Grâce à des propriétés physiques spécifiques différentes des matériaux massifs, les nanostructures ont mené à une rupture technologique importante. Le silicium étant le matériau prédominant en microélectronique, et du fait d’un rapport surface/volume important, les nanofils de silicium sont prometteurs dans de nombreux domaines d’applications comme l’optoélectronique ou les capteurs biologiques. Néanmoins les techniques de synthèse actuellement utilisées sont encore relativement complexes à mettre en œuvre et coûteuses et il existe encore un écart énorme entre la synthèse et la mise au point de démonstrateurs en laboratoire et la réalisation de dispositifs fonctionnels et commercialisables.Ce travail de thèse porte sur l’étude d’une nouvelle technique de synthèse bas coût, l’électrodépôt en liquide ionique, pour obtenir des nanofils de silicium ou de silicium incorporant des ions Terre-Rare avec des propriétés d’émission dans le visible ou le proche infrarouge. Un des objectifs de cette thèse étaient de comprendre l’influence des différents paramètres d’électrodépôt sur la croissance de films minces de silicium pur et de voir si il était possible de synthétiser par cette voie des films Silicium/terbium, le terbium émettant dans le visible, et Silicium/Erbium, l’erbium émettant à 1,55 µm. Grâce aux études électrochimiques et aux caractérisations structurales des films minces, nous avons montré que ce mode de synthèse permettait d’obtenir des films minces de silicium amorphe de très bonne qualité et sans impureté avec une croissance laminaire. En jouant sur le potentiel de dépôt, la température et la concentration en espèces actives, nous avons pu maîtriser et optimiser les conditions de croissance, ce qui nous a permis ensuite d’obtenir des nanofils de silicium amorphe avec des diamètres allant de quelques dizaines à quelques centaines de nanomètres en utilisant des membranes nanoporeuses comme moule. Ces nanofils sont passivés par une couche d’oxyde de surface après dissolution de la membrane et remise à l’air. Une propriété intéressante de ces nanofils de silicium amorphe est qu’ils possèdent une forte luminescence dans le rouge à température ambiante, en particulier pour des diamètres de l’ordre de 100 nm. Des études optiques et structurales ont permis de montrer que cette émission provenait du caractère amorphe des nanofils et qu’un mécanisme de recombinaison entre queues de bande et le confinement spatial des porteurs dans les nanofils permettait d’expliquer l’émission intense observéeLa 2ème partie importante de la thèse portait sur la possibilité de réaliser des films et des nanofils de type silicium / terres rares. Nous avons montré pour la 1ère fois, qu’il était de synthétiser des co-dépôts simultanés de silicium et d’éléments de terre rare pour le Tb et l’Er sous forme de films minces. En faisant varier le potentiel de dépôt, nous avons mis en évidence qu’il était possible de faire varier la concentration de terre-rare incorporée de quelques % à 20%. Les études structurales montrent que cette incorporation se fait de façon homogène dans l’épaisseur des films et sans changer la morphologie. Grâce à cette homogénéité, les films minces obtenus émettent à température ambiante et aux longueurs d’onde attendues pour les ions terre-rare. Suite à cette étude sous forme de films minces, nous avons ensuite réalisé la croissance de nanofils Si/Tb et Si/Er en utilisant des membranes nanoporeuses. Nous avons obtenu des nanofils de silicium incorporant du terbium ou de l’erbium avec des concentrations pouvant varier. Les nanofils ainsi synthétisés sont également homogènes en composition sur toute la longueur et émettent avec des fortes intensités à température ambiante pour le terbium. Pour les nanofils Si/Er, l’intensité d’émission est faible à température ambiante mais un recuit thermique permet d’activer les ions terbium et d’obtenir une émission intense à température ambiante. / Thanks to their specific physical properties different from the massive materials, nanostructured materials have led to important technological progress. Since silicon is the predominant material in microelectronics, and due to a large surface to volume ratio, silicon nanowires are promising in many fields of applications such as optoelectronics or biological sensors. Nevertheless, the synthesis techniques currently used are still relatively complex to implement and thus costly and there is still a huge gap between the synthesis and the development of laboratory demonstrators and the realization of functional and marketable devices.This thesis work deals with the study of a new low cost synthesis technique, the electrodeposition in ionic liquid, to grow nanowires of silicon or silicon incorporating Earth-Rare ions with emission properties of emission in the visible or the near infrared range. One of the objectives of this thesis was to understand the influence of the different electrodeposition parameters on the growth of pure silicon thin films and to see if it was possible to synthesize silicon/terbium films, the terbium emitting in the visible, and Silicon/Erbium, erbium emitting at 1.55 μm. Thanks to different electrochemical studies and structural characterization of thin films, we have shown that this mode of synthesis makes it possible to obtain thin films of amorphous silicon of very good quality and without impurity. By controlling the deposition potential, temperature, and active species concentration, we were able to control and optimize the growth conditions, which allowed us to obtain amorphous silicon nanowires with diameters ranging from a few tens to a few hundred nanometers using nanoporous membranes as a mold. These nanowires are passivated by a surface oxide layer after dissolution of the membrane and exposition to air. An interesting property of these amorphous silicon nanowires is that they have a high luminescence in the red range at room temperature, in particular for diameters in the order of 100 nm. Optical and structural studies showed that this emission was due to the amorphous nature of the nanowires and that a mechanism of band-tail recombination and the spatial confinement of the carriers whitin the nanowires made it possible to explain the intense emission observed.The second important part of the thesis was the possibility of making films and nanowires of the silicon/rare earth type. We have shown for the first time that it was possible to synthesize simultaneous co-deposited films of silicon and rare earth elements for Tb and Er. By varying the deposition potential, we have shown that it is possible to tune the incorporated rare earth concentration by a few % to 20%. The structural studies show that this incorporation is carried out homogeneously in the thickness of the films and without changing the morphology. Thanks to this homogeneity, the thin films obtained emit at ambient temperature and at the expected wavelengths for the rare earth ions. Following this study as thin films, we then carried out the growth of Si/Tb and Si/Er nanowires using nanoporous membranes. We have obtained nanowires of silicon incorporating terbium or erbium with varying concentrations. The nanowires thus synthesized are also homogeneous in composition over the entire length and emit with high intensities at ambient temperature for terbium. For Si/Er nanowires, the emission intensity is low at ambient temperature but thermal annealing makes it possible to activate the terbium ions and to obtain an intense emission at ambient temperature.

Cette thèse est consacrée à l'étude d'encres, de composites et de dépôts de nanotubes de carbone monofeuillets (SWNT). Le contrôle de la dispersion et de l'orientation des nanotubes dans ces matériaux composites nanostructurés vise à optimiser leurs propriétés, en particulier électriques et optiques.La première partie du travail est consacrée à l'optimisation de la dispersion des SWNT dans des suspensions aqueuses stabilisées par des tensio-actifs, des sels biliaires, et à l'étude de leurs propriétés optiques, et en particulier de leur photoluminescence (PL) dans le proche infrarouge. La spectroscopie d'absorption nous permet de sonder la dispersion des SWNT et de mesurer leur coefficient d'absorption. Nous montrons que ce dernier est très sensible au degré d'individualisation des nanotubes. Par ailleurs, nous revisitons l'interprétation des spectres de PL excités dans le proche infrarouge (en particulier à 1,17 et 1,58 eV) et attribuons les différents pics mesurés à différents mécanismes : transitions excitoniques directes, à des couplages exciton-phonon ou à des transferts d'énergie entre nanotubes. Nous montrons que l'évolution de l'intensité de PL avec l'individualisation permet de distinguer ces différents mécanismes.La seconde partie du travail est dédiée à la préparation de suspensions aqueuses stabilisées par des polymères hydrosolubles (PVA et PVP), et de composites SWNT/polymère, sans tensio-actifs. Les suspensions de nanotubes sont mélangées à des solutions de polymère, puis dialysées pour éliminer le tensio-actif. Le rendement, i.e. la concentration de la suspension finale, est de l'ordre de 75 fois plus élevée que pour une suspension préparée directement avec des polymères. Par ailleurs, les spectres de PL sont sensibles à l'environnement diélectrique des nanotubes et leur étude permet de mettre en évidence un échange entre les agents dispersants tensio-actifs/PVA à la surface des nanotubes, échange qui n'est pas observé dans le cas du PVP. Dans la troisième partie de la thèse, nous utilisons la technique d'impression jet d'encre pour imprimer des lignes continues micrométriques de SWNT, et proposons des méthodes originales pour étudier leur morphologie et leur anisotropie. La morphologie des dépôts peut varier entre deux cas limites, le dépôt homogène et la ‘‘paire de rails'', en faisant varier la concentration de nanotubes dans les encres, la distance entre gouttes et la température du substrat. L'orientation des nanotubes au bord des dépôts est très élevée (paramètre d'ordre orientationnel S entre 0,6 et 0,9), les nanotubes sont également bien orientés dans les rails (S~0.5) et dans une moindre mesure dans les lignes homogènes S~0.3. / This thesis focus on the study of inks, composites and deposits of single-wall carbon nanotubes (SWNT). The control of dispersion and orientation of nanotubes in such nanostructured composites materials allows to optimize their properties, and especially their electrical and optical properties.The first part of the work is devoted to the optimization of dispersion of SWNT in aqueous suspensions stabilized by bile salts surfactants, and to the study of their optical properties, and especially their near infrared photoluminescence (PL). Dispersion of the nanotubes is probed by absorption spectroscopy. We show that their absorption coefficient is very sensitive to the individualization of the nanotubes. On the other hand, we revisit the interpretation of the PL spectra excited in the near infrared (especially at 1.17 and 1.58 eV), and we assign the different peaks to different mechanisms, namely direct excitonic transitions, exciton-phonon coupling, and energy transfer between nanotubes. We show that the evolution of PL intensity as a function of individualization allows to distinguish the different mechanisms.The second part of the work is dedicated to the preparation of aqueous suspensionsstabilized by hydrosoluble polymers (PVA and PVP), and SWNT/polymer composites, without surfactants. SWNT suspensions are mixed with polymer solutions, and then the surfactant is removed by dialysis. The yield, i.e. the relative concentration of SWNT in the dialyzed suspension, is ~75 times higher than for a suspension prepared directly with polymers. On the other hand, PL signatures are sensitive to the dielectric environment of the nanotubes which allows to evidence an exchange between the dispersing agents bile salts/PVA on the nanotube surface, such an exchange is not observed in the case of PVP.In the third part of the thesis, we use the inkjet printing technique to print continuous micrometric lines of SWNT, and we propose original methods to study their morphology and their anisotropy. The morphology of the deposits varies between two limit cases, an homogeneous deposit and a ‘‘pair of tracks'', by varying nanotube concentration in the inks, inter-drop distance and substrate temperature. The orientation of the nanotubes is very high at the edge of the deposits (orientational order parameter S between 0.6 y 0.9), the nanotubes are well-oriented as well in the tracks (S~0.5) and to a lesser extent in the homogeneous lines (S~0.3).

As ferramentas computacionais utilizadas em diferentes áreas de pesquisa têm como vantagem sobre análises e ensaios reais a possibilidade de analisar sistemas em diferentes condições de forma mais ágil e com menor consumo de tempo e recursos. A modelagem óptica de dispositivos fotovoltaicos é bastante difundida. Existem diferentes trabalhos na área, com diferentes escopos e graus de detalhamento, que permitem a análise e melhor compreensão das diferentes etapas da conversão da radiação em energia elétrica, expandindo as possibilidades de otimização. No presente trabalho foi desenvolvida, em uma etapa inicial, uma metodologia computacional para análise óptica de módulos fotovoltaicos, para então, em uma segunda etapa, serem realizados estudos do desempenho de diferentes materiais inseridos no conjunto de camadas que compõe os módulos, através da metodologia. O modelo óptico que embasa o método tem como foco os módulos de silício monocristalino. Esses módulos agregam de três a quatro camadas transparentes sobre as células fotovoltaicas. Ao incidir nesse conjunto de camadas radiação é submetida a diferentes eventos de extinção, como função do comprimento de onda da radiação e ângulo de incidência, que devem ser previstos em um modelo de forma a obter-se resultados válidos de transmissividade. A metodologia propõe a realização de uma análise aprofundada dos fenômenos ópticos que ocorrem mediante a incidência de radiação em um módulo fotovoltaico de modo a auxiliar na análise da adequação e desempenho de diferentes materiais ao sistema óptico formado. A otimização da transmissão de radiação em um módulo fotovoltaico tem uma influência direta e significativa sobre a eficiência de tais dispositivos, justificando sua importância. A validação do modelo foi realizada através da literatura, em partes, e apresentou coerência com os resultados de referência. Foram produzidos na segunda etapa estudos de desempenho de materiais ou propriedades isoladamente. No primeiro estudo foram analisados três materiais para aplicação como filme de passivação sobre a célula, sendo eles Si3N4, SiO2, e TiO2; o filme de Si3N4 apresentou o melhor desempenho. O segundo estudo, de avaliação da influência do índice de refração do encapsulante na transmissividade do sistema, demonstrou que a variação desse parâmetro tem muito pouca influência. No terceiro estudo foi analisado o potencial dos materiais PDMS e TiO2 como filmes anti-reflexo sobre vidro. O PDMS gerou melhores resultados de transmissividade. Por fim um estudo de desempenho de um conjunto de materiais frente à mudança do espectro incidente foi realizado. Foi utilizado até então o espectro de referência, que foi então comparado a um espectro médio de um dia de equinócio da cidade de Porto Alegre. O desempenho do sistema foi em torno de 3% inferior em incidência normal. / Computational tools raise the possibility of studying and understanding systems under different conditions in a faster and less resource and time consuming way. The optical modeling of photovoltaic devices is a very developed issue, and paperworks and projects in different scopes e levels of detail were produced, providing a better understanding of the different steps of converting light into electricity, expanding optimization possibilities. For this project a computational methodology was developed, as an initial step, for the optical assessment of the transmission of radiation in photovoltaic modules. In a second step, studies were performed using the method as a tool for analyzing the system formed by the layers covering the cells embedded in modules. The optical model describes monocristalline silicon modules, which are constituted by three to four layers covering the cell. Once it penetrates the set of layers, incident light suffers different extinction phenomena, which are predicted in this model in order to generate valid results. It’s a function of wavelength and incidence angle of the incoming radiation. The model presented aims to deeply analyse and understand the optical phenomena light undergoes through its way from the external environment to the interior of the cell, supporting the process of observing the performance and adequacy of different materials as the referred layers. Optimizing transmission of radiation in a photovoltaic device plays a main role in increasing the efficiency of the energy conversion process, which is why it’s so important. The model was validated by literature in parts, and showed coherence within reference results. Studies were produced in a second step of this work, using the method, concerning optical issues, for the thin film on top of the cell, the refractive index of the encapsulating material, and the optical effect of coating the outer glass surface. In the first study Si3N4, SiO2 and TiO2 were analyzed; the Si3N4 film produced the best results. The second study, concerning encapsulant’s refractive index, demonstrates this parameter has a very weak influence in the system’s transmission. The third one observed the performance of two materials, PDMS and TiO2, as AR coating,. The PDMS film produced a better effect. At last, the best performance set of layers was analyzed under a representative spectral distribution of an equinox day of the city of Porto Alegre, considering so far it was used the standard. The transmission suffered a slight decrease, around 3%.

Nanocrystals are an important field of study in the 21st century. Crystallites that are nanometers in size have very different properties from their bulk analogs because quantum mechanical effects become dominant at such small length scales. When a crystallite becomes small enough, the quantum confinement of electrons in the material manifests as a size-dependence of the nanocrystal's properties. Electrical and optical properties such as absorbance, surface plasmon resonance, and photoluminescence are sensitive to the size of the nanocrystal and proffer an array of technological applications for nanocrystals in such fields as biological imaging, laser technology, solar power enhancement, LED modification, chemical sensors, and quantum computation.The synthesis of size-controlled nanocrystals is critical to using nanocrystal in applications for their size-dependent properties. The development of nanocrystal synthesis techniques has been its own entire field of study for two decades or more, and several successes have established novel, utilitarian protocols for the mass-production of nanocrystals with controlled size and very low polydispersity. However, the experimental successes are generally poorly understood and no theoretical framework exists to explain the dynamics of these processes and how to better control or optimize them. It is the goal of this thesis to develop novel theories of nanocrystal synthesis processes to describe these phenomena in theoretical detail and extract meaningful correlations and driving forces that provide the necessary insight to improve the technology and enhance our understanding of nanocrystal growth. Chapter 4, 5 and 6 comprise all the novel research conducted for this thesis, with Chapters 1, 2 and 3 serving as necessary background to understanding the current state of the art. In Chapter 4, we develop a quantitative describe of the process of size focusing, in which a population of polydisperse nanocrystals, which are useless for applications, can be made more monodisperse by the injection of new crystallizable material. We derive mass balance equations that relate the rate of new-material generation to changes in the growth patterns of the nanocrystals. Specifically, we determine that only when the rate of crystal-material production is sustained at a high level can size focusing occur and a monodisperse sample of nanocrystals be produced. Quantitative criteria are provided for how high the rate of production must be, and the quantitative effects on the nanocrystal size distribution function for various magnitudes of the production rate. The effect of the production rate on every facet of the size distribution function is evaluated analytically and confirmed numerically. Furthermore, through comparison of the theory to experimental data, it is determined that a typical nanocrystal synthesis accidentally correlates two variables that are critical to the phenomenon of size focusing. The unknowingly correlated variables have frustrated experimental investigations of the same insights we provided with theory. We recommend a new synthesis protocol that decouples the critical variables, and thus permit the quantitative control of nanocrystal size and polydispersity through theoretical relations, which can also be generalized for the a priori design and optimization of nanocrystal synthesis techniques. In Chapter 5, a theoretical investigation of the growth of surfactant-coated nanocrystals is undertaken. The surfactants create a layer around the nanocrystal that has different transport properties than the bulk solution, and therefore has a strong effect on diffusion-limited growth of nanocrystals. This effect of a surfactant layer is investigated through the lens of the LSW theory of Ostwald ripening as well as through the lens of our own theory of size focusing from Chapter 4. The quantitative effect of a surfactant layer on the various growth processes of spherical nanocrystals is determined, with the result that size focusing can potentially be enhanced by the choice of an appropriate surfactant for a particular nanocrystal material. In addition to the kinetic studies of Chapter 4 and 5, a thermodynamic investigation of surfactant-coated nanocrystals is conducted in Chapter 6, with the goal of understanding the process known as "digestive ripening". In digestive ripening, a population of polydisperse gold nanocrystals is exposed to a strongly binding surfactant, at which point the nanocrystals spontaneously shrink and become highly monodisperse. Different surfactants and different crystal materials can exhibit digestive ripening. Those same materials also have the capacity to be digested further from nanocrystals into molecular clusters that eliminate all crystalline material in favor of surfactant-crystal coordination. The outstanding question is, why does the spontaneous digestive ripening process appear to make large nanocrystals shrink to small nanocrystals, but it does not force small nanocrystals to shrink further to molecular clusters? We construct a full Gibbs free energy model, which we minimize under multiple constraints to obtain quantitative relations for what thermodynamic properties (such as the surfactant binding energy and the crystal-solvent surface energy) govern the existence and size-dependence of a thermodynamically stable nanocrystal. Through our model, we determine that a finite-size nanocrystal is only stable under two possible conditions: either the surfactant-crystal binding is stronger than the crystal-crystal binding and the system contains too few surfactants to form molecular clusters and thus "surfactant-lean" nanocrystals are created, or the surfactantsurfactant intermolecular interactions are sufficiently strong that the nanocrystal core is treated as a swollen micelle in a microemulsion and is stabilized by the surfactant tails' interactions. Quantitative equations are provided that establish what trends and values are expected for experimental results. The results are inconclusive: there is no evidence supporting either conclusion because the available experimental data is insufficient. More accurately, many thermodynamically critical parameters (like the crystal surface energy) are unknown and are practically immeasurable in experimental systems. Speaking generally, the evidence for the surfactant-lean condition is moderately better than the evidence for the microemulsion condition, but in both cases the evidence is insufficient to make a solid conclusion. We therefore use our quantitative results of the thermodynamic investigation to make recommendations to experimentalists as to what trends and what nanocrystal growth processes we expect to observe in either thermodynamic case. While our results are inconclusive in and of themselves, they will be used to highlight the exact thermodynamic driving forces of the experimental systems. We conclude by giving an overview of two new fields of study for theoretical descriptions of nanocrystal growth, specifically the growth of anisotropic nanocrystals and a practical theory for nanocrystal nucleation. Preliminary relations are constructed, with comments on what directions we expect the research to take and how the results would be useful in enhancing our understanding of nanocrystal growth behavior.

In this dissertation I present advances in the studies of artificial lattices with honeycomb topology, called artificial graphene (AG), in nano-patterned GaAs quantum wells (QWs). AG lattices with very small lattice constants as low as 40 nm are achieved for the first time in GaAs. The high quality AG lattices are created by optimized electron-beam (E-beam) lithography followed by inductively coupled plasma reactive-ion etching (ICP-RIE) process. E-beam lithography is used to define a honeycomb lattice etch mask on the surface of the GaAs QW sample and the optimized anisotropic ICP-RIE process is developed to transfer the pattern into the sample and create the AG lattices. Such high-resolution AG lattices with small lattice constants are essential to form AG miniband structures and create well-developed Dirac cones. Characterization of electron states in the nanofabricated artificial lattices is by optical experiments. Optical emission (photoluminescence) yields a determination of the Fermi energy of the electrons. A significant reduction of the Fermi energy is due to the nano-patterning process. Resonant inelastic light scattering (RILS) spectra reveal novel transitions related to the electron band structures of the AG lattices. These transitions exhibit a remarkable agreement with the predicted joint density of states (JDOS) based on the band structure calculation for the honeycomb topology. I calculate the electron band structures of AG lattices in nano-patterned GaAs QWs using a periodic muffin-tin potential model. The evaluations predict linear energy-momentum dispersion and Dirac cones, where the massless Dirac fermions (MDFs) appear, occur in the band structures. Requirements of the parameters of the AG potential to achieve isolated and well-developed Dirac cones are discussed. Density of states (DOS) and JDOS from AG band structures are calculated, which provide a basis to interpret quantitatively observed transitions of electrons involving AG bands. RILS of intersubband transitions reveal intriguing satellite peaks that are not present in the as-grown QWs. These additional peaks are interpreted as combined intersubband transitions with simultaneous change of QW subband and AG band index. The calculated JDOS for the electron transitions within the AG lattice model provide a remarkably accurate description of the combined intersubband excitations. Novel low-lying excitation peaks in RILS spectra, interpreted as direct transitions between AG bands without change in QW subband, provide a more direct insight on the AG band structures. We discovered that RILS transitions around the Dirac cones are resonantly enhanced by varying the incident photon energies. The spectral lineshape of these transitions provides insights into the formation of Dirac cones that are characteristic of the honeycomb symmetry of the AG lattices. The results confirm the formation of AG miniband structures and well-developed Dirac cones. The realization of AG lattices in a nanofabricated high mobility semiconductor offers the advantage of tunability through methods suitable for device scalability and integration. The last part of this thesis describes the growth of nanocrystalline single layer and bilayer graphene on sapphire substrates by molecular beam epitaxy (MBE) with a solid carbon source. Raman spectroscopy reveals that fabrication of single layer, bilayer or multilayer graphene crucially depends on MBE growth conditions. Etch pits revealed by atomic force microscopy indicate a removal mechanism of carbon by reduction of sapphire. Tuning the interplay between carbon deposition and its removal, by varying the incident carbon flux and substrate temperature, should enable the growth of high quality graphene layers on large area sapphire substrates.

Here, the design, synthesis and characterisation and the optoelectronic properties of Ir(III) complexes for application in nonlinear optical and electroluminescent devices are described. The type of complexes varies from those of the form [Ir(C^N)2(N^N)]+ with conjugated and nonconjugated ligands (where C^N = cyclometalating ligand and N^N = neutral ligand) to those of the form [Ir(C^N^C)(N^N)Cl] (where C^N^C = tridentate tripod ligand). Chapter 1 gives an introduction into photophysics occurring in transition metal complexes and possible applications in visual displays. The background of nonlinear optical (NLO) properties and the use of transition metal complexes as NLO chromophores is described. In Chapter 2, the impact of the use of sterically congested cyclometalating ligands on the photoluminescence properties of cationic iridium(III) complexes and their performance in light-emitting electrochemical cells is investigated. Chapter 3 explores the use of electron donors on the cyclometalating ligand towards modulating the NLO properties of the complexes. Combining strongly electron-donating substituents on the C^N ligand and electron-accepting substituents on the N^N ligand results in strong NLO activity. Chapter 4 summarises a new series of cationic iridium(III) complexes bearing benzylpyridinato as cyclometalating ligands. The methylene spacer in the C^N ligands provides flexibility, resulting in two conformers. NMR studies combined with density functional theory (DFT) studies show how the fluxional behaviour is influenced by the choice of the ancillary ligand. In Chapter 5, Ir(III) complexes bearing an unusual nonconjugated bis(six-membered) tridentate tripod ligand of the form [Ir(C^N^C)(N^N)Cl] are introduced. Depending on the substitutions of the C^N^C ligand phosphorescence ranging from yellow to red was obtained. Substitution of the N^N results in a panchromatic NIR dye, suitable for DSSC applications. In Chapter 6, the concept of a nonconjugated ligand was expanded to the N^N ligand. Blue-green and sky-blue emission was obtained, demonstrating a strategy to successfully tune the emission to the blue.

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Amostras foram preparadas pelo método de difusão a partir dos reagentes químicos SrCO3, Al2O3 e NiO em proporções estequiométricas. Medidas por difração de raios X mostraram que as amostras possuem uma única fase: SrAl2O4. Neste trabalho apresentamos imagens de microscopia eletrônica de varredura das amostras SrAl2O4 dopadas com 0,1%, 0,5%, 1,0%, 2,0%, 5,0% e 10,0% de íons de Ni2+, medidas de fotoluminescência, excitação da fotoluminescência da amostra SrAl2O4 dopada com 1,0% de íons de Ni2+, medidas de absorção fotoacústica das amostras SrAl2O4 dopadas com 1,0%, 2,0%, 5,0% e 10,0% de íons de Ni2+. Estas medidas foram realizadas a temperatura ambiente para investigar as transições eletrônicas dos íons divalente de níquel que entraram substitucionalmente nos sítios de Sr2+ da rede do SrAl2O4. Os resultados ópticos mostram a existência de três centros emissores de Ni2+. De acordo com a literatura, a estrutura do SrAl2O4 é composta de dois sítios octaédrico distintos de íons de Sr2+, o Sr12+ e o Sr22+, cujas distâncias médias Sr1 O e Sr2 O são, respectivamente, 2,800 Ǻ e 2,744 Ǻ. Visto que os íons de Ni2+ tendem a substituir os íons de Sr2+, devido ao fato de possuírem a mesma valência, é necessário considerar que uma parte dos íons de Ni2+ ocuparam os sítios dos íons de Al3+ na rede do SrAl2O4 para justificar a existência de um terceiro centro emissor de Ni2+ nesse composto. Uma novo sítio octaédrico para os íons de Ni2+ foi estimado a partir do valor da aresta do sítio tetraédrico ocupado pelos íons de Al3+ na rede do SrAl2O4 (considerando o raio iônico do Ni2+ como aproximadamente 40% maior do que o raio iônico do Al3+). As transições eletrônicas presentes nos espectros de excitação e absorção fotoacústica permitiram determinar os parâmetros de campo cristalino (Dq) e Racah (B e C) para os três sítios diferentes ocupados pelos íons de Ni2+ no SrAl2O4. Neste caso, os resultados mostraram que o sítio II dos íons de Ni2+ é associado à posição do Sr1 e possuem um parâmetro Dq menor e que o parâmetro Dq associado aos íons de Ni2+ que substituíram os íons de Sr no sitio I, o qual, por sua vez é associado à posição do Sr2. E, por fim, o sítio III que possui o menor parâmetro de campo cristalino Dq, portanto a maior distância íon ligante, é identificado como aquele relacionado ao rearranjo octaédrico local das antigas posições de Al3+. O caráter higroscópico do SrAl2O4:Ni2+ é observado a partir dos espectros de absorção fotoacústica e os modos de vibração de estiramento das ligações Ni OH e O H são identificadas nos espectros. / Samples were prepared by the conventional solid-state reaction using high purity SrCO3, Al2O3 and NiO as starting reagents in stoichiometric amounts. X-ray diffraction measurements showed that only one phase is present in the samples: SrAl2O4. In this work, qualitative analysis is also obtained from scanning eletronic microscopy (SEM) images of SrAl2O4 samples doped with 0.1%, 0.5%, 1.0%, 2.0%, 5.0% and 10.0% of Ni2+ ions. Emission and excitation spectra were obtained for SrAl2O4 samples doped with 1.0% of Ni2+ ions while photoacoustic spectroscopy were performed in the samples doped with 1.0%, 2.0%, 5.0% and 10.0% of divalent nickel ions. These measurements were performed at room temperature and the aim was to investigate the electronic transitions of divalent nickel ions which entered substitutionally in the Sr2+ sites of the SrAl2O4 compound. The optical results showed the existence of three emission centers of Ni2+ ions. According to the literature, the structure of SrAl2O4 is composed of two distinct octahedral sites of Sr2+ ions, namely Sr12+ and Sr22+, whose average distances Sr1 O and Sr2 - O are, respectively, 2,800 Ǻ and 2,744 Ǻ. Since the Ni2+ ions tend to replace the Sr2+ ions, due to the fact that they have the same valence, it is considered that a part of the Ni2+ ions occupy the sites of Al3+ ions in the SrAl2O4 structure in order to justify the existence of a third emitting center of Ni2+ ions in the compound. A new octahedral site for Ni2+ ions was estimated from the edge of the tetrahedral site occupied by Al3+ ions in the SrAl2O4 compound network (considering the ionic radius of Ni2+as approximately 40% larger than the ionic radius of Al3+). The electronic transitions in the excitation and photoacoustic absorption spectra have allowed to determine the crystal field parameters (Dq) and Racah (B and C) for the three different sites occupied by Ni2+ ions in SrAl2O4. In this case, the results showed that site II occupied by Ni2+ ions is associated with Sr1 position and has a lower Dq parameter than Dq parameter associated with Ni2+ ions which have replaced the strontium ion at the site I, associated with the Sr2 position. Finally, site III has the lowest crystal field parameter Dq, then the largest ion-ligand distance is identified as the site related to the local octahedral rearrangement of the old positions of Al3+ ions. The hygroscopic features of SrAl2O4:Ni2+ are observed from the photoacoustic absorption spectra and the stretching vibrational modes of the Ni - OH and OH bonds are identified in the spectra.

Made available in DSpace on 2014-06-11T19:31:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-02-29Bitstream added on 2014-06-13T20:21:46Z : No. of bitstreams: 1 martins_mr_dr_bauru.pdf: 576235 bytes, checksum: cae5dc5f897a536d60d112303dafaf34 (MD5) / Secretaria de Educação do Estado de São Paulo / Neste trabalho investigamos pontos quânticos de InAs sobre um substrato de GaAs crescidos pela técnica de epitaxia por feixe molecular (MBE, Molecular Beam Epitaxy). Esses pontos quânticos emitem radiação no intervalo de 1,3 üm a 1,5 üm (0,95 eV a 0,83 eV), que corresponde à janela óptica onde ocorre a mínima atenuação do sinal em redes de transmissão por fibras ópticas. Realizamos dois tipos de estudo em dois conjuntos de amostras. No primeiro caso analisamos a influência de alguns parâmetros de crescimento nas propriedades ópticas desses pontos quânticos. No segundo caso, analisamos a influência de um tratamento térmico nas propriedades ópyicas. Resultados de fotoluminescência (PL - photoluminescence) para o primeiro estudo mostraram uma grande influência da velocidade de crescimento nos espectros de emissão que apresentaram múltiplos picos, muito provavelmente associados com o estado fundamental e seus respectivos estados excitados dos pontos quânticos. Para o segundo estudo os resultados de PL mostraram que a emissão óptica consistia de uma larga banda situada entre 1,3 a 1,5 üm. Entretanto, observou-se que, após tratamento térmico durante 3 horas a uma temperatura de 550 ºC, a intensidade da PL aumentou por um fator 3. Além disso, a larga banda observada tornou-se um conjunto de pelo menos 5 picos discretos. O efeito de tratamentos térmicos em poços quânticos é bem conhecido e foi bem explorado na literatura. Em pontos quânticos, os mesmos efeitos também existem, porém, outros de igual importância tembém se apresentam. Dentre os mais importantes podemos citar a redistribuição dos tamanhos dos pontos quânticos, que podem em alguns casos limites fazer com que o ponto quântico desapareça, e a redistribuição das tensões entre a interface ponto quântico/matriz. Neste trabalho... / This study investigated InAs large quantum dot on GaAs substrate grown by the techique of molecular beam epitaxy (MBE). These quantum dots emit in the spectral range of 1.3 üm and 1.5 üm (0.95 eV to 0.83 eV), which corresponds to the window of minimal signal attenuation on transmission networks by optical fiber. We have performed two kinds of study into two different sets of samples. In the first case, we have analyzed the influence of some growth parameters on the optical properties of these quantum dots. In the second one, we have analyzed the influence of a thermal treatment on the optical properties. Results of photoluminescence (PL) on the first study showed a great influence of growth velocity in the PL spectra line shape. For the second study the results of PL on an as grown sample showed that the emission signal was a large optical band in the wave length range of 1.3 üm and 1.5 üm. However, it was observed that after the thermal treatment of 3 hours at a temperature of 550 ºC, the intensity of these PL emissions increased by a factor 3. Moreover, the observed large band has become a series of at least 5 discrete peaks. The effect of heat treatments in quantum wells is well known and has been well explored in literature. In quantum dot, the same effects are expected; however, other equally important effects are also present. The most important is the size redistribution of the quantum dots, which can in some limit cases, vanish these quantum dot. Our study identified the origin of these multiple peaks, and found emissions of PL at room temperature in the optical window between 1.3 and 1.5 üm.

Ilhas de InxGa1-xAs são de grande interesse no desenvolvimento tecnológico de lasers de diodos e diodos emissores de luz. As ilhas de InxGa1-xAs investigadas neste trabalho foram crescidas sobre um substrato semi-isolante de GaAs (001) pelo método de auto-organização usando epitaxia de feixe molecular. Este tipo de ilha, quando isolada e de pequeno tamanho, é considerada um ponto quântico ou sistema zero-dimensional. As amostras foram caracterizadas através do uso da microscopia de força atômica. A densidade e o tamanho dos pontos aumenta com a diminuição da fração molar de In, resultando em uma maior cobertura para o caso de x = O, 25. As características principais dos espectros Raman são os picos que correspondem aos modos LO e TO do substrato de GaAs. Duas estruturas adicionais aparecem no espectro: um pico estreito em 222 cm- 1 e uma banda larga de mais alta energia, que só é resolvida para x = O, 25, centrada em 245 cm-1. O pico em 222 cm-1 é provavelmente devido ao fônon LA(X) do GaAs normalmente proibido, induzido por defeitos. Para identificar a banda larga foi construído um modelo que considera: (i) a frequência Raman do modo tipo- InAs com caráter de LO como constante com a variação de x no InGaAs 3-D; (ii) efeitos de confinamento não afetam a frequência Raman dado ao tamanho dos pontos quânticos das amostras deste trabalho; (iii) A tensão escala com x e o valor máximo ocorre para o composto binário InAs. Este modelo permite prever um intervalo de frequências para os pontos quânticos. O valor medido, 245 cm- 1, está dentro deste intervalo e portanto foi atribuído ao modo tipo-InAs dos pontos quânticos de In0,25Ga0,75As Considerações de simetria reforçam esta designação. Contribuições adicionais de fônons foram consideradas no intervalo de energia de interesse. Para analisar estas contribuições, foi feito um estudo detalhado dos fônons induzidos por desordem em camadas de GaAs, e espalhamento Raman de As cristalino e amorfo. A desordem foi produzida através da erosão por laser e a amostra de As foi formada por um processo de oxidação de um filme de AlAs. Comparação dos espectros Raman permitiu concluir que não houve contribuição de fônons induzidos por desordem no espectro do ponto quântico, seja de GaAs ou arsênio. / InxGa1-x As islands are interesting for use in Laser diode and light-emitting diode technology. The InxGa1-x As islands investigated in this work were grown on semi-insulating (001) GaAs substrates by the self-organization method using molecular beam epitaxy. This type of island, when isolated and of small size, is considered as a quantum dot or zero-dimensional system. The samples were characterized by use of atomic force microscopy. The dot density and size were seen to increase as the In molar fraction decreased, resulting in a large dot­ coverage in the case of x = 0.25. The Raman spectra main features were the peaks corresponding to the LO and TO modes of GaAs-substrate. Second order structures were also present around 520 cm-1 (160 cm-1) for optical (acoustic) vibration of GaAs. Two additional structures appear as a sharp peak at 222 cm- 1 and higher energy broad band, which is resolved only for x = 0.25, at 245 cm- 1. The peak in 222 cm-1 is probably due to the normally forbidden GaAs LA(X) phonon induced by defects. To assign the broad band a model was constructed that considers: (i) the Raman frequency of the InAs-like mode with LO character as constant with x in bulk I nGaAs; (ii) confinement effects for the large dots formed has negligible effects in the quantum dot Raman frequency; (iii) The strain scale with x, the maximun value corresponds to that obtained for InAs. This model allowed to predict a range of frequencies for the dots. The value measured, 245 cm- 1, fit into this range and is, thus, attributed to the InAs-like mode of the In0.25Ga0.75As quantum dots. Selection rules arguments reinforces this assignment. Several additional contributions in the frequency range of interest were considered. In order to analyze those contributions, a detailed study of disorder induced phonons in GaAs, and Raman scattering of As-crystaline and amorphous, was realized. The disorder was produced by laser ablation and the As sample was formed by an oxidation process of an A1As film. Comparison of the Raman spectra allowed to conclude that neither As or GaAs disorder induced phonons contribute to the quantum-dot spectrum.

The propagation of light beams in inhomogeneous dielectric media is considered. The derivation begins with first principles and remains general enough to include off-axis asymmetric multimode input beams in tapered lenslike media with spatial variations of gain or loss. The tapering of lenslike media leads to a number of important applications. A parabolic taper is proposed as a model for a heated axially stretched fiber taper, and beams in such media are fully characterized. Other models are proposed by the concatenation of a parabola with other taper functions.