Shibata Kizuku, Fujii Sho, Sun Quan, Miura Atsushi, Ueno Kosei
Department of Chemistry, Faculty of Science, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, Hokkaido 060-0810, Japan.
J Chem Phys. 2020 Mar 14;152(10):104706. doi: 10.1063/1.5142569.
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.
金属纳米间隙二聚体对于增强表面增强拉曼散射以及利用由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极为有用。然而，由于两个金属纳米结构之间强烈的偶极 - 偶极相互作用，金属纳米间隙二聚体表现出强烈的光散射，因此，由于辐射损耗，它们不一定是呈现最高近场增强的结构设计。在此，我们提出利用准暗等离子体模式进一步增强金属纳米间隙二聚体上的近场。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，诱导出一种略微降低辐射损耗的准暗等离子体模式，从而导致等离子体退相时间延长。结果，与使用没有金纳米棒的金纳米间隙二聚体所测得的相比，吸附在金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增强了约三倍。进行了散射光谱测量以及电磁模拟以阐明近场进一步增强的机制。所提出的耦合等离子体系统预计将具有优势，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。
