Horák Michal, Konečná Andrea, Šikola Tomáš, Křápek Vlastimil
Central European Institute of Technology, Brno University of Technology, Purkyňova 123, 612 00 Brno, Czech Republic.
Institute of Physical Engineering, Brno University of Technology, Technická 2, 616 69 Brno, Czech Republic.
Nanophotonics. 2023 Jun 19;12(15):3089-3098. doi: 10.1515/nanoph-2023-0153. eCollection 2023 Jul.
Electron energy loss spectroscopy (EELS) is often utilized to characterize localized surface plasmon modes supported by plasmonic antennas. However, the spectral resolution of this technique is only mediocre, and it can be rather difficult to resolve modes close in the energy, such as coupled modes of dimer antennas. Here, we address this issue for a case study of the dimer plasmonic antenna composed of two gold discs. We analyze four nearly degenerate coupled plasmon modes of the dimer: longitudinal and transverse bonding and antibonding dipole modes. With a traditional approach, which takes into account the spectral response of the antennas recorded at specific points, the modes cannot be experimentally identified with EELS. Therefore, we employ the spectral and spatial sensitivity of EELS simultaneously. We propose several metrics that can be utilized to resolve the modes. First, we utilize electrodynamic simulations to verify that the metrics indeed represent the spectral positions of the plasmon modes. Next, we apply the metrics to experimental data, demonstrating their ability to resolve three of the above-mentioned modes (with transverse bonding and antibonding modes still unresolved), identify them unequivocally, and determine their energies. In this respect, the spatio-spectral metrics increase the information extracted from electron energy loss spectroscopy applied to plasmonic antennas.
电子能量损失谱（EELS）常用于表征等离子体天线所支持的局域表面等离子体模式。然而，该技术的光谱分辨率仅属中等，要分辨能量相近的模式相当困难，比如二聚体天线的耦合模式。在此，我们针对由两个金盘组成的二聚体等离子体天线的案例研究来解决这个问题。我们分析了二聚体的四种近乎简并的耦合等离子体模式：纵向和横向的成键与反键偶极子模式。采用传统方法，即考虑在特定点记录的天线光谱响应，这些模式无法通过EELS进行实验识别。因此，我们同时利用EELS的光谱和空间灵敏度。我们提出了几种可用于分辨这些模式的指标。首先，我们利用电动力学模拟来验证这些指标确实代表了等离子体模式的光谱位置。接下来，我们将这些指标应用于实验数据，证明它们能够分辨上述三种模式（横向成键和反键模式仍未分辨），明确识别它们，并确定其能量。在这方面，空间光谱指标增加了从应用于等离子体天线的电子能量损失谱中提取的信息。
