Practical Estimation of Analytical Sensitivity for EDS in an Intermediate Voltage FEG-STEM

Abstract

One of the ultimate objectives for energy-dispersive X-ray spectrometry (EDS) in the analytical electron microscope (AEM) is single-atom detection in thin specimens, as well as quantitative microanalysis with high accuracy approaching ±1% relative. In order to realize the single-atom analysis, the design of the AEM has to be optimized with respect to improvements in spatial resolution and detectability limits. The detectability limit, as defined by the minimum mass fraction (MMF), is given by:where P is the peak intensity of interest, (P/B) is the peak-to-background ratio for that peak, and r is the acquisition time. To improve the sensitivity for analysis, any or all of the variables P, (P/B), and τ should be increased. Intermediate-voltage analytical electron microscopes combined with high brightness field-emission gun (FEG) are expected to improve the MMF, while maintaining high spatial resolution. Additionally, the MMF should also be improved by maximizing the solid angle of X-ray collection.