Optical and Plasmonic Properties of Metallic Tip /Surface Junctions
Ali, Tamer Ashour
Nordlander, Peter J.
Doctor of Philosophy
Reducing symmetry of plasmonic nanostructures allows more in-depth engineering for plasmonic systems to support a range of optical phenomena prohibited by traditional symmetric systems. Symmetry reduction allows for nanoscale control of the near-field and far-field electric and magnetic resonances at optical frequencies. Introducing a nanopraticle or a tip to an infinite metallic surface breaks the continuity of the surface allowing coupling with light. This leads to remarkable nearfield focusing and enhancement at optical resonances through the gap between the metallic nanoparticle/tip and the metallic surface. In this work, we examine twodimensional and three-dimensional variations of reduced symmetry systems and we present a fully retarded electromagnetic study for the plasmon interaction through the tip/surface junction. A simple methodology is introduced for efficient, fast, and accurate simulation for such systems using the both Finite-Difference Time-Domain and Finite-Element methods. The proposed methods are used to predict the response of practical systems and the results are compared with previously reported experimental and electrostatic-theoretical results and a remarkable agreement is reported. A full study for the tip over film system is established to provide optimized geometries for Tip Enhanced Raman Spectroscopy (TERS) applications.