/ Auger Electron Spectroscopy (AES)

Auger Electron Spectroscopy (AES)

An Auger microscope can image samples at very high resolutions and give the elemental chemical composition (semi-quantitative) of an extremely small surface.

Once inside the Auger microscope, the sample is irradiated by an electron beam which causes the ejection of electrons from core levels of the atoms. After this first electron emission, the excited atom can relax by having an electron from a higher energy level fall into the hole left by the first electron and transferring the excess energy to another electron (the Auger electron) which will be emitted from the atom. The kinetic energy of the emitted Auger electrons is a signature of the elements from which they originate. Auger electron spectroscopy has multiple applications like the analysis of particles or defects in various industries such as microelectronics, biomedical and pharmaceuticals.

This microscope is also equipped with an electron backscatter diffraction (EBSD) detector which can be used to determine the crystal orientation at the surface of a sample. It can also be used to map a surface to obtain information about the crystalographic texture, pole figures, grain size. Moreover, because this system is in a ultra high vacuum chamber, it is perfectly suited for the analysis of materials composed of very small grains which often require longer analysis times.

 Analysis parameters

Materials: Inorganic solids
Type of information: Elementary, limited possibilities for chemical state
Precision: Semi-quantitative
Detection limit: 0.1% to 1 % atomic
Analysed depth: 5 nm, with possibility of depth profiling over one micron
Lateral resolution: around 10 nm

Use

Analysis of thin film composition

Analysis of defects

Surface analysis

Composition depth profile

Crystallographic analyses

 

Advantages:
-Analysis of very small regions (10 nm to microns)
-Semi-quantitative analysis
-High resolution imaging
-Determination of the oxidation state possible for some elements

Disavantages:
-Elemental composition only (limited information for organic compounds)
-Analysis performed under ultra high vacuum

Example 1

Auger electron spectroscopy can be used to distinguish elementary silicon (Si) and oxidized silicon (SiO2). Therefore, by Auger microscopy, it is possible to image the surface of an electronics chip and detect the distribution of Si and SiO2.

Example 2

Auger electron spectroscopy (AES) is a technique which is complementary to energy dispersive X-ray spectroscopy (EDX) often used in combination with scanning electron microscopy (SEM) for element identification. For instance, while EDX is not very sensitive to light elements, AES easily detects them. Moreover, AES is sensitive to the surface only with a probed depth around 5 nm whereas EDX has an information depth which is about 100 times larger. This surface sensitivity can permit the identification of surface segregation problems or impoverishment in alloys. Also, in combination with sputtering, it permits the execution of high resolution depth profiling, for instance in multilayered materials.

Example 3

Recently, some research groups have demonstrated that the thickness of graphene films, or the number of graphene monolayers, on different substrates could be determined from AES mesurements. The technique can also help to identify defects and dopants present in graphene films.

Elements detected : Lithium – uranium

Spatial resolution : ~ 10 nm

Other characteristics : EBSD-UHV, cpreparation chamber, heating stage, Ar+ sputtering

Manufacturer : Omicron Nanotechnology

Model : NanoSAM

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