Search results
Results From The WOW.Com Content Network
The work function W for a given surface is defined by the difference [1] =, where −e is the charge of an electron, ϕ is the electrostatic potential in the vacuum nearby the surface, and E F is the Fermi level (electrochemical potential of electrons) inside the material.
Transmission electron microscopes function like overhead projectors, with a beam of electrons passing through a slice of material then being projected by lenses on a photographic slide or a charge-coupled device. Scanning electron microscopes rasteri a finely focused electron beam, as in a TV set, across the studied sample to produce the image ...
The electron affinity of a surface is closely related to, but distinct from, its work function. The work function is the thermodynamic work that can be obtained by reversibly and isothermally removing an electron from the material to vacuum; this thermodynamic electron goes to the Fermi level on average, not the conduction band edge: =.
The minimum amount of energy needed for an electron to leave a surface is called the work function. The work function is characteristic of the material and for most metals is on the order of several electronvolts (eV). Thermionic currents can be increased by decreasing the work function.
Electron escape through the surface barrier into free-electron-like states of the vacuum. In this step the electron loses energy in the amount of the work function of the surface, and suffers from the momentum loss in the direction perpendicular to the surface.
For an isolated metal, the work function is defined as the difference between its vacuum energy (i.e. the minimum energy that an electron must possess to completely free itself from the material) and the Fermi energy, and it is an invariant property of the specified metal:
where Ψ(x) is the electron wave-function, expressed as a function of distance x measured from the emitter's electrical surface, [62] ħ is the reduced Planck constant, m is the electron mass, U(x) is the electron potential energy, E n is the total electron energy associated with motion in the x-direction, and M(x) = [U(x) − E n] is called ...
Electron gun from an oscilloscope CRT Setup of an electron gun. 1. Hot cathode.2. Wehnelt cylinder.3. Anode. A direct current, electrostatic thermionic electron gun is formed from several parts: a hot cathode, which is heated to create a stream of electrons via thermionic emission; electrodes generating an electric field to focus the electron beam (such as a Wehnelt cylinder); and one or more ...