Electron emission
Liberation of electrons from metal surfaces is known as the electron emission. Some of the metal is carried out at room temperature, the random movement of electrons shown in the figure.
However, they have another in the metal atoms, but the electrons of the metal surface, it can not leave the mission to the extent of these electrons. Start from the back of the metal free electron can not find a positive withdraw because of the nuclear nobody moves. Now the surface of the metal, leaving the metal so that the free electrons generated electricity. In other words, the metal surface, free electrons, their kinetic energy is an obstacle on the surface as a barrier to announce.
However, if enough energy is devoted to free electrons, because their kinetic energy increases and requires the cross-surface barrier to e-metal.Work function (W0) e in the minimum standards of energy performance of the job function, so that only metal metal (M0) of the surface (ie, zero speed) to escape. The work of the pure metal from the 6eV 2EV (about) is different. The value of the properties of the metal purity and surface vary. We are a low work function for electron emission selected by the metal.
Type of electron emission:
Electron emission from metal surfaces is possible to add enough energy (electric field, light energy or electrical heat sources such as the kinetic energy in the function of the operation, saving the energy corresponding to the case. Bomb charged metal surface, ie on the surface of the metal electronic The four most important methods for obtain the new version are:
In this process, metal on metal surfaces, a sufficiently high temperature to allow the free electrons (about 2500oC) heated at: thermionic emission. The number of electrons emitted depends on temperature. The higher the temperature, large emission of electrons. The emissions from these types of evacuated tubes used. Field Mission: This method is a strong electric field (ie a high positive voltage) is applied, the metal of the metal surface where the charm of the field by positive retreat from the free electron. Strong electric field, a large electron emission.
Optical emission: In this method, the light energy, so they do not leave, can the area to fall by the free electrons of the metal on metal. As the strength of the beam on the metal surface, a large photoelectric emission. Optical emission from the base of the TV and sound films.Secondary picture tube used in the release: In this way, electronic or other during the high-speed bimhapnida. Secondary emission intensity of the bombardment of the emitter material, the mass and energy of particles depends
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Tags: Electron Emission, Free Electron, Free Electrons, Metal Atoms, Metal Surfaces, Number Of Electrons