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The performance of solid oxide cells is known to be dependent upon the density of three phase boundaries (TPB), but the potential for improving their effective electrocatalytic activity by morphological adjustments is imprecisely known. A spilling algorithm was developed to characterize the surfaces available for diffusion at TPBs. It scans each slice in a 3-D imaging dataset to measure the interfaces between the solid and the pore phases at each TPB. Because of the stereological approach, these surfaces are defined as "available lengths" (L-A). The measurement was tested on artificial packed spheres structures with controlled properties and a percolation theory-based model before application to a real Ni-YSZ. The L-A distributions cover 2 orders of magnitude. The subset shorter than the extent of diffusion profiles reported in the literature is in the range of 3% and 20% for Ni and YSZ, respectively, suggesting possible limitations of their effective electrocatalytic properties. The average L-A is larger on YSZ than on Ni, which is a trend opposite to the phase diameter. The available length analysis revealed microstructural characteristics that stem from the manufacturing route and cannot be identified by the inspection of standard metric and topological properties. A strong correlation between the available length and the extension of TPB lines is observed for Ni but not for YSZ, despite the predominance of convex shapes, which likely originates from the Ni reduction. This suggests possibilities for controlling the available length by the manufacturing route, depending specifically on the electrocatalytic properties of the phases in composite materials. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd.

A solid oxide short stack composed of 6 Ni-YSZ supported cells, YSZ electrolyte and GDC-LSC oxygen electrode has been tested for 10,700 hours in steam electrolysis. Initial degradation was followed by a global stabilization of the performance after lowering the current density, with a degradation rate below 0.5% kh(-1). Post-test analysis has been conducted on two repeating units (RUs) to highlight the most significant microstructure alterations. Nickel depletion was observed in the hydrogen electrode close to the interface with the electrolyte. Formation of small pores in the electrolyte was detected along the grain boundaries. A consequent detachment related to this phenomenon was observed in proximity of the GDC compatibility layer. At the oxygen electrode side, the formation of a approximate to 1 mu m dense mixed layer of GDC and YSZ was observed. Strontium from the LSC electrode migrated through GDC pores and reacted with YSZ, forming evident SrZrO3 inclusions. Distinct accumulation of silicon at the Ni/YSZ interface and chromium on the GDC barrier layer have been observed in both RUs. Despite this range of alterations observed, the stack degradation remained limited, testified from the fact that performance decay between 4,000 and 10,000 hours of operation was virtually nil.

This paper presents a novel 3D method to correct for absorption in energy dispersive X-ray (EDX) microanalysis of heterogeneous samples of unknown structure and composition. By using STEM-based tomography coupled with EDX, an initial 3D reconstruction is used to extract the location of generated X-rays as well as the X-ray path through the sample to the surface. The absorption correction needed to retrieve the generated X-ray intensity is then calculated voxel-by-voxel estimating the different compositions encountered by the X-ray. The method is applied to a core/shell nanowire containing carbon and oxygen, two elements generating highly absorbed low energy X-rays. Absorption is shown to cause major reconstruction artefacts, in the form of an incomplete recovery of the oxide and an erroneous presence of carbon in the shell. By applying the correction method, these artefacts are greatly reduced. The accuracy of the method is assessed using reference X-ray lines with low absorption.

A simple model is proposed to account for the loss of collected X-ray signal by the shadowing of X-ray detectors in the scanning transmission electron microscope. The model is intended to aid the analysis of three-dimensional elemental data sets acquired using energy-dispersive X-ray tomography methods where shadow-free specimen holders are unsuitable or unavailable. The model also provides a useful measure of the detection system geometry.

This paper presents a method developed to quantify three-dimensional energy dispersive spectrometry (3D EDS) data with voxel size smaller than the volume from which X-rays are emitted. The influence of the neighboring voxels is corrected by applying recursively a complex quantification, improving thereby the accuracy of the quantification of critically small features. The enhanced quantification method is applied to simulated and measured data. A systematic improvement is obtained compared with classical quantification, proving the concept and the prospect of this method.

The favorable growth kinetics of twinned dendrites can be explained by their complex morphology, multiple side branching mechanisms, growth undercooling and tip morphology. Three models were proposed for the twinned dendrite tip shape: (i) a grooved tip satisfying the Smith condition at the triple line; (ii) a doublon, i.e. a double-tip dendrite that grows with a narrow and deep liquid channel in its center; and (iii) a pointed (or edgy) tip, with consideration of the solid-liquid interfacial energy anisotropy. In the first part of this work, phase field simulations of half a twinned dendrite with an appropriate boundary condition to reproduce the Smith condition supported the doublon conjecture, with a narrow liquid channel ending its solidification with the formation of small liquid droplets. In this part, experimental observations of twinned dendrite tips reveal the presence of a small, but well-defined, groove, thus definitely eliminating the edged tip hypothesis. Focused ion beam nanotomography and energy-dispersive spectroscopy chemical analysis in a transmission electron microscope reveal the existence of a positive solute gradient in a region localized within 2 μm around the twin plane. In Al-Zn specimens, small particles aligned within the twin plane further support the doublon conjecture and the predicted formation of small liquid droplets below the doublon root. © 2011 Acta Materialia Inc.

1.5 mu m-Ni55Mn23Ga22 ferromagnetic thin films were deposited onto silicon substrates and silicon single beam cantilever using radio-frequency magnetron sputtering. As-deposited sample and heat-treated thin films were studied on their silicon substrates and peeled off to determine the influence of the stress. Post-heat treatment process allows at the films to achieve the shape memory effect (SME). Vibrating sample magnetometer (VSM) and deflection measurement of the sample annealed at 873 K during 36 ks exhibit ferromagnetic martensitic structure with a typical SME response to the magnetic field induced strains which match the values of the bulk material.

Variations of Vickers hardness were observed in Al-Mg-Mn alloy and Al-Mg-Mn-Sc-Zr alloy at different ageing times, ranging from a peak value of 81.2 HV at 54 ks down to 67.4 HV at 360 ks, below the initial hardness value, 71.8 HV at 0 ks for the case of Al-Mg-Mn-Sc-Zr alloy. Microstructures of samples at each ageing stage were examined carefully by transmission electron microscopes (TEMs) both in two-dimensions and three-dimensions. The presence of different types, densities, and sizes of particles were observed dispersed spherical Al3Sc1-xZrx and also block-shaped Al3Sc precipitates growing along100Al with facets {100} and {110} of the precipitates. TEM analysis both in two-dimensions and three-dimensions, performed on various samples, confirmed the direct correlation between the hardness and the density of Al3Sc.

A three-step vacuum procedure for the fabrication of vertical TiO2 and ZnO nanotubes with three dimensional walls is presented. The method combines physical vapor deposition of small-molecules, plasma enhanced chemical vapor deposition of inorganic functional thin films and layers and a postannealing process in vacuum in order to remove the organic template. As a result, an ample variety of inorganic nanotubes are made with tunable length, hole dimensions and shapes and tailored wall composition, microstructure, porosity and structure. The fabrication of multishell nanotubes combining different semiconducting oxides and metal nanoparticles is as well explored. This method provides a feasible and reproducible route for the fabrication of high density arrays of vertically alligned nanotubes on processable substrates. The emptying mechanism and microstructure of the nanotubes have been elucidated through SEM, STEM, HAADF-STEM tomography and energy dispersive X-ray spectroscopy. In this article, as a proof of concept, it is presented the straightforward integration of ZnO nanotubes as photoanode in a photovoltaic cell and as a photonic oxygen gas sensor

The chemical composition of core–shell nanoparticle clusters have been determined through principal component analysis (PCA) and independent component analysis (ICA) of an energy-dispersive X-ray (EDX) spectrum image (SI) acquired in a scanning transmission electron microscope (STEM). The method blindly decomposes the SI into three components, which are found to accurately represent the isolated and unmixed X-ray signals originating from the supporting carbon film, the shell, and the bimetallic core. The composition of the latter is verified by and is in excellent agreement with the separate quantification of bare bimetallic seed nanoparticles.

An enhanced method to quantify energy dispersive spectra recorded in 3D with a scanning electron microscope (3D SEM–EDS) has been previously demonstrated. This paper presents an extension of this method using all the available X-ray lines generated by the beam. The extended method benefits from using high energy lines, that are more accurately quantified, and from using soft X-rays that are highly absorbed and thus more surface sensitive. The data used to assess the method are acquired with a dual beam FIB/SEM investigating a multi-element Ni-based superalloy. A high accelerating voltage, needed to excite the highest energy X-ray line, results in two available X-ray lines for several elements. The method shows an improved compositional quantification as well as an improved spatial resolution., Highlights • 3D SEM–EDS mapping of structures smaller than the X-ray generation volume is considered. • The influence of neighbouring voxels is corrected by a recursive quantification method. • The method is improved using all available X-ray lines. • The method is applied to simulated spectra and experimental dual beam FIB/SEM data. • The method is shown to improve both compositional accuracy and spatial resolution.

Acquisition of three-dimensional (3D) spectral data is nowadays common using many different microanalytical techniques. In order to proceed to the 3D reconstruction, data processing is necessary not only to deal with noisy acquisitions but also to segment the data in term of chemical composition. In this article, we demonstrate the value of multivariate statistical analysis (MSA) methods for this purpose, allowing fast and reliable results. Using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) coupled with a focused ion beam (FIB), a stack of spectrum images have been acquired on a sample produced by laser welding of a nickel–titanium wire and a stainless steel wire presenting a complex microstructure. These data have been analyzed using principal component analysis (PCA) and factor rotations. PCA allows to significantly improve the overall quality of the data, but produces abstract components. Here it is shown that rotated components can be used without prior knowledge of the sample to help the interpretation of the data, obtaining quickly qualitative mappings representative of elements or compounds found in the material. Such abundance maps can then be used to plot scatter diagrams and interactively identify the different domains in presence by defining clusters of voxels having similar compositions. Identified voxels are advantageously overlaid on secondary electron (SE) images with higher resolution in order to refine the segmentation. The 3D reconstruction can then be performed using available commercial softwares on the basis of the provided segmentation. To asses the quality of the segmentation, the results have been compared to an EDX quantification performed on the same data.

Compared with traditional drug solutions or suspensions, polymeric microparticles represent a valuable means to achieve controlled and prolonged drug delivery into joints, but still suffer from the drawback of limited retention duration in the articular cavity. In this study, our aim was to prepare and characterize magnetic biodegradable microparticles containing dexamethasone acetate (DXM) for intra-articular administration. The superparamagnetic properties, which result from the encapsulation of superparamagnetic iron oxide nanoparticles (SPIONs), allow for microparticle retention with an external magnetic field, thus possibly reducing their clearance from the joint. Two molecular weights of poly(lactic-co-glycolic acid) (PLGA) were used, 12 and 19 kDa. The prepared batches were similar in size (around 10 microm), inner morphology, surface morphology, charge (neutral) and superparamagnetic behaviour. The SPION distribution in the microparticles assessed by TEM indicates a homogeneous distribution and the absence of aggregation, an important factor for preserving superparamagnetic properties. DXM release profiles were shown to be quite similar in vitro (ca. 6 days) and in vivo, using a mouse dorsal air pouch model (ca. 5 days).

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

FIB-Tomography combines FIB milling with the imaging capabilities and the variety of different detection modes (SE, low kV BSE, EDX, EBSD) of a modern SEM in order to analyze the structure of the sample in 3 dimensions. In the interdisciplinary Center for Electron Microscopy (CIME) at EPFL FIB-Nanotomography has become an indispensible tool for the analysis of nanoscale structures in 3 dimensions. Through fully automated slicing and imaging it is possible to generate series of images with rate of 40-60 images (slices) per hour. These stacks (typically 1500-2500 images) can then be used to reconstruct the 3 dimensional microstructure of the sample. With a typical voxel size of 10x10x10 nm (3x3x3 nm or even smaller is possible) and accessible volumes of up to 20x20x20 micrometer FIB tomography closes nicely the gap between X-ray tomography and TEM tilt series tomography. Imaging parameters like high-tension, beam current and detector have to be chosen carefully in order to obtain a high acquisition rate, a high signal-to-noise ratio and the desired image contrast that allows a correct segmentation and analysis of the obtained image stack [1]. Modern electron microscopes like the ZEISS NVision40 allow recording the signal of more than one detector in one scan. Series of images with complementary information can be obtained in one scan. The following example shows how the use of the in-Lens secondary electron detector and the energy selective backscattered (EsB) electron detector has allowed segmenting the 3 chemically different phases of a Pb-free solder (Au, Ag, Cu). The FIB stack consists of 2000 slices (10nm slice thickness, 10x10nm image pixel size). In Fig. 1a the image was obtained at 1.8 keV detecting the backscattered electrons (EsB). We observe a grain orientation (channelling) contrast in the matrix phase and a strong material contrast in the precipitates (Cu rich). In Fig. 1b obtained with the inLens secondary electron detector the precipitates are bright while the channelling contrast in the matrix is still visible. Careful inspection shows that there are more bright grains in Fig. 1b than dark ones in Fig. 1a. EDX analysis reveals that the bright grains in Fig. 1b consist of 2 different phases: one rich in Ag and the other one rich in Cu. The darker ones in Fig. 1a however are the Cu-rich phase only. Using both images it is possible to segment the 3D data (Fig.2) based on the differences in the secondary (in-lens SE) and backscattered (EsB) electron yield. The recent technological progress in energy dispersive X-ray microanalysis with the introduction of large surface silicon drift detectors (SDD) has made it possible to acquire elemental maps within a few minutes. Fig. 3 shows a reconstructed volume of a laser solder joint between NiTi and stainless steel. The segmentation of the complex microstructure was based on 44 elemental maps and 360 secondary electron images acquired automatically over 14 hours. The acquisition of each elemental map took 6 minutes with an image pixel size of 100nm and 100nm spacing in the z direction. The secondary electron images were recorded at 12.5nm image pixel size and 12.5nm slice thickness (isometric voxel dimensions). The secondary electron images were used to refine at higher resolution the segmentation done through the analysis of the elemental distribution maps.

Billet Jean, Marie Christiane, Jail Marcel, Durand Geneviève, Dupont François, Barruet Josette, Tanitte Paul, Cocu Pierre, Bernard Marie-Thérèse, Burdet Pierre, Dumolard Pierre. Un remarquable terrain de recherches pour une politique d'aménagement de la montagne : la haute Maurienne. In: Revue de géographie alpine, tome 54, n°1, 1966. pp. 43-71.

The biomedical industry has an increasing demand for processes to join dissimilar metals, such as laser welding of NiTi and stainless steel wires. A region of the weld close to the NiTi interface, which previously was shown to be prone to cracking, was further analyzed by energy dispersive spectrometry (EDS) extended in the third dimension using a focused ion beam. As the spatial resolution of EDS analysis is not precise enough to resolve the finest parts of the microstructure, a new segmentation method that uses in addition secondary-electron images of higher spatial resolution was developed. Applying these tools, it is shown that this region of the weld close to the NiTi interface does not comprise a homogeneous intermetallic layer, but is rather constituted by a succession of different intermetallics, the composition of which can be directly correlated with the solidification path in the ternary Fe-Ni-Ti Gibbs simplex.

The understanding of the relationships between the microstructure and performance of heterogeneous materials for electrochemical energy conversion and storage have significantly benefited from the advances of 3-D imaging methods. The Ni and yttria-stabilized zirconia (YSZ) hydrogen electrode in solid oxide fuel/electrolysis cells (SOFC/SOEC) is for instance heterogeneous, comprising an assembly of reticulated phases that form and provide transport pathways to electrocatalytic sites. The morphology and topology of the phases is known to evolve during long-term operation. Despite the aggressive environment, the performance degradation has been reduced to less than a few percent per year. Yet, further efforts are required to guarantee the commercial viability. The remaining degradation stems from subtle morphological, chemical and crystallographic alterations that are increasingly difficult to detect and quantify. Analyses are commonly based upon the measurement of the evolution of the effective transport properties of the phases and of the connected triple-phase boundary length measured on 3-D reconstructions obtained by x-ray or electron microscopy. The properties are then implemented in continuum electrode models for the estimating and analyzing of material performance. One limitation of such averaged property-based approaches is that all the TPBs are assumed equally accessible. Therefore, information on the effects of 3-D microstructural features may be only partially retrieved. In this study, Ni-YSZ samples were extracted from cells in pristine state and after SOFC or SOEC operation in short-stacks and segmented-cells for up to 10,000 h. Regions including or close to the interface with the YSZ electrolyte were imaged by focused ion beam-scanning electron microscopy (FIB-SEM). For a sample aged for 10,000 h in SOEC mode, the data from the secondary electron/secondary ion (SESI), in-lens secondary electrons and energy-selective backscattered (EsB) detectors was complemented with 3-D energy dispersive x-ray spectroscopy (EDS) elemental maps by switching automatically the acceleration voltage from 1.7 kV to 10 kV every 10 slices. The 3-D reconstructions with an isometric voxel size of 10 nm were segmented for measuring a series of structural, material and electrochemical properties relevant for degradation analyses, such as tortuosity, polarization resistance and accessible TPB length. The latter is a newly proposed performance metric that combines geometrical and physical considerations to quantify the access to TPB sites. The measurement method consists in applying an analytical electrochemical fin model (ECF) to a 3-D discrete representation of the heterogeneous structure provided by skeleton-based partitioning to probe the resistance of the pathways to each TPB, within each phase separately. The measurement of structural properties highlights as expected a significant coarsening of the Ni phase upon aging, which modifies the transport properties of the Ni and pore phases and decreases the total TPB length. The degradation of the polarization resistance computed by ECF is in line with electrochemical impedance spectroscopy (EIS) measurements on segmented-cells. In all the phases, the TPBs were not observed to be equally accessible, even in the pristine sample. The variation exceeds one order of magnitude and a few connected TPBs can be even passivated because of diffusion limitations. Preferential pathways are clearly detected, which suggests a non-uniform utilization of the phases that is potentially detrimental for the performance and the resilience of the material to alterations caused by degradation operation. However, the accessible TPB remains almost unchanged after 4,700 h of SOFC operation. This is because the YSZ phase provides the best access to the TPBs, followed by Ni and pore, and is not significantly affected by 4,700 h of SOFC operation. Further, the changes in the spatial distribution of the TPBs caused by the coarsening of the Ni phase do not modify the access through YSZ. Therefore, during this operation window, the degradation scales with the decrease in the connected TPB. In contrast, micro-cracks were detected in the YSZ scaffold after 10,000 in SOEC mode, close to the YSZ electrolyte. The accessible TPB can capture the effects of such localized alterations, whereas standard volume-averaged measurements remain insensitive, showcasing the need for new 3-D measurements for understanding the long-term degradation in SOFC/SOEC materials.

This paper addresses the fabrication of vertically aligned ZnO@TiO2 multishell nanotubes by a combined full vacuum-plasma approach at mild temperatures. The growth is carried out within the premises of a one-reactor approach, i.e. minimizing the number of vacuum chambers and sample transferences. In this way, the interface between ZnO and TiO2 is fully preserved from humidity thus increasing ZnO durability and stability. These nanostructures are studied by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy in STEM (EDX-STEM). High density one-dimensional arrays of these nanotubes formed on FTO substrates are applied as photoanode in a dye-sensitized solar cell (DSC). The evolution of the dye adsorption capacity and solar cells parameters are explored as a function of the crystallinity and thickness of the TiO2 shell. The results show the critical effect of a full coverage by TiO2 of ZnO core to explain the mixed results found in the literature.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.