LAUSR

The size measurement of nanoparticles contributes to the understanding of their properties and, thus, to the assessment of the risks they pose to health and the environment. For such measurements to be comparable and legally recognized, they must be traceable to the SI unit meter. Recently, interest in traceable measurements of polystyrene particles with sizes up to 500 nm has aroused, e.g. in the aerosol community. To meet this demand, we adapted an established method to traceably measure nanoparticles with high precision in the transmission mode of a scanning electron microscope (STEM-in-SEM or TSEM). Since this method was geared towards smaller particles, we adapted it at two points: New simulations with the program Geant4SEM allow a more accurate modelling, especially of the inelastical scattering processes. In addition, the image evaluation procedure was revised to account for the non-linear signal response at the particle boundary. The measured values obtained in this manner show good agreement with the values of two international intercomparisons.