Visualizing optically-induced strains by five-dimensional ultrafast electron microscopy
Visualizing optically-induced strains by five-dimensional ultrafast electron microscopy
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DOI：
10.1039/d2fd00062h
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发表时间：
2022-06-05
影响因子：
3.4
通讯作者：
Ishizaka, K.
中科院分区：
文献类型：
--
作者：
Nakamura, A.;Shimojima, T.;Ishizaka, K.
应变的超快光学控制对于纳米声学器件的未来发展至关重要。虽然超快电子显微镜在GHz频率区域的应变动力学可视化中发挥了重要作用，但具有nm x ps时空分辨率的定量应变评估仍然具有挑战性。五维扫描透射电子显微镜（5D-STEM）是一种强大的技术，其测量电子束在真实的空间中的相应二维样品位置处的时间依赖性衍射或偏转。在本文中，我们表明，会聚束电子衍射（CBED）测量使用5D-STEM能够定量的时间依赖性应变映射在nm × ps尺度。我们观察到的产生和传播的声波在纳米制造的硅薄板的厚度为100 nm。通过CBED分析，定量地确定了在硅片中传播的声波的偏振态和振幅。进一步的傅立叶变换分析揭示了动量-频率空间中的应变分布，从而给出了沿板沿着任意方向的频散关系。5D-STEM-CBED分析的多功能性使得即使在复杂的纳米制造样品中也能够进行定量应变映射，如本研究所示。
Ultrafast optical control of strain is crucial for the future development of nanometric acoustic devices. Although ultrafast electron microscopy has played an important role in the visualization of strain dynamics in the GHz frequency region, quantitative strain evaluation with nm x ps spatio-temporal resolution is still challenging. Five-dimensional scanning transmission electron microscopy (5D-STEM) is a powerful technique that measures time-dependent diffraction or deflection of the electron beam at the respective two-dimensional sample positions in real space. In this paper, we demonstrate that convergent beam electron diffraction (CBED) measurements using 5D-STEM are capable of quantitative time-dependent strain mapping in the nm x ps scale. We observe the generation and propagation of acoustic waves in a nanofabricated silicon thin plate of 100 nm thickness. The polarization and amplitude of the acoustic waves propagating in the silicon plate are quantitatively determined from the CBED analysis. Further Fourier-transformation analysis reveals the strain distribution in the momentum-frequency space, which gives the dispersion relation in arbitrary directions along the plate. Versatility of 5D-STEM-CBED analysis enables quantitative strain mapping even in complex nanofabricated samples, as demonstrated in this study.