基于金属双纳米棒结构表面等离子体光镊的理论和实验研究

The surface plasmons excited on the surfaces of metallic nano-structures under light illumination exhibit special properties like highly localized and enhanced optical field, which enables the feasibility of surface plasmon tweezers that provide nano-scale trapping volume essential for trapping nano-particles. Aiming to study on the present problems of surface plasmon tweezers such as the unclear theoretical mechanism and the difficulty of sample fabrication and testing, this project will perform comprehensive studies on surface plasmon tweezers in theory and experiment, respectively, based on the metallic dual-nanorod configurations. We will explore the influences of the geometrical and physical parameters of the metallic dual-nanorod configurations, the polarization state and strength of incident light, the refractive index distribution of surrounding media on the trapping efficiency of nano-particles. The physical mechanism of the surface plasmons coupling effect between the nano-tweezers and the trapped metallic nano-particles will be illustrated, and its effect on the trapping efficiency will be analyzed simultaneously. The interactive relationship between the Brownian motion, the heating effect of surface plasmons and the trapping force will be demonstrated in details. Considering all the conditions mentioned above, the optimized parameters for the nano-tweezer configuration will be obtained theoretically. Finally, the dual-nanorod configurations will be fabricated by using micro-/nano-fabrication technique based on the theoretical results and experiments based on the trapping of nano-particles will be performed . This project will not only provide a new way for nano-trapping technology, but also promote the connection and combination research among the fields of micro- and nano-photonics, computing science, and material science, which is significantly meaningful for academic and applications.

金属纳米结构在入射光作用下激发的表面等离子体具有高度局域化和场增强特性，其纳米级光阱空间可构成表面等离子体光镊来捕获纳米粒子。针对表面等离子体光镊目前存在的理论机制不清晰和样品制备及测量困难等若干问题，本项目以金属双纳米棒结构作为基本形式，对上述问题进行深入系统的理论和实验研究。探讨金属双纳米棒结构的几何、物理参数和入射光、周围介质等外部条件对纳米粒子捕获效率的影响；阐明纳米光镊光场与金属纳米粒子激发的表面等离子体之间耦合作用的物理机制及其对捕获效率的影响；揭示纳米粒子布朗运动、表面等离子体的热效应与光阱力之间的相互作用关系；综合考虑上述因素，通过优化设计获得合适的纳米光镊结构参数；根据理论优化结果利用微纳加工技术制备金属双纳米棒结构，进行捕获纳米粒子的实验研究。本项目不仅为纳米粒子捕获提供一条新的技术途径，也可促进微纳光子学、计算科学和材料学的交叉融合，具有重要的学术意义和应用价值。

本项目研究了单个金纳米棒与PVA薄膜掺杂的复合结构光学特性，首次提出并验证了双SPR波长匹配的荧光增强物理机制，获得最强的“激发-辐射”效率，最大增强因子达20倍。利用数值仿真计算双金纳米棒局域场增强特性，得出了双金纳米棒在长度为L=1000nm、直径a=100nm、间距为d=40nm条件下的优化尺寸参数，可作为表面等离子体纳米光镊结构。将双金纳米棒结构平放在玻璃基底上，以高数值孔径聚焦入射光场作用下的高度局域化的增强光场作为纳米光镊，计算对硅纳米粒子和金纳米粒子捕获的光阱力，结果表明双金纳米棒光镊在相同功率相同数值孔径聚焦激光入射下、对同样大小和材料的纳米粒子捕获时，可以使光阱力比常规光镊高1个数量级，能够有效捕获30nm-100nm之间的硅和金纳米粒子。用离子刻蚀法制备了双纳米棒结构样品，利用双光镊结构对金纳米棒进行捕获和定向排列，发现当白光的偏振方向和光阱的偏振方向平行时，被捕获金棒的散射光强最强，由此推测金纳米棒在光阱中的长轴指向与光阱的偏振方向一致。通过角谱变换的方法，得到了在Kretschmann棱镜结构中的艾利光束的表面等离激元波，并且系统分析了其产生的光镊力；系统分析了一些特殊的加速光束的金属纳米颗粒的表面等离激元激发谱。本项目研究结果可为金纳米棒在纳米光场操控、纳米粒子操控的应用奠定理论基础，双金纳米棒结构纳米光镊在材料科学、生命科学、纳米科学等方面具有广泛的应用前景，是一种重要的新型光子器件，对其继续进行深入研究还可以有更多新的发现，会在将来更多领域有新的应用。