We have numerically investigated the influence of a nanoscale silicon tip in proximity to an illuminated gold nanoparticle. We describe how the position of the high-permittivity tip and the size of a nanoparticle impact the absorption, peak electric field and surface plasmon resonance wavelength under different illumination conditions. We detail the finite element method (FEM) approach we have used for this, whereby we specify a volume excitation field analytically and calculate the difference between this source field and the total field (i.e., scattered-field formulation). We show that a nanoscale tip can locally enhance the absorption of the particle as well as the peak electric field at length scales far smaller than the wavelength of the incident light.

Aerosols of nitrate solutions were irradiated in the presence of radical scavengers in an attempt to measure the yield of hydroxyl radical in both the aqueous phase and the gas phase. Carbon monoxide, benzoic acid, benzene and cyclohexane were used as scavengers to trap hydroxyl radical. The products from the reaction of these scavengers with hydroxyl radical were analysed with High Performance Liquid Chromatography and mass spectrometry. The radiant flux in the chamber was measured via ferrioxalate actinometry, both with bulk liquid and aerosol droplets. Many quantitative results were obtained but several anomalies were found. This suggests that Mie theory is not capable of predicting rates of photochemical reactions within droplets.

Ce travail présente la caractérisation des propriétés d'absorption de lumière par des nanofils uniques (NF) de silicium en utilisant la spectroscopie de photocourant, ainsi qu'une étude préliminaire des processus d'incorporation des dopants et de réalisation de jonction dans les NFs. Tout d'abord, nous commençons par décrire les méthodes de croissance utilisées pour synthétiser des NFs actifs pour la génération de photocourant, avec l'utilisation du chlorure d'hydrogène dans les procédés classiques de croissance CVD catalysée or de fils dopés. Cette méthode offre des structures très faiblement coniques, élargit les températures de procédé, permettant en particulier d'incorporer très efficacement le bore, avec des densités d'accepteurs ionisés allant jusqu'à 1.8E19 cm-3, tout en inhibant la diffusion d'or depuis le catalyseur. L'attention est ensuite portée à la fabrication de jonctions, l'étude de ses caractéristiques électriques, ainsi que sur l'influence de paramètres morphologiques (rayon, position axiale) du fil sur sa résistivité apparente. Dans une seconde partie, nous étudions la réponse en photocourant d'un jeu de NFs actifs de différents diamètres et corrélons nos résultats à un traitement analytique de l'absorption des photons à l'échelle du nanoobjet dans le cadre de la théorie de Mie adaptée au cas cylindrique. L'accord expérience-théorie est très bon pour les deux polarisations (TE-TM). Des résonances dans le spectre d'absorption sont mises en évidence, correspondant à l'excitation de modes propres du fil, et associées à des sections efficaces d'absorption pouvant être supérieures à l'unité. Dans une dernière partie, nous adaptons la stratégie de dépôt antireflet utilisée dans les cellules solaires pour améliorer le couplage de la lumière incidente aux NFs. Pour cela, des dépôts de SiO2 et Si3N4 sont réalisés sur des NFs via la technique de PECVD, nous fournissant par là-même un jeu de structures pourvues d'un dépôt de diélectrique à haute conformité. Se basant sur les spectres d'absorption ainsi acquis, nous obtenons les gains relatifs d'absorption induits par le dépôt de diélectrique et les comparons aux calculs analytiques développés spécifiquement pour obtenir l'absorption dans le cœur seulement du cylindre coaxial, ceci nous permettant également d'estimer la partie du rayonnement incident absorbé dans la coquille diélectrique. / In this work we present the characterization of the light absorption properties of single silicon NWs (NW) using photocurrent spectroscopy along with the preliminary work done at the wire scale to characterize the dopant incorporation and the fabrication of junctions. First, we start with a description of the growth methods used to synthesize active NW's for photocurrent generation, with results obtained on the use of hydrogen chloride in the CVD VLS growth of doped NWs. This method offers highly straight structures, widened process temperatures allowing in particular very efficient boron incorporation—ionized acceptors densities up to 1.8E19 cm-3—and inhibited gold diffusion, thereby greatly reducing elemental contamination from the catalyst. Focus is made on the junction formation, the study of its electrical characteristics and the influence of morphological parameters—radius, axial position—to obtain the desired doping properties. In a second part, we present the photocurrent response of a set of different diameter active Si NWs and correlate our results with an analytical treatment of the photon absorption at the nanoscale using the Lorentz Mie theory adapted to the cylindrical geometry under study. Very good agreement is found between experiment and theory for both polarization spectra (TE-TM). Absorption resonances are resolved, corresponding to leak resonant modes, and can display absorption efficiencies higher than one, making downscaling an efficient tool to increase energy harvesting capabilities. In a last part, we adapt the antireflective coating strategy used in solar cells to improve the coupling of the incoming light to Si NWs. For this, SiO2 and Si3N4 films are deposited on NWs using PECVD, providing a set of structures coated with a high level of conformity. Based on the new set of spectra we obtain the relative gain curves and compare them with analytical calculations specifically derived for getting the absorption in the core of coaxial nanocylinders only, which allows estimating the magnitude of the absorbed energy in the dielectric shell.

Orientador: Fernando Galembeck / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-15T06:51:39Z (GMT). No. of bitstreams: 1 SilvaeSouza_CristianeAparecida_D.pdf: 8520514 bytes, checksum: 17e73481eda5f744b4ec360be3455823 (MD5) Previous issue date: 2009 / Resumo: A morfologia de filmes compósitos preparados com fosfato de alumínio e látexes de poli(metacrilato de metila-co-acrilato de butila) e de poli(estireno-co-acrilato de butila) foi caracterizada por técnicas de microscopia eletrônica de transmissão e de varredura (TEM, SEM) e por técnicas de microscopia de varredura por sonda (AFM, DPFM). O grau de opacidade (razão de contraste) e os cálculos de coeficiente de espalhamento das partículas de fosfato de alumínio nos filmes compósitos foram obtidos através dos espectros de refletância. As micrografias das superfícies de desbaste dos filmes compósitos mostraram espaços vazios entre os agregados de partículas de fosfato de alumínio dispersos pela matriz polimérica. A adesão entre os agregados de partículas de fosfato de alumínio e polímero é muito boa nas interfaces de contato. A refletância dos filmes compósitos varia amplamente, dependendo da concentração das partículas de fosfato de alumínio, assim como da sua forma de uso em pó ou em dispersão e da dimensão dos espaços vazios entre os agregados de partículas. Os resultados das medidas óticas de opacidade mostraram que os filmes compósitos mais opacos foram os obtidos com fosfato de alumínio na forma de pó e com a dimensão dos vazios entre os agregados de partículas na mesma ordem de grandeza que o comprimento de onda da luz na região do visível (400 a 700 nm). Os coeficientes de espalhamento dos filmes de fosfato de alumínio/poli(estireno-co-acrilato de butila) foram calculados empiricamente usando o modelo de Kubelka-Munk e os resultados mostraram que os vazios contidos nos agregados de partículas de fosfato de alumínio justificam a opacidade dos filmes. O filme mais opaco, com razão de contraste de 88 %, apresentou ampla distribuição de dimensão dos vazios com média numérica igual a 650 nm. Além disso, os valores obtidos dos coeficientes de espalhamento experimentais são muito próximos dos coeficientes de espalhamento estimados pela teoria de Mie. A eficiência de espalhamento, predita pela teoria de Mie, de uma bolha de ar rodeada por fosfato de alumínio com diâmetro médio de 650 nm é apenas 12 % menor que a eficiência de espalhamento de uma partícula de dióxido de titânio, no seu diâmetro ótimo de 350 nm, dispersa no mesmo meio / Abstract: Composite films prepared with aluminum phosphate and latex of poly(methyl methacrylate-co-butyl acrylate) and poly(styrene-co-butyl acrylate) were characterized by electronic microscopy (TEM, SEM) and by different techniques of scanning probe microscopy (AFM, DPFM). Opacity (contrast ratio) and light scattering coefficients of composite films were obtained from reflectance spectra. SEM and TEM micrographs from composite films trimmed surfaces or thin cuts showed voids within aluminum phosphate particle aggregates. The adhesion between aluminum phosphate particle aggregates and polymer is very good at contact interfaces. Composite films reflectance changes widely, depending on void diameters, on aluminum phosphate particle concentration, as well as its use in the form of powder or dispersion. Opacity results showed that the most opaque composite films were obtained with aluminum phosphate powder and with void diameters in the same order of magnitude as the wavelength of light in the visible region (400 to 700 nm). Scattering coefficients of aluminum phosphate/poly(styrene-co-butyl acrylate) films were calculated empirically using the Kubelka-Munk model and the results showed that the observed voids account for films opacity. The most opaque composite film shows contrast ratio equal to 88 % and a broad distribution of void diameters, peaking at ca. 650 nm. Film scattering coefficient of the observed voids was calculated using Mie theory to evaluate their contribution to film opacity showing that the measured and estimated values are in reasonable agreement. The Mie calculations show that scattering efficiency for air trapped within the phosphate particles dispersed in polymer latex is in excess of 4 units in the 650 nm diameter range, which is only 12 % lower than the calculated values for optimum size TiO2 particles (350 nm) dispersed in the same polymer / Doutorado / Físico-Química / Doutor em Ciências

Anthropogenic gas- and particle-phase emissions affect the climate by absorbing and scattering radiation, and have been linked to adverse health effects. Black carbon (BC), a by-product of incomplete combustion, is the most potent light-absorbing component of atmospheric aerosols, with a top-of-the atmosphere direct radiative forcing estimated to be only second to CO2. However, there is a large uncertainty associated with BC’s total direct and indirect radiative forcings due to uncertain source emissions and optical properties and complex interactions with clouds. In this dissertation we investigate the direct radiative impact of two of the most important sources of BC particles: biofuel combustion and vehicles. Together these sources contribute around 40% of the global atmospheric BC burden. Recently, both of these energy sources are undergoing rapid technology changes, and the climate impacts from the emissions of these newly adopted technologies remain uncertain. We also investigate the role of atmospheric processing on the optical properties and growth rates of particles. This dissertation first assesses the climate impacts of aerosol emissions of two rapidly emerging technologies: improved cookstoves and gasoline direct injection (GDI) vehicles. We performed extensive measurements of gas- and particle emissions and optical properties of emissions from both these sources. Our data suggests that improved rocket cookstoves have, on average, a factor of two lower particulate matter (PM) emissions compared to traditional cookstoves but only a 4% climate benefits associated with their emissions. In contrast, we estimated a 30% climate benefit from switching traditional cookstoves to gasifier ones. Of all the stoves tested, charcoal stoves had the lowest emissions and climate impacts. Our data suggests the widespread deployment of improved cookstoves to replace existing, inefficient, traditional cookstoves will likely result in health and climate co-benefits. Similarly, we estimated that the rapid adoption of GDI vehicles to replace existing port fuel injection (PFI) vehicles will likely result in reduced warming from emissions. This is due to the higher fuel economy of GDI engines; we measured an average CO2 reduction of 57 g/mi, from switching engine technologies. GDI engine emissions had higher PM emissions compared to PFI engines, similar to previous findings. In addition, our data suggests that newer GDI engines have a factor of two lower PM emissions compared to older GDI engines. These improvements in emissions may enable GDI-equipped vehicles to meet the new Federal Tier 3 PM standard of 3.0 mg/mi without gasoline particulate filters (GPF, which would reduce their fuel economy). To better constrain the large uncertainty of radiative forcing associated with cookstove emissions, this dissertation examines emissions and optical properties from several cookstove and fuel combinations. We performed extensive laboratory measurements of the optical properties of fresh cookstove emissions using the newly developed firepower sweep protocol. Current model treatments of the optical properties of cookstove emissions assume: (1) complete internal mixture between BC and non-BC material and (2) absorption properties of organics based on parametrizations developed for biomass burning emissions. These assumptions do not accurately represent optical properties of fresh cookstove emissions. We developed new parametrizations of optical properties (BC-mass absorption cross section (MACBC), absorption angstrom exponent (AAE), and single scattering albedo (SSA)) of aerosol emissions from cookstoves as a function of the BC-to-PM mass ratio. These parametrizations are designed for use in climate models to more rigorously assess the global climate implications from adoption of improved stove technologies. Upon entering the atmosphere aerosol emissions undergo complex chemical transformations. Aerosol optical properties depend on their atmospheric processing which controls the amount of coating the particles accumulate and their lifetime. To assess the effects of coating on the optical properties, we performed targeted experiments using real world, size selected, BC particles emitted from a rocket improved cookstove, and coated with biogenic secondary organic aerosol (SOA) material. These experiments explicitly target to evaluate measurements and modeling using simple formulation like Mie theory. Measurements of MACBC and the mass scattering cross section (MSC) of coated BC particles were in good agreement with Mie predictions when the organic-to-BC mass ratio>5. Scattering (but not absorption) was sensitive to BC fractal-like morphology; Mie theory under-predicted measured scattering of fresh emissions. Our data suggest that Mie theory can be used in climate models to approximate the optical properties of coated BC particles emitted from cookstoves, if the mixing-state of BC particles is known. In this dissertation, we present initial evidence that particle growth rates depend on seed composition and gas-phase supersaturation. Current models do not account for seed-dependent growth rates. We conducted experiments to investigate the growth of diesel and biogenic SOA particles. Both seeds were exposed to the same gas-phase supersaturation, which allows us to accurately retrieve differences in growth rates and decouple the effects of surface activity and accommodation coefficients. We estimated that the accommodation coefficients of condensing material was 10% to 30% lower on the diesel particles compared to the SOA particles. Moreover, we measured larger surface activity of condensing material on the diesel particles, potentially due to less-miscible condensing vapors in the diesel particles compared to the SOA particles. Our data suggest that growth of BC (diesel) particles in the atmosphere is likely slower compared to SOA particles. Accurately representing these processes is important to estimate the lifetime and absorption enhancement from coated BC particles, as they compete with other particles for condensable vapors.

Standard optical microscopes cannot resolve images below 200 nm within the visible wavelengths due to optical diffraction limit. This Thesis reports an investigation into super-resolution imaging beyond the optical diffraction limit by microsphere optical nano-scopy (MONS) and submerged microsphere optical nano-scopy (SMON). The effect of microsphere size, material and the liquid type as well as light illumination conditions and focal plane positions on imaging resolution and magnification have been studied for imaging both biological (viruses and cells) and non-biological (Blu-ray disk patterns and nano-pores of anodised aluminium oxide) samples. In particular, sub-surface imaging of nano-structures (data-recorded Blu-ray) that cannot even be seen by a scanning electron microscope (SEM) has been demonstrated using the SMON technique. Adenoviruses of 75 nm in size have been observed with white light optical microscopy for the first time. High refractive index microsphere materials such as BaTiO3 (refractive index n = 1.9) and TiO2-BaO-ZnO (refractive index n = 2.2) were investigated for the first time for the imaging. The super-resolution imaging of sub-diffraction-limited objects is strongly influenced by the relationship between the far-field propagating wave and the near-field evanescent waves. The diffraction limit free evanescent waves are the key to achieving super-resolution imaging. This work shows that the MONS and SMON techniques can generate super-resolution through converting evanescent waves into propagating wave. The optical interactions with the microspheres were simulated using special software (DSIMie) and finite different in time domain numerical analysis software (CST Microwave Studio). The optical field structures are observed in the near-field of a microsphere. The photonic nanojets waist and the distance between single dielectric microsphere and maximum intensity position were calculated. The theoretical modelling was calculated for comparisons with experimental measurements in order to develop and discover super-resolution potential.

Black carbon (BC) is the light-absorbing component of soot, a combustion-generated aerosol that warms the climate by absorbing solar radiation. Its impacts on climate depend on its microphysical properties, which are modified by atmospheric processes including condensation, coagulation and wet removal. State of the art climate models consider soot in a concentric core/shell configuration, with a BC core coated by nonrefractory material such as organics or sulphate. Within this model, thicker coatings enhance visible light absorption, but also wet removal efficiency, and these have opposing effects on the total amount of light absorbed over BC’s lifetime. How well the core/shell model can calculate Mass Absorption Coefficient (MAC, the ratio of absorption to BC mass) is uncertain, as real soot forms more complex (often fractal) shapes, and detailed optical models using these morphologies predict the core/shell model may under- or over-estimate MAC depending on the precise properties of the particles. Few reliable measurements of variations in ambient MAC are available, as most older measurement techniques suffer from systematic uncertainties. In this work, a Single Particle Soot Photometer (SP2) and PhotoAcoustic Soot Spectrometer (PASS) were used to measure BC mass concentration and absorption, and these instruments do not suffer from such uncertainties. The SP2 was also used to report core size and coating thickness distributions that are required to test state of the art climate models. Firstly, a method was developed to minimise bias in the measured coating thicknesses related to the limited detection range of the SP2. The sensitivity of this technique to the assumed density and refractive index of the BC core was also explored, and the most appropriate parameters to use with ambient measurements were determined. Core and shell distributions were measured in Pasadena, California under a range of different photochemical ages. These were then used to calculate MAC, which was compared to that measured using the SP2 and PASS. The measured and modelled MAC agreed within 10% at 532 nm, though this was dependent on the assumed refractive index of the BC core. Overall MAC increased by 15 –25% in around one third of a day of photochemical ageing. This is quite modest compared to some climate models, but not compared to the previous best estimate, which predicted MAC may increase by a factor of ~1.5 over BC’s lifetime. Core and coating distributions were also measured in Canadian boreal biomass burning plumes. A case study was presented comparing the properties of BC in three plumes, one of which had passed through a precipitating cloud. It was demonstrated that larger and more coated BC-containing particles were removed more efficiently, in agreement with previous thermodynamic theory. By calculating MAC using the measured core/shell distributions and comparing to measured scattering, it was demonstrated that the MAC and single-scattering albedo in the plumes were likely not significantly affected by the wet removal, as greater differences were observed between the two plumes not affected by precipitation.

Particle analysis using multiwavelength UV-visible spectroscopy provides the potential for extracting quantitative red blood cell information, such as hemoglobin concentration, cell size, and cell count. However, if there is a significant presence of hypochromism as a result of the concentrated hemoglobin (physiological value of 33%), successful quantification of red cell values would require a correction. Hypochromism has been traditionally defined as a decrease in absorption relative to the values expected from the Beer-Lambert Law due to electronic interactions of chromophores residing in close proximity of one another. This phenomenon has been suggested to be present in macroscopic systems composed of strong chromophores such as nucleic acids, chlorophyll, and hemoglobin. The study presented in this dissertation examines the presence of hypochromism in red blood cells as a part of a larger goal to qualitatively and quantatively characterize red blood cells using multiwavelength UV-visible spectroscopy. The strategy of the study was three-fold: 1) to determine the instrumental configuration that would provide the most complete information in the acquired spectra, 2) to develop an experimental model system in which the hemoglobin content in red blood cells could be modified to various concentrations, and 3) to implement an interpretation model based on light scattering theory (which accounts for both the scattering and absorption components of the optical density spectrum) to provide quantitative information for the experimental system. By this process, hypochromicity was redefined into two categories with molecular hypochromicity representing the traditional definition and macroscopic hypochromicity being an attenuation of the absorption component due to a scattering-related effect. Successful simulations of experimental red cell spectra containing various amounts of hemoglobin were obtained using the theoretical model. Furthermore, successful quantitative interpretation of the red blood cell spectra was achieved in the context of corpuscular hemoglobin concentration, corpuscular volume, and cell count solely by accounting for the scattering and absorption effects of the particle, indicating that molecular hypochromicity was insignificant in this macroscopic system.

Ce travail de thèse porte sur la modélisation des propriétés optiques de diélectriques nanostructurés par des particules métalliques. Nous nous sommes intéressés à deux aspects du problème : la détermination de l’indice effectif et la distribution du champ du plasmon de nanoparticules métalliques dispersées dans de tels milieux. Nous avons développé deux approches numériques. La première étude a été consacrée à la modélisation des parties réelle et imaginaire de l’indice effectif d’un milieu hétérogène. Pour comparer nos résultats de simulations d’indice à l’expérience, nous avons proposé une méthode expérimentale pour la mesure de l'indice de réfraction effectif de solutions colloïdales comportant des nanosphères métalliques ou semiconductrices. La seconde étude traite de la méthode d’extraction de la distribution du champ du plasmon sur la surface d’une nanosphère métallique excitée par une onde électromagnétique plane. Pour l’ensemble de ce travail nous avons tenu compte des paramètres caractéristiques de la matrice hôte et des nanoparticules sur l’indice effectif et le champ du plasmon calculés / This thesis is devoted to modeling of the optical properties of nanostructured dielectrics by metal particles. We interested in two aspects of the problem: the determination of effective index and field distribution of plasmon nanoparticles dispersed in such media. We have developed two numerical approaches. The first is devoted to the simulation of real and imaginary parts of the effective index of heterogeneous medium. In order to compare experience and theory, we have proposed an experimental approach to measure the effective refractive index of colloidal solutions containing metal or semiconductor nanospheres. The second aspect deals with the method of extraction of the field plasmon on the surface of metal nanosphere when it is excited by electromagnetic plane wave. The calculated effective index and field plasmon are done in function of characteristic parameters of nanoparticles and host matrix

O espalhamento de ondas eletromagnéticas por partículas isoladas, com propriedades ópticas e formatos arbitrários, encontra aplicações nas mais diversas áreas do conhecimento. Usualmente, o espalhamento eletromagnético é investigado via grandezas auferidas na região de campo distante. Para partículas inomogêneas, no entanto, as ressonâncias nas seções de choque de espalhamento podem não corresponder a um aumento de intensidade do campo eletromagnético nas vizinhanças imediatas da partícula (região de campo próximo). Esse efeito pode ser induzido em nanopartículas dielétricas com revestimentos plasmônicos e foi recentemente explicado em termos da ressonância de Fano. Essa ressonância resulta da interferência entre um modo eletromagnético não ressonante (processo de fundo) e um modo discreto ressonante (ressonância de plásmon), produzindo um formato assimétrico de linha espectral. Para o entendimento de como os modos de superfície no campo próximo acoplam-se às ressonâncias nas seções de choque, é necessário o cálculo de funcionais dos campos eletromagnéticos internos às partículas ou em suas vizinhanças imediatas. Neste estudo, calculamos a energia eletromagnética no interior de centros espalhadores nas geometrias esférica e cilíndrica. Fazemos aqui o vínculo dos campos internos às grandezas de espalhamento no campo distante via seção de choque de absorção e conservação de energia. Aplicamos nossos resultados a metamateriais dispersivos, estudando as propriedades do espalhamento por esferas revestidas e por esferas quirais, no regime de refração negativa, e por cilindros revestidos sob incidência oblíqua de radiação. Mediante a energia interna às partículas, demonstramos novos efeitos de aumento de intensidade de campo interno fora da ressonância de espalhamento e fornecemos resultados analíticos para a análise dessas ressonâncias, tanto em espalhamento simples quanto múltiplo. / Electromagnetic wave scattering by single particles with both shapes and optical properties arbitrary finds applications in several areas of knowledge. Usually, the electromagnetic scattering is investigated via measured quantities in the far-field region. However, for inhomogeneous particles, resonances in scattering cross sections may not correspond to the electromagnetic field enhancement in the vicinity of a particle (near-field). This effect can be induced in dielectric nanoparticles with plasmonic coatings, and it has recently been explained in terms of the Fano resonance. The Fano resonance results from the interference between a non-resonant electromagnetic mode (background or continuous) and a resonant discrete mode (localized plasmon resonance), leading to an asymmetric lineshape. To understand how the surface modes in the near-field are connected to the cross section resonances, functionals of the electromagnetic fields within scatterers or in their vicinity are required. In this study, we calculate the electromagnetic energy inside scatterers in both cylindrical and spherical geometries. We obtain a connection between the internal energy and the scattering quantities in the far-field via absorption cross section and energy conservation. We apply our results to dispersive metamaterials, studying scattering properties of coated and chiral spheres in the negative refraction regime, and coated cylinders under oblique incidence of radiation. By the electromagnetic energy inside particles, we demonstrate new off-resonance field enhancement effects and provide analytical tools to analyze these resonances in both single and multiple scattering regimes.