Over the last five years hybrid organic-inorganic metal halide perovskites have attracted strong interest in the solar cell community as a result of their high power conversion efficiency and the solid opportunity to realise a low-cost as well as industry-scalable technology. Nevertheless, several aspects of this novel class of materials still need to be explored and the level of our understanding is rapidly and constantly evolving, from month to month. This dissertation reports investigations of perovskite solar cells with a particular focus on their local chemical composition. The analytical characterisation of such devices is very challenging due to the intrinsic instability of the organic component in the nanostructured compounds building up the cell. STEM-EDX (Scanning Transmission Electron Microscopy - Energy Dispersive X-ray spectroscopy) was employed to resolve at the nanoscale the morphology and the elemental composition of the devices. Firstly, a powerful procedure, involving FIB (Focus Ion Beam) sample preparation, the acquisition of STEM-EDX maps and the application of cutting edge post-processing data techniques based on multivariate analysis was developed and tested. The application of this method has drastically improved the quality of the signal that can be extracted from perovskite thin films before the onset of beam-induced transformations. Morphology, composition and interfaces in devices deposited by using different methodologies and external conditions were then explored in detail by combining multiple complementary advanced characterisation tools. The observed variations in the nanostructure of the cells were related to different photovoltaic performance, providing instructive indications for the synthesis and fabrication routes of the devices. Finally, the main degradation processes that affect perovskite solar cells were probed. STEM-EDX was used in conjunction with the application of in situ heating, leading to the direct observation of elemental species migration within the device, reported here for the first time with nanometric spatial resolution. Further analyses, involving a set of experiments aimed to study the effects of air exposure and light soaking on the cells, were designed and performed, providing evidence of the main pathways leading to the drastic drop in the device performance.

Four negative stains, hafnium chloride and europium, samarium and gadolinium nitrates, were tested in single particle electron microscopy as potential alternatives to uranyl acetate, which is recently being widely restricted for its toxicity. The new stains were applied to a structurally well-described plant photosystem I, visualized by a transmission electron microscope and classified in a single particle analysis. The quality of the stains was evaluated by the obtained resolution and ability to provide reliable structural information.

Made available in DSpace on 2014-06-11T19:32:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-07-20Bitstream added on 2014-06-13T19:02:32Z : No. of bitstreams: 1 volanti_dp_dr_araiq.pdf: 1844353 bytes, checksum: 8213435ede38e29d8f618a9b95eeb7c7 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O trabalho que se apresenta centra-se no estudo investigativo do crescimento de cristais de óxido de cobre (II), CuO, com cristais organizados em diferentes formas semelhantes à ouriços-do-mar, fibras, e nanobastões, com controle fino da morfologia e cristalizados pelo método hidrotérmico assistido por micro-ondas. Esses materiais foram previamente caracterizados por difração de raios X (DRX), medida de área de superfície específica, espectroscopia de fotoelétrons excitados por raios X, microscopia eletrônica de varredura de alta resolução e de transmissão, além de espectroscopia de absorção de raios X próxima à borda de absorção (XANES), e outras. Pelas técnicas de microscopia combinadas foi possível caracterizar detalhadamente os materiais sintetizados, como sua estrutura, forma, tamanho, composição química, direção de crescimento, etc. Os óxidos obtidos foram testados quanto suas propriedades catalíticas na reação de desidrogenação do etanol – atividade, seletividade, frequência de reação. A originalidade do trabalho é que ao compreender as relações entre a morfologia do cristal e a estrutura da superfície dos óxidos nanoestruturados será possível obter catalisadores mais sensíveis, seletivos e com maior atividade catalítica. Ademais, foram realizados experimentos in situ de redução e reoxidação a temperatura programada, monitorada por XANES e DRX, resolvidos no tempo e na temperatura. Assim obteve-se uma projeção semiquantitativa de diferentes espécies de clusters de cobre (Cu2+, Cu+, e/ou Cu0). Esses resultados sugerem particularidades intrínsecas devido às diferentes morfologias no estado ativo nas cinéticas de redução e reoxidação. Em suma, foi desenvolvida uma rota sintética rápida e eficaz para sintetizar estruturas de CuO com diversas morfologias. Os materiais foram... / The present work goal the crystal growth of copper (II) oxide (II), CuO, with in different particles assembly. Herein, we report results of three distinct controlled CuO morphologies, urchin-like, fiber-like and nanorods, with fine control of morphology and crystallized by microwave assisted hydrothermal method. These materials were previously characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy, surface area determination, scanning electron microscopy high-resolution and transmission electron microscopy, and absorption spectroscopy, X-ray absorption near edge (XANES), and others. The entire sequence of the crystallization procedure of CuO was monitored by field emission scanning electron microscopy in combination with transmission electron microscopy combined was possible to characterize in detail the materials synthesized, and its structure, shape, size, chemical composition, direction of growth, etc. The oxides obtained were tested for their catalytic properties in the reaction of dehydrogenation of ethanol – activity, selectivity, turnover frequency. The originality of this work is that by understanding the relationships between morphology and crystal structure of the surface oxides of nanostructured catalysts will be possible to obtain more sensitive and more selective catalytic activity. Copper-based catalysts obtained by microwave-assisted morphosynthesis were correlated with the dehydrogenation of ethanol. The degree of reduction and reoxidation was monitored using time-resolved in situ XANES and XRD during TPR under H2 and TPO under O2. A semiquantitative estimation of the different chemical forms (Cu2+, Cu+, and/or Cu0) was obtained. The results suggest intrinsic particularities due to different morphologies at the active state in reduction kinetics. In summary, we developed a rapid... (Complete abstract click electronic access below)

Metallophthalocyanine-single walled carbon nanotube conjugates were successfully synthesized and applied in the electrochemical characterizations of pesticides (amitrole and diuron) and 2-mercaptoethanol (2-ME). The formation of conjugates was confirmed through the use of the following analytical techniques: UV-vis, FTIR, Raman and XRD spectroscopies, atomic force and transmission electron microscopies and voltammetry. Chemically linking SWCNT to MPcs created platforms that offered efficient transfer of electrons and this was confirmed through electrochemical impedance studies (EIS) and voltammetry as shown by lower ΔEp values observed in conjugates. Carboxy carrying MPcs have very poor electron transfer kinetics (both tetrasubstituted and low symmetry), but the presence of SWCNTs activates their catalysis. All electrochemical studies were done at pH 4. Cyclic voltammetry, rotating disk linear sweep voltammetry, chronoamperometry and EIS were used in the electrochemical characterization of 2-ME and the pesticides on poly-Ni(OH)TAPc and MPc-SWCNT modified glassy carbon electrodes (GCEs). High Tafel slopes were observed for the pesticides relative to 2-ME, an indication of the passivating nature of their oxidation products. However, conjugates showed very high resistances to passivation and were easily regenerated by shaking in methanol. Improved catalysis of the conjugates is also indicated by the high catalytic rate constants for the analytes, observed on these electrodes. Conjugates of low symmetry MPcs with SWCNTs gave the highest catalytic rate constants, confirming better catalysis on these electrode surfaces. The nature of SWCNT functionalization also affected catalysis, with amine functionalized SWCNTs inducing better catalytic properties into the MPcs than carboxylic acid terminated CNTs. The presence of amine functionalized SWCNTs activates the catalysis of non-catalytic carboxy-carrying MPcs and this is more pronounced in conjugates of tetrasubstituted MPcs relative to those of low symmetry Pcs. Ethylene amine (EA) functionalized SWCNTs reduced redox overpotentials of the MPcs more than the phenyl-amine (PA) functionalized counterparts. Poly-NiTAPc was successfully converted to poly-Ni(OH)TAPc through cyclisation in pH 4 buffer and showed very good catalytic properties towards diuron, relative to the former.

A manutenção da morfologia normal do endotélio da córnea é um importante indicador da integridade funcional. A reparação endotelial frente a um trauma, em coelhos, ocorre por migração, hipertrofia e mitose celular. Objetivou-se comparar a morfologia das células do endotélio, da região periférica perincisional à região central, da córnea de coelhos (Oryctolagus cuniculus) em diferentes períodos pós-operatórios. Foram designados três grupos, com 5 animais cada, para avaliação pós-operatória, sendo G1 (7 dias); G2 (15 dias) e G3 (45 dias). Trinta bulbos dos olhos de coelhos, da raça Nova Zelândia, foram submetidos à incisão de córnea clara uniplanar com 3,2 mm. Ao fim dos períodos determinados, procedeu-se a avaliação da morfologia endotelial valendose da microscopia eletrônica de varredura. Realizaram-se seis eletromicrografias de varredura, de cada região da córnea, com aumento de 1000 vezes. Para análise do percentual do número de lados celular, foram analisadas 100 células endoteliais. Na região periférica perincisional, avaliada ao 7° dia de pós-operatório, foram encontradas células com 6 lados (47,8%), 5 lados (31,3%), 7 lados (13,9%), 3 lados (0,1%), 4 lados (4,9%), 8 lados (1,8%) e 9 lados (0,2%). Na avaliação ao 15° dia de pós-operatório, observaram-se células com 6 lados (45,6%), 5 lados (32,6%), 7 lados (17,4%), 4 lados (1,7%) e 8 lados (2,7%). No 45° dia de pós-operatório, verificou-se a presença de células com 6 lados (57%), 5 lados (24%), 7 lados (17,2%), 4 lados (0,1%), 8 lados (1,6%) e 9 lados (0,1%). Na área central, ao 7° dia de pós-operatório, detectaram-se células com 6 lados (75,6%), 5 lados (13,3%), 7 lados (10,8%) e 8 lados (0,3%). Na avaliação, ao 15° dia de pós-operatório, foi possível observar células com 6 lados (78,9%), 5 lados (11,5%) e 7 lados (9,6%). No 45° dia de pós-operatório identificaram-se células com 6 lados (74,8%), 5 lados (13,6%) e 7 lados (11,6%). Os resultados demonstraram que na região periférica perincisional ocorreu diminuição das células com seis lados e aumento do número de células com cinco e sete lados. Na região central manteve-se o padrão regular de hexagonalidade das células endoteliais nos diferentes períodos pós-operatórios. Conclui-se que houve alteração na morfologia das células endoteliais, da região periférica perincisional comparada à região central, da córnea de coelhos nos diferentes períodos pós-operatórios. / The maintenance of the normal corneal endothelium morphology is an important indicator of its functional integrity. In rabbits, endothelial repair in the event of traumas is made through cell migration, hypertrophy and mitosis. The purpose of this study was to compare the morphology of endothelial cells of the perincisional area with the central area of the cornea of rabbits (Oryctolagus cuniculus), in different post-operative periods. Three groups containing 5 animals each were designed for post-operative evaluation: G1 (7 days); G2 (15 days) and G3 (45 days). The clear cornea of thirty New Zealand rabbits was subjected to a single-planed incision of 3.2 mm. At the end of the established periods, a morphological evaluation of the endothelium was carried out using scanning electron microscopy. Six scanning electron micrographs of each corneal area were performed using a magnification of 1000 x. One hundred endothelial cells were analyzed to obtain the cell side count percentage. In the perincisional peripheral area, which was evaluated at the 7 post-operative day, 6-sided (47.8%), 5-sided (31.3%) and 7-sided (13.9%) cells were found, in addition to, 3-sided cells (0.1%), 4-sided cells (4.9%), 8-sided cells (1.8%) and 9-sided cells (0.2%). In the evaluation made on the 15th post-operative day, 6-sided (45.6%), 5-sided (32.6%) and 7-sided (17.4%) cells were observed, as well as 4-sided (1.7%) and 8-sided cells (2.7%). On the 45th postoperative day, the presence of 6-sided (57%), 5-sided (24%), 7-sided (17.2%), 4-sided (0,1%), 8-sided (1.6%) and 9-sided cells (0.1%) was verified. On the 7th post-operative day, 6-sided (75.6%), 5-sided (13.3%), 7-sided (10.8%) and 8-sided cells (0.3%) were observed in the central area .Upon evaluation made on the 15th post-operative day, it was possible to observe 6-sided (78.9%), 5-sided (11.5%) and 7-sided (9.6%) cells. Results have shown that there was a reduction of six-sided cells and an increase in the number of five and seven-sided cells in the perincisional peripheral area. The regular hexagonal standard of the endothelial cells was maintained in the central area in different post-operative periods. In comparison to the central area, there was a morphological alteration of the endothelial cells of the peripheral perincisional area in different post-operative periods of the cornea of rabbits.

abstract: Because of their favorable ionic and/or electronic conductivity, non-stoichiometric oxides are utilized for energy storage, energy conversion, sensing, catalysis, gas separation, and information technologies, both potential and commercialized. Charge transport in these materials is influenced strongly by grain boundaries, which exhibit fluctuations in composition, chemistry and atomic structure within Ångstroms or nanometers. Here, studies are presented that elucidate the interplay between macroscopic electrical conductivity, microscopic character, and local composition and electronic structure of grain boundaries in polycrystalline ceria-based (CeO2) solid solutions. AC impedance spectroscopy is employed to measure macroscopic electrical conductivity of grain boundaries, and electron energy-loss spectroscopy (EELS) in the aberration-correction scanning transmission electron microscope (AC-STEM) is used to quantify local composition and electronic structure. Electron diffraction orientation imaging microscopy is employed to assess microscopic grain boundary character, and links these macro- and nanoscopic techniques across length scales. A model system, CaxCe1-xO2-x-δ, is used to systematically investigate relationships between nominal Ca2+ concentration, grain boundary ionic conductivity, microscale character, and local solute concentration. Grain boundary conductivity varied by several orders of magnitude over the composition range, and assessment of grain boundary character highlighted the critical influence of local composition on conductivity. Ceria containing Gd3+ and Pr3+/4+ was also investigated following previous theoretical work predicting superior ionic conductivity relative to state-of-the-art GdxCe1-xO2-x/2-δ. The grain boundary conductivity was nearly 100 times greater than expected and a factor four enrichment of Pr concentration was observed at the grain boundary, which suggested electronic conduction that was cited as the origin of the enhanced conductivity. This finding inspired the development of two EELS-based experimental approaches to elucidate the effect of Pr enrichment on grain boundary conductivity. One employed ultra-high energy resolution (~10 meV) monochromated EELS to characterize Pr inter-bandgap electronic states. Alternatively, STEM nanodiffraction orientation imaging coupled with AC-STEM EELS was employed to estimate the composition of the entire grain boundary population in a polycrystalline material. These compositional data were the input to a thermodynamic model used to predict electrical properties of the grain boundary population. These results suggest improved DC ionic conduction and enhanced electronic conduction under AC conditions. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2016

abstract: Nanocrystalline (nc) thin films exhibit a wide range of enhanced mechanical properties compared to their coarse-grained counterparts. Furthermore, the mechanical behavior and microstructure of nc films is intimately related. Thus, precise control of the size, aspect ratio and spatial distribution of grains can enable the synthesis of thin films with exceptional mechanical properties. However, conventional bottom-up techniques for synthesizing thin films are incapable of achieving the microstructural control required to explicitly tune their properties. This dissertation focuses on developing a novel technique to synthesize metallic alloy thin films with precisely controlled microstructures and subsequently characterizing their mechanical properties using in situ transmission electron microscopy (TEM). Control over the grain size and distribution was achieved by controlling the recrystallization process of amorphous films by the use of thin crystalline seed layers. The novel technique was used to manipulate the microstructure of structural (TiAl) and functional (NiTi) thin films thereby exhibiting its capability and versatility. Following the synthesis of thin films with tailored microstructures, in situ TEM techniques were employed to probe their mechanical properties. Firstly, a novel technique was developed to measure local atomic level elastic strains in metallic glass thin films during in situ TEM straining. This technique was used to detect structural changes and anelastic deformation in metallic glass thin films. Finally, as the electron beam (e-beam) in TEMs is known to cause radiation damage to specimen, systematic experiments were carried out to quantify the effect of the e-beam on the stress-strain response of nc metals. Experiments conducted on Al and Au films revealed that the e-beam enhances dislocation activity leading to stress relaxation. / Dissertation/Thesis / Supplementary Video S1 / Supplementary Video S2 / Supplementary Video S3 / Doctoral Dissertation Materials Science and Engineering 2017

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