What Is Auger Electron Spectroscopy?

Auger Electron Spectroscopy (AES) is often used to determine the chemical composition of a thin, microscopic layer of a surface. Particles called electrons are typically aimed at the material, triggering the Auger effect, in which an electron from the inner shell of an atom is removed, a higher level particle takes its place, and another electron is emitted. Conducted in an ultra-high vacuum, the testing is usually accomplished with an electron gun, analyzer, detector, and data recorder. The information is typically analyzed graphically; the nature of the peaks usually helps identify what compounds are present in the sample.

Beams of electrons are often used, though x-rays are sometimes released instead. The type of material being tested determines which is used; oxides, for example, can degrade if exposed to high levels of electrons. Substances can be identified because the energy of an Auger electron is typically unique to the element. In Auger electron spectroscopy, the particles that escape are generally not as energetic as others. They generally need to be very close to the surface to be able to escape, and any gases present during AES can prevent the particle from reaching the detector.

An electron gun used in Auger electron spectroscopy usually consists of a source for the particles and a lens that focuses the beam. The lens can be either electrostatic or electromagnetic; which one is used depends on the resolution required. An electron energy analyzer that is part of an Auger electron spectroscopy technique can sort out the emitted particles by their energy levels. The analyzer can either be designed as a cylindrical mirror or two hemispherical concentric shells.

Single- or multi-channel detectors are often used for Auger electron spectroscopy. The data are then analyzed by sets of peaks on a graph. Scans usually take a few minutes to complete, while high-resolution measurements can take up to 25 minutes. A survey scan typically identifies what elements are present, while another scan can tell how concentrated certain atoms are. If the beam is scanned across the sample, then a map of the measured surface can be produced.

Auger electron spectroscopy science is often used in many physics and chemistry applications. In addition to identifying elements on surfaces, it can be used to detect oxidation and corrosion as well. Temperature response and related fatigue can be analyzed using AES. The technique can also be used to inspect integrated circuits for contaminants, but a limitation of the process is that there is often damage to the surface of the material tested.