The electrons in the Auger process as seen

The Auger effect was discovered by Pierre Auger while examining photoemission process by irradiating samples with X-rays in the 1920s. By 1953, J.J. Lander proposed using electron-stimulated Auger signals for chemical analysis.  This technique was further developed by Larry Harris in 1967 after employing differentiation to enhance Auger signals. 1

AES is a technique mainly employed to analyze the chemical composition of surfaces. This technique utilizes the emission of low energy electrons in the Auger process as seen in Figure 1.  When a focused electron beam is bombarded at the surface of a sample, a secondary electron is emitted. This phenomenon would result in a vacancy in the lower energy level. The electron-hole can be filled with higher-energy electron through the non-radioactive process also known as Auger process. When the higher energy electron fills the hole, energy is released. The released energy can eject the third electron. The kinetic energy of the third electron (Auger electron) corresponds uniquely to an atom. AES can detect other elements except for hydrogen and helium due to the Auger process which requires three electrons. 2,3

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Figure 2. Schematic Diagram of AES

The excitation device for AES is an electron gun which emits 3 to 5 keV electrons. The resulting Auger electrons are analyzed by the electron energy analyzers as a function of the electron energies. For most AES instruments, cylindrical mirror analyzer (CMA) is used. The CMA is comprised of two concentric cylinders, the inner cylinder with ground potential while the outer one with negative potential.  The inner cylinder is designed with two radial apertures with grids to allow Auger electrons with similar energies as the outer bias to enter in the space between the two cylinders. Auger electrons are chosen according to their energy by sweeping through 10 to 2000 eV. 2

After passing through the electron energy analyzer, the Auger electron energy are analyzed with respect to their time. The resulting peak is a result of Auger electrons on a background of secondary electrons recorded in a differential mode. This instrument is also equipped with ultra-high vacuum to prevent electron scattering and distortion of spectra due to contamination. It is also employed to increase the mean free path of the electrons.