Circular Dichroism Study Of Multilayer Nanostructure Arrays

Surface Plasmon (SP) is a kind of electromagnetic model caused by the interaction between the free electrons on the metal surface and photons. Chiral refers to a propertythat object can not superposition with its mirror image, and circular dichroism (CD) is a method of detect chiral. Chiral molecules are widespread in nature, but the CD signal is in ultraviolet band and very weak, which limits its applications. Chiral noble metal nanostructures has stronger CD singnal than chiral molecule due to it strongly interacting with light. For the past few years, the designs of chiral metal nano photonic devices and the studies of its characteristics which based on SP are very active.This paper designed and studied multilayer twist nanoslit-nanorod arrays structure, and the CD spectrum and its CD producing physical mechanism of film and bilayersplit-rings array structure, respectively. The specific contents of the research and results are as follows:1. A kind of metal/medium/metal nanometer multilayer twist nanoslit-nanorod arrays (TNNA) structure was designed and studied, using Finite Element Method studied its CD and produced physical mechanism. The researches show that, when circularly polarized light incident, the energy of TNNA mainly transferred through the slit. The equivalent electric dipole which oscillated perpendicular to nanoslit and the electric dipoleoscillated along with nanorod form bonding mode or anti-bonding mode. The CD system coincident with Born-Kuhn model. In addition, we also study the impact of structure parameters on TNNA CD effects. These research results will help us further understand the physical mechanism of CD.2. A kind of five-layer chiral structure -film and bilayersplit-rings array structure (FBS), using Finite Element Method studied its CD and produced physical mechanism. The researches indicate that, when circularly polarized light incident, four dipole and dipole are distributed on the two split-ring of up and down, respectively, the equivalent electric dipole of the upper split-ring and the bottomsplit-ring can form bonding mode or anti-bonding mode. The CD system coincident with Born-Kuhn model. Indirect and direct coupling mechanism between the upper level and lower level was proposed because of the gold film of FBS. Compared with the direct coupling, indirect coupling has a higher transmission. The CD effects of FBS structure strongly depends on the structure parameters. When the upper split-ring and the bottomsplit-ring achieving the impedance matching, the CD has maximum value. The results have certain guiding significance to design the metal chiral nanostructures.