Does the Energy-dispersive X-ray spectroscopy (EDX or EDS) provide the chemical composition of the material as metal or metal oxide? i.e the results obtained from the EDX are in percent for metal or for metal oxide?
I found in different published papers that the data obtained from EDX are in % of metals and other papers as % metal oxide. When we use it as metals and when as metal oxide?
Is the following sentence right or false? EDX determines the chemical composition of materials as metals and exposes them as oxides but it doesn't mean that they are oxides. Many thanks for your reply.
I'm not entirely sure if I understood your question well.
EDX determines the atomic composition of the specimen. It does not give chemical information (e.g. oxidation state, chemical bonds). For quantitative analysis EDX is not really suitable for light elements (like O). It can detect the presence of oxygen, but the quantification is tricky.
Therefore, what you most probably find in literature is that they determined the relative number of oxygen atoms in the (metal) specimen and assumed that the oxygen is present as metal oxide. From this one could determine the metal metal-oxide ratio (probably with a significant uncertainty)
I hope this helps.
EDX just show the relative amount of atoms. Chemical structure doesn't matter in this case. For example, if you have the result:
Cu: 40%
O: 40%
C: 20%
You can just guess what is it? Probably, it is contaminated CuO, but it is not surely.
Interpretation of EDX data is not obvious. If you use EDX with SEM it is necessary to remember that EDX works only for thin layer (few microns or less) on the surface and it is very sensible to contamination.
Good luck!
EDS gives you only atomic composition. It can tell you that the sample contains, for example, oxygen and a metal, and the proportion between them.
EDX software can be configured to report the data in many ways. You choose. Either 'all elements' (I think this is what you refer to as 'metals' - though the elements do not need to be metals to be detected - anything from boron to uranium is detectable); 'element by difference' - this is one element nominated, usually oxygen, and the weight % of that element is the difference between 100% and the total of all other elements; 'element by stoichiometry' (your metal oxide) - where one element is selected, again usually oxygen, and its percentage is calculated by combining oxygen with the other elements that can form oxides in stoichiometric proportions - elements such as F, Cl are not combined. "element by difference' is by convention normalised, but you can choose to display the results of 'all elements' and 'element by stoichiometry' either normalised or not. If you have measured standards, then choose non-normalised for a better understanding of the material - Standardless software generally normalises the results by default, this can cause problems if the sample contains bound water - it will overestimate the percentages. There are also the possibilities of reporting the results as wt% or atomic wt%, again it is up to you to decide for your application which to use. The field of mineralogical analysis where a lot of this software was first developed uses oxide percentages as a standard way of reporting elemental data, even though in the minerals the elements may be combined differently if they are not simple oxides.
So the EDX method is simply determines the quantity of the element present, it can be reported in any way you choose.
I can't express my thankfulness for your valuable comments and answers. Many thanks for all, Zoltan Hegedus, Denis Korneev, Rodrigo Magnabosco and Ian J Slipper .
Please, I have another inquiry; EDX quantification of rough materials (instead of smooth metal samples) can carry large errors. Is that right? I want to discuss this sentence.
Many thanks.
Yes it can have large errors as the assumptions for quantitative analysis are that geometry is correct (angle of beam, angle of sample, take-off angle of detector). Deviation from a constant flat surface will increase the error. However if the sample is homogeneous, (and not too rough!) you can minimise the error by analysing a large area rather than a spot. If the sample is rough then it is often best to leave the analysis as qualitative rather than semi-quant.
Dear Ian J Slipper,
really, I thank you very much for your valuable comments.
When you measure by stoichiometry, the system does not measure oxygen but only the other elements you had input. Oxygen is deducted from the concentrations found for the other elements. Stochiometry is a good way only if you are certain of the valence and certain that all oxygen is linked with other elements. If there is oxygen linked with an element that you can not measure (like H2O) it does not work. If there are several formulations between oxygen and one of the element (for example Fe2O3 and FeO or Fe3O4) it does not work.
Yes, quantification may carry VERY large error when the sample is not homogeneous or not flat or not horizontal or not at the good position with regard to the detector or if it is too small to contains all the interaction volume. That the reason why preparation of the sample is very important.
thanks everyone I also get my answer from your valuable discussion
Ian J Slipper Zoltan Hegedus why does one particular element has more than one peak in the edx spectrum sometimes? Like for fe304 nanoparticles I found 3 different peaks designated as iron. I thought may be it is because of the different oxidation states but here I gotta know edx doesn't reflect anything on the chemical composition. please help me out!
Arti Tyagi - it's because EDX is produced by fluorescence decay of the core hole produced by the electron beam. This means if there are different decay routes then you will have multiple peaks for the same element. for example lets say you create a hole in the 1s level of iron. This hole can be filled by a 2p or 3p electron which have different energies and so the resulting X-rays will also have different energies.
I have a question for the experts Ian J Slipper Ian J Slipper Zoltan Hegedus though - in the quantification I presume the software has some cross section factor included since surely the probability for knocking out a particular core electron depends on the energy of the incident electrons, and its decay pathway depends on the core levels involved (or else all peaks of a particular element would have the same intensity)?
Andrew G Thomas thank you. so when this analysis gives the % composition of each element, does all these different peaks (decay pathways) have equal weightage?
If normalization was not turned on, then sum of components almost certainly will be not 100%.
If it differs from 100% by just a few percent, it means analysis was good. If it differs a lot, it means analysis was bad; produced concentrations will not match the real ones.
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