Dear all,
we are using standartless quantification methodes with our EDX system.
The question arrises which combination of xray lines is the correct one for this quantification.
For example we have a mixture of Titaniumnitride, which we assume is not TiN, but TiN_(1-x). We want to investigate this with EDX.
Ti Ka1 = 4.51 eV
Ti La1 = 0.45 eV
N Ka1 = 0.39 eV
The measured ZAF corrected ratios of N Ka1/Ti Ka1 and N Ka1/Ti La1 are different for our sample. In litrature like [1] most of the quantification is done with only K-lines, but i dont find the correct reason.
My assumption is, that the uncertantie of the ZAF correction is dependend on the Energie. Hence, i would asume the comparison of lines with similar energy would lead to more accured results.
We are aware of the problem of detecting light elements. The same problem arrises if we want to investigate for example a mixture of galium and aluminium.
Kind regards,
Sascha Wolter
[1] Goldstein, J. et al. Scanning Electron Microscopy and Microanalysis. (Springer US, 2003). doi:10.1007/978-1-4615-0215-9
1. Standardless analysis for light element is not really reliable.
2. You have an overlapping of Ti and N peaks.
Rather tough task for EDS even with standards.
If you have a bulk specimen and do not really need the main advantage of EDS analysis, its high spatial resolution, the do not use EDS at all. There are other methods, much for suitable for your task.
Dear Mohammad Ebdah and Vladimir Dusevich,
thank you for your contribution. I agree with your statement, unfortunatly we dont have auger-spectroscopy, LIBS or XPS available for us. Please note that the TiN case is just one example, we also have the same questions for different material compostion, like Al and Ni. The question is which EDX lines to choose for quantifikation.
Kind regards,
Sascha
If you're planning on quantifying low energy X-rays you really need to worry about an accurate deconvolution method for separating out peaks and the background. In general it is better to quantify with K-lines because they have a higher fluorescence yield and likely to have less overlaps with neighbouring peaks (in general). This in addition to being higher energy so having lower rate of absorption. Normally the only reason to quantify with an L-line is because your accelerating voltage is too low to be able to detect the K-line. For an element like Ti I would try to quantify with the Ti-K shell at 4.5eV background subtraction will be easier and there will be less overlap.
In TEM many people look at the ratio between K and L to check that absorption correction has been correctly applied. You could also use knowledge from the Ti-K quantification to help with the peak separation at low values because you can feed in what the expected Ti-L x-ray counts should be.
In my knowledge
analysis of your sample for XRF and XPS. It is a better way to the determination of chemical composition % exactly.
I faced this problem more than 30 years ago, when I tried to analyze TiN and TiNO films, The big problem is that NK line interferes with TiLl, which is beyond the energ y resolution of even an automated electron microprobe with WDS spectrometer. EDS is ruled out in this stuff, as you can imagine. Yu can find some details in a paper I coauthored, published in 1983 in X-ray Spectrometry. It includes a combination of electron microprobe and nuclear reaction analysis (NRA). I gave up in analyzing N by the electron microprobe, its concentration was determined by NRA in a Van de Graaff 5 MeV accelerator.
Good luck
It is better to use lines with no overlapping and with good intensity at chosen accelerating voltage. For bulk analysis it is better to use other methods than EDS.
You use SEM-EDX method, which is also called as ED-EPMA. "Standardless" is not reliable. You must measure a reliable similar sample to check the validity of your analysis. Depending on the electron voltage, and detector window material & window thickness, the intensity ratio of Ti La/Ka changes. The reliability also depends on how homogeneous sample you measure as well as electron beam size. If you want to obtain only Ti:N=1:1(one digit precision), it may be possible. But 1.0:1.0, it is not easy. 1.00:1.00 is never achieved. But relative change of N is sometimes detectable, if you have several similar but differently processed samples.
N is a very difficult element to measure even WD-EPMA, which is higher precision and higher sensitivity than ED-EPMA.
If you use higher voltage electron beam, X-rays are produced deeper place. The absorption edge overlaps the emission line for low energy X-ray lines, then Ti La is heavily self-absorbed in the sample body itself, but Ti Ka is less self-absorbed. Thus La/Ka changes as the change of electron acceleration potential.
Please check my ResearchGate open papers on La/Lb intensity ratio for XRF and EPMA. This holds for La/Ka ratio.
I want to thank you all for your contributions.
But please note, the question arrising is not related only to the quantification of TiN. I am aware of all the problems of peak deconvolution, background, auger and xray yield etc. for nitride. The case of TiN is only an example.
I am still not sure which lines to choose for quantification. The only hints i got was from the answer of Katherine E. Macarthur, that the background will be lower for higher energies. And you only choose the L lines if the K-energy is too high. Additionally the answer from Jun Kawai indicates a reason depending on the detector. If anyone can add something to this point, i would be glad. (I am currently working on the papers of Jun Kawai)
But lets assume a mixture of Cr (Ka1=5.41eV, La1=0.57ev) and Mo (Ka1=17.4ev and La1=2.28ev). I would agree with all of your statements, i should avoid the lower energies, hence i will use the Cr Ka1 line for qunatification.
But which line should i choose for Mo? Both energies are high enough for quantification, we have no peak overlap and the background can be determined quite well.
Kind regards,
Sascha Wolter
There are no simple rule for choosing lines. All depends on the task.
Please, remember, that background will be not lower, but higher at higher energies. It's peak/background ratio that can be improved. But not always. For light elements absorption rise substantially with voltage increasing, and in combination with higher background makes higher voltages rather unsuitable for light elements quantification. So, if you have light elements in your specimen, you have to work with lower voltages and it may force you to choose L lines for some of elements.
For Cr-Mo mixture, if you are not concerned about spatial resolution, you can go to 30 kV and work fast and comfortably with strong K-lines. But if spatial resolution is important, you'd better work at 10 kV with Cr K-line and Mo L-line.
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