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Measuring with a high accuracy the size distribution of small metallic nanoparticles loaded in a mesoporous metal oxide matrix is of particular interest for many studies related to new generations of interesting metamaterials. Transmission electron microscopy (TEM) is a powerful tool to determine the nature and morphology of very small particles, but their reliable and automatic identification in an inhomogeneous environment where the nanoparticle/background contrast locally varies is not straightforward. Here, we present how a quantitative analysis of high-angle annular dark field scanning TEM (HAADF STEM) images, accounting for the chemical sensitivity of the technique, can improve the accuracy of semiautomatic segmentation methods based on morphological processing to calculate size histograms. The paper also provides an estimate of the reliability of this method through the analysis of numerically synthesized images. The latter are based on the simulation of HAADF STEM projections of a volume filled with titania, pores and silver particles, whose morphological features, such as dimensions, shapes and densities are evaluated from experimental measurements of real samples. The results obtained with synthesized images prove the performances of the quantitative analysis to suppress nonsilver nanoparticles from the statistics and allow to infer empirical rules to determine imaging parameters that ensure a good reliability of histograms. [ABSTRACT FROM AUTHOR]

The size distribution of second phase precipitates is frequently determined using conventional transmission electron microscopy (CTEM). However, other techniques, which present different advantages, can also be used for this purpose. In this paper, we focus on high angle annular dark field (HAADF) in TEM and scanning TEM (STEM) in scanning electron microscopy (SEM) imaging modes. The mentioned techniques will be first described, then compared to more conventional ones for the measurement of carbides size distribution in two FeCV and FeCVNb model alloys. This comparative study shows that STEM in SEM, a technique much easier to undertake compared to TEM, is perfectly adapted for size distribution measurements of second phase particles, with sizes ranging between 5 and 200 nm in these systems. [ABSTRACT FROM AUTHOR]

Summary Anisotropic effects in hexagonal aluminium nitride have been studied by electron energy-loss spectroscopy (EELS) in the N-K energy loss near edge structure (ELNES). Experimental data acquired with different collection angles and with a nearly parallel incident electron beam aligned along the c -axis have been compared to simulations based on ab initio calculations. The extraction of intrinsic parallel I| (with momentum transfer q | c axis) and perpendicular I⊥ (with momentum transfer q ⊥ c axis) components has been performed directly from the experimental spectra. This has been done according to their description as linear combinations of I| and I⊥ , with adequate weights deduced from a geometrical model of anisotropic behaviour. [ABSTRACT FROM AUTHOR]