This thesis is about new ways to experimentally realise materials with desired nano-structures for solution-processable optoelectronic devices such as solar cells and light-emitting diodes (LEDs), and examine structure-performance relationships in these devices. Short exciton diffusion length limits the efficiency of most exciton-based solar cells. By introducing nano-structured architectures to solar cells, excitons can be separated more effectively, leading to an enhancement of the cell’s power conversion efficiency. We use diblock copolymer lithography combined with solvent-vapour-assisted imprinting to fabricate nano-structures with 20-80 nm feature sizes. We demonstrate nanostructured solar cell incorporating the high-performance polymer PBDTTT-CT. Furthermore, we demonstrated the patterning of singlet fission materials, including a TIPS-pentacene solar cell based on ZnO nanopillars. Recently perovskites have emerged as a promising semiconductor for optoelectronic applications. We demonstrate a perovskite light-emitting diode that employs perovskite nanoparticles embedded in a dielectric polymer matrix as the emissive layer. The emissive layer is spin-coated from perovskite precursor/polymer blend solution. The resultant polymer-perovskite composites effectively block shunt pathways within the LED, thus leading to an external quantum efficiency of 1.2%, one order of magnitude higher than previous reports. We demonstrate formations of stably emissive perovskite nanoparticles in an alumina nanoparticle matrix. These nanoparticles have much higher photoluminescence quantum efficiency (25%) than bulk perovskite and the emission is found to be stable over several months. Finally, we demonstrate a new vapour-phase crosslinking method to construct full-colour perovskite nanocrystal LEDs. With detailed structural and compositional analysis we are able to pinpoint the aluminium-based crosslinker that resides between the nanocrystals, which enables remarkably high EQE of 5.7% in CsPbI3 LEDs.

Orientador: Alexys Bruno Alfonso / Banca: Lucila Helena Deliesposte Cesgato / Banca: Clarissa de Almeida Olivati / O Programa de Pós Graduação em Ciência e Tecnologia de Materiais, PosMat, tem carater institucional e integra as atividades de pesquisa em materiais de diversos campi / Resumo: Os cristais fotônicos têm recebido grande atenção da comunidade científica nos últimos anos. As suas aplicações incluem a construção de guias de onda, chips ópticos e células solares, o controle de emissão de radiação e o gerenciamento de informações. Neste trabalho são calculados os modos de propagação de ondas eletromagnéticas em cristais fotônicos bidimensionais. Os cristais estudados são arranjos de fios circulares infinitos de um tipo de meio óptico, imersos numa matriz de outro meio óptico. As estruturas cristalinas consideradas são a quadrada simples, hexagonal simples e honeycomb. É analisada a propagação perpendicular aos fios e, portanto, são consideradas duas polarizações: a transversão elétricas e a transversal magnética. Os cálculos numéricos são realizados para diferentes combinações dos materiais que compõem o cristal fotônico. Isto permite investigar como o espectro fotônico depende da geometria do cristal e do contraste entre os meios ópticos que o compõem. Para resolver a equação de ondas, o campo eletromagnético é expresso como combinação linear de um conjunto de ondas harmônicas planas. Foi encontrado bom acordo entre as frequencia calculadas e resultados disponíveis na literatura do tema, corroborando a existência de gaps fotônicos parciais nas estrutuaras simples e gaps fotônicos completos na estrutura honeycomb. Além disso, verificou-se que o surgimento de gaps requer menor constrate de índice de refração no caso hexagonal, quando comparado com o quadrado / Abstract: Photoic crystals have received some attention from the scientific community in the las years. Their applications include the fabrication of waveguides, optical chips and solar cells, control of radiation emission and information management. In this work, the propagation of electromagnetic waves in two-dimensional photonic crystals is theoretically investigated. The structures under study are periodic arrangements of infinite circular wires of a given optical medium, immersed in a matrix of another optical medium. The considered cyrstalline structures are the simple square, the simple hexagonal and the honeycomb lattices. Only the propagation perpendicular to the wires is analyzed. Hence, we consider two polarizations: transverse electrical and transverse magnetic. The calculations are performed for different combinations of the materials composing the crystal. This allows the investigation of how the photonic spectrum depends on both the crystal geometry and the contrast between the refractuve index of the composing materials. The wave equation is solved by expressing the solution as a linear combination of a set of harmonic plane waves. Good agreement between the calculated frequencies and the results available in the literature is found, thus confirming the existence of partial photonic gaps in the simple lattices and complete photonic gaps in the honeycomb lattice. Moreover, it was verified that occurrence of gaps in the hexagonal case requires less refractive-index contrast, when compared with the square one / Mestre

Orientador: Dayse Iara dos Santos / Banca: Alejandra Hortencia Miranda González / Banca: Marcela Mohallem Oliveira / Resumo: O campo dos nanomateriais tem se expandido enormemente nas últimas décadas principalmente devido às suas propriedades especiais. As experiências descritas na literatura em grande gama de aplicações mostram propriedades elétricas, magnéticas, ópticas e outras, extremamente aperfeiçoadas com relação aos sisstemas macroscópios. A ciência e tecnologia trabalham atualmente com inúmeras técnicas químicas para a obtenção de óxidos e dentre elas destaca-se o Método Poliol por ser vantajoso e adequado na preparação de nanopartículas com variadas morfologias, dimensões e crisalinidade. Entretanto, poucos estudos foram realizados sobre a síntese e a caracterização de compósitos com o propósito de investigar as propriedades resultantes da possível sinergia obtida a partir da interação entre dois óxidos nanoestruturados. Este trabalho teve como objetivo a síntese e a caracterização de compósito nanoestruturado formado de dois óxidos multifuncionais: o óxido de zinco e o dióxido de titânio. Para a síntese foram utilizados o acetato de zinco dihidratado e o isopropóxido de titânio para a obtenção do ZnO e do TiO2, respectivamente. o compósito foi obtido pelo Método Poliol a partir da interrupção momentânea da síntese dos óxidos isolados seguido da mistura das soluções. O compósito, assim como os óxidos sintetizados isoladamente, foram caracterizados po9r difração de raios X (DRX), análise térmicas (TG/DTA), medidas de adsorção de gás nitrogênio (BET), microscopia eletrônica de varredura (MEV), espectroscopia de adsorção de luz na região do ultravioleta, visível e infravermelho, espectroscopia Raman. O compósito formado pelo Método Poliol apresentou o ZnO na forma aglomerado, porém nanoestruturado, e o TiO2 após tratamento térmico de 400º C. Foi verificada ainda a presença de resíduos orgânicos nos materiais como... (Resumo completo, clicar acesso / Abstract: The field of nanomaterials has expanded greatly in recent decades mainly due to its special propoerties. The experiments described in the literature in a wide variety of applications show electrical properties, magnetic, optical and others, extremely improvement properties with respect to macroscopic systems. Science a technology are currently working with numerous chemical techniques to achieve oxides and them stands out the Polyol Method to be advantageous and appropriate in the preparation of nanoparticles with various morphologies, size and crystallinity. However, few studies have been done on the synthesis and characterization of composites in order to investigate the resultants properties from possible synergy obtained from the interaction between two nanoestructured oxides. This work aimed to the synthesis and characterization nanostructured composites formed by two multifunctional oxides, zinc oxide and titanium dioxide. For the synthesis were used zinc acetate dihydrate and titanium isopropoxide to obtain the ZnO and TiO2, respectively. The composite was obtained by Polyol from the interruption of the synthesis of single oxides followed by mixing the solutions. The composite, as weell as oxides separately synthesized, were characterized by X-ray diffraction (XRD), thermal analysis (TG/DTA), meassurements of nitrogen gas adsorption (BET), scanning electron microscopy (SEM), YV-VIS and IR absorption spectroscopy and Raman spectroscopy. The composite obtained by the Polyol Method presented ZnO as agglomerate, however nanostructured, and TiO2 after heat treatment of 400ºC. It was also verified the presence of organic waste in the materials as synthesized and titanium glycolate as an intermediate in the reaction of titanium dioxide. A comparison of optical behavior, as synthesized composite formed by ZnO and titanium... (Complete abstract click electronic access below) / Mestre

Atualmente, existem diversos produtos cosméticos de base nanotecnológica disponíveis no mercado nacional, incluindo protetores solares, produtos para a prevenção do envelhecimento cutâneo, ou ainda, produtos que veiculam uma ampla gama de componentes. Em contrapartida ao grande interesse industrial, várias organizações não governamentais têm expressado a sua preocupação acerca das incertezas do impacto dos novos nanomateriais sobre a saúde humana e sobre as possíveis aplicações e implicações sociais dessa nova tecnologia. Além disso, tem sido amplamente questionada a adequação dos atuais sistemas regulatórios governamentais no que diz respeito aos produtos oriundos da nanotecnologia. De fato, mundialmente, não existem requisitos específicos para o registro de produtos cosméticos de base nanotecnológica, sendo a análise realizada, de maneira geral, caso a caso. Dentro desse contexto, esse estudo traçou uma descrição do perfil da produção industrial de produtos cosméticos de base nanotecnológica no Brasil, buscando avaliar a disponibilidade dos mesmos no mercado nacional e a sua segurança de uso com base na análise das matérias primas constituintes dos produtos, determinação do seu diâmetro de partícula e dados disponíveis na literatura. Em uma última etapa, foram propostos alguns parâmetros para a regulação de produtos cosméticos de base nanotecnológica no Brasil, em especial, no que diz respeito à classificação dos produtos e a rotulagem dos mesmos. / There are a number of nanocosmetic products in the domestic market today, including sunblock, products for prevention against skin aging, or even products which circulate in a wide range components. Running counter to major industrial interests, many non-governmental organizations have expressed their concern regarding the uncertainties of the impact new nanomaterials may have on human health as well as the possible applications and social implications that this new technology may bring. Moreover, the adaptation of current governmental regulations has widely come under scrutiny regarding products stemming from nanotechnology. In fact, worldwide, there are no specific requirements to register nanotechological cosmetic products, as each is generally analyzed on a case by case basis. Within this context, this study traced the profile of the industrial production of nanotechnological cosmetic products in Brazil, with the aim of assessing the availability of these products in the domestic market and their safe usage based on the analysis of the raw materials which make up the products, the determining of particle diameter, and the data available in the literature. In the final stage, some parameters for the regulation of nanotechnological cosmetic products in Brazil are proposed, especially as regards the classification and labeling of products.

xiv, 114 p. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / Electron spin coherence can arise through a coherent superposition of two spin states in the conduction band of a semiconductor and can persist over remarkably long time and length scales. The robust nature of electron spin coherence makes it an excellent model system for exploring coherent quantum phenomena in semiconductors. This dissertation presents both spectral- and time-domain nonlinear optical studies of electron spin coherence through Λ-type three-level systems in two- and zero-dimensional semiconductor systems. The spectral domain study focuses on the experimental realization of electromagnetically induced transparency (EIT), a phenomenon that exploits destructive interference induced by the spin coherence. Coherent Zeeman Resonance (CZR), a precursor to EIT, is demonstrated in two 2D systems, a GaAs mixed-type quantum well (MTQW) and a modulation doped CdTe quantum well (QW). For these studies, Λ-type three-level systems are formed via dipole coupling of a trion to two electron spin states. The CZR response can be described qualitatively by effective density matrix equations. In addition, effects of manybody Coulomb interactions on CZR are investigated by varying the electron density in the MTQW via optical carrier injection. Time-domain studies based on transient differential transmission (DT) are carried out to explore the excitation, manipulation, and detection of electron spin coherence and to better understand how manybody interactions affect coherent nonlinear optical processes in semiconductors. While electron spin coherence can be formed and detected via resonant excitation of excitons or trions, a surprising observation is that injecting excitons into the 2D electron gas in a modulation doped CdTe QW can significantly alter the oscillatory nonlinear response of the electron spin coherence, while the response remains qualitatively unchanged when trions are injected. These behaviors are attributed to an interplay between manybody effects and carrier heating generated by trion formation from excitons. Finally, donor-bound electrons in GaAs are used as a model of localized electron spins. Spin decoherence of order 10 ns, limited by nuclear hyperfine interactions, is observed. Electron spin rotation induced by a nearly resonant laser pulse is also observed, opening the door for further work on mitigating electron spin decoherence time through optical spin echoes. / Adviser: Hailin Wang

Orientador: Prof. Dr. Jeverson Teodoro Arantes Junior / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2014. / Através da utilização de Métodos de Primeiros Princípios baseados na Teoria do Funcional da Densidade (DFT) foram avaliadas propriedades estruturais e eletrônicas de nanoestruturas de óxido de magnésio (MgO), nas fases cristalinas Rock Salt e Wurzita. Para a execução deste trabalho, calcularam-se as estruturas Rock Salt e Wurzita no material bulk, otimizando o parâmetro de rede que foi utilizado na montagem das nanoestruturas, nanoos da fase Rock Salt (Pequeno e Médio) e Wurzita (Pequeno, Médio e Grande). Após a relaxação das estruturas foram determinadas as bandas de energia, densidade de estados eletrônicos, densidade de estados eletrônicos projetada por orbital e densidade parcial de cargas para cada um dos nanoos. / Through the use of First Principles Methods based on Density Functional Theory, electronic properties of nanostructures of magnesium oxide (MgO) were evaluated in the crystalline phases Rock Salt and wurtzite. For the execution of this work, were calculated structures Rock Salt and wurtzite in bulk material, thus targeting the lattice parameter which were used in the mounting of nanostructures, nanowires phase Rock Salt (Thin and Medium) and wurtzite (Thin, Medium and Large). After the relaxation of the structures, energy bands, density of electronic states, electronic density of states projected by orbital and partial charge density for each of the nanowires were made. Nanowires evaluation allowed the observation of the quantum connement eect with decreasing size of the nanostructures.

Orientador: Prof. Dr. Flavio Leandro de Souza / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2015. / Iron oxide is one of the most promising semiconductors for applications as photoanodes in photoelectrochemical cells. A simple and cheap route to prepare hematite photoelectrodes is the sol-gel method. Hematite thin films can be also prepared by using the polymerized complex (PC) method that is a sol-gel method derived technique. This methodology involves the formation of complexes of metal ions that then undergo polymerization. In addition, the PC method allows an optimal control of stoichiometry and of the incorporation of impurities during the process. In this work, pure and doped hematite thin films were prepared by using the PC method at two different heat treatments (500°C and 800°C). The á-Fe2O3 thin films were modified with two differently charged dopants (Zn2+ and Sn4+), and their photoelectrochemical properties were studied in comparison with the pure hematite films. Hematite electrodes prepared at 800°C exhibited the best photocatalytic response in comparison with 500°C-treated hematite films. This effect was attributed to the higher roughness and surface area of films synthesized at higher temperatures. Furthermore, the modification of á-Fe2O3 with Zn2+ and Sn4+ ions resulted in a better photoresponse and stability as showed by the linear sweep voltammetry and chronoamperometry results. Dopants influenced differently on the photocurrent onset potential and the potential for the electrocatalytic oxygen evolution. In addition, results suggested that impurities were incorporated more efficiently into the hematite films prepared at 800°C. Nevertheless, the photocatalytic properties of the undoped and modified hematite films was poor, and two plausible hypothesis are proposed to explain the poor performance of hematite electrodes. First, most of dopants may have segregated, and, according to the previous reports in the literature, they may have acted as recombination sites that reduced the efficiency of the charge separation (photogenerated electron-hole pair). Second, poor contact between the hematite and F-SnO2 layer (from substrate) may have formed that severely hindered the harvesting of the photogenerated charges. The overall consequence of these two effects is the reduction in the activity of hematite films under illumination conditions. / O oxido de ferro e um dos semicondutores mais promissores para aplicacoes como fotoanodos em celulas fotoeletroquimicas. Uma rota simples e barata para preparar fotoeletrodos de hematita e o metodo sol-gel. Filmes finos de hematita podem tambem ser preparados utilizando o metodo do complexo polimerizado (CP) que e um metodo derivado da tecnica sol-gel. Esta metodologia envolve a formacao de complexos de ions metalicos que em seguida se polimerizam. Alem disso, o metodo do CP permite um controle optimo da estequiometria e da incorporacao de impurezas durante o processo. Neste trabalho, filmes finos de hematita pura e dopada foram preparados utilizando o metodo do CP em dois tratamentos termicos diferentes (500¿C e 800¿C). Os filmes finos de ¿¿-Fe2O3 foram modificados com dois dopantes de cargas diferentes (Zn2+ e Sn4+) e as suas propriedades fotoeletroquimicas foram estudadas em comparacao com os filmes de hematita pura. Os eletrodos de hematita preparados a 800¿C apresentaram a melhor resposta fotocatalitica em comparacao com os filmes de hematita preparados a 500¿C. Este efeito foi atribuido a maior rugosidade e area superficial dos filmes sintetizados a temperaturas mais elevadas. Alem disso, a modificacao de ¿¿-Fe2O3 com os ions Zn2+ e Sn4+ resultou em uma melhor fotoresposta e estabilidade como demonstrado pelos resultados da voltametria linear e cronoamperometria. Os dopantes influenciaram de forma diferente no potencial do comeco da fotocorrente e no potencial da evolucao de oxigenio eletrocatalitica. Alem disso, os resultados sugeriram que as impurezas foram incorporadas de forma mais eficiente nos filmes de hematita preparados a 800¿C. Porem, as propriedades fotocataliticas dos filmes de hematita nao dopada e modificada nao foram significativas, e duas hipoteses plausiveis sao propostas para explicar o baixo desempenho dos eletrodos de hematita. Em primeiro lugar, a maioria dos dopantes podem ter segregado, e, de acordo com o reportado na literatura, eles podem estar atuando como sitios de recombinacao que reduziram a eficiencia da separacao das cargas (par eletron-buraco fotogerado). Em segundo lugar, mau contato entre a camada de hematita e F-SnO2 (do substrato) pode ter sido formado que impediu severamente a colheita das cargas fotogeradas. A consequencia global destes dois efeitos e a reducao da atividade fotocatalitica dos filmes de hematita.

L’ADN (acide désoxyribonucléique) est le support de notre génome, c'est aussi un biopolymère dont les propriétés d’hybridation de deux simples brins complémentaires en une double hélice permettent son utilisation comme brique élémentaire pour l’auto-assemblage de structures avec une résolution de quelques nanomètres. Parmi les différentes méthodes développées, l'origami d’ADN dans lequel un simple brin d’ADN issu du génome d’un phage est replié algorithmiquement par un ensemble de brins synthétiques plus petits s'est démontré très robuste pour l'assemblage de structures bi ou tridimensionnelles. La conception de ces origami est basée sur la thermodynamique à l'équilibre, c'est à dire sur l'optimisation de l'appariement complémentaire des bases. Cependant, bien que des outils interactifs qui facilitent la conception de structures aient été développés, très peu de recherches se sont focalisées sur le processus du repliement et sur son optimisation. Notre travail a consisté à étudier la thermodynamique de nanostructures d'ADN afin de mieux comprendre le processus d'assemblage et d'en identifier des étapes clés.Nous avons effectué des mesures en calorimétrie différentielle à balayage (DSC) sur des structures modèles et des origami d'ADN. Ainsi, nous avons pu identifier la présence d'étapes clés dans le repliement de nanostructures comportant un petit nombre de brins d'ADN. Nous montrons qu'en modifiant les séquences il est possible de changer la coopérativité et la stabilité de l'assemblage des nanostructures et donc de modifier le chemin de repliement.L'étude d'origami simplifiés comportant une ou deux agrafes nous a permis de mesurer l'influence de la position des agrafes, des tailles de boucles et de l'orientations des brins d'ADN sur la thermodynamique du repliement.Enfin, les mesures calorimétriques effectuées sur des origami d'ADN nous ont permis de résoudre l'hybridation collective d'ensemble d'agrafes. Cela nous permet de hiérarchiser l'assemblage de l'origami en domaines distincts.Notre travail de thèse a également consisté au développement de méthodes innovantes de nanocalorimétrie ultrasensible intégrant de la microfluidique. Ces méthodes calorimétriques permettront d'accéder aux paramètres cinétiques de l’assemblage en plus des paramètres thermodynamiques à l'équilibre.Nos résultats obtenus sur les nanostructures modèles montrent qu'il est possible d'optimiser la conception des nanostructures d'ADN en intégrant dans la conception le processus d'assemblage. Des nanostructures d'ADN à l'assemblage performant permettront peut-être à l'avenir le développement d'automates moléculaires synthétiques qui sont une des applications très prometteuses de ces systèmes. / DNA is the support of genetic information. The property of self-assembly of two complementary single strands to form a double helix enable the use of this biopolymer as a building block for nanofabrication. DNA origami are a method which enable the self-assembly of 2D or 3D nanostructures. In this method, a long single-stranded DNA taken from the genome of a phage is folded on itself in a programmable way thanks to a lot of short synthetic DNA strands. The design of origami is based on thermodynamic and on the optimization of the base pairing in the structures. However, although interactive tools that facilitate the design of DNA nano-structures have been developed, we know little about the folding process and its optimization. In this work, we study the thermodynamics of DNA nanostructures in order to have a better understanding of the folding process and to identify the key steps.We performed differential scanning calorimetry (DSC) on model structures and DNA origami. Thus, we have been able to identify the presence of key steps in the folding of small nanostructures. We show that by changing the sequences of the strands, it is possible to change the cooperativity and the stability of the assembly of the nanostructure and thus change the folding path.The study of small origami with one or two staples allowed us the see the influence of the position of the staples, of the sizes of the loops and of the orientation of the staples on the thermodynamic of the folding.Finally, the calorimetric measurements performed on origami allowed us to solve the collective hybridization of staple sets. This enable us to prioritize the origami assembly into separate domains.This work also consisted of the development of innovative methods of ultra-sensitive nano-calorimetry integrating microfluidics. These calorimetric methods will give us the access to the kinetic parameters of the folding and to the equilibrium thermodynamic parameters.Our results obtained on model nano-structures show that it is possible to optimize the design of DNA nanostructures by integrating the assembly process in the design of the structures. Such high-performance DNA nanostructures may allow in the future the development of molecular robot which is a very promising application of DNA nanostructures.

O estudo do ordenamento de nanopartículas em estruturas bi e tridimensionais, também conhecidas como superredes, é de grande interesse científico e tecnológico, tanto pelo interesse em se explicar a origem e as consequências deste fenômeno, quanto pelas possibilidades de aplicação oriundas das propriedades observadas nestes sistemas. Quando são utilizados dois tipos de nanomateriais diferentes em tamanho e/ou composição química, tem-se a formação de superredes binárias. Estas estruturas apresentam propriedades que são resultado das propriedades individuais de seus constituintes e, além disso, do conjunto de interações que existem no sistema. Graças a este conjunto de propriedades e interações coletivas, o princípio de se empregar nanopartículas como \"building blocks\" para a criação ou aprimoramento de dispositivos funcionais. Assim, neste trabalho são discutidas as sínteses de óxidos magnéticos do tipo MFe2O4 (com M = Co, Fe ou Mn) e as características necessárias para o emprego destes na formação de superredes de nanopartículas. Os materiais foram sintetizados procurando-se alcançar uma estreita distribuição de tamanho e homogeneidade quanto à forma. Foram empregados sistemas de nanopartículas nos estudos para a formação de superredes que apresentaram polidispersividade entre 6 e 20%, de forma a discutir o efeito desta propriedade no ordenamento das nanopartículas. Observou-se que o ordenamento em escala macroscópica é fortemente influenciado pela tensão de superfície da subfase, enquanto que o arranjo local das nanopartículas em relação aos seus vizinhos mais próximos é mais influenciado pela taxa de evaporação do solvente e pelas interações interpartículas. Para a formação de superestruturas binárias foram empregadas as nanopartículas de CoO/CoFe2O4 com 9,6 nm ou de Fe3O4 de 10,7 nm, com nanopartículas de CdSe de 3,6 nm. Os sistemas de nanopartículas binárias apresentaram arranjos do tipo AlB2 e tiveram, em sua maioria, crescimento na forma de supercristais facetados. A formação de estruturas bidimensionais com crescimento ao longo do plano da membrana foi favorecida pelo aumento na proporção das nanopartículas de maior diâmetro em relação às menores. A compreensão do fenômeno de auto-organização em membranas de superredes binárias possibilita a obtenção de novos materiais nanoestruturados e que apresentem propriedades moduladas. / Self-assembly nanoparticles into superlattices array have attracted significant attention both for the scientific understanding of nanocrystals ordering process and the development of new functional devices using bottom up techniques. The co-assembly of two types of nanoparticles in binary nanoparticles superlattices provides a new way to design metamaterials with unusual and modulated properties. These unusual properties arise from interparticle interactions in the superlattice structure, and from nanoparticles physical properties. To obtain highly ordered structures, it is required that nanocrystals have narrow size distribution. This thesis presents the synthesis of oxide magnetic nanoparticles (MFe2O4; M = Co, Fe, or Mn) and their application as building blocks in nanocrystal superlattices. Nanoparticles presented size distribution from 6% to 20%, and their assemblies has shown amorphous structure when samples have size distribution above 10%. Self-assembled nanoparticles superlattices in the liquid-air interface were obtained using either single or binary components. Single component superlattices were used as model for the understand of self-assembly process, which depends on subphase surface tension and dispersion evaporation rate. Nanocrystals superlattices were obtained from CdSe nanoparticles, with average size of 3,6 nm, and CoO/CoFe2O4 with size of 9,6 nm, and was observed a AlB2-type superstructure. The same superlattice structure was obtained for CdSe and Fe3O4, with average size of 10,7 nm, which indicate that AlB2 is the equilibrium phase for a rage of radii ratios and nanoparticles stoichiometry. These findings enable to better understand self-assembled binary nanocrystal superlattices formation and how to manipulate interparticle interactions in order to synthesize highly ordered structures.

Made available in DSpace on 2014-10-09T12:35:01Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:02Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP