Toward an uncertainty budget for measuring nanoparticles by AFM

This article reports on the evaluation of an uncertainty budget associated with the measurement of the mean diameter of a nanoparticle (NP) population by Atomic Force Microscopy. The measurement principle consists in measuring the height of a spherical-like NP population to determine the mean diameter and the size distribution. This method assumes that the NPs are well-dispersed on the substrate and isolated enough to avoid measurement errors due to agglomeration phenomenon. Since the measurement is directly impacted by the substrate roughness, the NPs have been deposited on a mica sheet presenting a very low roughness. A complete metrological characterization of the instrument has been carried out and the main error sources have been evaluated. The measuring method has been tested on a population of SiO₂ NPs. Homemade software has been used to build the height distribution histogram taking into account only isolated NP. Finally, the uncertainty budget including main components has been established for the mean diameter measurement of this NP population. The most important components of this uncertainty budget are the calibration process along Z-axis, the scanning speed influence and then the vertical noise level.