Optical Properties of Chiral Plasmonic Tetramers: Circular Dichroism and Multipole Effects
Optical Properties of Chiral Plasmonic Tetramers: Circular Dichroism and Multipole Effects
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DOI：
10.1021/jp404987v
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发表时间：
2013-07-18
影响因子：
3.7
通讯作者：
Govorov, Alexander O.
中科院分区：
文献类型：
--
作者：
Fan, Zhiyuan;Zhang, Hui;Govorov, Alexander O.
手性金属纳米粒子组装在可见光区表现出等离子体圆二色谱(CD)。以往的研究发现，在手性组装中，纳米粒子之间的偶极相互作用可以诱导圆二色信号。为了增强等离子体圆二色响应，可以利用纳米结构的多极效应和各向异性。用相互作用点-偶极方法和基于离散偶极近似(DDA)的纯数值方法计算了几种纳米粒子(NP)组装体的等离子体二向色性。我们发现，由DDA计算揭示的多极效应对于描述和理解紧密堆积组件的CD响应是至关重要的。手性等边四面体4-NP络合物特别有趣，因为它们对CD信号没有偶极贡献。因此，等边四面体4-NP络合物的CD信号完全来源于多极相互作用。CD信号的强度随着颗粒-颗粒距离的增大而迅速减弱，螺旋结构为1/R-9.7，正四面体4-NP络合物为1/R-18.1，其中R为颗粒-颗粒距离。结果表明，与消光光谱相比，CD光谱对等离子体络合物的几何形状更为敏感。几何形状的微小变化可能会导致CD响应的大变化。这项研究可用于设计用于光学和传感器应用的强镉纳米结构。
Chiral metal nanoparticle assemblies exhibit plasmonic circular dichroism (CD) in the visible spectral interval. It was found previously that the circular dichroism signals can be induced by dipolar interactions between nanoparticles in a chiral assembly. In order to enhance plasmonic circular dichroism response, one can take advantage of multipole effects and anisotropy of nanostructures. We calculate the plasmonic circular dichroism of several nanoparticle (NP) assemblies using the interacting point-dipole approach and the purely numerical method based on the discrete dipole approximation (DDA). We found that the multipole effects revealed by the DDA calculations are crucial to describe and understand CD responses of tightly packed assemblies. The chiral equilateral tetrahedral 4-NP complexes are especially interesting because they do not have the dipolar contribution to the CD signal. Therefore, CD signals of equilateral tetrahedral 4-NP complexes originate solely from the multipole interactions. The strength of CD signals rapidly decreases with the particle-particle distance as 1/R-9.7 for the helices and as 1/R-18.1 for the equilateral tetrahedral 4-NP complexes, where R is a particle-particle distance. We show that the CD spectra are much more sensitive to the geometry of a plasmonic complex compared to the extinction spectra. Small variations in geometry can result in large changes in CD responses. This study can be used to design nanostructures with strong CD for optical and sensor applications.