Detection limits for Analytical Electron Microscopy with Electron Energy Loss Spectrometry and energy-dispersive x-ray spectrometry

Abstract

The measurement of trace level constituents, arbitrarily defined for this study as concentration levels below 1 atom percent, has always been considered problematic for analytical electron microscopy (AEM) with energy dispersive x-ray spectrometry (EDS) and electron energy loss spectrometry (EELS). In a landmark study of various microanalysis techniques, Wittry evaluated the influence of various instrumental factors (source brightness, detection efficiency, accumulation time) and physical factors (cross section, peak-to-background) upon detection limits. Although the ionization cross section, fluorescence yield, and collection efficiency favor EELS over EDS, the peak-to-background ratio of EELS spectra is much lower than that of EDS spectra, leading Wittry to suggest that the limit of detection should be 0.1 percent for EDS and 1 percent for EELS for practical measurement conditions. Recent developments in parallel detection EELS (PEELS) indicate that a re-evaluation of the situation for trace constituent determination is needed for those elements characterized by "white line" resonance structures at the ionization edge.