Auger electron spectrometry (AES)
is a surface sensitive analytical technique used mainly to determine the elemental composition of materials and, in certain cases to identify the chemical states of surface atoms.
- The sample is irradiated by a primary electron beam, typically 3…10 keV (our machine: Auger Microprobe JEOL JAMP 9500F).
- The effect and the electrons produced thereby are named after Pierre Auger who - among others - investigated this process in the years 1923…25.
- All elements with Z >= 3 (Li) emit Auger electrons (The Auger process).
- The energy distribution of the electrons emitted from the sample is analyzed in a spectrometer.
- The Auger electrons, when analyzed as a function of energy, are used to identify the elements and - to a lower extent - chemical states (see Local analysis by the Auger microprobe).
- The sensitivity for the elements varies over the periodic table; using Auger electrons the detection limit is about <= 1 %.
- The information depth for Auger analysis is the top 0.5…5 nm of the sample, and can be used in depth profiling applications in conjunction with ion beam sputtering (see Depth profile analysis).
- Because mainly a scanning primary beam is used, the secondary electron images yield information related to surface topography.
- Regions of interest can be selected in the SEM images and local analysis (points, areas, lines) is possible with a resolution in the order of the primary beam diameter.
- When the spectrometer is set to a fixed Auger peak, the lateral distribution of the element can be measured by scanning the beam over the sample (see Elemental mapping by the Auger microprobe ).
The Auger process
- The inner shell of an atom is ionized (1), mainly by electron bombardment.
- The vacancy (2) is filled by an electron from an outer shell (3).
- The released energy is emitted as (characteristic) X-ray (4a) or is transferred by electromagnetic interaction to a 3rd electron. If it gets sufficient energy it can leave the atom as Auger electron (4b).
- The energy of both radiations (4a, b) is determined by the energy levels of the atom and makes analysis of the composition possible.