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This dissertation presents new insight into the ability of small molecule passivated NCs to achieve intimate approach distances, despite being well passivated, while developing guiding principles in the area of ligand mediated microstructure control and the resulting macroscopic optical and electronic properties that close packing of high quality NCs enables. NC ligand coverage will be characterized quantitatively through thermogravimetric analysis (TGA), and qualitatively by photoluminescence and electroluminescence, in the case of functional devices; illustrating the importance of practitioner dependent control of ligand coverage through variations in the dispersion precipitation purification procedure. A unique examination of the relative contribution of energy and charge transfer in NC LEDs will demonstrate the ability to achieve charge transfer, at a level competitive with energy transfer, to well passivated NCs at various wt% loading in a polymer matrix. The observation of potential dependent recombination zones within an active layer further suggest novel, NC surface passivation mediated control of blend microstructure during solution processing towards the development of a bi-continuous network. Next, NC self-assembly and resulting microstructure dependent optical and electronic properties will be examined through electroluminescence and high-resolution transmission electron microscopy (TEM) micrographs of functional NC/polymer bulk heterojunction LEDs. The joint characterization of NC optical properties, and self-assembly microstructure provide a deeper understanding of the significant and inseparable effects of minimal changes in NC surface passivation on structure and function, and emphasize the potential to rely on strongly passivating ligands to control physical properties and processing parameters concurrently towards higher efficiency devices via low cost processing. Finally, micro-contact printing of blazed transmission gratings, using stable dispersions of core and core/shell NCs will be shown to produce close packed assemblies of NCs forming near-wavelength luminescent superstructures separated in space. We show the dominant contribution of a two-monolayer thick sharp interface CdS shell to the diffraction efficiency, and necessarily the refractive index, of the NCs, independent of core size. Utilization of these gratings as in-coupling elements at various positions within a device architecture are also examined. These new observations were achieved by unprecedented control of NC architecture during dispersion processing, while maintaining high luminescence, made possible by optimized NC surface passivation. These studies enable the formation of new LED architectures, and new optoelectronic devices based on angle resolved, monochromatic fluorescence from diffraction gratings prepared from simple solution processing approaches. Further, the novel observation of angle amplified interfering fluorescence from these features is argued to be a result of long range radiative coupling and superradiance enabled by the monodispersity and high-quality NC surface passivation described herein.

Stress corrosion cracking of a 14 wt% Cr martensitic stainless steel, with commercial names PH-15Cr5Ni, FV520B or X4CrNiCuMo15-5, used for the manufacture of low pressure turbine blades, has been studied with the intention of gaining a better understanding of the processes involved, how they occur and why. Industrially this is very important as stress corrosion cracking is considered to be a delayed failure process, whereby microscopic cracks can potentially propagate through a metal undetected until catastrophic failure occurs. The aim of this work is to establish links between crack length and external factors, such as exposure time, in order to devise a method of dating stress corrosion cracks and therefore predicting their possible occurrence in-service.

Ce mémoire de thèse est consacré à une étude du fluage isotherme et anisotherme à diversniveaux de température et à l’analyse fine des évolutions microstructurales associées à diverschargements thermomécaniques imposés du superalliage monocristallin, CMSX-4®. Cetravail est complété par la validation d’un modèle de comportement mécanique permettantd’intégrer ces évolutions microstructurales (fraction volumique des phases en présence,largeur des couloirs de matrice gamma, ...) pour déterminer la durée de vie du matériau.Parallèlement, le rôle de la microstructure initiale du matériau associée aux traitementsthermiques imposés dans la phase d’élaboration a été étudié. Il a été montré un effet marquéde cette microstructure initiale lors des essais de fluage à basse température (< 900°C), ainsique lors des essais de fluage anisotherme. Une microstructure de précipitation en radeaux detype N a été montrée comme particulièrement néfaste pour la résistance en fluageanisotherme. Enfin, le comportement du CMSX-4® est systématiquement comparé à celuiprécédemment établi dans des conditions similaires sur d’autres superalliages monocristallinspour pales haute pression. / This thesis is dedicated to the study of the isothermal and non-isothermal creep behavior in awide temperature range, and to the analysis of the microstructural evolution during differentthermomechanical paths on the superalloy single crystal, CMSX-4®. Moreover, the validationof a mechanical behavior model validation completes this work. This model takes intoaccount the microstructural evolutions (e.g. phase volume fraction, gamma-matrix channelwidth…) to predict the creep life. Additionally, the effect of the initial microstructure fromthe heat treatment has been investigated. It has been shown a strong impact of the as-receivedmicrostructure on the low temperature isothermal creep properties, and during non-isothermalcreep. A N-type rafted microstructure has been shown to be particularly detrimental to thenon-isothermal creep properties. Finally, the behavior of the CMSX-4® has been comparedwith the previous studies realized in the same conditions on other single crystal superalloysfor blades applications.