| ABSTRACT:Along with the progress and maturity of surface plasmon resonance technology and nanometer manufacturing technology, the research based on localized surface plasmon resonance field enhancement of metallic nanoparticles has been hot in the modern world. In recent years, due to its spatial resolution at molecular level, the nanosensor based on localized surface plasmon resonance field enhancement has become one of tools for researching single molecular dynamics especially life activities of living cells. In order to achieve detection at single molecule level, field enhancement should be up to three orders of magnitude. Therefore, it has very important practical significance to design nanostructure with high field enhancement. By optimizing the geometry of a nanoparticle, this paper has obtained the conclusion that the field enhancement reached by gold nano spherical cap cone is largest.The main research content of this paper is as follows:In order to simulate on personal computer, this paper has compared common methods of numerical calculation, such as finite difference time domain method, finite element method and method of moments. As for the problems considered by this paper, it has concluded that the method of moments occupy less resource, high speed, high accuracy. This paper has obtained the accuracy of method of moments by comparing the result calculated by it with the result calculated by Mie theory:except the region near the outer surface, the relative error of field distribution is less than1%.This paper has used the method of moments to calculate and compare the maximum field enhancement on gold nanoparticles surface with different geometries when the curvature radius is lnm, obtaining that the field enhancement factor of the spherical cap cone is largest, it can be up to2000times in the range of visible or near infrared region, which is2times than that of ellipsoid when the curvature radius is also1nm. By analyzing the propagation behavior of the surface plasmon waves on the cone surface, this paper has concluded that the convergence waves which propagate toward the top of cone can lead to the localized electric field on the surface of the cone top further enhanced, which is excited by incident wave on the surface of cone. When the curvature radius of the top of the cone is in the range of1-5nm, this paper has gotten that the maximum field enhancement factor of the surface of the cone top is roughly proportional to negative3/2power of the curvature radius on the top of the cone. And when the field enhancement factor on the outer surface of the top is maximum, there is a substantially linear relationship between the length of the spherical cap cone L and the wavelength λ, obeying the relationship L=0.55484λ-134.4(nm), so the spherical cap cone can be regarded as half wave length antenna.When the spherical cap cone is regarded as the refractive index sensor, its sensitivity can be up to513nm/RIU at wavelength is λ=800nm;811nm/RIU at wavelength λ=1500nm. It can be used as living cells sensors for detecting the life activities of cells at real time. What’s more, the spherical cap cone can also be used to achieve the removal of a single specific diseased cell by light and heat therapy, since it has an asymmetric structure, it has only one resonance-enhanced hot spot and its power loss density on the top is nearly20000times higher than that on the bottom. |
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