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The investigation of the optical properties of noble metal nanostructures encapsulated bydielectrics is one of the hot topic in nano optics. Noble metal nanostructures have found wideapplications in biology, chemical detection, sensing, optical communication, information storage,microscopy, imaging, etc. This is owing to their unique optical properties, which can be tuned by thenanostructure size, morphology, material, optical properties of the surrounding media. Adopting thenumerical simulations based on finite element method, we investigated the near-field optical propertiesof individual Ag nanowire dimers encapsulated by symmetric and eccentric dielectric layers. Accordingto optimization, a good cancadidate for SERS substrate is provided. The main research results andcontents of this theis are as below:Firstly, to confirm the reliability of our numerical simulation method, we reproduced the work ofG. Bachelier etc., and the obtained results show good consistence.Secondly, the near-field optical properties of individual Ag nanowire dimers encapsulated bydielectrics were studied. The effects of the dielectric layer thickness (t) and the refractive index (n) ofthe surrounding medium were discussed. It is revealed that the electric field enhancement of thenanosystem is a function of the incident light wavelength for different n and t. Considering theindependence of the two parameters of n and t, the electric field enhancement was optimized accordingto one parameter while the other parameter fixed, then to optimize the other parameter. It is alsodemonstrated that the resonant wavelength of the surface plasmons the nanosystem red shift withincreasing n and t, which is a linear and nonlinear function of n and t, respectively.Thirdly, we simulated the near-field optical properties of individual Ag nanowire dimerseccentric-encapsulated by dielectrics and investigated the effects of n and R, the radius of the dielectriclayer. It is demonstrated that the obtained electric field enhancement is functions of n and R. Byconsidering the repeatable simulating results and the magnitude of the enhanced electric field peak, weoptimize the geometric parameters of the nanosystem for SERS enhancement, which provide a goodcancadidate for SERS substrates. Our results also successfully demonstrate that the SP resonantwavelength of the nanosystem red shifts with the increasing of n and R.
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