In the last fifteen years a significant work on the interpretation of Backscattered Electron (BSE) and Secondary Electron (SE) compositional imaging has been performed. The starting point of the research was represented by the experimental evidence of nanometric resolution of compositional features in BSE and SE imaging at relatively high energy (20–30 keV). The interpretation of these results required a reconsideration of the resolution definition, usually associated to the Full Width Half Maximum (FWHM) of the collected signal and to the local variations of the SE yield. In fact, this approach was not able to justify the experimental results with BSE because an interaction volume of the order of a µm and an exit profile of the BSE signal having a comparable FWHM did not appear compatible with the observed resolution of a few nm. Also the SE images were hard to interpret because the yield is practically …