Alexander Duncan T L, Flauraud Valentin, Demming-Janssen Frank
Electron Spectrometry and Microscopy Laboratory (LSME), Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland.
Microsystems Laboratory (LMIS1), Microengineering Institute (IMT), École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland.
ACS Nano. 2021 Oct 26;15(10):16501-16514. doi: 10.1021/acsnano.1c06065. Epub 2021 Sep 29.
Recently, there has been significant interest in using dielectric nanocavities for the controlled scattering of light, owing to the diverse electromagnetic modes that they support. For plasmonic systems, electron energy-loss spectroscopy (EELS) is now an established method enabling structure-optical property analysis at the scale of the nanostructure. Here, we instead test its potential for the near-field mapping of photonic eigenmodes supported in planar dielectric nanocavities, which are lithographically patterned from amorphous silicon according to standard photonic principles. By correlating results with finite element simulations, we demonstrate how many of the EELS excitations can be directly corresponded to various optical eigenmodes of interest for photonic engineering. The EELS maps present a high spatial definition, displaying intensity features that correlate precisely to the impact parameters giving the highest probability of modal excitation. Further, eigenmode characteristics translate into their EELS signatures, such as the spatially and energetically extended signal of the low -factor electric dipole and nodal intensity patterns emerging from excitation of toroidal and second-order magnetic modes within the nanocavity volumes. Overall, the spatial-spectral nature of the data, combined with our experimental-simulation toolbox, enables interpretation of subtle changes in the EELS response across a range of nanocavity dimensions and forms, with certain simulated resonances matching the excitation energies within ±0.01 eV. By connecting results to far-field simulations, perspectives are offered for tailoring the nanophotonic resonances manipulating nanocavity size and shape.
近年来，由于介电纳米腔能支持多种电磁模式，人们对利用其实现光的可控散射产生了浓厚兴趣。对于等离子体系统，电子能量损失谱（EELS）现已成为一种成熟的方法，能够在纳米结构尺度上进行结构 - 光学性质分析。在此，我们转而测试其对平面介电纳米腔中所支持的光子本征模进行近场映射的潜力，这些纳米腔是根据标准光子原理由非晶硅光刻图案化而成。通过将结果与有限元模拟相关联，我们展示了许多EELS激发如何能直接对应于光子工程中各种感兴趣的光学本征模。EELS图谱呈现出高空间分辨率，显示出与给出最高模态激发概率的碰撞参数精确相关的强度特征。此外，本征模特征转化为它们的EELS信号，例如低因子电偶极子在空间和能量上扩展的信号，以及纳米腔内体积中环形和二阶磁模激发产生的节点强度图案。总体而言，数据的空间光谱特性与我们的实验 - 模拟工具箱相结合，能够解释在一系列纳米腔尺寸和形式下EELS响应的细微变化，某些模拟共振与激发能量的匹配在±0.01 eV范围内。通过将结果与远场模拟相联系，为通过操纵纳米腔尺寸和形状来定制纳米光子共振提供了思路。
