Plasmon hybridization in individual gold nanocrystal dimers: direct observation of bright and dark modes.
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.
Yang
Shu-Chun
SC
Department of Physics, National Tsing-Hua University, Hsinchu30013, Taiwan.
Kobori
Hiromu
H
He
Chieh-Lun
CL
Lin
Meng-Hsien
MH
Chen
Hung-Ying
HY
Li
Cuncheng
C
Kanehara
Masayuki
M
Teranishi
Toshiharu
T
Gwo
Shangjr
S
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
D006046:Gold