Circular Dichroism Study Of Metal Chiral Nanorod Composite Structures

Surface plasmon (SP), which is the electromagnetic model formed by the interaction of free electrons of the surface of the metal and photons. SP is widely used in nonlinear optics, catalyst, surface enhanced raman scattering and other fields. Surface plasmon is very sensitive to the shape and size of the nanostructure, the environmental material and the arrangement of the nanostructures. Therefore, we can manipulate the surface plasmon of nanostructures to achieve some unique functions.Chiral structure is a object that can't overlap with the mirror image. Circular dichroism (CD) spectroscopy is a method to explore the chiral molecular characteristics by absorbing different for left-handed and right-handed circularly polarized light. Chiral metal nanostructures can produce stronger CD signal and widely used in the circular polarization transformation biomedical diagnosis and biological molecular detection. This paper designs the chiral metal nanorods composite structure array, used the finite element method to study the physical mechanism of CD effects, and studied the effect of structural parameters to the CD. The specific contents and results are as follows:(1) This paper proposed the perpendicular double metal composite structure array. Studied the CD effect of this structure and its physical mechanism, and calculates the effect of structural parameters on the CD. The upper short rod equivalent electric dipole and the lower short stick equivalent electric dipole can form antibonding mode in short wavelength resonance, The upper long stick equivalent electric dipole and the lower long stick equivalent electric dipole can also form the antibonding mode in long wavelength resonance when left handed circularly polarized light illuminate this structure. The upper short rod equivalent electric dipole and the lower short stick equivalent electric dipole can form bonding mode in short wavelength resonance; The upper long stick equivalent electric dipole and the lower long stick equivalent electric dipole also can form bonding mode in long wavelength resonance when right-handed circularly polarized light illuminate this structure. CD effect produced by the physical mechanism conforms to the Born-Kuhn model. CD effect of the double metal nanorods strongly depends on structure parameters.(2) This paper proposed the structure composed with three metal nanorods. studied its physical mechanism of CD produce when left-hand circularly polarized light and right-handed circularly polarized illuminate respectively this structure, and calculate structural parameters to effect of CD. The results show that the upper metal nanorods equivalent electric dipole and the lower metal nanorods equivalent electric dipole can form bonding mode when left-hand circularly polarized light incident, the middle metal nanorods effect is very weak to the lower level metal bar coupled. The three metal nanorods equivalent electric dipole moment can form resonance strong bonding and the antibonding pattern when right-handed circularly polarized light incident. The metal nanorods CD effect strongly depends on structure parameters. These results not only understand the physical mechanism of CD effect, but also design a metal composite structure to enhance CD effect.