Liu Huan, Wang Chong, Liu Dameng, Luo Jianbin
State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, People's Republic of China.
Nanoscale. 2019 Apr 23;11(16):7913-7920. doi: 10.1039/c9nr00967a.
As defects and exciton-exciton annihilation (EEA) frequently govern the properties of nanoscale optoelectronic devices based on monolayer transition metal dichalcogenides (TMDCs), understanding the interaction between defects and EEA is of fundamental importance. Here we perform a systematic investigation of the effect of defects on EEA of neutral excitons and defect-bound excitons in monolayer WS2, using fluorescence lifetime imaging technology. Scanning transmission electron microscopy confirms the creation of atomic-scale defects introduced by argon plasma treatment in defective WS2. Defects can bind neutral excitons or trions to form defect-bound excitons. And defects have a slight effect on the lifetime of neutral excitons. However, owing to the impeded exciton diffusion caused by defects, the EEA rate of neutral excitons reduces from 0.26 cm2 s-1 in the pristine monolayer to 0.16 cm2 s-1 in the defective monolayer. For defect-bound excitons, the EEA rate of 0.068 cm2 s-1 is obtained, which results from the localized nature of defect-bound excitons and suppressed exciton diffusion. Our results reveal the important role of defect-EEA interactions in tailoring the properties of monolayer TMDCs.
由于缺陷和激子-激子湮灭（EEA）常常决定基于单层过渡金属二卤化物（TMDCs）的纳米级光电器件的性能，了解缺陷与EEA之间的相互作用至关重要。在此，我们使用荧光寿命成像技术，对单层WS2中缺陷对中性激子和缺陷束缚激子的EEA的影响进行了系统研究。扫描透射电子显微镜证实了在有缺陷的WS2中通过氩等离子体处理引入的原子尺度缺陷的产生。缺陷可以束缚中性激子或三重态激子以形成缺陷束缚激子。并且缺陷对中性激子的寿命有轻微影响。然而，由于缺陷导致激子扩散受阻，中性激子的EEA速率从原始单层中的0.26 cm2 s-1降低到有缺陷单层中的0.16 cm2 s-1。对于缺陷束缚激子，获得的EEA速率为0.068 cm2 s-1，这是由缺陷束缚激子的局域性质和抑制的激子扩散导致的。我们的结果揭示了缺陷-EEA相互作用在调整单层TMDCs性能方面的重要作用。
