Numerical Investigation Of LSPR And Fano Resonance Characteristics Of Noble Metal Composition Nanostructures

As a powerful implement for nanoscale optical control, local surface plasmon resonances(LSPR) can effectively command the spread of free waves in the space local area within the scope which is the smaller than the diffraction limit. Due to its special optical characters of breaking through the diffraction limit, realizing the local field enhancement and highly sensitive to dielectric environment, LSPR has wide application prospect in nonlinear optics, molecular specific imaging and spectroscopy, biological sensing and surface enhanced Raman scattering(SERS).The LSPR properties of noble metal composition nanostructures are strongly affected by their nanostructure morphology, size, gap, metal type, and the refractive index of the surrounding medium. Comparing with the nanoparticles with simple geometry, the composition nanostructures have peculiar optical properties because of complicated internal physical mechanism. In this paper, we have investigated several noble metal composition nanostructures with theoretical numerical simulation. Combined with compound nanostructure parameters, the LSPR characteristics are analyzed and explained by using the theory of plasmon hybridization and the extinction spectra. The main content of this paper is as follows:In the first chapter, a general literature review of LSPR and Fano resonances and their physical mechanism are introduced, meanwhile, the main research methods are listed and our main work is simply provided.In the second chapter, the optical properties of a Fe2O3/Au core-shell nanorice dimer are theoretically investigated by means of the finite element method. It is presented that the response line shape of the multipolar plasmon Fano-like resonances can be controlled by modulating the relative positions of the two nanorices in the nanorice dimer. We further show that the coherent coupling of the bright and dark modes can lead to a distinct Fano dip in the extinction spectra of the nanorice dimer and Fano-like resonances evoke giant electric field enhancement at the interparticle gap.In the third chapter, we numerically study the plasmon resonance properties of gold nanostructure consisting of a nanocrescent and a nanoring by using the two-dimensional finite element method. It is desired to acquire intense multiple plasmon resonance peaks in the extinction spectra of the proposed gold nanostructure denoted as nanocrescent/nanoring(NCNR) structure. By adjusting structural parameters, the plasmon resonance peaks can be effectively tuned. These resonance peaks can be explained by the physical mechanism of plasmon hybridization. In addition, the local electric fields around the tips of the nanocrescent have a strong enhancement by the coherent couplings of the multipolar modes of nanoring and nanocrescent.In the fourth chapter, the LSPR and Fano resonances properties of asymmetric NCNR structures are also theoretically discussed. We have found that the different parameters of asymmetric NCNR structures can obtain disparate intensity of plasmon resonances. By analyzing the extinction spectra and electric field enhancement, it is presented that the interactions between the plasmon modes of nanocrescent and nanoring of asymmetric NCNR structures can generate relative special optical line shapes.In the fifth chapter, the main work of this paper is summarized and the next step study and its potential application in this field are discussed.