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arXiv 1702.00359cond-mat.mtrl-scicond-mat.mes-hall
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少层MoS2中激子和等离子体激元的局域性质

Probing the local nature of excitons and plasmons in few-layer MoS2

Hannah Catherine Nerl, Kirsten Trøstrup Winther, Fredrik Sydow Hage, Kristian Sommer Thygesen, Lothar Houben, Claudia Backes, Jonathan N Coleman, Quentin M Rama… 展开作者

Hannah Catherine Nerl, Kirsten Trøstrup Winther, Fredrik Sydow Hage, Kristian Sommer Thygesen, Lothar Houben, Claudia Backes, Jonathan N Coleman, Quentin M Ramasse, Valeria Nicolosi

摘要:

激子和等离子体激元是发生在固体中的两种最基本的集体电子激发。传统上,他们已经分别研究使用散装技术,探测其平均能量结构在大的空间区域。然而,随着材料和器件尺寸的不断缩小,理解这些激发如何依赖于原子尺度上晶体和化学结构的局部变化变得至关重要。在这里,我们使用单色低损耗扫描透射电子显微镜电子能量损耗(LL-STEM-EEL)光谱,提供迄今为止实现的最佳同时能量和空间分辨率,以在宽能量范围内解开几层MoS 2纳米片中的全套电子激发。使用第一性原理多体计算,我们确认的激子性质的峰在~ 2 eV和~3eV的实验EEL光谱和较高的能量损失峰的等离子体性质。我们还合理化的非平凡的依赖性的EEL光谱的光束和样品的几何形状,如原子层的数量和距离的步骤和边缘。此外,我们表明,激子功能占主导地位的长波长(q=0)的探测场的组件,而等离子体功能是敏感的更广泛的范围内的q矢量,表明定性差异的空间特征的两种类型的集体激发。我们的工作提供了一个模板协议,用于映射电子激发的局部性质,为研究纳米尺度上的光吸收和能量转移过程开辟了新的可能性。

英文摘要:

Excitons and plasmons are the two most fundamental types of collective electronic excitations occurring in solids. Traditionally, they have been studied separately using bulk techniques that probe their average energetic structure over large spatial regions. However, as the dimensions of materials and devices continue to shrink, it becomes crucial to understand how these excitations depend on local variations in the crystal- and chemical structure on the atomic scale. Here we use monochromated low-loss scanning-transmission-electron-microscopy electron-energy-loss (LL-STEM-EEL) spectroscopy, providing the best simultaneous energy and spatial resolution achieved to-date to unravel the full set of electronic excitations in few-layer MoS2 nanosheets over a wide energy range. Using first-principles many-body calculations we confirm the excitonic nature of the peaks at ~2eV and ~3eV in the experimental EEL spectrum and the plasmonic nature of higher energy-loss peaks. We also rationalise the non-trivial dependence of the EEL spectrum on beam and sample geometry such as the number of atomic layers and distance to steps and edges. Moreover, we show that the excitonic features are dominated by the long wavelength (q=0) components of the probing field, while the plasmonic features are sensitive to a much broader range of q-vectors, indicating a qualitative difference in the spatial character of the two types of collective excitations. Our work provides a template protocol for mapping the local nature of electronic excitations that open new possibilities for studying photo-absorption and energy transfer processes on a nanometer scale.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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