Spatial Resolution and Detection Limits of Analytical STEM

7 Spatial Resolution and Detection Limits of Analytical STEM 

Williams et al. (2002) have reviewed the current state of AEM X-ray microanalysis, and they suggest ways in which the highest resolution of X-ray mapping may be achieved in the STEM with an EDS spectrometer. Because of their small collection angles and thin specimens, very small numbers of X-ray counts are generated, so the minimum detection limit is typically at best 0.1 wt%. This value is an order of magnitude worse than the 0.01 wt% figure for bulk-specimen in an SEM/EPMA. 

Ziebold (1967) has defined the detection limit of any analytical technique in terms of the minimum mass fraction (MMF) detectable according to the expression  

With regard to X-ray microanalysis in the AEM, the bolometer detectors can lower the detectability limits from 0.03 wt% to 0.006 wt% in 100 nm thick Cu-Mn specimens. Even in 10-nm-thick specimens, 0.02wt% will be detectable with these detectors. 

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