Comparison of nanoparticle diameter measurements by Atomic Force Microscopy and Scanning Electron Microscopy

Using combined AFM (Atomic Force Microscope) and a SEM (Scanning Electron Microscope) makes it possible to accurately measure a nano-object in 3 dimensions. This paper deals with the traceable measurements of the size and the size distribution of a SiO2 sphericalshaped nanoparticle population performed by both microscopy techniques. The complementary nature of AFM and SEM is investigated. The construction of size distribution histogram was carried out by means of a homemade program described here. This semi-automatic program is capable of counting only isolated nanoparticles and eliminating measurement artefacts and aggregates. Finally, a comparison between both measurement types is proposed. 1 CARMEN: the LNE’s platform dedicated to the nanometrology LNE is developing a platform dedicated to the metrological characterization of nanomaterials (CARMEN platform) that will supply a complete offer for measuring main parameters characterizing a nanoobject: size, shape, size distribution, chemical composition, agglomeration/aggregation state, crystal structure, surface charge, specific surface area. In a first step, the LNE’s nanometrology team is focusing on the measurement of the mean diameter and size distribution of a spherical nanoparticles (NPs) population by Atomic Force Microscopy (AFM). From sampling method to statistical tools, through instrument calibration and imaging, we propose a method for traceable measurements of the nanoparticle height. The same approach is developed for Scanning Electron Microscopy (SEM). Thanks to SEM, the lateral dimension of particles can be obtained with a high resolution. In this paper, we investigate the complementary nature of both instruments, AFM and SEM, for a nanoparticle size measurement in the 3 dimensions. Using both techniques induces some constraints on sampling described in this paper. 1.1 Traceability of the measurements at the nanoscale Figure 1 : Traceability routes of a nano-object measurement. The traceability route of the dimensional measurements at the nanoscale implementing a metrological AFM (mAFM) is reminded in Figure 1. The mAFM is a reference instrument enabling to link the nanoscale dimensional measurements to the SI units through a calibration process performed by means of transfer standards like periodic 1D or 2D gratings. Since 2007, LNE has been developing such an instrument implementing interferometers with laser sources calibrated in wavelength and measuring in real time the relative position of the tip with respect to the surface. Thus, for each point of the image, the XYZ coordinates are assumed to be absolute and, so, are linked to the SI DOI: 10.1051/ C © Owned by the authors, published by EDP Sciences, 2013 201 / 06007 (2013) 306007 16 th metrology International Congress of Metrology, This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2 0 , which . permits unrestricted use, distributi and reproduction in any medium, provided the original work is properly cited. on, Article available at http://cfmetrologie.edpsciences.org or http://dx.doi.org/10.1051/metrology/201306007