Fujiyoshi Yoshifumi, Nemoto Takashi, Kurata Hiroki
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
Ultramicroscopy. 2017 Apr;175:116-120. doi: 10.1016/j.ultramic.2017.01.006. Epub 2017 Jan 18.
In this study, electron energy-loss spectroscopy (EELS) in conjunction with scanning transmission electron microscopy (STEM) was used to investigate surface plasmons in a single silver nanoparticle (NP) on a magnesium oxide substrate, employing an incident electron trajectory parallel to the substrate surface. This parallel irradiation allowed a direct exploration of the substrate effects on localized surface plasmon (LSP) excitations as a function of the distance from the substrate. The presence of the substrate was found to lower the symmetry of the system, such that the resonance energies of LSPs were dependent on the polarization direction relative to the substrate surface. The resulting mode splitting could be detected by applying different electron trajectories, providing results similar to those previously obtained from optical studies using polarized light. However, the LSP maps obtained by STEM-EELS analysis show an asymmetric intensity distribution with the highest intensity at the top surface of the NP (that is, far from the substrate), a result that is not predicted by optical simulations. We show that modifications of the applied electric field by the substrate cause this asymmetric intensity distribution in the LSP maps.
在本研究中，电子能量损失谱（EELS）与扫描透射电子显微镜（STEM）相结合，用于研究氧化镁衬底上单个银纳米颗粒（NP）中的表面等离子体激元，采用平行于衬底表面的入射电子轨迹。这种平行照射使得能够直接探究衬底对局域表面等离子体激元（LSP）激发的影响，该影响是作为与衬底距离的函数。发现衬底的存在降低了系统的对称性，使得LSP的共振能量取决于相对于衬底表面的极化方向。通过应用不同的电子轨迹可以检测到由此产生的模式分裂，其提供的结果与先前使用偏振光的光学研究获得的结果相似。然而，通过STEM-EELS分析获得的LSP图显示出不对称的强度分布，在NP的顶面（即远离衬底处）强度最高，这一结果是光学模拟所无法预测的。我们表明，衬底对施加电场的修改导致了LSP图中的这种不对称强度分布。
