What is thermionic field-emission?
Thermionic emission is the liberation of electrons from an electrode by virtue of its temperature (releasing of energy supplied by heat). The classical example of thermionic emission is that of electrons from a hot cathode into a vacuum (also known as thermal electron emission or the Edison effect) in a vacuum tube.
What are field-emission devices?
A field-emission display (FED) is a flat panel display technology that uses large-area field electron emission sources to provide electrons that strike colored phosphor to produce a color image. As of 2016, no large-scale commercial FED production has been undertaken.
What causes field-emission?
When exposed to an intense, properly oriented electric field, a conducting surface can emit electrons. In the case of an accelerating cavity, these electrons are accelerated by the RF field in the cavity.
What is Schottky emission?
Schottky-emission electron gun,SE electron gun An electron gun that utilizes the Schottky effect, in which thermoelectrons are easily emitted due to lowering potential barrier when a strong electric field is applied to a heated metal surface. Thus, the Schottky-emission electron gun is used for high-resolution imaging.
Why does thermionic emission occur?
Thermionic emission is the emission of electrons from a heated metal (cathode). As the temperature increases, the surface electrons gain energy. The energy acquired by the surface electrons allows them to move a short distance off the surface thus resulting in emission.
What causes thermionic emission?
What is field emission used for?
The resulting current of electrons through the surface of a material under the influence of a strong electric field is called field emission. This effect is utilized in the field-emission electron microscope, which in some instances achieves resolution of atomic dimensions.
How does field emission work?
Field electron emission, also known as field emission (FE) and electron field emission, is emission of electrons induced by an electrostatic field. The field-induced promotion of electrons from the valence to conduction band of semiconductors (the Zener effect) can also be regarded as a form of field emission.
How is Schottky defect calculated?
The number of Schottky defects (n) present in an ionic compound containing N ions at temperature Tis given by n = Ne E/2KT, where E is the energy required to create ‘n’ Schottky defects and K is the Boltzmann constant. If the mole fraction of Schottky defect in NaCl crystal at 2900 K is X.
What is Schottky defect give an example?
Examples. This type of defect is typically observed in highly ionic compounds, highly coordinated compounds, and where there is only a small difference in sizes of cations and anions of which the compound lattice is composed. Typical salts where Schottky disorder is observed are NaCl, KCl, KBr, CsCl and AgBr.
At what temperature does thermionic emission occur?
The energy acquired by the surface electrons allows them to move a short distance off the surface thus resulting in emission. A pure tungsten filament must be heated to a temperature of 2200°C to emit a useful number of electrons. The electrons emitted from the surface are limited by the space charge effect.
What is the basic principle of thermionic emission?
Thermionic emission is the emission of electrons from a heated metal (cathode). This principle was first used in the Coolidge tube and then later in the modern day x-ray tubes. Before the discovery of the principle, gas tubes were used for x-ray production.
Which is an electron source based on field emission?
While electron sources based on field emission have a number of applications, field emission is most commonly an undesirable primary source of vacuum breakdown and electrical discharge phenomena, which engineers work to prevent.
Why was the development of field emission important?
The development of large-area field emission sources was originally driven by the wish to create new, more efficient, forms of electronic information display. These are known as “field emission displays” or “nano-emissive displays”.
What kind of emission is caused by an electrostatic field?
Field electron emission (also known as field emission ( FE) and electron field emission) is emission of electrons induced by an electrostatic field. The most common context is field emission from a solid surface into vacuum.
How is the barrier field related to the emission area?
Strictly, if the barrier field in Fowler-Nordheim 1928 theory is exactly proportional to the applied voltage, and if the emission area is independent of voltage, then the Fowler-Nordheim 1928 theory predicts that plots of the form (log(i/V2) vs. 1/V) should be exact straight lines.