AbstractsPhysics

The vast array of potential applications for plasmons has laid bare the need for a detailed understanding of the complex interactions that occur between multiple plasmons and between plasmons and near-field probes. In this dissertation, the capacity of electron energy-loss spectroscopy (EELS) to probe plasmons is examined in detail. EELS is shown to be able to detect both electric hot spots and Fano resonances in contrast to the prevailing knowledge prior to this work. The most detailed examination of magnetoplasmonic resonances in multi-ring structures to date and the utility of electron tomography to computational plasmonics is explored, and a new tomographic method for the reconstruction of a target is introduced.\\ Since the observation of single-molecule surface-enhanced Raman scattering (SMSERS) in 1997, questions regarding the nature of the electromagnetic hot spots responsible for such observations still persist. A computational analysis of the electron- and photon-driven surface-plasmon resonances of monomer and dimer metal nanorods is presented to elucidate the differences and similarities between the two excitation mechanisms in a system with well understood optical properties. By correlating the nanostructure's simulated electron energy loss spectrum and loss-probability maps with its induced polarization and scattered electric field we discern how certain plasmon modes are selectively excited and how they funnel energy from the excitation source into the near- and far-field. Using a fully retarded electron-scattering theory capable of describing arbitrary three-dimensional nanoparticle geometries, aggregation schemes, and material compositions, we find that electron energy-loss spectroscopy (EELS) is able to \emph{indirectly} probe the same electromagnetic hot spots that are generated by an optical excitation source. EELS is then employed in a scanning transmission electron microscope (STEM) to obtain maps of the localized surface plasmon modes of SMSERS-active nanostructures, which are resolved in both space and energy. Single-molecule character is confirmed by the bianalyte approach using two isotopologues of Rhodamine 6G. The origins of this observation are explored using a fully three-dimensional electrodynamics simulation of both the electron energy loss probability and the near-electric field enhancements. The calculations suggest that electron beam excitation of the hot spot is possible, but only when the electron beam is located outside of the junction region, and further that the location of the hot spot can be inferred from the node in the loss probability in the junction along with the high loss probability on the edges away from the junction.\\ The optical-frequency magnetic and electric properties of cyclic aromatic plasmon-supporting metal nanoparticle oligomers are explored through a combination of STEM/EELS simulation and first-principles theory. A tight-binding type model is introduced to explore the rich hybridization physics in these plasmonic systems and tested with full-wave…