Department of Chemistry, ‡Department of Physics and Astronomy, and §Department of Electrical and Computer Engineering, Laboratory for Nanophotonics, Rice University , Houston, Texas 77005, United States.
ACS Nano. 2014 Jan 28;8(1):572-80. doi: 10.1021/nn405183r. Epub 2013 Dec 10.
We investigated the effects of cross sectional geometry on surface plasmon polariton propagation in gold nanowires (NWs) using bleach-imaged plasmon propagation and electromagnetic simulations. Chemically synthesized NWs have pentagonally twinned crystal structures, but recent advances in synthesis have made it possible to amplify this pentagonal shape to yield NWs with a five-pointed-star cross section and sharp end tips. We found experimentally that NWs with a five-pointed-star cross section, referred to as SNWs, had a shorter propagation length for surface plasmon polaritons at 785 nm, but a higher effective incoupling efficiency compared to smooth NWs with a pentagonal cross section, labeled as PNWs. Electromagnetic simulations revealed that the electric fields were localized at the sharp ridges of the SNWs, leading to higher absorptive losses and hence shorter propagation lengths compared to PNWs. On the other hand, scattering losses were found to be relatively uncorrelated with cross sectional geometry, but were strongly dependent on the plasmon mode excited. Our results provide insight into the shape-dependent waveguiding properties of chemically synthesized metal NWs and the mode-dependent loss mechanisms that govern surface plasmon polariton propagation.
我们使用漂白成像等离子体传播和电磁模拟研究了金纳米线（NWs）中横截面几何形状对表面等离激元传播的影响。化学合成的 NW 具有五重孪晶结构，但最近的合成进展使得能够放大这种五角形状，从而产生具有五角星形横截面和尖锐端的 NW。我们实验发现，具有五角星形横截面的 NW（称为 SNWs）在 785nm 处的表面等离激元传播长度更短，但与具有五重边形横截面的光滑 NW（标记为 PNWs）相比，有效耦合效率更高。电磁模拟表明，电场被局限在 SNWs 的尖锐脊处，导致与 PNWs 相比，更高的吸收损耗，从而导致更短的传播长度。另一方面，发现散射损耗与横截面几何形状没有明显相关性，但与激发的等离子体模式密切相关。我们的研究结果为化学合成金属 NW 的形状依赖性导波特性和控制表面等离激元传播的模式相关损耗机制提供了深入的了解。
