Graphene-based textured surface by pulsed laser deposition as a robust platform for surface enhanced Raman scattering applications

International audienceWe have developed a surface enhanced Raman scattering (SERS)-active substrate based on gold nanoparticles-decorated few-layer (fl) graphene grown by pulsed laser deposition. Diamond-Like Carbon film has been converted to fl-graphene after thermal annealing at low temperature. The formation of fl-graphene was confirmed by Raman spectroscopy, and surface morphology was highlighted by scanning electron microscopy. We found that textured fl-graphene film with nanoscale roughness was highly beneficial for SERS detection. Rhodamine 6G and p-aminothiophenol proposed as test molecules were detected with high sensitivity. The detection at low concentration of deltamethrin, an active molecule of a commercial pesticide was further demonstrated

Etude Raman des alliages à base de Be ou N, à liaison fortement contrastées : modèle de percolation

We propose a 1 bond->2 modes model for the long wavelength optical phonons in zinc-blende ternary/quaternary alloys, based on the percolation site theory. There is no additional input with respect to the usual 1 bond->1 mode modified-random-element-isodisplacement model, based on a description of the crystal according to the virtual crystal approximation. Our model takes into account the fractal->normal object transition which goes with the dispersion->continuum topology transition at the percolation thresholds of the bonds. The model is built from ternaries and multinaries involving the first row elements in substitution, Be and N, which open the attractive class of mixed crystals with highly contrasted bond stiffness. A simplified version is derived for current alloys which display a much weaker contrast in the bond stiffness. This is tested with GaAs-InAs, taken here as a typical challenging system. The multi-phonon behavior of this alloy is re-examined in the light of percolation model, with much success. In order to gain a microscopic insight to support the percolation model, we performed in collaboration with an inveterate theoricien a first-principles study of the bond properties in a fully relaxed Zn26Be6Se32 supercell with Be Se bonds located in a continuous chain and isolated Be-Se bondsNous proposons dans ce mémoire un modèle de percolation du type 1 liaison->2 modes pour la compréhension de base des phonons optiques à grande longueur d'onde dans les alliages ternaires/quaternaires à symétrie zinc-blende. Le modèle de percolation sans paramètre ajustable fonctionne sur la base des mêmes données empiriques nécessaires à la mise en ?uvre du modèle standard plus simple de type 1 liaison->1 mode, qui repose sur une description de l'alliage en terme de cristal virtuel, c'est-à-dire à désordre moyenné': cependant le modèle de percolation prend en compte la transition fractal->normal qui accompagne la transition topologique majeure dispersion->continuum au passage des seuils de percolation des liaisons. Le modèle est établi à partir des ternaires et multinaires impliquant en substitution les éléments Be et N de la première rangée du tableau périodique, qui ouvrent la classe extrêmement attrayante des alliages à contraste mécanique. Une version simplifiée est ensuite dérivée pour les alliages usuels, c'est à dire qui ne montrent pas de contraste marqué entre les propriétés mécaniques des matériaux parents. Cette version est finalement testée à l'aide du système GaAs-InAs, ce qui constitue une véritable gageure. Le comportement multi mode extrêmement controversé de ce système stimulant se voit ainsi ré examiné à la lumière du modèle de percolation, et ce avec beaucoup de profit. Enfin nous réalisons, en collaboration avec un théoricien confirmé, une étude par des méthodes premiers principes des effets de percolation sur les propriétés physiques des liaisons dans ZnBeSe, pour asseoir à l'échelle microscopique les hypothèses de base de notre modèle phénoménologiqu

Etude Raman des alliages à base de Be ou N, à liaison fortement contrastées (modèle de percolation)

Nous proposons dans ce mémoire un modèle de percolation du type 1 liaison->2 modes pour la compréhension de base des phonons optiques à grande longueur d'onde dans les alliages ternaires/quaternaires à symétrie zinc-blende. Le modèle de percolation sans paramètre ajustable fonctionne sur la base des mêmes données empiriques nécessaires à la mise en œuvre du modèle standard plus simple de type 1 liaison->1 mode, qui repose sur une description de l'alliage en terme de cristal virtuel, c'est-a -dire à désordre moyenné': cependant le modèle de percolation prend en compte la transition fractal->normal qui accompagne la transition topologique majeure dispersion->continuum au passage des seuils de percolation des liaisons. Le modèle est établi à partir des ternaires et multinaires impliquant en substitution les éléments Be et N de la première rangée du tableau périodique, qui ouvrent la classe extrêmement attrayante des alliages à contraste mécanique. Une version simplifiée est ensuite dérivée pour les alliages usuels, c'est à dire qui ne montrent pas de contraste marqué entre les propriétés mécaniques des matériaux parents. Cette version est finalement testée à l'aide du système GaAs-InAs, ce qui constitue une véritable gageure. Le comportement multi mode extrêmement controversé de ce système stimulant se voit ainsi ré examiné à la lumière du modèle de percolation, et ce avec beaucoup de profit. Enfin nous réalisons, en collaboration avec un théoricien confirmé, une étude par des méthodes premiers principes des effets de percolation sur les propriétés physiques des liaisons dans ZnBeSe, pour asseoir à l'échelle microscopique les hypothèses de base de notre modèle phénoménologique.We propose a 1 bond->2 modes model for the long wavelength optical phonons in zinc-blende ternary/quaternary alloys, based on the percolation site theory. There is no additional input with respect to the usual 1 bond->1 mode modified-random-element-isodisplacement model, based on a description of the crystal according to the virtual crystal approximation. Our model takes into account the fractal->normal object transition which goes with the dispersion->continuum topology transition at the percolation thresholds of the bonds. The model is built from ternaries and multinaries involving the first row elements in substitution, Be and N, which open the attractive class of mixed crystals with highly contrasted bond stiffness. A simplified version is derived for current alloys which display a much weaker contrast in the bond stiffness. This is tested with GaAs-InAs, taken here as a typical challenging system. The multi-phonon behavior of this alloy is re-examined in the light of percolation model, with much success. In order to gain a microscopic insight to support the percolation model, we performed in collaboration with an inveterate theoricien a first-principles study of the bond properties in a fully relaxed Zn26Be6Se32 supercell with Be Se bonds located in a continuous chain and isolated Be-Se bonds.METZ-SCD (574632105) / SudocSudocFranceF

Influence of oxygen on the formation mechanism of silver nanoparticles formed by laser exposure of glassy matrix.

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Influence of oxygen on the formation mechanism of silver nanoparticles formed by laser exposure of glassy matrix

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Sol-Gel Processing of Bismuth Germanate Thin-Films

This study aims to obtain uniform and homogeneous bismuth germanate oxides thin films by spin coating and using the sol-gel technique with different precursors, followed by low-temperature annealing at 560 °C. By using Bi(NO3)3 precursors, we have obtained transparent, yellowish thin films with a 200 nm thickness. The structural analysis of the initial sol-gel powder has shown the presence of two crystalline structures, the cubic Bi4Ge3O12 (BGO) and monoclinic Bi2GeO5 crystallites, which evolves towards the BGO structure after annealing. The elemental analysis confirmed the composition of the desired compound Bi4Ge3O12 with 60 wt % GeO2 and 40 wt % Bi2O5. On the other hand, by changing the precursor to (Bi(CH3COO)2, the film thickness increased to 500 nm thicker due to the high viscosity of the sol, and a dominant monoclinic Bi2GeO5 crystalline structure appeared. The elemental analysis revealed a nonstoichiometric composition with 38 wt % GeO2 and 62 wt % Bi2O3. Due to the low GeO2 phase content that reacted with metastable Bi2GeO5, we obtained cubic Bi4Ge3O12 as a secondary phase, with Bi2GeO5 as a dominant crystalline phase. The redshifts of both absorptions and emissions spectra peaks confirmed a different disorder structure as an interplay between the cubic Bi4Ge3O12 (BGO) and monoclinic Bi2GeO5 phases

Synthesis of Vanadium oxides by Pulsed Laser Deposition and Rapid thermal annealing

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Control of the Graphite Femtosecond Ablation Plume Kinetics by Temporal Laser Pulse Shaping: Effects on Pulsed Laser Deposition of Diamond-Like Carbon

International audienceThis study proposes to consider the effect of temporal laser pulse shaping on graphite femtosecond laser ablation plume composition and kinetics, and its potential for depositing diamond-like carbon (DLC) films. Double pulses and long pulses with up to 100-ps delay and 10-ps duration, respectively, are used. The plasma composition and kinetics are investigated by using an optical emission spectroscopy system with a spatial resolution along the ejection axis. Temporal pulse shaping is shown to strongly modify the quantities of the different ejected species in the plume. In particular, it reduces the number of slow C2 or C3 radicals and increases the proportion of monomers, adding ionized species in front of the plume. At the same time, the different components of the multimodal plasma plume maintain their average speed whatever temporal pulse shape is used, thus demonstrating the kinetic modifications. The multiwavelength Raman study of DLC films deposited using different temporal pulse shapes does not reveal significant structural differences between the films. This was found to be in accordance with a prevalence of neutral C atoms and radicals in all the generated plumes, the former being responsible for the subplantation process

Calculation of temperature distribution induced by ultraviolet continuous wave laser exposure of silver-exchanged glass

International audienceSilver nanoparticles embedded in glass matrix have attracted much interest because they confer optical properties to the glass that can be adjusted by varying the size, shape and packing density of the particles. We are previously demonstrated the growth of silver NPs in silver-exchanged soda-lime glasses by ultraviolet continuous wave laser irradiation. As reported elsewhere, this kind of cw irradiation leads to the formation of micro-lenses, due to local melting of the glass. Indeed, due to the locally high absorption of light, the glass is heated to temperatures higher than the glass transition temperature and after cooling, maintains the shape of a liquid droplet, which behaves as a micro-lens. In this work, we present the calculation of the temperature distribution induced by the irradiation of the glass which explains the shape of the droplet observed in our samples. Two parameters are required to perform the calculation: thermal conductivity and absorption coefficient of the glass. Since the measurement of the absorption coefficient remains tricky, it has been deduced from the calculations and then the temperature profile was optimized. From surface profile measurements, we determine the experimental radius of the micro-lenses for various powers. Finally, we calculate the temperature distribution of our samples for various powers. The maximum temperature, obtained in our case, varies between 1190 K and 1380 K for power from 100 mW to 130 mW, which is suitable for the formation of glass liquid droplets

Ag nanoparticles in soda-lime glass grown by continuous wave laser irradiation as an efficient SERS platform for pesticides detection

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