College of Opto-Electronic Science and Engineering, National University of Defense Technology, Changsha 410073, P. R. China.
Nanoscale. 2018 Jan 25;10(4):1650-1659. doi: 10.1039/c7nr05542k.
The idea of fabricating artificial solids with band structures tailored to particular applications has long fascinated condensed matter physicists. Heterostructure (HS) construction is viewed as an effective and appealing approach to engineer novel electronic properties in two dimensional (2D) materials. Different from common 2D/2D heterojunctions where energy transfer is rarely observed, CsPbBr quantum dots (0D-QDs) interfaced with 2D materials have become attractive HSs for exploring the physics of charge transfer and energy transfer, due to their superior optical properties. In this paper, a new 0D/2D HS is proposed and experimentally studied, making it possible to investigate both light utilization and energy transfer. Specifically, this HS is constructed between monolayer WS and CsPbBr QDs, and exhibits a hybrid band alignment. The dynamics of energy transfer within the investigated 0D/2D HS is characterized by femtosecond transient absorption spectrum (TAS) measurements. The TAS results reveal that ultrafast energy transfer caused by optical excitation is observed from CsPbBr QDs to the WS layer, which can increase the exciton fluence within the WS layer up to 69% when compared with pristine ML WS under the same excitation fluence. Moreover, the formation and dynamics of interlayer excitons have also been investigated and confirmed in the HS, with a calculated recombination time of 36.6 ps. Finally, the overall phenomenological dynamical scenario for the 0D/2D HS is established within the 100 ps time region after excitation. The techniques introduced in this work can also be applied to versatile optoelectronic devices based on low dimensional materials.
具有特定应用带宽结构的人工固体的制造理念长期以来一直吸引着凝聚态物理学家。异质结构（HS）的构建被认为是一种有效且有吸引力的方法，可以在二维（2D）材料中设计新型电子特性。与能量转移很少观察到的常见 2D/2D 异质结不同，与二维材料界面的 CsPbBr 量子点（0D-QDs）已成为探索电荷转移和能量转移物理的有吸引力的 HS，因为它们具有优异的光学特性。在本文中，提出并实验研究了一种新的 0D/2D HS，从而有可能同时研究光利用和能量转移。具体而言，该 HS 是在单层 WS 和 CsPbBr QDs 之间构建的，并表现出混合能带排列。通过飞秒瞬态吸收光谱（TAS）测量对所研究的 0D/2D HS 内的能量转移动力学进行了表征。TAS 结果表明，在相同的激发光强度下，观察到由光激发引起的超快能量转移从 CsPbBr QDs 到 WS 层，这可以将 WS 层内的激子强度提高 69%。此外，还研究并证实了 HS 中的层间激子的形成和动力学，计算出的复合时间为 36.6 ps。最后，在激发后的 100 ps 时间区域内建立了 0D/2D HS 的整体现象动态情景。本工作中引入的技术也可以应用于基于低维材料的各种光电设备。
