Ultrafast Three-Dimensional X-ray Imaging of Deformation Modes in ZnO Nanocrystals
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- 作者：Mathew J. Cherukara ; Kiran Sasikumar ; Wonsuk Cha ; Badri Narayanan ; Steven J. Leake ; Eric M. Dufresne ; Tom Peterka ; Ian McNulty ; Haidan Wen ; Subramanian K. R. S. SankaranarayananRoss J. Harder
- 刊名：Nano Letters
- 出版年：2017
- 出版时间：February 8, 2017
- 年：2017
- 卷：17
- 期：2
- 页码：1102-1108
- 全文大小：462K
- ISSN：1530-6992
文摘
Imaging the dynamical response of materials following ultrafast excitation can reveal energy transduction mechanisms and their dissipation pathways, as well as material stability under conditions far from equilibrium. Such dynamical behavior is challenging to characterize, especially operando at nanoscopic spatiotemporal scales. In this letter, we use X-ray coherent diffractive imaging to show that ultrafast laser excitation of a ZnO nanocrystal induces a rich set of deformation dynamics including characteristic “hard” or inhomogeneous and “soft” or homogeneous modes at different time scales, corresponding respectively to the propagation of acoustic phonons and resonant oscillation of the crystal. By integrating the 3D nanocrystal structure obtained from the ultrafast X-ray measurements with a continuum thermo-electro-mechanical finite element model, we elucidate the deformation mechanisms following laser excitation, in particular, a torsional mode that generates a 50% greater electric potential gradient than that resulting from the flexural mode. Understanding of the time-dependence of these mechanisms on ultrafast scales has significant implications for development of new materials for nanoscale power generation.