Ag-Au二元纳米微粒吸收谱的计算

Calculation of absorption spectrum of silver-gold bimetallic nanoparticles

纳米微粒的光学性能与其表面等离子体共振关系密切.本文利用推广的Mie理论计算研究了Au-Ag体系单质、合金以及核壳结构纳米颗粒的消光、吸收和散射的性能(包括壳核结构Ag-Au微粒在紫外-可见光的吸收性能),计算结果与实验值相符合得很好.研究表明,随着粒径的增加,微粒表面等离子体共振偶极吸收峰出现红移,波峰位置与纳米微粒的尺寸具有线性关系.壳核结构中,粒径与核壳比决定了整个微粒的吸收性能.进一步研究表明,当Au壳层较薄时,可以获得具有可调光学性能的壳核纳米结构;而当Au壳层较厚时,其光学性能与同尺寸单质Au微粒一致.通过计算分析,本文还将Mie理论推广到具有空腔结构并且壳层厚度达到一定值的纳米微粒.另外,研究发现合金结构纳米微粒的吸收峰位置与合金成分有着线性关系.本研究表明,人们可以通过控制纳米微粒的尺寸、形貌和结构,调节其表面等离子体共振峰位,这大大拓展了纳米微粒的应用范围.

Optical properties of nanoparticles are related to their surface plasmon resonance. In this work, we use Mie theory to compute the extinction, absorption, and scattering properties of noble metal nanoparticles. The calculated results agree well with the experimental values. With increasing particle size, particle dipole absorption peak will be red-shifted; and the peak position and the size of the nanoparticles have a linear relationship. It is found that the ratio of core to shell size determines the absorption properties of spherical Au/Ag core/shell nanoparticles. When the Au shell is thin, the optical properties vary with the adjustable shell. When the Au shell is thick, its optical properties are similar to the pure Au nanoparticle. Through the calculation and analysis we made, the Mie theory can be generalized to nanocavity structures when the shell thickness reaches a certain value. Furthermore, it is found that the absorption peaks of alloy nanoparticles have a linear relationship with the alloy composition.