提出了一种在银层上面覆盖一层金的四棱台复合纳米结构。采用离散偶极子近似(DDA)方法,针对光激发复合金属纳米粒子的局域表面等离子体共振(LSPR)进行研究,讨论了四棱台纳米粒子金银复合结构在不同尺寸、不同混合比等条件下的消光特性及折射率灵敏度。计算结果显示,在银层厚度为50 nm的四棱台纳米粒子上覆盖金层,其折射率灵敏度不变。同时,四棱台银纳米粒子厚度的增加会使其消光峰值波长蓝移。金材料比例的增加会使金银复合纳米结构的消光峰值波长红移。当金银复合结构的纳米粒子的厚度大于自由电子的平均自由程时,其局域表面等离子体激发强度不发生变化。

A type of quadrangular frustum pyramid composition nanostructure with silver in bottom layer and gold in top layer is investigated. Based on discrete dipole approximation,localized surface plasmon resonances of metal composition nanoparticles induced by optical excitation is investigated. A detail discussion is given on the extinction properties and the refractive index sensitivity of quadrangular frustum pyramid nanoparticles in different sizes,metal composition ratios and so on. The result of calculation shows that the refractive index sensitivities of quadrangular frustum pyramid composition nanoparticles with sliver layer in 50 nm thickness keep the same value as increasing the thickness of gold layer. It is also observed that the peak wavelength blue shifts as increasing the thickness of quadrangular frustum pyramid nanoparticles and red shifts as increasing the Ag concentration in the composition nanoparticles with the same shape. Especially,if the thickness of quadrangular frustum pyramid nanoparticles with structure of gold adding to silver is more than the mean free path of conduction electrons,the excitation intensity of localized surface plasmon resonances won′t change any more with increasing the thickness of added gold.