The EDS detector should be above your sample with an angle tilt α. I suppose if you check the EDS with sufficient energy, the signal near the surface and inside of your sample will overlap.

Dear Anna Neubeck ,

when having the detector below the sample the x-rays produced at the top*) of the sample have to penetrate the whole sample and will undergo attenuation which among other parameters depends on the sample thickness. I must admitt that in the case of TEM the sample thickness is quite low, but the x-ray energies involved can be also very low, especially for quite low Z elements. The X-ray attenuation is this energy regime is quite high.

So for having the detector in front of the sample ( 'back scatter geometry') mainly the penetration depth of the exciting electrons and the escape depth of the x-rays affect the x-ray yield. There is only minor dependence on the sample thickness in this case.

*) at the top of the sample you have the largest x-ray yield due to the highest electron beam flux there.

Dear Anna Neubeck ,

As Dr An-Giang Nguyen already pointed out, the detector should be above your sample with an angle tilt α.

Nevertheless, one area detector may be positioned in the TEM experiment, collecting the emerging scattered photons wavelengths. However, the TEM beam may lose some energy by elastic and inelastic scattering inside the sample, as it came from the transmission.

At this limit, a false identification may occur, based only on the photon's emerging energy. A piece of concise previous information from the sample's origin is essential.

The detectors already positioned below the sample are for the transmitted electrons for the TEM imaging.

Best regards,

WNM

in addtion to what Gerhard Martens has already mentioned, I think that you'll get a much higher background due to Bremsstrahlung radiation in foreward direction. So smaller peaks are added on a larger background ... Best regards, Dirk

Thank you all for your informative answers.