金纳米棒复合体的消光特性

金属纳米颗粒局域表面等离激元共振时能够产生消光和近场增强效应已经成为国内外研究的热点. 应用时域有限差分法对L形纳米棒与普通纳米棒构成的金纳米棒复合体的消光光谱及其近场增强和电流矢量密度分布进行了研究. 计算结果表明, 普通纳米棒和L形纳米棒二聚体的光谱响应与纳米棒间的间距有关, 而金纳米棒复合体的消光光谱可通过调整L形纳米棒与普通纳米棒间的间距、L形纳米棒的臂长度以及普通纳米棒的长度进行调谐. 此外金纳米棒复合体可以分解成L形纳米棒二聚体和普通纳米棒二聚体两个部分, 通过分别改变L形纳米棒的臂长和普通纳米棒的长度, 对比L形纳米棒二聚体和普通纳米棒二聚体间的共振峰位置变化, 可以更直观地了解金纳米棒复合体消光光谱线型的变化. 这些结果可用于指导金纳米棒复合体纳米光子器件的设计, 以满足其在表面增强拉曼散射和生物传感等方面应用.

Extinction properties of gold nanorod complexes

Plasmonics with subwavelength characteristics can break the diffraction limit of light and be used to produce the sub-wavelength optoelectronic device, thus it has aroused great interest for decades. Local surface plasmon resonance of metal nanoparticles has become one of the research hotspots due to the fact it can produce extinction and near-field enhancement effect. How to achieve controllable plasmon line shape and generate strong electromagnetic field enhancement is of great significance for improving the sensing performance, nonlinear effect and surface enhanced Raman factor of metallic nanostructures. The optical properties of plasmonic oligomer clusters composed of normal and L-shaped nanrod dimers are investigated by using the finite-difference time-domain method in this paper. There are two energy modes for an L-shaped nanorod due to its shaped anisotropy, where plasmons oscillate along the arms of the L-shaped nanorod or oscillate over the whole length of the L-shaped nanorod. Therefore, two bonding resonances appear in the spectrum of an L-shaped nanorod dimer, while only one bonding resonance exists for normal nanorod dimer. When a normal nanorod dimer and an L-shaped nanorod dimer are aligned together to form a quadrumer, the three bonding resonances can be excited simultaneously and radiative damping can be suppressed effectively around the dip spectral positions. It is shown that the optical responses of quadrumer can be strongly tuned by manipulating the geometry parameters. For example, the coupling between the two dimers can be modified by adjusting the separation, and the three resonances shift toward higher energies with the increasing of the separation. In addition, the optical responses of individual nanorod depend on the corresponding arm length. As a result, the three resonances of the quadrumer can also be well tuned by adjusting the arm length. Comparing the variation of resonance peak positions between L-shaped nanorod dimer and normal nanorod dimer, we can more intuitively understand spectral lineshape variation of quadrumer. These results can be used for guiding the design of nano-photonic devices for plasmonic oligomer clusters and also for developing the application of surface-enhanced Raman scattering and biological sensing.