Accurate measurement of absolute experimental inelastic mean free paths and EELS differential cross-sections.

Methods are described for measuring accurate absolute experimental inelastic mean free paths and differential cross-sections using DualEELS. The methods remove the effects of surface layers and give the results for the bulk materials. The materials used are VC0.83, TiC0.98, VN0.97 and TiN0.88 but the method should be applicable to a wide range of materials. The data was taken at 200keV using a probe half angle of 29mrad and a collection angle of 36mrad. The background can be subtracted from under the ionisation edges, which can then be separated from each other. This is achieved by scaling Hartree-Slater calculated cross-sections to the edges in the atomic regions well above the threshold. The average scaling factors required are 1.00 for the non-metal K-edges and 1.01 for the metal L-edges (with uncertainties of a few percent). If preliminary measurements of the chromatic effects in the post-specimen lenses are correct, both drop to 0.99. The inelastic mean free path for TiC0.98 was measured as 103.6±0.5nm compared to the prediction of 126.9nm based on the widely used Iakoubovskii parameterisation.