Publications by authors named "Viau G"
Article Synopsis
- A novel microreactor platform enables extremely fast reagent mixing in under 300 microseconds, allowing for detailed studies of the synthesis of ultra-small gold nanoparticles (NPs).
- By pairing the microreactor with advanced characterization techniques, researchers can investigate reaction pathways and phase transitions more effectively without the limitations of traditional methods.
- The study reveals the kinetics of gold nanoparticle formation from Au(III) precursors and identifies the presence of prenucleation clusters and a temporary Au(I) phase, proposing different reaction pathways that bypass classical mechanisms in NP formation.
Article Synopsis
- 2D ultrathin metal nanostructures, specifically nanosheets of face-centered cubic (fcc) metals like platinum, have unique properties and advantages for catalysis due to their high surface-to-volume ratios and low-coordinated sites.
- The selective synthesis of platinum nanosheets is achieved through a seeded-growth method, focusing on preserving defects in the precursor seeds to promote effective 2D growth.
- Testing the catalytic performance of these platinum nanosheets in phenylacetylene hydrogenation reveals that they outperform traditional commercial Pt/C catalysts in terms of stability and selectivity to styrene.
Article Synopsis
- The integration of tiny magnetic materials into circuits is crucial for creating portable devices used in various fields like telecommunications and biomedical applications, but it's challenging to achieve.
- This study presents a method for fabricating and directly integrating nanostructured magnetic materials onto silicon substrates, producing high-performance magnets.
- The successful demonstration of using these magnets to control a micro-electromechanical system shows their potential as effective magnetic materials in portable technology.
Article Synopsis
- The synthesis of metal nanoparticles using apolar solvents and long chain surfactants effectively controls particle size and shape, but understanding the nucleation and growth mechanisms is complex due to the multiple roles of surfactants.
- This study utilizes in situ techniques like SAXS, XAS, and HE-XRD to explore the formation of ultra-small gold particles, suggesting that they emerge from stable pre-nucleation clusters (PNCs) rather than following classical nucleation pathways.
- The research highlights the influence of the oleylamine surfactant on the reactivity and size of gold precursors, establishing its critical role throughout the nanoparticle formation process, including solubilization, size determination, and final particle stabilization.
Article Synopsis
- Cobalt nano-rods with a hexagonal structure were created using a reduction method involving a cobalt precursor, with an external magnetic field applied during their formation.
- * The external magnetic field altered both the aspect ratio and morphology of the nano-rods, eliminating conical heads and reducing stacking faults in the structure.
- * These enhanced properties led to a higher coercive field for the nano-rods, making them promising candidates for developing new permanent magnets.
Article Synopsis
- The one-step seed-mediated synthesis method is popular for creating ferromagnetic metal nanoparticles due to its ability to control particle shape, but it has limited mechanistic studies.
- This research focuses on the heteronucleation process during the synthesis of cobalt nanoparticles in liquid polyols, using high-resolution imaging and hydrogen evolution measurements to track nucleation and growth.
- The study reveals that iridium and ruthenium seeds play a crucial role in the nucleation, and their influence on cobalt's microstructure varies, showcasing the relationship between the nucleating agent and particle formation.
Article Synopsis
- * The type of ligands used in the synthesis significantly influenced the reactivity of the precursors and the resulting chemical structure of the nanoparticles.
- * This synthesis method achieved the formation of a B2 short-range order in FeCo nanoparticles without needing any additional annealing process, resulting in strong magnetic properties and successful applications in inductor-based filters.
Article Synopsis
- Researchers focused on thin gold nanowires synthesize long, ultrathin versions using liquid-phase methods and in situ high-energy X-ray diffraction to uncover their formation mechanisms.
- They discovered that the growth of these nanowires involves transient linear gold complexes that self-assemble under controlled conditions, differing from the typical structure of bulk gold.
- The unique tetrahedrally close-packed structure of these nanowires is attributed to geometrical frustration, affecting atomic packing and leading to cylindrical shapes, offering insights for future applications and synthesis methods.
After about three decades of development, the polyol process is now widely recognized and practised as a unique soft chemical method for the preparation of a large variety of nanoparticles which can be used in important technological fields. It offers many advantages: low cost, ease of use and, very importantly, already proven scalability for industrial applications. Among the different classes of inorganic nanoparticles which can be prepared in liquid polyols, metals were the first reported.
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- This study focuses on the electrical and structural characterization of nano-sized platinum (Pt) tribranches to assess their applications in microelectronics.
- The researchers found that these Pt nanostars, created from HPtCl salt reduction in oleylamine, exhibit excellent crystalline structure and metallic properties even with mild synthesis conditions.
- The devices made from these nanostars can handle current densities over 200 MA/cm² and function effectively as compact frequency multiplexers in a non-ohmic context.
Article Synopsis
- Gold nanowires with a tiny 1.7 nm diameter were created by reducing HAuCl in a hexane solution mixed with oleylamine.
- Analysis showed that the nanowires had a bilayer of oleylammonium chloride and oleylamine at their surface, which could be partially replaced by a phosphine layer without changing the nanowire shape.
- Different ligands impacted the nanowires' crystalline structure and stability, with phosphine-coated nanowires demonstrating longer-lasting properties compared to other coatings like thiols.
Article Synopsis
- The study investigates how laser alloying affects cobalt (Co) nanorods and aluminum (Al) nanoparticles mixed in liquid ethanol.
- After laser exposure, Co nanorods change shape into Co nanospheres that are coated with Al, altering their initial structure.
- The research also explores how the size of these nanoparticles evolves over time, finding an optimal laser exposure time that leads to the largest average size of the particles.
We demonstrate in this paper the feasibility to elaborate rare-earth free permanent magnets based on cobalt nanorods assemblies with energy product (BH)max exceeding 150 kJ m(-3). The cobalt rods were prepared by the polyol process and assembled from wet suspensions under a magnetic field. Magnetization loops of dense assemblies with remanence to a saturation of 0.
View Article and Find Full Text PDFBottom-up fabrication of a flexible multi-touch panel prototype based on transparent colloidal indium tin oxide (ITO) nanocrystal (NC) films is presented. A series of 7% Sn(4+) doped ITO NCs protected by oleate, octanoate and butanoate ligands are synthesized and characterized by a battery of techniques including, high resolution transmission electron microscopy, X-ray diffraction, (1)H, (13)C and (119)Sn nuclear magnetic resonance spectroscopy, and the related diffusion ordered spectroscopy. Electrical resistivities of transparent films of these NCs assembled on flexible polyethylene terephthalate substrates by convective self-assembly from their suspension in toluene decrease with the ligand length, from 220 × 10(3) for oleate ITO to 13 × 10(3)Ω cm for butanoate ITO NC films.
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- Researchers created ultrathin gold nanowires (NWs) and nanospheres (NSs) using a chemical reduction process and stabilized them with oleylammonium chloride surfactants.
- Using atomic force microscopy (AFM) nanoxerography, they directed the assembly of these nano-objects on surfaces, with NWs attracted to positively charged areas and NSs to negatively charged ones, indicating different charge characteristics.
- The study demonstrated successful assembly of single gold NWs on defined sites without damaging the surface, paving the way for future tests on their electrical and mechanical properties.
Article Synopsis
- A study investigates how nanoparticle-based strain gauges behave under different strain conditions using techniques like small angle X-ray scattering (SAXS) and grazing incidence SAXS.
- The strain gauges were made from gold nanoparticles on flexible materials, and the research found that stretching caused certain microstructural and electrical resistance changes in the nanoparticle wires.
- Results indicate that while longitudinal stretching occurs, there’s a decrease in width and a loss of directional sensitivity in the strain gauges due to transversal current flow through the nanoparticle wires.
Article Synopsis
- Ultrathin gold nanowires, created through chemical processes, experience permanent structural changes when subjected to external forces.* -
- Advanced imaging techniques allowed for real-time observation of damage caused by electron beams, leading to the creation of linear chains of gold atoms and reactive clusters.* -
- These findings suggest exciting potential uses for these modified nanowires in catalytic processes and improving electronic conductivity.*
Article Synopsis
- An experimental study on elementary excitations in gold nanocrystals was conducted using plasmon resonance Raman scattering, focusing on phonons and electron-hole pairs.
- The analysis covered three types of excitations: quasi-acoustical vibrations (Lamb's modes), electron-hole excitations (linked to surface-enhanced Raman scattering), and atomic vibrations (bulk phonons).
- Findings highlighted the significant influence of surface atoms on lattice dynamics, including implications for thermodynamic properties like a reduction in the Debye temperature.
Article Synopsis
- Scientists made tiny gold wires that stick together in special patterns while floating in liquid.
- They used X-ray tools to learn how these tiny wires grow, finding that they're kept stable by a special coating.
- This research helps understand how to control the growth of these tiny gold wires for future uses.
Article Synopsis
- * The study utilizes both experimental techniques and theoretical calculations to explore how cobalt ferromagnetic nanoparticles grow, revealing that the growth occurs mainly along the c axis with a consistent diameter of about 15 nm.
- * Findings indicate that the shape of these nanoparticles is influenced by the chemical potential of carboxylate ligands, where increasing ligand concentration can change the shape from rod-like to platelet forms, suggesting broader applications for this approach in nanoparticle synthesis.
Formation of 3D close-packed assemblies of upconverting NaYF4 colloidal nanocrystals (NCs) on surfaces, by Atomic Force Microscopy (AFM) nanoxerography is presented. The surface potential of the charge patterns, the NC concentration, the polarizability of the NCs and the polarity of the dispersing solvent are identified as the key parameters controlling the assembly of NaYF4 NCs into micropatterns of the desired 3D architecture. This insight allowed us to fabricate micrometer sized Quick Response (QR) codes encoded in terms of upconversion luminescence intensity or color.
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- The study focuses on understanding how electrons move in strain gauges made from gold colloidal nanoparticles (NPs) that are coated with different organic ligands.
- The research shows that the electron transport happens through tunneling, which is affected by the type of ligands used; specifically, phosphine and thiol ligands resulted in higher gauge sensitivity.
- Temperature resistance tests revealed two different behavior regimes (strong and weak coupling), with the weak-coupling regime gauges demonstrating higher tunneling decay constants and significant Coulomb charging energy affecting electron transport.
Article Synopsis
- A new method called "PlasMag" for real-time immunodiagnostics allows testing directly in sample solutions like serum, eliminating the need for sample preparation.
- It uses advanced plasmon-optical techniques to detect changes in the relaxation dynamics of magnetic nanoparticles when target molecules bind to their surfaces.
- The ideal nanoprobes for this method are core-shell nanorods made of cobalt and gold, designed to optimize detection in the near-infrared range and work effectively with low frequency magnetic fields.
Article Synopsis
- The authors introduce a quick and simple method for arranging nanoparticles using charge patterns created by atomic force microscopy on a thin film of polymethylmethacrylate applied to silicon wafers.
- The protocol involves two main steps: placing an aqueous colloidal dispersion onto the charge patterns and then immersing it in a specific water-soluble alcohol to facilitate the assembly process.
- This method allows for the construction of diverse assemblies of various nanoparticles, including organic and inorganic types, and enables the creation of more complex patterns with both positively and negatively charged particles in a single step, which could benefit the development of advanced nanoparticle-based devices.