Ultrafast Kikuchi Diffraction: Nanoscale Stress鈥揝train Dynamics of Wave-Guiding Structures
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- 作者：Aycan Yurtsever ; Sascha Schaefer ; Ahmed H. Zewail
- 刊名：Nano Letters
- 出版年：2012
- 出版时间：July 11, 2012
- 年：2012
- 卷：12
- 期：7
- 页码：3772-3777
- 全文大小：520K
- 年卷期：v.12,no.7(July 11, 2012)
- ISSN：1530-6992
文摘
Complex structural dynamics at the nanoscale requires sufficiently small probes to be visualized. In conventional imaging using electron microscopy, the dimension of the probe is large enough to cause averaging over the structures present. However, by converging ultrafast electron bunches, it is possible to select a single nanoscale structure and study the dynamics, either in the image or using electron diffraction. Moreover, the span of incident wave vectors in a convergent beam enables sensitivity levels and information contents beyond those of parallel-beam illumination with a single wave vector Bragg diffraction. Here, we report the observation of propagating strain waves using ultrafast Kikuchi diffraction from nanoscale volumes within a wedge-shaped silicon single crystal. It is found that the heterogeneity of the strain in the lateral direction is only 100 nm. The transient elastic wave gives rise to a coherent oscillation with a period of 30 ps and with an envelope that has a width of 140 ps. The origin of this elastic deformation is theoretically examined using finite element analysis; it is identified as propagating shear waves. The wedge-shaped structure, unlike parallel-plate structure, is the key behind the traveling nature of the waves as its angle permits 鈥渢ransverse鈥?propagation; the parallel-plate structure only exhibits the 鈥渓ongitudinal鈥?motion. The studies reported suggest extension to a range of applications for nanostructures of different shapes and for exploring their ultrafast eigen-modes of stress鈥搒train profiles.