of an Electron microscope. A field emission gun (FEG) is a type of electron gun in which a sharply pointed Müller-type [clarification needed] emitter [1]: 87–128 is held at several kilovolts negative potential relative to a nearby electrode, so that there is sufficient potential gradient at the emitter surface to cause field electron emission.
Electron gun from an oscilloscope CRT Setup of an electron gun. 1. Hot cathode.2. Wehnelt cylinder.3. Anode. A direct current, electrostatic thermionic electron gun is formed from several parts: a hot cathode, which is heated to create a stream of electrons via thermionic emission; electrodes generating an electric field to focus the electron beam (such as a Wehnelt cylinder); and one or more ...
The resulting strong electric field near the cathode accelerates ions to a sufficient velocity to create free electrons from the cathode material. Another mechanism to generate free electrons from a cold metallic surface is field electron emission. It is used in some x-ray tubes, the field-electron microscope (FEM), and field-emission displays ...
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:
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 ...