Made available in DSpace on 2014-06-11T19:25:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-12-20Bitstream added on 2014-06-13T20:53:40Z : No. of bitstreams: 1 eliziario_sa_dr_araiq.pdf: 5799705 bytes, checksum: 475fdd38575a6c0423c92bf7f59d2328 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O presente trabalho teve como objetivo estudar a formação dos pós com sistemas Pb1-xBaxTiO3, Pb1-xCaxTiO3 e Pb1-xSrxTiO3, em que x = 0; 0,25; 0,5; 0,75 e 1, por intermédio do método hidrotermal associado ao aquecimento em forno de microondas. Estudos foram realizados para a obtenção de um maior entendimento das diferentes propriedades ópticas e eletrônicas das perovskitas, em função da concentração dos dopantes e dos diferentes tempos utilizados nas sínteses. A fim de verificar as suas características estruturais estes pós foram analisados por difração de raios X (DRX), espectroscopia de absorção na região do ultravioleta visível (UV-vis), espectroscopia na região do infravermelho (IV) e de fotoluminescência (FL). Os resultados de DRX confirmaram a presença da fase Pb1-xBaxTiO3 juntamente com a fase BaCO3, enquanto que as fases Pb1-xCaxTiO3 e Pb1-xSrxTiO3 apresentam-se monofásicas. As micrografias obtidas por microscopia eletrônica de varredura com canhão de elétrons por emissão de campo (FEG-MEV) indicam o mecanismo de cristalização-dissolução-recristalização para as amostras do sistema Pb0,5Ba0,5TiO3 e formação de mesocristais para as amostras de PCT. Todos os materiais sintetizados apresentaram propriedades fotoluminescentes, apresentando emissões na região de diferentes comprimentos de onda, sugerindo que as amostras possuem propriedades estruturais que dependem do cátion adicionado. Dessa forma, a emissão pode ser atribuída a distorções nos clusters [TiO6], bem como a existência de clusters complexos de [TiO5], [BaO11], [CaO11] e [SrO11] associados as vacâncias de oxigênio. Testes de aplicação de ferroeletricidade foram realizados, porém as amostras sofreram baixa densificação devido a volatilização do chumbo, no aquecimento em forno convencional / In this work, were studied the formation of powders by microwave hydrothermal method in systems Pb1-xBaxTiO3, Pb1-xCaxTiO3 and Pb1-xSrxTiO3, where x = 0, 0.25, 0.5, 0, 75 and 1. Studies were conducted to obtain a greater understanding of the different optical and electronic properties of perovskites, depending on the concentration of dopants and different times used in the synthesis. These powders were analyzed by X-ray diffraction (XRD), scanning electron microscopy field emission gun (FEG-SEM), ultraviolet visible spectroscopy (UV-vis) infrared spectroscopy (IV) and photoluminescence spectroscopy (PL). The XRD patterns confirmed the second phase BaCO3 in Pb1-xBaxTiO3, while the phase Pb1-xSrxTiO3 present single-phase and the phase Pb1-xCaxTiO3 present two structural phases of same composition at 140 °C. FEG-SEM micrographs indicate the mechanism of crystallization-dissolution-recrystallization for samples of the system Pb0,5Ba0,5TiO3 and „„non-classical crystallization‟‟ with mesocrystal formation for samples of the system PCT. All materials synthesized showed photoluminescent properties, showing regions emissions of different wavelengths, suggesting that samples have structural properties that depend on the cation added. Thus, the emission can be attributed distortions in the clusters [TiO6], and existence of complex clusters [TiO5], [BaO11], [CaO11] e [SrO11] associated oxygen vacancies. Tests were performed applying ferroelectricity, but the samples were subjected to low densification due to volatilization of lead in the conventional oven heating

No description available.

In this dissertation, Zinc oxide (ZnO) nanorods grown by a two-step chemical bath deposition method on Si substrate is characterized. Research was conducted on ZnO nanorods for the understanding of their optical properties at room temperature (RT), with the emphasis on the visible luminescence. To this end, controlled thermal treatments of as-grown ZnO nanorods were conducted under different conditions, such as annealing time and environment, at atmospheric pressure. Results related to the following studies are reported: an investigation of the structure of ZnO nanorods, an analysis of the chemical composition of the surface, an investigation of the surface stoichiometry of the rods, and a study of defect-related photoluminescence of ZnO nanorods upon thermal treatment in different ambients.To achieve this, the samples were investigated by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) and room temperature (RT) photoluminescence Spectroscopy (PL). As-grown ZnO nanorods exhibit a hexagonal shape and have the wurtzite structure; they have, respectively, an average length and diameter of ~900 nm and ~50 nm, and most of the rods are perpendicular to the substrate. The main extrinsic species found in as-grown nanostructures are C, H, F, S, and Cl. ToF-SIMS and XPS confirmed the presence of H related-defects, and the oxygen 1 S XPS peak at 531.5 eV is therefore assigned to oxygen bound to H-related defects. Based on stoichiometry studies, it is found that the near surface regions of as-grown ZnO nanorods (2 to 10 monolayers) are rich in Zn. The RT luminescence of as-grown ZnO nanorods exhibits a near band edge emission centered at ~379.5 nm and deep level emission extending from ~450 nm to ~850 nm. When these nanorods are thermally treated at high temperatures (>850 oC), it is found that even though their crystalline quality is preserved, their morphology is significantly affected, regardless of annealing ambient. Furthermore, in the near surface regions of annealed ZnO nanorods it is found that the Zn/O stoichiometric ratios deviate from unity. Specifically, oxygen vacancies form within the first 100 nm from the sample surface. Further from the surface, the material is deficient in Zn. It is deduced from XPS and AES that the ambient affects the activation rate of intrinsic defects. Furthermore, the only extrinsic defects that are affected by thermal treatment are found to be H-related defects. At high annealing temperatures (300 oC to ~700 oC), H-related defects are removed, and this removal process is found to affect significantly the RT luminescence properties of ZnO nanorods. Specifically, hydrogen passivates vacancy-related defects, depending on the thermal treatment. PL spectroscopy is used to follow this passivation effect as a function of annealing temperature, which causes an initial quenching followed by an enhancement of the green and the red luminescence, regardless of the ambient. Finally, the green luminescence that arises following annealing above ~800 oC is assigned to Zn vacancy-related defects, while the red luminescence that dominates the visible band of ZnO nanorods upon annealing between 400 oC and 600 oC is suggested to be due to oxygen vacancy-related defects.

MgxZn1-xO has emerged as a material of great technological importance. Having a direct energy band gap that is tunable throughout much of the ultraviolet (UV) region of the spectrum from the near-UV (~370 nm) to the deep-UV (~176 nm), this compound is of interest for a variety of optoelectronic devices operating in this part of the electromagnetic spectrum. MgxZn1-xO offers advantages over the more mature compound semiconductor AlGaN which stem mainly from the unusually high exciton binding energy (60 meV in ZnO). In this study the growth of ZnO and MgxZn1-xO thin films using metal organic chemical vapour deposition (MOCVD) is systematically investigated. The films are mainly grown on c-Al2O3 and Si (100) and characterized using various techniques, such as photoluminescence (PL), x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and auger electron spectroscopy (AES). The optical and the structural properties are essentially inspected in order to improve their quality. In this thesis the optimisation of ZnO grown using oxygen gas as a new oxidant in our reactor is investigated. The growth temperature and VI/II ratio are varied in order to find optimum parameters giving high quality layers. The effects of Si (100), Si (111), c- and r-sapphire, glass, GaAs and ZnO substrates on the optical, structural and morphological properties of ZnO thin films grown with tert-butanol (TBOH) is examined. Similar morphologies are observed for all substrates, with the films comprising hexagonal columns having cone shaped ends. The photoluminescence spectra are similar, but the various transitions have different relative intensities. It is clear that the different substrates influence neither the orientation of the films, nor the surface morphology, significantly. The photoluminescence hints at larger stacking fault densities in films grown on silicon and glass, however, as evidenced by stronger basal plane stacking fault-related luminescence at ~3.319 eV in the relevant low temperature photoluminescence spectra. The morphology changes with Mg incorporation, from hexagonal columnar structures to cubic faceted columns. From PL, the full with at half maximum is found to gradually increase with Mg content due to alloy broadening. The deep level emission (DLE) is observed to shift with Mg content. By changing the Mg content, the band gap of MgxZn1-xO film is tuned by ~450 meV, which provides an excellent opportunity for band gap engineering for optoelectronic applications. The c-lattice constant of ZnO (5.205 Å) decreases by only 0.6% when the Mg content reaches x=0.39. The introduction of Mg into ZnO is shown to increase the relative PL intensity of stacking fault-related transitions (at 3.314 eV for ZnO). This becomes the dominant near band edge emission. Using TEM a thin Mg rich layer is observed at the interface between the film and the Si or Al2O3. Temperature dependent PL measurements on layers with low Mg concentration (x=0.05 and 0.1) show that the main bound exciton peak exhibits an “s-shaped” temperature dependence, characteristic of localization in a disordered alloy. The origin of the PL line broadening of MgxZn1-xO (x≤0.04) is also analyzed with respect to alloy broadening, taking into account a random cation distribution and alloy clustering. The influence of various MOCVD growth parameters such as growth temperature and VI/II ratio is studied. Varying the temperature from 280 ˚C to 580 ˚C reveals strong morphological changes and optical degradation of the films. Low (<280 ˚C) and high (>580 ˚C) growth temperatures reduce the Mg incorporation. High VI/II ratios also decrease the Mg incorporation, as evidenced by the red-shift of the donor bound exciton (D°X) line. This is ascribed to a stronger premature reaction between (MeCp)2Mg and the oxidant or a preferential heterogeneous interaction between the Mg and oxygen species on the growth front. For both oxidizing agents (O2 and TBOH), the growth at 420 ˚C and a VI-II ratio of 60 on c-Al2O3 gave optimal quality layers in terms of their optical and structural quality. A comparison of films grown using TBOH and O2 gas as oxidizing agent shows no major difference in terms of Mg incorporation. The effect of annealing, the inclusion of a buffer layer and the influence of growth rate on the properties MgxZn1-xO thin films are also reported.

Le niobate de lithium (LN), en raison de ses propriétés, électro-optiques, optiques non linéaires et photoréfractives (PR) , s'impose comme un matériau de choix pour des applications en modulation, filtrage, stockage holographique ou conversion de fréquence optique. L'effet PR est gouverné à la fois par les centres profonds extrinsèques (Fe2+ et Fe3+ le plus souvent) et par les antisites niobium en site (Nbli5+), qui constituent des pièges préférentiels pour les électrons arrachés aux donneurs profonds et forment ainsi des polarons liés Nbli4+, caractérisables par une large bande d'absorption photo-induite (API) s"étendant dans le rouge et le proche infrarouge, ainsi que par une bande de photoluminescence (PL) légèrement décalée en longueur d'onde par rapport à la précédente. Nous présentons ici une étude expérimentale de la PL polaron dans le LN congruent dopé fer, fonction de la température et de l'intensité lumineuse excitatrice, en régime continu et en régime pulsé, ainsi qu'un modèle phénoménologique à trois centres permettent d'interpréter toutes les caractéristiques observées. Nous montrons que la PL permet en principe de doser les donneurs profonds dans le LN congruent en qualité infime, que soit leur nature. Pour les ions Fe2+, la détectivité est typiquement de 0,25 ppm à l'ambiante, ce qui est bien meilleur que la spectroscopie d'absorption. La PL résolue spatialement permet en outre, contrairement aux autres techniques, de cartographier la concentration de donneurs profonds à l'échelle micrométrique, d'où son potentiel pour la caractérisation de guides d'onde, de composants optiques intégrés ou autres microstructures / Because of their electro-optical, non-linear optical and photorefractive effet, lithium niobate crystals (LN) are used in many applications such as modulation, filtering, holographic storage or frequency conversion. Its known that the photorefractive effect is influenced by both extrincic deep centers (Fe2+ and Fe3+ in most cases) and by niobium antisites (Nbli5+) which constitute preferential sites to trap an electron hence giving a small bound polaron (Nbli4+). This defect is characterized by a photo_indiced obsorption (API) broad band in the NIR range, as well as slightly Stokes shifted photoluminescence band (PL). We presnt nerein an experime,tal study of the polaron related PL in iron doped congruent lithium niobate as a function of temperature and incident intensity in CW and pulsed regime. We also propose a phenomenological threecenter model as an interpretation of all observed results. We show that the PL permits one to determine the concentration of deep centres in congruent LN in trace amounts, whatever their nature. For Fe 2+ ions, the sensitivity is typically around 0,25 ppm at RT, which is better than absorption spectroscopy. In addition, unlike other techniques, the PL is spatially resolved (micrometer scale) which allows to maps the concentration of deep donors, hence its potential for characterizating waveguides, integrated optical components and other microstructures

The photoluminescence spectrum of phosphorus-doped silicon at 17 _ 3 19-3 dopant concentrations ranging from 1.2 x 10¹⁷ cm⁻³ to 4.0 x 10¹⁹ cm⁻³ is studied as a function of excitation intensity. The spectra are interpreted tn terms of two types of recombination events', one' attributed to the recombination of oppositely charged carriers inside an electron-hole droplet and the other outside due to the recombination -of free holes with electrons in the impurity band. The latter type of event gives rise to a new photoluminescence peak observed for the first time. The line shape of this peak compares very well with a first principle calculation of the impurity band density of states within the Hubbard model. Existing theories for the ground state energy of an electron-hole droplet in n-type heavily doped silicon are reviewed and new numerical results are presented. However, within the present model droplets are not theoretically understood at this time in heavily-doped silicon. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

III-V nitrides have been put to use in a variety of applications including laser diodes for modern DVD devices and for solid-state white lighting. Plasmonics has come to the foreground over the past decade as a means for increasing the internal quantum efficiency (IQE) of devices through resonant interaction with surface plasmons which exist at metal/dielectric interfaces. Increases in emission intensity of an order of magnitude have been previously reported using silver thin-films on InGaN/GaN MQWs. the dependence on resonant interaction between the plasmons and the light emitter limits the applications of plasmonics for light emission. This dissertation presents a new non-resonant mechanism based on electrostatic interaction of carriers with induced image charges in a nearby metallic nanoparticle. Enhancement similar in strength to that of plasmonics is observed, without the restrictions imposed upon resonant interactions. in this work we demonstrate several key features of this new interaction, including intensity-dependent saturation, increase in the radiative recombination lifetime, and strongly inhomogeneous light emission. We also present a model for the interaction based on the aforementioned image charge interactions. Also discussed are results of work done in the course of this research resulting in the development of a novel technique for strain measurement in light-emitting structures. This technique makes use of a spectral fitting model to extract information about electron-phonon interactions in the sample which can then be related to strain using theoretical modeling.

This dissertation is a study of two major topics that involve synthetic strategies for new classes of phosphorescent gold(I)-based metallodendrimers. The phosphorescence of organic and inorganic luminophores originates from spin-orbit coupling owing to internal or external heavy atom effects as well as metal-centered emissions. Previous work in the Omary group entailed systematically designed small molecules, metallopolymers, and unconjugated metallodendrimers that contain d10 and d8 metals, whereas this dissertation aims in part to expand such strategies to the conjugated metallodendrimer regime. In one approach novel synthetic strategies were used to make first-generation phenyl acetylene dendrimers and phosphine derivatives thereof. The phosphine dendrimers are made by tethering one of the phosphines to an unsaturated dendrimer, as such phosphine dendrimers are better chromophores and luminophores due to their structural rigidity and extended conjugation. In another approach, 2- and 3-coordinate Au(I) dendritic complexes are synthesized from these phosphine dendrimers. This study is further extended to study metallodendritic complexes with different cores, for example triphenylene-based metallodendritic complexes with six acetylene branches. The physical properties of the metallodendrimers can be modulated upon proceeding to further dendrimer generations or by using solubilizing groups on the peripheral phosphines, thus allowing better processability for thin-film fabrication as required for molecular electronic devices and higher chance for crystal growth toward accurate structural characterization. Other data produced in this project suggested that some structural alterations led to porous solids that render them suitable for realized and potential applications in energy storage and carbon capture. The interesting luminescence properties of the metallodendrimers and porous extended solids produced in this dissertation are significant toward utilizing such materials for optoelectronic applications such as energy-saving organic light-emitting diodes and optical sensors for environmental pollutants.

No description available.

Surface modification of polystyrene thin films was achieved using a plasma process with reactive gases to form functional groups. Advancing contact angles were measured after modification. Polystyrene surfaces were observed to reach a minimum average wetting contact angle of 7 degrees. The time required to achieve this contact angle decreased significantly by increasing the power of the discharge or by lowering the discharge source closer to the polymer substrate. Characterization studies of power, height, and corona exposure time versus contact angle led to the formation of surface energy gradients across the substrate. Photoluminescent tagging agents were used to quantify the degree of carboxyl modification achieved with water plasma and amine modification achieved with ammonia plasma. AMCA (7-amine-4-methyl coumarin hydrazide) was used to show that surface modification reaches a maximum functionalization before degradation of the polymer substrate occurs with water vapor. A parallel study with OPA (O-phthaldialdehyde) yielded similar results when ammonia was ionized over the surface. Additionally, stable surfaces were created by chemical reaction of zinc acetate with the freshly modified polymer. Zinc sulfide particles were formed within the polymer surface by reaction with hydrogen sulfide gas. Flourescence spectroscopy was used to verify the formation of zinc sulfide. / Master of Science