Large on-chip bandwidths required for high performance electronic chips will render optical components essential parts of future on-chip interconnects. Silicon photonics enables highly integrated photonic integrated circuit (PIC) using CMOS compatible process. In order to maximize the bandwidth density and design flexibility of PICs, vertical integration of electronic layers and photonics layers is strongly preferred. Comparing deposited silicon, single crystalline silicon offers low material absorption loss and high carrier mobility, which are ideal for multi-layer silicon PIC. Three different methods to build multi-layer silicon PICs based on single crystalline silicon are demonstrated in this dissertation, including double-bonded silicon-on-insulator (SOI) wafers, transfer printed silicon nanomembranes, and adhesively bonded silicon nanomembranes. 1-to-12 waveguide fanouts using multimode interference (MMI) couplers were designed, fabricated and characterized on both double-bonded SOI and transfer printed silicon nanomembrane, and the results show comparable performance to similar devices fabricated on SOI. However, both of these two methods have their limitations in optical interconnects applications. Large and defect-free silicon nanomembrane fabricated using adhesive bonding is identified as a promising solution to build multi-layer silicon PICs. A double-layer structure constituted of vertically integrated silicon nanomembranes was demonstrated. Subwavelength length based fiber-to-chip grating couplers were used to couple light into this new platform. Three basic building blocks of silicon photonics were designed, fabricated and characterized, including 1) inter-layer grating coupler based on subwavelength nanostructure, which has efficiency of 6.0 dB and 3 dB bandwidth of 41 nm, for light coupling between layers, 2) 1-to-32 H-tree optical distribution, which has excess loss of 2.2 dB, output uniformity of 0.72 dB and 3 dB bandwidth of 880 GHz, 3) waveguide crossing utilizing index-engineered MMI coupler, which has crossing loss of 0.019 dB, cross talk lower than -40 dB and wide transmission spectrum covering C-band and L-band. The demonstrated integration method and silicon photonic devices can be integrated into the CMOS back-end process for clock distribution and global signaling. / text

Uranium-zirconium (U-Zr) alloys comprise a class of metallic nuclear fuel that is regularly considered for application in fast nuclear energy systems. The U-10wt%Zr alloy has been demonstrated to very high burnup without cladding breach in the Experimental Breeder Reactor-II (EBR-II). This was accomplished by successfully accommodating gaseous fission products with low smear density fuel and an enlarged cladding plenum. Fission gas swelling behavior of the fuel has been experimentally revealed to be significantly affected by the temperature gradient within a fuel pin and the multiple phase morphologies that exist across the fuel pin. However, the phase effects on swelling behavior have not been yet fully accounted for in existing fuel performance models which tend to assume the fuel exists as a homogeneous single phase medium across the entire fuel pin. Phase effects on gas bubble nucleation and growth in the alloy were investigated using transmission electron microscopy (TEM). To achieve this end, a comprehensive examination of the alloy system was carried out. This included the fabrication of uranium alloys containing 0.1, 2, 5, 10, 20, 30, 40, and 50 wt% zirconium by melt-casting. These alloys were characterized using electron probe micro-analysis (EPMA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Once the alloys were satisfactorily characterized, selected U-Zr alloys were irradiated with 140 keV He^(+) ions at fluences ranging from 1 × 10^(14) to 5 × 10^(16) ions/cm^(2). Metallographic and micro-chemical analysis of the alloys indicated that annealing at 600 °C equilibrates the alloys within 168 h to have stable α-U and δ-UZr_(2) phase morphologies. This was in contrast to some reported data that showed kinetically sluggish δ-UZr_(2) phase formation. Phase transformation temperatures and enthalpies were measured using DSC-TGA for each of the alloys. Measured temperatures from different time annealed alloys have shown consistent matches with most of the features in the current U-Zr phase diagram which further augmented the EPMA observed microstructural equilibrium. Nevertheless, quantitative transformation enthalpy analysis also suggests potential errors in the existing U-Zr binary phase diagram. More specifically, the (β-U, γ2) phase region does not appear to be present in Zr-rich (> 15 wt%) U-Zr alloys and so further investigation may be required. To prepare TEM specimens, characterized U-Zr alloys were mechanically thinned to a thickness of ~150 μm, and then electropolished using a 5% perchloric acid/95% methanol electrolyte. Uranium-rich phase was preferentially thinned in two phase alloys, giving saw-tooth shaped perforated boundaries; the alloy images were very clear and alloy characterization was accomplished. During in-situ heating U-10Zr and U-20Zr alloys up to 810 °C, selected area diffraction (SAD) patterns were observed as the structure evolved up to ~690 °C and the expected α-U → β-U phase transformation at 662 °C was never observed. For the temperature range of the (α-U, γ2) phase region, phase transformation driven diffusion was observed as uranium moved into Zr-rich phase matrix in U-20Zr alloy; this was noted as nonuniform bridging of adjacent phase lamellae in the alloy. From the irradiation tests, nano-scale voids were discovered to be evenly distributed over several micrometers in U-40Zr alloys. For the alloys irradiated at the fluences of 1 × 10^(16) and 5 × 10^(16) ions/cm^(2), estimated void densities were proportional to the irradiation doses, (250 ± 40) and (1460 ± 30) /μm^(2), while void sizes were fairly constant, (6.0 ± 1.5) and (5.2 ± 1.2) nm, respectively. Measured data could be foundational inputs to the further development of a semi-empirical metal fuel performance model.

<p>In this study, the OMCVD method is demonstrated as a powerful, fast, economic and environmental friendly method to produce a set of PGMelectrocatalysts with different supports, metal content and metal alloys in one step and without the multiple processing stages of impregnation, washing, drying, calcinationsand activation.</p>

In this study, the OMCVD method is demonstrated as a powerful, fast, economic and environmental friendly method to produce a set of PGMelectrocatalysts with different supports, metal content and metal alloys in one step and without the multiple processing stages of impregnation, washing, drying, calcinationsand activation.

L'optimisation des performances d'une pile à combustible (PEMFC) requiert la compréhension microscopique des mécanismes de transport de l'eau et du proton confinés au sein de la membrane électrolyte polymère. La membrane est un matériau nanostructuré chargé, caractérisé par une dynamique de l'eau et du proton complexe et multi-échelle étroitement corrélée à la morphologie confinante. Nous nous sommes intéressés à la relation structure - transport dans i) L'Aquivion, un ionomère perfluorosulfonique récent présentant de bonnes performances en pile, ii) des systèmes " modèles " auto-assemblés de tensioactifs perfluorés formant des phases lamellaires et hexagonales et iii) une nouvelle membrane hybride préparée par dopage en tensioactif. La nano-structuration des différents systèmes a été étudiée par diffusion de rayonnement (X et neutrons), pour caractériser l'évolution de la structure (géométrie de la matrice hôte, taille de confinement) avec l'hydratation. Ensuite, nous avons sondé la dynamique de l'eau à l'échelle moléculaire (de la picoseconde à la nanoseconde) par diffusion quasi-élastique des neutrons (QENS) et à l'échelle micrométrique par RMN à gradients de champs pulsés. La comparaison membranes commerciales / systèmes modèles permet de discuter l'impact de la connectivité, du confinement et de la géométrie sur le transport ionique. Enfin, des membranes hybrides à fort potentiel ont été obtenues par dopage du Nafion et de l'Aquivion avec des tensioactifs. Ces nouveaux matériaux ouvrent une voie prometteuse pour la préparation de membranes polymères fortement anisotropes avec des chemins de conduction préférentiellement orientés.

This dissertation is focused on the interaction between femtosecond laser and patterned two-dimensional gold nanostructures. The sample was prepared by two different lithographic techniques, the nanosphere lithography and the electron beam lithography. Characterization was carried out with scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and UV-vis absorption spectroscopy. Femtosecond transient absorption spectroscopy was used to answer a number of fundamental questions regarding the laser-nanostructure interaction. Under a low density irradiation of a femtosecond laser, we examined the effect of the lattice crystallinity on the electron-phonon relaxation in monolayer periodic array nanoparticles prepared with nanosphere lithography. We found that the electron-phonon relaxation rate was faster in polycrystalline nanoparticles and decreases greatly in single crystalline nanospheres, which is explained by the presence of high density grain boundaries. The ultrafast laser-induced coherent phonon oscillations in patterned gold nanoparticles are also fully characterized. We studied the effect of size, shape, thickness, monitoring wavelength, and materials of the prismatic array nanoparticles on the period of their coherent phonon oscillations. In a gold nanodisk pair system, we found that the fractional change in the vibration frequency increases exponentially with decreasing the ratio of the interparticle separation to the particle diameter, which is explained by the coupling of the induced electric field in one nanodisk by the strong surface plasmon field of its pair partner. Based on the coherent phonon oscillation of gold caps on a polystyrene sphere monolayer array, a new all-optical gigahertz modulation technique is developed. Under a high density irradiation of a femtosecond laser, the melting and ablation processes can be induced in gold nanoparticles. We studied femtosecond laser induced shape and localized surface plasmon resonance band changes of gold prismatic array nanoparticles. We also observed that the femtosecond laser irradiation of the nanoprisms at the surface plasmon resonance absorption maximum can cause them to detach from the substrate and 'fly away'. Atomic force microscopy and scanning electron microscopy measurements revealed that the displaced nanoparticles are thinner and smaller than the undisplaced ones, which supports an atomic ablation mechanism.

Nanoscale particles based on the nature of building blocks often self-assemble into superstructures with distinctive spatial arrangements which can be used as functional materials for different application. Micro-phase separated hairy nanoparticle with helical hair can self-assemble to form supramolecular material which may mimic the properties and functions of the natural polymers such as protein and cellulose. Beside this hairy/core-shell nanoparticles also may find many applications such as in asymmetric catalysis, nano-fillers in tire and rubbers, model systems for biology, lithography and as sensors. In this work, we have successfully synthesized two hairy nanoparticles both of which has cross-linked polystyrene core with helical poly (3- methyl 4- vinyl pyridine) and poly (2- methoxystyrene) brushes respectively by living anionic polymerization via one-pot synthesis. NMR spectroscopy was used to determine that polymerization was successful and compositions of HNPs have the agreement with the targeted HNPs structure. By tailoring the architecture (functionalization of polymer chains, the degree of polymerization, grafting density) of HNPs, it is possible to control the final properties of the system. Differential Scanning Calorimetry was used to demonstrate the thermal properties of the synthesized HNPs which corresponds to polymer composition. Dynamic light scattering, SEM and AFM images were recorded to measure the particle size and morphology of the particles. Circular dichroism spectroscopy was used to determine the induced chirality of helical polymer brushes by complexing it with the small chiral molecule. SEM and AFM imaging were recorded to find out the morphology and hierarchically self-assembly of the hairy nanoparticle system. The synthesized particles may have great potential to successfully generate self-assembled suprastructures which can further solve the chiral resolution problem and can also find different applications.

Orientador: Prof. Dr. Wendel Andrade Alves / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2015. / Com o desenvolvimento da nanociencia e nanotecnologia tem sido possivel construir e manipular diferentes materiais na escala nanometrica para as mais diversas aplicacoes como: em medicina, em cosmeticos, dispositivos eletronicos, sensores, biossensores, entre outras. Neste trabalho, apresentamos um estudo baseado na auto-organizacao de micro/nanoestruturas de peptideo (MNTs-FF), via fase solidavapor, sobre um eletrodo de ouro modificado com 4-mercaptopiridina (Au/MCP), visando aplicacao para deteccao de ureia. Estudamos a influencia do solvente no processo de nanoestruturacao do peptideo e observamos que o arranjo estrutural na qual a MNTs se cristaliza interfere fortemente na estabilidade do eletrodo, sendo a estrutura ortorrombica P22121, obtida em vapor de anilina, mais estavel do que a hexagonal P61, em vapor de agua. Essa diferenca estrutural e a chave para o bom desempenho do sensor, porque fornece uma interface contendo sitios de nitrogenio e oxigenio capaz de estabelecer ligacoes com a piridina do substrato (Au) e com os ions amonio e ureia, via interacoes cations ¿Î e ou ligacoes de hidrogenio, apresentando valor de sensibilidade e limite de deteccao para ureia de aproximadamente 81,3 ¿ÊA cm.2 mmol.1 L e 0,06 mmol L-1, respectivamente. A funcionalizacao das MNTs-FF com polianilina e pireno permitiu o ancoramento covalente da enzima urease a superficie do eletrodo Au/MCP/MNTs-FF, com sensibilidade e limite de deteccao frente a deteccao de ureia de 30.0 ¿ÊA cm-2 mmol L-1 e 0.17 mmol L-1 para o eletrodo contendo PANI/Urs, e 4.57 ¿ÊA cm-2 mmol L-1 e 0.15 mmol L-1 para o eletrodo pireno/Urs respecticamente. As MNTs-FF sintetizadas na presenca de nanotubos de carbono (NTc) nao apresentaram alteracao morfologica, porem, estudos de espectroscopia de impedancia eletroquimica (EIE) apontaram uma diminuicao na resistencia a transferencia de carga para o tres sistemas estudados: Au/MCP/MNTs-FF, Au/MCP/NTc/MNTs-FF, Au/MCP/NTc/MNTs-FF/Urs, Rtc 35,0, 0,80, 0,14 k¿¶, respectivamente, apresentando sensibilidade e limite de deteccao frente a deteccao de ureia de 1,5 ¿ÊA cm-2 mmol L-1 e 0,1 mmol L-1 respectivamente. / The development of nanoscience and nanotechnology open up possibilities for the building and construction of distinct materials in the nanometric scale for many different application, such as: in medicine, cosmetics, electronic devices, (bio) sensors, among others. In this work, we presented the self-assembly of peptide micro/nanostructures based in diphenylalanine (MNTs-FF), via solid-vapor phase, on gold electrode modified with 4-mercaptopyridine (Au/MCP), for urea sensing. We studied the influence of the solvent on the peptide self-assembly process, and observed that the structural arrangement in which the MNTs-FF crystallizes strongly influences the electrode stability, the orthorhombic P22121 structure were obtained under aniline vapor, that is more stable than the hexagonal P61 obtained under water vapor interaction. This structural difference is the key to the good sensing performance, because it provides an appropriate interface, containing nitrogen and oxygen sites able to establish bonds with the pyridine, and the ammonium ion or urea molecule, via cation ð interactions and or hydrogen bonds, with the sensitivity and detection limit for the urea sensing of ~ 81.3 ìA cm-2 mmol L-1 and 0.06 mmol L-1, respectively. The functionalization of MNTs-FF with polyaniline and pyrene allowed the covalent anchoring of the enzyme urease the surface of the electrode Au/MCP/MNTs-FF, with sensibility and detection limit for urea sensing of 30.0 ìA cm- 2 mmol L-1 and 0.17 mmol L-1 for the PANI/Urs, and 4.57 ìA cm-2 mmol L-1 and 0.15 mmol L-1 for the pyrene/Urs electrode respectively. The MNTs-FF synthesized in the presence of carbon nanotubes (NTC) showed no morphological change, however, studies of electrochemical impedance spectroscopy (EIS) showed a decrease in charge transfer resistance for the three systems studied, Au/MCP/MNTs-FF, Au/MCP/NTc/MNTs-FF, Au/MCP/NTc/MNTs-FF/Urs, Rtc 35,0, 0,80, 0,14 kÙ, respectively, the sensibility and detection limit for urea detection of 1.5 ìA cm-2 mmol L-1 and 0.1 mmol L-1 respectively.

Dans cette thèse nous considérons un semi-conducteur de GaAs dopé, où nous étudions la relaxation du spin du côté métallique de la transition metal-isolant. Nous considérons deux types différents d'interaction de spin-orbite. Le premier d'entre eux est associé aux impuretés et l'autre est de type Dresselhaus. La dynamique du spin est traitée à travers une formulation analytique basée sur la diffusion du spin de l'électron, et un calcul numérique de la durée de vie du spin.Ensuite, nous considérons une boîte quantique hébergée dans un nanofil de matériau InAs (avec une structure cristalline de type wurtzite), afin d'étudier l'effet de l'interaction spin-orbite sur les états propres du système. Nous développons ici une solution analytique pour la boîte quantique en incluant l'interaction spin-orbite (de type Dresselhaus propre à la structure wurtzite). Nous avons calculé le facteur g effectif, ainsi que la relaxation du spin dûe aux phonons acoustiques, en utilisant les potentiels d'interaction electron-phonon propres à la structure wurtzite. / In the first part of this thesis we consider a doped GaAs semiconductor and study the spin relaxation on the metallic side of the metal-insulator transition. We take into account two different types of spinorbit coupling, the first of them being associated to the presence of extrinsic impurities, while the other one is the Dresselhaus coupling. To tackle the spin dynamics problem, we develop an analytical formulation based on the spin diffusion of an electron in the metallic regime of conduction of the impurity band. The full derivation provides us with an expression for the spin-relaxation time ,which is free of adjustable parameters. We complement this approach and back our analytical results with the numerical calculation of the spin lifetime.In the second part of the thesis we consider a quantum dot hosted in an InAs nanowire (with awurtzite crystalline structure) and study the effect of spin-orbit coupling on the eigenstates of the zero-dimensional system. We develop here an exact analytical solution for the quantum dot, takinginto account the proper effective spin-orbit coupling for this type of material. We focus on the Dresselhaus coupling, which presents a cubic-in-k term, along with a linear term, characteristic of wurtzite materials. A Zeeman interaction from an external magnetic field is included as well and we compute the effective g-factor as a function of the dot size. Finally, we calculate the spin-relaxation due to acoustic phonons, taking into account the phonon potentials corresponding to the wurtzite structure.

Orientadores: Daniela Zanchet, Jose Antonio Brum / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-10T04:28:03Z (GMT). No. of bitstreams: 1 Rocha_TulioCostaRizutida_D.pdf: 8952935 bytes, checksum: 2283ed573c4cf94d5cba5aa42d7b2113 (MD5) Previous issue date: 2008 / Resumo: Nanopartículas de metais nobres têm atraído uma renovada atenção nos últimos anos devido às novas aplicações científicas e tecnológicas explorando suas propriedades ópticas únicas. No regime nanométrico, é bem conhecido que a resposta óptica de metais, associada aos plásmons de superfície, depende fortemente do tamanho e também da forma. De fato, grande parte das aplicações ópticas de nanopartículas de ouro e prata baseia-se na exploração dos efeitos de forma. Porém, apesar dos esforços realizados, os processos que levam à formação de morfologias anisotrópicas ainda não são bem compreendidos e a formulação de um mecanismo geral ainda é um desafio. Nesse trabalho, foram abordados os mecanismos de formação e crescimento de nanoprismas triangulares de prata produzidos por métodos de síntese coloidal. Uma combinação de diferentes técnicas experimentais foi utilizada para estudar diversos aspectos da síntese fotoquímica, dentre eles, a evolução morfológica, a cinética da reação e a estrutura cristalina das nanopartículas. As sólidas evidências experimentais obtidas associadas a outras observações da literatura foram utilizadas na formulação de um modelo fenomenológico para explicar a formação e crescimento dos nanoprismas de prata em métodos fotoquímicos. Esse modelo baseia-se na influência dos defeitos cristalográficos, que induzem a formação dos nanoprismas nos momentos iniciais da síntese, e na excitação de plásmons de superfície, que ocorre em estágios avançados, sendo responsável pela definição do tamanho final dos nanoprismas. Adicionalmente, cálculos teóricos indicaram que aspectos energéticos podem ter um papel ativo nesse sistema, favorecendo o crescimento dos nanoprismas em relação às nanopartículas esféricas durante os estágios iniciais da síntese. Finalmente, os nanoprismas triangulares de prata produzidos foram aplicados ao estudo de efeitos de intensificação do espalhamento Raman de moléculas. Medidas espectroscópicas de moléculas depositadas na superfície de nanoprismas com diferentes tamanhos foram realizadas e a comparação quantitativa dos resultados indicou a presença de um tamanho ótimo, que é determinado por processos de perda de energia dos plásmons de superfície / Abstract: Noble metal nanoparticles have attracted a recent renewed interest due to the new scientific and technological applications exploiting their unique optical properties. At nanometric scale, it is well known that the optical response of metals, related to the excitation of surface plasmons, strongly depends not only on the size of the particles but also on their shape. Several methodologies to produce silver and gold nanoparticles with different shapes are available in the literature. However, notwithstanding the efforts that have been made, the process that lead to the formation of anisotropic morphologies has not been fully understood yet and a general mechanism is still a challenge. In this work, we address the formation and growth mechanisms of silver triangular nanoprisms produced by photochemical methods. A set of characterization tools was used to study different aspects of the photochemical synthesis, namely, the morphological evolution, the reaction kinetics and the crystalline structure of the nanoprisms. The solid experimental evidences obtained here were used to build a phenomenological model that explains the formation and growth of silver triangular nanoplates in photochemical methods. This model was based on the influence of crystallographic defects, which induce the formation of the nanoprismas in the initial stages of the synthesis, and on the excitation of surface plasmons, which occurs in advanced stages and it is responsible for the definition of the final size of the nanoprismas. Additionally, theoretical calculations indicate that energetics might play an important role in this system, favoring the growth of nanoprismas relative to spheres. Finally, the silver triangular nanoprisms were used to study enhancement effects in the Raman scattering of molecules. We performed spectroscopic measurements for nanoplates with different sizes and the quantitative comparison of the curves indicated the existence of an optimum size that is dictated by surface plasmon energy losses / Doutorado / Física da Matéria Condensada / Doutor em Ciências