Lateral sensitivity in electron probe microanalysis studied by Monte Carlo simulations involving fluorescence enhancements.

In electron probe microanalysis, secondary fluorescence can occur leading to an increase of the volume analysed, degrading the lateral resolution of this technique. An adequate knowledge of the interaction volumes from where the different signals of interest are detected is determinant to estimate the minimum size of the zone that can be characterized. In this work, the size of the signal source volume is surveyed for a wide set of samples at different beam energies. To this aim, the PENELOPE software package was chosen to run Monte Carlo simulations for several experimental situations in order to produce the various lateral radiation distributions of interest. A comparison between the interaction volumes of the different signals was performed by taking into account the different fluorescence enhancement possibilities. An unexpected behaviour was found in the particular cases of aluminium and alumina, where the secondary photons signal exhibits a decreasing trend up to certain beam energy (∼17 keV); this implies that lower beam energies may degrade the lateral resolution of the technique in these materials.