Plasmonic gap modes provide the ultimate confinement of optical fields. Here, we show that by 3D EELS tomography the gap mode LDOS of a vertically stacked nanotriangle dimer can be fully imaged. Besides probing the complete mode spectrum, we demonstrate that the tomographic approach allows disentangling the signal contributions from the two nanotriangles that superimpose in a single measurement with a fixed electron trajectory.

“3D Imaging of Gap Plasmons in Vertically Coupled Nanoparticles by EELS Tomography” G. Haberfehlner, F.-P. Schmidt, G. Schaffernak, A. Hörl, A. Trügler, A. Hohenau, F. Hofer, J. R. Krenn, U. Hohenester, G. Kothleitner Nano Letters 17 (2017) 6773-6777
DOI: 10.1021/acs.nanolett.7b02979

The photonic local density of states (LDOS) governs the enhancement of light-matter interaction at the nanoscale, but despite its importance for nanophotonics and plasmonics experimental LDOS imaging remains extremely challenging. Here we introduce a tomography scheme based on electron microscopy that allows retrieval of the three-dimensional LDOS of plasmonic nanoparticles with nanometer spatial and sub-eV energy resolution.

“Tomographic imaging of the photonic environment of plasmonic nanoparticles” A. Hörl, G. Haberfehlner, A. Trügler, F.-P. Schmidt, U. Hohenester, G. Kothleitner
DOI: 10.1038/s41467-017-00051-3