1,721,058 research outputs found
Plasmonic anisotropic nanocomposite based on block copolymers and gold nanoparticles
No full textLa nanochimie et l’auto-assemblage sont des voies prometteuses de fabrication de matériaux nanostructurés aux propriétés optiques innovantes dans le domaine visible. Dans cette étude, des nanocomposites plasmoniques anisotropes sont formulés en introduisant sélectivement des nanoparticules métalliques dans des phases ordonnées de copolymères diblocs symétriques selon différentes stratégies d’incorporation. Pour la stratégie de post-incorporation, des nanoparticules d’or présynthétisées en milieu aqueux sont introduites sélectivement dans des phases pré-ordonnées d’un copolymère dibloc amphiphile. L’incorporation directe consiste àmélanger des nanoparticules d’or présynthétisées et un copolymère dibloc dans un solvant commun.La synthèse in situ de nanoparticules consiste à réduire des précurseurs métalliques préalablement introduits dans un des deux blocs d’un copolymère via une étape de réduction. Nous étudions, en particulier, comment la taille des nanoparticules d’or et leur fraction volumique influencent la nanostructure et les propriétés optiques de ces films nanocomposites. La morphologie des films macroscopiques est étudiée par microscopie électronique à transmission et diffusion des rayons Xaux petits angles. Les films minces de nanocomposites sont caractérisés structurellement parmicroscopie à force atomique, microscopie électronique à transmission et réflectivité des rayons X. Les indices optiques déterminés par ellipsométrie spectroscopique peuvent être décrits par un modèle de Maxwell-Garnett, prenant éventuellement en compte de façon phénoménologique les effets de couplage entre nanoparticules d’or.Nanochemistry and self-assembly are promising ways to fabricate nanostructuredmaterials with innovative optical properties for visible light. In this work, anisotropic plasmonicnanocomposites are formulated by selectively introducing metallic nanoparticles in ordered phasesof symmetric dibloc copolymers with different strategies. For the strategy of post-incorporation, presynthesizedgold nanoparticles in aqueous medium are selectively introduced in pre-ordered phasesof an amphiphilic dibloc copolymer. Direct incorporation consists in mixing pre-synthesized goldnanoparticles and dibloc copolymer in a common solvent. In situ synthesis of nanoparticles consistsin reducing metallic precursors previously introduced in one of two blocks of a copolymer via areduction step. The influence of the size and the volume fraction of gold nanoparticles on thenanostructure and the optical properties of the nanocomposite films have been particularly studied.Morphology of macroscopic films is studied by transmission electron microscopy and small angle Xrayscattering. The nanocomposite thin films are structurally characterized by force atomicmicroscopy, transmission electron microscopy and X-ray reflectivity. The optical indices obtained byspectroscopic ellipsometry can be described with Maxwell-Garnett models, which can take intoaccount phenomenologically the effects of coupling between gold nanoparticles
Fabrication and optimization of optical resonators via an emulsion route for the elaboration of metasurfaces
No full textLe contrôle d'assemblages colloïdaux complexes peut mener à la fabrication de nano-objets possédant des propriétés de résonance optique spécifiques et originales, pouvant être utilisées pour contrôler la propagation de la lumière. Cette thèse vise ainsi à fabriquer et optimiser des nano-résonateurs optiques plasmoniques pour les utiliser comme briques de base de métasurfaces de Huygens, efficaces dans le domaine du visible pour diffuser la lumière de manière directionnelle. Ces résonateurs sont des assemblages denses de nanoparticules d’argent, appelés clusters. Leur production repose sur la formulation puis le séchage d’une émulsion, dont les gouttes confinent l’auto-assemblage des nanoparticules et permettent l’obtention de clusters finaux de géométrie et de structure contrôlées. Cette dernière dépend de plusieurs paramètres, dont le principal est la nature et la longueur du ligand des nanoparticules. Les clusters synthétisés sont caractérisés à l’aide de plusieurs techniques, permettant de déterminer leur taille, leur forme, la qualité de leur assemblage et leur densité en argent. Une étude optique de ces résonateurs permet de déterminer leurs propriétés d’interaction avec la lumière. Les résultats montrent la présence d’une réponse dipolaire magnétique forte, dont l’amplitude et la longueur d’onde sont similaires à celles de la réponse dipolaire électrique des résonateurs. Ceci leur permet de diffuser la lumière de façon directionnelle, vers l’avant, et donc d’agir comme des résonateurs de Huygens. De ce fait, des dépôts de clusters d’argent ont été élaborés au cours de cette thèse, dans le but d’obtenir des métasurfaces de Huygens, selon deux stratégies principales : la synthèse d’une dispersion de clusters puis son dépôt sur un substrat ; la synthèse et le dépôt simultanés des clusters sur un substrat. Cette dernière stratégie, impliquant le dépôt puis le séchage sur un substrat d’une émulsion contenant dans ses gouttes une suspension de nanoparticules d’argent, a permis d’obtenir des surfaces finales homogènes et densément recouvertes de clusters de Huygens. Leur étude optique a démontré qu’elles interagissent de manière intense et résonante avec la lumière incidente.The control of complex colloidal assemblies can lead to the fabrication of nano-objects with specific and original optical resonance properties, which can be used to control the propagation of light. The aim of this thesis is to fabricate and optimise plasmonic optical nano-resonators for use as building blocks for Huygens metasurfaces, which are effective in the visible range for scattering light directionally. These resonators are dense assemblies of silver nanoparticles, known as clusters. They are produced by formulating then drying an emulsion whose droplets confine the self-assembly of the nanoparticles and enable the final clusters to be obtained with a controlled geometry and structure. The latter depends on several parameters, the main one being the nature and length of the nanoparticle ligand. The synthesised clusters are characterised using several techniques to determine their size, shape, assembly quality and silver density. An optical study of these resonators was carried out to determine their interaction properties with light. The results show the presence of a strong magnetic dipolar response, the amplitude and wavelength of which are similar to those of the resonators' electrical dipolar response. This allows them to scatter light directionally, in a forward direction, and therefore to act like Huygens resonators. Therefore, deposits of silver clusters were developed in the course of this thesis, in order to obtain Huygens metasurfaces, using two main strategies: the synthesis of a dispersion of clusters and then their deposition on a substrate; the simultaneous synthesis and deposition of clusters on a substrate. The latter strategy, involving the deposition then drying on a substrate of an emulsion containing a suspension of silver nanoparticles in its droplets, resulted in homogeneous final surfaces densely covered with Huygens clusters. Their optical study showed that they interact intensely and resonantly with incident light
Effective optical properties of polymer - gold nanoparticle composite films
No full textNous étudions, par ellipsométrie spectroscopique, les propriétés optiques dans le domaine de l'UV-Visible-Infrarouge de films composites constitués de polymère et de nanoparticules d'or. Nous étudions la relation entre ces mesures et la structure des nanocomposites, que nous étudions par microscopie à force atomique en particulier. Nous distinguons l’analyse de films épais (tri-dimensionnels) et minces (quasi-bidimensionnels). Dans les deux cas, nous confrontons les résultats expérimentaux à des modèles théoriques de milieux effectifs dérivés de Maxwell-Garnett, en particulier.By spectroscopic ellipsometry, we study the optical properties in the range of UV-Visible-Infrared of composites films made of polymer and gold nanoparticles. We study the relation between these measurement and the structure of the nanocomposites, that we study by atomic force microscopy in particular. We distinguish the analysis of thicks films (tridimensionals) and thins (quasi-bidimensionals). In both of case, we confronte these experimentals results to the theoric models of effectives medium derivated for Maxwell-Garnett in particular
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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