Within the European iMERA-Plus project 'Traceable Characterisation of Nanoparticles' various particle measurement procedures were developed and finally a measurement comparison for particle size was carried out among seven laboratories across six national metrology institutes. Seven high quality particle samples made from three different materials and having nominal sizes in the range from 10 to 200 nm were used. The participants applied five fundamentally different measurement methods, atomic force microscopy, dynamic light scattering (DLS), small-angle x-ray scattering, scanning electron microscopy and scanning electron microscopy in transmission mode, and provided a total of 48 independent, traceable results. The comparison reference values were determined as weighted means based on the estimated measurement uncertainties of the participants. The comparison reference values have combined standard uncertainties smaller than 1.4 nm for particles with sizes up to 100 nm. All methods, except DLS, provided consistent results.

A conventional scanning electron microscope operated in transmission mode (TSEM) was used for imaging silica, gold and latex nanoparticles. Particles were applied to conventional transmission electron microscope (TEM) grids with different supporting films. A semiconductor detector capable of accomplishing both bright-field and dark-field imaging was used to record transmitted electrons. Particle diameter was determined from the images by comparing measured data with the results of corresponding Monte Carlo simulations which took into account particle and instrument properties. Measured and simulated line profiles agreed well; the method is sensitive to changes in diameter in the nano- and sub-nanometre range. It is concluded that TSEM imaging is a promising tool for dimensional characterization of nanoparticles. Necessary extensions to the technique in order to achieve traceable measurements are discussed.

Traceable size measurements of nanoparticles are accomplished by means of a calibrated scanning electron microscope operated in transmission mode (TSEM). An image analysis tool was developed which individually determines the boundary and size of every particle based on modelled TSEM signals obtained by Monte Carlo simulations. The model relies on first-principle electron scattering theory taking into account particle and instrument properties. A series of TSEM images containing thousands of particles can be analysed in automated batch processing to attain a particle size distribution. As examples, nanoparticles of three different material classes (gold, silica, latex) with sizes ranging from about 5 to 60 nm are analysed. An uncertainty analysis reveals expanded measurement uncertainties (95% confidence interval) of the mean diameter in the range of 1 to 3 nm.

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