AI 中文总结
该研究利用特定设备分析单晶CaNb2O6的多电子激发和带间跃迁，在低损失区域观察到多种等离子体激元和混合体，通过多种装置和方法成像并分析相关特性，发现[NbO6]八面体的作用，证明Cs-STEM-EELS可用于可视化复杂晶体纳米结构特性。
AI 中文摘要
尽管过去二十年电子光学和光谱仪设计取得了进展，但由于非弹性电子散射的离域性，原子分辨率价电子能量损失光谱成像仍具有挑战性。本研究使用配备混合像素直接电子探测器和球差校正扫描透射电子显微镜的能量过滤光谱仪，分析单晶铌酸钙CaNb2O6中多电子激发和带间跃迁，空间分辨率从纳米到原子尺度。在约3.8 eV带隙以上的低损失区域，观察到体积等离子体激元、约6 eV和15 eV能量损失处的情况，以及约7.3 eV能量损失处的强相关等离子体激元和激子混合体（plexcitons）。还采用轴上电子能量损失谱装置进行原子分辨率零损失峰成像，可视化了plexcitons和VPs的能量和原子分辨图像，其显示出与高角度环形暗场图像相反的对比度。为研究弹性对比度保留，分析了收集角度的影响并将其影响最小化以产生离域VP图像。使用弱束装置获得的ZLP和VEELS图像表明，两种情况下对比度都类似于Z对比度。此外，发现[NbO6]八面体直接对3.2 eV至3.5 eV能量损失范围内的带间跃迁横向图有贡献。这些发现表明，检查与低能量损失相关的原子尺度对比度的Cs-STEM-EELS可成为可视化复杂晶体纳米结构的结构、键合和电子性质的有力工具，包括单个原子位点、间隙位点和点缺陷。
英文摘要
Despite advancements in electron optics and spectrometer design over the past twenty years, atomic-resolution valence-electron energy-loss spectroscopy imaging remains challenging due to the delocalization of inelastic electron scattering. In this study, we used an energy-filtered spectrometer equipped with a hybrid-pixel direct electron detector and spherical aberration-corrected scanning transmission electron microscopy to analyze many-electron excitations and interband transitions in a single-crystal calcium niobate, CaNb2O6, with spatial resolution ranging from the nanometers to the atomic scale. In the low-loss region above the bandgap at about 3.8 eV, we observed volume plasmons, around 6 eV and 15 eV energy loss, as well as a mix of strongly correlated plasmons and excitons, known as plexcitons, at approximately 7.3 eV energy loss. Additionally, we employed an on-axis EELS setup for atomic-resolution zero-loss peak (ZLP) imaging and visualized energy- and atom-resolved images of plexcitons and VPs, which showed contrast reversal relative to high-angle annular dark-field images. To investigate elastic contrast preservation, we also analyzed the effect of the collection angle and minimized its influence to produce delocalized VP images. In fact, the ZLP and VEELS images obtained using the weak-beam setup demonstrate that, in both cases, the contrast resembles Z-contrast. Moreover, we found that [NbO6] octahedra directly contributed to the lateral maps of interband transitions in the range from 3.2 eV to 3.5 eV energy loss. These findings demonstrate that Cs-STEM-EELS, which examines atomic-scale contrast associated with low-energy losses, can be a powerful tool for visualizing the structure, bonding, and electronic properties of complex crystalline nanostructures, including individual atomic sites, interstitial sites, and point defects.
Comments30 pages, 7 figures
