What is the Effective Geometrical Collection Efficiency of Your XEDS Detector? A Routine Procedure Applied in a SEM Laboratory.

Abstract

In this contribution, two large-area EDS detectors were tested according to the procedure proposed recently by Procop et al. In a first step, the optimal working distance (WD) in the two different SEM chambers was determined by moving the sample stage in the Z direction and monitoring the count rates from a field of view of 25.6 μm. The WD at which the highest intensity was measured was selected as the optimal position. Next the Cu Kα peak was measured at different relative EDS positions while it was partially removed from the fully inserted position. The spectrum at each location was collected for 10 sec using the highest pulse rate and intermediate current (2.3 nA) to minimize pile up effects (13% dead time). The ‘inverse squared normalized intensities vs. relative EDS position’ used to extract the true detector – specimen distance shows a non-linear relationship even at the minimal relative positions, which indicates shadowing due to obstruction or use of an unsuitable and/or off-centered collimator. The normalized count rates measured as a function of the EDS distances, results in a too low GCE (too low true solid angles) for both tested detectors. The search for sources of losses of signal due to possible shadowing effects is in progress.