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Anisotropic structural dynamics of monolayer crystals revealed by femtosecond surface X-ray scattering
Nature Photonics ( IF 32.3 ) Pub Date : 2019-03-11 , DOI: 10.1038/s41566-019-0387-5
I-Cheng Tung , Aravind Krishnamoorthy , Sridhar Sadasivam , Hua Zhou , Qi Zhang , Kyle L. Seyler , Genevieve Clark , Ehren M. Mannebach , Clara Nyby , Friederike Ernst , Diling Zhu , James M. Glownia , Michael E. Kozina , Sanghoon Song , Silke Nelson , Hiroyuki Kumazoe , Fuyuki Shimojo , Rajiv K. Kalia , Priya Vashishta , Pierre Darancet , Tony F. Heinz , Aiichiro Nakano , Xiaodong Xu , Aaron M. Lindenberg , Haidan Wen

Ultrafast X-ray scattering is one of the primary tools to track intrinsic crystallographic evolution with atomic accuracy in real time. However, its application to study nonequilibrium structural properties at the two-dimensional limit remains a long-standing challenge due to a significant reduction of diffraction volume and complexity of data analysis. Here, we report femtosecond surface X-ray diffraction in combination with crystallographic model-refinement calculations to quantify the ultrafast structural dynamics of monolayer WSe2 crystals supported on a substrate. We found the absorbed optical photon energy is preferably coupled to the in-plane lattice vibrations within one picosecond whereas the out-of-plane lattice vibration amplitude remains unchanged during the first ten picoseconds. The model-assisted fitting suggests an asymmetric intralayer spacing change upon excitation. The observed nonequilibrium anisotropic structural dynamics agrees with first-principles modelling in both real and momentum space, marking the distinct structural dynamics of monolayer crystals from their bulk counterparts.



中文翻译:

飞秒表面X射线散射揭示单层晶体的各向异性结构动力学

超快X射线散射是实时跟踪原子内在晶体演化的主要工具之一。然而,由于衍射体积的显着减少和数据分析的复杂性,其在二维极限条件下研究非平衡结构性质的应用仍然是一个长期的挑战。在这里,我们报告飞秒表面X射线衍射结合晶体学模型优化计算,以量化单层WSe 2的超快结构动力学支撑在基板上的晶体。我们发现吸收的光子能量最好在一皮秒内耦合到平面内晶格振动,而平面外晶格振动幅度在前十皮秒内保持不变。模型辅助拟合表明,激发后不对称的层内间距会发生变化。所观察到的非平衡各向异性结构动力学与真实原理和动量空间中的第一性原理模型相吻合,标志着单层晶体与它们的整体对应物截然不同的结构动力学。

更新日期:2019-03-12
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