Chebl Mazhar, He Xing, Yang Ding-Shyue
Department of Chemistry, University of Houston, Houston, Texas 77204, United States.
Nano Lett. 2022 Jul 13;22(13):5230-5235. doi: 10.1021/acs.nanolett.2c01019. Epub 2022 Jun 28.
Black phosphorus (bP) exhibits highly anisotropic properties and dynamical behavior that are unique even among two-dimensional and van der Waals (vdW) layered materials. Here, we show that an interlayer lattice contraction and concerted, symmetric intralayer vibrations occur concurrently within few picoseconds following the photoinjection and relaxation of carriers, using ultrafast electron diffraction in the reflection geometry to probe the out-of-plane motions. A strong coupling between the photocarriers and bP's puckered structure, with the alignment of the electronic band structure, is at work for such directional atomic motions without a photoinduced phase transition. Three temporal regimes can be identified for the phonon thermalization dynamics where a quasi-equilibrium without anisotropy is reached in about 50 ps, followed by propagation of coherent acoustic phonons and heat diffusion into the bulk. The early time out-of-plane dynamics reported here have important implications for single- and few-layer bP and other vdW materials with strong electronic-lattice correlations.
黑磷（bP）展现出高度各向异性的性质和动力学行为，即便在二维和范德华（vdW）层状材料中也是独一无二的。在此，我们利用反射几何中的超快电子衍射来探测面外运动，结果表明，在光注入和载流子弛豫后的几皮秒内，层间晶格收缩以及协同、对称的层内振动会同时发生。光生载流子与bP的褶皱结构之间存在强耦合，且电子能带结构呈对齐状态，这种强耦合作用于此类定向原子运动，而不会发生光致相变。对于声子热化动力学，可识别出三个时间区域，其中在约50皮秒内达到无各向异性的准平衡状态，随后是相干声子的传播以及热量扩散到体相中。此处报道的早期面外动力学对单层和少层bP以及其他具有强电子 - 晶格相关性的vdW材料具有重要意义。
