Department of Materials Science and Engineering, Stanford University , Stanford, California 94305, United States.
SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
Nano Lett. 2015 Oct 14;15(10):6889-95. doi: 10.1021/acs.nanolett.5b02805. Epub 2015 Sep 8.
Two-dimensional materials are subject to intrinsic and dynamic rippling that modulates their optoelectronic and electromechanical properties. Here, we directly visualize the dynamics of these processes within monolayer transition metal dichalcogenide MoS2 using femtosecond electron scattering techniques as a real-time probe with atomic-scale resolution. We show that optical excitation induces large-amplitude in-plane displacements and ultrafast wrinkling of the monolayer on nanometer length-scales, developing on picosecond time-scales. These deformations are associated with several percent peak strains that are fully reversible over tens of millions of cycles. Direct measurements of electron-phonon coupling times and the subsequent interfacial thermal heat flow between the monolayer and substrate are also obtained. These measurements, coupled with first-principles modeling, provide a new understanding of the dynamic structural processes that underlie the functionality of two-dimensional materials and open up new opportunities for ultrafast strain engineering using all-optical methods.
二维材料受到固有和动态的波纹调制，从而调节其光电和机电性能。在这里，我们使用飞秒电子散射技术作为具有原子级分辨率的实时探针，直接可视化单层过渡金属二卤化物 MoS2 中这些过程的动力学。我们表明，光学激发会在皮秒时间尺度上诱导单层在纳米长度尺度上的大振幅面内位移和超快起皱。这些变形与百分之几的峰值应变相关，在数千万个循环中完全是可逆的。还直接测量了电子-声子耦合时间以及随后在单层和衬底之间的界面热流。这些测量结果与第一性原理模型相结合，为二维材料功能背后的动态结构过程提供了新的认识，并为使用全光方法进行超快应变工程开辟了新的机会。
