BACK to Techniques

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BACK to Techniques

 


Auger Electron Spectroscopy (AES)

Description

In AES the sample of interest is irradiated with a high energy (2 - 10 keV) primary electron beam. This bombardment results in the emission of backscattered, secondary, and Auger electrons that can be detected and analyzed. The backscattered and the secondary electrons are used for imaging purposes similar to that in scanning electron microscopy (SEM). The Auger electrons are emitted at discrete energies (see Auger Effect for more details), that are characteristic of the elements present on the sample surface. When analyzed as a function of energy, the peak positions are used to identify the elements and the chemical states present.All elements in the periodic table, except hydrogen and helium, can be detected, and the depth of analysis is in the range of 3 - 5 nm or top 2-20 atomic layers. If a scanning primary beam is used, the secondary electron images yield information related to surface topography. As the electron beams can be focused to a very small probe size, excellent spatial resolution (0.5 um) can be achieved.
Auger point analysis and scanning analysis can be performed with a spatial resolution down to 250 nm, while SEM resolution is around 100 nm. When ion gun is used for sputtering of top layers,
depth profiles can be run automatically and maps and line scans of Auger electron distributions can be generated

Comparison to XPS

Auger and X-ray photoelectron spectroscopy give similar information, and the choice should be based on advantages and disadvantages. The Auger spot size is much smaller than the XPS and has the capability of identifying fine features on the surface. The XPS has the capability of determining surface chemical structure and bonding through the use of chemical shifts. Although Auger lines also exhibit chemical shifts, these are not generally as large or as well-documented as those obtained by XPS. Also, X-radiation used in XPS imparts less damage to the sample surface than does the electron beam used in SAM. As mentioned above, the spatial analysis and imaging capabilities of the scanning Auger microprobe make it a very useful and complementary technique to XPS.

Modes of Operation

The Auger analysis can include Survey Scans, High-Resolution spectra, Depth Profiles, Imaging, Mapping, and Point Analysis. Survey scans of the entire range of Auger electron energies, carried out by detecting and counting the number of Auger electrons, could reveal the presence of contaminants on the sample surface. By taking into account the sensitivity factors of the elements detected, quantification is possible. This is useful in identifying the unknown elements and estimating their concentration on the surface. With argon ion bombardment, the surface layers can be removed gradually, and analysis carried out on new layers exposed after each sputtering cycle. This is known as depth profiling, and it provides the relative concentrations of elements of interest as a function of depth. Finally, the Auger elemental maps display the presence and the distribution of elements of interest within the area analyzed.
A typical analysis of an unknown surface region (survey scan on the as received surface and after three different sputter intervals) would take 1 - 2 hours.

Instrumentation

AES is available on AXIS 165 spectrometer and on JAMP 9500F microprobe..

Applications

AES is used mainly to determine the composition of small areas on the surface, either as point analysis or mapping. Typical applications include corrosion, plating, integrated circuits etc.different sputter intervals) would take 1 - 2 hours.

Examples

AES spectrum from a Cu grid: on the top is the measured spectrum, below is its derivative

 

More examples:

Analysis of Mayerthorpe meteorite

Imaging of Ag nanoclusters on silicon

Palladium nanowires on silicon

Oxidation of grain boundaries in TRIP steels

Composition depth profiles of thin films: linescans of GLAD cross-sections