What is field enhanced thermionic emission?

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.

What do you mean by thermionic emission?

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 is Schottky effect in physics?

Schottky effect, increase in the discharge of electrons from the surface of a heated material by application of an electric field that reduces the value of the energy required for electron emission. The effect is named after its discoverer, the German physicist Walter Schottky.

What is Richardson constant?

But Richardson is a constant of material, which is independent of temperature. A* is the Richardson constant and was theoretically calculated (A* = 4πqk2m*/ h3) , where m* is effective mass of the material used and it is assumed constant value with the varying temperature.

What do you mean by space charge?

Space charge refers to the collection of electrons which are emitted from the metal surface, after the application of tube current, at a short distance away from the metal surface. These electrons collect and form a cloud of negative charge around the metal surface.

What is Schottky defect class 12?

-A Schottky defect is a type of vacancy defect which is found in ionic solids. It is a stoichiometry defect (thermodynamic defect), which means that such defects do not change or distort the stoichiometry of the solid.

What are the differences between Schottky and Frenkel defect?

In Schottky defect the difference in size between cation and anion is small. Frenkel defect contains ionic crystals where the anion is larger than the cation. Both anion and cation leave the solid crystal. Usually the smaller ion cation leaves its original lattice structure.

What is the Richardson Dushman equation?

thermionic emission emitter is given by the Richardson–Dushman equation; i.e., where T is the absolute temperature in kelvins of the emitter, e is the electronic charge in coulombs, and k is Boltzmann’s gas constant in joules per kelvin.

What is child’s law?

Child law can be described as the sum of all the law that in any way handles or regulates children’s life situations, including children’s rights as expressed in the UN Convention on the Rights of the Child. Child law has a distinct interdisciplinary character and lies at the interstices of public and private law.

What is space charge effect?

: the limitation of flow of plate current in an electron tube produced by repulsion exerted on electrons leaving the filament by the other electrons in the region between filament and plate.

Which is the best description of the Schottky effect?

Dobretsov, L. N., and M. V. Gomoiunova. Emissionnaia elektronika. Moscow, 1966. Nenakalivaemye katody. Moscow, 1974. The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved. The enhancement of the thermionic emission of a conductor resulting from an electric field at the conductor surface.

What is the definition of a Schottky defect?

Definition. Schottky defect is a type of point defect or imperfection in solids which is caused by a vacant position that is generated in a crystal lattice due to the atoms or ions moving out from the interior to the surface of the crystal.

How does the Schottky defect affect the density of a compound?

Schottky defect reduces the density of ionic compounds because a fraction of ions leaves the crystal, hence reducing the overall mass at the same crystal volume.

Where does the Schottky effect take place in an electron microscope?

Schottky-emitter electron source of an Electron microscope Electron emission that takes place in the field-and-temperature-regime where this modified equation applies is often called Schottky emission. This equation is relatively accurate for electric field strengths lower than about 10 8 V m −1.