Surface Plasmonic Properties Of Several Nanostructures In The Optical Frequency Regime

Surface plasmons, the external electromagnetic field coupling with electron collective oscillations of metal (or metallic compound), is an electromagnetic wave propagating along a metal/dielectric interface. In the direction perpendicular to the metal/dielectric interface, surface plasmons are evanescent waves whose electric field amplitude decays exponentially into each medium with increasing distance from the interface. The half-wavelength diffraction limit in traditional optics thus can be broken up. Surface plasmons therefore attracts wide attentions and are well applied in chemical and biological sensing, surface-enhanced Raman scattering, enhanced transmitting through subwavelength hole, nano-lithography and near-field optical data storage. It also provides the possibility of all-optical integrated circuits in micro-meter and nano-meter in the future.The thesis bases on "antenna-aperture" and "gain medium-metallic shell dimer" nanostructures aiming at understanding the property and effect of surface plasmons in such structures. Our investigation provides a theoretical basis for applications of the two structures in nano-lithography, nano-photonics device and surface enhanced Raman scattering.The thesis consists six chapters.In chapter1, the physical principle of the diffraction limit breaking by surface plasmons is first explained. Then, the basic concepts, development history and applications of plasmonics are reviewed. At the end of this chapter, the research purpose and main work of this thesis are presented.In chapter2, there is a thorough introduction about the finite difference time domain method used in this thesis, including physical concept, difference scheme, numerical stability conditions, plane wave source setting, absorbing boundary setting and error analysis. We also show the parameter setting of Drude model of sliver in the finite difference time domain method.In chapter3, the interaction between the two perpendicular Fabry-Perot-like resonances of the nanoantenna-dielectric layer-slit structure and their influences on the transmission enhancement are investigated. It is also shown that the enhanced transmission can be realized in a wide range of incident wavelengths from the visible to near-infrared regime for different slit geometries and dielectric layer thicknesses. Our numerical results are demonstrated by the theoretical dispersion relationship of surface plasmon polaritons wavelength based on the metal-insulator-metal model. Therefore, it is reasonable to approximately describe the transmission process of the antenna-dielectric layer-slit structure with the metal-isolator-metal theory.In chapter4, the transmission process of bowtie aperture and the antenna-dielectric-bowtie system is investigated. It is shown that the localized surface plasmons of bowtie aperture is sensitive to the structural parameters near the metal tip, such as bowtie angle, gap size, but it is less affected by the outline size. Besides transmission enhancement, an optical-switch effect is also found as the antenna longitudinal width varies. By comparing the antenna-assisted transmission behavior of a rectangular aperture, the transmission enhancement corresponds to a Fabry-Perot-like resonance in the antenna-dielectric-metal cavity and the cutoff phenomenon can be understood as a result of the diffraction limit effect. Such a phenomenon is important for nano-lithography and nano-photonic device applications.In chapter5, the effect of gain medium on the electric energy of the nanoshell dimer and the interaction between the two nanoshells are investigated. The results show that the electric field enhancement in the gap of the nanoshell dimer is due to the gain core compensation of localized surface plasmon in the metallic shell. The smaller the extinction coefficient is, the larger the electric energy enhancement will be. In addition, when the inter-particle distance is smaller, the coupling between the two nanoshells induced by the gain medium is more obvious. The optimized shell thickness of the active nanoshell dimer is also given out. The results provide a reference for experimental nanoparticle synthesis and Raman scattering improvement in the future.The thesis is concluded in chapter6with a further plan of our research work. The major new progresses of this thesis are also summarized.