Energy Dispersive X-ray Spectroscopy

Energy Dispersive X-ray Spectroscopy
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Technology Details
Other Names	EDS, EDX, %other names and abbreviations, separated by commas%
Technology	Characterization
Equipment	List of EDS, EDX equipment
Materials	%Optional materials processed%

Energy Dispersive X-ray Spectroscopy (EDS, EDX) or Energy Dispersive Analysis is an analytical technique that can give quantitave and qualitative information on the elements that are present in an specimen. EDS takes advantage of the x-ray generated on a sample by the high energy electron beam of the Scanning Electron Microscope (SEM). Each atom releases x-rays whose finger print is unique.

Equipment

Both technique use the same exciting source and are housed in the same equipment.

Method of operation

The electron beam (>15KV) generates mainly two types of excited electrons (secondaries and primary backscattered) as the electrons leave the sample, the specimen charges (ionizes) in order to relax (neutralize) the atoms, a higher level electron moves into a lower level and the extra energy is released in the form of x-rays. These x-rays are a result of energy level transition within the energy levels of the atom therefore the eneryy liberated is characteristic of each atom.
E=hc/ʎ̩, E= E_high-E_low
It is this characteristic energy that can then be associated to the electromagnetic radiation emitted, the x-rays. The x-rays intensity are measured versus their energy (dispersive).

Parameters

Electron Beam Energy, this must be high enough to excite core electrons
Atomic number of the elements, EDS works better for higher Z elements
Sample preparation, sample should be flat and clean
Similar elements, elements that are close in the periodic table, or belong to the same group, often have overlapping peaks which difficult their identification

Subtechnology

Both techniques take place in the same instrument, use same exciting source, but different detectors.

Applications

This technique is a very useful tool for the identification and quantification of the elements present in a sample. It relies on the SEM highly energetic beam to create x-ray emission in a sample, therefore it is not suitable for thin films <100nm analysis; it is also not recommended for the analysis of low z elements. This technique does not give oxidation state information i.e. elemental metal and metal oxide both contribute to the metal atom signal and are undistinguishable.

Periodic table showing the energies of x-ray emitted by different elements.

References

"Scanning Electron Microscopy and X-ray Microanalysis", 3rd Ed.,Goldstein, Newbury, Joy, Lyman, Echlin, Lifshin and Sawyer, 2003, Plenum Publishing Corp., ISBN13: 978-0306472923