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Interaction of Localized Surface Plasmons of a Silver Nanosphere Dimer Embedded in a Uniform Medium: Scanning Transmission Electron Microscopy Electron Energy-Loss Spectroscopy and Discrete Dipole Approximation Simulation

Sakaguchi, Norihito, Matsumoto, Shuji, Kunisada, Yuji, Ueda, Mikito
Journal of physical chemistry 2019 v.123 no.11 pp. 6735-6744
electric field, energy, glass, nanosilver, nanospheres, physical chemistry, silicates, silver, spectroscopy, surface plasmon resonance, transmission electron microscopy
Localized surface plasmon resonance (LSPR) in a silver (Ag) nanosphere dimer embedded in silicate glass was investigated using scanning transmission electron microscopy electron energy-loss spectroscopy (STEM–EELS). Passing the electron probe near the Ag nanospheres excited the LSPR in the multipole as well as the dipole. STEM–EELS analysis of the Ag dimer indicated that some LSPR coupling modes appeared because of energy loss from the coupling of two dipoles or multipoles. When the electron beam was incident on the outside of the Ag dimer, a longitudinal bonding mode of two dipoles appeared and its resonance energy was lower than that of the dipole of a single Ag nanosphere. Conversely, when the electron beam was incident between the Ag nanospheres of the dimer, two more modes appeared at higher energies than the resonance energy of a single Ag nanosphere. Analysis of the electric field distribution around the Ag dimer suggested that these modes had the nature of the classical longitudinal antibonding LSPR mode of two dipoles. Furthermore, the discrete dipole approximation simulation suggested the possibility that the mode on the highest energy may include a negligible contribution of an antibonding-type quadrupolar interaction.