bei48482_FM

258 Chapter Seven

Figure 7.21When an electron from an outer shell of an atom with a missing inner electron drops to

fill the vacant state, the excitation energy can be carried off by an x-ray photon or by another outer

electron. The latter process is called the Auger effect.

From Eq. (7.21) we have

Z 1    26

Z 27

The element with atomic number 27 is cobalt.

(4)(1.67 1018 Hz)



(3)(3.00 108 m /s)(1.097 107 m^1 )

4



3 cR

Auger Effect

A

n atom with a missing inner electron can also lose excitation energy by the Auger effect

without emitting an x-ray photon. In this effect, which was discovered by the French physi-

cist Pierre Auger, an outer-shell electron is ejected from the atom at the same time that another

outer-shell electron drops to the incomplete inner shell. Thus the ejected electron carries off the

atom’s excitation energy instead of a photon doing this (Fig. 7.21). In a sense the Auger effect

represents an internal photoelectric effect, although the photon never actually comes into being

within the atom.

The Auger process is competitive with x-ray emission in most atoms, but the resulting

electrons are usually absorbed in the target material while the x-rays emerge to be detected.

Those Auger electrons that do emerge come either from atoms on the surface of the material

or just below the surface. Because the energy levels of an atom are affected by its participa-

tion in a chemical bond, the energies of Auger electrons provide insight into the chemical

environment of the atoms involved. Auger spectroscopy has turned out to be a valuable

method for studying the properties of surfaces, information especially needed by manufac-

turers of semiconductor devices that consist of thin layers of different materials deposited on

one another.

X-ray photon

X-ray

emission

Auger Outer electron

High-energy effect

electron

dislodges

inner atomic

electron

OR

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