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In this study, the atomic and chemical structure and the optical response of AxB1−x bimetallic nanoparticles (BNPs) combining gold or silver (A) with aluminium or indium (B) were investigated at various stoichiometries in order to examine if stable alloyed phases could exist and promote the emergence of localized surface plasmon resonance (LSPR) in the UV range. The structure and morphology of BNPs of a few nanometres, produced by laser vaporization, were analysed by transmission electron microscopy (TEM) and optical absorption measurements were performed on matrix-embedded BNPs. Information about the oxidation state of the BNPs can be inferred from a comparison between experimental optical spectra and Mie calculations in the dipolar approximation. The BNPs' internal structures were further investigated by additional characterization techniques. Firstly, in situ X-ray photoelectron spectroscopy provided information about the chemical state of the constituent elements and their evolution with time. Secondly, synchrotron-based X-ray scattering techniques were performed on Ag–Al BNPs in a wide-angle configuration under grazing incidence, giving complementary information about structural and morphological heterogeneities in the BNPs. Finally, the restructuring of the partially oxidized Au0.33Al0.67 BNPs annealed in a reducing atmosphere was also attempted by environmental TEM. The complementary techniques of characterization show that silver-based Ag–In and Ag–Al BNPs form metallic silver-rich alloyed cores surrounded by an indium or aluminium oxide shell. The initial LSPR is in the UV range for both systems, but the difference in the kinetics of oxidation between indium and aluminium involves less blue-shifted LSPR for Ag–Al BNPs. In the case of gold-based BNPs, we show evidence of ordered nanoalloys just after air exposure and the appearance of gold and indium (or aluminium) demixing during oxidation. The initial LSPR of Au–In BNPs is the one the most in the UV range among the four systems, with an LSPR peak centred at 254 nm, which may be a sign of the formation of the Au0.33In0.67 alloy. Nevertheless, strategies to preserve BNPs from oxidation have to be developed. [ABSTRACT FROM AUTHOR]

Herein, a multistep synthesis method was implemented to prepare nanoscale core@shell spherical heterostructures for H2 optical detection. The resulting nanoheterostructures are built with gold cores and silica shells further coated by a thin layer of spherical palladium nanoparticles. Samples with various thicknesses of silica and densities of palladium nanoparticles were synthesized and characterized by transmission electron microscopy. In particular, the three-dimensional core@shell configuration was confirmed by electron tomography. The optical properties of the obtained nanostructures were first analyzed by optical absorbance measurements, and their potential use for H2 detection was evaluated by simulations based on the discrete dipole approximation method. Thus, the optical response of the studied nanostructures is investigated theoretically when the Pd layer is hydrogenated, showing the great sensitivity achievable with these nanostructures. [ABSTRACT FROM AUTHOR]

Bimetallic nanoparticles (BNPs) are promising candidates for fundamental research and applications, as their physico-chemical properties can, in many cases, be tuned continuously, or enhanced with respect to the mono-metallic particles. Here we investigate the possibility of fabricating silver-indium and silver-aluminium BNPs in the range of 4–5 nm diameter and of varying stoichiometry by laser vaporization and gas condensation in the gas phase. We analyse their crystalline structure and segregation behaviour using transmission electron microscopy and probe their oxidation state in optical absorption measurements by tracking spectral changes of the localized surface plasmon resonance (LSPR). These complementary techniques show that, despite the small size and the high reactivity especially of aluminium, the BNPs form a silver-rich alloyed core surrounded by an oxide shell. Exposure to air leads to consecutive oxidation, whereas annealing the BNPs in a reducing atmosphere stabilizes the alloyed particle cores, as demonstrated by a narrow and blue-shifted LSPR. This is a first step towards the stabilization of non-oxidized bimetallic nanoparticles combining a noble and a trivalent metal. [ABSTRACT FROM AUTHOR]

In recent decades, nanostructured silica has become a key component in several materials developed at the industrial length scale. Used for its outstanding ability to structure food, drugs, and rubber, to fulfil specific needs in numerous applications, it has also led to the widespread development of sustainable energy-based materials. Superinsulation materials endowed with an exceptionally low thermal conductivity are a major goal regarding energy consumption and carbon dioxide emission. However, because the properties of insulation materials greatly depend on their nanostructures, it is crucial to ensure their hygrothermal stability, by limiting ageing phenomena. Here, we thoroughly characterize the hygrothermal ageing of a fractal industrially relevant silica using a complementary set of experimental techniques, providing local (TEM and electron tomography) and statistical indicators of structural evolution. For the first time, we unambiguously evidence the smoothing of elementary particles and quantify their growth (from 4.3 to 10.0 nm), which results in the densification of aggregates at the upper length scale. [ABSTRACT FROM AUTHOR]

Electron Tomography (ET) is of greatest interest in studying nano- and biological materials since it gives access to 3D morphological, chemical and physical features. Even though ET techniques have been continuously improved in the last decades, they are still limited: lengthy time scales (tens of minutes) are generally needed for the tilt series acquisition prior to the volume reconstruction step. Such long exposures to a relatively intense electron beam lead to large electron doses received by the sample. This may promote extensive irradiation damage in the case of soft materials like polymers and bio-materials when they are not protected through dedicated sample preparation methods, and any tomographic reconstruction will then be meaningless. More importantly, the time constraints drastically limit 3D investigations during dynamic in-situ experiments where the sample rapidly evolves during the acquisition. We present here developments for acquiring tilt series of projections in very short time scales, readily down to a few seconds. After an outlook of possible ways to speed up the data acquisition in the bright field imaging mode (BF-TEM), strategies for the fastest methods in 'step-by-step' and 'continuous tilt' ET will be described. Applications of these procedures are presented on various systems, including metallic Pd nanoparticles deposited on alumina, and soft materials like polymer nanocomposites and biological matter. A special reference is made to fast operando nano-tomography performed on nanomaterials during their dynamic evolution. The feasibility of fast ET is exemplified by a calcination study of Pd catalysts supported by SiO 2 at 400 °C and 500 °C under 4 mbar H 2 in a dedicated Environmental Transmission Electron Microscope (ETEM). Unlabelled Image • Fast image acquisition for Electron Tomography (ET) can take only a few seconds. • A continuous rotation of the sample allows relevant and fast acquisition for ET. • Fast ET is possible under gas and temperature conditions in-situ in a ETEM. • Repeated acquisitions on the same object allow to follow its evolution in operando. • The resistance to sintering of Pd@SiO 2 nanocatalyst is quantified in situ in 3D. [ABSTRACT FROM AUTHOR]

Repeated attacks using organophosphorus compounds, in military conflicts or terrorist acts, necessitate developing inexpensive and readily available decontamination systems. Nanosized cerium oxide is a suitable candidate, acting as a heterogeneous catalyst for the degradation of organophosphorus compounds such as VX agent or sarin. However, the reaction mechanism of the phosphatase mimetic activity of CeO2 nanoparticles is not fully described. Adsorption, surface-promoted hydrolysis, and desorption cycles strongly depend on the physico-chemical characteristics of the facets. In this study, CeO2 nanoparticles with different shapes were elaborated by hydrothermal synthesis. Nano-octahedra, nanocubes, or nanorods were selectively obtained under different conditions (temperature, concentration and nature of the precursors). The degradation activity according to the crystal faces was evaluated in vitro by measuring the degradation kinetics of paraoxon organophosphate in the presence of CeO2 nanoparticles. The results show an influence of both specific surface area and crystal faces of the nanoparticles, with higher activity for {111} facets compared to {100} facets at 32 °C. The relative activity between the facets is ascribed to the adsorption probability, assuming coordination between the phosphoryl oxygen and cerium atoms, but also to the surface density of the Ce doublets with relevant spacing for phosphatase mimetic activity. [ABSTRACT FROM AUTHOR]

With its unique redox properties, ceria is an oxide with a range of applications, including automotive catalytic converters, which consist of platinum-group metal nanoparticles on ceria-containing supports. In this work, the 3 D architecture of a ceria-based material synthesized by the widely employed glycine-nitrate solution combustion method is revealed for the first time. Together with N2 adsorption volumetry, scanning transmission electron microscopy (STEM) and scanning electron microscopy (SEM), STEM tomography provides a comprehensive picture of the multimodal porous network of a pre-reduced Pt-CeO2 catalyst, from the nanometer to the micrometer scale. This material consists of ceria nanocrystallites forming 3 D aggregates and puzzle-like 2 D walls separating large roundish mesopores and macropores. The small voids between imperfectly assembled crystallites give rise to some microporosity. In addition, it is demonstrated that a significant proportion of platinum nanoparticles (3-4 nm) are not located at the ceria surface following the one-step synthesis process, about half of them are buried within ceria. This result is valid for another metal (Rh) and another fuel (oxalyl dihydrazide), and has important implications for heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

The ability of energy-filtered transmission electron microscopy (EFTEM) tomography to provide 3 D chemical maps at the nanoscale opens a new way to analyse heterogeneous materials quantitatively. In association with other techniques, EFTEM tomography has been employed in the study of amorphous silica-alumina catalyst supports. Two types of samples prepared either by mechanical mixing (MM) or by the precipitation of silica on boehmite (PSB) that have similar proportions of silica and alumina were analysed. The sample synthesised by the PSB method shows a smaller degree of heterogeneity than the sample obtained by MM. For both types of samples, a higher concentration of alumina was found at the surface, whereas silica mostly constituted the core of the sample. A thermal treatment in a humid atmosphere was shown to redistribute the silica inside the sample as well as on its surface, which decreased the specific surface area at the same time. The acid sites localisation was defined as a specific curve at the interface between the two components upon reaching the surface of the support. The length of this curve, the 'alumina-silica boundary line', was estimated by using EFTEM tomography and discussed qualitatively with the chemical inter-mixing information deduced from additional techniques such as FTIR and NMR spectroscopy. [ABSTRACT FROM AUTHOR]

Bulk nanoporous silicon prepared by top-down method form Li-ion batteries was investigated combining different conventional technique such as nitrogen physisorption and high resolution electron microscopy with electron tomography. It was found that the Si nanorods are forming porous aggregates with a half of the volume of the particle occupied by pores. The nanorods are preferentially oriented along the main axis of the aggregate. The porosity and the lack of compaction between the aggregates provide space for the Si expansion during the lithiation process. It was found that the Si nanorods mainly expose the {111} family plane as an external faces. The size distributions of the porous and solid phases in a granule were found to be similar. The pores represent 50% of the total volume of an aggregate. The shape orientation of the particles was quantified and it was found to exhibit a narrow distribution. [ABSTRACT FROM AUTHOR]

Analytical electron tomography combined with more classical techniques such as X-ray fluorescence and X-ray photoelectron spectroscopy were performed with a series of titania-alumina catalyst supports prepared by using the swing-pH method. The bulk proportion of titania and alumina was varied along the sample series. It was observed that, independently of this bulk proportion, only 30 % of the surface of the grains of the resulting catalysts was titania covered. It was also shown that the porosity of the material was driven by alumina, and for low titania contents, alumina formed a layer close the surface of the grains. At concentrations higher than 30 % titania, the layer was broken and aggregates covered by alumina were formed, which may have an impact on catalysis if these materials are used as supports for an active phase. [ABSTRACT FROM AUTHOR]

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]

A titanium nitride ( TiN)/mesoporous carbon nanocomposite with a high surface area (320 m2/g) has been successfully synthesized by a direct route based on a concomitant polymerization of organic and inorganic species (phenol-formaldehyde resin and TiO2-based oligomers, respectively). These polymers self-assemble in the presence of a pore-structuring agent, an amphiphilic copolymer ((poly(ethylene oxide))106-(poly(propylene oxide))70-(poly(ethylene oxide))106) during the solvent evaporation step and yield to an ordered mesostructured hybrid organic/inorganic materials. Its heat treatment in ammonia led to the carbonization of the organic part and to the nitridation of the TiO2-based part. A TiN/mesoporous C nanocomposite constituted of TiN (61 wt%) nanocrystallites (from 10 to 50 nm in diameter) embedded into a mesoporous carbon matrix was obtained. [ABSTRACT FROM AUTHOR]

Silver nanoparticles are currently one of the most studied nanostructured nanomaterials. Because nanoparticle size and dispersion act together in determining a material's physical and chemical properties, there is a continuous quest to develop size-controlled synthesis methods. Nonetheless, the instability of the nanometer-sized particles, which is caused by their tendency to aggregate irreversibly into larger particles, remains a recurrent problem. The use of confining scaffolds, such as the regular system of cages in a crystalline zeolite-type material, is often reported in the literature as an efficient solution to overcome particle migration at the surface. Silver nanoparticles encapsulated in ZSM-5 (Ag@ZSM-5) represent a new generation of adsorbent for Xe enrichment from the atmosphere that is currently being developed at the pilot scale in a Temperature Swing Adsorption (TSA) process. In this study, we have found that the presence of Cl-containing compounds in the air (VOCs) leads to a poisoning of the active silver phase by the formation of silver chloride. By a careful study of process parameters, we have found that most of the chlorine can be removed by heat treatment above 573 K so that the adsorption properties of silver are regenerated. That said, when applying 573 K temperature regeneration at the pilot scale, we observe a very minor but observable decay of xenon adsorption capacity that continues cycle after cycle. The mechanism of capacity decay is discussed in terms of (i) the residual presence of Cl at the surface of silver nanoparticles, (ii) the aggregation of silver nanoparticles into larger particles (sintering mechanism), and (iii) the acceleration of silver particle migration to the surface and sintering. [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]

OBJECTIVES: This study aimed to present 3 different clinical stages in patients presenting with superior semicircular canal dehiscence (SSCD) by the superior petrosal sinus (SPS). A specific 3-class classification based on clinical, radiological, and audio-vestibular arguments is proposed. MATERIALS AND METHODS: We retrospectively compared clinical and radiological findings in 3 patients with different degrees of audio-vestibular dysfunction in whom the imagery evocated the diagnosis of SSCD by SPS. Imaging sensitivity was improved by combining inner ear high-resolution computed tomography (HRCT) scan and magnetic resonance imaging in fusion, allowing us to compare and corroborate clinical and audio-vestibular findings in each case with the imagery. RESULTS: HRCT and 3T inner ear fusion imaging highlighted a direct contact and/or compression between SPS and the membranous superior semicircular canal (SSC). We propose a new classification of SSCD by SPS. Class "A" corresponds to an HRCT image with a "cookie bite" and thin bone still covering the SSC. Class "B" corresponds to a "cookie bite" image with confirmed contact between the SPS wall and the membranous SSC in MRI labyrinthine sequences. Class "C" type corresponds to a "cookie bite" image, contact, and obvious compression of the membranous SSC by SPS on MRI sequences. CONCLUSION: Anatomical systematization is needed for daily practice. This classification of SSCD by SPS would contribute to a better understanding of the wide variety and variability in the occurrence and onset of symptoms. [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]

Fast tomography in Environmental Transmission Electron Microscopy (ETEM) is of a great interest for in situ experiments where it allows to observe 3D real-time evolution of nanomaterials under operating conditions. In this context, we are working on speeding up the acquisition step to a few seconds mainly with applications on nanocatalysts. In order to accomplish such rapid acquisitions of the required tilt series of projections, a modern 4K high-speed camera is used, that can capture up to 100 images per second in a 2K binning mode. However, due to the fast rotation of the sample during the tilt procedure, noise and blur effects may occur in many projections which in turn would lead to poor quality reconstructions. Blurred projections make classical reconstruction algorithms inappropriate and require the use of prior information. In this work, a regularized algebraic reconstruction algorithm named SIRT-FISTA-TV is proposed. The performance of this algorithm using blurred data is studied by means of a numerical blur introduced into simulated images series to mimic possible mechanical instabilities/drifts during fast acquisitions. We also present reconstruction results from noisy data to show the robustness of the algorithm to noise. Finally, we show reconstructions with experimental datasets and we demonstrate the interest of fast tomography with an ultra-fast acquisition performed under environmental conditions, i.e. gas and temperature, in the ETEM. Compared to classically used SIRT and SART approaches, our proposed SIRT-FISTA-TV reconstruction algorithm provides higher quality tomograms allowing easier segmentation of the reconstructed volume for a better final processing and analysis. [ABSTRACT FROM AUTHOR]