Plasmonic tapers have been studied intensively due to the ability of adiabatically coupling the propagating surface plasmon polaritons along their shaft to the nanolocalized plasmons at their apex. Therefore, they can find applications in the fields of sub-diffraction-limit nanofocusing, ultrafast photoemission, and near-field optical microscopy.
We investigate the plasmonic modes of three-dimensional single crystalline gold tapers by means of EELS (electron energy loss spectroscopy) and FDTD (finite-difference time-domain) numerical calculation. We observe a broadband excitation in the proximity of the apex and discrete higher-order azimuthal plasmonic modes along the taper shaft in the gold taper with an opening angle of ~45°. Interestingly, the energy dispersions of these higher-order plasmonic modes are roughly proportional to the inverse local radius. The importance of phase-matching between electron field and radiative taper modes in mesoscopic structure is demonstrated . The role of an alternative mechanism suggested by Schröder et al.  was analyzed by systematically studying changes in the dispersion of higher-order plasmonic modes of gold tapers for different opening angles.
 N. Talebi, W. Sigle, R. Vogelgesang, M. Esmann, S. F. Becker, C. Lienau, P. A. van Aken. ACS Nano, 2015, 9 (7), 7641–7648.
 B. Schröder, T. Weber, S. V. Yalunin, T. Kiel, C. Matyssek, M. Sivis, S. Schäfer, F. v. Cube, S. Irsen, K. Busch, C. Ropers, S. Linden, Phys. Rev. B 2015, 92, 085411.
To cite this abstract:Surong Guo, Nahid Talebi, Wilfried Sigle, Ralf Vogelgesang, Martin Esmann, Simon F. Becker, Christoph Lienau, Peter van Aken; Investigation of Plasmonic Modes of Gold Tapers by EELS. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/investigation-of-plasmonic-modes-of-gold-tapers-by-eels/. Accessed: February 23, 2019
EMC Abstracts - https://emc-proceedings.com/abstract/investigation-of-plasmonic-modes-of-gold-tapers-by-eels/