Electron Emission: Full Explanation
Electron emission refers to the process by which electrons are ejected from a material, typically from
the surface of a metal. This process is crucial in various applications, including vacuum tubes,
cathode ray tubes, and electron microscopes. There are four primary types of electron emission:
1. Thermionic Emission
Thermionic emission occurs when a metal is heated to a high temperature, providing enough
thermal energy for electrons to escape from the metal surface.
Principle:
- Metals have a work function (phi), the minimum energy needed to remove an electron.
- When heated, electrons gain kinetic energy.
- If an electron gains energy greater than the work function, it escapes the metal surface.
Formula:
J = A T^2 e^(-phi/kT)
Applications: Vacuum tubes, CRTs, electron guns.
2. Field Emission (Cold Emission)
Field emission occurs when a strong external electric field pulls electrons out of the metal without
the need for heating.
Formula:
J = A (E^2/phi) e^(-B phi^(3/2)/E)
Applications: SEM, FED, vacuum microelectronics.
3. Photoelectric Emission
Photoelectric emission occurs when light (photons) strikes a metal surface and transfers energy to
electrons, ejecting them.
Formula:
Electron emission refers to the process by which electrons are ejected from a material, typically from
the surface of a metal. This process is crucial in various applications, including vacuum tubes,
cathode ray tubes, and electron microscopes. There are four primary types of electron emission:
1. Thermionic Emission
Thermionic emission occurs when a metal is heated to a high temperature, providing enough
thermal energy for electrons to escape from the metal surface.
Principle:
- Metals have a work function (phi), the minimum energy needed to remove an electron.
- When heated, electrons gain kinetic energy.
- If an electron gains energy greater than the work function, it escapes the metal surface.
Formula:
J = A T^2 e^(-phi/kT)
Applications: Vacuum tubes, CRTs, electron guns.
2. Field Emission (Cold Emission)
Field emission occurs when a strong external electric field pulls electrons out of the metal without
the need for heating.
Formula:
J = A (E^2/phi) e^(-B phi^(3/2)/E)
Applications: SEM, FED, vacuum microelectronics.
3. Photoelectric Emission
Photoelectric emission occurs when light (photons) strikes a metal surface and transfers energy to
electrons, ejecting them.
Formula:
