金纳米球-银纳米线耦合结构量子点荧光自发辐射增强及表面等离激元传导

Enhancement of Spontaneous Emission and Surface Plasmon Polariton Propagation of Quantum Dots Fluorescence in a Coupling Structure of Gold Nanosphere and Sliver Nanowire

利用原子力显微镜(AFM)、荧光显微成像系统以及时间分辨单光子计数(TCSPC)系统,对金纳米球(AuNS)-银纳米线(AgNW)耦合结构纳米间隙内的量子点荧光自发辐射增强以及表面等离激元(SPP)传导特性进行研究。实验使用两种方式实现了金纳米球和银纳米线间的耦合。第一种方式为:将金纳米球和量子点的混合溶液及银纳米线溶液依次涂覆到SiO2基片上,寻找随机存在的金纳米球-银纳米线耦合结构。第二种方式为:利用AFM进行纳米操纵,在SiO2基片上实现了可控的金纳米球和银纳米线耦合结构。利用该结构,实现了最高达到611的量子点自发辐射速率增强因子,同时也观测到了被增强的荧光激发SPP沿银纳米线传导。利用COMSOL Multiphysics仿真软件,对金纳米球-银纳米线耦合结构附近不同位置和偏振的量子点自发辐射速率增强因子进行了模拟计算,并且和单个金纳米球、单根银纳米线附近量子点自发辐射速率增强因子进行了对比,结果表明金纳米球-银纳米线耦合结构能够获得更高的自发辐射速率增强因子。计算了量子点激发的银纳米线上SPP的场分布,得到了与实验相符的结果。

Based on the atomic force microscope (AFM), the fluorescence microscopic imaging system and the time-correlated single photon counting (TCSPC) system, the spontaneous emission enhancement of quantum dots and the fluorescence surface plasmon polariton (SPP) propagation are studied in a coupling structure of a gold nano-sphere (AuNS) and a sliver nano-wire (AgNW). The coupling between the AuNS and the AgNW is achieved in two ways. Firstly, a mixed solution of AuNSs and quantum dots, and the solution of AgNWs are successively coated on a SiO2 substrate to look for the AuNS-AgNW coupling structures that are randomly formed. Secondly, a controlled AuNS-AgNW coupling structure is achieved by using the AFM nano-manipulation. Based on the AuNS-AgNW coupling structure with quantum dots in its nano-gap, the experimental results show that the enhancement factor of the spontaneous emission rate of the quantum dots fluorescence can be up to 611 and the propagation of the fluorescence SPP along the AgNW is also observed. COMSOL Multiphysics software is used to simulate the enhancement factor of the spontaneous emission rate of a quantum dot with different positions and polarizations near the AuNS-AgNW coupling structure. The results are compared with those of a quantum dot coupled with single AuNS and single AgNW, showing that the AuNS-AgNW coupling structure can provide a higher enhancement factor of the spontaneous emission rate. The propagation of the SPP along the AgNW excited by the point source is also calculated. The simulation results agree well with the experimental results.