The Auger effect (; ) or Meitner-Auger effect is a physical phenomenon in which

atom Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...

s eject

electrons The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

. It occurs when an inner-shell vacancy in an

is filled by an electron, releasing energy that causes the emission of another electron from a different shell of the same atom. When a core electron is removed, leaving a vacancy, an electron from a higher energy level may fall into the vacancy, resulting in a release of

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

. For light atoms (Z<12), this energy is most often transferred to a valence electron which is subsequently ejected from the atom. This second ejected electron is called an Auger electron. For heavier atomic nuclei, the release of the energy in the form of an emitted

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...

becomes gradually more probable.

Effect

Upon ejection, the

kinetic energy In physics, the kinetic energy of an object is the form of energy that it possesses due to its motion. In classical mechanics, the kinetic energy of a non-rotating object of mass ''m'' traveling at a speed ''v'' is \fracmv^2.Resnick, Rober ...

of the Auger electron corresponds to the difference between the energy of the initial electronic transition into the vacancy and the

ionization energy In physics and chemistry, ionization energy (IE) is the minimum energy required to remove the most loosely bound electron of an isolated gaseous atom, Ion, positive ion, or molecule. The first ionization energy is quantitatively expressed as : ...

for the electron shell from which the Auger electron was ejected. These energy levels depend on the type of atom and the chemical environment in which the atom was located. Auger electron spectroscopy involves the emission of Auger electrons by bombarding a sample with either

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

s or energetic electrons and measures the intensity of Auger electrons that result as a function of the Auger electron energy. The resulting spectra can be used to determine the identity of the emitting atoms and some information about their environment. Auger recombination is a similar Auger effect which occurs in

semiconductor A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

s. An electron and

electron hole In physics, chemistry, and electronic engineering, an electron hole (often simply called a hole) is a quasiparticle denoting the lack of an electron at a position where one could exist in an atom or crystal structure, atomic lattice. Since in ...

(electron-hole pair) can recombine, giving up their energy to an electron in the conduction band, increasing its energy. The reverse effect is known as impact ionization. The Auger effect can impact biological molecules such as DNA. Following the K-shell ionization of the component atoms of DNA, Auger electrons are ejected, leading to damage to its sugar-phosphate backbone.

Discovery

The Auger emission process was observed and published in 1922 by

Lise Meitner Elise Lise Meitner ( ; ; 7 November 1878 – 27 October 1968) was an Austrian-Swedish nuclear physicist who was instrumental in the discovery of nuclear fission. After completing her doctoral research in 1906, Meitner became the second woman ...

, an Austrian-Swedish physicist, as a side effect in her competitive search for the nuclear beta electrons with the British physicist Charles Drummond Ellis. The French physicist Pierre Victor Auger independently discovered it in 1923 upon analysis of a Wilson cloud chamber experiment and it became the central part of his PhD work. High-energy X-rays were applied to ionize gas particles and observe photoelectric electrons. The observation of electron tracks that were independent of the frequency of the incident photon suggested a mechanism for electron ionization that was caused by an internal conversion of energy from a radiationless transition. Further investigation and theoretical work using elementary quantum mechanics and transition rate/transition probability calculations showed that the effect was a radiationless effect more than an internal conversion effect.

References

{{Authority control Atomic physics Foundational quantum physics Electron spectroscopy

Effect

Discovery

See also

References