We report on a combined far- and near-field study of surface plasmon polaritons on freestanding perforated gold films. The samples were fabricated by focused ion beam milling of a periodic hole array into a carbon membrane followed by thermal evaporation of gold and plasma ashing of the carbon film. Optical transmission spectra showed a series of characteristic features, which can be attributed to the excitation of surface plasmon modes via the periodic nanohole array. The corresponding near-field distributions were mapped by electron energy loss spectroscopy. In addition to the optically bright surface plasmon modes, we observed in the near-field a dark plasmon mode which is absent in the normal incidence far-field spectra. Our experimental results are in good agreement with numerical computations based on a discontinuous Galerkin time-domain method.

中文翻译：

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独立式穿孔金膜的电子能量损失谱

我们报告了独立的穿孔金膜上的表面等离激元极化子的远，近场组合研究。通过将周期性孔阵列的聚焦离子束铣削到碳膜中，然后热蒸发金和碳膜的等离子灰化，来制造样品。光学透射光谱显示出一系列特征，这可以归因于通过周期性纳米孔阵列对表面等离子体激元模式的激发。相应的近场分布通过电子能量损失谱图绘制。除了光学上明亮的表面等离子体激元模式，我们还在近场中观察到了垂直入射远场光谱中不存在的黑暗等离子体激元模式。