Investigations towards optimizing EDS analysis by the Cliff‐Lorimer method in scanning transmission electron microscopy

The critical specimen thickness up to which the Cliff‐Lorimer method can be used without additional corrections was measured on some steels and nickel‐base alloys for soft x‐rays with line energies between 1 and 3 keV. The critical thickness values measured are 50 nm at 1 keV and 450 to 500 nm at 3 keV. These results indicated that verification of the calibration measurements used for determining the correction factors was necessary in the case of soft radiation. The measurements led to a further optimization of the parameters in the equation used for calculating the ionization cross‐section The published equations for absorption correction, which becomes necessary when the critical specimen thickness is exceeded, were found to lead to an overcorrection in the case of very thin foils and an insufficient correction in the case of thicker specimens. However, it is only of significance if the specimens are very thick or errors less than 5% are aimed for.