title: Exploring Coupled Plasmonic Nanostructures in the Near Field by Photoemission Electron Microscopy.
abstract: The extraordinary optical properties of coupled plasmonic nanostructures make these materials potentially useful in many applications; thus, they have received enormous attention in basic and applied research. Coupled plasmon modes have been characterized predominantly using far-field spectroscopy. In near-field spectroscopy, the spectral response of local field enhancement in coupled plasmonic nanostructures remains largely unexplored, especially experimentally. Here, we investigate the coupled gold dolmen nanostructures in the near field using photoemission electron microscopy, with wavelength-tunable femtosecond laser pulses as an excitation source. The spatial evolution of near-field mapping of an individual dolmen structure with the excitation wavelength was successfully obtained. In the near field, we spatially resolved an anti-bonding mode and a bonding mode as the result of plasmon hybridization. Additionally, the quadrupole plasmon mode that could be involved in the formation of a Fano resonance was also revealed by spatially resolved near-field spectra, but it only contributed little to the total near-field enhancement. On the basis of these findings, we obtained a better understanding of the near-field properties of coupled plasmonic nanostructures, where the plasmon hybridization and the plasmonic Fano resonance were mixed.
authors: Research Institute for Electronic Science, Hokkaido University , Sapporo 001-0021, Japan.
authors: Han
authors: H
authors: Yu
authors: Research Institute for Electronic Science, Hokkaido University , Sapporo 001-0021, Japan.
authors: Quan
authors: Q
authors: Sun
authors: Research Institute for Electronic Science, Hokkaido University , Sapporo 001-0021, Japan.
authors: Kosei
authors: K
authors: Ueno
authors: Research Institute for Electronic Science, Hokkaido University , Sapporo 001-0021, Japan.
authors: Tomoya
authors: T
authors: Oshikiri
authors: Institute of Physics, University of Tsukuba , Tsukuba 305-8571, Japan.
authors: Atsushi
authors: A
authors: Kubo
authors: Research Institute for Electronic Science, Hokkaido University , Sapporo 001-0021, Japan.
authors: Yasutaka
authors: Y
authors: Matsuo
authors: Research Institute for Electronic Science, Hokkaido University , Sapporo 001-0021, Japan.|Department of Applied Chemistry & Institute of Molecular Science, National Chiao Tung University , Hsinchu 30010, Taiwan.
authors: Hiroaki
authors: H
authors: Misawa
keywords: Fano resonance; femtosecond laser pulses; near-field mapping; photoemission electron microscopy (PEEM); plasmon hybridization