Plasmon-Enabled Physical and Chemical Transformations of Nanomaterials
Abstract
When the electromagnetic field of light is incident on metallic nanostructures of dimensions smaller than the incident wavelength of the light, there is a strong interaction, resulting in an enhanced, highly confined electromagnetic field in the vicinity of the nanostructure. This effect is referred to as a localized surface plasmon resonance, most commonly exploited for plasmon-enhanced spectroscopies, such as surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS). The location, number and intensity of these regions of enhancement, or “hotspots”, can be tuned by changing the nature of the metal, the size, shape and arrangement of the nanoparticles, its surroundings, or the wavelength of the incident light. When a molecule is located within these nanoscale hotspots, it is possible to obtain detailed spectroscopic information about the molecule with high sensitivity.
The decay process of these plasmon resonances can result in the ejection of high energy “hot” carriers, either hot electrons or hot holes, and the subsequent heating of the nanoparticle lattice. When a molecule is adsorbed to the surface of the nanoparticle, the presence of hot electrons and holes or the elevation of temperature can favour a chemical reaction. This effect is most prevalent in metallic nanostructures that exhibit hotspots at their surface, that can in turn be used to photocontrol surface reactions through plasmon excitation.
In this thesis, plasmon-mediated reactions are investigated using a variety of spectroscopic and microscopic techniques, along with the modelling of the light-matter interaction. The reduction of aryl diazonium salts on a gold nanostructured surface is plasmon-catalyzed. For a tip-enhanced Raman spectroscopy system involving a gold tip and a silver nanoplate as a substrate, plasmonic heating is discussed and modelled using finite element methods. New fractal metallic nanostructures are developed and studied for future applications in plasmon-mediated chemistry.