基于时域有限差分法的核壳双金属纳米颗粒光吸收率反转行为

Reversal behavior of optical absorption rate of bimetallic core-shell nanoparticles based on finite-difference time-domain method

双金属纳米颗粒能够有效整合两种金属的物理和化学性质并同时表达每种金属的独特性质,是提高光散射、光热转换、等离激元共振衰变和光子激发的重要材料.基于单独纳米颗粒的研究可以避免实验研究过程中纳米颗粒之间的相互影响,更能够有效分析入射光与纳米颗粒之间的相互作用.本文采用时域有限差分法计算了等离激元双金属核壳纳米颗粒的光谱学性能和能量传递衰减过程中的磁场、电场及吸收功率分布,以探讨其光谱吸收特性.结果表明,随着核芯粒径的增大,共振波长红移,当核芯粒径大于100 nm时,Ag@Pt双金属纳米颗粒吸收率高于纯金属纳米颗粒,这是由于壳层与核芯金属材料之间强烈的屏蔽效应使入射光仅与外层原子相互作用发生共振.同时,相对于Pt壳层而言,Ag核芯等离激元衰减更快,因此更多的能量转移到了Pt壳中,使Pt壳表面的磁场、电场较为集中且吸收功率较大.此外,Ag核芯中的能量更趋向于向邻近Pt壳转移,表现为靠近Ag核芯的区域能量吸收更为集中.本文为设计满足特定光谱响应需求的等离激元核壳结构双金属纳米颗粒提供了理论指导.

The bimetallic nanoparticle can effectively integrate the physical and chemical properties of two metals and simultaneously exhibits the unique natures of each metal.It also serves as a good candidate for improving light scattering,photothermal conversion,plasmon resonance decay,and photon excitation.Investigating the optical properties of an individual nanoparticle can avoid the interaction between nanoparticles during experimental research,which allows us to more effectively analyze the interaction between the incident light and nanoparticles.In this work,the finite-difference time-domain method is used to study the spectral absorption characteristics of the plasmon bimetallic core-shell nanoparticles by calculating the spectroscopic properties,and also the distributions of the magnetic field,electric field,and absorption power during energy transmission and decaying.The results show that the resonance wavelength is red-shifted if the core diameter is increased.In addition,the absorption rate of Ag@Pt bimetallic nanoparticles is higher than that of pure Ag@Ag nanoparticles when the core diameter is bigger than 100 nm.This is because the strong shielding effect between the shell metal material and the core metal material leads the incident light to interact only with the outer atoms,resulting in resonance.Meanwhile,the plasmon of the Ag core decays faster than that of the Pt shell and more energies are transferred to the Pt shell.As a result,the surface of the Pt shell shows more concentrated magnetic and electric fields associated with an enlarged absorbing power.Moreover,the energy in the Ag core tends to transfer to the nearby Pt shell,which is characterized by the energy absorption in the Pt shell close to the Ag core,and is more concentrated.This paper provides theoretical guidance for designing plasmon bimetallic core-shell nanoparticles,thereby satisfying the demands for special spectral responses.