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 held-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 ( similar to 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. (C) 1999 Published by Elsevier Science B.V. All rights reserved.