Enhanced Light Absorption Of Graphene And Excitations Of All-dielectric Optical Magnetic Resonances Using Core-shell Nanostructures

With the continuous development of the nanofabrication technology, the core-shell nanostructures composed of inner core and outer shell, which is an important branch of composite nanoparticles, has attached much attention. The core-shell nanostructures have more unique physical and chemical characteristics than the inner core, outer shell and the simple sum of their characteristics, which shows great potential in many fields such as biomedicine, chemistry, physical, materials science, catalytic and so on.In our thesis, we focus on the research of the optical properties of plasmonic core-shell resonator and the all-dielectric core-shell nanostructure. Besides, we also discuss the possibility of using the plasmonic core-shell resonator to enhance the absorption of graphene as well as realizing the magnetic resonance in the optical region by all-dielectric core-shell nanostructure. The main results are as follows.First, we discuss the absorption properties of graphene in multilayer dielectric-metal-graphene nanostructure. We find that LSP supported by dielectric-metal plasmonic core-shell nanostructure could greatly enhance the absorption of graphene. We could vary the absorption peak from visible to NIR region by adjust the size of the dielectric core and the metallic layer. Meanwhile, we can reach maximal absorption efficiency of the certain wavelength by changing the parameter of the nanostructure. Compared with metal-graphene core-shell nanostructure, the absorption efficiency of graphene can be enhanced by two orders of magnitude.Next, we theoretically study the optical characteristics of the core-shell nanostructure composed of dielectric layers with lower and higher refractive index respectively and find that the all-dielectric core-shell nanostructure could realize the magnetic resonance in the optical region. In experimental study, we first acquire a free-standing polystyrene sphere array using self-assembling method. Then silicon layers are coated on the upper and lower surfaces of this array using sputtering method to get the final core-shell nanostructure. The magnetic resonances are observed corresponding to the theoretical prediction. The position and intensity of this resonance could be adjusted by varying the parameters of the inner core and silicon shell. Our study provides theoretical and experimental supports on realizing the lossless all-dielectric metamaterials.We prove this enhancement of magnetic resonance in this acquired core-shell structure.