Further enhancement of the near-field on Au nanogap dimers using quasi-dark plasmon modes
Further enhancement of the near-field on Au nanogap dimers using quasi-dark plasmon modes
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DOI：
10.1063/1.5142569
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发表时间：
2020-03-14
影响因子：
4.4
通讯作者：
Ueno, Kosei
中科院分区：
文献类型：
--
作者：
Shibata, Kizuku;Fujii, Sho;Ueno, Kosei
金属纳米间隙二聚体在增强表面增强拉曼散射和利用局域表面等离子体共振引起的近场增强效应的各种非线性光学效应方面非常有用。然而，由于两个金属纳米结构之间强烈的偶极子-偶极子相互作用，金属纳米间隙二聚体表现出强烈的光散射，因此，由于辐射损失，不一定是一种表现出最高近场增强的结构设计。本文提出利用准暗等离激元模式进一步增强金属纳米间隙二聚体的近场。通过与具有相同等离子体共振波长但尺寸完全不同的金（Au）纳米棒耦合，诱导出一种准暗等离子体模式，略微降低了辐射损失，从而延长了等离子体脱相时间。结果表明，吸附在Au纳米间隙二聚体上的结晶紫分子的表面增强拉曼散射信号比使用没有Au纳米棒的Au纳米间隙二聚体测量的信号增强了约三倍。通过散射光谱测量和电磁模拟来阐明进一步增强近场的机理。所提出的耦合等离子体系统有望具有优势，特别是在利用等离子体增强效应增强非线性光学效应方面。
Metallic nanogap dimers are extremely useful for enhancing surface-enhanced Raman scattering and various nonlinear optical effects employing near-field enhancement effects induced by the localized surface plasmon resonance. However, the metallic nanogap dimers exhibit an intense light scattering due to the strong dipole-dipole interaction between two metallic nanostructures and, therefore, are not necessarily a structural design that exhibits the highest near-field enhancement due to the radiation loss. Here, we propose further enhancement of the near-field on metallic nanogap dimers using quasi-dark plasmon modes. By coupling with gold (Au) nanorods having the same plasmon resonant wavelength, but completely different sizes, a quasi-dark plasmon mode, which reduces the radiation loss slightly, is induced, resulting in the elongation of the plasmon dephasing time. As a result, the signal of surface-enhanced Raman scattering of crystal violet molecules adsorbed on the Au nanogap dimer is enhanced up to about three times as compared to that measured using the Au nanogap dimer without the Au nanorods. Scattering spectrum measurements as well as electromagnetic simulations were performed to clarify the mechanism for further enhancement of the near-field. The proposed coupled plasmonic system is expected to be advantageous, especially in enhancing nonlinear optical effects using plasmonic enhancement effects.