An ‘Auger effect’ is a physical phenomenon which was observed by Lise Meitner, an Austrian Swedish physicist in 1922. She has also worked remarkably on radioactivity and nuclear physics. This effect was discovered as a side effect during her competitive search for the nuclear beta electrons with one of the British physicist C. D. Ellis. Later, Pierre Victor Auger independently discovered this effect in a short time just after this and thus he is credited with this discovery in most of the scientific community.


The auger effect can be seen very frequently when a core electron (electron that is located in the inner shells and does not participate in bonding) is removed. This tends on leaving a vacancy at that atom, an electron from a higher energy level then comes and falls into the vacancy to fulfill its place. This results in the release of energy. Although we can say that most often this energy is released in the form of an emitted photons, this energy can also be transferred to another electron present there, which ultimately is then ejected from the atom. This second ejected electron is called as an ‘Auger electron’. Auger electrons may be defined as those atomic electrons that are emitted from atoms after attaining some energy from an atomic electron movement within the atom that is from higher to lower and vice versa. Electron transitions will somehow only occur when an atom becomes ionized by the loss of an electron from an inner shell.


An auger effect can now be explained as a phenomenon that takes place when the filling of an inner-shell vacancy of an atom takes place which is further accompanied by the emission of an electron from the same atom. Upon being ejected, the kinetic energy (energy possessed by a moving object) of the Auger electron can be studied by taking out the difference between the energy with which the initial electron passed onto the vacancy and the ionization energy for that electron shell from which the Auger electron was ejected. It is also to be noted here that the Ionization energy is the amount of energy that is required to remove the loosely bound electron. These energy levels depend on two factors, first, what type of the atom it is, and second, the environment in which the atom was initially located.


In semiconductors, a similar auger effect is known as ‘Auger recombination’. Auger recombination states that an electron and a hole (a place where an electron is not present) can recombine when they give up their energy to an electron in the conduction band and therefore increasing its energy. The just opposite effect of this is known as impact ionization. Impact ionization is the process in any material by which one charge carrier that has some energy can lose energy by the creation of other charged carriers. The auger effect can have a damaging effect on biological molecules as well such as DNA and it is also seen that the auger electron of this effect can destroy the sugar-phosphate backbone present in nucleotides.

As already known that all atoms consist of a nucleus and concentric shells a few that are situated around the nucleus. These concentric shells have electrons that are at different energy levels. If an electron in one of the inner shells is removed with the help of the bombardment of electron, absorption process into the nucleus, or by any other way, an electron from another shell will always tend to jump into the vacancy created by the previous electron. This will release some energy that is instantaneously dispersed either by producing an X-ray or with the Auger effect.


In the Auger effect, the available energy throws an electron from one of the shells which will give rise to two-electron vacancies in the residual atom. The process may be repeated as many times as the new vacancies are filled to prevent the X-rays to be given out. The probability that an Auger electron will be emitted is called the Auger yield against that shell. The Auger yield progressively decreases as the atomic number of an element decreases. The probabilities that the x rays will be emitted from the innermost shell and of the emission from the Auger electrons are about the same. The Auger effect is useful in many areas such as it can help in studying the properties of elements and compounds, the nuclei, and the other subatomic particles.

If the electron situated in an inner shell is removed from an atom, an electron from a higher level will quickly make its way downwards to fill the vacancy created from the removed electron. Sometimes this transition will be accompanied by a photon whose quantum energy is somewhat equal to the energy gap held between the upper and lower energy level. If we talk about the heavy atoms this quantum energy will be in the x-ray region of the spectrum which is commonly called the x-ray fluorescence. Thus, the line spectra arise as a result of the emission process for lighter atoms and outer electrons.


In cases where the energy that is released by the downward movement of the electron is given to one of the outer electrons in place of giving it to a photon, this electron is then ejected from the atom with some amount of energy. This energy is equal to the energy lost by the electron which made the downward movement subtracted by the binding energy of the electron that is ejected from the atom. This explains the auger effect. Thus, the Auger effect, effectively explains the movement of electrons and its emission.

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