Far-field and Near-field Optical Properties Of Strongly Interacting Silver Nanocrystals

Noble metal nanocrystals are known for their remarkable optical properties that are caused by the result of their ability to support a localized surface plasmon resonance (LSPR). These optical properties can be observed in the far-field, through their optical extinction or in the near-field by a highly enhanced electric-field localised to the surface of the particles. The goal of this work was to study properties of supported silver nanocrystal ensembles as they interact with their substrate, neighbouring nanocubes and the resulting mutual interactions. Demonstrated is the ability to finely tune plasmonic properties of silver nanocube monolayers by controlling the interparticle spacing and the properties of the underlying substrate. Control over these properties is applied to the optimisation of substrates used for surface-enhanced Raman spectroscopy (SERS). Control over the plasmonic properties is achieved by directing the assembly of silver nanocube (AgNC) ensembles. The primary means to do so is by using the Langmuir-Blodgett technique to control nanoparticle surface density. These monolayers are placed on a number of substrates such as glass, silicon thin films, and titanium oxide thin films. Demonstrated in this work is the ability to shift plasmonic modes using interparticle interactions or particle-substrate interactions. The local electric field enhancement in these monolayers is investigated thoroughly by SERS, and demonstrated is the dependence of the enhancement on particle cluster size, charge transfer processes, and the location of the target molecule in the monolayer. By gaining insight into how these interactions affect the local electric field at the surface of the nanoparticles, lessons gained through this work could be applied towards the optimization of surface enhanced Raman spectroscopy.