Near- and Far-Field Plasmonic Properties of Different Types of Eccentric Core-Shell Nanodimers
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Near- and Far-Field Plasmonic Properties of Different Types of Eccentric Core-Shell Nanodimers Gour Mohan Das 1 & Venkata Ramanaiah Dantham 1 Received: 10 September 2019 / Accepted: 4 December 2019 # Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract Finite element method (FEM) simulations have been carried out on free-standing and finite dielectric substrate-supported eccentric (i) silica core-gold nanoshell dimers and (ii) gold core-silica nanoshell dimers for understanding their near- and farfield plasmonic properties. In the case of eccentric silica core-gold nanoshell dimers, multiple peaks are observed in the near- and far-field spectra due to the plasmon hybridization. The number of peaks is found to be sensitive to the core offset parameters of the nanoshells forming nanodimer. The wavelength locations of the peaks due to the constructive coupling of the lower order modes found relatively more sensitive to the dielectric substrate. The number of peaks in the near- and far-field spectra found the same presence and absence of the dielectric substrate. The values of full width at half maximum (FWHM) of the peaks observed in the near-field spectra are found larger as compared to those observed in the far-field spectra. In contrast, in the case of eccentric gold core-silica nanoshell dimers, multiple peaks have not been observed. The FWHM of the observed peak is found sensitive to the core offset parameters of the nanoshells, and the number of peaks in the near field- and far-field spectra found not same in the presence and absence of the dielectric substrate. Moreover, the differences in near- and far-field spectra of plasmonically coupled (i) concentric nanoshells, (ii) eccentric nanoshells, and (iii) concentric and eccentric nanoshells also investigated numerically. Keywords Near-field . Far-fieldscattering . Eccentric core-shellnanodimer . Localizedsurface plasmonresonance . Finite element method . Multipolar plasmon modes . Finite dielectric substrate
Introduction In the field of nanoplasmonics, concentric dielectric coremetal nanoshells have found useful for several applications [1–5]. The near-field and localized surface plasmon resonance (LSPR) wavelength of the nanoshells can be tuned easily by varying the radius, electric permittivity of the dielectric core as well as metal nanoshells, and thickness of the nanoshells [6–9]. For a few specific applications, bumpy nanoshells were used instead of smooth nanoshells due to the larger electric field that develops on the surface of the bumps [10, 11]. However, the bumps were found in random size and shape. Therefore, it was difficult to explain the experimentally observed results either with theoretical or numerical results [12]. Due to this reason, researchers have started using reduced symmetry core-shell nanoparticles or eccentric nanoparticles * Venkata Ramanaiah Dantham [email protected] 1
Department of Physics, Indian Institute of Technology Patna, Patna, Bihar 801103, India
in which the inner dielectric core is displaced w
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