Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Nanoscale. 2017 Sep 14;9(35):13313-13319. doi: 10.1039/c7nr04162d.
We investigate the ultrafast structural dynamics of multi-walled boron nitride nanotubes (BNNTs) upon femtosecond optical excitation using ultrafast electron diffraction in a transmission electron microscope. Analysis of the time-resolved (100) and (002) diffraction profiles reveals highly anisotropic lattice dynamics of BNNTs, which can be attributed to the distinct nature of the chemical bonds in the tubular structure. Moreover, the changes in (002) diffraction positions and intensities suggest that the lattice response of BNNTs to the femtosecond laser excitation involves a fast and a slow lattice dynamic process. The fast process with a time constant of about 8 picoseconds can be understood to be a result of electron-phonon coupling, while the slow process with a time constant of about 100 to 300 picoseconds depending on pump laser fluence is tentatively associated with an Auger recombination effect. In addition, we discuss the power-law relationship of a three-photon absorption process in the BNNT nanoscale system.
我们使用透射电子显微镜中的超快电子衍射研究了飞秒光激发下多壁氮化硼纳米管（BNNTs）的超快结构动力学。对时间分辨（100）和（002）衍射谱的分析揭示了 BNNTs 的各向异性晶格动力学，这归因于管状结构中化学键的独特性质。此外，（002）衍射位置和强度的变化表明，BNNTs 对飞秒激光激发的晶格响应涉及快速和缓慢的晶格动力学过程。时间常数约为 8 皮秒的快速过程可以理解为电子-声子耦合的结果，而时间常数约为 100 至 300 皮秒的缓慢过程（取决于泵浦激光强度）则与俄歇复合效应有关。此外，我们还讨论了 BNNT 纳米尺度系统中三光子吸收过程的幂律关系。
