Surface plasmons have been attracted extensive interests in recent decades due to the novel properties in nanometer sized dimensions. My work focused on the novel optical properties of metal nanostructures based on surface plasmons using theoretical simulation methods. In the first part, we investigated metal nanofilms and nanorods and demonstrated that extremely low scattering efficiency, high absorption efficiency and propagation with long distance could be obtained by different metal nanostructures. With a perforated silver film, we demonstrated that an extremely low scattering cross section with an efficiency of less than 1% can be achieved at tunable wavelengths with tunable widths. The resonance wavelength, width, and intensity are influenced by the shape, size and arrangement pattern of the holes, as well as the distance separating the holes along the polarization direction. The extremely low scattering could be used to obtain high absorption efficiency of a two-layer silver nanofilm. Using the discrete dipole approximation method, we achieved enhanced absorption efficiencies, which are close to 100%, at tunable wavelengths in a two-layer silver thin film. The film is composed of a 100 nm thick perforated layer facing the incident light and a 100 nm thick solid layer. Resonance wavelengths are determined by the distances between perforated holes in the first layer as well as the separation between two layers. The resonance wavelengths shift to red with increasing separation distance between two layers or the periodic distance of the hole arrays. Geometries of conical frustum shaped holes in the first layer are critical for the improved absorption efficiencies. When the hole bottom diameter equals the periodic distance and the upper diameter iv is about one-third of the bottom diameter, close to unit absorption efficiency can be obtained. We examined the electromagnetic wave propagation along a hollow silver nanorod with subwavelength dimensions. The calculations show that light may propagate along the hollow nanorod with growing intensities. The influences of the shape, dimension, and length of the rod on the resonance wavelength and the enhanced local electric field, |E|2 , along the rod were investigated. In the second part, a generalized electrodynamics model is proposed to describe the enhancement and quenching of fluorescence signal of a dye molecule placed near a metal nanoparticle (NP). Both the size of the Au NPs and quantum yield of the dye molecule are crucial in determining the emission intensity of the molecule. Changing the size of the metal NP will alter the ratio of the scattering and absorption efficiencies of the metal NP and consequently result in different enhancement or quenching effect to the dye molecule. A dye molecule with a reduced quantum yield indicates that the non-radiative channel is dominant in the decay of the excited dye molecules and the amplification of the radiative decay rate will be easier. In general, the emission intensity will be quenched when the size of metal NP is small and the quantum yield of dye molecule is about unity. A significant enhancement factor will be obtained when the quantum yield of the molecule is small and the particle size is large. When the quantum yield of the dye molecule is less than 10-5 , the model is simplified to the surface enhanced Raman scattering equation

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Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

<p> The effect of surface active on the rate of gas absorption into water was investigated. Pure oxygen was absorbed into quiescent de-gasified distilled water through-adsorbed monomolecular films of alkylbenzene Sulphonate (ABS) or sodium lauryl sulphate (NaLS).</p> <p> The rate of absorption was characterized by effective diffusivity as measured in detergent solutions up to 20 mg/1 and temperatures between 10 and 30°C.</p> <p> Gas transfer mechanistic models plus physical and chemical properties of surface films were reviewed in order to understand the fundamental processes of interfacial interference which would account for anomolies in results reported in the literature.</p> / Thesis / Master of Engineering (MEngr)

<p> An important aspect in spatial analysis is a digital separation technique. There are several techniques possible, but trend-residual techniques and filtering techniques are emphasized in this report. The areas studied were a 9.6 km^2 gridded area in the Mammoth Cave region in Kentucky and the Lewisburg region in West Virginia. The basic geology and surface patterns are described. Although they are similar in respect to geology, the doline distribution is much smaller and more dense in Kentucky than in West Virginia. Both areas appear stable and subsidence dolines appear dominantly. The two doline development models are presented and the evidence cited tends to support the MDCP model. The predicted clustering of daughters about uniform/randomly distributed parents is found in Kentucky, no study was found for West Virginia. Both areas show that doline long axis are oriented parallel to regional joint sets.</p> <p> A uniformly dense grid proves accurate and unbiased when the elevation data are contoured. The Surface II Graphics package proves more than adequate in producing all the maps needed for this study despite the lack of flexibility in some areas.</p> <p> A trend-residual analysis was conducted to the fourth order for both the Kentucky and West Virginia areas. Despite minor technical problems, the results are positive. The method clearly separates the local doline variance from the regional trend, but there does appear to be a consistent bias towards nearby ridges. It also appears that there is an enhancement-suppression effect from the residual analysis such that certain doline forms are enhanced while others are suppressed as the trend order progresses from the first to the fourth order.</p> <p> The filtering technique also shows some excellent results from the digital separation method. Several filter types are discussed and the theory of their design is also presented. Very successful results were achieved by a zero summed filter as well as a 3 x 3 moving average filter. Several maps are produced from the analyses and are computer generated and these are also presented. There are several conclusions given at the end.</p> / Thesis / Candidate in Philosophy

Wetland systems have been widely studied and found to have enhanced capacity to transform meaningful amounts of nitrate (NO3-N) from shallow subsurface water before the improved-quality water is delivered to lake, river, and groundwater systems. Wetland are characterized by the abundant presence of electron donors and acceptors (i.e., organic carbon & NO3-N, respectively) as well as anoxic and reducing conditions which are crucial for supporting denitrification processes and the reduction of excessive nitrate levels in the environment. When favorable conditions within the wetland systems are not present, denitrification is often limited to the biofilm-protected bacteria hosted on the sediment surfaces. However, there is still a need to determine if floodplain wetlands are being utilized to their maximum potential in excess nitrate removal.

For applications of MoS2 in batteries, supercapacitors, electrocatalysts, solar cells and water quality sensors, a substantially increased conductivity is required in order to achieve reasonable currents. Popularly, the metallic 1T-MoS2 phase is used, which can be prepared via a lithium intercalation process, requiring inert atmosphere processing and safety procedures. In this thesis, I demonstrate a safer and more efficient process to yield conductive MoS2 (c-MoS2). This simple and effective way to prepare few layer c-MoS2 utilizes ambient conditions and 0.06 vol% aqueous hydrogen peroxide. Part of the research effort has been to enhance the conductivity of MoS2 using the idea of green solvents (like pure water). The bulk conductivities of both peroxide and water exfoliated MoS2 are up to seven orders of magnitude higher than that of the semiconducting 2H-MoS2 phase. The samples were characterized with Hall measurements, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Trace amounts of hydrogen molybdenum bronze (HxMoO3-y) and sub stoichiometric MoO3-y were shown to help tune the conductivity of the nanometer-scale thin films without impacting the sulfur-to-molybdenum ratio. c-MoS2 was further functionalized with thiols to determine the number of residual reactive sites. I also studied the mechanism of surface functionalization of MoS2 with diazonium molecules (both direct and in-situ approach) to understand the surface properties of our material and tune the chemical and mechanical properties of conductive MoS2. An important goal of my work is to control the conductivity of the MoS2 thin films in safe and facile ways that enable their application in low-cost chemiresistive sensors for liquid environments. I fabricated chemiresistive sensors with centimeter channel lengths while maintaining low measurement voltages for pH sensing. I further measured the catalytic activity of c-MoS2 films in 0.5 M H2SO4 electrolyte solution using linear sweep voltammetry (LSV) which showed a lower Tafel value at 10 mA/cm2 current density. The lower Tafel value demonstrated that c-MoS2 has potential to use as catalyst for hydrogen evolution reaction. My study furthers the understanding of conductive forms of MoS2 and opens up a new pathway for next generation electronic and energy conversion devices. / Thesis / Doctor of Philosophy (PhD) / For applications of MoS2 in batteries, supercapacitors, electrocatalysts, solar cells and water quality sensors, a substantially increased conductivity is required in order to achieve reasonable currents. Popularly, the metallic 1T-MoS2 phase is used, which can be prepared via a lithium intercalation process, requiring inert atmosphere processing and safety procedures. In this thesis, I demonstrate a safer and more efficient process to yield conductive MoS2 (c-MoS2). This simple and effective way to prepare few layer c-MoS2 utilizes ambient conditions and 0.06 vol% aqueous hydrogen peroxide. Part of the research effort has been to enhance the conductivity of MoS2 using the idea of green solvents (like pure water). The bulk conductivities of both peroxide and water exfoliated MoS2 are up to seven orders of magnitude higher than that of the semiconducting 2H-MoS2 phase. The samples were characterized with Hall measurements, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Trace amounts of hydrogen molybdenum bronze (HxMoO3-y) and sub stoichiometric MoO3-y were shown to help tune the conductivity of the nanometer-scale thin films without impacting the sulfur-to-molybdenum ratio. c-MoS2 was further functionalized with thiols to determine the number of residual reactive sites. I also studied the mechanism of surface functionalization of MoS2 with diazonium molecules (both direct and in-situ approach) to understand the surface properties of our material and tune the chemical and mechanical properties of conductive MoS2. An important goal of my work is to control the conductivity of the MoS2 thin films in safe and facile ways that enable their application in low-cost chemiresistive sensors for liquid environments. I fabricated chemiresistive sensors with centimeter channel lengths while maintaining low measurement voltages for pH sensing. I further measured the catalytic activity of c-MoS2 films in 0.5 M H2SO4 electrolyte solution using linear sweep voltammetry (LSV) which showed a lower Tafel value at 10 mA/cm2 current density. The lower Tafel value demonstrated that c-MoS2 has potential to use as catalyst for hydrogen evolution reaction. My study furthers the understanding of conductive forms of MoS2 and opens up a new pathway for next generation electronic and energy conversion devices.

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