Imaging of Plasmonic Eigen Modes in Gold Triangular Mesoplates by Near-Field Optical Microscopy
Imaging of Plasmonic Eigen Modes in Gold Triangular Mesoplates by Near-Field Optical Microscopy
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DOI：
10.1021/acs.jpcc.8b00678
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发表时间：
2018-04-05
影响因子：
3.7
通讯作者：
Imura, Kohei
中科院分区：
文献类型：
--
作者：
Imaeda, Keisuke;Hasegawa, Seiju;Imura, Kohei
利用孔径型扫描近场光学显微镜研究了化学合成三角形金纳米和微孔板中等离子体激元的光谱和空间特征。在等离子体共振波长下拍摄的近场透射图像显示了平板内部的二维振荡模式。这些空间特征可以通过局限于二维三角形势阱的计算本征函数的平方模很好地再现。从特征函数的不可约表示中，发现在近场图像中可以清晰地显示出面外模式和面内模式。我们将三角形纳米片的近场透射图像与相似尺寸的截断纳米片的近场透射图像进行了比较，发现纳米片顶点几何形状的精细细节对实验观察到的本征模结构有很大影响。我们还进行了微米尺度三角形板的近场透射测量，发现沿板的边缘观察到波浪图案。波状特征可以解释为具有相似特征能量的本征模式的叠加。这些发现证明，近场透射成像可以直接看到被限制在粒子中的等离子体本征模式，不仅为更深入地了解等离子体，而且为等离子体光场的设计和主动控制的应用提供了丰富的信息。
We investigated the spectral and spatial characteristics of plasmons induced in chemically synthesized triangular gold nano- and microplates by aperture-type scanning near field optical microscopy. Near-field transmission images taken at plasmon resonance wavelengths showed two-dimensional oscillating patterns inside the plates. These spatial features were well reproduced by the square moduli of calculated eigen functions confined in the two-dimensional triangular potential well. From the irreducible representations of the eigen functions, it was found that both the out-of-plane modes and in-plane modes were clearly visualized in the near-field images. We compared near-field transmission images of a triangular nanoplate to those of a truncated one with a similar dimension and revealed that the fine details of the geometrical shape of the apex on the plate strongly influence the experimentally observed eigen mode structures. We also performed near-field transmission measurements of micrometer-scale triangular plates and found that wavy patterns were observed along the edges of the plates. The wavy features can be interpreted as the superposition of eigen modes with similar eigen energy. These findings prove that near-field transmission imaging enables one to directly visualize plasmonic eigen modes confined in the particle and provide fruitful information not only for a deeper understanding of plasmons but also for the application of the design and active control of plasmonic optical fields.