EDS/WDS Measurements of Sulfur (S)
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Table 1384 lists the main lines of sulfur (S) used in EDS analysis. However, it is very often that the S K line overlaps with X-ray lines from other elements, e.g. molybdenum (Mo).

Table 1384. Main lines of sulfur (S) used in EDS analysis.

Line
Energy (keV)
K ~2.3

It is very general to use SEM-EDS and TEM-EDS techniques to qualitatively map the distribution of sulfur in structures and nanoparticles. However, quantification of sulfur content using EDS technique is very challenging because:
        i) The quantification precision for light elements is still a question.
        ii) It is very common that the sulfur content determined from EDS analysis is slightly lower than the real sulfur content due to the unavoidable sublimation of sulfur in the high vacuum environment during the measurement.

For MoS2, the overlap between the L series peaks of Mo and the S Kα peak is very pronounced: only a broadened peak with a tail towards the high energy end can be seen with EDS. Figure 1384 shows the sulfur and molybdenum peaks overlap in the EDS spectrum, but are separated and sharp in the WDS spectrum.

Comparison of the EDS and WDS spectra taken from MoS2
(a)
Comparison of the EDS and WDS spectra taken from Molybdenite (MoS2)
(b)
Figure 1384. Comparison of the EDS and WDS spectra taken from Molybdenite (MoS2): (a) and (b) are obtained from different measurements. [1]

INCA EDS software is used to extract the maps in Figure 1384b.

EDS measurements of MoS2 nanosheets
EDS measurements of MoS2 nanosheets
(a)
(b)
EDS measurements of MoS2 nanosheets
(c)
Figure 1384b. EDS measurements of MoS2 nanosheets: Elemental mapping images of Mo (a) and S (b), and (c) Spectroscopy indicating the presence of Mo, S, and O. Adapted from [2]

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 Table 1384 lists S-examples of thicknesses at which the thin-film approximation is no longer valid due to X-ray absorption effects in specific materials.

Table 1384. 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)
FeS
180 50 S Kα Fe Kα (6.398 keV) and S Kα (2.307 keV)

 

 

 

 

 

 

 

[1] www.bruker.com.
[2] Revannath Dnyandeo Nikam, Ang-Yu Lu, Poonam Ashok Sonawane, U. Rajesh Kumar, Kanchan Yadav, Lain-Jong Li, and Yit-Tsong Chen, Three-Dimensional Heterostructures of MoS2 Nanosheets on
Conducting MoO2 as an Efficient Electrocatalyst To Enhance Hydrogen Evolution Reaction, ACS Appl. Mater. Interfaces 2015, 7, 23328−23335.

 

 

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