Surface Enhanced Field Of Nano Core Capped Array-Au Film System Excited By SPR

Surface enhanced electric field is the enhancement of the local electromagnetic field generated on the surface of nanostructure when the light interacts with the noble metal nanostructure,which has great application value in the fields of bio-sensing detection.The weak signals can be amplified by applying surface enhanced fields,mainly in the areas of surface-enhanced Raman,surface fluorescence enhancement,and infrared absorption.Generally,enhanced fields exist in the form of ‘hot spots’ at the nanostructure gaps or tip.Although it has strong reinforcing effect,there are some limits for the detection of biological macromolecules.Therefore,the realization of a wide range of surface electric fields with an average enhancement effect promotes the development of bio-sensing.This paper mainly studies the scattering effect and enhanced electric field of NPs under the action of surface plasmon resonance excited by Au film.The position of the enhanced field is different from the conventional nano-tip and nano-gap,resulting in a uniform enhancement on the surface of the nanostructure.The enhancement effect amplifies the weak signal of the surface.In this paper,the optical properties of the nanostructures on Au film are designed and studied.The Finite Difference Time Domain(FDTD)method is used to numerically calculate the scattering spectrum and the electric field magnitude distribution of the nanostructures.The array of dielectric spheres is firstly designed.Its scattering of the evanescent field on Au film and the enhanced near field are calculated.In order to further enhance the electric field,the optical properties of noble metallic core capped structures are investigated.The optical response of a single core capped structure is mainly calculated,providing the basis for the study of the optical properties for the array composed by the core capped structures.Finally,an array with a noble metallic core capped structure as a unit is designed.The coupling conditions of surface plasmon resonance(SPR)with localized surface plasmon resonance(LSPR)in a nano core capped array – Au film system is calculated by numerical simulation,and thus obtained the enhanced surface electric field.Based on the analysis of scattering spectra and near field distribution of nanostructures,a uniform surface enhanced field generated by a regular nanoarray composed by dielectric spheres is obtained.The enhanced field(about 6 times)is generated by the scattering of dielectric array is excited by the evanescent field of Au film and the filtering of the scattering band can be achieved by adjusting the cycle of the array.The LSPR of core capped structure can be used to further enhance the electric field.For a single noble metallic core capped NP,the coupling between surface plasmon resonance(SPR)of continuous Au film and localized surface plasmon resonance(LSPR)of core capped structure is realized,which effectively enhances the effect of the polarization parallel to the symmetry axis of the core capped nanostructure,thereby the enhanced field on the surface of the structure is achieved,the LSPR is generated by the polarization parallel to the axis of symmetry of the nano core capped structure.When the single core capped nanoparticle(NP)is expanded into an array with a certain period,similar to a single core capped NP,the coupling between SPR and the LSPR under the polarization parallel to the symmetry axis of the core capped NP not only produces a large range of enhanced electric field on the surface of the array,but also generates gap field which is 2 times the enhanced electric field on the surface of the array.