Electron energy loss spectroscopy (EELS) is often utilized to characterize localized surface plasmon modes supported by plasmonic antennas. However, the spectral resolution of this technique is only mediocre, and it can be rather difficult to resolve modes close in the energy, such as coupled modes of dimer antennas. Here, we address this issue for a case study of the dimer plasmonic antenna composed of two gold discs. We analyze four nearly degenerate coupled plasmon modes of the dimer: longitudinal and transverse bonding and antibonding dipole modes. With a traditional approach, which takes into account the spectral response of the antennas recorded at specific points, the modes cannot be experimentally identified with EELS. Therefore, we employ the spectral and spatial sensitivity of EELS simultaneously. We propose several metrics that can be utilized to resolve the modes. First, we utilize electrodynamic simulations to verify that the metrics indeed represent the spectral positions of the plasmon modes. Next, we apply the metrics to experimental data, demonstrating their ability to resolve three of the above-mentioned modes (with transverse bonding and antibonding modes still unresolved), identify them unequivocally, and determine their energies. In this respect, the spatio-spectral metrics increase the information extracted from electron energy loss spectroscopy applied to plasmonic antennas.

Central European Institute of Technology Brno University of Technology Purkyňova 123 612 00 Brno Czech Republic

Institute of Physical Engineering Brno University of Technology Technická 2 616 69 Brno Czech Republic

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Cherqui C., Thakkar N., Li G., Camden J. P., Masiello D. J. Characterizing localized surface plasmons using electron energy-loss spectroscopy. Annu. Rev. Phys. Chem. . 2016;67:331. doi: 10.1146/annurev-physchem-040214-121612. PubMed DOI

Krivanek O., Dellby N., Hachtel J., et al. Progress in ultrahigh energy resolution EELS. Ultramicroscopy . 2019;203:60. doi: 10.1016/j.ultramic.2018.12.006. PubMed DOI

García de Abajo F. J. Optical excitations in electron microscopy. Rev. Mod. Phys. . 2010;82:209. doi: 10.1103/revmodphys.82.209. DOI

García de Abajo F. J., Kociak M. Probing the photonic local density of states with electron energy loss spectroscopy. Phys. Rev. Lett. . 2008;100:106804. doi: 10.1103/physrevlett.100.106804. PubMed DOI

Hohenester U., Ditlbacher H., Krenn J. R. Electron-energy-loss spectra of plasmonic nanoparticles. Phys. Rev. Lett. . 2009;103:106801. doi: 10.1103/physrevlett.103.106801. PubMed DOI

Kociak M., Stéphan O. Mapping plasmons at the nanometer scale in an electron microscope. Chem. Soc. Rev. . 2014;43:3865. doi: 10.1039/c3cs60478k. PubMed DOI

Hörl A., Haberfehlner G., Trügler A., Schmidt F.-P., Hohenester U., Kothleitner G. Tomographic imaging of the photonic environment of plasmonic nanoparticles. Nat. Commun. . 2017;8:37. doi: 10.1038/s41467-017-00051-3. PubMed DOI PMC

Haberfehlner G., Schmidt F.-P., Schaffernak G., et al. 3D imaging of gap plasmons in vertically coupled nanoparticles by EELS tomography. Nano Lett. 2017;17:6773. doi: 10.1021/acs.nanolett.7b02979. PubMed DOI PMC

Archanjo B. S., Vasconcelos T. L., Oliveira B. S., et al. Plasmon 3D electron tomography and local electric-field enhancement of engineered plasmonic nanoantennas. ACS Photonics . 2018;5:2834. doi: 10.1021/acsphotonics.8b00125. DOI

Horák M., Křápek V., Hrtoň M., et al. Limits of Babinet’s principle for solid and hollow plasmonic antennas. Sci. Rep. . 2019;9:4004. doi: 10.1038/s41598-019-40500-1. PubMed DOI PMC

Křápek V., Konečná A., Horák M., et al. Independent engineering of individual plasmon modes in plasmonic dimers with conductive and capacitive coupling. Nanophotonics . 2020;9:623. doi: 10.1515/nanoph-2019-0326. DOI

Schmidt F. P., Ditlbacher H., Hofer F., Krenn J. R., Hohenester U. Morphing a plasmonic nanodisk into a nanotriangle. Nano Lett. 2014;14:4810. doi: 10.1021/nl502027r. PubMed DOI PMC

Křápek V., Koh A. L., Břínek L., et al. Spatially resolved electron energy loss spectroscopy of crescent-shaped plasmonic antennas. Opt. Express . 2015;23:11855. doi: 10.1364/oe.23.011855. PubMed DOI

Prodan E., Radloff C., Halas N. J., Nordlander P. A hybridization model for the plasmon response of complex nanostructures. Science . 2003;302:419. doi: 10.1126/science.1089171. PubMed DOI

Koh A. L., Fernández-Domínguez A. I., McComb D. W., Maier S. A., Yang J. K. W. High-resolution mapping of electron-beam-excited plasmon modes in lithographically defined gold nanostructures. Nano Lett. 2011;11:1323. doi: 10.1021/nl104410t. PubMed DOI

Wen F., Zhang Y., Gottheim S., et al. Charge transfer plasmons: optical frequency conductances and tunable infrared resonances. ACS Nano . 2015;9:6428. doi: 10.1021/acsnano.5b02087. PubMed DOI

Zohar N., Chuntonov L., Haran G. The simplest plasmonic molecules: metal nanoparticle dimers and trimers. J. Photochem. Photobiol., C . 2014;21:26. doi: 10.1016/j.jphotochemrev.2014.10.002. DOI

Tian L., Wang C., Zhao H., et al. Rational approach to plasmonic dimers with controlled gap distance, symmetry, and capability of precisely hosting guest molecules in hotspot regions. J. Am. Chem. Soc. . 2021;143:8631. doi: 10.1021/jacs.0c13377. PubMed DOI

Song J.-H., Raza S., van de Groep J., et al. Nanoelectromechanical modulation of a strongly-coupled plasmonic dimer. Nat. Commun. . 2021;12:48. doi: 10.1038/s41467-020-20273-2. PubMed DOI PMC

Kinkhabwala A., Yu Z., Fan S., Avlasevich Y., Müllen K., Moerner W. E. Large single-molecule fluorescence enhancements produced by a bowtie nanoantenna. Nat. Photonics . 2009;3:654. doi: 10.1038/nphoton.2009.187. DOI

Bitton O., Gupta S. N., Houben L., et al. Vacuum Rabi splitting of a dark plasmonic cavity mode revealed by fast electrons. Nat. Commun. . 2020;11:487. doi: 10.1038/s41467-020-14364-3. PubMed DOI PMC

Barrow S. J., Collins S. M., Rossouw D., et al. Electron energy loss spectroscopy investigation into symmetry in gold trimer and tetramer plasmonic nanoparticle structures. ACS Nano . 2016;10:8552. doi: 10.1021/acsnano.6b03796. PubMed DOI

Ringe E., DeSantis C. J., Collins S. M., et al. Resonances of nanoparticles with poor plasmonic metal tips. Sci. Rep. . 2015;5:17431. doi: 10.1038/srep17431. PubMed DOI PMC

Hajebifard A., Berini P. Fano resonances in plasmonic heptamer nano-hole arrays. Opt. Express . 2017;25:18566. doi: 10.1364/oe.25.018566. PubMed DOI

Bellido E. P., Zhang Y., Manjavacas A., Nordlander P., Botton G. A. Plasmonic coupling of multipolar edge modes and the formation of gap modes. ACS Photonics . 2017;4:1558. doi: 10.1021/acsphotonics.7b00348. DOI

Das P., Lourenço-Martins H., Tizei L. H. G., Weil R., Kociak M. Nanocross: a highly tunable plasmonic system. J. Phys. Chem. C . 2017;121:16521. doi: 10.1021/acs.jpcc.7b05548. DOI

Smith K. C., Olafsson A., Hu X., et al. Direct observation of infrared plasmonic fano antiresonances by a nanoscale electron probe. Phys. Rev. Lett. . 2019;123:177401. doi: 10.1103/physrevlett.123.177401. PubMed DOI

Kejík L., Horák M., Šikola T., Křápek V. Structural and optical properties of monocrystalline and polycrystalline gold plasmonic nanorods. Opt. Express . 2020;28:34960. doi: 10.1364/oe.409428. PubMed DOI

Alexander D. T. L., Flauraud V., Demming-Janssen F. Near-field mapping of photonic eigenmodes in patterned silicon nanocavities by electron energy-loss spectroscopy. ACS Nano . 2021;15:16501. doi: 10.1021/acsnano.1c06065. PubMed DOI

Lagos M. J., Trügler A., Hohenester U., Batson P. E. Mapping vibrational surface and bulk modes in a single nanocube. Nature . 2017;543:529. doi: 10.1038/nature21699. PubMed DOI

Li X., Haberfehlner G., Hohenester U., Stéphan O., Kothleitner G., Kociak M. Three-dimensional vectorial imaging of surface phonon polaritons. Science . 2021;371:1364. doi: 10.1126/science.abg0330. PubMed DOI

Yamamoto N. Development of high-resolution cathodoluminescence system for STEM and application to plasmonic nanostructures. Microscopy . 2016;65:282. doi: 10.1093/jmicro/dfw025. PubMed DOI

Schmidt F.-P., Losquin A., Horák M., Hohenester U., Stöger-Pollach M., Krenn J. R. Fundamental limit of plasmonic cathodoluminescence. Nano Lett. . 2021;21:590. doi: 10.1021/acs.nanolett.0c04084. PubMed DOI PMC

García de Abajo F. J., Konečná A. Optical modulation of electron beams in free space. Phys. Rev. Lett. . 2021;126:123901. doi: 10.1103/physrevlett.126.123901. PubMed DOI

Horák M., Bukvišová K., Švarc V., Jaskowiec J., Křápek V., Šikola T. Comparative study of plasmonic antennas fabricated by electron beam and focused ion beam lithography. Sci. Rep. . 2018;8:9640. doi: 10.1038/s41598-018-28037-1. PubMed DOI PMC

Horák M., Šikola T. Influence of experimental conditions on localized surface plasmon resonances measurement by electron energy loss spectroscopy. Ultramicroscopy . 2020;216:113044. doi: 10.1016/j.ultramic.2020.113044. PubMed DOI

Hohenester U., Trügler A. MNPBEM – a Matlab toolbox for the simulation of plasmonic nanoparticles. Comput. Phys. Commun. 2012;183:370. doi: 10.1016/j.cpc.2011.09.009. DOI

Waxenegger J., Trügler A., Hohenester U. Plasmonics simulations with the MNPBEM toolbox: consideration of substrates and layer structures. Comput. Phys. Commun. 2015;193:138. doi: 10.1016/j.cpc.2015.03.023. DOI

Johnson P. B., Christy R. W. Optical constants of the noble metals. Phys. Rev. B . 1972;6:4370. doi: 10.1103/physrevb.6.4370. DOI