Quantum confinement structures are attractive for their unconventional size dependence of the optical and electrical properties. There are still challenges to control the size uniformity for the application. The thesis studies the correlation between the size distribution of CdSe/ZnS quantum dots (QD), and the fluorescence properties to understand the shape and size influences of their fluorescence properties. Results from the transmission electron microscopy (TEM) provide the structure and size distribution of the samples. Excitation dependent fluorescence spectra as well as the PL excitation at various emission wavelength confirm that the inhomogeneous distribution of the samples. The results show that the samples are mostly composed of QDs with quasi-spherical structure (aspect ration between 1.1 and 1.5 ;76%) and spherical structure ( aspect ratio < 1.1; 12.8%). In addition, it exhibits a distribution of the long axis of 5.4nm¡Ó1.3nm. By measuring the fluorescence spectra of individual QDs, we construct the distribution. The peaks of the fluorescence spectra show a Gaussian distribution with center at 615.7 nm and width 13.8 nm. In addition, the spectra exhibit a width of 19.7¡Ó8.0nm. This is consistent with the ensemble measurement of the fluorescence from a solution (peak at 616 nm, and width 25 nm). Results of the fluorescence lifetime on the individual QDs indicate the lifetime distribution of 10.3¡Ó5.6ns. Further analyze the size distribution by constructing the size ¡V fluorescence spectrum relationship. By analysis the distribution of the fluorescence spectra, it results the corresponding size distribution of width 0.7 nm. This is much narrower than the size distribution of the long axis measured by TEM, but is more consistent with the corrected size distribution considering the short axis contribution. We conclude that the deviation results from the non-spherical structures in the samples.

Foram utilizadas proteínas da famÌlia das GFPs e nanocristais fluorescentes de CdSe/ZnS para caracterização da interação e verificação de transferência de energia por ressonância (FRET) entre estes compostos. Formou-se dois pares doador-receptor onde ora uma proteína figurava como doadora, ora um nanocristal ocupava este papel. Verificou-se que, em ambos os casos, o doador sofre supressão da fluorescência após a formação de complexo com o receptor, complexo este motivado por interação eletrostática e dependente de pH. Foi possível comprovar, através da observação de emissão sensitizada e redução da anisotropia, que entre o par formado por nanocristal com emissão no verde e proteína HcRed1 como receptora, de fato ocorre FRET. As distâncias aparentes entre doador e receptor foram determinadas a partir da eficiência da supressão da fluorescência do doador e da distância de Förster. As distâncias assim obtidas são compatíveis com as dimensões das proteínas e dos nanocristais / Proteins belonging to the GFP family were used to characterize their interaction with fluorescent CdSe/ZnS nanocrystals and to verify the occurrence of resonance energy transfer (FRET) among these elements. Two donor-acceptor pairs were established, one having a protein as donor and the other having a nanocrystal as donor. In both cases the donor suffers quenching of its fluorescence after the formation of a complex with the acceptor. The complex formation is dependent on pH and is due to electrostatic interaction. It was possible to prove the occurrence of FRET between CdSe/ZnS nanocrystals emitting green fluorescence as donors and the protein HcRed1 as acceptor, through the detection of sensitized emission and anisotropy reduction. Apparent donor-acceptor distances were determined from efficiency measurements and Förster distances. The obtained distances agreed with the protein and nanocrystal dimensions

Foram utilizadas proteínas da famÌlia das GFPs e nanocristais fluorescentes de CdSe/ZnS para caracterização da interação e verificação de transferência de energia por ressonância (FRET) entre estes compostos. Formou-se dois pares doador-receptor onde ora uma proteína figurava como doadora, ora um nanocristal ocupava este papel. Verificou-se que, em ambos os casos, o doador sofre supressão da fluorescência após a formação de complexo com o receptor, complexo este motivado por interação eletrostática e dependente de pH. Foi possível comprovar, através da observação de emissão sensitizada e redução da anisotropia, que entre o par formado por nanocristal com emissão no verde e proteína HcRed1 como receptora, de fato ocorre FRET. As distâncias aparentes entre doador e receptor foram determinadas a partir da eficiência da supressão da fluorescência do doador e da distância de Förster. As distâncias assim obtidas são compatíveis com as dimensões das proteínas e dos nanocristais / Proteins belonging to the GFP family were used to characterize their interaction with fluorescent CdSe/ZnS nanocrystals and to verify the occurrence of resonance energy transfer (FRET) among these elements. Two donor-acceptor pairs were established, one having a protein as donor and the other having a nanocrystal as donor. In both cases the donor suffers quenching of its fluorescence after the formation of a complex with the acceptor. The complex formation is dependent on pH and is due to electrostatic interaction. It was possible to prove the occurrence of FRET between CdSe/ZnS nanocrystals emitting green fluorescence as donors and the protein HcRed1 as acceptor, through the detection of sensitized emission and anisotropy reduction. Apparent donor-acceptor distances were determined from efficiency measurements and Förster distances. The obtained distances agreed with the protein and nanocrystal dimensions

Les gisements de type Mississippi Valley Type (MVT) du centre et de l’est du Tennessee, respectivement MTM (Middle Tennessee Mine) et ETM (East Tennessee Mine), renferment des réserves importantes de zinc sous forme de sphalerite, mais aussi de germanium en substitution du zinc dans la sphalerite. Cependant seuls les gisements du district de MTM contiennent des teneurs économiquement exploitables de germanium. Ces deux districts miniers, observés dans les mêmes formations géologiques et de minéralogies comparables, sont comparés afin de comprendre la distribution du germanium et des autres éléments traces dans les MVT. Les analyses à l’échelle de l’atome par spectroscopie d’absorption X, XANES et EXAFS, ont mis en évidence plusieurs configurations de germanium dans la sphalerite : le germanium peut être en substitution du zinc dans ZnS sous forme 2+ ou 4+, mais il peut aussi être sous forme d’oxyde de germanium en inclusions nanométriques dans la sphalerite. Les analyses à l’échelle du minéral, par microsonde électronique, LA-ICP-MS et spectroscopie Raman, ont mis en évidence deux groupes d’éléments traces : i) le premier composé des éléments Fe et Cd, est préférentiellement incorporé suivant les faces (110) de la sphalerite, ii) le second composé des éléments Cu, Ga et Ge, est préférentiellement incorporé suivant les faces (010) de la sphalerite. Le couplage de la spectroscopie Raman avec l’ablation laser ICP-MS a permis de mettre en évidence un partitionnement des éléments traces entre la forme cubique et hexagonale de ZnS : les éléments Fe et Cd sont plus concentrés dans la forme cubique, alors que les éléments Cu, Ga et Ge sont plus concentrés dans la forme hexagonale de ZnS / Mississippi Valley-type Type deposits (MVT) in central and eastern Tennessee, respectively MTM (Middle Tennessee Mine) and ETM (East Tennessee Mine), contain large reserves of zinc in the form of sphalerite, but also germanium in substitution of zinc in sphalerite. However, only the deposits District MTM contain economic concentrations of germanium. These two mining districts hosted in the same geological formations and with a comparable mineralogy, are compared in order to understand the distribution of germanium and other trace elements in MVT. Analyses at atomic scale by atomic absorption spectroscopy X, XANES and EXAFS, revealed several of germanium configurations in sphalerites: germanium can substituted to zinc in ZnS under 2 + and 4+ form, but it can be under the form of nanoscale inclusions of germanium oxide associated with sphalerite. Analyses at mineral scale by electron microprobe, LA-ICP-MS and Raman spectroscopy showed two groups of trace elements: i) the first group composed by Fe and Cd is preferentially incorporated following (110) faces of sphalerite, ii) the second group composed by Cu, Ga and Ge, is preferably incorporated following (010) faces of sphalerite. The coupling of Raman spectroscopy with laser ablation ICP-MS revealed a partitioning of trace elements between the cubic and hexagonal forms of ZnS: the elements Cd and Fe are more concentrated in the cubic form, while Cu, Ga and Ge are more concentrated in the hexagonal ZnS

No description available.

Hypereutectic Al-Si alloys are of increasing interest for applications that require a combination of light weight and high wear resistance, such as pistons, liner-less engine blocks and pumps. The wear resistance of this class of alloys is due to the presence of hard primary Si particles formed during casting. The objective of this work was to develop one or more methods of refining primary silicon in cast hypereutectic Al-Si alloys to compete with the conventional process of adding phosphorous and to achieve the simultaneous modification of silicon in the Al-Si eutectic. A robust sampling/casting technique was developed to minimise macro-segregation of primary silicon during solidification of hypereutectic Al-Si alloys by using water cooled steel mould with cooling rate in excess of 15 K/s. The morphology of silicon phases was found to change with increasing melt temperature and cooling rate. The high cooling rate and superheat temperature produces a good distribution of polyhedral primary silicon particles in a refined lamellar eutectic matrix in solidification of commercial purity Al-Si alloys. Removing Ca by fluxing with K2SiF6 prior to casting can improve the refinement and modification effect of Mg and Sb respectively. Effects of various inoculants were studied. Microstructural analysis showed that Mg and ZnS refined primary Si whereas MgO, CaO and Na2S coarsened the primary Si together with a modification effect on the eutectic Si. Adding Zn had no effect on morphology of Si phases. Refinement of both primary and eutectic silicon phases was observed for the Al-15Si alloy with Mg content ≤ 0.3 wt%. P-doped γ-Al2O3 was found to be a potent substrate to nucleate primary silicon whilst good modification of the eutectic matrix is retained during solidification of hypereutectic Al-Si alloys. On using P-doped γ-Al2O3 could be a perfect and clean source of P without additional impurities. A new solid-liquid duplex casting process was devised to achieve simultaneous refinement and modification of Si phases in hypereutectic Al-Si alloys with improvement in mechanical properties. The static mechanical properties of Al-Si produced by the solid-liquid duplex casting process are significantly better than conventionally cast untreated Al-Si and slightly better than conventionally cast Al-Si treated with P and/or Sr. A novel Al-ZnS master alloy was developed by in situ reaction of Zn and Na2S in the Al melt. The results from this study leave little doubt that this novel Al-ZnS master alloy is a promising refiner in solidification of hypereutectic Al-Si alloys. It refines primary silicon to the same extent as that achieved by adding P via Cu-P following the same refinement mechanism.

Motivated by a desire to understand the basic concepts of one-dimensional nanostructure growth, the research described in this thesis aims at understanding the basic mechanisms controlling the synthesis and formation of a specific group of II-VI semiconducting nanostructures. In particular, this thesis examines one-dimensional nanostructures (such as nanobelts and nanowires) and different morphologies of ZnS that result from the interesting properties that the materials have at the nanoscale. In order to understand how to tune these properties in the nanostructure, it is necessary to have an understanding of the growth mechanism that dictates the morphology, structure, and rate of growth of the nanomaterial. It is necessary to understand what impact changes to the macroscopic setup in the experiment have on the nanoscopic scale of the nanomaterials. Having a larger understanding and exerting more precise control over the growth of nanomaterials will allow a higher level of selectivity, more control over dimensionality and the type of morphology, easier manipulation, and the simpler incorporation of these structures into a nanotechnological device. The main focus of the research was on CdSe and ZnS, with the bulk of the research being conducted on ZnS nanostructures. These materials were chosen for their potential for extensive research, their possible applications in optoelectronics, their potential to form the wurtzite crystal structure, and the potential generalization of results to other nanomaterials. The framework for the research is given first. Then a description of the experimental setup and a model for the growth of nanostructures is discussed. A brief overview of the synthesis of CdSe nanostructures is given and then a detailed analysis of the synthesis of specific ZnS one-dimensional morphologies is presented.

L’aquifère de la craie est un milieu hétérogène complexe lié à une large gamme de porosités (matrice, fractures et conduits karstiques), entrainant une forte hétérogénéité des processus et des vitesses de transfert (de 10-8 m s-1 à plusieurs mètres par jour). De plus, l’aquifère de la craie est recouvert par des formations superficielles (argiles à silex, lœss et dépôts argilo-sableux) d’épaisseurs variables, dont l’influence sur les écoulements au sein de la ZNS est encore mal connue. Le but de cette thèse est d’étudier le fonctionnement hydrodynamique et géochimique des eaux souterraines libres de la craie, et en particulier le rôle de la ZNS et des formations superficielles. L’approche suivie a consisté à étudier la variabilité spatio-temporelle du niveau d’eau de la nappe, des débits de percolation et de la géochimie des eaux souterraines et à rechercher les facteurs de contrôle de cette variabilité en la croisant aux caractéristiques de la ZNS de la craie, des formations superficielles, de l’occupation des sols et du climat. Cette approche a été mise en place à deux échelles spatiales : à une échelle régionale au Nord-Ouest du Bassin de Paris, autour de l’anticlinal de Bray et à une échelle locale sur le site de la carrière souterraine de Saint-Martin-le-Nœud (site particulièrement intéressant de moins d’un km2, donnant accès aux eaux de la nappe et aux eaux provenant de la ZNS). Les chroniques de pluie efficace, de débit de percolation et de variation du niveau d’eau ont été analysées grâce à des méthodes de traitement du signal. La géochimie des eaux a été étudiée statistiquement et par l’utilisation de traceurs naturels (ions majeurs, conductivité électrique) ou anthropiques (pesticides). A Saint-Martin-le-Nœud, l’épaisseur et la nature de la ZNS et des formations superficielles ont été étudiées grâce à des méthodes géophysiques et par le creusement de trois fosses en surfaces de la cavité. Les résultats ont montrés pour les deux échelles spatiales (1) Une variabilité temporelle relativement faible : la réponse de la nappe et l’arrivée des eaux de percolation après une période de recharge sont lentes et tamponnées ; A l’échelle régionale, les variations temporelles de la géochimie sont faibles. A l’échelle locale, l’évolution de la conductivité électrique des eaux des lacs montre des variations temporelles de la minéralisation des eaux relativement lentes. Cependant, les concentrations en NO3-, Cl- et SO42- des eaux des lacs varient significativement. (2) Une variabilité spatiale très marquée : à l’échelle régionale, les variations piézométriques sont très différentes d’un forage à l’autre. De même, dans la cavité de Saint-Martin-le-Nœud, les variations du niveau des lacs et les flux de percolation diffèrent spatialement ; La géochimie des eaux présente également une forte hétérogénéité spatiale, que ce soit à l’échelle régionale ou locale. / The Chalk aquifer is a complex and heterogeneous system associated with a wide range of porosity (matrix, fractures and karstic conduits). These characteristics lead to a high heterogeneity of transfer processes and speed (ranging between 10-8 m s-1 and several metres per day). Furthermore, the Chalk aquifer is overlaid by superficial layers (clay-with-flints, loess and clayey-sandy deposits) with varying thicknesses. The impact of these formations on groundwater flows in the unsaturated zone (UZ) is still poorly understood. The aim of this thesis was to study the hydrodynamics and geochemical characteristics of free Chalk groundwater and particularly the role of the UZ and superficial layers. The chosen approach consisted in studying the spatial and temporal variability of groundwater level, dripping water discharges and groundwater geochemistry and search for controlling factors of this variability and compare it to the characteristics of the UZ of Chalk, the superficial layers, the land use and the climate. This approach was implemented at two spatial scales: at the regional scale of the North-West of the Paris Basin, around the Bray anticlinal and at the local scale of the underground quarry of Saint-Martin-le-Nœud which is a particularly interesting site (area below 1 km2) giving access to both the water table and the UZ water. Effective rainfall (Peff), dripping water discharge and water level variation chronicles were analysed using signal processing methods. Groundwater geochemistry has been studied statistically and using natural (major ions, electric conductivity) and anthropic (pesticides) tracers. At Saint-Martin-le-Nœud, the nature and thickness of the UZ and the superficial layers have been investigated with a geophysical survey and three holes were dug in the fields above the quarry. The results showed at both spatial scales a relatively low temporal variability with low and smooth water table responses and long time between reload periods and dripping water arrival. At the regional scale, the temporal variations of groundwater geochemistry are low. At the local scale, the evolution of underground lakes water electric conductivity indicates that water mineralization displays relatively low temporal variations. However, NO3-, Cl- and SO42- concentrations in lakes water varied significantly during the study. The results also highlighted a strong spatial variability. Thus, at the regional scale, piezometric variations are very different from one borehole to the next. Similarly, in the quarry of Saint-Martin-le-Nœud, lakes water level and dripping water discharges are spatially heterogeneous. Water geochemistry also displays a strong spatial variability at both regional and local scales.

No / During the last decades of nanoparticles research, many nanomaterials have been developed for applications in the field of bio-labelling. For the visualization of transport processes in the body, organs and cells, luminescent quantum dots (QDs) make for highly useful diagnostic tools. However, intercellular routes, bio-distribution, metabolism during degradation or quantification of the excretion of nanoparticles, and the study of the biological response to the QDs themselves are areas which to date have not been fully investigated. In order to aid in addressing those issues, CdSe/CdS/ZnS QDs were radioactively labelled, which allows quantification of the QD concentration in the whole body or in ex vivo samples by gamma-counting. However, the synthesis of radioactively labelled QDs is not trivial since the coating process must be completely adapted, and material availability, security and avoidance of radioactive waste must be considered. In this contribution, the coating of CdSe/CdS QDs with a radioactive (65)ZnS shell using a modified, operator-safe, SILAR procedure is presented. Under UV illumination, no difference in the photoluminescence of the radioactive and non-radioactive CdSe/CdS/ZnS colloidal solutions was observed. Furthermore, a down-scaled synthesis for the production of very small batches of 5 nmol QDs without loss in the fluorescence quality was developed. Subsequently, the radio-labelled QDs were phase transferred by encapsulation into an amphiphilic polymer. gamma-counting of the radioactivity provided confirmation of the successful labelling and phase transfer of the QDs.

Les nanocristaux d'AgInS2-ZnS sont des candidats prometteurs pour le développement de nano-luminophores non-toxiques et performants. Grâce à leur taille et à leur forte absorption, ces nano-luminophores permettent l'exploitation d'effets nano-optiques pouvant augmenter leur efficacité à l'absorption ou à l'émission. Ce document présente, dans un premier temps, une méthode d'analyse qui couple la mesure du rendement quantique à celle du temps de vie de luminescence et permet l'étude des contributions radiatives et non-radiatives des différents mécanismes de luminescence des nanocristaux d'AgInS2-ZnS. En modifiant la taille, la chimie de surface et la structure du cœur de ces nanocristaux, nous construisons un modèle global expliquant le rôle de leur composition et soulignant l'importance de leur surface. De nouvelles stratégies sont identifiées pour optimiser ces nanomatériaux. Leur application conjointe permet d'envisager des rendements quantiques proches de 90%. Dans un second temps, une méthode de simulation numérique générale a été développée pour prédire l'effet produit par le couplage nano-optique entre une particule plasmonique et un luminophore. Cette méthode a été appliquée au cas des structures cœur/coquille/coquille (métal/isolant/AgInS2-ZnS) et les configurations optimales du système ont été déterminées. Une nanostructure particulièrement performante permettant de combiner les effets du couplage à l'absorption et à l'émission a été identifiée. Une méthode de synthèse de ces nanostructures est développée. Les résultats expérimentaux obtenus sont en accord à la fois avec la compréhension de la fluorescence des nanocristaux d'AgInS2-ZnS et la prédiction obtenue par simulation. / AgInS2-ZnS nanocrystals are promising materials for the development of non-toxic, highly efficient nano-phosphors. Their size and strong absorption allow them to exploit nano-optical effects potentially enhancing both their absorption and emission processes. This work presents a method combining quantum yield measurements with time resolved emission spectroscopy allowing for the study of both radiative and non-radiative properties of each recombination pathways. Modifying the size, surface chemistry, and core structure of the nanocrystals, we construct a global model explaining the role of their composition and emphasizing the critical aspect of their surface. New strategies are identified to increase the internal quantum yield of these materials. Combining these approaches, it is now possible to expect 90% efficiencies. In a second step, a simulation method was developed to predict the nano-optical effects induced by a plasmonic nanostructure on a given phosphor. We applied this method on core/shell/shell (metal/insulator/AgInS2-ZnS) nanostructures and theoretically determined optimal configurations of the system. A particularly efficient nanostructure achieving coupling on both absorbed and emitted light is identified. Hybrid plasmonic nanostructures are synthesized. Their performances are in accordance with both our understanding of the fluorescence mechanisms of AgInS2-ZnS nanocrystals and the predictions made via simulation.