Influence of electron landing energy on the measurement of the dimensional properties of nanoparticle populations imaged by SEM.

Scanning Electron Microscopy (SEM) technique is widely used to characterize nanoparticle (NP) size. The landing energy (LE) of the primary electron beam is considered to be a key parameter related to the ability of electrons to penetrate the sample. However, few studies have been carried out so far on the influence of this parameter on the measurement of NP size by SEM. The increasing needs for reference materials consisting of size-controlled NP suspension for microscope calibration induce new issues. This paper focuses on the effect of electron landing energy on the measurement of the equivalent diameter of several NP populations by SEM. To evaluate the influence of LE, particles of different sizes and chemical compositions were analyzed. The results showed the variation of the measured diameter as a function of LE. SEM secondary electron (SE) yield modeling by the Monte Carlo method allowed us to relate this variation to the information volume in the material. Finally, the use of reference particles and transmission electron microscopy (TEM) allowed us to determine an optimal value of LE to be applied, depending on the chemical composition and particle size to limit the bias in the SEM measurement. We showed that this operating point can be simply determined without reference nanomaterials by scanning an LE range.