京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21811号 / 農博第2324号 / 新制||農||1066(附属図書館) / 学位論文||H31||N5183(農学部図書室) / 京都大学大学院農学研究科農学専攻 / (主査)教授 松村 康生, 教授 白岩 立彦, 教授 丸山 伸之 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23233号 / 工博第4877号 / 新制||工||1761(附属図書館) / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 宮原 稔, 教授 佐野 紀彰, 教授 松坂 修二 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Colloidal quantum dots (CQDs) are potentially low-cost, solution-processable semiconductors which are endowed, through their nanoscale dimensions, with strong absorption, band gap tunability, high dielectric constants and enhanced stability. CQDs are contenders as a standalone PV technology as well as a potential back layer for augmenting established photovoltaic (PV) technologies, such as Si. However, owing to their small size (ca. few nanometers), CQDs are prone to surface trap states that inhibit charge transport and threaten their otherwise wonderful optoelectronic properties. Surface traps have also, indirectly, impeded scalable and industry-compatible fabrication of these solar cells, as all of the reports, to date, have relied on spin-coating with sophisticated and tedious ligand exchange schemes, some of which need to be performed in low humidity environments. In this thesis, we posit that an in-depth understanding of the process-structure-property-performance relationship in CQDs can usher in fresh insights into the nature and origin of surface traps, lead to novel ways to mitigate them, and finally help achieve scalable fabrication. To this end, we probe the CQD surfaces and their interactions with process solvents, linkers, and ambient environment employing a suite of spectroscopic techniques. These fundamental insights help us develop facile chemical and physical protocols to mitigate surface traps such as solvent engineering, remote molecular doping, and oxygen doping, directly leading to better-performing solar cells. Our efforts finally culminate in the realization of >10% efficient, air-stable CQD solar cells scalably fabricated in an ambient environment of high, uncontrolled R.H. (50-65%). As-prepared solar cells fabricated in high humidity ambient conditions are found to underperform, however, an oxygen-doping recipe is devised to mitigate the moisture-induced surface traps and recover device performances. Importantly, these solar cells are fabricated at coating speeds of >15 m min-1 with roll-to-roll compatible techniques such as blade and bar coating requiring 1/25th the CQD material consumed by the standard spin-coated devices, overcoming the two major challenges of manufacturability and scalability faced by CQD PV.

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In this thesis, the local field enhancement from multiple plasmonic structures were studied in different experiments. A new approach was applied to enhance the emission from upconverting nanoparticles to harvest energy from photons below the bandgap. A novel nanofabrication method was introduced to make double nanoholes for use in optical trapping, which was implemented to observe the nonlinear response from 2D materials and the enhanced emission from upconverting single nanoparticles. This method makes a large amount of apertures and is inexpensive. Selective plasmon-enhanced emission from erbium-doped nanoparticles using gold nanorods was demonstrated. Upconversion nanoparticles were excited with a dual-wavelength source of 1520~nm and 1210~nm simultaneously. The power dependence of the observed upconversion emission confirmed the contribution of both excitation bands in the upconversion process. Gold nanorods with resonances at 980~nm and 808~nm were implemented to selectively enhance the upconversion emission in order to harvest light with Si and GaAs solar cells, respectively. I also used colloidal lithography to fabricate double nanoholes which were plasmonic structures used for protein and nanoparticle trapping. This bottom-up technique enabled the fabrication of a large number of structures at low cost. Plasma etching of polystyrene nanoparticles using this technique tuned the cusp separation of double nanoholes down to 10~nm. The smaller cups separation enables to have more confined field in the gap which can be used in plasmonic sensing and plasmon enhanced upconversion processes. This technique can be used to fabricate plasmonic structures for nanoparticle trapping, spectroscopy, and sensing. In the next project, hexagonal boron nitride nanoflakes were trapped in a double nanohole fabricated with the colloidal lithography method. A second harmonic signal was detected at 486.5~nm where the particle was trapped and pumped with an ultra-low power laser at 973~nm. The power dependence measurements supported the second order process for second harmonic generation. Finite-difference time-domain (FDTD) simulations showed a 500-fold field intensity enhancement at the fundamental wavelength and a 450-fold enhancement in the Purcell factor at the second harmonic generation wavelength. This scheme is promising for ultra-fast imaging nonlinear optics technologies. In the last project, colloidal lithography double nanoholes were used to trap upconverting nanocrystals. Colloidal lithography double nanoholes with 32~nm cusp separation achieved 50 times larger emission compared to rectangular apertures. FDTD simulations showed the largest field enhancement in the aperture with the largest upconversion enhancement. 1550~nm emission from the trapped nanoparticle can be used as single-photon source. / Graduate

The presented diploma thesis deals with the potential use of colloidal silica in cement composites. Investigation is focused primarily on selected properties of cement pastes and mortars with colloidal silica content. Two selected types of colloidal silica (particles with average size of 14 nm) have been used as a cement addition and partial replacement of cement, respectively. The experimental program for cement pastes with colloidal silica included tests for isothermal calorimetry (the study of cement hydration) and thermal analysis (determining the portlandite content). Hardened cement pastes have been studied through measurements of compressive strength. The microstructure was examined by scanning electron microscopy. Hardened mortars with colloidal silica have been studied through measurements of compressive strength, flexural strength, modulus of elasticity and fracture mechanics parameters. Fracture mechanics tests show that 5 % and 20 % addition of colloidal silica can enhance after 28 days of curing fracture energy up to 18,4 % and 32,7 %, respectively. For the compressive strength enhancing effect of colloidal silica, it was found to be more pronounced in the early age, while rate of strength gain can be lower than the control in the later ages. Our investigations revealed that the silica sol will coagulate immediately when the cement is mixed into the water containing sol. The ionic composition of pore fluid significantly influences the stability of colloidal silica and lead to their aggregation. After additional tests it has been found that small addition of calcium hydroxide greatly improved the compressive strength of the resulting cement pastes with colloidal silica content. Addition of calcium hydroxide in conjunction with modified cement paste preparation can enhance compressive strength after 3 days of curing up to 64,4 % in comparison with the blank paste.

L’analyse de la stabilité de formulations est primordiale dans de multiples secteurs industriels : pharmaceutique, cosmétique, agroalimentaire… Il existe donc de nombreuses techniques permettant de caractériser la stabilité de solutions colloïdales. Les méthodes les plus communément utilisées reposent sur l’analyse par diffraction de la lumière, comme le Turbiscan, développé par la société Formulaction, qui est un instrument de référence dans ce domaine. Cependant, de par leur principe de mesure, ces techniques ne sont pas suffisamment sensibles pour l’analyse d’échantillons fortement absorbants. Les autres méthodes existantes – l’analyse par ultrasons, par rayons X… - sont quant à elles complexes, requièrent la connaissance de propriétés difficilement accessibles, voire sont insensibles de par leur principe physique aux produits à base de noir de carbone, qui constituent la majeure partie du marché des produits dits noirs. Il existe donc un besoin concernant une méthode de mesure simple et non-intrusive qui permette d’étudier la stabilité de dispersions fortement absorbantes. Nous présentons dans ce manuscrit une nouvelle méthode de caractérisation, basée sur l’interaction entre les ondes électromagnétiques hyperfréquences et la dispersion fluidique à l’étude. Dans un premier temps, une modélisation des capteurs ainsi que de l’interaction entre ondes hyperfréquences et liquide est présentée, afin de comprendre les mécanismes de fonctionnement du système développé et d’en optimiser la sensibilité. Par la suite, nous avons corroboré les résultats de modélisation par des simulations hyperfréquences démontrant la sensibilité de la technique à une variation de permittivité effective du liquide, et par extension à une variation de fraction volumique. Forts de ces résultats, l’intégration du système de mesure complet comportant quatre capteurs a été réalisée puis le fonctionnement de la technique a été validé par mesures de solutions colloïdales modèles. Enfin, le système de mesure a été testé sur diverses dispersions plus complexes, permettant ainsi de valider la capacité de la technique hyperfréquence à caractériser la stabilité des solutions colloïdales, et par extension la stabilité de solutions colloïdales fortement absorbantes. / Stability analysis of formulations is essential in several industrial fields: pharmaceutical, cosmetics, agri-food… Therefore, many technics were developed to characterize the stability of colloidal suspensions. The most commonly used ones are based on light diffraction analysis, such as the Turbiscan developed by Formulaction, which is a reference instrument in the field. Nevertheless, because of the measurement principle, those techniques are not suitable for the analysis of highly absorbing samples. There are several other methods – acoustic measurements, X-rays diffraction spectrometry… - to analyse absorbing samples but they are complex, require a good knowledge of the sample properties or even are not sensitive to carbon based products, due to their physical principle, which constitute the larger part of the black products market. Therefore, there is a need for a new measurement method, simple and non-intrusive, that allows to study highly absorbing solutions stability. In this manuscript, we present a new characterization method, based on the interaction between microwaves and the fluidic dispersion under study. In a first time, a modelling of the sensors and the interactions between microwaves and the liquid will be presented, to understand the working of the developed system and to optimize it. Thereafter, we will corroborate the modelling results with microwave simulations, to demonstrate the sensitivity of the method to a variation of the effective permittivity of the liquid, and so to a variation of the volume fraction. Based on those results, the integration of the whole system, with the four sensors, will be realised and the functioning of the system will be validated by measuring reference colloidal suspensions. Finally, the measurement system will be tested on several complex suspensions, to validate the ability of the microwave method to characterise the stability of colloidal suspensions, and by extension of highly absorbing colloidal suspensions.

Inorganic colloidal synthesis, without a doubt, lies at the foundation of many contemporary areas of nanoscience and nanotechnology. At the advent of the 21st century, much progress has been made in the size, shape / morphological control and surface engineering of metal oxides resulting in a diverse library of macroscopic crystal architectures with well-defined surface properties. In this thesis, we start by introducing the self-assembly of the iron(oxy-, hydro-)xide while briefly reviewing some fundamental concepts of solid-state chemistry. Specific information on the family of iron oxide and iron(oxy-, hydro-)xide, as relevant to crystalline phase control, has been highlighted to direct our discussion of the synthesis of diverse crystal morphologies. Furthermore, we briefly underline and discuss the kinetic and thermodynamic control of colloidal crystal morphologies through reasonably established knowledge of anisotropic growth rates in the perspective of iron oxides' facets or crystalline planes. Lastly, we review the state-of-the-art wet chemical synthetic approaches, while using different iron(oxy-, hydro-)xide crystals as examples, for the purpose of explaining our synthetic work of choice. The main work of this thesis is entirely focused on the "facile synthesis and fine morphological tuning of branched hematite (??-Fe2O3) crystals for photodegradation of azo-type dyes".. We would discuss the crucial parameters for fine morphological tuning in the context of controlling the anisotropic growth rates of branched ??-Fe2O3 crystals instead of phase transformation. In our work, we have significantly improved the synthesis of dendritic "feather-like" and "starfish-like" for their size reduced variants for use in photocatalysis.

Nanoparticles are very interesting components. Due to their very large specific surface area they possess properties in between molecules and macroscopic materials. In addition, a material built up of hierarchically assembled nanoparticles could obtain unique properties, not possessed by the nanoparticles themself. A very interesting group of nanoparticles is the cellulose nanofibrils. The fibrils are found in various renewable resources such as wood, bacteria and tunicates. In this work fibrils extracted from wood is studied. In wood the fibrils are the smallest fibrous component with the approximate dimensions; 4 nm in width and length in the micrometer range, providing a high aspect ratio. In addition, they have a crystallinity above 60% and, hence, a high stiffness. These fibrils are hierarchically ordered in the wood fiber to give it its unique combination of flexibility and strength. The properties of the fibrils make them very suitable to be used as reinforcement elements in composites and, due to their ability to closely pack, to make films with excellent gas barrier properties. The key aspect to design materials, efficiently utilizing the properties of the individual fibrils, is to control the arrangement of the fibrils in the final material. In order to do so, the interactions between fibrils have to be well characterized and controlled. In this thesis the interaction between fibrils in aqueous dispersions is studied, where the main interactions are attractive van der Waals forces and repulsive electrostatic forces. The electrostatic forces arise from carboxyl groups at the fibrils surface, which either are due to hemicelluloses at the fibrils surfaces or chemically introduced to the cellulose chain. This force is sensitive to the chemical environment. It decreases if the pH is reduced or if the salt concentration is increased. If it is strongly reduced the system aggregates. In dilute dispersions aggregation causes formation of multiple clusters, whereas in semi-dilute dispersions (above the overlap concentration) a volume filling network, i.e. a gel, is formed. The tendency of aggregation, i.e. the colloidal stability, can be predicted by using the DLVO theory. In this thesis DLVO predictions are compared to aggregation measurements conducted with dynamic light scattering. Good agreement between experiments and the designed theoretical model was found by including specific interactions between added counter-ions and the carboxyl groups of the fibrils in the model. Thus, the surface charge is both reduced by protonation and by specific interactions. This emphasizes a much larger effect of the counter-ions on the stability then generally thought. Hence, this work significantly improves the understanding of the interfibril interactions in aqueous media. As mentioned above, the fibrils can be physically cross-linked to form a gel. The gelation is an instant process, occurring at pH or salt levels causing the interfibril repulsion to decrease close to zero. If a well dispersed stationary dispersion is gelled, the homogenous and random distribution of the fibrils is preserved in the gel. These gels can be used as templates to produce composites by allowing monomers or polymers to enter the network by diffusion. In an effort to mimic processes occurring in the tree, producing materials with fibrils aligned in a preferred direction, the ability to form gels with controlled fibril orientation were studied. Such networks were successfully produced by applying strain to the system prior or past gelation. Orientation prior gelation was obtained by subjecting the dispersion to elongational flow and freezing the orientation by “turning off” the electrostatic repulsion. Orienting the fibrils after gelation was achieved by applying shear strain. Due to the physical nature of the crosslinks, rotation in the fibril-fibril joints can occur, enabling the fibrils to align in the shear direction. This alignment significantly increased the stiffness of the gels in the shear direction. / QC 20111205

The next generation of optoelectronic applications like stimuli-responsive sensors, functional displays or nanophotonic circuits demands a basic understanding of lightmatter interactions on the nanoscale. Top-down fabrication has been employed in the past to demonstrate coherent energy transfer in functional nanostructures, yet these fabrication methods are problematic due to their limited scalability and high costs as well as the high optical losses. This work adapted physical principles like radiation properties of metallic nanoantennas and Bragg diffraction in periodic nanostructures and realized these concepts using bottom-up self-assembly methods based on colloidal chemistry. With this approach, single plasmonic nanoparticles and semiconductor quantum emitters were co-assembled into complex structures. This work took the colloidal concept from plasmonics and introduced quantum dots in order to characterize the radiative and non-radiative decay processes as well as the arising light-matter interactions. Due to electromagnetic coupling between the components, hybridized modes were detected instead of the single particle resonances observed in the isolated case. It was furthermore shown that these colloidal building blocks can be assembled into functional optical grids on a large scale using template-assisted self-assembly. Thus, this work established spectroscopic principles for self-assembled colloidal building blocks that can be integrated in parallelized processes in the future.