Cooperative inter- and intra-layer lattice dynamics of photoexcited multi-walled carbon nanotubes studied by ultrafast electron diffraction
Cooperative inter- and intra-layer lattice dynamics of photoexcited multi-walled carbon nanotubes studied by ultrafast electron diffraction
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超快电子衍射研究光激发多壁碳纳米管层间和层内协同晶格动力学
作者：
Sun Shuaishuai;Li Zhongwen;Li Zi-An;Xiao Ruijuan;Zhang Ming;Tian Huanfang;Yang Huaixin;Li Jianqi;Li Zhongwen;Zhang Ming;Yang Huaixin;Li Jianqi;Li Jianqi;Li JQ;Li JQ;Li JQ
电子激发驱动的纳米材料的光学调谐和探测超快结构响应构成了一种具有挑战性但有前途的方法，用于理解微机电系统和光电器件中的微观机制和应用。在这里，我们使用脉冲电子衍射在透射电子显微镜研究激光诱导的管状晶格动力学的多壁碳纳米管（MWCNTs）与不同的激光能量密度和初始试样温度。我们的光激发实验表明，在层内和层间方向的合作和逆集体原子运动，其强度和速率依赖于泵注量。电子驱动和热驱动的结构响应具有相反的幅度，导致层内和层间方向之间的交叉。我们的从头计算结果支持这些发现，并揭示了在碳管中从π到π* 轨道激发的电子削弱了层内键，同时加强了层间键沿着径向方向。此外，通过探测在初始温度为300和100 K的多壁碳纳米管的结构动力学，我们揭示了热动力学和非热动力学过程的伴随及其相互影响的多壁碳纳米管。我们的研究结果说明了电子驱动的非热过程和电子声子热化在多壁碳纳米管的性质，并承担复杂的能量转换和转移在纳米材料的影响。
Optical tuning and probing ultrafast structural response of nanomaterials driven by electronic excitation constitute a challenging but promising approach for understanding microscopic mechanisms and applications in microelectromechanical systems and optoelectrical devices. Here we use pulsed electron diffraction in a transmission electron microscope to investigate laser-induced tubular lattice dynamics of multi-walled carbon nanotubes (MWCNTs) with varying laser fluence and initial specimen temperature. Our photoexcitation experiments demonstrate cooperative and inverse collective atomic motions in intralayer and interlayer directions, whose strengths and rates depend on pump fluence. The electron-driven and thermally driven structural responses with opposite amplitudes cause a crossover between intralayer and interlayer directions. Our ab initio calculations support these findings and reveal that electrons excited from π to π* orbitals in a carbon tube weaken the intralayer bonds while strengthening the interlayer bonds along the radial direction. Moreover, by probing the structural dynamics of MWCNTs at initial temperatures of 300 and 100 K, we uncover the concomitance of thermal and nonthermal dynamical processes and their mutual influence in MWCNTs. Our results illustrate the nature of electron-driven nonthermal process and electron–phonon thermalization in the MWCNTs, and bear implications for the intricate energy conversion and transfer in materials at the nanoscale.