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A three-dimensional (3D) study of multiphase nanostructures by chemically selective electron tomography combining tomographic approach and energy-filtered imaging is reported. The implementation of this technique at the nanometer scale requires careful procedures for data acquisition, computing, and analysis. Based on the performances of modern transmission electron microscopy equipment and on developments in data processing, electron tomography in the energy-filtered imaging mode is shown to be a very appropriate analysis tool to provide 3D chemical maps at the nanoscale. Two examples highlight the usefulness of analytical electron tomography to investigate inhomogeneous 3D nanostructures, such as multiphase specimens or core-shell nanoparticles. The capability of discerning in a silica-alumina porous particle the two different components is illustrated. A quantitative analysis in the whole specimen and toward the pore surface is reported. This tool is shown to open new perspectives in catalysis by providing a way to characterize precisely 3D nanostructures from a chemical point of view. [ABSTRACT FROM AUTHOR]

• Careless TEM imaging on silica induces greater pore sizes and misinterpretation of the aggregates morphology. • Low-dose TEM enables accurate 3D Particle/Pore/Neck multi-scale anisotropic structures imaging. • Electron Tomography shades light on pattern-less structure, within large aggregate. • Ageing is evidenced at the particle, neck and aggregate lengthscales with SANS and Electron Tomography. Image, graphical abstract Due to their versatile properties, nanostructured silicas are used in numerous applications for which structural properties are decisive. Being able to thoroughly understand porous multi-scale structures is therefore a means of improving composites and ensuring their fast processing and their durability. In this framework, electron tomography (ET) is a convenient tool that permits analysing the inner structure of any nano-object made of particles, necks, aggregates and pores. However, some materials are very sensitive to the electron beam, which can lead to misinterpretation. In this article, we highlight how any fractal silica, whether precipitated, fumed or in aerogel form, can be effectively characterized and described. Step-by-step low-dose tomography allows the unprecedented visualisation and quantification of architectures on large volumes, essential to feed numerical simulations. This local analysis is strengthened by statistical observation provided by Small Angle Neutron Scattering (SANS). We finally show how this kind of work can benefit an ageing study. [ABSTRACT FROM AUTHOR]

This work was focused on the characterization of plasmonic thin films composed of Au–Ag nanoparticles dispersed in a TiO 2 dielectric matrix in comparison with the monometallic Au/TiO 2 plasmonic system. The thin films were prepared by reactive DC magnetron sputtering, followed by thermal annealing at different temperatures to promote nanoparticles' growth. Thermal treatment from 400 °C induced the appearance of Localized Surface Plasmon Resonances (LSPRs) in both Au/TiO 2 and Au–Ag/TiO 2 thin films. The latter showed a wider LSPR response, due to the broader size distribution of nanoparticles (analyzed by transmission electron microscopy, TEM). Further nanometer-scale chemical analysis allowed to confirm the presence of Au–Ag bimetallic nanoparticles. To thoroughly study the influence of the annealing treatment on the nanoparticles' growth, Au–Ag/TiO 2 was also deposited on heating TEM nano-chips for in-situ annealing experiments. The formation of silver aggregates was found in the sample as-deposited, with these precipitates dissolving in the matrix with the increase of annealing temperature up to 200 °C. For higher temperatures, nanoparticles' real-time growth was observed, together with the crystallization of the TiO 2 matrix above 550 °C. Besides, the plasmonic Au–Ag/TiO 2 thin films revealed LSPR sensitivity when in contact with different dielectric media, highlighting their potential as refractive index sensors. • Thin films composed of Au–Ag nanoparticles dispersed in TiO 2 matrix were prepared. • Elemental mapping through STEM-EDX unravel the formation of Au–Ag nanoparticles. • Crystallization of nanoparticles and dielectric matrix revealed by in-situ annealing. • Au–Ag/TiO 2 thin films are responsive to changes in the nanoparticles surrounding medium. [ABSTRACT FROM AUTHOR]

• The genesis of Pd nanocatalysts on Al 2 O 3 can be adequately followed by in situ ETEM. • Fast tomography in ETEM unravels the 3D evolution of NPs during calcination. • Oxidation and reduction of Pd NPs is followed down to the atomic scale in ETEM. • In situ tracking of Pd NPs in ETEM evidences that they grow by Ostwald Ripening. The quality of metallic nanoparticles (NPs) used in heterogeneous catalysis relies through many aspects on their small size, on the homogeneity of their spatial distribution on their supports and on their ability to resist to sintering or coalescence. It is thus very important to quantify these parameters and understand the mechanisms controlling the growth of NPs during the genesis process of the catalyst. Whereas conventional Transmission Electron Microscopy (TEM) is currently used for these purposes, it most frequently remains a 'static' method where results are obtained in high vacuum and post mortem, i.e. after the typical drying, calcination and reduction steps without the possibility to follow directly the evolution of both NPs and supports during those treatments. Environmental TEM (ETEM) unlocks this blocking and allows elementary mechanisms, such as Ostwald Ripening and coalescence to be unravelled through direct in situ observations. We report here an ETEM study of the preparation of Pd-based narrow NPs, less than 5 nm in size, deposited on a δ-alumina support. We focused on 3 main objectives: (i) quantifying the sizes of NPs at each preparation step performed in situ under environmental (i.e. respectively oxygen or air and hydrogen atmospheres at working temperatures) and comparing them to post mortem measurements; (ii) identify the oxidation state of the NPs through an in situ High Resolution imaging study of their crystallographic structure; (iii) explore the possibilities of environmental tri-dimensional (3D) studies by tilt series based Electron Tomography. This last item represents a challenging breakthrough in the characterization of nanocatalysts; it will be demonstrated that the use of modern instruments (microscope and accessories) allows tomographic acquisitions to be performed very fast, within a few minutes and even seconds, which opens the way to the 3D tracking of microstructures almost in real time during their evolution under gas and at high temperature. [ABSTRACT FROM AUTHOR]

Abstract We focus on describing the multi-scale structure of a fumed silica characterized by remarkably low thermal conductivity (ca. 2–5 mW m−1 K−1) when used as a core material in vacuum insulating panels. While such powders are known to be highly polydisperse at different lengthscales (hardly quantifiable), we propose to adapt a recent methodology based on small-angle X-ray scattering experiments with the aim of providing simple criteria for characterizing the morphology of these nanostructured silicas. Combining this technique with transmission electron microscopy, electron-tomography and mercury intrusion porosimetry then allows assigning the origin of the super-insulation to the low dimensionality of the silica aggregates at lengthscales smaller than 500 nm. Remarkably, by using independently these three techniques, we always find the compacity of the aggregates (radius of ca. 40 nm) to be equal to 0.29 ± 0.01. This study proposes therefore a robust methodology, potentially of a great interest for industrial applications. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]