AbstractThe aim of this thesis is to systematically investigate the physics of coupling a spherical gold nanoparticle on a mirrored (NPoM) substrate. When this occurs, both the localised surface plasmons on the particle and propagating surface plasmons at both of the interfaces of the substrate can be excited. The reflectivity and permittivity of the substrate plays a key role in the plasmonics of a NPoM. As reflectivity increases, a vertical dipole plasmon modes develops, while increasingly negative permittivities give rise to surface plasmons in the film, which are sensitive to film thickness and hybridise with the particle’s plasmons, causing them to shift. Furthermore, since much of the charge in a vertically polarised particle is localised to the gap region, large amounts of opposite charges are induced on the opposite side of the gap. This is vital in the implementation of NPoM in strong coupling between plasmons in the nanoparticle and excitons in carbon molecules inside the gap created by using single layer graphene as a spacing layer. This thesis demonstrates that optical spectroscopy is an effective method for characterising single layers of graphene. This is confirmed by comparing the experimental results to a theoretical method, which takes into account contributions from a wide range of incident angles and both TE and TM polarisations.
It is also shown that coupling strength can be collectively tuned within the visible spectrum using a low-powered incident laser. This works by photobleaching carbon molecules in the gap (grown under the influence of the intense gap mode in the NPoM) and reducing its oscillating strength. This is confirmed both experimentally and theoretically, and may help with the development of new optoelectronic and molecular devices.
|Date of Award||Jul 2019|
|Sponsors||Northern Ireland Department for the Economy|
|Supervisor||Fumin Huang (Supervisor)|