Polarization Dependence Of Surface Enhanced Raman Scattering In Ag Nanoparticle Dimer

Surface Plasmons(SPs)are electron waves that are propagated along the Surface of the metal by the interaction of free vibrating electrons and photons which exist on the Surface of the metal.The SPs which exist in the surface of metal nanostructures can greatly enhance the local electromagnetic field and can even break through the diffraction limit of transmission,surface plasmon has these properties,so it can be applied to the ultrasensitive detection technology.Metal nanostructures,especially in Au,Ag,Pt,Cu nanostructures which has surface plasmon can produce local field enhancement effect,the metal nanoparticle has abundant optical properties bbecause its local field enhancement effect.Surface Enhanced Raman Scattering(SERS)enhances very weak Raman signal by using the local field enhancement effect of metal nanoparticle structure,which can measure the chemical structure and composition from the Raman signal.However,the Raman enhancement effect in metal nanostructures has a great relationship with the materials,morphology,size and structural characteristics of nanoparticles.In this paper,anisotropic nanoparticle dimers are studied such as nanorice dimer and nanoparticle-nanowire dimer,using 4NBT molecules,2A-5NBT and BDT molecules as a probe molecule to study SERS polarization dependent with different angle of incident light and emission light.Nanoparticle dimers have anisotropic,so the experimental results and simulation results show that the maximum SERS intensity is obtained as the polarization of incident laser is perpendicular to the nanowire's or nanorice's and minimum SERS intensity could be generated under parallel conditions.Beyond that,there is a surprised result that small particles have a stronger ability to collect charge when silver nanorice dimer is consisted of two different particle sizes,and which has no relation with the angle of laser.In nanorice dimer study,the SERS spectra of Ag nanorice dimer on different films(Au,ITO,glass)are investigated,the result is that the films have no effection on SERS polarization dependent.Au film has the strongest SERS intensities than ITO and glass film because the coupling between the image charge of Au film and the free charge of nanoparticle dimer.In nanoparticle-nanowire dimer studying,the gaps between nanoparticles or between nanoparticles and film have SERS polarization dependent with different angle of emission laser.Studying SERS polarization dependent with different anisotropic nanoparticles is helpful for understanding the mechanism of SERS,as well as,which is helpful for regulating SERS intensities without using other setup.