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Abstract: The central theme of this thesis is the application of radial and pair distribution function analysis to materials characterisation problems for nanotechnology. These concepts are introduced in Chapter 1, and the associated methods are described in Chapter 2. Chapter 3 details the first of the results which discusses the design and development of a software tool called ImageDataExtractor. This auto-extracts microscopy images and then analyses them to afford quantitative information regarding particles in a sample, such as shape, size and distribution. It realises an opportunity for data-mining the ubiquity of readily available images in the literature. Chapter 4 presents results of the development and execution of a novel experimental technique, called glancing-angle pair distribution function (gaPDF) analysis, applied to the structure of the working electrode in dye-sensitised solar cells (DSSCs). This structure was successfully observed, validating this novel method. The investigation also suggested preferred binding modes of the carboxylic acid anchoring groups present in this interfacial structure. Chapters 5 and 6 demonstrate the application of PDF analysis to synchrotron-based powder diffraction data of two material case studies: the rare earth phosphate glass (REPG) (Gd2O3)0.230(P2O5)0.770, and four Ru based photo-isomers. The closest R…R rare earth separation, which governs optical properties of REPGs, was determined to be 4.2(1) Å, aided by various statistical techniques. Analysis on four Ru-based photo-isomers confirmed: the existence of local structure in such compounds, their ability to be photo-isomerised in powder form, the theoretical models constructed using computational techniques, and the lack of heterogeneity in photo-isomerisation throughout a given light-induced sample. Chapter 7 concludes the work and offers a future outlook.

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Abstract: The crystal structure of the organic pigment 2-mono­methyl-quinacridone (Pigment Red 192, C21H14N2O2) was solved from X-ray powder diffraction data. The resulting average structure is described in space group [P\overline 1], Z = 1 with the molecule on the inversion centre. The molecules are arranged in chains. The molecules, which have no inversion symmetry, show orientational head-to-tail disorder. In the average structure, the methyl group is disordered and found on both ends of the molecule with an occupancy of 0.5 each. The disorder and the local structure were investigated using various ordered structural models. All models were analysed by three approaches: Rietveld refinement, structure refinement to the pair distribution function (PDF) and lattice-energy minimization. All refinements converged well. The Rietveld refinement provided the average structure and gave no indication of a long-range ordering. The refinement to the PDF turned out to be very sensitive to small structural details, giving insight into the local structure. The lattice-energy minimizations revealed a significantly preferred local ordering of neighbouring molecules along the [0[\bar 1]1] direction. In conclusion, all methods indicate a statistical orientational disorder with a preferred parallel orientation of molecules in one direction. Additionally, electron diffraction revealed twinning and faint diffuse scattering.

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Abstract: The efficient transport of electrons from the sunlight-harvesting dye molecules into the electrical circuit of a dye-sensitized solar cell (DSSC) is imperative to its effective operation. A dye···semiconductor interface comprises the working electrode of a DSSC. Dye molecules adsorb onto the semiconductor surface, whereupon they transfer electronic charge into the conduction band of the semiconductor; this process initiates the electrical circuit. It is therefore important to characterize this interfacial structure in order to understand how efficiently the dye binds, or anchors, onto the semiconductor surface and imparts charge transfer to it. Armed with such knowledge, the performance of DSSCs may then be improved systematically. The structural determination of a thin-film interface is nonetheless a challenging task. We herein report the results of a glancing-angle pair distribution function (gaPDF) experiment that generated synchrotron x-ray diffraction patterns of N3- and N749-sensitized DSSC working electrodes. This gaPDF experimental approach represents the first diffraction-based strategy for the characterization of intact DSSC working electrodes. The gaPDF structural signatures were compared with PDFs simulated from two possible interfacial structures that were computed using density functional theory (DFT); these simulated structures showed the dyes anchoring in two distinct modes: a bridging bidentate and a monodentate ester configuration. The differences between the experimental observation and these simulated structures revealed a preference for each dye, N3 and N749, to adopt a bidentate bridging dye anchoring mode when sensitized onto TiO2. This work not only demonstrates the successful application of a gaPDF method to DSSC research, it also advocates the applicability of gaPDF to many types of thin-film samples.

Open Access

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Abstract: This study combines bulk structural and spectroscopic investigations of Eu3+- or Y3+/Eu3+ co-doped tetragonal and cubic zirconia polymorphs to gain an in-depth understanding of the solid solution formation process. Our bulk structural characterizations show that the dopant is homogenously distributed in the ZrO2 host structure resulting in an increase of the bulk symmetry with increasing dopant substitution (from 8 to 26 mol%). The local site symmetry around the Eu3+ dopant, however, determined with luminescence spectroscopy (TRLFS), remains low in all samples. Results obtained with X-ray pair distribution function and X-ray absorption spectroscopy show that the average coordination environment in the stabilized zirconia structures remains practically unchanged. Despite this very constant average dopant environment, site-selective TRLFS data show the presence of three nonequivalent Eu3+ environments in the ZrO2 solid structures. These Eu3+ environments are assumed to arise from Eu3+ incorporation at superficial sites, which increase in abundance as the size of the crystallites decrease, and incorporation on two bulk sites differing in the location of the oxygen vacancies with respect to the dopant cation.

Open Access

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Abstract: The mechanisms by which organisms control the stability of amorphous calcium carbonate (ACC) are yet not fully understood. Previous studies have shown that the intrinsic properties of ACC and its environment are critical in determining ACC stability. Here, the question, what is the effect of bulk incorporation versus surface adsorption of additives on the stability of synthetic ACC, is addressed. Using a wide range of in situ characterization techniques, it is shown that surface adsorption of poly(Aspartic acid) (pAsp) has a much larger stabilization effect than bulk incorporation of pAsp and only 1.5% pAsp could dramatically increase the crystallization temperature from 141 to 350 °C. On the contrary, surface adsorption of PO43− ions and OH− ions does not effectively stabilize ACC. However, bulk incorporation of these ions could significantly improve the ACC stability. It is concluded that the stabilization mechanism of pAsp is entirely different from that of PO43− and OH− ions: while pAsp is effectively inhibiting calcite nucleation at the surface of ACC particle, the latter acts to modify the ion mobility and delay crystal propagation. Thus, new insights on controlling the stability and crystallization processes of metastable amorphous materials are provided.