Au-中间层-Ag纳米核壳的法诺共振特性研究

Fano resonance properties of Au-interlayer-Ag multilayer nanoshells

为研究不同中间层材料对局域表面等离子体共振(LSPR)特性的影响,采用离散偶极近似(DDA)方法系统研究Au-中间层-Ag纳米核壳的LSPR消光特性,并利用等离激元杂化理论对其法诺共振现象进行解释。结果表明:具有对称结构的3层纳米核壳结构可实现法诺共振;法诺共振峰峰位强烈依赖于纳米核壳的中间层材料、内核半径和外界介质折射率;Au-Ni-Ag纳米核壳LSPR峰位随金核半径的增大而红移,且只有1个共振峰,归因于金核对LSPR的压缩作用;而金核半径和外界介质折射率的增大导致Au-Si3N4-Ag纳米核壳LSPR峰位的红移,且有3个共振峰,归因于中间层Si3N4对LSPR的增强作用。上述现象可利用纳米核壳的电场分布进行分析。通过选择合适的几何参数,Au-中间-Ag纳米核壳法诺共振峰峰位可调谐至600~1 200 nm。

In order to investigate the influence of LSPR properties of multilayer nanoshells with different interlayer materials,the extinction properties of Au-interlayer-Ag multilayer nanoshells were investigated systematically based on the discrete dipole approximation. Using the theory of plasmon hybridization,fano resonances of Au-interlayer-Ag multilayer nanoshells were explained. The numerical results indicate that fano resonance can be achieved by the symmetric multilayer nanoshells. Fano resonance peaks are dependent strongly on the materials of interlayer,Au core radius and refractive index of the surrounding medium. The resonance peak of Au-Ni-Ag is red-shifted with the increase of gold core radius and only one resonance peak exists in the extinction spectrum,and the contribution of the Au core to LSPR is found to be suppressed,whereas the peak of Au-Si3N4-Ag is red-shifted with the increase of gold core ratio and refractive index of the surrounding medium and three resonance peaks exist in the spectrum,and the interlayer Si3N4 can enhance this contribution of LSPR. These phenomena were analyzed by using the distribution of electric field in and near nanoshells. By selecting the suitable geometric parameters,the fano resonance peaks of Au-interlayer-Ag multilayer nanoshells can be tuned between 600 and 1 200 nm.