Dissertations / Theses on the topic 'Catalytic and optical properties'
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Tabor, Christopher Eugene. "Some optical and catalytic properties of metal nanoparticles." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31794.
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Thesis (Ph.D)--Chemistry and Biochemistry, Georgia Institute of Technology, 2010.Committee Chair: El-Sayed, Mostafa; Committee Member: Perry, Joseph; Committee Member: Wang, Zhong; Committee Member: Whetten, Robert; Committee Member: Zhang, John. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Fan, Yinan. "Rational synthesis of plasmonic/catalytic bimetallic nanocrystals for catalysis." Thesis, Sorbonne université, 2022. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2022SORUS189.pdf.
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Parmi les différents nanocatalyseurs, ceux constitués de nanoparticules de métaux nobles méritent une attention particulière en raison de leurs propriétés électroniques, chimiques et même optiques (dans le cas de transformations renforcées par les plasmons). Le platine ou le palladium sont bien connus pour leurs remarquables propriétés catalytiques, mais ils sont chers et leurs ressources sont limitées. En outre, les nanocatalyseurs monométallique ne peuvent conduire qu'à une gamme limitée de réactions chimiques. Ainsi, notre stratégie a été de développer des nanocatalyseurs bimétalliques composés de deux éléments métalliques qui peuvent présenter des effets synergiques entre leurs propriétés physicochimiques et une activité catalytique accrue. Nous avons ainsi conçu des nanocatalyseurs bimétalliques de type cœur-coquille composés d'un cœur en argent et d'une coquille en platine. L'intérêt est de combiner les activités catalytiques élevées et efficaces de la coquille de platine avec le cœur d'argent hautement énergétique, capable de renforcer les activités de la coquille grâce à ses propriétés plasmoniques. En outre, ces nanoparticules bimétalliques présentent souvent une activité catalytique supérieure en raison de la modification de la distance inter-atomique Pt-Pt (c'est-à-dire l'effet de contrainte). Dans ce travail de thèse, les nanoparticules Ag@Pt ont été synthétisées via un processus en deux étapes utilisant d'une part des nanoparticules d'Ag synthétisées chimiquement comme germes et d'autre part des complexes platine-oleylamine qui sont ensuite réduits à la surface des germes à une température contrôlée. Différentes tailles de germes d'Ag de 8 à 14 nm avec une très faible distribution de taille (<10%) ont été obtenues en ajustant le temps de réaction, la rampe de température, la concentration en précurseur d'Ag et la température finale pendant la synthèse. Différentes épaisseurs de coquille (de 1 à 6 couches atomiques) ont été obtenues en ajustant le rapport entre les concentrations de précurseur de platine et de germe d'argent. L'activité catalytique des nanoparticules Ag@Pt a été testée en considérant une réaction modèle de réduction du 4-nitrophénol en 4-aminophénol par NaBH4 en phase aqueuse. Nous avons observé que l'épaisseur de la coquille de Pt et la taille du noyau d'Ag influençaient les propriétés catalytiques et conduisaient à une activité catalytique accrue par rapport à l'argent ou au platine pur. Ceci a été attribué à des effets synergiques. De plus, nous avons observé une augmentation de l'activité catalytique des nanoparticules Ag et Ag@Pt sous irradiation lumineuse. Ce phénomène a été corrélé à la génération d'électrons chauds dans les noyaux d'Ag. Afin de développer une plateforme de nanocatalyse supportée, nous avons fabriqué des auto-assemblages 3D appelés aussi supercristaux composés de nanoparticules d'Ag@Pt obtenus spontanément après dépôt sur un substrat solide en raison de leur distribution de taille étroite et de leur forme homogène. L'activité catalytique de ces supercristaux pour la réaction d'évolution de l’hydrogène (HER) a été étudiée en suivant in situ par microscopie optique la production de nanobulles de gaz H2. Trois comportements distincts dans l'activité photo-catalytique (activité, activité intermittente et non-activité) ont été observés sur les supercristaux dans la même région d'intérêt. En outre, 50 % des assemblages ont été déterminés comme étant actifs pour l'HER qui a été démontrée comme étant accompagnée par une corrosion oxydative de l’argentAmong several nanocatalysts, those based on noble metal NPs deserve particular attention because of their electronic, chemical and even optical properties (in the case of plasmonic-enhanced transformations). Platinum or palladium are well known for their remarkable catalytic properties, but they are expensive and their resources are limited. In addition, single component nanocatalysts can only lead to a limited range of chemical reactions. Thus, our strategy was to develop bimetallic nanocatalysts composed of two metal elements that can exhibit synergistic effects between their physicochemical properties and enhanced catalytic activity. We have thus designed bimetallic nanocatalysts of the core-shell type composed of a silver core and a platinum shell. The interest is to combine the high and efficient catalytic activities of the platinum shell surface with the highly energetic silver core capable of enhancing the activities of the shell through its plasmonic properties. In addition, these bimetallic NPs often exhibit superior catalytic activity due to the modification of the Pt-Pt atomic bonding distance (i.e. the strain effect). In this thesis work, Ag@Pt NPs have been synthesized via a two-step process using chemically synthesized spherical Ag NPs as seeds on the one hand and platinum complexes with oleylamine on the other hand which are then reduced on the surface of the seeds at a controlled temperature. Different Ag seed sizes from 8 to 14 nm with a very low size distribution (<10%) have been obtained by adjusting the reaction time, temperature ramp, Ag precursor concentration and final temperature during the synthesis. The control of the shell thicknesses (from 1 to 6 atomic layers) has been possible by adjusting the ratio of platinum precursor to silver seed concentrations. The catalytic activity of the core-shell Ag@Pt NPs was tested by a model reaction of reduction of 4-nitrophenol to 4-aminophenol by NaBH4 in aqueous phase. We have observed that the thickness of the Pt shell and the size of the Ag core influence the catalytic properties and led increased catalytic activity compared to pure silver or platinum. This was attributed to synergistic effects. Furthermore, we have observed an enhancement of the catalytic activity of Ag and Ag@Pt NPs under light irradiation. This is correlated to the generation of hot electrons in the Ag core. Finally, in order to develop a supported nanocatalysis platform, 3D self-assemblies also called supercrystals composed of Ag@Pt nanoparticles have been spontaneously obtained after deposition on a solid substrate due to their narrow size distribution and homogeneous shape. The catalytic activity of these supercrystals for the hydrogen evolution reaction (HER) has been studied by following in situ by optical microscopy the production of H2 gas nanobubbles. Three distinct behaviors in photo-catalytic activity (activity, intermittent activity and non-activity) have been observed on the supercrystals in the same region of interest. In addition, 50% of the assemblies were determined to be active for HER which was shown to be accompanied by oxidative corrosion of silver
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Schwenk, Nicola [Verfasser], Todd B. [Gutachter] Marder, and Ulrich [Gutachter] Schatzschneider. "Seeing the Light: Synthesis of Luminescent Rhodacyclopentadienes and Investigations of their Optical Properties and Catalytic Activity / Nicola Schwenk ; Gutachter: Todd B. Marder, Ulrich Schatzschneider." Würzburg : Universität Würzburg, 2018. http://d-nb.info/1160188025/34.
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Mildner, Stephanie [Verfasser], Christian [Akademischer Betreuer] Jooß, Michael [Akademischer Betreuer] Seibt, and Peter [Akademischer Betreuer] Crozier. "Pr1-xCaxMnO3 for Catalytic Water Splitting - Optical Properties and In Situ ETEM Investigations / Stephanie Mildner. Gutachter: Christian Jooß ; Michael Seibt ; Peter Crozier. Betreuer: Christian Jooß." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2015. http://d-nb.info/1076673627/34.
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Lee, Suyeon. "Synthesis and properties of mono and bi- metallic nanoparticles of noble metals; towards fabrication of novel functional nanoparticles assemblies." Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS580.
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Les nanoparticules de métaux nobles ont suscité un grand intérêt ces dernières années dans divers domaines en raison de leurs propriétés physiques et chimiques distinctes telles que les propriétés optiques, catalytiques ou magnétiques. Dans cette thèse, nous avons étudié les différentes approches permettant d'intégrer deux métaux dans un même système, comme les nanoparticules bimétalliques, ou les super-réseaux binaires pour obtenir de nouvelles propriétés. Nous avons mis au point une méthode de croissance à partir de graines pour synthétiser de manière rationnelle des nanoparticules cœur-coquille Au(ou Ag)@M (M=Ag, Pd, Pt). L'impact des paramètres de synthèse tels que la concentration des précurseurs métalliques, la nature des ligands ou la température sur les paramètres clés des nanoparticules (taille du noyau, épaisseur de la coque, dispersion) a été étudié. Les propriétés optiques, vibratoires et catalytiques des différentes nanoparticules bimétalliques ont été caractérisées en fonction de leur structure, de leur composition chimique, du nombre de couches atomiques de la couche et de la cristallinité du noyau. En outre, des super-réseaux binaires de NP, qui sont co-assemblés à partir de deux composants complémentaires différents, ont également été signalés. Plusieurs conditions d'assemblage (rapport de taille effective, rapport de concentration, température de dépôt, méthode de dépôt) ont été explorées. Le mécanisme physique responsable de la variation structurelle observée a ainsi été identifié. Une variété de structures cristallines pour les super-réseaux binaires telles que AlB2, NaZn13, NaCl ont été produites. Enfin, les propriétés magnétiques des super-réseaux binaires de nanoparticules Fe2O3/Au ont été étudiées. Elles sont déterminées par la distance interparticulaire des nanoparticules Fe2O3 modulée par l'insertion des nanoparticules AuNoble metal nanoparticles (NPs) have attracted a great interest last years in various domains due to their distinct physical and chemical properties such as optical, catalytic or magnetic properties. In this thesis, we investigated the various approaches to integrate two metals in the same system, such as bimetallic nanoparticles, or binary superlattices to obtain new properties. We have developed seed-mediated growth method to rationally synthesis core-shell NPs Au(or Ag)@M (M=Ag, Pd, Pt). The impact of synthesis parameters such as concentration of metallic precursors, nature of ligands or temperature on key NPs parameters (core size, shell thickness, dispersity) was studied. The optical, vibrational and catalytic properties of different bimetallic NPs were characterized according to their structure, chemical composition, number of shell atomic layer and core crystallinities. In addition, binary NP superlattices, which are co-assembled from of two different complementary components were also reported. Several assembly conditions (effective size ratio, concentration ratio, deposition temperature, deposition method) were explored. The physical mechanism responsible for the observed structural variation was thus identified. A variety of crystalline structures for the binary superlattices such as AlB2, NaZn13, NaCl were produced. Finally, the magnetic properties of Fe2O3/Au NP binary superlattices were studied. They are determined by the interparticle distance of Fe2O3 NPs modulated by the insertion of Au NPs
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Gozin, Yael. "Catalytic antibody 1E9: properties and selectivity /." Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16475.
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Hörnlund, Erik. "Catalytic Properties of Protective Metal-Oxides." Doctoral thesis, KTH, Materials Science and Engineering, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3506.
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Diddams, P. A. "Sheet silicates : structure and catalytic properties." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356665.
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Sesay, I. M. "Redox properties of some catalytic oxides." Thesis, Queen's University Belfast, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379618.
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Dordick, Jonathan Seth. "Unusual catalytic properties of horseradish peroxidase." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/16488.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Applied Biological Sciences, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE
Bibliography: leaves 217-231.
by Jonathan Seth Dordick.
Ph.D.
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Lesik, S. M., and I. M. Ivanenko. "Nickel ferrites and its catalytic properties." Thesis, Sumy State University, 2018. http://essuir.sumdu.edu.ua/handle/123456789/67686.
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Cymes, Brittany Allison. "Catalytic Properties of Novel Microporous Minerals." Miami University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=miami1587730697926361.
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Ziegler, Christoph. "Syntheses and Assemblies of Noble Metal Nanostructures." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-101781.
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Shape and size control as well as the control of the assembly of nanostructures are current challenges in nano sciences. Focussing on metal nanostructures all of these aspects have been addressed in the frame of the present work. It was possible to develop a new aqueous seeded growth method that produces gold nanoparticles with adjustable diameters over a large range of sizes. The spherical particles obtained show very low polydispersities and a good long term stability. Furthermore it was possible to reveal the growth mechanism of these particles utilizing electron microscopy and optical investigations coupled with theoretical calculations. It was found that there is a formation of small nucleation sites on the surface of the seeds in the beginning of the growth process. These sites then subsequently grow into "blackberry-like" intermediate particles. A final intraparticle ripening step leads to smooth and uniform spherical gold nanoparticles. By correcting the dielectric function of gold for charging and the free mean path effect and taking into account the particle size distribution it was possible to accurately model the optical properties of the gold sols obtained using Mie theory.
By controlling the concentration of chloride ions it was possible to influence both the ripening of the "blackberry-like" shaped particles and the morphology of gold nanoparticles. An increased concentration of the chloride ions in the standard citrate reduction procedure leads to larger and elongated particles, whereas the complete removal of the chloride ions made it possible to obtain star shaped, decahedral and \"desert-rose\" shaped particle morphologies. Using the layer-by-layer technique gold nanoparticles of different sizes could be immobilized on glass substrates. The surface-enhanced Raman scattering intensity of these mixed films were about 60% higher than compared to a film made of a single particle size. The optical properties were further investigated by comparing experimentally obtained UV/Vis spectra with generalized Mie theory simulations.
Additionally it could be shown that tetrazole and its derivatives are suitable stabilizing agents in the aqueous synthesis of silver nanoparticles. It was found that depending on the tetrazole derivative used the tendencies of the nanoparticles to agglomerate vary significantly. Different agglomeration stages have been investigated by UV/Vis and Raman spectroscopy. The removal of the ligands used and a resulting improvement of the applicability of the silver nanostructures as SERS substrates is still a challenge.
In the last part of this work the focus was changed from the optical properties of noble metal nanoparticles to their catalytic properties. Therefore gold and palladium nanoparticles have been successfully immobilized on highly porous zinc oxide aerogels. It was possible to synthesize sponge-, flake-, and ribbon-like zinc oxide gels with high specific surface areas. The facile approach of generating mixed metal oxide/noble metal aerogels is very promising for the preparation of highly selective and highly active heterogenous catalysts. First catalytic investigations of a sponge-like palladium loaded zinc oxide aerogel toward the semi-hydrogenation of acetylene showed very high selectivities of up to 85%.
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Silva, Patrícia Rodrigues da. "Lanthanide-organic frameworks for optical and catalytic applications." Doctoral thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/11659.
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Doutoramento em QuímicaEste projecto de doutoramento tem como objetivo isolar e caracterizar sistematicamente novos polímeros de coordenação, no estado sólido. A presença de grupos rígidos possuindo, em particular, átomos de oxigénio e de azoto, deverá induzir interessantes propriedades fotoluminescentes (rendimentos quânticos e tempos de vida elevados, assim como vias de transferência de energia eficientes), que poderão permitir a utilização dos compostos poliméricos na produção de dispositivos funcionais. As diferentes abordagens sintéticas foram ajustadas para cada material e basearam-se, preferencialmente, nas sínteses hidrotérmicas e nas assistidas por radiação de microondas. A estrutura dos materiais foi elucidada a partir de métodos de difracção de raios X (de cristal único ou de pós) em conjunto com outras técnicas, tais como RMN de estado sólido, microscopia eletrónica, análises térmicas, espectroscopia vibracional e estudos de composição elementar. Os compostos microcristalinos foram sistematicamente estudados a fim de investigar outras propriedades além das de fotoluminescência. Alguns dos materiais revelaram multifuncionalidade apresentando simultaneamente tempos de vida na ordem dos milisegundos, elevados rendimentos quânticos e elevado desempenho como catalisadores heterogéneos. As propriedades magnéticas de um composto baseado em érbio foram igualmente estudadas, assim como as de adsorpção e permuta de solvente de uma estrutura porosa baseada em cério.
This PhD programme aims to systematically isolate and characterise, in the solid state, novel coordination polymers. The presence of rigid groups having, in particular, oxygen and nitrogen atoms, is expected to induce interesting photoluminescent properties (high quantum yields and lifetimes, e cient energy transference pathways) which may allow the use of the polymeric compounds in the production of functional devices. Synthetic approaches have been ne-tuned for each material and were preferably based on hydrothermal and microwave-assisted syntheses. The structure of the materials was elucidated from X-ray di raction methods (single-crystal or powder data) in tandem with other techniques such as solid-state NMR, electron microscopy, thermal analyses, vibrational spectroscopy and elemental composition studies. The microcrystalline compounds were systematically studied in order to investigate other properties besides the photoluminescence. Some of the materials revealed multifunctional behaviour since they presented simultaneously life times in the order of milliseconds, high quantum yields and high performance as heterogeneous catalysts. The magnetic properties of an erbium-based compound were also studied, as well as the adsorption and solvent exchange behavior of a porous structure based on cerium.
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Bi, Melody. "Characterization and Catalytic Properties of Sulfated Zirconia." TopSCHOLAR®, 1996. http://digitalcommons.wku.edu/theses/895.
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Sulfated zirconia has attracted extensive attention due to its superactivity to isomerize alkane and alkenes. Platinum or iron/manganese promoted sulfated zirconia has been shown to increase the reaction rate. These catalysts are normally activated to 650-725°C in air before use. Through on-line analysis of evolved gas species during dynamic heating of the catalysts, some significant information can be obtained concerning the activation mechanism. In the present investigation, combined TG-FTIR, TG-MS and TGDTA techniques were utilized to measure the weight loss of the samples, analyze the evolved gas species and to monitor the phase transformation temperature of the solid. Four samples [(1%) 5% Pt/S04 2-VZr02, 2% Fe/0.5% Mn (iron(III)nitrate, maganese(II) nitrate treated/iron(III) sulfate, maganese(II) sulfate treated)/S04 2-/Zr02] were studied by thermal analysis. Also, the catalytic activity of 0.4% Pt/S04 2-/Zr02 was evaluated the isomerization and oligomerization of 1-hexene. It was found that this type of catalyst has high catalytic activity even at ambient and subambient temperatures.
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Simmons, Donald Karl. "Acid catalytic properties of metallosilicate molecular sieves." Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/10151.
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Carabineiro, Hugo. "Structure and catalytic properties of tungstated zirconia." Paris 6, 2005. http://www.theses.fr/2005PA066122.
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Raj, A. "Catalytic properties of some metallosilicate molecular sieves." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 1993. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/3065.
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Urban, Joanna. "Optical and vibrational properties." Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30092.
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Les matériaux bidimensionnels avec une faible symétrie, conduisant à une anisotropie dans le plan des propriétés électroniques et optiques sont particulièrement intéressants du point de vue de l'application. Dans cette thèse, les propriétés optoélectroniques de trois matériaux stratifiés à anisotropie dans le plan, phosphore noir, disulfure de rhénium et franckéite, sont étudiées par spectroscopie optique. Le phosphore noir (BP), avec une structure orthorhombique plissée, présente une anisotropie significative dans le plan et une bande interdite directe qui varie fortement selon le nombre de couches. Un obstacle important du point de vue de la réalisation de dispositifs basés sur BP est sa dégradation dans les conditions ambiantes, qui peut être évitée par encapsulation, par exemple en utilisant du nitrure de bore hexagonal (h-BN). Nous avons étudié les propriétés vibratoires du phosphore noir encapsulé dans le h-BN à l'aide de la spectroscopie Raman et nous présentons ici la première observation expérimentale d'un nouveau pic théoriquement prévu légèrement au-dessus du mode A1g. Nous expliquons son apparition par une différence des fréquences de modes vibratoires dans les couches internes et les couches de surface, et nous discutons de cet effet dans le contexte du fort couplage entre couches dans BP et de l'influence de l'encapsulation sur les propriétés du réseau cristallin. La deuxième partie de cette thèse présente les résultats d'études de photoluminescence du disulfure de rhénium avec une épaisseur de quelques couches atomiques. La réponse optique de ReS2 est dominée par deux excitons anisotropes énergétiquement non dégénérés X1 autour de 1,55eV et X2 autour de 1,57 eV qui peuvent être observés en absorption et émission de la lumière polarisée linéairement. Une controverse existe sur le caractère de bande interdite de ReS2, en particulier sur la présence d'un passage de gap direct à gap indirect avec la variation de l'épaisseur. Nous avons étudié l'émission polarisée liée aux états excitoniques à basse température en fonction du nombre de couches et comparé les résultats expérimentaux avec les prédictions d'un modèle cinétique décrivant la recombinaison radiative et la diffusion entre états excitoniques. Nous concluons d'une part que les caractéristiques observées en photoluminescence sont liées à l'émission des états excitoniques associés à une bande interdite directe, et d'autre part que la bande interdite fondamentale est indirecte. Nous proposons un modèle ou un état excitonique associé à une bande interdite indirecte de plus basse énergie assiste au dépeuplement des états excitoniques directs. Sa présence explique l'intensité d'émission relativement faible et le rapport d'émission X1et X2observé.La franckéite, un minéral sulfuré complexe, a attiré l'attention en tant qu'hétérostructure na-turelle de type II composée de couches alternées pseudohexagonales et pseudotétragonales. Le caractère incommensurable des deux réseaux mène à une ondulation unidimensionnelle. La dernière partie de cette thèse décrit notre observation de la dépendance de polarisation anormale des modes Raman dans les couches de franckéite exfoliées, ce qui suggère la présence d'une anisotropie optique. L'observation de cette dépendance de polarisation pourrait être utilisée comme une méthode rapide et non invasive pour identifier la direction des ondulationsAtomically thin layered materials with low symmetry which leads to in-plane anisotropy of electronic and optical properties are particularly interesting from the point of view of applications. In this thesis, the optoelectronic properties of three layered materials within-plane anisotropy, black phosphorus, rhenium disulfide and franckeite are investigated using optical spectroscopy. Black phosphorus (BP), with a puckered orthorhombic structure, has significant in-plane anisotropy and a direct bandgap which varies strongly with the number of layers. A significant hindrance from the point of view of the realization of BP-based devices is its degradation in ambient conditions, which can be prevented by encapsulation, for example using hexagonal boron nitride (h-BN). We have investigated the vibrational properties of h-BN encapsulated black phosphorus using Raman spectroscopy and report the first experimental observation of a theoretically predicted new peak slightly above the A1g mode. We explain its appearance by a difference of the mode frequencies in the inner and surface layers and discuss this effect in the context of the strong interlayer coupling in BP and the influence of the encapsulation on the lattice properties. The second part of this thesis presents the results of photoluminescence studies of few-layer rhenium disulfide. The optical response of ReS2is dominated by two energetically nondegenerate anisotropic excitons X1around 1.55 eV and X2 around 1.57 eV which can be observed in polarized absorption and emission. A controversy exists regarding the nature of the fundamental bandgap of ReS2, in particular the presence of a crossover from indirect to direct bandgap with changing thickness. We have studied the polarized emission related to the excitonic states at low temperature as a function of the number of layers and compared the experimental results with the predictions of a kinetic model describing the radiative recombination and scattering between excitonic states. We conclude that the features observed in photoluminescence arise due to hot emission from direct excitonic states and that a smaller, indirect bandgap and a related excitonic state are responsible for the depopulation of the direct states, the relatively weak emission intensity and the observed X1and X2 emission ratio. Franckeite, a complex sulfide mineral, has attracted attention as a natural type-II heterostructure composed of alternating pseudo-hexagonal and pseudo-tetragonal layers. The incommensurate character of the two lattices leads to one-dimensional rippling. The last part of this thesis describes our observation of anomalous polarization dependence of the Raman modes in exfoliated franckeite flakes, which suggested the presence of optical anisotropy and could be used as a rapid and non-invasive method to identify the rippling direction
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Gleeson, H. F. "Optical and electro-optical properties of chiral mesophases." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383374.
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Alshammary, Marzook. "Optical and magneto-optical properties of doped oxides." Thesis, University of Sheffield, 2011. http://etheses.whiterose.ac.uk/2066/.
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This study aimed to understand the optical and magneto-optical properties of pure, transition metals doped, and tin and transition metals co-doped In2O3 thin films grown in various growth conditions, and aimed to investigate the role of the oxygen defect states in every situation. Indium oxide doped with magnetic transition metals is a promising material for spintronics. This study presents results on the magnetic, transport, optical and magneto-optical properties of thin films of pure and transition metal (Fe,Co) doped In2O3 investigated at different transition metal concentrations and at different growth conditions. The optical and magneto-optical measurements at low temperature confirmed the formation of the defect states associated with oxygen vacancies within the forbidden range of the optical band gap energy of In2O3 and located below the conduction band. The density of the donor states is tuned using the oxygen partial pressureto give oxygen vacancies or by doping with tin; this gives control over the carrier concentration in the system as well as affecting the magnetic properties. This study developed optical and magneto-optical systems and undertook the world's first optical and magneto-optical measurements of In2O3. A new lab-based alternative technique to the Extended X-ray Absorption Fine Structurewas developed to identify the existence of magnetic nanoparticles in addition to provide the fraction and the contribution of these nanoparticles to the magnetisation and magneto-optical properties. The Maxwell-Garnett analysis of magnetic circular dichroism was used to obtain quantitative measures of the amount of defect phases present for Co metal. Similar to Maxwell-Garnett analysis, a new equation for Fe3O4 nanoparticles was developed in this study. This magneto-optical method was found to be more precise than EXAFS in determining the fraction and the contribution of nanoparticles to the total response of the system. However, these nanoparticles disappeared when thin films were co-doped with tin, indicating that doping with Sn not only introduced more carriers but also inhibited the growth of defect phases in semi magnetic semiconductor thin films. Finally, this study identified the origin of the magnetism in the class of magnetic oxides whereferromagnetism originated from the polarized electrons in localized donor states associated with the oxygen vacancy defect.
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Hathcock, David Jackson. "Dynamic and Catalytic Properties of Some Metallic Nanoparticles." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5134.
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Using a variety of techniques including femtosecond transient absorption spectroscopy, optical absorption, atomic force microscopy, the hot electron cooling dynamics of lithographically prepared gold nanoarrays, the effect of the surrounding environment, and the phonon oscillations of gold and silver nano-arrays were investigated. The cooling dynamics of gold nanoarrays on a glass substrate were found to be different from those of either colloidal nanodots in colloidal solution or films on glass substrate. The electron-phonon component of the electronic relaxation in the arrays was found to be longer than that in the dots or the films. The spatially isolated nanoarray particles experience a significantly different environment than the gold nanodots in solution, thus the long phonon-phonon component resulting from the coupling of particles to the medium, is not observed. The catalytic effectiveness of platinum nanoparticles for the hydrogenation of propene was investigated. The system with platinum particles was found to have a slightly lower activation energy than other systems in the literature. The effect of encapsulating the platinum particles in alumina was also investigated and it was found that the activation energy for the reaction was even lower. The effect of adding platinum, palladium, and rhodium particles to the proton exchange membrane of polymer electrolyte fuel cells, on the output power of the cells was also investigated. The effects of pH and precursor salt concentration, and particle composition were also investigated.
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Stanbridge, Nicholas Henry John. "Physical and catalytic properties of high silica faujasites." Thesis, University of Nottingham, 1995. http://eprints.nottingham.ac.uk/13649/.
Full textAbstract:
The research described in this thesis was conducted over a total of three years during the period October 1990 to October 1994, and is the sole work of the author, unless indicated otherwise by reference. A series of mildly dealuminated Y zeolites has been prepared by hydrothermal treatment using a low partial pressure of water vapour. These materials, together with samples previously dealuminated under more severe conditions, were characterised by the temperature programmed desorption of ammonia and the catalytic activity for suitable test reactions. Advances in technique permitted simultaneous monitoring of both the deammoniation and dehydroxylation processes. Interesting features were observed in the dehydroxylation traces which were related to changes in the acid site strength and amount of extraframework aluminium. The activity for both n-hexane cracking and toluene disproportionation reaches a maximum, corresponding to a framework concentration of 25-30 structural aluminium atoms per unit cell, consistent with the maximum number of strong acid sites. Slight deviation from this behaviour was noted, with the mildly steamed catalysts having lower activities than would be expected on the basis of their framework compositions alone. An in-depth analysis of the cracking of n-hexane has revealed that the extent of reaction is also critically dependent on the density of the available acid sites, which is explained in terms of the reaction mechanism. The disproportionation of toluene has highlighted differences in the nature of the extrastructural aluminium. The catalytic activity of the materials is either decreased or enhanced on extraction depending on whether the catalysts have been prepared by mild or severe dealumination. Variations in product distribution with time on stream have been observed and accounted for by changes in the reaction. The lifetime and activity profile of the catalyst could be altered by exposure of the catalyst to small amounts of toluene prior to the main reaction. This supports the concept of active coke enhancing this reaction. Cumene dealkylation was found to proceed on weaker acid sites than the cracking of n-hexane and the disproportionation of toluene, although a maximum in activity was still observed. This indicates that the weakest sites are not capable of catalysing this reaction, and that some heterogeneity of site strength exists between strong and weak acid sites. The dehydration of propan-2-01 was confirmed as a reaction which assesses the total number of acid sites, regardless of strength. However, changes in the selectivity of the products with the strength of the acid sites were found, implying that the formation of di-isopropylether is favoured by strong sites. Deliberate coking of the catalyst surface by exposure to propan-2-01 at elevated temperatures was found to increase the measured activity, in addition to changing the selectivity almost entirely in favour of propene. Extraframework aluminium was found to play an important role in all of the reactions studied. This emphasises the view that although structural aluminium has the larger influence on the overall activity of a catalyst for a particular reaction, the nature of the extraframework aluminium cannot be overlooked.
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Gleeson, David. "Preparation, characterisation, catalytic properties of novel mesoporous materials." Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265634.
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Linaza, Sabin. "Catalytic properties of antibodies in [4+2] cycloaddition." Thesis, University of Strathclyde, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248702.
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Jacobsen, S. M. "Chemical, catalytic and spectroscopic properties of titanium (II)." Thesis, University of Strathclyde, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381356.
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Xu, Jiahui. "Catalytic properties of nano ceria in heterogeneous catalysis." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:02e68ff9-ce28-475a-bd08-6b60bcda64e7.
Full textAbstract:
There have been many applications of cerium oxide in oxidation catalysis but the understanding of its role in catalysis is rather limited. This research is concerned with the use of nano-size cerium oxide in methane steam reforming reaction. It is found that addition of cerium oxide to the commercial supported Ni catalysts can dramatically reduce the undesirable carbon deposition (through surface oxidation), which is thermodynamically favorable under low steam conditions. In order to understanding the fundamental role of oxidation activity of the cerium oxide, different sizes of nano-crystallined cerium oxides have been carefully prepared by micro-emulsion technique. Their reactivity is clearly shown to be size dependent. We found that ceria particle sizes of lower than 5.1 nm are able to activate molecular oxygen, which accounts for the unprecedentedly reported critical size effect on oxidation. Characterizations by EPR, XPS, TPR suggest that a substantially large quantity of adsorbed oxygen species (O2 -) is preferentially formed in the small size ceria from air. Also, it is found that the oxygen vacancies are formed in the interface of metal and oxide, and the strength of the metal oxide interaction may influence the formation of the efficient oxygen vacancies, which are responsible for the adsorbed surface oxygen.
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Lee, Adam Fraser. "Structural and catalytic properties of bimetallic Pd systems." Thesis, University of Cambridge, 1995. https://www.repository.cam.ac.uk/handle/1810/273061.
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Măicăneanu, A. "Atomistic simulation of oxide materials with catalytic properties." Thesis, Department of Environmental and Ordnance Systems, 2009. http://hdl.handle.net/1826/3249.
Full textAbstract:
When supported, thin films demonstrate remarkable structural
transformations, with important implications for catalysis, sensors,
electrochemistry, semiconductors or superconductors. At present, the tools
available to characterize solid-solid systems cannot provide atomic level
resolution of, for example mixed screw-edge dislocations. Therefore
atomistic simulation can provide an invaluable complement to experiment.
In this work atomistic simulation was employed to generate models
of oxide thin films. First an atom deposition methodology was used to create
an SrO thin film on a BaO(001) support. The evolution of the thin film from
small clusters (submonolayer coverage), to five atomic layers, which
includes cracks in its structure, was studied. Specifically, information
related to growth and nucleation processes can be explored using this
methodology.
Secondly an amorphisation and recrystallisation methodology was
developed to explore the more complex system, that of ceria deposited on
zirconia and yttrium stabilized zirconia. Simulated amorphisation and
recrystallisation involves forcing the thin film to undergo a transformation
into an amorphous state prior to recrystallising and therefore the
recrystallisation process rather than the (perhaps artificial) initial structure
will dictate the final structure. The recrystallisation process enables the
evolution of all the important structural modifications as the thin film
evolves structurally in response to the support. These include dislocations
(pure edge and mixed screw-edge), dislocation networks, grain-boundaries
and defects (interstitials, vacancies and substitutionals, including complex
defect association) all within a single simulation cell.
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Dylla, Anthony Greg. "Synthesis, characterization and catalytic properties of bimetallic nanoparticles." College Park, Md.: University of Maryland, 2009. http://hdl.handle.net/1903/9609.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2009.Thesis research directed by: Dept. of Chemistry and Biochemistry. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Cui, Jianyi. "Catalytic properties, densification and mechanical properties of nanocrystalline yttria-zirconia-based materials." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/41679.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Includes bibliographical references.
Alumina, titania, ceria and manganese oxide were either coated onto or doped in cubic 7 mol% Y203-ZrO2 (7YZ) nanocrystals to form nanocomposites for methane combustion. These novel catalysts were very active and thermally stable. In particular, 25 wt% Mn203-coated 7YZ and 25 wt% Mn203-doped 7YZ showed remarkably low light-off temperatures of 3750C and 3580C, respectively. These catalysts were highly attractive as they were competitive with the much more expensive supported noble metal catalysts. Their catalytic activity could be attributed to the availability of active surface oxygen species, which facilitated the methane activation at low temperatures. Nanocrystalline 3 mol% and 8 mol% Y203-ZrO2 (3YZ and 8YZ) were successfully densified with an ultrafine grain size of < 90 nm by pressureless sintering at 11000C and 11500C, respectively. The low-temperature sinterability could be attributed to the well-defined nanocrystalline particles obtained via hydrothermal synthesis, and the effective elimination of secondary porosity through the dry compact processing. Submicron-sized 3 mol% Y203-ZrO2 ceramics with a grain size of - 150 nm was also obtained with commercial TOSOHC powders. Grain growth during densification of TOSOH© powders was successfully suppressed by presintering to 93% density under an argon atmosphere, followed by hot isostatic pressing at a temperature lower than the presintering temperature. The grain sizes of dense 3YZ and 8YZ ceramics were controlled between 100 nm and 5 glm. This allowed for the systematic study of 3YZ and 8YZ in indentation hardness, Young's modulus and fracture toughness as a function of grain size through micro-indentation and instrumented nano-indentation.
(cont.) The Hall-Petch effect was found to be extended to the nanocrystalline regime for 3YZ. 8YZ showed the Hall-Petch effect only in the micrometer and submicrometer regime. Maximum Hv values of 19 and 20 GPa were achieved for 3YZ and 8YZ, respectively. A continuous decrease in Young's modulus with decreasing grain size was observed in both 3YZ and 8YZ. This could be partially explained by the percolation theory. Transgranular fracture was observed in 3YZ as the grain size approached - 100 nm. This was in contrast with the dominant intergranular fracture mode observed in ceramics with fine grain sizes. Transgranular fracture was found in 8YZ over an even broader range of grain sizes (150 nm to 5.0 glm). A significant reduction in fracture toughness from 7.9 MPam-1/2 to 3.1 MPa-m1/2 was observed as the grain size was reduced from 1.1 im to 100 nm in 3YZ. Fracture toughness was much lower for 8YZ than for 3YZ, and showed little dependence on grain size. The stability of tetragonal phase at small grain sizes could account for the considerable reduction in the fracture toughness in 3YZ, and the transgranular fracture mode as grain size approached 100 nm.
by Jianyi Cui.
Ph.D.
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Millesi, Salvatrice. "Assembly of Functional Nanostructures for Optical, Electrical or Catalytic Systems." Doctoral thesis, Università di Catania, 2016. http://hdl.handle.net/10761/3962.
Full textAbstract:
The aim of this PhD thesis is the fabrication and study of nanostructures showing optical, electrical or catalytic properties in the perspective of applications in different fields of the nanotechnology. An important aspect is represented by the method we used to manufacture these nanostructures. In fact, all synthesized systems are based on the covalent assembly of discrete molecules (organic molecules or inorganic complexes) on inorganic surfaces. The present molecules (building blocks) show interesting properties e.g. optical or catalytic activity, while the substrate materials are appropriate for applications of the final structures in the optoelectronic, microelectronic or catalytic industries.
Often, by changing just the inorganic substrate the same covalently assembled building blocks exhibit different properties and this is an evidence of the fact that single-molecules properties can be affected by the substrate nature upon anchoring. For example, anchoring of optically active molecules such as porphyrins to Si(100) substrates allows to exploit optoelectronic properties while the same porphyrin molecules on SnO2 and TiO2 nanocrystals provide electron injection on the semiconducting surfaces useful for photovoltaics.
Moreover, we also investigated optical active surfaces upon the self-assembly of porphyrin molecules functionalised with luminescent Eu(III) complexes in order to exploit the mutual interaction of systems whose luminescence is based on different mechanisms. In the same context, we functionalised a covalent polystirene film on a quartz substrates with an Eu(III) complex to examine the possibility to obtain tunable light emitting properties useful to transfer optical information.
The covalent assembly of porphyrins and Eu(III) complexes can be applied also to electroactive substrates as CdO, ITO, ZnO, etc. in the perspective of microelectronic applications. For this reason we optimized the deposition of high conducting CdO thin films by a metallorganic chemical vapour deposition route.
Finally, we studied the activity of some (salen)Mn(III) molecules covalently assembled on glass beads in the epoxidation of unfunctionalised prochiral olefins with the aim of increasing the catalytic behaviour upon heterogeneization thus obtaining huge turnover numbers.
In summary the most important achievement of this thesis is to have demonstrated that the covalent assembly of suitable molecules on appropriate inorganic surfaces allows the synthesis of molecular architectures showing unique properties appealing for future technologies.
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Papapanayotou, I. "Chemical properties and optical properties of carbonaceous particles." Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383288.
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Auguié, Baptiste. "Optical properties of gold nanostructures." Thesis, University of Exeter, 2009. http://hdl.handle.net/10036/73955.
Full textAbstract:
The optical properties of gold in the visible are dominated by the response of the free conduction electrons to light. In gold nanostructures, the surface charge density adopts a configuration that is constrained by the shape of the nanoparticles. As a result, the scattering of light by gold nanoparticles exhibits a resonant response characterised by a strong scattering and absorption in a narrow range of frequencies. The spectral range of this \emph{localised surface plasmon resonance} (LSPR) can be tuned by varying the size and shape of the gold nanoparticle --- the nanoparticles act as nanoscale antennas for the visible light. Confirmation of this scaling rule is obtained by conducting experiments with nanoparticles of varying size and aspect ratio. Such particles are fabricated by electron-beam lithography, and characterised by dark-field spectroscopy. Not only does the LSPR shift in frequency with a change of particle size, but its spectral lineshape is also modified. The intensity and width of the LSPR are dictated by a variety of factors that are related to the intrinsic material properties (the complex dielectric function of gold), and to the particle geometry and environment. The optical response of small gold nanorods is well described by a simple oscillating dipole model --- the incident electromagnetic field induces a current in the particle that re-radiates light (scattering). A series of refinements can be made to model more accurately the optical response of realistic particles. If the dipole moment characterising the particle is allowed to vary in phase across the particle, retardation effects provide a correction for the effective dipole moment of the particle. As the particle size approaches the wave length in the surrounding medium, the dipolar approximation breaks down and higher order multipoles need to be considered. The Mie theory provides a very accurate description of the response of spheres of arbitrary size. Further, the T-matrix and other numerical techniques can be employed to accurately reproduce the scattering properties of particles of arbitrary shapes. When the scattering sample consists of a collection of gold nanoparticles, the collective optical response is affected by two key factors. First, the measured LSPR is a convolution of the distribution of particle sizes with the individual response of a single particle. This leads to an inhomogeneous broadening of the LSPR lineshape. Second, the light that is scattered by one such particle near resonance can strongly affect its neighbours which scatter light in proportion to the net field they experience, that is the sum of the incident field plus the perturbation arising from the neighbouring particles. The onset of such multiple scattering events is observed even for particle separations that are several times larger than the particle size. Several regimes of interaction can be distinguished according to the ratio separation / wavelength. First, when the particles are in close proximity (separation $\ll$ wavelength), near-field interactions dominate and result in a spectral shift of the LSPR accompanied with a spectral broadening. Second, when the separation is commensurate with the wavelength, a coherent interaction can develop that couples a large number of particles. In ordered arrays, such coupling gives rise to a geometrical resonance that can strongly affect the LSPR of the particles. In particular a sharp spectral feature is observed that depends on both the single particle response and the geometrical arrangement of the particles in the array. The coherence of such multiple scattering in diffractive arrays of gold nanoparticles can be broken by introducing disorder in the distribution of particle sizes, or in the particle positions. The optical properties of an irregular array reflect the departure from a periodic system and the spectral lineshape evolves as the level of disorder is increased. In the limit of uncorrelated positions, the diffractive coupling is suppressed and the response of the collection of the particles rejoins the response of isolated particles.
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Crook, Robert J. "Optical properties of organic waveguides." Thesis, University of Exeter, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359604.
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Zhou, Yuming. "Optical properties of living organisms." Thesis, Open University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301878.
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Wan, Wai Man Vivian. "Optical properties of conjugated polymers." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621328.
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Rosenow, Judith. "Optical Properties of Condensation Trails." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-205659.
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Persistent condensation trails are clouds, induced by the exhaust of an aircraft engine in a cold and ice-supersaturated environment. These artificial ice clouds can both cool and heat the atmosphere by scattering solar radiation and absorbing terrestrial radiation, respectively. The influence of condensation trails on the Earth-atmosphere energy balance and therewith the answer to the question of the dominating process had been mostly approximated on a global scale by treating the condensation trail as plane parallel layer with constant optical properties. Individual condensation trails and the influence of the solar angle had been analyzed, always using a course spatial grid and never under consideration of the aircraft performance, generating the condensation trail. For a trajectory optimization, highly precise results of the impact of condensation trails on the radiation budget and the influence of the aircraft performance on this impact is needed, so that future air traffic may consider the main factors of flight performance on the environmental impact of condensation trails. That’s why, a model is developed in this thesis to continuously estimate the scattering and absorption properties and their dependence on the aircraft performanceLanglebige Kondensstreifen sind Eiswolken, welche durch Kondensation von Wasserdampf an Rußpartikeln in einer eisübersättigten Atmosphäre entstehen. Der Wasserdampf entstammt einerseits aus dem Triebwerkabgas und andererseits aus der Atmosphäre. Kondensstreifen können die Atmosphäre durch Rückstreuung solarer Strahlung kühlen und durch Rückstreuung und Absorption terrestrischer Strahlung erwärmen. Der Einfluss von Kondensstreifen auf den Wärmehaushalt der Atmosphäre und damit die Antwort auf die Frage nach dem dominierenden Effekt wurde bisher zumeist auf globaler Ebene ermittelt, wobei der Kondensstreifen als planparallele Schicht mit konstanten optischen Eigenschaften angenähert wurde. Individuelle Kondensstreifen und der Einfluss des Sonnenstandes wurden bisher nur mithilfe eines groben Rasters betrachtet und niemals unter Berücksichtigung der Flugleistung des Luftfahrzeuges, welches den Kondensstreifen generiert hat. Für eine Trajektorienoptimierung sind jedoch präzise Berechnungen des Strahlungseinflusses und eine gewissenhafte Berücksichtigung der Flugleistung notwendig. Nur so kann der zukünftige Luftverkehr die Haupteinflussfaktoren der Flugeigenschaften auf den Strahlungseinfluss der Kondensstreifen berücksichtigen. Aus diesem Grund wurde in dieser Arbeit ein Modell entwickelt, welches die Eigenschaften des Strahlungstransfers durch den Kondensstreifen kontinuierlich bestimmt und die aus der Flugleistung resultierenden Parameter berücksichtigt
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Khan, Saima Ishfaque. "The optical properties of metamaterials." Thesis, University of Glasgow, 2016. http://theses.gla.ac.uk/7781/.
Full textAbstract:
This thesis studies the parametric investigation, polarisation dependence and characterization of fishnet structure at near infrared wavelengths. Detailed simulations are performed to understand the behaviour of the structure at near infrared and optical wavelengths. Simulations are performed to obtain negative refractive index of the fishnet structure formed from nanoimprint lithography (NIL) by taking into account the effect of substrate and polymethyl methacrylate (PMMA) beneath it. Two different structures have been designed and fabricated of varying dimensions using NIL and their resonant wavelength measured in the near infrared at 1.45 µm and 1.88 µm. Simulations suggest that a negative refractive index real part with the magnitude -0.24 is found at 1.53 µm and this decrease to a maximum magnitude of -0.57 at 1.9 µm. The PMMA and suppressed pillars are here responsible for the increasing material losses and limiting the value of negative refractive index. An analytical approach has been suggested to characterise fishnet structures at oblique incidence. The expressions for an absorbing medium are rewritten for an alternative definition of refractive index. The expressions are initially validated for a dielectric slab and a metal film. These results provide the possibility that this proposal may yield a general algorithm for obtaining the complex reflection and transmission coefficients for artificial structures. FDTD simulations have been extensively used in this thesis to understand the optical metamaterials and their characterization.
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González, Ganzábal A. (Alejandro). "Optical properties of leaf replicas." Master's thesis, University of Oulu, 2018. http://urn.fi/URN:NBN:fi:oulu-201808232657.
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In order to fulfill the increasing energy demand, several improvements can be done in already existing means of producing energy. Based on the idea of light harvesting, several main ideas of optimizing natural leaves (or even creating from a master), such as morphology, super-hydrophobity and waterproofing, among others, have been analyzed.
Experimentally, it has been shown that by means of applying natural coatings of wax (from bilberry and lingonberry) onto the surface of silicon and PDMS the reflectance varies in the visible spectrum. In the case of silicon the reflectance decreased on average 17.5% in the case of the bilberry wax and 18.4% for lingonberry wax. For PDMS, the curves were more complex and implied an increase of reflectance of 1.3% for bilberry and 2.4% for lingonberry.
Finally, a Scanning Electron Microscope imaging experiment was carried out, revealing that for a film coating of wax bigger specks formed (circa 0.1 mm), thus leading to the conclusion that a spin coating is the best option to achieve optimal properties, since the smaller specks would not override other applied coating and natural properties.
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Lee, Timothy. "Nonlinear properties of optical microfibres." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/355529/.
Full textAbstract:
Glass microfibre waveguides offer an intriguing platform for the investigation of nonlinear effects, due to their high effective nonlinearity which arises from the tight modal confinement down to dimensions comparable to the wavelength of guided light. This thesis presents theoretical and experimental work towards achieving efficient third and second harmonic generation in silica microfibres, as well as in microfibre loop resonators for enhancing the conversion. Since microfibre resonators themselves exhibit interesting nonlinear behaviour, the polarisation dependent properties of microcoil resonators were also studied. Efficient third harmonic generation is possible through intermodal phase matching, and experiments using short tapers have demonstrated significant efficiencies up to 10
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Molloy, Peter J. "Optical properties of concentrated dispersions." Thesis, London Metropolitan University, 1986. http://repository.londonmet.ac.uk/2939/.
Full textAbstract:
Apparatus and methods have been developed to measure the diffuse transmittance T and reflectance R of multiple scattering, concentrated, colloidal dispersions. The variation of R and T with pathlength, wavelength, and concentration has been investigated for non-spherical particles in concentrated dispersions, over a range of pH and surfactant concentrations. Measurements of diffuse transmittance and reflectance required large corrections to be made for the presence of any specular interfaces i.e. windows. These corrections were minimised by developing a bifurcated fibre optic bundle reflectance method, which allowed R and T to be measured at volume fractions up to at least 0.3. Using magnetic, acoustic and shear fields to align the non-spherical kaolinite particles changes In R and T were measured at volume fractions upto 0.3. The amplitude of the changes and the relaxation of the changes Induced by the applied fields were measured. The amplitude of the change was found to vary strongly with pH and surfactant concentration. For any particular face diameter platelet, the amplitude of the change followed closely the flocculation process, and was sensitive to the mode of particle-particle aggregation, e.g. face-face, or face-edge. The amount of surfactant per unit mass of kaolinite required to stabilise dispersions Is found to vary with particle size and concentration. This showed that information about particle orientation can be obtained through multiple scattering systems when subjected to an aligning field. Kubelka-Munk two flux theory was used to relate R and T to the diffuse flux scattering parameter S. A simple theory was developed relating S to the size shape and orientation of the non-spherical particles, hence allowing the particle orientation to be determined for any aligning field The insight Into particle behaviour given by the optical method Is superior to that given by rheology alone, which does not provide an unambiguous measure of the mode of particle alignment.
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Black, Serra Ashley Phillip. "New oxynitride materials with luminescent, magnetic and catalytic properties." Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/405378.
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En les darreres dècades els oxinitrurs han rebut un interès creixent degut al vast rang d'aplicacions en els quals han mostrat una aplicabilitat potencial. Destaquen les seves propietats com fotocatalitzadors actius en el visible en processos de fotòlisi d'aigua, pigments inorgànics no tòxics, fòsfors per a LEDs (light emitting diodes) de llum blanca, materials amb magneto resistència colossal i materials dielèctrics o ferroelèctrics.
En aquesta tesi presentem la síntesi i caracterització de dos nous fòsfors amb potencial aplicació en tecnologia LED de llum blanca. Els oxinitrursilicats LaSrSiO3N i LaBaSiO3N quan són activats amb Eu2+ emeten llum de color vermell ataronjat sota excitació amb radiació blava o UV. La solució sòlida Sr2-xLaxSiO4-xNx (0 ≤ x ≤ 1) es pot obtenir per la substitució concomitant de Sr2+ per La3+ i O2- per N3- en l’òxid Sr2SiO4. Mitjançant el control de la composició, es pot modificar el color de l'emissió des del grog (x = 0.2) fins a vermell ataronjat (x = 1) quan es dopa amb Eu2+ i des del blau verdós (x = 0.2) fins taronja groguenc (x = 1) quan es dopa amb Ce3+.
D'altra banda, aquesta tesi també ha tingut com a objectiu la síntesi i estudi de nous oxinitrurs amb estructura de perovskita extenent el rang d’aquest grup de compostos als metall de transició Cr i Hf.
Les perovskites LnCrO3-xNx amb Ln = La, Pr, Nd i continguts de nitrogen fins x = 0.59 van ser sintetitzats per mitjà de la amonòlisis dels precursors LnCrO4. La substitució d'oxigen per nitrogen indueix l'oxidació de Cr3+ a Cr4+ com a mecanisme de compensació de càrrega i les conseqüències que comporta sobre les propietats magnètiques han sigut investigades. El dopatge amb forats en les perovskites LnCrO3 produït mitjançant la substitució dels anions O2- per N3- suprimeix l'ordre magnètic però menys dràsticament que quan és induït per la substitució catiònica de Ln3+ per M2+ (M = Ca, Sr ).
Finalment, presentem la síntesi, caracterització estructural i l'estudi de les propietats elèctriques i fotocatalítiques dels nous oxinitrurs amb estructura de perovskita de hafni LnHfO2N (Ln = La, Pr, Nd, Sm) i del compost anàleg LaZrO2N. Aquests materials cristal·litzen en una estructura ròmbica de tipus GdFeO3 i presenten band gaps entre 3.4 i 2.8 eV. L'evolució d'H2 i O2 produïda sota la il·luminació amb radiació d'un llum de Xenó de 300 W va demostrar que les perovsquites de hafni tenen els potencials de reducció i oxidació adequats per dur a terme dissociació de la molècula d'aigua en presència dels convenients agents de sacrifici. Les mesures de permitivitat dielèctrica i resistivitat elèctrica van mostrar que els compostos LnHfO2N (Ln = La, Pr, Nd, Sm) són aïllants elèctrics amb constants dielèctriques entre 16 i 30 a temperatura ambient.In recent years oxynitride materials have received increasing attention because of their emerging applications as photocatalysts, phosphors, pigments, dielectrics and magnetic materials. This thesis reports the synthesis and characterization of two new oxynitride phosphors with potential application in warm white light LED technologies. The new compounds LaSrSiO3N and LaBaSiO3N activated with Eu2+ are orange-red light-emitting luminescent materials under excitation in the UV-blue range. We also report that the solid solution Sr2-xLaxSiO4-xNx (0≤ x ≤1), can be obtained by concomitant substitution of Sr2+ by La3+ and O2- by N3- in Sr2SiO4. By controlling the composition the emission colours can be tuned from yellow (x = 0.2) to orange-red (x = 1) for Eu2+ phosphors and from blue-green (x = 0.2) to orange-yellow (x = 1) in Ce3+ doped samples. On the other hand, this thesis has been directed towards the synthesis and study of new oxynitride perovskites extending the range of this group of compounds to the transition metals Cr and Hf. LnCrO3-xNx perovskites with Ln = La, Pr and Nd and nitrogen contents up to x = 0.59 have been synthesised through ammonolysis of LnCrO4 precursors. Nitride substitution induces oxidation of Cr3+ to Cr4+ as the mechanism of charge compensation and the consequences of this on magnetic ordering transitions have been studied. Hole-doping through O2-/N3- anion substitution suppresses magnetic order but far less drastically than Ln3+/M2+ (M = Ca, Sr) cation substitutions. Finally, we show the synthesis, structure, electrical and photocatalytic properties of new hafnium oxynitride perovskites LnHfO2N where Ln= La, Pr, Nd and Sm, and the previously reported analogous compound LaZrO2N. They crystallize in the orthorhombic GdFeO3-type superstructure and show band gaps between 3.4 and 2.8 eV. The time course of O2 and H2 evolution under Xenon lamp 300 W irradiation showed that the hafnium perovskites have the adequate oxidation and reduction potential to conduct the overall water splitting reaction in presence of a sacrificial agent. Dielectric and resistivity measurements showed that both Hf and Zr perovskite oxynitrides are electric insulators with dielectric constants between 16 and 30 at room temperature.
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Roychowdhury-Saha, Manami. "Ribonucleic acid architecture dictates its binding and catalytic properties." [Bloomington, Ind.] : Indiana University, 2005. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3204290.
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Thesis (Ph. D.)--Indiana University, Dept. of Chemistry, 2005.Source: Dissertation Abstracts International, Volume: 67-01, Section: B, page: 0253. Adviser: Donald H. Burke. "Title from dissertation home page (viewed Feb. 9, 2007)."
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Duarte, M. A. "Structure and catalytic properties of platinum on vanadium oxides." Thesis, Brunel University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375486.
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Huang, Xing. "Structure and Catalytic Properties of Ultra-Small Ceria Nanoparticles." UKnowledge, 2014. http://uknowledge.uky.edu/cme_etds/25.
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Cerium dioxide (ceria) is an excellent catalytic material due to its ability to both facilitate oxidation/reduction reactions as well as store/release oxygen as an oxygen buffer. The traditional approach to assess and improve ceria's catalytic behavior focuses on how efficiently O-vacancies can be generated and/or annihilated within the material, and how to extend established understandings of "bulk" ceria to further explain the greatly enhanced catalytic behavior of ultra-small ceria nanoparticles (uCNPs) with sizes less than 10 nm. Here, using density functional theory (DFT) calculations, we reexamine the atomic and electronic structures of uCNPs, especially their surface configurations. A unique picture dissimilar to the traditional point of view emerges from these calculations for the surface structure of uCNPs. uCNPs similar to those obtained by experimental synthesis and applied in catalytic environments exhibit core-shell like structures overall, with under-stoichiometric, reduced CNP "cores" and over-stoichiometric, oxidized surface "shell" constituted by various surface functional groups, e.g.,-Ox and/or -OH surface groups. Therefore, their catalytic behavior is dominated by surface chemistry rather than O-vacancies. Based on this finding, reaction pathways of two prevalent catalytic reactions, namely CO oxidation and the water-gas shift reaction over uCNPs are systematically investigated. Combined, these results demonstrate an alternative understanding of the surface structure of uCNPs, and provide new avenues to explore and enhance their catalytic behavior, which is likely applicable to other transition metal oxide nanoparticles with multivalent ions and very small sizes.
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Ono, Luis. "IN-SITU GAS PHASE CATALYTIC PROPERTIES OF METAL NANOPARTICLES." Doctoral diss., University of Central Florida, 2009. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3277.
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Recent advances in surface science technology have opened new opportunities for atomic scale studies in the field of nanoparticle (NP) catalysis. The 2007 Nobel Prize of Chemistry awarded to Prof. G. Ertl, a pioneer in introducing surface science techniques to the field of heterogeneous catalysis, shows the importance of the field and revealed some of the fundamental processes of how chemical reactions take place at extended surfaces. However, after several decades of intense research, fundamental understanding on the factors that dominate the activity, selectivity, and stability (life-time) of nanoscale catalysts are still not well understood. This dissertation aims to explore the basic processes taking place in NP catalyzed chemical reactions by systematically changing their size, shape, oxide support, and composition, one factor at a time. Low temperature oxidation of CO over gold NPs supported on different metal oxides and carbides (SiO2, TiO2, TiC, etc.) has been used as a model reaction. The fabrication of nanocatalysts with a narrow size and shape distribution is essential for the microscopic understanding of reaction kinetics on complex catalyst systems ("real-world" systems). Our NP synthesis tools are based on self-assembly techniques such as diblock-copolymer encapsulation and nanosphere lithography. The morphological, electronic and chemical properties of these nanocatalysts have been investigated by atomic force microscopy (AFM), scanning tunneling microscopy (STM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). Chapter 1 describes briefly the basic principles of the instrumentation used within this experimental dissertation. Since most of the state-of-art surface science characterization tools provide ensemble-averaged information, catalyst samples with well defined morphology and structure must be available to be able to extract meaningful information on how size and shape affect the physical and chemical properties of these structures. In chapter 2, the inverse-micelle encapsulation and nanosphere lithography methods used in this dissertation for synthesizing uniformly arranged and narrow size- and shape-selected spherical and triangular NPs are described. Chapter 3 describes morphological changes on individual Au NPs supported on SiO2 as function of the annealing temperature and gaseous environment. In addition, NP mobility is monitored. Chapter 4 explores size-effects on the electronic and catalytic properties of size-selected Au NPs supported on a transition metal carbide, TiC. The effect of interparticle interactions on the reactivity and stability (catalyst lifetime) of Au NPs deposited on TiC is discussed in chapter 5. Size and support effects on the formation and thermal stability of Au2O3, PtO and PtO2 on Au and Pt NPs supported on SiO2, TiO2 and ZrO2 is investigated in chapter 6. Emphasis is given to gaining insight into the role of the NP/support interface and that played by oxygen vacancies on the stability of the above metal oxides. Chapter 7 reports on the formation, thermal stability, and vibrational properties of mono- and bimetallic AuxFe1-x (x = 1, 0.8, 0.5, 0.2, 0) NPs supported on TiO2(110). At the end of the thesis, a brief summary describes the main highlights of this 5-year research program.Ph.D.
Department of Physics
Sciences
Physics PhD
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Bartley, G. J. J. "Preparation and catalytic properties of zirconium pillared interlayer clays." Thesis, University of Reading, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379305.
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Davis, Jack B. A. "Elucidating the structures and catalytic properties of metallic nanoparticles." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/6297/.
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The publications contained within this thesis present the application and development of computational methods for the study of metallic nanoparticles and nanoalloys. Principally these studies are dedicated to their structural characterisation and their interactions with small molecules; vital first steps toward understanding their role in key catalytic processes. Publications have also assessed the applicability of statistical mechanical methods and dispersion corrected DFT to these studies. Palladium-iridium nanoalloys, which are under current investigation for their catalytic properties, are studied extensively using a range of computational methods. Their interactions with hydrogen and benzene are probed in order to better understand their role in tetralin hydroconversion and the preferential oxidation of CO. Structures are revealed to reflect the strongly demixing behaviour of the bulk alloy, with nanosize effects seen in their interactions with hydrogen. The Birmingham Parallel Genetic Algorithm is presented and applied to the direct density functional theory global optimisation of Iridium and both gas-phase and surface supported gold-iridium nanoparticles. The program is shown to be capable of overcoming previous size restrictions while characterising quantum size effects in the iridium and gold-iridium structures. Significant differences are seen between the surface supported and gas-phase gold-iridium structures.
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Islam, Shams Tania Afroza. "The catalytic properties of Fe-S cluster containing enzymes." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:eba9a2de-52fb-4da8-88e2-1fb0c2f69998.
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Many enzymes contain iron- sulfur (Fe-S) clusters which have a huge impact on their catalytic properties. These clusters may form part of the active site or form an electron relay system from the surface of the protein to the active site. Protein film electrochemistry (PFE) was utilized to elucidate the properties of some Fe-S cluster enzymes, namely, Hyd-1(a hydrogenase with an Fe-S electron relay), PceA (a reductive dehalogenase containing Fe-S clusters to facilitate electron transfer with redox partner) and CODH ICh and CODH IICh (carbon monoxide dehydrogenases with Fe-S electron relay systems and Ni-incorporated Fe-S clusters as active sites). The role of a proline residue at the active site in Hyd-1 was investigated and it was concluded that some local instability and adverse effect on H2 activation were introduced upon replacement of proline with an alanine residue. The PceA dehalogenase was studied with PFE in terms of their interactions with various substrates and inhibitors. Furthermore, a method for performing 'film correction' for liquid substrates as that of the dehalogenase was established. Aspects of the catalytic cycle and effects of oxygen (O2), peroxide (H2O2) and hydroxylamine (NH2OH), a nitrogen-containing peroxide analogue on CODH ICh and CODH IICh were investigated with PFE. Finally, Electrochemical Impedance Spectroscopy (EIS), a technique involving application of alternating current (AC), was added to the portfolio was PFE techniques to compare CpI and CrHydA1 (hydrogenases with and without Fe-S electron relay system, respectively) in terms of time-dependent and time-independent processes within them. A novel term, exchange catalytic rate, for expressing inherent proficiency of the enzyme at zero-current potential was proposed and quantified. A means for measuring electroactive coverage and theoretical turnover during catalysis in PFE experiments was developed.