Measurements of the quantitative analytical depth resolution at evaporated aluminium- and silver-layers with the FEG-EPMA JEOL JXA-8530F

Abstract

The aim of this study is to extend our general approach to the spatial resolution in the quantitative element analysis that can be achieved with a FEG-EPMA by systematic measurements of the depth resolution. The test specimens are Al and Ag surface layers with various thicknesses on top of non-fluorescent substrates. By choosing an appropriate X-ray line and by varying the primary electron energy, E0 , we determined the minimum value of E0 for which the depth of the signal source volume is identical to the layer thickness. This value is defined as the depth resolution. With respect to the excitation energy of the characteristic X-rays, the depth resolution for the quantitative element analysis is found to be below 150 nm for Al (Kα at 3 kV) as well as for Ag (Lα at 5 kV).The prediction of the depth resolution at low primary electron energy E0 by means of calculations of the ionisation range of electrons or by Monte Carlo (MC) simulations is quite inaccurate because both predict better values compared to the measurements. Since we regard test specimens without disturbing secondary fluorescence it is obvious that both calculations and simulation predict too small signal source volumes for a so far unknown reason. The same discrepancy was observed for the determination of the lateral quantitative resolutions in previous studies. Therefore systematic measurement errors can be excluded. The measurements presented in this paper are very helpful for further improvements of calculations and MC-simulations at low primary electron energies E0 because specimens without secondary fluorescence are considered only.