I'm doing SEM/EDX for nanofiber with some additives and EDX results change from time to time for the same sample. Also the results are not consistent with the amounts of materials I use in my experiment. I'm thinking about test period, is there specific time requirement for the test? Is the time controllable or it's automatically determined by the device? And if detection period changes, will the results be the same or it is updated with time due to enhanced detection??
Of course, the acquisition time is affecting the results:
1. Obviously, there is just a statistical effect: number of counts. The columns in the histogram are "jumping", then become stable. Just the law of large numbers.
2. Beam damages. The beam destroys the sample. This is especially important for thin samples (films, coatings, etc).
3. Carbon deposition under the beam. Even the purest chamber has some carbon contamination (SEM users know this annoying effect very well - dark spots).
4. Charging. Including local degradation of conductive coating.
Thus, in ideal world it would be easy: more counts, higher precision. But the real physical world is more complex. Experienced operators can choose the most optimal parameters of analysis. Sometimes, it is a kind of art.
Good luck!
If your sample is strongly charging, there may be an effect of that.
Also, since you say you're making nanofibers, there may be some sort of beam damage by the high impact to the sample.
Of course, the acquisition time is affecting the results:
1. Obviously, there is just a statistical effect: number of counts. The columns in the histogram are "jumping", then become stable. Just the law of large numbers.
2. Beam damages. The beam destroys the sample. This is especially important for thin samples (films, coatings, etc).
3. Carbon deposition under the beam. Even the purest chamber has some carbon contamination (SEM users know this annoying effect very well - dark spots).
4. Charging. Including local degradation of conductive coating.
Thus, in ideal world it would be easy: more counts, higher precision. But the real physical world is more complex. Experienced operators can choose the most optimal parameters of analysis. Sometimes, it is a kind of art.
Good luck!
Yes the post synthesis duration had an impact on the composition.
Also the method employed has a lot to do with the stoichiometry of the material, like in case of chemical methods, there is always formation of carbon which is there always and hence disturbs the stoichiometry.
The post synthesis duration like in case of transition metal oxides or pervoskites or chalcogenides causes increase of oxygen content that might be the result of oxidation of samples.
This phenomenon usually observed in FE-SEM during EDX analysis. It could be related to charging effect, which finally contribute to post synthesis composition variation.
A user with good experience can really avoid this problem with technical knowledge and carefully choosing the operational parameters.
In addition to Denis Korneev's post:
If your specimen is really a nanofiber, forget about quantification. Treat your results as pure qualitative ones, means use them only to detect presence/absence of elements, not to compare their quantities. SEM beam diameter (X-ray excitation area) are bigger than diameter of your fiber, so amount of detected X-rays will depend heavily on position of a fiber under the beam and will change every time you move your specimen.
Try to calibrate EDX often and check on standard sample each time before analysis.
That might also help to improve consistent in results.
EDX analysis requires optimization of the acceleration voltage (HV) by using a standard sample.
also the area analysis when you run the SEM/EDX on your sample might be effected. I mean when you wanted the fit morphology what you want to. Immediately, sometimes that area represents your composition.
Dear Hanaa Aamer ,
The switching time has a strong influence on the results. The power of the beam also has a natural effect. The greater the power, the greater the change. Therefore, we are looking for regimes that do not change the morphology of the thin coating. Good professionals know the problem and know what regimes to do it. This is often achieved by compromising power and time.
Adding to Denis, the voltage kV used also does matter in detection and quantification.
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