Comparison of detection limits for EELS and EDXS

Simultaneous measurements have been made in the scanning transmission electron microscope to determine relative microanalytical sensitivities for electron energy loss (EELS) and energy-dispersive x-ray spectroscopies (EDXS). A photodiode-array parallel detector was used for EELS, and an ultrathin window Si(Li) detector subtending a solid angle of 0.18 sterad was used for EDXS. Energy loss spectra were acquired in the first or second difference mode to reduce channel-to-channel gain variations and to detect weak signals on large backgrounds. Both EELS and EDXS data were analyzed using multiple least squares procedures to fit reference spectra; this gave not only the fitting coefficients but also their standard deviations. Results showed that EELS is the method of choice for analysis of elements with Z 20 boosts the advantage of EELS for calcium but at iron EELS and EDXS have about the same sensitivity. Calculated estimates of the relative sensitivities for EELS and EDXS are in reasonable agreement with the experimental data