Research On Superstructures Based On Localized Surface Plasmon Resonance

Local surface plasmon resonance(LSPR)is a kind of resonance wave which is shown by the interaction between light and surface charge of nanostructure.LSPR is very sensitive to the change of shape,size,material parameters and refractive index of external value of nanostructure.Through the design and processing of nanostructures,the electromagnetic properties of materials can be changed,so that they have excellent electromagnetic properties that the naturally formed materials do not have,which can provide a new way for human beings to realize the manipulation of electromagnetic waves.Local surface plasmon resonance(LSPR),as an important method to control the electromagnetic wave from visible to near infrared,has become one of the research hotspots in the field of nanophotonics.Because of its effective local electric field enhancement and high sensitivity to environmental media,nanostructures are widely used in surface enhanced Raman scattering,biosensor,medical diagnosis and treatment,biomedical imaging and other fields.In this paper,we design and analyze the extinction characteristics of double-layer nanodisk structure,concentric dual-ring nanodisk structure and symmetric plasmonic split-ring/ring dimer nanostructures by using the finite difference time domain(FDTD),finite element method(FEM)and discrete dipole approximation(DDA)methods.The double-layer nanodisk structure is designed and its local surface plasmon resonance characteristics are analyzed by the FDTD method.The results show that the plasmon resonance peak of ITO nanodisk structure wrapped by gold and silver is related to the radius of the inner and outer walls of the metal shell,and is very sensitive to the refractive index of the external medium.Moreover,by optimizing the geometry,it can excite the obvious fno resonance linearity,which has potential application in high sensitivity biochemical sensor.The structure of concentric dual-ring nanodisk is designed,and its LSPR characteristics are analyzed and studied by using the method of discrete dipole approximation.s Through the analysis of the extinction spectrum and the electric field diagram,it is proved that the geometrical size and refractive index of the surrounding medium have a significant effect on the hybridization of plasmons and the displacement of the extinction peak.The coupling resonance wavelength depends on the structural parameters of the disk and the ring,and the flexible tunable multipole resonance is realized in the near infrared region.The physical nature of the coupling resonance is described by using the theory of plasmon hybridization.The symmetric plasmonic split-ring/ring dimer nanostructures are designed and analyzed by the finite difference time domain method,the finite element method and the discrete dipole approximation method.The analysis of scattering spectrum and electric field distribution shows that the splitting ring ring dimer has strong local electric field enhancement and typical fno resonance linearity due to the existence of cavity between the two rings when the polarization direction of incident light is perpendicular to the splitting gap.Compared with the way to obtain the Fano resonance by destroying the symmetry of the ring disk structure,the split ring ring dimer can adjust the Fano linearity in the visible to near infrared band by adjusting the structural parameters flexibly and simply.Its obvious local electric field enhancement and high sensitivity make it have a broad application prospect in the field of surface enhanced Raman scattering and biochemical sensing.