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Plasmonic properties, such as refractive index sensitivity (RIS), surface enhancement of the Raman signal (SERS), fluorescence quenching, and photocatalytic activity, of monolayers of weakly interacting monodisperse silver nanocubes were qualitatively modified in a very well controlled manner by supporting them on thin silicon films with varying thickness. Such fine tunability is made possible by the strong dependence of the nanocube dipolar (D) and quadrupolar (Q) plasmon mode hybridization on the refractive index of the supporting substrate. By increasing the Si film thickness from zero to ~25 nm we were able to "shift" the D resonance mode by up to 200 nm for ~80 nm cubes without significantly affecting the Q mode. The silicon supported nanocubes showed a significant improvement in RIS via the Q mode with a figure of merit greater than 6.5 and about an order of magnitude enhancement of the SERS signal due to the stronger electric field created by the D mode. Such substrates also showed a ~10 times decrease in rhodamine 6G fluorescence as well as the rates of amorphous carbon formation. The study proposes a new way to design and engineer plasmonic nanostructures.

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In the present work we investigated the properties and behavior of plasmonic modes of silver nanocube monolayers with respect to reflection and transmission of visible radiation. Uniform monolayers of low particle densities were created using the Langmuir-Blodgett technique using the phospholipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) as a passive spacer. Dipole-dipole coupling modes were avoided by depositing at low pressures to ensure sufficient spacing between the nanocubes. The refractive index sensitivities of plasmonic modes for monolayers on glass, silicon thin films, and bulk silicon wafers were measured using varying solutions of water and ethylene glycol. By varying the refractive index of the substrates it is possible to investigate the relative contribution of plasmonic modes with respect to absorption of the incident signal.

The undersigned hereby recommends to the Department of Chemistry acceptance of the thesis Examining the gilded cage: synthesis, optical properties and plasmonic applications of gold nanocages Submitted by Alyssa Staff in partial fulfillment of the requirements for the degree of Abstract The methods of synthesis and characterization of the optical properties of gold nanocages produced by templated galvanic exchange of silver nanocubes is reported. The effect of surface modifications and substrate interactions were observed using ultra-violet, visible and near-infrared spectrophotometry and fluorescence spectroscopy. The refractive index sensitivity of the gold nanocage structures was altered using various combinations of conditions including size, shape, surface functionalization, substrate support, and capping with dielectric shells. Atomic force, scanning electron, and transmission electron microscopic methods were used for imaging and characterization of the gold nanocages. The potential applications of gold nanocages with various environmental and surface conditions were investigated based on the ability to tune the localized surface plasmon resonance modes to a series of desired wavelengths and bandwidths.Collaboration with the Albert group (Department of Electronics) was carried out with the successful assembly, as well as limit of detection and sensitivity improvements, of a protein biosensor supported on a titled fibre Bragg grating.Investigations into the fluorescence quenching effects of silica-capped gold nanocages was carried out using a tailored selection of fluorescent dyes to enable potential enhancement and/or quenching using the same nanostructure.The optical properties of gold nanocages allow for many potential uses of the same nanostructure in a wide variety of applications, including biomedical and biosensing applications. iv