Chebl Mazhar, He Xing, Yang Ding-Shyue
Department of Chemistry, University of Houston, Houston, Texas 77204, USA.
J Chem Phys. 2024 Mar 28;160(12). doi: 10.1063/5.0193613.
Revived attention in black phosphorus (bP) has been tremendous in the past decade. While many photoinitiated experiments have been conducted, a cross-examination of bP's photocarrier and structural dynamics is still lacking. In this article, we provide such analysis by examining time-resolved data acquired using optical transient reflectivity and reflection ultrafast electron diffraction, two complementary methods under the same experimental conditions. At elevated excitation fluences, we find that more than 90% of the photoinjected carriers are annihilated within the first picosecond (ps) and transfer their energy to phonons in a nonthermal, anisotropic fashion. Electronically, the remaining carrier density around the band edges induces a significant interaction that leads to an interlayer lattice contraction in a few ps but soon diminishes as a result of the continuing loss of carriers. Structurally, phonon-phonon scattering redistributes the energy in the lattice and results in the generation of out-of-plane coherent acoustic phonons and thermal lattice expansion. Their onset times at ∼6 ps are found to be in good agreement. Later, a thermalized quasi-equilibrium state is reached following a period of about 40-50 ps. Hence, we propose a picture with five temporal regimes for bP's photodynamics.
在过去十年中，对黑磷（bP）的关注度大幅回升。尽管已经进行了许多光引发实验，但仍缺乏对bP光载流子和结构动力学的交叉研究。在本文中，我们通过检查使用光学瞬态反射率和反射超快电子衍射在相同实验条件下获得的时间分辨数据，提供了这样的分析。在高激发通量下，我们发现超过90%的光注入载流子在第一皮秒（ps）内湮灭，并以非热、各向异性的方式将其能量转移给声子。从电子学角度来看，带边周围剩余的载流子密度会引发显著的相互作用，导致在几皮秒内发生层间晶格收缩，但由于载流子的持续损失，这种收缩很快就会减弱。在结构上，声子 - 声子散射在晶格中重新分配能量，导致面外相干声子的产生和晶格热膨胀。它们在约6皮秒时的起始时间被发现吻合得很好。随后，在大约40 - 50皮秒的时间段后达到热准平衡状态。因此，我们提出了一个关于bP光动力学的具有五个时间阶段的图景。
