Light-matter interactions on nano-structured metallic film

Abstract

This thesis describes a study into the optical properties of nano-structured metallic films. Structures are produced by electrochemically depositing metal through a self-assembled template of polymer micro-spheres. This versatile technique allows nano-structured surface made from almost any metal to be produced quickly and cheaply. Geometries ranging from array of shallow dishes, to sharp metallic spikes and encapsulated spherical cavities can all be produced on the same sample. This thesis presents an in-depth study into the properties delocalised and localised surface plasmon polaritons. These plasmons can be tuned in energy by controlling the sample geometry and angle of the incident light. The coupling between these two types of plasmon is also investigated and theories are put forward to understand the observed results. These findings could prove useful in the design of plasmon guiding and computing devices. With an understanding into the plasmonic properties of the metallic nanostructures, research is undertaken to explore how the associate local electric field couples to molecules adsorbed onto a samples surface. A strong correlation between surface plasmons and enhanced Raman scattering is found, leading the observation of the beaming of the Raman scattered light. The nano-structured substrates are also shown to have excellent reproducibility as well as enhancement of the Raman signals, leading to applications such as high sensitivity molecular sensors. Finally, the interaction between organic semiconductor molecules and surface plasmons is explored. A strong interaction between the different states is found and plasmon enhanced fluorescence is also observed. These studies open the way for greater control over the exciton states, which have potential for the use in novel laser systems.

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