I use EDAX package and would like to know if there is any specific method to get reliable and nice EDS maps out of thin lamellae (in SEM).
Thermal drifting is one of the main issues. Besides, getting proper special resolution for nanometric precipitates in metallic alloys seems to be challenging.
Can you tell us a little more, how thin is thin? Are you using a TEM or SEM or STEM, and what type? How have you prepared your samples for EM? EDAX package has 'Smart Drift Correction', are you using that? What metals are you interested in?
I don't know which microscope you are using but certainly if you are planning to do EDS maps of thin lamellae then i would recommend you to go for EFTEM images Energy filter transmission electron imaging. By this unique technique one may acquire the TEM images at various energy losses and superimposed them to get the RGB (red, green and blue) images. These images are much better in terms of resolution which you can not achieve by SEM maps.
Thanks you all for your inputs.
I am focused on metallic alloys including light alloys and ferrous alloys.
By thin lamellae I mean
The main problem of transmission EDS is that the X-ray signal is very low compared to normal EDS: a major portion of the primary electron beam would penetrate the material without much interaction at all, especially at high energy. The interaction volume is mainly determined by the sample thickness. In this aspect you need a very efficient SDD detector to cover a large solid angle from the sample surface, else you need to image the sample for very long time. You can also try to increase the current, b but too much current will increase the electron spot size, which defeat the propose of doing transmission EDS. For a properly aligned system one can get 1 nm spot size with 1 nA beam current at 30 kV beam energy, which should be sufficient for transmission EDS analysis.
And the sample should be very thin for transmission in SEM, 100 nm is still way too thick according to my taste.
Another effect that might need notice is that the transmitted electron from the sample would hit any material in the chamber, especially the STEM detector. If the SDD detector is not well positioned, you might observe a lot of signal from silicon, which comes from electron hitting the STEM detector.
Thanks Luyang.
The lamella thickness seems to be good enough as far as I can see by STEM images. I can manage the 1 nm spot size at 30kV, but as you mentioned I normally get a lot of Si signals from the detector itself, which is one of the main challenges. If I push out the detector also, I would not get a nice image then using other detectors....
Dear Ehsan,
I don't think you can change the relative position of the EDS detector to the STEM detector. You may try to modify your STEM sample holder in order to block the X-ray from the STEM detector: quick and dirty, you can use some Al foil around your STEM sample holder.
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