How Dark Are Radial Breathing Modes in Plasmonic Nanodisks?

Franz-Philipp Schmidt (1, 2) , Arthur Losquin (3, 4) , Ferdinand Hofer (2) , Andreas Hohenau (1) , Joachim R Krenn (5) , Mathieu K Kociak (5)

1 Institute of Physics [Graz]
2 IEMN - Institute for Electron Microscopy and Nanoanalysis [Graz]
3 LOMA - Laboratoire Ondes et Matière d'Aquitaine
4 Skane University Hospital [Lund]
5 LPS - Laboratoire de Physique des Solides

Due to a vanishing dipole moment, radial breathing modes in small flat plasmonic nanoparticles do not couple to light and have to be probed with a near field source, as in electron energy loss spectroscopy (EELS). With increasing particle size, retardation gives rise to light coupling, enabling probing breathing modes optically or by cathodoluminescence (CL). Here, we investigate single silver nanodisks with diameters of 150−500 nm by EELS and CL in an electron microscope and quantify the EELS/CL ratio, which corre sponds to the ratio of full to radiative damping of the breathing mode. For the investigated diameter range, we find the CL signal to increase by about 1 order of magnitude, in agreement with numerical simulations. Due to reciprocity, our findings corroborate former optical experiments and enable a quantitative understanding of the light coupling of dark plasmonic modes.

Mots clés: plasmonics; electron energy loss spectroscopy; cathodoluminescence; transmission electron microscopy; nanoparticles

Domaines: Optique [physics.optics]

Franz-Philipp Schmidt, Arthur Losquin, Ferdinand Hofer, Andreas Hohenau, Joachim R Krenn, et al.. How Dark Are Radial Breathing Modes in Plasmonic Nanodisks?. ACS photonics, 2018, 5 (3), pp.861-866. ⟨10.1021/acsphotonics.7b01060⟩. ⟨hal-01804349⟩