Backscattered electron effects in a high-angle EDXS

The performance of a high take-off angle energy dispersive X-ray spectrometer (EDXS) on a 200 keV STEM has been investigated. A simple modification to the multichannel analyser (MCA) was used to extend the energy range beyond 200 keV to confirm that high energy, backscattered electrons were entering the detector. Up to 50% of the total count rate was observed to be due to these electrons. The spectrometer performance was determined both with and without a carbon filter which was used to stop the backscattered electrons entering the detector. It is shown that these electrons reduce the resolution and increase the dead-time and background noise in the X-ray spectra. The performance of the high take-off angle detector is compared with that of a horizontally mounted detector on a similar 200 keV STEM and a 300 keV STEM.