题    目：Ultrahigh Enhancement of Electromagnetic Fields by Exciting Localized Surface Plasmon with Propagating Surface Plasmon 
主讲人：李述周教授 
单    位：南洋理工大学材料科学与工程学院 
时    间：2017年10月25日10:00AM
地    点：纳米楼一楼报告厅
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附简介： 
    李述周，新加坡南洋理工大学材料科学与工程学院副教授。他在南开大学获得化学学士学位后，就读于北京大学化学与分子工程学院并且获得物理化学硕士学位。在威斯康星州麦迪逊大学时，他采用原子分子动力学模拟和第一性原理计算研究叠氮化物在水中光谱扩散和振动能量弛豫，并获得物理化学博士。加入南洋理工大学之前,他在西北大学做博士后,他通过各种计算电动力学方法研究了表面等离子体共振，采用理论和计算的方法探索纳米材料的光学性质。目前,他的研究将集中在三个方向: 纳米材料的自组装, 高灵敏度基质表面增强光谱学, 金属和半导体复合材料的光电性质。
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Abstract:
        Excitation of localized surface plasmons (LSPs) of metal nanoparticles (NPs) residing on a flat metal film has attracted great attentions recently due to the enhanced electromagnetic (EM) fields found to be higher than the case of NPs on a dielectric substrate. In the present work, it is shown that even much higher enhancement of EM fields is obtained by exciting the LSPs through extended surface plasmons (ESPs) generated at the metallic film surface using the Kretschmann-Raether configuration. We show that the largest EM field enhancement and the highest surface-enhanced fluorescence intensity are obtained when the incidence angle is the ESP resonance angle of the underlying metal film. The finite-difference time-domain simulations indicate that excitation of LSPs using ESPs can generate 1-3 orders higher EM field intensity than direct excitation of the LSPs using incidence from free space. The ultrahigh enhancement is attributed to the strong confinement of the ESP waves in the vertical direction. With this unique configuration, we also found that an array of particles shows a critical importance of the inter-particle gap on the enhancement factor, which was confirmed experimentally using surface-enhanced Raman scattering (SERS). A monomolecular layer of 4-Aminothiophenol sandwiched in between the silver film and the gold nanoparticles showed SERS enhancement factor of the order of 10¹⁰ per molecule in the hotspots. It is demonstrated that the ultra-high SERS enhancement does occur only when the ESP is coupled to the LSP at an optimized inter-particle gap. Further, highly sensitive detection of glycerol in ethanol is demonstrated using the optimum structure with detection limit of the order of 10^-12 to the weight percentage of ethanol, which is equivalent to a few molecules detection. This ultrahigh enhancement is useful in realizing various highly sensitive biosensors when strong enhancement is required as well as in highly efficient optoelectronic and energy devices.