Nanocatalysis has emerged in the last decades as an interface between homogeneous and heterogeneous catalysis, offering simple solutions to problems that conventional materials have not been able to solve. In fact, nanocatalyst design permits to obtain structures with high superficial area, reactivity and stability, and at the same time presenting good selectivity and facility of separation from reaction mixtures. In this work, we prepared hybrid structures comprising gold, palladium and silver nanoparticles (Au, Pd and Ag NPs), titanate nanosheets (TixO2), graphene oxide (GO), and partially reduced graphene oxide (prGO). We focused on bi- and tri-components hybrids, namely TixO2, M/(pr)GO and M/TixO2/(pr)GO (M = Au, Pd or Ag) and developed facile, versatile and environment-friendly preparation methods with an emphasis on control over physicochemical features such as size, shape and composition. In order to exploit the catalytic applications, we employed the reduction of 4-nitrophenol as a model reaction, followed by visible-light assisted oxidation of p-aminothiophenol (PATP). With these tests, we unraveled metal-support interactions and cooperative effects that render hybrid structures superior to their individual counterparts. / A nanocatálise surgiu nas últimas décadas como uma interface entre catálise homogênea e heterogênea, oferecendo soluções simples a problemas que os materiais convencionais não conseguiram resolver. De fato, o design de nanocatalisadores permite obter estruturas com grande área superficial, reatividade e estabilidade, e ao mesmo tempo apresentando boa seletividade e facilidade de separação de misturas reacionais. Neste trabalho apresentamos a preparação de estruturas híbridas compostas por nanopartículas de ouro, paládio e prata (Au, Pd e Ag NPs), nanofolhas de titanato (TixO2), óxido de grafeno (GO) e óxido de grafeno parcialmente reduzido (prGO). Focamos em híbridos do tipo M/TixO2, M/(pr)GO e M/TixO2/(pr)GO (M = Au, Pd ou Ag) e desenvolvemos métodos de preparação simples, versáteis e ambientalmente amigáveis, com ênfase no controle sobre tamanho, forma e composição. Para explorar as potencialidades catalíticas utilizamos a redução do 4-nitrofenol como reação modelo, e em seguida a oxidação assistida por luz do p-aminotiofenol (PATP). Com esses testes, investigamos interações metal-suporte e efeitos cooperativos que tornam as estruturas hibridas superiores a cada um dos materiais que as compõem.

This dissertation is directed towards the fundamental understanding of the controlled synthesis of noble-metal (silver, gold, and palladium) and metal oxide (manganese and copper oxide) nanostructures as well as their applications in heterogeneous and plasmonic catalysis. In the first part of this work (Section 1), we provided a general background concerning the science of controlled nanomaterials, their syntheses, properties, and applications in catalysis and plasmonic catalysis. Then, we describe and developed a series of protocols for the synthesis of these nanomaterials with controlled sizes and structures (spheres, cubes, rods, shells, flowers, dendrites, and tadpoles), mainly focusing on the mechanistic understanding of their formation and how physical and chemical parameters (size, shape, composition, surface morphology) may influence/modify their catalytic properties (Sections 2 and 3). In Section 4, we turned our attention for the design of simple protocols for the synthesis of advanced nanomaterials that are interesting for green catalytic transformations applications. In this case, we envisioned the use of MnO2-Au nanomaterials (nanowires and nanoflowers) displaying several properties (unique pore structure, high surface area, ultrasmall Au NPs at the surface, high concentration of oxygen vacancies and Auδ+ species, strong metal-support interactions, and uniform shapes and sizes) that are desirable for catalyzing a series of green oxidation reactions in mild conditions (low temperatures and molecular oxygen or atmospheric air as the oxidants). In Section 5, we have demonstrated that catalysis and optical properties can be merged together to improve catalytic processes, the so called-plasmonic catalysis. This allowed us the use of visible light as the energy input to drive chemical transformations in mild conditions and then provide new insights regarding the various factors that affect SPR-mediated catalytic activities in plasmonic nanostructures. Finally, in Section 6, we focused our attention on how important is to introduce both nanoscience and the synthesis/characterization of nanomaterials having controlled physicochemical features to undergraduate students. Specifically, we have described simple laboratory experiments for the synthesis of nanomaterials (gold nanospheres and Cu(OH)2/CuO nanowires) displaying uniform sizes and shapes in order to investigate and explain their optical properties, catalytic activities and formation mechanisms. / Não consta resumo na publicação.

Fluorescence from endogenous molecules and exogenous contrast agents can provide morphological, spectral, and lifetime contrast that indicates disease state in epithelial tissues. Recently, nonlinear microscopy has emerged as a potential tool for the early detection, case-finding, and monitoring of epithelial cancers because it permits non-invasive, three-dimensional fluorescence imaging of subcellular features hundreds of microns deep. This dissertation explores the use of nonlinear microscopy for cancer diagnostics on two fronts: (1) we examine the fundamental limitations governing the maximum nonlinear imaging depth in epithelial tissues, and (2) we investigate the use of a new class of nonlinear contrast agent---plasmonic gold nanoparticles---for molecularly specific imaging of cancer cells. We built and optimized a nonlinear microscope for deep tissue imaging, and studied the image contrast as a function of imaging depth in ex-vivo human biopsies and tissue phantoms. With this system we demonstrated imaging down to 370 [mu]m deep in a human biopsy, which is significantly deeper than imaging depths achieved in comparable studies. We found that the large scattering coefficient and homogenous fluorophore distribution typical of epithelial tissues limit the maximum imaging depth to 3-5 mean free scattering lengths deep in conventional nonlinear microscopy. Beyond this imaging depth, the increasing contribution of out-of-focus emission limits the contrast to insufficient levels for diagnostic imaging. We support these observations with time-dependent Monte Carlo simulations. We exploited the intense interaction of gold nanoparticles with light, enhanced by surface plasmon resonance effects, to create extremely bright nonlinear contrast agents. These contrast agents proved to be several orders of magnitude brighter than the brightest organic fluorophores and at least one order of magnitude brighter than quantum dots. We targeted gold nanoparticles to a biomarker for carcinogenesis and demonstrated molecularly specific imaging of cancer cells. We demonstrated that unlike emission from traditional bandgap fluorophores, nonlinear luminescence from gold nanoparticles was weakly dependent on excitation pulse length for short pulse durations. This finding supports the hypothesis that nonlinear excitation in plasmonic nanoparticles involves sequential rather than simultaneous absorption of excitation photons. The remarkable brightness of gold nanoparticles makes them an attractive contrast agent for nonlinear diagnostics. / text

Metallic nanostructures such as nanoparticles, nanowires and nanoapertures exhibit extraordinary optical properties in absorption, scattering and transmission of electromagnetic radiation due to the excitation of surface plasmons. This allows them to provide applications in converting photon energy to other forms of energy such as heat, mechanical work and electricity in a more efficient or controlled manner. When incorporated into an amorphous silicon thin film solar cell, nanoparticles were found to substantially increase the light absorption in the photoactive layer within certain wavelength range. The mechanism of this optical absorption was studied using three-dimensional finite element method. It was found that intensified Fabry-Perot resonance in the active layer due to the addition of the nanostructures and enhanced light scattering by the plasmonic nanostructures were both responsible for this phenomenon. Interestingly, higher absorption only occurs at wavelength range outside the surface plasmons resonance of the nanostructures. A further study on the absorption of the nanoparticles themselves revealed that enhanced near field associated with the SP resonance of particles causes extraordinary energy dissipation in the particles, resulting in decreased light scattering. Strong power dissipation accompanied with the surface plasmons resonance becomes desirable when nanostructures are used as heat generator. Using the new technique of three-dimensional localization of the metallic nanoparticles on polymer microstructures, wavelength dependent controlling of a light-driven microactuator was achieved by selectively coating it with nanoparticles of different materials. Another important plasmonic nanostructure is the subwavelength hole arrays perforated on a metal film. The optical transmission through these nanometer scaled apertures whose dimensions are smaller than the wavelength of the incident light can be several orders of magnitude larger than expected. Based on this property, a novel tandem solar cell structure was proposed. A metal film perforated with periodic subwavelength hole arrays was inserted in a tandem solar cell as a light transmittable intermediate common electrode for the top and the bottom cell. The perforated electrode removes the current matching restriction in conventional tandem cells and allows active materials with different energy conversion and charge transport mechanisms to be combined in the same device. If used in a multi-junction solar cell, the new design can also save the power loss across the tunnel junction. The perforated intermediate electrode was modeled and its optical performance in the tandem solar cell was investigated. / text

Noble metal nanoparticles are of great interest due to their tunable optical and radiative properties. The specific wavelength of light at which the localized surface plasmon resonance occurs is dependent upon the shape, size and composition of the particle as well as the dielectric constant of the host medium. Thus, the optical properties of noble metal nanoparticles can be systematically tuned by altering these specific parameters. The purpose of this thesis is to investigate some of these properties related to metallic nanoparticles. The first several chapters focus on theoretical modeling to predict and explain various plasmonic properties of gold and silver nanoparticles while the later chapters focus on more accurately combining experimental and theoretical methods to explain the plasmonic properties of hollow gold nanoparticles of various shapes. The appendix contains a detailed description of the theoretical methods used throughout the thesis. It is intended to serve as a guide such that a user could carry out the various types of calculations discussed in this thesis simply by reading this appendix.

The content in the dissertation is divided into two main categories: (1) micro-particle characterization techniques based on elastic light scattering, and (2) ultra-compact on-chip plasmonic light concentration and its applications. For category (1), I developed two techniques, one is in vitro and the other is in the scenario of flow cytometry. I investigated theoretically and experimentally the spectra of scattered light from spherical dielectric particles at certain fixed angles, and demonstrate the linearity between the peak positions in the Fourier domain and the diameter of the particle. Based on this discovery, I demonstrate an efficient and accurate technique for in-vitro micro-particle sizing. Moreover, I theoretically analyzed the far-field elastic scattering signals from micro-particles passing through a flow cytometer with tightly focused incident beams, and established an algorithm to extract size information from the detected signals with higher accuracy than that in conventional flow cytometry systems. For category (2), I proposed an on-chip plasmonic nanofocusing technique whose unit device is a plasmonic triangle-shaped nanotaper mounted upon a dielectric optical waveguide. This structure provides highly efficient and robust light concentration into the tip of the nanotaper. Near-field measurements were performed to thoroughly investigate a fabricated sample and prove the concept. I also proposed theoretically a novel concept named phase-induced local-field configuration with logic behaviors, whose actuators are composite devices built on units of single on-chip plasmonic light concentrators mentioned above.

The study and applications of surface plasmon polaritons (SP) – also known as plasmonics – has attracted the interest of a wide range of researchers in various fields such as biology, physics, and engineering. Unfortunately, the large propagation losses of the SP severely limit the usefulness of plasmonics for many practical applications. In this dissertation a new wave guiding mechanism is proposed in order to address the large propagation losses of the plasmonic guides. Possible applications of this guiding scheme are also investigated. The proposed hybrid plasmonic waveguide (HPWG) consists of a metal layer separated from a high index slab by a low index spacer. A detailed analysis is carried out to clarify the wave guiding mechanism and it is established that the mode guided by the HPWG results from the coupling of a SP mode and a dielectric waveguide mode. A two dimensional HPWG is proposed and the effects of various parameters on the HPWG performance are analyzed in detail. This structure offers the possibility of integrating plasmonic devices on a silicon platform. The proposed waveguide supports two different modes: a hybrid TM mode and a conventional TE mode. The hybrid TM mode is concentrated in the low index layer, whereas the conventional TE mode is concentrated in the high index region. This polarization diversity is used to design a TM- and a TE-pass polarizer and a polarization independent coupler on a silicon-on-insulator (SOI) platform. Moreover, the performance of a HPWG bend is investigated and is compared with plasmonic waveguide bends. The proposed devices are very compact and outperform previously reported designs. The application of HPWG for biosensing is also explored. By utilizing the polarization diversity, the HPWG biosensor can overcome some of the limitations of plasmonic sensors. For example, unlike plasmonic sensors, the HPWG biosensor can remove the interfering bulk and surface effects.

Le concept de metamatériaux est apparu au cours des années 2000 avec la réalisation de structures artificielles permettant une propagation non-conventionnelles des ondes électromagnétiques. La réponse électromagnétique des metamatériaux est liée à la présence d’éléments optiquement résonants, de dimensions inférieures aux longueurs d’onde d’excitation, arrangés dans une structure périodique prédéfinie.Afin de produire les structures géométriques inhérentes au design de metamatériaux, l’auto-assemblage des copolymères à blocs constitue une méthodologie émergente. En effet, les structures périodiques produites lors de la séparation de phase de ces matériaux peuvent être utilisées en tant que canevas pour la création de réseaux périodiques de nanoparticules. L’objectif principal de ces travaux de thèse a ainsi été de démontrer la validité de cette stratégie pour la réalisation, d’une manière simple et reproductible, d’une large gamme de nanostructures et de corréler les paramètres structuraux de ces réseaux de nanoparticules aux propriétés optiques.Une première démonstration de ce concept a été obtenue en utilisant un copolymère à blocs formant une structure lamellaire afin de réaliser des surfaces possédant des indices de réfraction élevés. La formation contrôlée de particules métalliques au sein de cette structure a permis de produire des surfaces décorées par ces nanoparticules, pour lesquelles une corrélation entre la teneur en or et l’indice de réfraction résultant a pu être établie. Ce concept a été poussé plus en avant en utilisant une gamme des copolymères à blocs de différentes masses molaires et formant une morphologie cylindrique. En effet, un contrôle accru des paramètres structuraux des réseaux de nanoparticules (diamètre et distance inter-particules) a permis la réalisation de metasurfaces aux propriétés optiques variées. Enfin la mise au point d’une stratégie d’auto-assemblage itérative nous a permis d’obtenir des metasurfaces au design complexe, avec notamment la production de surfaces décorées par des clusters bimétalliques ou des multicouches hybrides polymère/metal. Dans l’ensemble des cas, les surfaces décorées de nanoparticules ont été minutieusement caractérisées par des techniques de microscopie et de diffraction RX afin de mieux appréhender les propriétés optiques dérivées d’analyses d’ellipsométrie spectroscopique à angle variable. / The concept of metamaterials appeared in the years 2000 with the achievement of artificial structures enabling nonconventional propagation of electromagnetic waves. The electromagnetic response of metamaterials is based on the presence of optically resonant elements of sub-wavelength size and well-designed morphology and organization.In order to create controlled geometrical structures inherent to metamaterials design, block copolymer self-assembly constitutes an emerging strategy. Indeed, the periodic structures inherent to their segregation behavior can be used as scaffolds to create various regular or ordered nanoparticles arrays. The main objectives of this study is to demonstrate that block copolymer can indeed lead to a high level of control of a variety of designed nanostructures, in an easy and scalable method, and to correlate the structural parameters of the nanoparticles arrays and their optical properties.As a first demonstration, a lamellar-forming (poly(styrene)-block-poly(2-vinylpyridine) was used to create high refractive index surfaces. The selective and customizable metal incorporation within the out-of-plane lamellae produces azimuthally isotropic metallic nanostructures of defined geometries, for which a clear relationship between the gold content and the refractive index was established. Further studies were dedicated to the correlation between the geometrical parameters of the nanoparticles arrays and the optical properties through the macromolecular engineering of a series of cylinder-forming block copolymers having a wide range of molecular weights. Through this strategy, the particle diameter and the inter-particle distance were tuned leading to the production of metasurfaces with various optical characteristics. More complex metasurface designs were also obtained using a layer-by-layer self-assembly strategy, i.e. bimetallic raspberry nanoclusters or layered hybrid (metallic/polymer) structures. In all cases, the nanoparticles arrays were thoroughly analyzed using microscopy and small-angle X-ray scattering techniques in order to better apprehend the optical properties derived from variable-angle spectroscopic ellipsometry analysis.

Dans la réalisation de circuits intégrés hybrides électroniques - photoniques pour les réseaux télécom, les modulateurs intégrés plasmoniques pourront jouer un role essentiel de codage de l'information en signaux optiques. Cette thése montre la réalisation d'une approche modulateur plasmonique a effet de champ, intégrée en silicium en utilisant les technologies CMOS standards. Ce modulateur MOS plasmonique présente diverses propriétés intéressantes, a savoir un confinement optique fort, permettant une augmentation de l'interaction lumiére matiére. Ces modulateurs plasmoniques permettent aussi de réduire l'inadéquation entre la taille des dispositifs en photonique Si et celle de l' électronique, ce qui permet d'envisager une convergence de leur fabrication en technologie VLSI sur une meme puce. Le modulateur étudié dans ce mémoire repose sur l'accumulation de porteurs dans un condensateur MOS a grille cuivre integer dans un guide d'onde en silicium, nécessitant aux technologies front end et back end Cu d etre combinés de quelques nanométres l'une de l'autre. Nous présentons aussi de nouveaux designs pour injecter de la lumiére a partir de guide d'onde SOI dans un guide a nanostructure plasmonique et les mesures d'une modulation électro-optique dans les structures MOS plasmoniques / Compact and low energy consumption integrated optical modulator is urgently required for encoding information into optical signals. To that respect, the use of plasmon modes to modulate light is of particular interest when compared to the numerous references describing silicon based optical modulators. Indeed, the high field confinement properties of those modes and the increased sensitivity to small refractive index changes of the dielectric close to the metal can help decrease the characteristic length scales of the devices, towards to that of microelectronics.This thesis investigates the realization of Si field-effect plasmonic modulator integrated with a silicon-on insulator waveguide (SOI-WG) using the standard CMOS technology. The material aspects and also the technological steps required in order to realize an integrated plasmonic modulator compatible with requirements of CMOS technology were investigated. First, we demonstrate a Metal-Nitride-Oxide-Semiconductor (MNOS) stack for applications in electro-optical plasmonic devices, so that a very low optical losses and reliable operation is achieved. This objective is met thanks to a careful choice of materials: (i) copper as a metal for supporting the plasmonic mode and (ii) stoechiometric silicon nitride as an ultrathin low optical loss diffusion barrier to the copper. Final electrical reliability is above 95% for a 3 nm thick Si3N4 layer, leakage current density below 10-8 A.cm-2 and optical losses as low as 0.4 dB.μm-1 for a 13 nm thick insulator barrier, in agreement with the losses of the fundamental plasmonic mode estimated by 3D FDTD calculations, using the optical constant of Cu measured from ellipsometry. After demonstrating the MNOS as an appropriate structure for electro-optical CMOS plasmonics, we fabricate a vertical Metal-Insulator-Si-Metal (MISM) waveguide integrated with an SOI-WG, where the back metal was fabricated by flipping and molecular bonding of the original SOI wafer on a Si carrier wafer. The active device area varies from 0.5 to 3 μm2, 0.5 μm width and length varying from 1 to 6 μm.An efficient and simple way to couple light from Si-WG to vertical MISM PWG was experimentally realized by inserting a Metal-Insulator-Si-Insulator (MISI) coupling section between the two waveguides. We demonstrate that such couplers operates at 1.55 μm with the highest efficiency geometry corresponds to a compact length of 0.5 μm with coupling loss of just 2.5 dB (50 %) per facets. This value is 3 times smaller compared to the case of direct coupling (without any MISI section). High-k dielectrics are demonstrated as promising solution to reduce both the MISM absorption loss and the operation voltage. Given that interest, we experimental demonstrate an electrical reliable high-k stack for future applications to the MOS plasmonic modulators.A few μm long plasmonic modulator is experimentally investigated. Devices show leakage current below 10 fA through the copper electrodes based MOS capacitance. The accumulation capacitance (few fF) was found to scale with the surface of the device, in consistent with the expected equivalent oxide thickness of the MOS stack of our modulator. A low electro-absorption (EA) modulation showing capacitive behaviour was experimentally demonstrated in agreement with simulations. Finally, low energy consumption devices 6 fJ per bit was demonstrated.

abstract: Colloidal quantum dots (QDs) or semiconductor nanocrystals are often used to describe 2 to 20 nm solution processed nanoparticles of various semiconductor materials that display quantum confinement effects. Compared to traditional fluorescent organic dyes, QDs provide many advantages. For biological applications it is necessary to develop reliable methods to functionalize QDs with hydrophilic biomolecules so that they may maintain their stability and functionality in physiological conditions. DNA, a molecule that encodes genetic information, is arguably the smartest molecule that nature has ever produced and one of the most explored bio-macromolecules. DNA directed self-assembly can potentially organize QDs that are functionalized with DNA with nanometer precision, and the resulting arrangements may facilitate the display of novel optical properties. The goal of this dissertation was to achieve a robust reliable yet simple strategy to link DNA to QDs so that they can be used for DNA directed self assembly by which we can engineer their optical properties. Presented here is a series of studies to achieve this goal. First we demonstrate the aqueous synthesis of colloidal nanocrystal heterostructures consisting of the CdTe core encapsulated by CdS/ZnS or CdSe/ZnS shells using glutathione (GSH), a tripeptide, as the capping ligand. We next employed this shell synthesis strategy to conjugate PS-PO chimeric DNA to QDs at the time of shell synthesis. We synthesized a library of DNA linked QDs emitting from UV to near IR that are very stable in high salt concentrations. These DNA functionalized QDs were further site-specifically organized on DNA origami in desired patterns directed by DNA self-assembly. We further extended our capability to functionalize DNA to real IR emitting CdxPb1-xTe alloyed QDs, and demonstrated their stability by self-assembling them on DNA origami. The photo-physical properties of the QDs were further engineered by attaching a QD and a gold nanoparticle in controlled distances on the same DNA origami, which revealed a much longer range quenching effect than usual Forster Resonance Energy Transfer. We are currently engaged in enhancing photoluminescence intensity of the QDs by bringing them in the plasmonic hot spots generated by cluster of larger plasmonic nanoparticles. / Dissertation/Thesis / Ph.D. Chemistry 2014