Evidence of strong coupling between plasmons and molecular excitons for plasmonic nanoparticle (NP) dimers exhibiting ultra-sensitive surface enhanced resonant Raman scattering is the observation of anti-crossing in the coupled resonance. However, experimentally tuning the plasmon resonance of such dimers for the observation is difficult. In this work, we calculate the anti-crossing property of dimers coated with thin dye films according to the classical electromagnetism. This property is quantitatively evaluated according to the coupled oscillator model composed of a plasmon and a molecular exciton representing the molecular multi-level system. A comparison of the film thickness dependences of dimer spectral changes with those of silver ellipsoidal NPs indicates that the dipole plasmons localized in the dimer gap are coupled with molecular excitons of the film much stronger than the dipole plasmons of ellipsoidal NPs. Furthermore, the anti-crossing behavior of coupled resonances is investigated while tuning plasmon resonance by changing the morphology and refractive index of the surrounding medium. The spectral changes observed for ellipsoidal NPs clearly exhibit anti-crossing property; however, the anti-crossing behavior of dimers is more complex due to the strong coupling of dipoles and higher-order plasmons with multiple molecular excitons. We find that the anti-crossing for dimers is clearly confirmed by the refractive index dependence of coupled resonance.
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7 February 2020
Research Article|
February 04 2020
Anti-crossing property of strong coupling system of silver nanoparticle dimers coated with thin dye molecular films analyzed by electromagnetism
Special Collection:
Emerging Directions in Plasmonics
Tamitake Itoh
;
Tamitake Itoh
a)
1
Nano-Bioanalysis Research Group, Health Research Institute, National Institute of Advanced Industrial Science and Technology (AIST)
, Takamatsu, Kagawa 761-0395, Japan
a)Author to whom correspondence should be addressed: tamitake-itou@aist.go.jp
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Yuko S. Yamamoto
;
Yuko S. Yamamoto
2
School of Materials Science, Japan Advanced Institute of Science and Technology (JAIST)
, Nomi, Ishikawa 923-1292, Japan
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Takayuki Okamoto
Takayuki Okamoto
3
Advanced Device Laboratory, RIKEN
, Hirosawa, Wako, Saitama 351-0198, Japan
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a)Author to whom correspondence should be addressed: tamitake-itou@aist.go.jp
Note: This paper is part of the JCP Special Topic on Emerging Directions in Plasmonics.
J. Chem. Phys. 152, 054710 (2020)
Article history
Received:
October 29 2019
Accepted:
January 19 2020
Citation
Tamitake Itoh, Yuko S. Yamamoto, Takayuki Okamoto; Anti-crossing property of strong coupling system of silver nanoparticle dimers coated with thin dye molecular films analyzed by electromagnetism. J. Chem. Phys. 7 February 2020; 152 (5): 054710. https://doi.org/10.1063/1.5133875
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