The performance of analytical EMS and EDX systems, measured with a nickel oxide test specimen

Abstract

A test specimen consisting of a 50nm film of NiO on a 200-mesh molybdenum grid can be used to evaluate the diffraction, EELS and EDX capabilities of an analytical TEM. Several laboratories have utilised this specimen and their results have been compared. One measurement is the Mo-Kα/Ni-Kα ratio, which characterizes the amount of stray radiation within a TEM column; values are typically in the range 3 to 10 for conventional TEM's and as high as 40 for instruments in which beryllium sheet is used to shield the upper and lower polepieces; see Fig. 1. Another criterion is the peak/background ratio of the Ni-Kα peak, the background being measured within a lOeV window beneath the peak. This ratio reflects electronic noise as well as column radiation but correlates well with the Ni-Kα/Mo-Kα ratio (see Fig. 1), indicating that column radiation can substantially affect the EDX background.The variations in performance visible in Fig. 1 are partly due to differences in TEM accelerating voltage. Fig. 2 shows that higher peak/background is possible at higher voltage, as would expected if the background were entirely bremsstrahlung radiation.