Next-Generation Nanospectroscopy: Analytical and Numerical Models of New Developments in Electron Beam and Scanning Probe Experiments

Abstract

The research field of nanophotonics, which aims to understand the propagation of light at the nanoscale and design novel optically-active materials, has risen to prominence since the discovery of the surface plasmon in 1957. Early efforts to describe the intertwined motion of electrons, atomic nuclei, and electromagnetic waves inside small crystals have been built upon in recent decades, producing an increasingly precise picture of the spatial and spectral characteristics of polaritonic surface waves. The resulting range of proposed applications for materials and machines with nanoscopic components is enormously broad, stemming from ultrathin lenses to nanoscopic chemical reactors to biosensors. Recent work toward the design and realization of new optical nanotechnologies has relied on the invention of near-field spectroscopic probes, or probes that bring free or bound charges near a sample to characterize its response to electrical stimulus. In contrast to optical microscopes, which rely on freely-propagating light to interact with a sample, near-fieldprobes have much smaller fundamental resolution limits and are more capable of investigating the nanoscopic features and local fields of individual nanostructures. In this dissertation, theoretical models are developed to improve the understanding of the coupling of two important surface phenomena, namely surface plasmons and surface phonons, with their environments in the context of electron beam and scanning-probe spectroscopies. These models are built with an eye toward the augmentation of existing experimental techniques and the invention of new ones. In particular, the influence of substrates on the plasmonic properties of mounted nanoparticles, the quantum-mechanical processes governing laser-stimulated electron-plasmon interactions, the extraction of intrinsic material properties from electron energy-loss spectroscopy, and the influence of the motion of hybridized plasmon-phonon polaritons on the radiation from nearby atomic force microscopy tips are discussed in detail. Finally, the models herein are combined with numerical simulations and compared with experimental data provided by collaborators to provide an intuitive and quantitative theoretical framework with which to interpret the observed signals.