EDS Measurement of Nitrogen
- Practical Electron Microscopy and Database -
- An Online Book -
Electron microscopy
  Microanalysis | EM Book                                                                   http://www.globalsino.com/EM/  
 

 

Light elements such as nitrogen (N K) and oxygen (O K) are detectable with different modern EDS detectors, e.g. ultra-thin window X-ray detectors (see page4589). However, an absorption correction will be needed even for the thinnest TEM specimens. Note that absorption does not only happen in the specimen itself but also in surface layers, e.g. contamination, and intentionally coated carbon and metal conductive layers, and in the detector window. For instance, the X-ray transmission of Be window is close to 100% for energies down to 2 keV, while it drops rapidly to about zero at 0.5 keV. For instance, nitrogen X-ray line is almost fully absorbed by such a window. Significant decrease of detection efficiency for N Kα can be induced by carbon contaminants due to the high mass absorption coefficient (25500 cm2g-1) of this X-ray line.

Figure 1738 shows the deconvolution of an EDX spectrum with peak overlaps, taken from a material that contains O, Ti, N, and C elements.

Deconvolution of an EDX spectrum with peak overlaps

Figure 1738. Deconvolution of an EDX spectrum with peak overlaps. [1]

For most common detector designs, nitrogen produces a very weak response, resulting in its unreliable detection for most materials.

As discussed on page4650, X-ray absorption is a function of the energy of X-rays. Low energy peaks will be more strongly absorbed than high energies ones. For thick TEM samples, k-factor correction due to X-ray absorption is needed in order to accurately quantify EDS measurements. Table 1738 lists N-examples of thicknesses at which the thin-film approximation is no longer valid due to X-ray absorption effects in specific materials.

Table 1738. Examples of limits to the thin-film approximation caused by X-ray absorption: Maximum thicknesses of thin specimens for which the absorption correction (or error) is less than ±10% and ±3%.

Material

10% error in kAB
3% error in kAB
Absorbed X-ray lines
Primary X-ray lines
Thickness (nm)
Si3N4
413 6 Si Kα and N Kα Si Kα (1.739 keV) and N Kα (0.392 keV)

[1] J. Berlin, T. Salge, M. Falke, and D. Goran, Recent Advances in EDS and EBSD Technology: Revolutionizing the Chemical Analysis of Chondritic Meteorites at the Micro- and Nanometer Scale, 42nd Lunar and Planetary Science Conference, 2723, (2011).

;