The limited Photoluminescence (PL) quantum yield of monolayer Transition metal dichalcogenides (1L-TMDs) are surprisingly shown to increase up to ~ 100 % by defect passivation mechanism i.e. suppressing the exciton quenching caused by the structural defects by simple chemical treatment. However, the mechanism behind it is in veil due to lack of experimental results in atomic level. In this work, we carried out bis(trifluoromethane) sulfonimide (TFSI) treatment of 1L-MoS2 and 1L-WS2 with different defects domains grown by chemical vapor deposition (CVD) and found drastically enhanced PL intensity in case of 1L-MoS2 while about 5 fold enhancement in case of 1L-WS2. Similarly the Raman intensity of both 1L-TMDs were increased and the intensity ratio of 2LA(M) to A1g peaks for 1L-WS2 were increased in different defect domains after TFSI treatment which are the strong evidence of defect passivation. We directly observed the atomic healing of 1L-TMDs by TFSI molecules under scanning transmission electron microscopy (STEM) analysis of pristine and TFSI treated 1L-TMDs and found that about ~ 90 % sulfur vacancies of 1L-TMDs were filled after treatment. The direct anchoring of dissociated sulfur atoms from TFSI molecules to the sulfur vacancies of 1L-TMDs was found to be energetically favorable by density functional theory calculations. Our observation shed light on the mechanism of intriguing healing process of lattice defects of 1L-TMDs and suggests that 1L-TMDs can be made defect-free which widens and prompts the practical uses of 1L-TMDs in nanophotonics applications. Furthermore, correlated experimental results and details will be presented.
Shrawan Roy, Wooseon Choi, Sera Jeon, Do-Hwan Kim, Hyun Kim, SeokJoon Yun, Yongjun Lee, Jaekwang Lee, Young-Min Kim, and Jeongyong Kim, "Effect of chemical treatment on structural defects and optical properties of two-dimensional semiconductors (Conference Presentation)," Proc. SPIE 10725, Low-Dimensional Materials and Devices 2018, 107250N (Presented at SPIE Nanoscience + Engineering: August 23, 2018; Published: 17 September 2018); https://doi.org/10.1117/12.2320484.5836012285001.
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