Neste trabalho foi estudada a otimização de síntese de nanocristais de KY3F10 pelo método de co-precipitação utilizando óxidos de terras raras (TR2O3) dissolvidos em HCl ou seus cloretos (TRCl3), fluoreto de potássio (KF) e bifluoreto de amônio (NH4HF2) como materiais de partida. A composição inicial dos reagentes precursores nas proporções molares de 1KF:1YCl3:3NH4.HF2 foi estabelecida para a obtenção do material monofásico. Constatou-se também que a diminuição da concentração por evaporação da concentração de amônio contido na solução aquosa do bifluoreto de amônio foi essencial para garantir o sucesso deste método. Nanopós puros e dopados foram caracterizados com relação à sua estrutura cristalina, tamanho e forma dos cristalitos e presença de fases secundárias. Foram obtidos aglomerados de partículas contendo nanocristais aproximadamente esféricos com tamanhos em torno de 10 nm. Os dopantes incorporados foram estudados através de emissão óptica e seus mecanismos de transferência de energia foram comparados àqueles obtidos nos cristais volumétricos. Através deste estudo foi possível determinar a eficiência de emissão de nanocristais de KY3F10:Er, KY3F10:Nd, KY3F10:Eu e KY3F10:Yb:Nd:Tm com relação ao tamanho dos nanocristais e com relação ao efeito da adsorção dos reagentes precursores. A emissão do túlio (Tm3+) na região do azul, através do fenômeno de conversão ascendente, na amostra triplamente dopada (Yb/Nd/Tm), com excitação em 802 nm, foi obtida com sucesso. Um estudo preliminar das propriedades dosimétricas foi feito através da detecção da termoluminescência de pastilhas irradiadas com radiação gama e apresentaram picos termoluminescentes em torno de 180°C e 225ºC, além disso, verificou-se a reprodutibilidade e a linearidade da resposta às doses aplicadas. / In this work, it was studied the optimization of the synthesis of KY3F10 nanocrystals by the coprecipitation method using rare earth oxides ( TR2O3 ) dissolved in HCl or their chlorides (TRCl3), potassium fluoride (KF) and ammonium bifluoride (NH4HF2) as starting materials. The initial composition of the precursor reagents in molar proportions of 1KF:1YCl3:3NH4.HF2 was established for obtaining single-phase material. It was also established that the concentration reduction by evaporation of the ammonia contained in the ammonium bifluoride aqueous solution was essential to ensure the success of this route. Pure and doped nanopowders were characterized related to crystal structure, size and shape of the crystallites and to the presence of secondary phases. Agglomerates containing approximately spherical nanocrystals with size of around 10 nm were obtained. The incorporated dopants were studied by optical emission and their energy transfer mechanisms were compared to those obtained in volumetric crystals. Through this study, it was possible to determine the emission efficiency of KY3F10:Er, KY3F10:Nd , KY3F10:Eu and KY3F10:Yb:Nd:Tm with respect to the nanocrystals size and to the precursor reagents adsorption effect. The blue emission of Thulium (Tm3+) by upconversion in triply doped samples (Yb/Nd/Tm) was successfully obtained with excitation at 802 nm. A preliminary study was made of the dosimetric properties by detecting the thermoluminescence of irradiated pellets with gamma radiation and the curves showed peaks around 180°C and 225°C, moreover, reproducibility and linearity of the response to the doses applied were checked.

La perspective d'une société utilisant l'énergie de la lumière du soleil pour séparer la molécule d'eau en dihydrogène et en dioxygène, ces deux gaz servant de moyens de stockage et de vecteurs d'énergie, nécessite de nombreux développements. En particulier, il est nécessaire de choisir un matériau pouvant absorber la lumière et transférer son énergie aux charges électriques afin de générer un courant électrique. Parmi toutes les possibilités, ce mémoire étudie l'applicabilité des bâtonnets semiconducteurs de tailles nanométriques constitués d'un cœur de séléniure de cadmium et d'une coquille de sulfure de cadmium. Profitant des méthodes décrites ces dernières années et d'une méthodologie de fonctionnalisation, les objets obtenus présentent une grande monodispersité et peuvent être dispersés en milieu aqueux. Les propriétés photoélectrochimiques des nanobâtonnets sont explorées par microscopie électrochimique. Cette méthode permet de déterminer s'il y a un transfert de charge entre des molécules en solution et un substrat constitué des bâtonnets, et le cas échéant son sens. Ainsi les nanoparticules, soumises à une excitation lumineuse, transfèrent des électrons vers les molécules dans l'ensemble des cas explorés, révélant ainsi un caractère plus réducteur que la para-benzoquinone. Ce transfert est réalisé d'autant plus rapidement que le rapport entre la longueur et le diamètre des bâtonnets augmente, jusqu'à un optimum, mais aussi que la taille de la couche organique isolante les recouvrant diminue, comme l'ont révélé des suivis de réduction d'une sonde rédox moléculaire colorée, la résazurine. Ces charges ont été mises à profit pour fonctionnaliser les nanoparticules, au travers de la réduction d'un pont disulfure ou d'un sel d'or. Enfin des stratégies ont été explorées pour permettre aux particules de réaliser la réduction photosensibilisée de l'eau, au travers de la synthèse d'une cobaloxime, un catalyseur moléculaire, ou de la réduction de sels métalliques à propriété catalytique tels que le cobalt et le nickel. / The development of a society based on solar energy requires a way to store it. One possibility consists in water splitting that needs a material to collect and transform the energy contained in light beam in an electric charges movement. Among all possibility, we hereby explore the applicability of nanometers-sized semiconductor rods composed of a cadmium selenide core and a cadmium sulfide shell. Based on methods already developed and a new functionalization methodology, the obtained particles exhibit a high monodispersity and can be dispersed in water, a useful property for the final purpose. Their photo-electrochemical properties have been explored by electrochemical microscopy that allowed to determine whether there is charge transfer between mediators in solution and quantum rods deposited as substrate and its direction. It reveals that under light irradiation and in all cases herein experimented, they transfer electrons to the mediators, making them more reductive than para-benzoquinone. This transfer is fastened when the ratio between the length and the diameter of the rods increased until an optimum, but also when the width of the organic isolating shell decreases, as revealed by time-resolved reduction of resazurin, a colored rédox molecular probe. These charge transfer have been used to functionalize particles by reduction of a disulfide bridge or a gold salt. Finally, strategies have been explored to make these quantum rods able to photosensibilized water reduction through synthesis of a cobaloxime, a molecular catalyst, or metal salt reduction as cobalt and nickel known to exhibit catalytic activity.

Made available in DSpace on 2017-07-10T17:37:11Z (GMT). No. of bitstreams: 1 Jessica Cristina Urbanski Laureth.pdf: 1753789 bytes, checksum: 5516d92f3757c43a94720173f562bc89 (MD5) Previous issue date: 2016-02-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Edible coatings may assist improvement of quality and conservation of fruits. Polysaccharide polymers, such as starch, pectin and cellulose have been constantly used as base to form coatings, but their physical properties do not provide proper barrier to gas and water vapor diffusion. Cellulose nanocrystals, when incorporated to edible coatings may improve their barrier properties. The addition of a natural antioxidant to the coating may improve conservation capacity of fruit. Natural antioxidants have relative instability, which may limit its reducing properties. Nevertheless, including nanocrystals may aggregate higher stability to added antioxidant. Thus, the objective of this research was assessing the effect of polymeric coatings, along with cellulose nanocrystals and vegetable extract on the physiology of Persian lime. It consisted of two experiments, the first assessed the effect of pectin (PEC), starch (ST) and cellulose gum (CMC) polymers added to cellulose nanocrystals (CN). The second differed from the first due to the addition of peanut peel extract, chosen because it has higher rates of antioxidant activity by DPPH, ABTS and FRAP methods in comparison with extracts of Persian lime and Rangpur seeds. In both experiments the assessments occurred during nine storage days under 23 °C ± 2 °C. Ethylene, CO2, fresh mass loss, firmness and chlorophyll were assessed. In the second were included DPPH, ABTS and FRAP antioxidant activity analyses, as well as total phenolic composites and ascorbic acid. In the first experiment, coatings formed by CMC, PEC and ST pure polymers with their respective nanocomposites called NCMC, NPEC and NST were efficient to reduce ethylene production until first three storage days. Among tested treatments, NPEC nanocomposite (12.01 mg CO2 kg-1 h-1) was more efficient than PEC (14.93 mg CO2 kg-1 h-1) to inhibit CO2 diffusion. PEC polymer when reinforced by NC (NPEC) was the only coating to reduce fresh mass loss of Persian lime, and it was also more efficient than PEC pure polymer when it comes to retention of chlorophyll. All tested nanocomposites and pure polymers were similarly efficient to keep fruit s firmness. In the second experiment the combination of pectin, cellulose gum, nanocrystals and extract was responsible to present lower ethylene and CO2 production rates. All tested coatings slowed fresh mass and firmness loss of fruits, but pectin and cellulose gum active nanocomposite was the coating able to contribute to the lowest rate of fresh mass loss and to highest rate of fruit s firmness retention, but the addition of extract did not influence these results. The reinforcement with cellulose nanocrystals was able to retain antioxidant activity off added coatings, which consisted of peanut peel extract. This research showed that pectin coatings, based on nanocrystals and the coatings from polymeric combination of pectin and cellulose gum, along with peanut peel extract and nanocrystals, presented better barrier properties against gases and water vapor, based on physiologic and physicochemical indicators / Revestimentos comestíveis podem auxiliar na qualidade e conservação de frutos. Polímeros de polissacarídeos, como amido, pectina e celulose têm sido muito utilizados como base de formação de revestimentos, mas suas propriedades físicas não proporcionam barreira adequada à difusão de gases e vapor d´água. Nanocristais de celulose, quando incorporados a revestimentos comestíveis, podem melhorar suas propriedades de barreira. A adição de um antioxidante natural ao revestimento pode melhorar a capacidade de conservação do fruto. Antioxidantes naturais possuem relativa instabilidade que pode limitar suas propriedades redutoras. No entanto, a inclusão de nanocristais pode agregar maior estabilidade ao antioxidante adicionado. Assim, o objetivo deste trabalho foi avaliar o efeito de revestimentos poliméricos, adicionados com nanocristais de celulose e extrato vegetal na fisiologia e qualidade pós-colheita da lima ácida Tahiti. O trabalho foi dividido em dois experimentos. O primeiro consistiu na avaliação do efeito de polímeros de carboximetilcelulose (CMC), pectina (PEC) e amido (AM), adicionados de nanocristais de celulose (NC). O segundo diferiu do primeiro pela adição de extrato de película de amendoim, escolhido por possuir maiores valores de atividade antioxidante pelos métodos DPPH, ABTS e FRAP em comparação aos extratos de casca de lima ácida Tahiti e semente de limão Cravo. Em ambos experimentos as avaliações ocorreram durante 9 dias de armazenamento a 23 °C ± 2 °C. Etileno, CO2, perda de massa fresca, firmeza e clorofila foram avaliados nos dois experimentos. No segundo foram incluídas as análises de atividade antioxidante pelos métodos DPPH, ABTS e FRAP, compostos fenólicos totais e ácido ascórbico. No primeiro experimento, os revestimentos formados com os polímeros puros CMC, PEC e AM e com os seus respectivos nanocompósitos chamados NCMC, NPEC e NAM foram eficazes em reduzir a produção de etileno até os primeiros três dias de armazenamento. Entre os tratamentos testados, o nanocompósito NPEC (12,01 mg CO2 kg-1 h-1) foi mais eficiente em inibir a difusão de CO2 do que o polímero puro PEC (14,93 mg CO2 kg-1 h-1). O polímero PEC quando reforçado com NC (NPEC) foi o único revestimento que pôde reduzir a perda de peso fresco de lima ácida Tahiti, e também foi mais eficiente na retenção de clorofila do que o polímero puro PEC. Todos os nanocompósitos ou polímeros puros testados foram similarmente eficientes em reter a firmeza dos frutos. No segundo experimento a mistura de pectina e carboximetilcelulose, nanocristais e extrato foi responsável por apresentar as menores taxas de produção de etileno e CO2. Todos os revestimentos testados retardaram as perdas de massa fresca e de firmeza dos frutos, mas o nanocompósito ativo de pectina e carboximetilcelulose foi o revestimento capaz de influenciar a menor perda de massa fresca e reter a maior firmeza, mas a adição de extrato não influenciou esses resultados. O reforço com nanocristais de celulose foi capaz de reter atividade antioxidante dos revestimentos adicionados de extrato de película de amendoim. Este estudo mostrou que revestimentos de pectina, baseados em nanocristais e revestimentos da mistura polimérica de pectina e carboximetilcelulose, adicionais de extrato de película de amendoim e nanocristais, apresentaram melhores propriedades de barreira a gases e ao vapor de água, baseados nos indicadores fisiológicos e físico-químicos

Xiao, Manda = 金納米晶修飾的空心介孔二氧化矽微球在表面等離子體激元調製下的光散射行為 / 肖蔓達. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references. / Abstracts in English and Chinese. / Xiao, Manda = Jin na mi jing xiu shi de kong xin jie kong er yang hua xi wei qiu zai biao mian deng li zi ti ji yuan diao zhi xia de guang san she xing wei / Xiao Manda. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgement --- p.iv / Table of Contents --- p.vi / List of Figures --- p.viii / List of Tables --- p.x / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Plasmonic Properties of Noble Metal Nanocrystals --- p.1 / Chapter 1.2 --- Light Scattering from Dielectric Spheres --- p.6 / Chapter 1.3 --- Motivations and Outline of the Thesis --- p.9 / Chapter 2 --- Characterization Techniques --- p.17 / Chapter 2.1 --- Instrumentation --- p.17 / Chapter 2.2 --- Extinction Measurement of Au Nanocrystals and the HMSMSs Decorated with the Au Nanocrystals --- p.17 / Chapter 2.3 --- Sample Preparation for the TEM and SEM Characterization --- p.18 / Chapter 2.4 --- Dark-Field Imaging and Spectroscopy of the Individual Microspheres --- p.19 / Chapter 3 --- Fabrication of Hollow Mesoporous Silica Microspheres Decorated with the Au Nanocrystals --- p.25 / Chapter 3.1 --- Preparation of the Hollow Mesoporous Silica Microspheres --- p.25 / Chapter 3.2 --- Growth of the Au Nanocrystals --- p.29 / Chapter 3.3 --- Assembly of the Au Nanocrystals onto the Hollow Mesoporous Silica Microspheres --- p.32 / Chapter 4 --- Resonant Scattering Properties of the Hollow Mesoporous Silica Microspheres --- p.38 / Chapter 4.1 --- Experimental Results --- p.38 / Chapter 4.2 --- Calculation of the Scattering Spectra by Mie Theory --- p.42 / Chapter 4.3 --- Summary --- p.46 / Chapter 5 --- Resonant Scattering Properties of the Au Nanocrystal-Decorated Hollow Mesoporous Silica Microspheres --- p.49 / Chapter 5.1 --- Effect of the Plasmon Resonances of the Au Nanocrystals on the Resonant Scattering Behaviors of the HMSMSs --- p.49 / Chapter 5.2 --- Estimation of the Scattering Enhancement Factors --- p.54 / Chapter 5.3 --- Summary --- p.59 / Chapter 6 --- Summary --- p.61

Grâce à leurs propriétés optiques et électroniques uniques, les nanocristaux de semi-conducteurs colloïdaux bidimensionnels tels que les nanoplaquettes de chalcogénure de cadmium ont émergé comme une nouvelle classe de nanomatériaux. Tout comme les puits quantiques, ces nanocristaux ont un confinement electronique limité à une seule direction, l'épaisseur qui est contrôlée au niveau atomique. Ces nanoplaquettes colloïdales apparaissent ainsi comme de bons candidats pour la fabrication de dispositifs optoélectroniques. Cependant, leur mécanisme de formation reste sujet à discussion. Ainsi, cette thèse se concentre tout d’abord sur l'étude de la synthèse de nanoplaquettes de CdSe zinc blende et l’effet de la longueur de la chaine aliphatique des carboxylates sur ces dernières, ouvrant ainsi la voie à une meilleure compréhension de la croissance des nanocristaux bidimensionnels.Par la suite, la nature et la localisation de ces ligands carboxylates en surface des nanoplaquettes a été étudié par des techniques de RMN. Cette étude semble confirmer l’effet de la gêne stérique sur la croissance des nanoplaquettes. La RMN du solide en corrélation 13C-1H 2D, se basant sur l’interaction dipolaire, indique que les acétates et les carboxylates à longue chaîne sont très probablement distribués de manière homogène à la surface des nanoplaquettes de CdSe. Dans une dernière partie, j’explore la possibilité d’améliorer les propriétés optiques de nanoplaquettes synthetisées par déposition de couches atomiques en voie colloïdale (c-ALD) en utilisant des recuits, visant à améliorer la structure et la surface des matériaux. / Colloidal two-dimensional semiconductor nanocrystals such as nanoplatelets of cadmium chalcogenides, have emerged as a new class of nanomaterials due to their unique optical and electronic properties. These nanocrystals possess exciton confinement along one direction in analogy to quantum wells, with their thickness controlled at atomic level.Although colloidal two-dimensional nanoplatelets have been considered as potential candidates for the fabrication of optoelectronic devices, their formation mechanism e.g. zinc blende CdSe nanoplatelets is still under debate. Thereby this thesis first focuses on the study of CdSe nanoplatelets synthesis and size of the aliphatic chain in the carboxylate, paving the way to a better understanding of two-dimensional nanocrystals’ growth.Successively surface carboxylate ligands are investigated by NMR techniques which gives us an idea of how surface ligands are composed and relocated. Our study of ligand quantification on nanoplatelets’ surface appears to support the proposed effect from steric hinderance on NPLs growth. 13C-1H 2D correlation solid state NMR based on the dipolar interaction indicates that acetates and long alkyl chain carboxylates should be distributed homogenously on the surface of the CdSe NPLs. In the last part, I explore the possibility of improving the optical features of nanoplatelets synthesized from colloidal atomic-layer-deposition technique through optimizing both interior and surface structures by an annealing process.

Puisque cette thèse présente deux études indépendantes sur les nanocristaux de cellulose, le résumé a été divisé en deux sections qui font référence aux chapitres II et III, respectivement.Investigation morphologique et structurelle des nanocristaux de cellulose I et II préparés par hydrolyse à l'acide sulfuriqueLe but du travail de recherche présenté dans le chapitre II était de produire, de caractériser et de comparer les CNC obtenus à partir de la pâte de bois d'eucalyptus en utilisant trois méthodes différentes: i) l'hydrolyse classique à l'acide sulfurique (CN-I), ii) l'hydrolyse acide de la cellulose précédemment mercerisée par traitement alcalin (MCN-II), et iii) la solubilisation de la cellulose dans l'acide sulfurique et la recristallisation subséquente dans l'eau (RCN-II). Les trois types de CNC préparés présentent des morphologies et des structures cristallines différentes. Lorsque les conditions d'hydrolyse acide sont mises en place de telle sorte que les domaines cristallins dans la pâte de bois initial et la cellulose mercerisée (WP et MWP, respectivement) sont préservés (60 wt% H2SO4, 45°C, 50 min), les nanocristaux résultants conservent la nature fibrillaire des fibres d’origine (c'est-à-dire que l'axe de la chaîne est parallèle au grand axe des particules aciculaires) et leur type allomorphe initial (I pour WP et II pour la MWP). Dans les deux cas, les particules sont principalement composées de quelques cristallites élémentaires liées latéralement. Les nanocristaux unitaires dans les CNC préparés à partir de cellulose mercerisée (MCN-II) sont plus courts, mais plus larges que ceux préparés à partir des fibres de cellulose I (CN-I). Si des conditions plus sévères sont considérées (64 wt% H2SO4, 40°C, 20 min), ce qui entraîne la dépolymérisation et la dissolution de la cellulose native, les chaînes courtes recristallisent en rubans de Cell-II lors de la régénération dans l'eau à température ambiante. Dans ces rubans tortueux, l'axe de la chaîne serait perpendiculaire au grand axe du nanocristal et parallèle à son plan basal.La structure moléculaire et cristalline unique des nano-rubans implique qu'un nombre plus élevé d'extrémités de chaîne réductrice sont situées à la surface des particules, ce qui peut être important pour des modifications chimiques subséquentes et pour de potentielles applications spécifiques telles que la biodétection et la bio-imagerie. Donc, cette étude permet de mieux comprendre la structure cristalline et la morphologie de la CNC obtenue par régénération à l'acide sulfurique.Propriétés mécaniques de nanocomposites de caoutchouc naturel renforcé avec des nanocristaux de cellulose à facteur de forme élevé extraits de la coque de sojaDans cette étude, les CNCs ont été isolés des coques de soja à partir d’un traitement par hydrolyse avec de l'acide sulfurique. Ces CNCSH ont été utilisés comme phase de renfort dans une matrice NR par casting à différents taux de charge, à savoir 1, 2.5 et 5% en poids. Les effets des CNCSH sur la structure ainsi que sur les propriétés thermiques et mécaniques du NR ont été étudiés. Par exemple, en ajoutant seulement 2,5% en poids de CNC, le module de conservation en traction du nanocomposite à 25 °C est environ 21 fois plus élevé que celui de la matrice NR non chargée. Cet effet de renfort est supérieur à celui observé pour les CNCs extraits d'autres sources. Il peut être attribué non seulement au facteur de forme élevé de ces CNCs, mais aussi à la rigidité du réseau percolant de nanoparticules formé au sein de la matrice polymère. De plus, il a été constaté que la sédimentation des CNC pendant la mise en œuvre du film nanocomposite par casting joue un rôle crucial sur les propriétés mécaniques. Une contribution importante de ce travail est de mettre en évidence l'importance de la sédimentation des CNCs, pendant l'étape d'évaporation sur les propriétés mécaniques des nanocomposites, ce qui est rarement mentionné dans la littérature. / Since this thesis presents two independent studies on cellulose nanocrystals, the abstract was divided in two sections referring to chapters II and III, respectively.Comprehensive morphological and structural investigation of cellulose I and II nanocrystals prepared by sulfuric acid hydrolysisCellulose nanocrystals (CNCs) were produced from eucalyptus wood pulp using three different methods: i) classical sulfuric acid hydrolysis (CN-I), ii) acid hydrolysis of cellulose previously mercerized by alkaline treatment (MCN-II), and iii) solubilization of cellulose in sulfuric acid and subsequent recrystallization in water (RCN-II). The three types of CNCs exhibited different morphologies and crystal structures that were characterized using complementary imaging, diffraction and spectroscopic techniques. CN-I corresponded to the type I allomorph of cellulose while MCN-II and RCN-II corresponded to cellulose II. CN-I and MCN-II CNCs were acicular particles composed of a few laterally-bound elementary crystallites. In both cases, the cellulose chains were oriented parallel to the long axis of the particle, although they were parallel in CN-I and antiparallel in MCN-II. RCN-II particles exhibited a slightly tortuous ribbon-like shape and it was shown that the chains lay perpendicular to the particle long axis and parallel to their basal plane. The unique molecular and crystal structure of the RCN-II particles implies that a higher number of reducing chain ends are located at the surface of the particles, which may be important for subsequent chemical modification. While other authors have described nanoparticles prepared by regeneration of short-chain cellulose solutions, no detailed description was proposed in terms of particle morphology, crystal structure and chain orientation. Was provide such a description in the present document.Mechanical properties of natural rubber nanocomposites reinforced with high aspect ratio cellulose nanocrystals isolated from soy hullsCellulose nanocrystals (CNCs) were isolated from soy hulls by sulfuric acid hydrolysis. The resulting CNCs were characterized using TEM, AFM, WAXS, elemental analysis and TGA. The CNCs have a high crystallinity, specific surface area and aspect ratio. The aspect ratio (around 100) is the largest ever reported in the literature for a plant cellulose source. These CNCs were used as a reinforcing phase to prepare nanocomposite films by casting/evaporation using natural rubber as matrix. The mechanical properties were studied in both the linear and non-linear ranges. The reinforcing effect was higher than the one observed for CNCs extracted from other sources. It may be assigned not only to the high aspect ratio of these CNCs but also to the stiffness of the percolating nanoparticle network formed within the polymer matrix. Moreover, the sedimentation of CNCs during the evaporation step was found to play a crucial role on the mechanical properties.

Le tissu osseux est un matériau composite biologique principalement constitué de molécules de collagène, de nanocristaux minéraux et d'eau et qui est organisé en plusieurs niveaux hiérarchiques dont les dimensions caractéristiques s’étendent sur plus de 8 ordres de grandeur. Une compréhension fondamentale de l’organisation de la structure minérale du tissu osseux aux différentes échelles représente un enjeu important pour la communauté biomédicale. Pour répondre à cette demande, nous avons appliqué de nouvelles méthodes actuellement en développement pour la science des matériaux afin de caractériser la phase minérale: l’imagerie par diffraction cohérente des rayons X (CXDI), par la microscopie électronique à transmission avec cartographie d'orientation cristalline automatisée (ACOM-TEM) et l’analyse de la fonction de distribution de paires (PDF) des diagrammes de diffraction des rayons X.Le tissu osseux a été étudié depuis l’échelle de l’angström, pour l’arrangement atomique, en tenant compte de la composition chimique et des variations de longueur des liaisons interatomique, en passant par l'organisation individuelle des cristaux (et entre cristaux), jusqu’à leur organisation à l’échelle du micron avec une résolution nanométrique, permettant également de résoudre la structure de la nano porosité du tissu.Les preuves de principe ont été réalisées sur un modèle bovin et en utilisant des os traités thermiquement pour tester l'applicabilité et la sensibilité des différentes méthodes. En outre, ces résultats sont d'un intérêt direct pour l'archéologie, l'anthropologie et la science médico-légale. De plus, nos premières études réalisées sur des tissus osseux humains affectés par diverses pathologies ont permis de montrer que les différences structurales induites par les pathologies peuvent être détectées à l’échelle du cristal.La description de la préparation des échantillons, les configurations expérimentales et les analyses de données pourraient, ainsi, être appliquées à d'autres tissus osseux, ex. avec un degré différent de maturation ou de différentes espèces. Les tissus de structure et composition similaires aux os tels que la dentine ou le bois de rennes, ainsi que des matériaux poreux inorganiques multi-échelles pourraient également être analysés avec les protocoles proposés.Comprendre les caractéristiques nanostructurales du tissu osseux est donc indispensable afin d’identifier des marqueurs structuraux clés des pathologies de l'os humain. Cette stratégie pourra avoir un impact sur les futurs développements de nouveaux outils pour le diagnostic ou pour évaluer l'efficacité des thérapies pharmaceutiques actuelles. / Bone tissue is a biological composite material organized in several hierarchical levels that spread over more than 8 orders of magnitude in length scales, which is made of three principal components: collagen molecules, mineral nanocrystals and water. A fundamental understanding of how the mineral structure of bone tissue is organized at different length scales is essential for the biomedical community. To answer this demand, we applied novel methods currently in development for materials science to characterize the mineral phase: coherent X-ray diffraction imaging (CXDI), automated crystal orientation mapping with transmission electron microscope (ACOM-TEM) and pair distribution function analysis (PDF) of X-ray diffraction patterns.Bone tissue was investigated from its sub-angstrom arrangement, taking into account chemical composition and interatomic bond lengths shifts, through individual crystal organization (one crystal with respect to the next), to their micrometer organization with nanometer resolution, also allowing resolving the nanoporosity structure within the tissue.Beside the investigation of native bovine tissues, heated bones that are of interest in archeology, anthropology and forensic science, were used as a model to test for the applicability and sensitivity of the different methods for such biological materials. Moreover, a first insight into pathological bone tissues enabled to show that the structural differences of particular pathologies in comparison to healthy state can be observed already at the sub-angstrom scale (as seen from interatomic bonds shifts).The sample preparation described, the experimental setups and data analysis schemes could, furthermore, be applied to bone tissue at different anatomical location, with different degree of tissue maturation, to different species and pathological cases. Bone-like tissues such as dentin and antler as well as inorganic multiscale-porous materials could also be analyzed by the proposed scheme.Understanding the nanostructural characteristics of bone tissue is therefore useful to identify key structural markers of pathological human bone. This strategy could have an impact on future developments of new tools for diagnostic or to assess the effectiveness of pharmaceutical treatments.

This thesis examines the optical properties of nanoscale silicon and the sensitization of Er with Si. In this context, it predominantly investigates the role of defects in limiting the luminescence of Si nanocrystals, and the removal of these defects by hydrogen passivation. The kinetics of the defect passivation process, for both molecular and atomic hydrogen, are studied in detail. Moreover, the optical absorption of Si nanocrystals and the effect of annealing environment (during nanocrystal synthesis) on the luminescence are investigated. The effect of annealing temperature and hydrogen passivation on the coupling (energy transfer) of Si nanocrystals to optically active centres (Er) is also examined.¶ The electronic structure of silicon-implanted silica slides is investigated through optical absorption measurements. Before and after annealing to form Si nanocrystals, optical absorption spectra from these samples show considerable structure that is characteristic of the particular implant fluence. This structure is shown to correlate with the transmittance of the samples as calculated from the modified refractive index profile for each implant. Due to the high absorption coefficient of Si at short wavelengths, extinction at these wavelengths is found to be dominated by absorption. As such, scattering losses are surprisingly insignificant. To eliminate interference effects, photothermal deflection spectroscopy is used to obtain data on the band structure of Si in these samples. This data shows little variance from bulk Si structure and thus little effect of quantum confinement. This is attributed to the dominance of large nanocrystals in the absorption measurements.¶ The effect of annealing environment on the photoluminescence (PL) from silicon nanocrystals synthesized in fused silica by ion implantation and thermal annealing is studied as a function of annealing temperature and time. Interestingly, the choice of annealing environment (Ar, N2, or 5 % H2 in N2) is found to affect the shape and intensity of luminescence emission spectra, an effect that is attributed both to variations in nanocrystal size and the density of defect states at the nanocrystal/oxide interface.¶ The passivation kinetics of luminescence-quenching defects, associated with Si nanocrystals in SiO2, during isothermal and isochronal annealing in molecular hydrogen are studied by time-resolved PL. The passivation of these defects is modeled using the Generalized Simple Thermal model of simultaneous passivation and desorption, proposed by Stesmans. Values for the reaction-rate parameters are determined for the first time and found to be in excellent agreement with values previously determined for paramagnetic Si dangling-bond defects (Pb type centers) found at planar Si/SiO2 interfaces; supporting the view that non-radiative recombination in Si nanocrystals is dominated by such defects.¶ The passivation kinetics of luminescence-quenching defects during isothermal and isochronal annealing in atomic hydrogen are studied by continuous and time-resolved PL. The kinetics are compared to those for standard passivation in molecular hydrogen and found to be significantly different. Atomic hydrogen is generated using the alneal process, through reactions between a deposited Al layer and H2O or –OH radicals in the SiO2. The passivation and desorption kinetics are shown to be consistent with the existence of two classes of nonradiative defects: one that reacts with both atomic and molecular hydrogen, and the other that reacts only with atomic hydrogen. A model incorporating a Gaussian spread in activation energies is presented that adequately describes the kinetics of atomic hydrogen passivation and dissociation for the samples.¶ The effect of annealing temperature and hydrogen passivation on the excitation cross-section and PL of erbium in silicon-rich silica is studied. Samples are prepared by co-implantation of Si and Er into SiO2 followed by a single thermal anneal at temperatures ranging from 800 to 1100 degrees C, and with or without hydrogen passivation performed at 500 degrees C. Using time-resolved PL, the effective erbium excitation cross-section is shown to increase by a factor of 3, while the number of optically active erbium ions decreases by a factor of 4 with increasing annealing temperature. Hydrogen passivation is shown to increase the luminescence intensity and to shorten the luminescence lifetime at 1.54 micron only in the presence of Si nanocrystals. The implications of these results for realizing a silicon-based optical amplifier are also discussed.

Arsenic and uranium in the environment are hazardous to human health and require better methods for detection and remediation. Nanocrystalline iron oxides offer a number of advantages as sorbents for water purification and environmental remediation. First, highly uniform and crystalline iron oxide nanocrystals (nMAG) were prepared using thermal decomposition of iron salts in organic solutions; for the applications of interest in this thesis, a central challenge was the adaptation of these conventional synthetic methods to the needs of low infrastructure and economically disadvantaged settings. We show here that it is possible to form highly uniform and magnetically responsive nanomaterials using starting reagents and equipment that are readily available and economical. The products of this approach, termed the 'Kitchen Synthesis', are of comparable quality and effectiveness to laboratory materials. The narrow size distributions of the iron oxides produced in the laboratory synthesis made it possible to study the size-dependence of the magnetic separation efficiency of nanocrystals; generally as the diameter of particles increased they could be removed under lower applied magnetic fields. In this work we take advantage of this size-dependence to use magnetic separation as a tool to separate broadly distributed populations of magnetic materials. Such work makes it possible to use these materials in multiplexed separation and sensing schemes. With the synthesis and magnetic separation studies of these materials completed, it was possible to optimize their applications in water purification and environmental remediation. These materials removed both uranium and arsenic from contaminated samples, and had remarkably high sorption capacities -- up to 12 wt% for arsenic and 30 wt% for uranium. The contaminated nMAG is removed from the drinking water by either retention in a sand column, filter, or by magnetic separation. The uranium adsorption process was also utilized for the enhanced detection of uranium in environmental matrices. By relying on α-particle detection in well-formed and dense nMAG films, it was possible to improve soil detection of uranium by more than ten-thousand-fold. Central for this work was a detailed understanding of the chemistry at the iron oxide interface, and the role of the organic coatings in mediating the sorption process.

Mn-doped II-VI semiconductor nanocrystals exhibit bright dopant photoluminescence that has potential usefulness for light emitting devices, temperature sensing, and biological imaging. The bright luminescence comes from the 4T1→6A1 transition of the Mn2+ d electrons after the exciton-dopant energy transfer, which reroutes the exciton relaxation through trapping processes. The driving force of the energy transfer is the strong exchange coupling between the exciton and Mn2+ due to the confinement of exciton in the nanocrystal. The exciton-Mn spatial overlap affecting the exchange coupling strength is an important parameter that varies the energy transfer rate and the quantum yield of Mn luminescence. In this dissertation, this correlation is studied in radial doping location-controlled Mn-doped CdS/ZnS nanocrystals. Energy transfer rate was found decreasing when increasing the doping radius in the nanocrystals at the same core size and shell thickness and when increasing the size of the nanocrystals at a fixed doping radius. In addition to the exciton-Mn energy transfer discussed above, two consecutive exciton-Mn energy transfers can also occur if multiple excitons are generated before the relaxation of Mn (lifetime ~10^-4 - 10^-2 s). The consecutive exciton-Mn energy transfer can further excite the Mn2+ d electrons high in conduction band and results in the quenching of Mn luminescence. The highly excited electrons show higher photocatalytic efficiency than the electrons in undoped nanocrystals. Finally, the effect of local lattice strain on the local vibrational frequency and local thermal expansion was observed via the temperature-dependent Mn luminescence spectral linewidth and peak position in Mn-doped CdS/ZnS nanocrystals. The local lattice strain on the Mn2+ ions is varied using the large core/shell lattice mismatch (~7%) that creates a gradient of lattice strain at various radial locations. When doping the Mn2+ closer to the core/shell interface, the stronger lattice strain softens the vibrational frequency coupled to the 4T1→6A1 transition of Mn2+ (Mn luminescence) by ~50%. In addition, the lattice strain also increases the anharmonicity, resulting in larger local thermal expansion observed from the nearly an order larger thermal shift of the Mn luminescence compared to the Mn-doped ZnS nanocrystals without the core/shell lattice mismatch.