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Field emission, also known as Fowler-Nordheim tunneling, is a form of quantum tunneling in which electrons pass through a barrier in the presence of a high electric field. This phenomenon is highly dependent on both the properties of the material and the shape of the particular cathode, so that higher aspect ratios produce higher field emission currents. The current density produced by a given electric field is governed by the Fowler-Nordheim equation. Quantum tunneling is the quantum-mechanical effect of transitioning through a classically-forbidden energy state. ...
For other uses, see Electron (disambiguation). ...
In physics, the space surrounding an electric charge or in the presence of a time-varying magnetic field has a property called an electric field. ...
Diagram of a copper cathode in a Daniells cell. ...
The aspect ratio of a two-dimensional shape is the ratio of its longer dimension to its shorter dimension. ...
In electricity, current is the rate of flow of charges, usually through a metal wire or some other electrical conductor. ...
The Fowler-Nordheim equation relates current, work and electronic field strength and has two parts: an equation for field emitted current density, and the equation for total current. ...
History
The phenomenon of field emission was first noticed by R. W. Wood in 1897, while doing experiments with his discharge tube. Late in 1922, Lilienfeld made observations on this effect in his high vacuum X-ray tube with pointed cathode. A very good account of early work is found in review article by R. O. Jenkins. Classical theories failed to explain the experimental results that field emission was independent of temperature in the region well below onset of thermionic emission. The basic process was then explained by Sir Ralph H. Fowler and Lothar Wolfgang Nordheim in 1928 using wave-mechanical formulation. (Reference: R.H. Fowler and L. Nordheim. "Electron emission in intense electric fields", Proceedings of the Royal Sociey, vol. 119 (1928), pp. 173-181.) Sir Ralph Howard Fowler FRS (January 17, 1889 – July 28, 1944) was a British physicist and astronomer. ...
Lothar Wolfgang Nordheim (November 7, 1899, München - October 5, 1985, La Jolla, California, USA) was a German-born Jewish theoretical physicist. ...
Applications Applications of field emission include its use as an electron source in electron microscopy, MEMS systems, and field emission displays.In the field of vacuum electronics, field emission is seen as an alternative to thermionic emission, with advantages such as dramatically higher efficiency, less scatter of emitted electrons, faster turn-on times, compactness, and, in many cases, redundancy. Some disadvantages include lower current per emission source and, often, lower overall current density. Field emission limits the maximum operating voltage for high voltage vacuum devices such as vacuum capacitors and vacuum switches. The electron microscope is a microscope that can magnify very small details with high resolving power due to the use of electrons rather than light to scatter off material, magnifying at levels up to 500,000 times. ...
A mite next to a gear set produced using MEMS. Courtesy Sandia National Laboratories, SUMMiTTM Technologies, www. ...
A field emission display (FED) is a type of flat panel display using phosphor coatings as the emissive medium. ...
Closeup of the filament on a low pressure mercury gas discharge lamp showing white thermionic emission mix coating on the central portion of the coil. ...
Scattering is a general physical process whereby some forms of radiation, such as light, sound or moving particles, for example, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which it passes. ...
In engineering, the duplication of critical components of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe, is called redundancy. ...
See Capacitor (component) for a discussion of specific types. ...
Electrical switches. ...
Vacuum tubes based on thermionic emission require several seconds to warm up before they can be used; by contrast, the function of field emission devices is effectively instantaneous. Furthermore, their microscopic size allows for switching times of many megahertz. The ability to modulate the electron source, rather than modifying a stream of electrons from a constant source (i.e., by velocity modulation), has allowed many vacuum devices to be greatly simplified. For instance, the Klystrode functions much like the two-chamber klystron, without the need for a first chamber. MegaHertz (MHz) is the name given to one million (106) Hertz, a measure of frequency. ...
The inductive output tube or IOT is a variety of vacuum tube which evolved in the 1980s to meet increasing efficiency requirements for high-power RF amplifiers having their primary commercial use in UHF television transmitters, in which application they have mostly replaced klystrons. ...
Reflex klystron Type 2K25 or 723 A/B. The threaded adjustment rod on the right side allows the position of the reflector to be adjusted (by compressing the reflex cavity), and thus the natural resonant frequency of the device. ...
Field Electron Emission Process The field emission process is based on the Fowler-Nordheim Model which assumes that, - The temperature of the metal is zero kelvin.
- Inside the metal the free electron model is valid
- The surface is a smooth plane &
- The potential barrier close to the surface in the vacuum region consists of an image force potential and a potential due to the applied electric field
In solid-state physics, the free electron model is a simple model for the behaviour of valence electrons in a crystal structure of a metallic solid. ...
See also Note: Principles are mostly the same for cold cathode ion sources as in particle accelerators to create electrons. ...
Field emission microscopy (FEM) is an analytical technique used in materials science. ...
A vacuum electronics device, made of a substrate on which small Spindt tips are microfabricated. ...
External links - Field emission - Fowler-Nordheim tunneling, Principles of Semiconductor Devices, Bart Van Zeghbroeck, 1997
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