Surface Plasmons Coupling For Dual-band Resonance SERs Substrates

The interaction between electromagnetic waves and metallic nanostructures brings optical properties which are unavailable for bulk metal materials, results in a series of new phenomena or effects, for example Surface Plasmons and "Meta-materials" which can realize some interesting electromagnetic properties not found in naturally occurring materials. With the development of manufacturing technology on the nanoscale, people can almost fabricate nano-scale metal structures with arbitrary geometries and accelerate the development of these new subjects and fields, The poor reproducibility and stability of Raman signals for traditional SERS substrates prevents the application of surface optical spectral technology seriously. Considering the lack of control in traditional SERS produced by chemical process, we proposed a kind of periodic structures based on the properties of surface plasmons. Dual-band resonance, large SERS enhancement factor and good reproducibility and stability make the structure attractive as SERS substrate.The thesis is divided into five parts. The introduction mainly presents the origin and actuality of SERS, and the idea and main tasks of this work. In chapter two, we mainly introduce the surface plasmon properties of metallic nanostructure and the corresponding localized field enhancement effects. In chapter three, after a brief introduction to basic electromagnetic theory, particular attention is devoted to the numerical method of discrete dipole approximation (DDA) and its credibility to deal with the interaction of light with periodic metallic nanostructures. In chapter four, the optical properties of the proposed structure are investigated using the discrete dipole approximation (DDA) method. Due to coupling between the particles and the gold film, the proposed structure exhibits higher absorption and larger field enhancement compared to the nanoring array alone. In addition, periodic nanorings as grating couples to surface plasmon polaritons (SPP). The plasmonic coupling between localized surface plasmon resonance (LSPR) of the nanorings and SPP can enhance the electric field around gold rings further and gives rise to dual-band resonance absorptions. The corresponding Raman signal enhancement factors can reach 1.5×107 and 1.4×106, respectively. The fifth section is in summary and prospect.The main progresses and innovation of this work are listed as follows:1. A large proportional of nanoparticles as SERS substrates can realize single band resonance for field enhancement. The proposed structure is attractive for applications as double-resonance plasmon substrates due to the coupling between LSPR and SPP. In addition, the absorption coefficient of 97.97% is potentially helpful for perfect absorber and thin solar cells in near-infrared spectrum.2. DDA method'credibility to deal with the interaction of light with periodic metallic nanostructures is proved by calculate the optical properties of periodic nanostructures in reference which is in accordance with the experimental results.3. We investigate the localized field enhancement effects of metallic nanostructures systematically. The coupling effects between surface plasmons modes are key point for improving the SERS enhancement factor.