The Trapping Properties And Photothermal Effect Of Silver Nano Triangular Dimer Optical Tweezers

Metal nanostructures have the unique property of producing localized surface plasmon fields by focusing light beams on the sub-wavelength scale.By combining metal nanoparticles with surface plasmons,technology of surface plasmon optical tweezers has been developed,which brings new prospects and opportunities to the field of nanotechnology.Among many metal nanomaterials,silver triangular nanoprime can be used to precisely control the optical properties such as electromagnetic field distribution through the control of their structural parameters and arrangement.Thus,this project aims at studying optical trapping characteristics of the optical tweezers structure of silver triangular nanoprime.And has demonstrated the influence of the structure's photothermal effect on the stable capture performance.From basic principles of surface plasmon,this project has studied the electric field enhancement effect of silver triangular nanoprime under different wavelengths of incident light.It was found that when incident light of the wavelength corresponding to the dipole resonance peak,the maximum multiple of electric field enhancement had been obtained.The surface electric field enhancement characteristics of three typical silver triangular nanoprime dimers under different polarized light conditions were calculated respectively,corner-to-corner,corner-to-edge,and edge-to-edge.Different coupling structures have two parallel bottom edges.It was found that a hundred-fold electric field enhancement had been obtained when the incident light polarization direction was perpendicular to this side.Then,the project examined the capturing abilities of the designed optical tweezers system,using Maxwell Stress Tensor(MST)to calculate the light capturing force of the three structures.The results showed that the corner-to-edge configuration dimer failed to capture.By investigating the trapping properties of dielectric microspheres(n = 1.6,r = 20 nm),it was found that that when the corner-corner configuration dimers have gaps of 1,3,5 nm,the required incident light energies were 6.50,7.04,and 8.93(m W/?m~2),respectively;when the edge-to-edge configuration dimers have gaps of 3 or 5 nm,the required incident light energies were 16.39 or 22.52(m W/?m~2),respectively.By comparing the two structures,it was found that the range of the stable capture area of the corner-corner configuration was larger than that of the edge-to-edge configuration.Finally,this project examined the photothermal effect of the dimer with the diagonal configuration by finite element methods.When the gap was 1,3,and 5 nm,the temperature generated on the metal surface due to the photothermal effect was 142,118,and 131 ?,respectively.Considering the effect of temperature on the velocity and diffusion range of the Brownian motion of the medium microspheres,we concluded that corner-corner configuration with 3 nm gap could best facilitate capture performance of the dimer.Through comprehensive analysis of the light trapping properties and photothermal effect of the silver triangular nanoprime dimer.This paper has provided further implications for future studies on the stable capturing characteristics of nano optical tweezers.