Study On Extinction Characteristics Of Noble Metal Nanostructures

Surface plasmon resonance which induced by metal nanostructures can broke up diffraction limit in traditional optics and provide a new way for sub-wavelength optics. This phenomenon will stimulate the development of some novel optical materials, at the same time, it will offer a way to transmit and process optical information in nanoscale and create new devices of miniaturization and integration.Surface plasmon can enhance the local electromagnetic field that is very sensitive to the change of metal material properties, nanostructure morphology and dielectric environment of nanostructures, and it can be used in sensor with high sensitivity and the detection of enhanced Raman spectroscopy. Therefore, researches about metallic nanostructures which based on surface plasmon resonance have attracted wide attention and formed a subject named plasmonics gradually. Plasmonics show great application prospect in physics, materials, chemical, biological sensing and many other research fields.The appearance of plasmonics make people realize that some special shape of metal or surface plasmon nanostructures can be designed. Effective high-performance computer electromagnetic simulation software can predict the performance of nanostructures and promote the development of surface plasmon technology. Based on the FEM software COMSOL Multiphysic, this paper studies several different metal nanostructures such as silver-gold core-shell composite nanoparticles based on ITO, SiO2/Ag/SiO2/Au multilayer nanoshells and noble metal disk-ring nanostructures. We simulated the extinction spectra of above nanostructures in different conditions, and the factors which influence the extinction properties of nanostructures were investigated in detail. The results are as follow:(1) The influences of the ITO substrate dielectric constant, gold-shell size, silver-core radius and dielectric environment of silver-gold core-shell composite nanoparticles based on ITO to extinction spectra are significant. If the total size of silver-gold core-shell composite nanoparticles is fixed, its optical properties are mainly determined by core-shell ratio. When the gold-shell is thin enough, its optical properties are dominated by the silver-core and fine-tuned by gold-shell.(2) The SiO2/Ag/SiO2/Au multilayer nanoshells can achieve Fano resonance, and its Fano resonances are induced by dipole-dipole hybridization of the inner nanoshell and the outer nanoshell. By adjusting the parameters of SiO2/Ag/SiO2/Au multilayer nanoshells including composition, size of nanoparticles, thickness of inner dielectric, thickness of gold nanoshell and the dielectric environment, the position of Fano resonance can be tuned.(3) For noble metal disk-ring nanostructure, symmetry of nanostructures is broken when the relative position of nanodisk and nanoring is displaced, and then high order Fano resonance can be induced. This phenomenon arises from the coupling between the dipole mode of displaced nanodisk and the multiple mode of nanoring. The tuning of high order resonance of nonconcentric disk-ring nanostructure is limited by its composition, size of nanodisk, nanogap between disk and ring and the dielectric environment.These researches about high order Fano resonance help to improve the detection sensitivity in sensing field.