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Martinez-Prieto L.M.,CNRS Coordination Chemistry | Martinez-Prieto L.M.,National Polytechnic Institute of Toulouse | Philippot K.,CNRS Coordination Chemistry | Philippot K.,National Polytechnic Institute of Toulouse | Chaudret B.,LPCNO
Technical Proceedings of the 2014 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2014 | Year: 2014

Three samples of organometallic ruthenium nanoparticles (RuNPs) namely Ru-PVP (PVP=polyvinylpyrrolidone; 1.3 nm), Ru-dppb (dppb= diphenylphosphinobutane; 1.9 nm) and Ru-heptanol-dppb (3.1 nm) were prepared and investigated in a model Fischer-Tropsch Synthesis (FTS) reaction. Our aim was to shed some light on the influence of the metal core size and of the chemical environment at the metal surface on the surface reactivity of these RuNPs through the hydrogenation of CO into hydrocarbons (olefins and paraffins). For that purpose, we used a combination of spectroscopic techniques such as gas phase and solid state NMR, MS and FTIR. The results evidence that the size increase of the metal core does not affect significantly the catalytic properties of the RuNPs since comparable conversion and selectivity are obtained with Ru-dppb and Ru-heptanol-dppb. In the contrary, the stabilizer seems to have a crucial role in directing the catalytic reaction. Source


Reveret F.,University of Auvergne | Reveret F.,CNRS Pascal Institute | Andre Y.,University of Auvergne | Andre Y.,CNRS Pascal Institute | And 13 more authors.
Journal of Crystal Growth | Year: 2015

Hydride Vapor Phase Epitaxy (HVPE) growth process is still efficient for the growth of high quality GaN material. In situ-characterization techniques are extremely difficult to implement inside HVPE hot wall reactors. A method based on selective area growth coupled to spatially resolved optical spectroscopies, micro-photoluminescence and micro-reflectivity is developed for a control of GaN optical quality and strain at different growth stages. As highly reproducible HVPE process is used with a two-step epitaxial lateral overgrowth procedure to produce 80 μm thick GaN layers presenting a weak residual strain with high optical quality comparable to free-standing GaN layers. © 2015 Elsevier B.V. Source


Mallet E.,CNRS Pascal Institute | Disseix P.,CNRS Pascal Institute | Lagarde D.,LPCNO | Mihailovic M.,CNRS Pascal Institute | And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Excitonic parameters of ZnO have been determined from 5 to 300 K using the combination of time-integrated four-wave mixing, continuous wave reflectivity, autocorrelation of reflectivity at the femtosecond scale, and photoluminescence spectroscopy. These techniques allow an accurate determination of both inhomogeneous and homogeneous linewidths, oscillator strength, and other parameters characteristic for excitonic resonances. It turns out that, due to impurity-exciton scattering, the homogeneous damping of A and B excitons (0.55 and 1.35 meV, respectively) predominates over inhomogeneous one in high-quality ZnO at low temperature. Our data also prove that the strong exciton-phonon coupling enhances the excitonic broadening at room temperature up to 47 meV. This approach, which combines various sophisticated spectroscopy experiments, can be employed for an accurate determination of excitonic parameters in other semiconductor compounds and in any system where excitons are confined. © 2013 American Physical Society. Source


Lara P.,CNRS Coordination Chemistry | Lara P.,Toulouse 1 University Capitole | Rivada-Wheelaghan O.,University of Seville | Conejero S.,University of Seville | And 4 more authors.
Angewandte Chemie - International Edition | Year: 2011

NHCs go nano: Ruthenium nanoparticles were formed from (cyclooctadiene) (cyclooctatriene)ruthenium(0) and stabilized by N-heterocyclic carbenes (NHCs). Solid-state NMR spectroscopy revealed both the coordination of the NHC ligands on the surface of the particles and their surface reactivity. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Martinez-Prieto L.M.,LPCNO | Ferry A.,University of Munster | Rakers L.,University of Munster | Richter C.,University of Munster | And 4 more authors.
Chemical Communications | Year: 2016

The synthesis and catalytic activity of long-chain NHC-stabilized RuNPs are presented. Full characterization of these novel nanostructures including surface state studies show that the ligand influences the number and the location of Ru active sites which impacts the NP catalytic activity, especially in hydrogenation reactions. The high stability and versatility of these nanosystems make them successful catalysts for both oxidation and hydrogenation reactions that can even be performed successively in a one pot-fashion. © 2016 The Royal Society of Chemistry. Source

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