Surface Plasmon And Fano Resonance Effects In Silver Nanostructures

Noble metal nanostructures,which support surface plasmons,have gained extensive attention due to the ability to manipulate light at nanoscale.The surface plasmon resonant effect at noble metal nanostructures is very sensitive to the shape and size of the nanostructure,the refractive index of surrounding medium,direction and polarization of the incident light.These properties have very important significance for spectrum control.Fano resonances can be achieved by the destructive interference between the bright mode and dark mode of the plasmonic systems.Finer spectrum and stronger enhancement of local field can be observed in the systems due to the existence of Fano resonances.Therefore,surface plasmons have tremendous potential applications in biosensing,surface-enhanced spectroscopy,plasmon waveguide and solar cells.Taking the fact that current researches focus on the complex nanostructure,and the researches on magnetic Fano resonance is relatively insufficient,silver ellipsoid/double split-ring and split ring-perfect ring nanostuctures are designed.The optical properties of these structures have also been investigated systematically.This thesis has been divided into three sections.Main contents of each section are descr:ibed as follow.In the first section of this thesis,several popular calculation methods are introduced respectively,including discrete dipole approximation(DDA)method,finite difference time domain(FDTD)method and finite element method(FEM).We focus on introducing finite element method and the corresponding simulation software COMSOL Multiphysics in setting models and its characteristics.In the second section,the plasmonic properties of a silver ellipsoid/double split-ring nanostructure are investigated theoretically.Anti-bonding and bonding dipole-dipole mode are excited in the extinction cross section of the structure.The anti-bonding dipole-dipole mode can be enhanced or suppressed by adjusting of the rotation angle of the ellipsoid.With symmetry breaking introduced by moving the ellipsoid,Fano resonances can be stimulated,which can be manipulated by modifying the offset of the ellipsoid.On account of the tunable Fano spectra of this nanostructure,it has potential applications in biosensing.In the third section,the optical properties of split ring-perfect ring,including local surface plasmon resonance and enhancement of local field,is analyzed theoretically.The plasmonic system could support both electric and magnetic Fano resonances,which can be adjusted by tuning the geometrical parameters.We find that the plasmonic system responds to a normal incident plane wave mainly by exciting the magnetic Fano resonances with uneven displacement current loops and uneven magnetic hot spots,and the adjacent current loops are always anti-phase.In addition,great enhancement of electric field and magnetic field can be achieved simultaneously at magnetic Fano modes.Calculation results exhibit that this structure is sensitive to the refractive index of surrounding medium.Therefore,this nanostructure has significant potential applications in sensor,surface-enhanced spectroscope,the propagation of low-loss magnetic plasmons and other optical devices based on magnetic Fano resonance.