Atomic-level detection by X-ray microanalysis in the analytical electron microscope

Experimental measurements and calculations have demonstrated the detecton of 2 atoms, and the feasibility of detecting single atoms, in the analysis volume of thin specimens using X-ray energy-dispersive spectrometry (XEDS). The use of a 300 kV VG HB 603 field-emission gun analytical electron microscope, with the highest possible X-ray collection efficiency is required. Experiments with the only available thin-film standard (NIST standard reference material 2063) indicate that, even when seeking relatively high atomic number elements in a low atomic number matrix, specimen thickness (101 nm in this case) limits attempts to detect single atoms. Comparison of simulated and experimental spectra confirm the need for thin (∼10 nm) specimens and the validity of the Goldstein–Romig–Michael equation defining the detection limit. Using 10 nm foils of homogenized Cu–0.12 wt% Mn alloys it is shown that detection limits of 2 Mn atoms can be achieved with a 99% confidence limit. The principal instrumental factor that controls the detection limit is the XEDS detector count rate rather than the detector resolution.