Studies On Localized Electromagnetic Enhancement Of Metallic Nanoparticle By Numerical Simulation

Surface enhancement Raman scattering has been proved to be the powerful tool for the detection of molecular structure adsorbed on the surface of metallic layer.As the substrate of the surface enhancement Raman scattering,the metallic nanoparticle plays an important role. If the metallic nanoparticles are prepared with suitable shape,size and arrangement,the signal of Raman scattering can be highly improved,further,the information of molecular structure could be detected more clearly.The surface plasmon resonance could be induced on the surface of the metallic nanoparticle illuminated by the exterior electromagnetic field,and the localized electromagnetic enhancement are also presented in the vicinity of the surface.This mechanism explains the enhancement of the signal of surface enhancement raman scattering. Besides,the highly localized electromagnetic enhancement of the metallic nanoparticle has a vast potential to become an important element in the biosensor,nano-scale integrated optical device,near-field optics and nanophotonics.In this work,the local field electromagnetic enhancement of two nanostructures is mainly studied:(1) The localized electric field enhanced-property in vicinity of Au/Ag immersed in air and water is studied,respectively.The results show that,Comparing Resonance peaks to silver,the case of gold presents to long wavelength;To extent the tip length and to change the environment permittivity from air to water,both of silver and gold exhibit the peaks with red-shift;the silver tip has better enhanced property than the gold under 600 nm wavelength, while the opposite case is larger than 700nm.These results are good for the context of tip enhanced-spectroscopy analysis.(2) Local field electromagnetic enhancement of several silver nanosphere pairs interacting with incident plane wave are simulated by three-dimensional finite-difference time-domain(FDTD) method in visible-nearinfrared light region.The array of nanosphere pairs enables the investigation of particle-particle interaction as well as pair-pair interaction. Influences of incident wavelength,radius of nanospheres and number of pairs on local field enhancement are discussed.Electromagnetic enhancement are generated in the vicinity of nanospheres,and the highest enhancement are always in the gap of penultimate pair.With the increasing wavelength,the resonant peaks shift to larger radius,and the intensities increase remarkably.