Optical and Plasmonic Properties of Metallic Tip/Surface Junctions

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 near-field focusing and enhancement at optical resonances through the gap between the metallic nanoparticle/tip and the metallic surface. In this work, we examine two-dimensional and three-dimensional variations of reduced symmetry systems and we present a hilly 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.