title: Reflection and Phase Matching in Plasmonic Gold Tapers.
abstract: We investigate different dynamic mechanisms, reflection and phase matching, of surface plasmons in a three-dimensional single-crystalline gold taper excited by relativistic electrons. Plasmonic modes of gold tapers with various opening angles from 5° to 47° are studied both experimentally and theoretically, by means of electron energy-loss spectroscopy and finite-difference time-domain numerical calculations, respectively. Distinct resonances along the taper shaft are observed in tapers independent of opening angles. We show that, despite their similarity, the origin of these resonances is different at different opening angles and results from a competition between two coexisting mechanisms. For gold tapers with large opening angles (above ∼20°), phase matching between the electron field and that of higher-order angular momentum modes of the taper is the dominant contribution to the electron energy-loss because of the increasing interaction length between electron and the taper near-field. In contrast, reflection from the taper apex dominates the EELS contrast in gold tapers with small opening angles (below ∼10°). For intermediate opening angles, a gradual transition of these two mechanisms was observed.
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstraße 1, 70569 Stuttgart, Germany.
authors.forename: Surong
authors.initials: S
authors.lastname: Guo
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstraße 1, 70569 Stuttgart, Germany.
authors.forename: Nahid
authors.initials: N
authors.lastname: Talebi
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstraße 1, 70569 Stuttgart, Germany.
authors.forename: Wilfried
authors.initials: W
authors.lastname: Sigle
authors.affiliation: Institute of Physics and Center of Interface Science, Carl von Ossietzky University of Oldenburg , 26129 Oldenburg, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Vogelgesang
authors.affiliation: Max Planck Institute for Intelligent Systems , Heisenbergstr. 3, 70569 Stuttgart, Germany.
authors.forename: Gunther
authors.initials: G
authors.lastname: Richter
authors.affiliation: Institute of Physics and Center of Interface Science, Carl von Ossietzky University of Oldenburg , 26129 Oldenburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Esmann
authors.affiliation: Institute of Physics and Center of Interface Science, Carl von Ossietzky University of Oldenburg , 26129 Oldenburg, Germany.
authors.forename: Simon F
authors.initials: SF
authors.lastname: Becker
authors.affiliation: Institute of Physics and Center of Interface Science, Carl von Ossietzky University of Oldenburg , 26129 Oldenburg, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Lienau
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstraße 1, 70569 Stuttgart, Germany.
authors.forename: Peter A
authors.initials: PA
authors.lastname: van Aken
keywords: Phase matching; electron energy-loss spectroscopy; gold taper; numerical simulations; plasmons; reflection