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STEM-EDXS System for Atomic-Sensitivity Elemental Mapping

The Nion UltraSTEM aberration-corrected cold field emission scanning transmission electron microscope (AC-CFE-STEM) can focus a beam current of about 0.2 nA into an atom-sized (~1.5 Å large) electron probe at a primary energy of 60 keV (and about 1 nA at 200 keV). Using such an electron probe with an ultra-thin window silicon drift detector (SDD) of 30 mm (0.1 sr solid angle) in a Mark I system at 60 keV allowed energy dispersive X-ray spectroscopy (EDXS) to identify individual atoms while tracking their occasional hops to neighboring lattice sites [1]. Here we report on the design and performance of a Mark II STEM-EDXS system with about 10x higher efficiency, which allows single impurity atoms to be identified even when they are very mobile.