Organic semiconductors show promise to yield a novel class of bendable electronic devices, and much research efforts have focused on the optimization of these films for device performance. It is well known that the structure of organic films has a large influence over the electronic properties. In particular, the carrier mobility is often highly anisotropic, and domain boundaries have a detrimental effect on charge transport. Therefore the domain structure and lattice orientation are of particular interest. However, little is known about the domain structure of organic films, and techniques to study these properties have only begun to emerge in recent years. In this thesis, we apply two experimental techniques, Grazing-Incidence X-ray Diffraction (GIXD) and Lateral Force Microscopy (LFM), toward studying the lattice and domain structure of tetracene films grown on the silicon(001)-monohydride surface. We describe the necessary steps toward optimizing the sensitivity of these techniques to the domain structure. Results show that the crystalline tetracene films form a layered morphology in which the a-b plane lies parallel to the substrate surface. The film lattice structure is similar to bulk tetracene, and the lattice is confined to two orthogonal orientations, forming a partially-commensurate relationship with the substrate surface lattice along the film 'a' axis. LFM images reveal two types of polycrystalline domains. The first type ("major domains") are tens of microns in size, and are classified by their lattice orientation. They are subdivided into the second type ("sub-domains"), which range from 0.1 to 5um in size, and are argued to represent regions of uniform molecular tilt direction. The GIXD data show that the single-crystal domains which comprise these two larger domain types are anisotropic in size, being up to two times longer along the film 'b' axis than along 'a'. The single-crystal domains range from 0.05 to 0.2um in size, depending on lattice orientation and film thickness. The mathematical basis for these single-crystal domain size calculations is presented. The single-crystal domain sizes are thickness-dependent, and are two orders of magnitude smaller than a typical surface island observed in atomic-force microscopy (AFM) topographs. Substrate steps can also significantly influence the film structure by inducing boundaries in the single-crystal domains and sub-domains, but not in the major domains. This detailed knowledge of the domain structure of organic thin-films may assist in our understanding of the factors which affect charge transport in thin films, and may help to direct research efforts in optimizing the film structure for device performance. / Natural Sciences and Engineering Research Council (NSERC), Canadian Foundation for Innovation (CFI), Ontario Innovation Trust (OIT).

Orientadores: Gustavo de Medeiros Azevedo, Ângelo Malachias de Souza, Eduardo Granado Monteiro da Silva / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-19T08:06:03Z (GMT). No. of bitstreams: 1 Gasperini_AntonioAugustoMalfatti_D.pdf: 9911404 bytes, checksum: e5b4150f5a1f5f42c4d0e24b92e46c65 (MD5) Previous issue date: 2011 / Resumo: Neste trabalho estudamos a formação e estrutura de nanopartículas (NPs) de GeSi encapsuladas em sílica, utilizando técnicas baseadas em luz síncrotron, complementadas com imagens de microscopia eletrônica de transmissão. Obtivemos a forma, o diâmetro médio e a dispersão de tamanhos usando espalhamento de raios X a baixos ângulos em incidência rasante (GISAXS). A partir dos dados de difração de raios X (XRD) foi possível obter a fase cristalina, o parâmetro de rede e o tamanho médio dos cristalitos. Estes resultados serviram como dados de entrada em um modelo para análise através da técnica de estrutura fina de absorção de raios X (EXAFS), a qual forneceu informações sobre a estrutura local na vizinhança dos átomos de Ge. Apesar dos resultados de cada uma das técnicas acima serem comumente analisados de forma separada, a combinação destas técnicas leva a uma melhor compreensão das propriedades estruturais das NPs. Através da combinação dos resultados tivemos acesso a informações tais como a deformação da rede cristalina (strain), a fração de átomos cm ambientes cristalino e amorfo, a fração de átomos de Ge diluída na matriz e a possibilidade de formação de estruturas do tipo core-shell cristalino-amorfo. Resultados adicionais como a origem do strain e a temperatura de solidificação das NPs, dentre outros, foram obtidos através de um experimento in situ de absorção de raios X em energia dispersiva (DXAS), inédito na análise deste sistema. Por fim, utilizamos as técnicas acima citadas para acompanhar a evolução dos parâmetros estruturais em amostras tratadas termicamente durante diferentes intervalos de tempo / Abstract: In this work we study the formation and structure of GeSi nanoparticles embedded in silica matrix using synchrotron-based techniques complemented by TEM images. Shape, average diameter and size dispersion were obtained from grazing incidence small angle X-ray scattering. X-ray diffraction measurements were used to obtain crystalline phase, lattice parameter and crystallite mean sizes. By using these techniques as input for extended X-ray absorption fine structure analysis, the local structure surrounding Ge atoms is investigated. Although the results for each of the methods mentioned above are usually analyzed separately, the combination of such techniques leads to an improved understanding of nanoparticle structural properties. Crucial indirect parameters that cannot be quantified by other means are accessed in our work, such as local strain, possibility of forming core-shell crystalline-amorphous structures, fraction of Ge atoms diluted in the matrix and amorphous and crystalline Ge fraction. Additional results as the origin of the strain and temperature of solidification of NPs, among others, were obtained through an in situ energy dispersive X-ray absorption experiment (DXAS), unheard in this system. Finally, we use the techniques mentioned above to monitor the evolution of the structural parameters of samples annealed during different time intervals / Doutorado / Física / Doutor em Ciências

La toxine bactérienne de Shiga se lie au glycosphingolipide (GSL) globotriaosylcéramide (Gb3) afin d’entrer par endocytose dans les cellules en utilisant une voie dépendante et indépendante de la clathrine. Dans la voie indépendante de la clathrine, la toxine de Shiga réorganise les lipides de la membrane de façon à imposer une contrainte mécanique sur la bicouche, conduisant ainsi à la formation de pic d’invagination d'endocytose profonds et étroits. Mécaniquement ce phénomène n’est pas encore compris, notamment il reste énigmatique, comment se traduisent les propriétés géométriques de l’agrégation des glycosphingolipides GSLS et de la toxine. Dans mon travail de thèse, via l’utilisation de la sous-unité B de la toxine de Shiga (STxB) comme un modèle, différentes espèces moléculaires de son récepteur Gb3 ont été synthétisés avec des structures délibérément choisis. Les études réalisées par imagerie de haute résolution et par la modélisation informatique ont permis d’élucider les contraintes mécano-chimique sous-jacente conduisant à une réorganisation efficace qui a pour résultat l’agrégation de la toxine et la réorganisation des lipides. En combinant des expériences de simulation sur ordinateur de dynamique des particules dissipatives (DPD) et des expériences sur des modèles de membranes cellulaires, nous avons fourni la preuve de l’induction d’une force de fluctuation-membrane, de type « force de Casimir », conduisant à l'agrégation des molécules de toxines associées à la membrane à des échelles de longueur mésoscoiques. Nous avons observé et mesuré, en outre la condensation lipidique induite par la toxine, quantitativement sur des monocouches de Langmuir en utilisant la réflectivité des rayons X (XR) et par la mesure de la diffraction des rayons X par incidence rasante (GIXD), fournissant ainsi une preuve directe de l'hypothèse que la toxine a le potentiel de réduire de façon asymétrique la surface moléculaire sur la partie membranaire exoplasmique, ce qui conduit à une déformation locale de la membrane. Durant ma thèse, nos efforts ont été consacrés à la réalisation de nouveaux glycosphinolipides (GSL) comme outils chimiques à visée biologique. Par ailleurs, une nouvelle stratégie de reconstitution de GSL fonctionnels sur la membrane cellulaire, basée sur une réaction de ligation de type « click » entre un glycosyl-cyclooctyne et un azido-sphingosine a été étudiée. Les résultats obtenus sur les cellules se sont avérés beaucoup moins efficace que ceux in vitro. Une poursuite de l'optimisation de cette méthodologie est actuellement en cours. Une sonde fluorescente du glycosphinolipide Gb3, marquée à l’Alexa Fluor 568 lui-même lié par l'intermédiaire d'un bras PEG-α à la position de la chaîne acyle, a été synthétisée. Cette sonde se lie à la STxB sur couche mince de TLC, mais pas sur des membranes modèles. D'autres améliorations sont discutées. / Bacterial Shiga toxins bind to the glycosphingolipid (GSL) globotriaosylceramide (Gb3) to enter cells by clathrin-dependent and independent endocytosis. In the clathrin-independent pathway, Shiga toxin reorganizes membrane lipids in a way such as to impose mechanical strain onto the bilayer, thus leading to the formation of deep and narrow endocytic pits. Mechanistically how this occurs is not yet understood, and notably how the geometric properties of toxin-GSLs complexes translate into function has remained enigmatic. In my thesis work, using the B-subunit of Shiga toxin (STxB) as a model, different molecular species of its receptor Gb3 have been synthesized with deliberately chosen structures, coupled with high resolution imaging and computational modeling, to understand the underlying mechano-chemical constraints leading to efficient toxin clustering and lipids reorganization. By combining dissipative particle dynamics (DPD) computer simulation and experiments on cell and model membranes, we provided evidence that a membrane fluctuation-induced force, termed Casimir-like force, drives the aggregation of tightly membrane-associated toxin molecules at mesoscopic length scales. Furthermore, toxin-induced lipid condensation was observed and measured quantitatively on Langmuir monolayers using X-ray reflectivity (XR) and grazing incidence x-ray diffraction (GIXD), thereby providing direct evidence for the hypothesis that the toxin has the potential to asymmetrically reduce the molecular area of the exoplasmic membrane leaflet, leading to local membrane deformation. During my PhD, effort was also invested to develop new GSL tools applied to the biological setting. A novel strategy based on the Cu-free click reaction between glycosyl-cyclooctyne and azido-sphingosine was designed with the goal to functionally incorporate GSLs into cellular membranes. Following the synthesis work, click reactions have been performed in solution and on cells. Compared to the former, results on cells were far less efficient. Further optimization is currently ongoing. A fluorescently labeled Gb3 probe with Alexa Fluor 568 coupled via a PEG linker to the α-position of the acyl chain, was synthesized, to which STxB bound on TLCs, but not on model membranes. Further improvements are discussed.

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