Nanomaterials such as carbon nanotubes, gold nanorods, magnetic nanocrystals, and binary nanocrystal superlattices have exciting potential applications. However, before these ideas can be applied, it is imperative to fully understand the materials synthesis. Multiwall carbon nanotubes were synthesized in supercritical toluene using cobaltocene, nickelocene, ferrocene, or metal nanocrystals as catalysts. Toluene served as both the solvent and carbon source for nanotube growth. The reaction was optimized by introducing supplemental carbon sources; either hexane or ethanol increased the yield relative to pure toluene and catalytic amounts of water minimized carbon filament and amorphous carbon formation. Gold nanorods were synthesized by the colloidal seed-mediated, surfactantassisted approach using cetyltrimethylammonium bromide (CTAB) obtained from ten different suppliers. The gold nanorod yield depended strongly on the CTAB used: with the same recipe, three of the CTABs produced only spherical particles, whereas the other CTABs produced nanorods with nearly 100% yield. Inductively coupled plasma mass spectrometry revealed a trace iodide impurity in the CTABs that did not yield nanorods. Further experiments introducing potassium iodide to the nanorod synthesis verified the detrimental effect of iodide on nanorod formation. Multifunctional colloidal core-shell nanoparticles of magnetic nanocrystals or gold nanorods coated with a fluorescent dye (Tris(2,2 -bipyridyl)dichlororuthenium(II) hexahydrate) doped silica shells were also synthesized. The as-prepared magnetic nanocrystals were initially hydrophobic and silica coated using a microemulsion approach, while the gold nanorods were hydrophilic and silica coated using a Stöber process. These colloidal heterostructures have the potential to be used as dual-purpose tags, exhibiting a fluorescent signal that could be combined with either dark-field optical contrast or enhanced contrast in magnetic resonance imaging. Binary superlattices (BSLs) of large iron oxide and small gold nanocrystals were assembled by slow evaporation of colloidal dispersions on tilted substrates. SEM and grazing incidence small angle X-ray scattering (GISAXS) confirmed the BSLs were simple hexagonal AB2 superlattices with long range order. GISAXS also revealed that the superlattice was slightly contracted perpendicular to the substrate as a result of solvent drying during the deposition process. Additionally, in some BSLs nearly periodic superlattice dislocations consisting of inserted half-planes of gold nanocrystals were observed. / text

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.

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.

No / The latest advances in mesocrystal formation and non-classical crystallization of pre-synthesised nanoparticles have been reviewed with the focus on providing a fuller description of a number of complex systems and their properties and applications through examination of the crystallisation mechanisms at work. Two main crystallization principles have been identified; classical crystallization and particle based aggregation modes of non-classical pathways. To understand the non-classical pathways classical crystallization and its basics are introduced before non-classical pathways, such as oriented attachment and mesocrystal formation, are examined. In particular, the various destabilization mechanisms as applied to the pre-synthesized building blocks in order to form mesocrystalline materials as well as the interparticular influences providing the driving forces are analyzed and compared to the mechanisms at work within classical crystallization. Furthermore, the new properties of the mesocrystalline materials that derive from the collective properties of the nanoparticular building units, and their applications potential are presented. It is shown that this new class of materials has the potential to impact in a number of important areas such as sensor applications, energy conversion, photonic crystals as well as for energy storage, optoelectronics and heterogeneous catalysis or photocatalysis.