Directed assembly of metallic nanocrystals

Le contrôle de l'organisation bidimensionnel de nanoparticules est primordial dans le défi que représentent l'enregistrement magnétique et l'augmentation de la capacité de stockage. Plus particulièrement, c'est ici la diminution de la taille des bits d'informations qui est ciblée. La conséquence serait alors une augmentation de la capacité de stockage de deux à trois ordres de grandeurs. Mais pour ce faire, il est nécessaire d'avoir une organisation bidimensionnelle de nanoparticules magnétiques de taille, forme et composition contrôlée. Via deux méthodes de synthèse, des nanoalliages de CoPt et Co33Pt67 de l'ordre de 2 nm ont été synthétisées. Ces derniers ont présenté alors des températures de blocage et des champs coercitifs ne permettant pas leurs utilisations dans des applications dans l'enregistrement magnétique. Cela s'explique par le fait qu'après synthèse, ces nanoparticules sont désordonnées chimiquement. Afin d'améliorer l'ordre chimique et donc les propriétés magnétiques, des recuits thermiques ont été effectués. Il a été montré que la mise en ordre a lieu vers 400°C et que, dans le cas de nanocristaux de Co33Pt67, la forme et la taille restent inchangées. Ces derniers pourraient être utilisés dans l'enregistrement magnétique à condition de pouvoir contrôler la distance interparticulaire. C'est pourquoi nous avons utilisé des molécules organiques capables de s'auto-assembler sur surface sur de longues distances et formant des réseaux nanoporeux aptes à servir de systèmes hôte et à capter les nanoparticules. Nous avons alors montré que des nanoparticules de platine possèdent une organisation quasi-hexagonale et monoclinique à moyenne distance.The fine control of nanoparticles bi-dimensional organization remains a main challenge for magnetic recording applications. Although the current size for a data bit is around a few tens of nanometers, it could be reduced to the nanometer scale simply through using magnetic nanoparticles. Nonetheless, intrinsic parameters of the nanoparticles such as their sizes, shapes and chemical compositions have a direct incidence on their periodic arrangement. Two different chemical routes were used to synthesize 2 nm CoPt and Co33Pt67 nanoalloys. Due to the high chemical disordering of these nanocrystals, the blocking temperature and coercive fields were lower than wished for data storage applications. In order to exhibit a higher chemical ordering, in situ annealing of these nanocrystals was carried out. It has been shown that ordering occurred around 400°C. Plus, size and shape for Co33Pt67 were kept after annealing but not for equiatomic composition. Nevertheless, only poor mesoscopic ordering between nanoparticles is observed, as reported elsewhere. This hurdle could be overcome in using organic molecules able to self-assemble on graphite and forming a porous two-dimensional supramolecular template. Thus, such template was designed and used to demonstrate that 2 nm Pt nanoparticles can locally organize in quasi-hexagonal or monoclinic lattices

Assemblage dirigé de nanocristaux métalliques

The fine control of nanoparticles bi-dimensional organization remains a main challenge for magnetic recording applications. Although the current size for a data bit is around a few tens of nanometers, it could be reduced to the nanometer scale simply through using magnetic nanoparticles. Nonetheless, intrinsic parameters of the nanoparticles such as their sizes, shapes and chemical compositions have a direct incidence on their periodic arrangement. Two different chemical routes were used to synthesize 2 nm CoPt and Co33Pt67 nanoalloys. Due to the high chemical disordering of these nanocrystals, the blocking temperature and coercive fields were lower than wished for data storage applications. In order to exhibit a higher chemical ordering, in situ annealing of these nanocrystals was carried out. It has been shown that ordering occurred around 400°C. Plus, size and shape for Co33Pt67 were kept after annealing but not for equiatomic composition. Nevertheless, only poor mesoscopic ordering between nanoparticles is observed, as reported elsewhere. This hurdle could be overcome in using organic molecules able to self-assemble on graphite and forming a porous two-dimensional supramolecular template. Thus, such template was designed and used to demonstrate that 2 nm Pt nanoparticles can locally organize in quasi-hexagonal or monoclinic lattices.Le contrôle de l'organisation bidimensionnel de nanoparticules est primordial dans le défi que représentent l'enregistrement magnétique et l'augmentation de la capacité de stockage. Plus particulièrement, c'est ici la diminution de la taille des bits d'informations qui est ciblée. La conséquence serait alors une augmentation de la capacité de stockage de deux à trois ordres de grandeurs. Mais pour ce faire, il est nécessaire d'avoir une organisation bidimensionnelle de nanoparticules magnétiques de taille, forme et composition contrôlée. Via deux méthodes de synthèse, des nanoalliages de CoPt et Co33Pt67 de l'ordre de 2 nm ont été synthétisées. Ces derniers ont présenté alors des températures de blocage et des champs coercitifs ne permettant pas leurs utilisations dans des applications dans l'enregistrement magnétique. Cela s'explique par le fait qu'après synthèse, ces nanoparticules sont désordonnées chimiquement. Afin d'améliorer l'ordre chimique et donc les propriétés magnétiques, des recuits thermiques ont été effectués. Il a été montré que la mise en ordre a lieu vers 400°C et que, dans le cas de nanocristaux de Co33Pt67, la forme et la taille restent inchangées. Ces derniers pourraient être utilisés dans l'enregistrement magnétique à condition de pouvoir contrôler la distance interparticulaire. C'est pourquoi nous avons utilisé des molécules organiques capables de s'auto-assembler sur surface sur de longues distances et formant des réseaux nanoporeux aptes à servir de systèmes hôte et à capter les nanoparticules. Nous avons alors montré que des nanoparticules de platine possèdent une organisation quasi-hexagonale et monoclinique à moyenne distance

Assemblage dirigé de nanocristaux métalliques

The fine control of nanoparticles bi-dimensional organization remains a main challenge for magnetic recording applications. Although the current size for a data bit is around a few tens of nanometers, it could be reduced to the nanometer scale simply through using magnetic nanoparticles. Nonetheless, intrinsic parameters of the nanoparticles such as their sizes, shapes and chemical compositions have a direct incidence on their periodic arrangement. Two different chemical routes were used to synthesize 2 nm CoPt and Co33Pt67 nanoalloys. Due to the high chemical disordering of these nanocrystals, the blocking temperature and coercive fields were lower than wished for data storage applications. In order to exhibit a higher chemical ordering, in situ annealing of these nanocrystals was carried out. It has been shown that ordering occurred around 400°C. Plus, size and shape for Co33Pt67 were kept after annealing but not for equiatomic composition. Nevertheless, only poor mesoscopic ordering between nanoparticles is observed, as reported elsewhere. This hurdle could be overcome in using organic molecules able to self-assemble on graphite and forming a porous two-dimensional supramolecular template. Thus, such template was designed and used to demonstrate that 2 nm Pt nanoparticles can locally organize in quasi-hexagonal or monoclinic lattices.Le contrôle de l'organisation bidimensionnel de nanoparticules est primordial dans le défi que représentent l'enregistrement magnétique et l'augmentation de la capacité de stockage. Plus particulièrement, c'est ici la diminution de la taille des bits d'informations qui est ciblée. La conséquence serait alors une augmentation de la capacité de stockage de deux à trois ordres de grandeurs. Mais pour ce faire, il est nécessaire d'avoir une organisation bidimensionnelle de nanoparticules magnétiques de taille, forme et composition contrôlée. Via deux méthodes de synthèse, des nanoalliages de CoPt et Co33Pt67 de l'ordre de 2 nm ont été synthétisées. Ces derniers ont présenté alors des températures de blocage et des champs coercitifs ne permettant pas leurs utilisations dans des applications dans l'enregistrement magnétique. Cela s'explique par le fait qu'après synthèse, ces nanoparticules sont désordonnées chimiquement. Afin d'améliorer l'ordre chimique et donc les propriétés magnétiques, des recuits thermiques ont été effectués. Il a été montré que la mise en ordre a lieu vers 400°C et que, dans le cas de nanocristaux de Co33Pt67, la forme et la taille restent inchangées. Ces derniers pourraient être utilisés dans l'enregistrement magnétique à condition de pouvoir contrôler la distance interparticulaire. C'est pourquoi nous avons utilisé des molécules organiques capables de s'auto-assembler sur surface sur de longues distances et formant des réseaux nanoporeux aptes à servir de systèmes hôte et à capter les nanoparticules. Nous avons alors montré que des nanoparticules de platine possèdent une organisation quasi-hexagonale et monoclinique à moyenne distance

Role of the nanocrystallinity on the chemical ordering of Co x Pt 100-x nanocrystals synthesized by wet chemistry

International audienceCo x Pt 100-x nanoalloys have been synthesized by two different chemical processes either at high or at low temperature. Their physical properties and the order/disorder phase transition induced by annealing have been investigated depending on the route of synthesis. It is demonstrated that the chemical synthesis at high temperature allows stabilization of the fcc structure of the native nanoalloys while the soft chemical approach yields mainly poly or non crystalline structure. As a result the approach of the order/disorder phase transition is strongly modified as observed by high-resolution transmission electron microscopy (HR-TEM) studies performed during in-situ annealing of the different nanoalloys. The control of the nanocrystallinity leads to significant decrease in the chemical ordering temperature as the ordered structure is observed at temperatures as low as 420 ºC. This in turn preserves the individual nanocrystals and prevents their coalescence usually observed during the annealing necessary for the transition to an ordered phase

Platinum and platinum based nanoalloys synthesized by wet chemistry

International audiencePlatinum nanocrystals and their derivatives with palladium and cobalt are of fundamental interest due to their wide field of application in chemistry and physics. Their properties are strongly dependent on their shape and composition. However the chemical route is far from allowing control of both shape and composition. In this paper, we show both experimentally and theoretically the important role of the interaction of small adsorbed molecules on the shape but also on the composition. This has been studied by comparing the case of pure palladium and platinum nanocrystals and the case of PtPd and PtCo nanoalloys synthesized by the liquid–liquid phase transfer method

Photopolymerization at the nanoscale triggered by optical near−field

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Photopolymerization at the nanoscale triggered by optical near−field

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Plasmonic Au Nanoparticle Arrays for Monitoring Photopolymerization at the Nanoscale

International audienceThe localized surface plasmon resonance (LSPR) of Au nanoparticles (NPs) was used to monitor photopolymerization at the nanoscale, by in situ monitoring the optical response of AuNPs during the light-induced polymerization process. To show the interest of this approach, two configurations were used which correspond to a resonant and a non-resonant excitation regime between the photopolymer and the AuNPs used as nanoprobes. We show that not only this method enables the progress monitoring of the photopolymerization reaction at the nanometric scale but also can highlight the near-field coupling effect responsible for the acceleration of the photoinduced reaction. This methodology appears very interesting to study the photoinduced nanofabrication processes of metal/polymer hybrid nanoparticles and more globally as a methodology to study the photopolymerization reactions at the nanometric scale

Probing Plasmon-Induced Chemical Mechanisms by Free-Radical Nanophotopolymerization

International audienceLocalized surface plasmon-induced photopolymerization of free-radical acrylate monomers is an efficient, smart, and versatile method for preparing metal/polymer hybrid nanoparticles (NPs) with accurate control of the thickness and spatial distribution of the polymer on the NP surface. Despite a growing number of practical demonstrations, the mechanism leading to polymerization of the acrylate monomer by localized surface plasmon resonance (LSPR) is still controversial. It could be related to either a photochemical mechanism enhanced by electromagnetic hot spots (enhanced near field) or thermoplasmonic (photothermal heating) or electrochemical (via hot-carrier injection) mechanisms, as proposed in different studies. After developing a high-resolution characterization method based on transmission electron microscopy and by tuning the photopolymer composition and the irradiation conditions, the LSPR-induced physicochemical mechanism is revealed. We demonstrate that the photochemical pathway is the main mechanism under the mild irradiation conditions chosen for this process. In a more general way, photopolymerization proves to be a powerful tool to investigate the coupling between metal nanostructures and organic moieties

Directed Organization of Platinum Nanocrystals through Organic Supramolecular Nanoporous Templates

International audienceWe propose a novel approach to trap 2 nm Pt nanocrystals using nanoporous two-dimensional supramolecular networks for cavity-confined host-guest recognition process. This will be achieved by taking advantage of two features of supramolecular self-assembly at surfaces. First, its capability to allow to the formation of complex 2D architectures, more particularly nanoporous networks, through non-covalent interactions between organic molecular building-blocks. Second, the ability of the nanopores to selectively host and immobilize a large variety of guest species. In this paper, for the first time, we will use isotropic honeycomb networks and anisotropic linear porous supramolecular networks to host 2nm Pt nanocrystals