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The work function is the minimum energy (usually measured in electron volts) needed to remove an electron from a solid to a point immediately outside the solid surface. Here "immediately" means that the final electron position is far from the surface on the atomic scale but still close to the solid on the macroscopic scale. The work function is an important property of metals. The magnitude of the work function is usually about a half of the ionization energy of a free atom of the metal. An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. ...
e- redirects here. ...
The ionization energy (IE) of an atom or of a molecule is the energy required to strip it of an electron. ...
Work Function and Surface Effect
Work function W of a metal is closely related to its Fermi energy level  yet the two quantities are not exactly the same. This is due to the surface effect of a real-world solid: a real-world solid is not infinitely extended with electrons and ions repeatedly filling every primitive cell over all Bravais lattice sites. Neither can one simply take a set of Bravais lattice sites  inside the geometrical region V which the solid occupies and then fill undistorted charge distribution basis into all primitive cells of . Indeed, the charge distribution in those cells near the surface will be distorted significantly from that in a cell of an ideal infinite solid, resulting in an effective surface dipole distribution, or, sometimes both a surface dipole distribution and a surface charge distribution. In solid state physics and mineralogy, particularly in describing crystal structure, a primitive cell is a minimum volume cell corresponding to a single lattice point. ...
In geometry and crystallography, a Bravais lattice, named after Auguste Bravais, is an infinite set of points generated by a set of discrete translation operations. ...
It can be proven that if we define work function as the minimum energy needed to remove an electron to a point immediately out of the solid, the effect of the surface charge distribution can be neglected, leaving only the surface dipole distribution. Let the potential energy difference across the surface due to effective surface dipole be  . And let be the Fermi energy calculated for the finite solid without considering surface distortion effect, when taking the convention that the potential at  is zero. Then, the correct formula for work function is: The Fermi energy is a concept in quantum mechanics referring to the energy of the highest occupied quantum state in a system of fermions at zero temperature. ...
Where is negative, which means that electrons are bound in the solid.
Example For example, Caesium has ionization energy 3.9 eV and work function 1.9 eV. General Name, Symbol, Number caesium, Cs, 55 Chemical series alkali metals Group, Period, Block 1, 6, s Appearance silvery gold Standard atomic weight 132. ...
Photoelectric work function The work function is the minimum energy that must be given to an electron to liberate it from the surface of a particular metal. In the photoelectric effect if a photon with an energy greater than the work function is incident on a metal photoelectric emission occurs. Any excess energy is given to the electron as kinetic energy. A diagram illustrating the emission of electrons from a metal plate, requiring energy gained from an incoming photon to be more than the work function of the material. ...
In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ...
The photoelectric effect is the emission of electrons from a surface (usually metallic) upon exposure to, and absorption of, electromagnetic radiation (such as visible light and ultraviolet radiation) that is above the threshold frequency particular to each type of surface. ...
Photoelectric work function is
where h is the Planck's constant and f0 is the minimum (threshold) frequency of the photon required to produce photoelectric emission. When an electron gains energy, it jumps from one energy level to another in "quantum leaps". This process is called exciting an electron, and the higher energy levels are called "excited states" while the bottom level is called "grounded state". A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin. ...
Thermionic work function The work function is also important in the theory of thermionic emission. Here the electron gains its energy from heat rather than photons. In this case, as for an electron escaping from the heated negatively-charged filament of a vacuum tube, the work function may be called the thermionic work function. Tungsten is a very common metal for vacuum tube elements, with a work function of approximately 4.5 eV. Thermionic emission (archaically known as the Edison effect) is the flow of electrons from a metal or metal oxide surface, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface. ...
Structure of a vacuum tube diode Structure of a vacuum tube triode In electronics, a vacuum tube, electron tube, or (outside North America) thermionic valve or just valve, is a device used to amplify, switch or modify a signal by controlling the movement of electrons in an evacuated space. ...
General Name, Symbol, Number tungsten, W, 74 Chemical series transition metals Group, Period, Block 6, 6, d Appearance grayish white, lustrous Standard atomic weight 183. ...
Thermionic emission requires a filament heating current (if), to maintain a temperature of 2000-2700 K. A saturation state of the filament current is reached, where a minor change in the filament current does not affect the beam current. The electron gun is then operated with the filament current very near the potential to overcome the work function (W)(Goldstein, 2003) The thermionic work function depends on the orientation of the crystal and will tend to be smaller for metals with an open lattice, larger for metals in which the atoms are closely packed. The range is about 1.5–6 eV. It is somewhat higher on dense crystal faces than open ones. Josephson junction array chip developed by NIST as a standard volt. ...
Applications In electronics the work function is important for design of the metal-semiconductor junction in Schottky diodes and for design of vacuum tubes. Electronics is the study of the flow of charge through various materials and devices such as, semiconductors, resistors, inductors, capacitors, nano-structures, and vacuum tubes. ...
Hot metal work from a blacksmith In chemistry, a metal (Greek: Metallon) is an element that readily loses electrons to form positive ions (cations) and has metallic bonds between metal atoms. ...
A semiconductor is a fuckin solid whose electrical conductivity is in between that of a metal and that of an insulator, and can be controlled over a wide range, either permanently or dynamically. ...
Schottky diode schematic symbol The Schottky diode (named after German physicist Walter H. Schottky; also known as hot carrier diode) is a semiconductor diode with a low forward voltage drop and a very fast switching action. ...
Structure of a vacuum tube diode Structure of a vacuum tube triode In electronics, a vacuum tube, electron tube, or (outside North America) thermionic valve or just valve, is a device used to amplify, switch or modify a signal by controlling the movement of electrons in an evacuated space. ...
Measurement Many techniques have been developed based on different physical effects to measure the electronic work function of a sample. One may distinguish between two groups of experimental methods for work function measurements: absolute and relative.
Methods of the first group employ electron emission from the sample induced by photon absorption (photoemission), by high temperature (thermionic emission), due to an electric field (field emission), or using electron tunnelling. Also known as Fowler-Nordheim tunneling, field emission is a form of quantum tunneling in which electrons pass through a barrier in the presence of a high electric field. ...
In quantum mechanics, the tunneling effect refers to various processes whereby particles appear to violate classical physics by instantaneously changing their location within the space-time continuum without passing observably through the intervening space. ...
All relative methods make use of the contact potential difference between the sample and a reference electrode. Experimentally, either an anode current of a diode is used or the displacement current between the sample and reference, created by an artificial change in the capacitance between the two, is measured (the Kelvin Probe method, Kelvin probe force microscope). In Kelvin probe force microscopy, a conducting cantilever is scanned over a surface at a constant height in order to map the work function of the surface. ...
Methods Based on Photoemission Photoelectron emission spectroscopy (PES) is the general term for spectroscopic techniques based on the outer photoelectric effect. In the case of Ultraviolet Photoelectron Spectroscopy (UPS), the surface of a solid sample is irradiated with ultraviolet (UV) light and the kinetic energy of the emitted electrons is analysed. As UV light is electromagnetic radiation with an energy hν lower than 100 eV it is able to extract only valence electrons. Due to limitations of the escape depth of electrons in solids UPS is very surface sensitive, as the information depth is in the range of 2 – 3 monolayers. At the same time the measurement principle restricts PES to be used in UHV conditions. The resulting spectrum reflects the electronic structure of the sample providing information on the density of states, the occupation of states, and the work function. Spectroscopy is the study of spectra, ie. ...
“UV†redirects here. ...
The kinetic energy of an object is the extra energy which it possesses due to its motion. ...
Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ...
In chemistry, valence electrons are the electrons contained in the valence shell of an atom, and which are likely to participate in a chemical reaction through bonding with other atoms or molecules. ...
The University of Houston–Victoria, located in Victoria, Texas, was founded as an upper-level institution in 1973 as the University of Houston Victoria Center and became a permanent part of the University of Houston System in 1983. ...
Methods Based on Thermionic Emission The retarding diode method is one of the simplest and oldest method of measuring work functions. It is based on the thermionic emission of electrons from an emitter. The current density J of the electrons collected by the sample depends on the work function φ of the sample and is given by the Richardson–Dushman equation J = AT2e − φ / kT where A, the Richardson constant, is a specific material constant. The current density increases rapidly with temperature and decreases exponentially with the work function. Changes of the work function can be easily determined by applying a retarding potential V between the sample and the electron emitter; φ is replaced by e(Φ + V) in above equation. The difference in the retarding potential measured at constant current is equivalent to the work function change, assuming that the work function and the temperature of the emitter is constant. Types of diodes. ...
An emitter is any device used to emit any signal, beacon, light, odor, liquid, fragrance, or the like. ...
Thermionic emission (archaically known as the Edison effect) is the flow of electrons from a metal or metal oxide surface, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface. ...
One can use the Richardson–Dushman equation directly to determine the work function by temperature variation of the sample, as well. Rearranging the equation yields ln(J / T2) = ln(A) − φ / kT. The line produced by plotting ln(J / T2) vs. 1 / T will have a slope of − φ / k allowing to determine the work function of the sample.
See also The electron affinity, Eea, of an atom or molecule is the energy required to detach an electron from a singly charged negative ion, i. ...
References As a book: - Solid State Physics, by Ashcroft and Mermin. Thomson Learning, Inc, 1976
- Goldstein, Newbury, et al, 2003. Scanning Electron Microscopy and X-Ray Microanalysis. Springer, New York.
For a quick reference to values of work function of the elements: - Herbert B. Michaelson, "The work function of the elements and its periodicity". J. Appl. Phys. 48, 4729 (1977)
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