Institute of Physics, University of Graz, Universitätsplatz 5, 8010, Graz, Austria.
Graz Centre for Electron Microscopy, Steyrergasse 17, 8010, Graz, Austria.
Nat Commun. 2017 Jun 26;8(1):37. doi: 10.1038/s41467-017-00051-3.
The photonic local density of states (LDOS) governs the enhancement of light-matter interaction at the nanoscale, but despite its importance for nanophotonics and plasmonics experimental local density of states imaging remains extremely challenging. Here we introduce a tomography scheme based on electron microscopy that allows retrieval of the three-dimensional local density of states of plasmonic nanoparticles with nanometre spatial and sub-eV energy resolution. From conventional electron tomography experiments we obtain the three-dimensional morphology of the nanostructure, and use this information to compute an expansion basis for the photonic environment. The expansion coefficients are obtained through solution of an inverse problem using as input electron-energy loss spectroscopy images. We demonstrate the applicability of our scheme for silver nanocuboids and coupled nanodisks, and resolve local density of states enhancements with extreme sub-wavelength dimensions in hot spots located at roughness features or in gaps of coupled nanoparticles.Imaging the photonic local density of states of plasmonic nanoparticles remains extremely challenging. Here, the authors introduce a tomography scheme based on electron microscopy that allows retrieval of the three-dimensional local density of states with nanometre spatial and sub-eV energy resolution.
光子局域态密度（LDOS）控制着纳米尺度上光物质相互作用的增强，但尽管它对纳米光子学和等离子体学很重要，实验上的局域态密度成像仍然极具挑战性。在这里，我们引入了一种基于电子显微镜的层析成像方案，该方案允许以纳米级空间和亚电子伏特能量分辨率来获取等离子体纳米粒子的三维局域态密度。从传统的电子层析成像实验中，我们获得了纳米结构的三维形态，并利用该信息计算光子环境的展开基。通过使用电子能量损失谱图像作为输入来解决逆问题，获得了展开系数。我们展示了我们的方案在银纳米立方体和耦合纳米盘上的适用性，并在位于粗糙度特征或耦合纳米粒子间隙处的热点中解析出具有极端亚波长尺寸的局域态密度增强。对等离子体纳米粒子的光子局域态密度进行成像仍然极具挑战性。在这里，作者引入了一种基于电子显微镜的层析成像方案，该方案允许以纳米级空间和亚电子伏特能量分辨率来获取三维局域态密度。
