A STUDY OF COUPLING BETWEEN EXTENDED AND LOCALIZED SURFACE PLASMONS

Abstract

Placing a molecule near a roughened metal surface or a metallic nanoparticle highly enhances the magnitude of its Raman signal, leading to an effect known as surface-enhanced Raman spectroscopy (SERS). SERS is a promising non-invasive technique that could study the interactions between biological molecules and even detect them in minuscule amounts. In this thesis, SERS due to the coupling between localized and extended surface plasmons (ESP-LSP coupling) for a silver film coated on top of the SF11 glass substrate was experimentally studied. The film’s surface morphology was modi fied by electrostatically binding 60 nm gold nanoparticles on a previously coated layer of 4-Aminothiophenol molecules. Surface plasmon resonance (SPR) and the strong coupling effect were also dis cussed. Several computations in COMSOL multiphysics were also performed to look for configurations that gave rise to ESP-LSP coupling between the metal film and nanoparticles. Specifically, the configurations studied were the nanoparticle on a mirror and the Kretschmann configuration with an array of nanoparticles on top of the metal film. A search for signatures of strongly coupled Rabi split in the SER spectra of the previously described system was also undertaken. No such signature was observed. However, visible enhancement, as predicted, in the Raman signal was observed when the 4-ATP molecules were electrostatically bound to gold nanoparticles due to metal-covalent bonds.