The emission of electrons from cold metals by electric fields. In order to build up sufficiently large electric fields, the metal is usually shaped to a sharp needle point. Field emission is an example of the tunnel effect in quantum mechanics, with an electron in the metal being in a potential barrier. In field emission the probability of tunnelling, which can be calculated using the semiclassical approximation, is related to the work function of the metal. An important application of field emission is the field-emission microscope.
A type of emission in which the presence of a large external accelerating electric field reduces the potential barrier at the surface of the emitter (see Schottky effect) and allows electrons to escape from the surface. The potential barrier is shown in the diagram as the work done, W, for an electron to escape.
The distortion of the potential barrier at sufficiently large values of the field results in an effective narrowing of the barrier and allows the tunnel effect to operate: electrons with energies around the Fermi energy EF (see energy bands) may also be emitted. The current density j has been shown to vary with the electric field E as:
where C and D are approximately constant. The very intense fields required are of the order of 1010 volts per metre and are usually only obtained at sharp points on the emitter surface.
Field emission
- dimensions
- dimension stone
- dimension(topology)
- dimer
- dimethylbenzenes
- dimethylformamide
- dimethylglyoxime
- dimethyl sulphoxide
- Dimetrodon angelensis
- dimictic lake
- diminished radix complement
- diminishing increment sort
- diminishing marginal product
- diminishing marginal utility
- diminishing returns, law of
- diminishing returns to scale
- Dimitrov, Georgi (1882–1949)
- DIMM
- dimorphism
- dim spot
- dimyarian
- Dinantian
- DIN connector
- Dingaan (1843)
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