title: Plasmon hybridization in individual gold nanocrystal dimers: direct observation of bright and dark modes.
abstract: We apply a nanomanipulation technique to assemble pairs of monodispersed octahedral gold nanocrystals (side length, 150 nm) along their major axes with a varying tip-to-tip separation (25-125 nm). These pairs are immobilized onto indium tin oxide coated silica substrates and studied as plasmonic dimers by polarization-selective total internal reflection (TIR) microscopy and spectroscopy. We confirm that the plasmon coupling modes with the scattering polarization along the incident light direction result from the transverse-magnetic-polarized incident light, which induces two near-field-coupled dipole moments oriented normal to the air-substrate interface. In such cases, both in-phase (antibonding) and antiphase (bonding) plasmon coupling modes can be directly observed with the incident light wave vector perpendicular and parallel to the dimer axis, respectively. The observation of antiphase plasmon coupling modes ("dark" plasmons) is made possible by the unique polarization nature of the TIR-generated evanescent field. Furthermore, with decreasing nanocrystal separation, the plasmon coupling modes shift to shorter wavelengths for the incident light perpendicular to the dimer axis, whereas relatively large red shifts of the plasmonic coupling modes are found for the parallel incident light.
authors.affiliation: Department of Physics, National Tsing-Hua University, Hsinchu30013, Taiwan.
authors.forename: Shu-Chun
authors.initials: SC
authors.lastname: Yang
authors.forename: Hiromu
authors.initials: H
authors.lastname: Kobori
authors.forename: Chieh-Lun
authors.initials: CL
authors.lastname: He
authors.forename: Meng-Hsien
authors.initials: MH
authors.lastname: Lin
authors.forename: Hung-Ying
authors.initials: HY
authors.lastname: Chen
authors.forename: Cuncheng
authors.initials: C
authors.lastname: Li
authors.forename: Masayuki
authors.initials: M
authors.lastname: Kanehara
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Teranishi
authors.forename: Shangjr
authors.initials: S
authors.lastname: Gwo
mesh_terms: D019281:Dimerization; D006046:Gold / Q000737:chemistry*; D008027:Light; D008280:Magnetics; D053768:Metal Nanoparticles / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning / Q000379:methods; D053758:Nanoparticles / Q000737:chemistry; D049329:Nanostructures / Q000737:chemistry; D036103:Nanotechnology / Q000379:methods*; D055095:Optics and Photonics; D013053:Spectrophotometry / Q000379:methods; D020349:Surface Plasmon Resonance
chemical_list: D006046:Gold