Very low energy peak shifts in EDS spectra

Abstract

Abstract The response function of energy-dispersive X-ray spectrometers (EDS) has been a topic for investigation as long as EDS has been used. This work systematically investigates soft X-ray peaks with energies below 150 eV in regard to the detector energy calibration linearity. It was found that Si-L (92 eV) and Al-L (73 eV) lines are not shifted in energy position in comparison to higher energy K-lines of boron, carbon and nitrogen. The reason is simply the silicon detector material has a large absorption jump at 99 eV (Si-L2/Si-L3), which causes much higher detection depths of photons with energies below 99 eV. There is also less shift than assumed with older approaches in the energy region 100 to 149 eV (Si-L1). It is also expected that Li-K radiation will not be affected by an energy shift due to detector artefacts. The authors propose a modified shift-correction which corrects this detector artefact and linearizes the energy calibration of measured EDS spectrum below 600 eV. This energy shift effect of the measured X-ray lines is in principle with any silicon-based X-ray detector. But the shift value depends also on the front contact layer design and quality. The novelty with changed correction is that no shift is applied for X-ray peaks below 99 eV. Older applied correction procedures were found to produce a line energy misplacement in spectrum for this energy region.