The electron emission resulting from heating is called thermionic emission (TE). The TE phenomenon is widely used in vacuum and gas-filled devices.

• Electrostatic or Autoelectronic emission

Electrostatic (field emission) is called the emission of electrons due to the presence of a strong electric field near the surface of the body. In this case, additional energy is not imparted to the electrons of the solid body, but due to a change in the shape of the potential barrier, they acquire the ability to go into vacuum.

Photoelectronic emission (PE) or external photoelectric effect - the emission of electrons from a substance under the action of radiation incident on its surface. FE is explained on the basis of the quantum theory of a solid body and the zone theory of a solid body.

Emission of electrons by the surface of a solid when it is bombarded by electrons.

Emission of electrons by a metal when it is bombarded with ions.

Emission of electrons as a result of local explosions of microscopic areas of the emitter.

• Cryogenic electron emission

Emission of electrons by ultracold surfaces cooled to cryogenic temperatures. little studied phenomenon.

see also

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See what "Electronic emission" is in other dictionaries:

Emission of electrons by the surface of a condensed medium. E. e. occurs in cases where part of the body's electrons acquires as a result of external. impact energy sufficient to overcome the potential. barrier on its border, or if external ... ... Physical Encyclopedia

Emission of electrons by the surface of a condensed medium. E. e. arises in cases where a part of the body's electrons acquires as a result of external. impacts, energy sufficient to overcome the potential barrier at its border, or if external ... ... Physical Encyclopedia

ELECTRONIC emission, the emission of electrons by a solid or liquid under the influence of an electric field (field emission), heating (thermionic emission), electromagnetic radiation (photoelectronic emission), electron flow ... ... Modern Encyclopedia

Big encyclopedic Dictionary

Electronic emission- ELECTRONIC EMISSION, the emission of electrons by a solid or liquid under the influence of an electric field (field emission), heating (thermionic emission), electromagnetic radiation (photoelectronic emission), electron flow ... ... Illustrated Encyclopedic Dictionary

electronic emission- Emission of electrons from the surface of the material into the surrounding space. [GOST 13820 77] Topics electrovacuum devices ... Technical Translator's Handbook

The emission of electrons from the surface of a solid or liquid. E. e. occurs in cases where, under the influence of external influences, a part of the electrons of the body acquires energy sufficient to overcome the potential barrier (See ... ... Great Soviet Encyclopedia

electronic emission- the emission of electrons by the surface of a solid or liquid. Electronic emission occurs when, under the influence of external influences, a part of the body's electrons acquires energy sufficient to overcome ... ... Encyclopedic Dictionary of Metallurgy

The emission of electrons by a solid or liquid under the influence of an electric field (field emission), heating (thermionic emission), electromagnetic radiation (photoelectronic emission), electron flow (secondary electron ... ... encyclopedic Dictionary

Emission of electrons in vom. Depending on the method of excitation, a trace is distinguished. main types of E. e .: thermionic emission, photoelectron emission (see External photoelectric effect), secondary electron emission, field emission ... Big encyclopedic polytechnic dictionary

Books

• Explosive electron emission, G. A. Mesyats, ... Category: Electricity and Magnetism
• Secondary electron emission , I. M. Bronshtein , B. S. Freiman , The book is devoted to one of the issues of modern physical electronics - secondary electron emission. Measurement methods are considered: secondary emission coefficient (SE), inelastic and elastic ... Category: Solid state physics. Crystallography Series: Engineer's Physical and Mathematical Library Publisher:

the release of an excess of energy equal to the difference between the energy levels of an electron in the body and in the ion ε 1 – ε i 1 . This energy can either be transferred to another electron of the body with initial energy ε 2 (Auger process) or released as a quantum of light. The second process is less likely. If the energy of an excited electron ε = ε 2 + (ε 1 – ε i 1 ) is greater than zero, it will be able to leave the emitter. Thus, two electrons of the body participate in the act of emission: one releases energy by tunneling from the body to the ion with the neutralization of the latter, the other receives this excitation energy and leaves the body, i.e. we have both a tunnel transition process and an excitation process.

10.7 Hot electron emission

The emission of hot electrons is the emission of electrons by a semiconductor in the presence of an electric field in it. Hot electrons are emitted from the conduction band. That's why necessary condition The possibility of the appearance of emission of these electrons is their preliminary thermal excitation from the main band or from donor levels to the conduction band. Thus, during the emission of hot electrons, two different mechanisms of electron excitation are actually implemented: 1) their excitation into the conduction band due to the thermal energy of the lattice; 2) excitation of electrons in the conduction band to energy levels exceeding the vacuum level. This type of excitation occurs due to the work of the electric field forces in the semiconductor; Ultimately, this energy is taken from external source field-generating voltage. The presence of an electric field in a semiconductor causes the acceleration of electrons located in the conduction band. These electrons interact with the phonons of the body. In such collisions of electrons, a sharp change in the direction of their movement can occur and only a small loss of their speed occurs. As a result, the average electron energies are higher than those for ions; we can say that the temperature of the electron gas is higher than the temperature of the crystal lattice. This leads to the appearance of electron emission, which could be conditionally called "thermal emission", but the temperature that determines it will be higher than the lattice temperature.

10.8 Combined emissions

The most commonly used is the combined type of emission based on the Schottky effect. As already discussed in paragraph 2, when an external electric field is applied, the barrier height decreases and thereby decreases effective work exit. Therefore, in this case, a smaller (in terms of energy) preliminary excitation of electrons is required in order to transfer them to energy levels of higher potential barrier heights. Thus, the imposition of an electric field stimulates all types of emission with pre-excitation. Therefore, the combined type of emission will primarily include the following: auto-

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What does "electronic emission" mean?

Encyclopedic Dictionary, 1998

electronic emission

the emission of electrons by a solid or liquid under the action of an electric field (field emission), heating (thermionic emission), electromagnetic radiation (photoelectronic emission), electron flow (secondary electron emission), etc.

Electronic emission

the emission of electrons from the surface of a solid or liquid. E. e. arises in cases when, under the influence of external influences, a part of the electrons of the body acquires energy sufficient to overcome the potential barrier at the boundary of the body, or if, under the influence of an electric field, the surface potential barrier becomes transparent for a part of the electrons that have the highest energies inside the body. E. e. can occur when bodies are heated (thermionic emission), when bombarded by electrons (secondary electron emission), ions (ion-electron emission) or photons (photoelectron emission). Under certain conditions (for example, when passing current through a semiconductor with high electron mobility or when a strong electric field pulse is applied to it), conduction electrons can “heat up” much more than the crystal lattice, and some of them can leave the body (emission of hot electrons) .

For observation E. e. it is necessary to create an externally accelerating electric field near the surface of the body (emitter), which "sucks" the electrons from the surface of the emitter. If this field is large enough (³ 102v / cm), then it reduces the height of the potential barrier at the boundary of the body and, accordingly, the work function (Schottky effect), as a result of which E. e. increases. In strong electric fields (~107 V/cm), the surface potential barrier becomes very thin and tunneling "leakage" of electrons through it (tunneling emission), sometimes also called field emission, occurs. As a result of the simultaneous action of 2 or more factors, thermoauto- or photoautoelectronic emission may occur. In very strong pulsed electric fields (~ 5 × 107 V/cm), tunnel emission leads to rapid destruction (explosion) of micropoints on the emitter surface and to the formation of a dense plasma near the surface. The interaction of this plasma with the surface of the emitter causes a sharp increase in the current E. e. up to 106 A with a duration of current pulses of several tens of ns (explosive emission). With each current pulse, microquantities (~ 10-11 g) of the emitter substance are transferred to the anode.

Vacuum is understood as a gas or air in a state of the highest rarefaction (pressure of the order of ). Vacuum is a non-conductive medium, since it contains an insignificant amount of electrically neutral particles of matter.

To obtain an electric current in vacuum, a source of charged particles - electrons is needed, and the movement of electrons in vacuum occurs practically without collisions with gas particles.

The source of electrons is usually a metal electrode - the cathode. In this case, the phenomenon of the release of electrons from the cathode surface into environment called electron emission.

Free electrons in a metal in the absence of an external electric field randomly move between the ions of the crystal lattice.

Rice. 13-6. Double electrical layer on the metal surface.

At room temperature, no electrons escape from the metal due to the insufficient value of their kinetic energy. Part of the electrons with the highest kinetic energy, during their movement, goes beyond the surface of the metal, forming an electron layer, which, together with the layer of positive ions of the crystal lattice located under it in the metal, forms a double electric layer (Fig. 13-6). The electric field of this double layer counteracts the electrons tending to leave the conductor, i.e., it is inhibitory for them.

For an electron to go beyond the metal surface, it is necessary for the electron to impart energy equal to the work that it must do to overcome the retarding effect of the double layer field. This work is called the work function. The ratio of the output energy to the electron charge is called the output potential, i.e. .

The work (potential) of the output depends on the chemical nature of the metal.

The values ​​of the output potential for some metals are given in Table. 13-1.

Table 13-1

Depending on how the additional energy necessary to exit the metal is imparted to the electrons, the types of emission are distinguished: thermionic, electrostatic, photoelectronic, secondary, and under the impact of heavy particles.

Thermionic emission is the phenomenon of the release of electrons from the cathode, due solely to the heating of the cathode. When a metal is heated, the speeds of electrons and their kinetic energy increase and the number of electrons leaving the metal increases. All electrons emerging from the cathode per unit time, if they are removed from the cathode by an external field, form electricity emissions. As the cathode temperature rises, the emission current increases slowly at first, and then faster and faster. On fig. 13-7 curves of the emission current density, i.e., the emission current per unit cathode surface, expressed in A/cm2, are given depending on the temperature T for various cathodes.

Rice. 13-7. Curves of emission current density depending on temperature for various cathodes: a - oxide; b - tungsten, covered with thorium; c - uncoated tungsten.

The dependence of the emission current density on temperature and work function is expressed by the Richardson-Dashman equation:

where A is the emission constant; for metals it is equal to; T is the absolute temperature of the cathode, K; - base of natural logarithms; - work function, eV; is the Boltzmann constant.

Thus, the emission current density increases proportionally and so that a cathode made of a material with a low work function and a high operating temperature is needed to obtain a large emission current.

If the electrons that have flown out of the cathode (the emitted electrons) are not removed from it by an external accelerating field, then they accumulate around the cathode, forming a volume negative charge (electron cloud), which creates a decelerating electric field near the cathode, which prevents the further escape of electrons from the cathode.

Electrostatic electron emission is the phenomenon of the release of electrons from the cathode surface, due solely to the presence of a strong electric field near the cathode surface.

The force acting on an electron in an electric field is proportional to the charge of the electron and the field strength F - ee. At a sufficiently high strength of the accelerating field, the forces acting on an electron located near the cathode surface become large enough to overcome the potential barrier and eject electrons from the cold cathode.

Electrostatic emission finds use in mercury valves and some other appliances.

Photoelectronic emission is the phenomenon of the release of electrons, due solely to the action of radiation absorbed by the cathode, and not associated with its heating. In this case, the cathode electrons receive additional energy from light particles - photons.

Radiant energy is emitted and absorbed by certain portions - quanta. If the quantum energy, determined by the product of the Planck constant of the radiation frequency v, i.e., more work exit for the material of this cathode, then the electron can leave the cathode, i.e., photoelectron emission will take place.

Photoelectronic emission is used in solar cells.

Secondary electron emission is the phenomenon of the exit of secondary electrons, due solely to the impact of primary electrons on the surface of a body (conductor, semiconductor). Flying electrons, called primary, meeting a conductor on their way, hit it, penetrate into its surface layer and give part of their energy to the electrons of the conductor. If the additional energy received by the electrons upon impact is greater than the work function, then these electrons can go beyond the conductor.

Secondary electron emission is used, for example, in photomultipliers to amplify the current.

Secondary emission can be observed in vacuum tubes in which the anode is exposed to electrons flying from the cathode. In this case, secondary electrons can create a flow that is opposite to the "working" one, which worsens the operation of the lamp.

Electron emission under the impact of heavy particles is the phenomenon of the release of electrons, due solely to the impact of ions or excited atoms (molecules) on the surface of the body - the electrode. This type of emission is similar to the secondary electron emission considered above.

An important role in ensuring the conductivity of the arc gap is played by electrons supplied by the cathode under the influence of various reasons. This process of release of electrons from the surface of the cathode electrode or the process of release of electrons from the bond with the surface is called electron emission. For the process of emission, it is necessary to expend energy.

The energy that is sufficient to release electrons from the surface of the cathode is called the work function ( U out )

It is measured in electron volts and is usually 2-3 times less work ionization.

There are 4 types of electron emission:

1. Thermionic emission

2. Field emission

3. Photoelectronic emission

4. Emission under the impact of heavy particles.

Thermionic emission proceeds under the influence of strong heating of the surface of the electrode - cathode. Under the action of heating, the electrons located on the cathode surface acquire such a state when their kinetic energy becomes equal to or more strength their attraction to the atoms of the electrode surface, they lose their connection with the surface and fly out into the arc gap. Strong heating of the end of the electrode (cathode) occurs because at the moment of its contact with the part, this contact occurs only at certain points on the surface due to the presence of irregularities. This position, in the presence of current, leads to a strong heating of the contact point, as a result of which an arc is initiated. The surface temperature greatly affects the simulation of electrons. The emission is usually estimated by the current density. The relationship between thermionic emission and cathode temperature was established by Richardson and Deshman.

where j0 is the current density, A/cm2;

φ is the electron work function, e-V;

BUT- a constant, the theoretical value of which is A \u003d 120 a / cm 2 deg 2 (experimental value for metals A \u003e 62.2).

In autoelectronic emission, the energy necessary for the release of electrons is imparted by an external electric field, which, as it were, “sucks” the electrons beyond the limits of the influence of the electrostatic field of the metal. In this case, the current density can be calculated from the formula

, (1.9)

where E is the electric field strength, V/cm;

With an increase in temperature, the value of autoelectronic emission decreases, but at low temperatures its influence can be decisive, especially at a high electric field strength (10 6 - 10 7 V / cm), which, according to Brown M.Ya. and G.I. Pogodin-Alekseev can be obtained in the near-electrode regions.

When radiation energy is absorbed, electrons of such high energy can appear that some of them leave the surface. The photoemission current density is determined by the formula

where α - reflection coefficient, the value of which for welding arcs is unknown.

The wavelengths that cause photoemission as well as for ionization are determined by the formula

In contrast to ionization, the emission of electrons from the surface of alkali and alkaline earth metals caused by visible light.

The surface of the cathode can be subjected to impacts of heavy particles (positive ions). Positive ions in case of impact on the cathode surface can:

Firstly, give away the kinetic energy they possess.

Secondly, can be neutralized on the cathode surface; while they give the electrode ionization energy.

Thus, the cathode acquires additional energy, which is used for heating, melting and evaporation, and some part is spent again on the escape of electrons from the surface. As a result of a sufficiently intense emission of electrons from the cathode and the corresponding ionization of the arc gap, a stable discharge is established - an electric arc with a certain amount of current flowing in the circuit at a certain voltage.

Depending on the degree of development of a particular type of emission, three types of welding arcs are distinguished:

Hot cathode arcs;

Cold cathode arcs;