The Auger effect was discovered byPierre Auger while examining photoemission process by irradiating samples withX-rays in the 1920s. By 1953, J.J. Lander proposed using electron-stimulatedAuger signals for chemical analysis. This technique was further developed by Larry Harris in 1967 afteremploying differentiation to enhance Auger signals.
1AES is a principaltechnique utilized to analyze the chemical composition of surfaces. Thistechnique utilizes the emission of low energy electrons in the Auger process asseen in Figure 1. When a focused electron beam is bombarded at thesurface of a sample, a secondary electron is emitted. This phenomenon wouldresult in a vacancy in the lower energy level.
This vacancy can be filled withelectron with higher energy by two possibilities, the radioactive andnon-radioactive process. The latter is also known as Auger process. When thehigher energy electron fills the hole, energy is released.
This energy caneject the third electron from another orbit. Through the measurement of thekinetic energy of the third ejected electron or the Auger electron, the atomcan be identified. The kinetic energy of the Auger electron is a fixedvalue and a unique characteristic of an element.
Auger process requires threeelectrons, thus it can detect other elements except for hydrogen and helium.2,3The excitationdevice for AES is an electron gun which emits 3 to 5 keV electrons. Theresulting Auger electrons are analyzed by the electron energy analyzers as afunction of the electron energies. For most AES instruments, cylindrical mirroranalyzer (CMA) is used. CMA consists of two concentric cylinders, the innercylinder with ground potential while the outer one with negative potential. The inner cylinder is designed with two radial apertures with grids toallow Auger electrons with energies as the outer bias to enter in the spacebetween the two cylinders.
Auger electrons are chosen according to theirenergy by sweeping through 10 to 2000 eV. 2After passingthrough the electron energy analyzer, the Auger electron energy are analyzedwith respect to their time data. The resulting peak is a result of Augerelectrons on a background of secondary electrons recorded in a differentialmode. This instrument is also equipped with ultra-high vacuum to avoid electronscattering and distortion of spectra due to contamination. It is also employedto increase the mean free path of the electrons. 3