Surface Plasmon Resonance And Optical Properties Of Noble Metal Nanoparticles

Noble metal nanostructures that support surface plasmons have gained increasing attention due to their unusual optical properties and abilities to manipulate light in some unique ways. Surface plasmon is quite sensitive to the shape and size of the nanostructure, the environmental material, the direction and polarization of incident light, and the alignment of the nanostructures. By adjusting the factors mentioned above, we can manipulate the surface plasmon of nanostructures to achieve some unique functions, which present great application potentials to many fields including surface enhanced spectroscope, solar cells, plasmon optical waveguide, biosensor and so on. With the development of theory and advances in micro fabrication technology, the design of various nanostructures becomes a hot research topic, and the research of metal nanostructure system becomes a new quickly developing subject, namely surface plasmonics.Taking the fact that most of the current researches focus on the surface plasmon resonance of symmetrical nanostructures in2-D plane while many nanostructures in real applications are asymmetrical and in3-D space into consideration, we design a novel nanostructure in3-D space and a structure in2-D plane with asymmetrical geometry, and systematically investigated their optical property. The thesis is divided into two parts. In part one, the optical property of a3-D nanostructure, a side-by-side tangent nanospheroid homodimer (TNSHD), is studied. In part two, we design and investigated a structure in2-D plane with asymmetrical geometry, which is a disk-ring plasmonic nanostructures with double symmetry breaking.Part one:the optical property of TNSHD.The plasmon resonance and electric field enhancement in TNSHD have been investigated theoretically by using DDA and FDTD methods, respectively. The effects of the rotation angle and the polarization of incident light on this nanostructure are systematically investigated by changing the rotation angle to different values and changing the polarization of the incident light. The simulation results indicate that this side-by-side TNSHD has its novel optical properties. The plasmon resonance with a distinct Fano lineshape can be achieved and the electric field intensity can be enhanced strongly. The tunability of the Fano resonance could provide important applications in biosensing. The obtained electric field enhancement might open a promising pathway for surface-enhanced Raman scattering (SERS) and light trapping in solar cells.Part two:optical properties of disk-ring plasmonic nanostructures with double symmetry breaking.Optical properties of disk-ring plasmonic nanostructures with double symmetry breaking are investigated theoretically with finite element method (FEM). By tunning the asymmetry degree of the nanoring, the offset and the size of the nanodisk, systematically investigated their effects on the optical property of this nanostructure. The research results indicate that tunable higher order Fano resonance originate from the destructive interference between the bright mode of the displaced nanodisk and the dark mode of the asymmetric nanoringcan be achieved. By tunning the size of the nanodisk, certain higher order Fano resonances can be suppressed or enhanced, and thus it can decrease the overlap in spectral measurements. Double asymmetry breaking allows the realization of the stronger electric field enhancement as a result of the stronger interaction between the displaced nanoplate and asymmetric nanoring.