ECE Seminar: Plasmonics At The Nanometer Scale With Electron Energy-loss Spectroscopy
Wednesday, May 10, 2017 - 12:00pm to 1:00pm
Nicolas Stenger, Department of Photonics Engineering, Technical University of Denmark
Light incident on silver particles with spherical shape and diameters below 100 nanometers excites primarily the dipolar plasmonic mode. The modes with larger angular momentum such as the quadrupole mode, are strongly damped as their higher resonance energy tends to be positioned in the range of interband transitions in silver. By encapsulating silver nanospheres in a dielectric medium, we redshift the plasmon modes and thereby get access to the higher-order resonances. We map the dipolar and higher-order modes of individual silver nanoparticles with electron energy-loss spectroscopy (EELS). For particle radii smaller than 4 nanometers, we observe a strong blueshift of the dipolar mode of 0.9 eV and a strong damping of the higher-order modes in qualitative agreement with nonlocal optical response theory. I will also present recent work on the exploration of thin gold films close to percolation threshold with EELS. We map and identify the different plasmonic resonances with a nanometer-scale spatial resolution and in particular the presence of strongly localized plasmonic hot spots. We observe a strong localization of the plasmonic modes for resonance energies in the visible range and delocalized modes in the NIR range. I will conclude my talk by showing that gold films close to percolation and subsequently illuminated by high-power lasers can offer a new inexpensive, easy-to-fabricate and highly scalable platform for optical sensing to ultra-dense optical data-storage.