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Title: Engineering plasmonic light scattering with thin dielectric films : towards enhanced light trapping and novel sensing elements
Author: Powell, Alexander
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2015
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Plasmonic research is becoming increasingly focused on the integration of noble metal nanostructures with planar devices to enhance their performance. Whilst the physics of noble metal nanoparticles at a simple interface is well studied, their behaviour inside a thin film structure is not. This work investigates the effect that placement in a thin dielectric film has on the excited modes and the directional scattering from various geometries of nanoparticle; the focus is on the fundamental principles but the application of this work in light trapping and nanoantenna design is also discussed. Research is conducted using finite-difference time-domain simulations and a custom built dark-field Fourier-space microscope, designed to interrogate individual particles and measure their angular scattering in thin films for the first time. It is found that the excited modes, large angle scattering and substrate coupling of the nanoparticles can be manipulated and improved considerably through careful choice of the materials and dimensions of the layers. Scattering from silver nanowires into a substrate is observed experimentally for the first time and an overcoating thin film is exploited to create highly directional emission, which is compared with nanoantennas in the literature. The potential to use this system as a novel sensing element is discussed. Following on from this, the nanocube patch antenna system is reviewed and its operation as a subwavelength plasmonic gas sensor is demonstrated for the first time to test for relative humidity using the Nafion polymer. This easily fabricable system shows superior sensitivities to other single-particle sensors across a range of humidities and simulations predict that by using sharper cubes and different deposition processes a further tripling of the recorded efficiency is achievable. The nanopatch structure can be readily adapted to detect a variety of other gases, and has the potential for integration into photonic circuitry.
Supervisor: Smith, Jason ; Watt, Andrew ; Assender, Hazel Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available