Development of a microfurnace dedicated to in situ scanning electron microscope observation up to 1300 °C. III. In situ high temperature experiments.

The FurnaSEM microfurnace was installed in the chamber of a scanning electron microscope to carry out in situ experiments at high temperatures and test its limits. The microfurnace was used in combination with different types of detectors (Everhart-Thornley for the collection of secondary electrons in a high vacuum, gas secondary electron detector for the specific collection of secondary electrons in the presence of gas, and Karmen© detector for the collection of backscattered electrons at high temperature). Experiments carried out on various samples (metal alloys and ceramics) show that the microfurnace operates in both high-vacuum and low-vacuum modes. Temperature ramp rates during temperature cycles applied to the sample range from 1 to 120 °C/min (temperature rise) and 1 to 480 °C/min (controlled and natural cooling). The maximum temperature at which images were recorded up to 25 k × magnification was 1340 °C, with a residual air atmosphere of 120 Pa. The choice of a flat furnace with the sample placed directly above it has enabled innovative experiments to be carried out, such as low-voltage imaging (using a shorter working distance-up to 10 mm-than is possible with conventional furnaces), 3D imaging (by tilting the stage by up to 10°), and high-temperature backscattered electron imaging (using a dedicated detector).

Toward Distinguishing between the Superchaotropic and Hydrophobic Characters of Nanometric-Sized Ions in Interaction with PEGylated Surfaces.

In this study, we explore the superchaotropic effect of various polyoxometalate or boron cluster nano-ions on hydrophilic neutral surfaces. Nano-ions, characterized by low charge densities, exhibit strong adsorption on non-ionic hydrophilic surfaces like PEGylated micelles. This adsorption phenomenon was attributed to the enthalpically favorable dehydration of nano-ions, the so-called superchaotropic effect. Here, we investigate the adsorption of three nano-ions, α-SiW12O404-, α-PW12O403-, and B12I122-, with decreasing charge density or increasing superchaotropicity (or hydrophobicity), on hydrophilic solid surfaces, PEGylated gold nanoparticles, and PEGylated gold-coated quartz crystal. Solid surfaces are devoid of hydrophobic regions, enabling the study of the subtle nuance between hydrophobic and superchaotropic effects. Unlike adsorption on PEGylated micelles, the adsorption constant decreases with a reduced charge density, aligning with the well-established principle that hydrophobic ions do not adsorb on hydrophilic surfaces. This research improves our understanding of the subtle difference between superchaotropic and hydrophobic effects in nano-ion adsorption phenomena.

How colloid nature drives the interactions between actinide and carboxylic surfactant in sol: Towards a mesostructured nanoporous actinide oxide material.

HYPOTHESIS: The key to prepare a mesostructured porous material by a soft-template route coupled to a colloidal sol-gel process is to control the surfactant-colloid interface. In the case of tetravalent actinide ions, their high reactivity in aqueous media always leads to uncontrolled and irreversible condensation. The addition of a complexing agent to the sol may moderate these reactions and enhances the interaction between the colloids and the surfactant to in fine prepare a mesostructured nanoporous actinide oxide material. EXPERIMENTS: Several colloidal sols were prepared without and with formic acid as complexing agent by varying the molar ratios between thorium, carboxylic surfactant and pH. Small and Wide Angle X-ray Scattering were used to characterize the nature of the colloids, their interaction with the surfactant and the final ThO2 materials. FINDINGS: Depending on the colloid nature, hexagonal or worm-like hybrid mesophase is formed. The thermal treatment of the worm-like mesophase with a sufficient amount of Th-formic acid hexameric species coated at the surface of surfactant micelles generates micrometric ThO2 nanofibers. This material having an accessible porosity opens new perspectives to be impregnated with minor actinide solutions offering a promising safety method for the fabrication of mixed oxide nuclear fuel and the minor actinide transmutation.

Facile Preparation of Macro-Microporous Thorium Oxide via a Colloidal Sol-Gel Route toward Safe MOX Fuel Fabrication.

The identification of new colloidal sol-gel routes for the preparation of actinide oxides, which have a homogeneous and accessible porosity that can easily be impregnated by any concentrated actinide solution, opens new perspectives for the preparation of homogeneous nuclear fuel for minor actinide transmutation. This homogeneity allows us to avoid "hot spot" formation due to the local accumulation of more fissile elements. Here, we report the preparation of macro-microporous ThO2 materials by a colloidal sol-gel route. Using a thorium salt with 6-aminocaproic acid as a complexing agent at a controlled pH, we were able to pilot the condensation of thorium hydroxo species forming colloids of tuned nanometric size and thus the sol stability. After a freeze-drying process to concentrate colloids and a thermal treatment allowing complexing agent removal and macroporosity formation by a brutal gas release during combustion, a loose packing of ThO2 nanoparticles with an ordered distribution of interparticular porosity and a fraction of nanometric crystallites, whose size depends on the initial colloidal size, were obtained. The sols, pastes, and final materials were characterized by small- and wide-angle X-ray scattering to determine the colloidal size and the final structure of the materials, which was also confirmed by transmission electron microscopy. The most promising material was finally successfully impregnated by a simulating minor actinide solution and thermally treated to prepare a mixed actinide oxide material. This safe technology, relying on the colloidal sol-gel process and the formulation of complex fluids forming tunable precursors, opens new perspectives for the reuse of nuclear waste solutions as new fuel.

Direct Observation of the Surface Topography at High Temperature with SEM.

High-temperature scanning electron microscopy allows the direct study of the temperature behavior of materials. Using a newly developed heating stage, tilted images series were recorded at high temperature and 3D images of the sample surface were reconstructed. By combining 3D images recorded at different temperatures, the variations of material roughness can be accurately described and associated with local changes in the topography of the sample surface.

Uranium removal from mining water using Cu substituted hydroxyapatite.

In this study, synthetic copper substituted hydroxyapatite (Cu-Hap), CuxCa10-x(PO4)6(OH)2 were prepared by co-precipitation method and were used as reactive materials in batch experiments to immobilize uranyl. The limit of incorporation of Cu into a single-phased Cu-Hap reached xCu ≤1.59. The synthetic Cu-Hap samples obtained with various Cu contents were contacted with synthetic uranyl doped solutions and with real mining waters showing various pH and chemical compositions. A fast and strong decrease of the uranium concentration was observed, followed by the establishment of an equilibrium after 1-4 days of contact with the solutions. Examination of the solid phase after uranium uptake was performed using a combination of techniques. Depending on the composition of the solution and the copper content of the Cu-Hap, various mechanisms of uranium removal were observed. Based on the experimental results and geochemical simulations, it appeared that the main interest for using Cu-Hap is to enlarge the domain of water compositions for which the precipitation of meta-torbernite, (H3O)0.4Cu0.8(UO2)2(PO4)2·7.6 H2O is the predominant mechanism associated to the uranium removal, especially for pH > 6.7 where carbonate uranium species are predominant.

Full determination of single ferroelectric nanocrystal orientation by Pockels electro-optic microscopy.

We present a nanoscale electro-optic imaging method allowing access to the phase response, which is not amenable to classical second-harmonic generation microscopy. This approach is used to infer the vectorial orientation of single domain ferroelectric nanocrystals, based on polarization-resolved Pockels microscopy. The electro-optic phase response of KTP nanoparticles yields the full orientation in the laboratory frame of randomly dispersed single nanoparticles, together with their electric polarization dipole. The complete vector determination of the dipole orientation is a prerequisite to important applications including ferroelectric nanodomain orientation, membrane potential imaging, and rotational dynamics of single biomolecules.

Three-dimensional organic microlasers with low lasing thresholds fabricated by multiphoton and UV lithography.

Cuboid-shaped organic microcavities containing a pyrromethene laser dye and supported upon a photonic crystal have been investigated as an approach to reducing the lasing threshold of the cavities. Multiphoton lithography facilitated fabrication of the cuboid cavities directly on the substrate or on the decoupling structure, while similar structures were fabricated on the substrate by UV lithography for comparison. Significant reduction of the lasing threshold by a factor of ~30 has been observed for cavities supported by the photonic crystal relative to those fabricated on the substrate. The lasing mode spectra of the cuboid microresonators provide strong evidence showing that the lasing modes are localized in the horizontal plane, with the shape of an inscribed diamond.

Efficient antifouling surface for quantitative surface plasmon resonance based biosensor analysis.

Non-specific binding to biosensor surfaces is a major obstacle to quantitative analysis of selective retention of analytes at immobilized target molecules. Although a range of chemical antifouling monolayers has been developed to address this problem, many macromolecular interactions still remain refractive to analysis due to the prevalent high degree of non-specific binding. In this manuscript we explore the dynamic process of the formation of self-assembled monolayers and optimize physical and chemical properties thus reducing considerably non-specific binding while maintaining the integrity of the immobilized biomolecules. As a result, analysis of specific binding of analytes to immobilized target molecules is significantly facilitated.

Electro-optical Pockels scattering from a single nanocrystal.

The electro-optical Pockels response from a single non-centrosymmetric nanocrystal is reported. High sensitivity to the weak electric-field dependent nonlinear scattering is achieved through a dedicated imaging interferometric microscope and the linear dependence of electro-optical signal upon the applied field is checked. Using different incident light polarization states, a priori random spatial orientation of the crystal can be inferred. The electro-optical response from a nanocrystal provides local subwavelength sensor of quasi-static electric fields with potential applications in physics and biology. It also leads to a new sub-wavelength microscopy towards the nanoscale investigation of interesting phenomena such as nanoferroelectricity.