VERY LOW ENERGY PEAK SHIFTS IN EDS SPECTRA

摘要

The response function of energy-dispersive X-ray spectrometers (EDS) has been a topic of investigation for as long as the EDS has been used. Full physics-based models were developed, which allow the calculation of the detector response function depending on detector construction parameters and in relation to the measured X-ray energies [1,2]. It is known that the low energy side of the detector response function (peak shapes) depends much from the detected photon energy, because it is important how deep the X-rays interact within the detector material to create an electron-hole pair cloud. If the interaction is near the detector surface, electron escape is likely and then the total measured energy of the photon has a loss, due to different effects of the incomplete charge collection (ICC) [2]. With photon energies < 500 eV, the typical low energy tailing in peak shapes morphs into 'all photons ICC", Finally visually as a complete peak shift having a lower measured energy than the original X-ray energy (combined with higher peak width than expected by theory). Usually the photon interaction depth decreases with lower energies, so the shift is increasing. In [2], X-rays in the energy range from 100 eV to 10 keV were investigated for three spectrometer systems different in construction, including one of which was already an SDD. The more recent SDD technology [3] and X-ray entrance windows [4] allowed investigations of X-rays even < 100 eV, which came with a surprise, because suddenly the peaks with < 100 eV photon energy are not shifted. We have modified empirically an old used shift-correction, which had a further rise of shift down to 0 eV, replaced by one which drops down below 150 eV (see Fig. 1). Finally, the measured shifts of Al-L and Si-L is calculated practically with zero and the Be-K shift is less with the modified correction curve.