Evolution of defect formation during atomically precise desulfurization of monolayer MoS2

Abstract

Structural symmetry-breaking is a key strategy to modify the physical and chemical properties of two-dimensional transition metal dichalcogenides. However, little is known about defect formation during this process. Here, with atomic-scale microscopy, we investigate the evolution of defect formation in monolayer MoS2 exposed indirectly to hydrogen plasma. At the beginning of the treatment only top-layer sulfur atoms are removed, while vacancies and the molybdenum atomic layer are maintained. As processing continues, hexagonal-shaped nanocracks are generated along the zigzag edge during relaxation of defect-induced strain. As defect density increases, both photoluminescence and conductivity of MoS2 gradually decreases. Furthermore, MoS2 showed increased friction by 50% due to defect-induced contact stiffness. Our study reveals the details of defect formation during the desulfurization of MoS2 and helps to design the symmetry-breaking transition metal dichalcogenides, which is of relevance for applications including photocatalyst for water splitting, and Janus heterostructures.

Oxygen-Driven Growth Regulation and Defect Passivation in Chemical Vapor Deposited MoS2 Monolayers

“…However, defects in MoS 2 , in particular, the vacancy defects, could strongly alter the position of both the modes. Studies show that a significant frequency decrease of the E 1 2g mode occurs, as the restoring force constant is dramatically reduced by the creation of sulfur vacancies. − While we attribute the observed downshifting of E 1 2g mode in sample B due to unpassivated sulfur vacancies based on the findings from PL results (will be discussed later), the splitting of the A 1g mode, which is rarely observed in monolayer MoS 2 previously, needs to be understood and will be addressed later.…”

Stepwise growth of crystalline MoS2 in atomic layer deposition

“…It was reported that exposure to low-energy remote H 2 plasma resulted in the removal of sulfur atoms in MoS 2 . 31 Accordingly, the composition of the grown MoS 2 was examined. Despite this concern, the S/Mo atomic ratio of the films was very close to the stoichiometric value, irrespective of the injection of H 2 plasma (Fig.…”

STEM Image Analysis Based on Deep Learning: Identification of Vacancy Defects and Polymorphs of MoS2

“…Remote hydrogen plasma treatment has recently demonstrated its utility to introduce sulfur vacancy defects in MoS2 under a controlled manner 43 . Figure 4b and 4g are exemplary input STEM images of as-synthesized MoS2 and plasma-treated MoS2, respectively.…”

“…As shown in Figure 4k and 4m, the intensity histogram at localized atomic sites typically shows two strong peaks; a peak at the center position of 1.0 is from double occupancy of sulfur atoms and another peak at around 1.5 is from Mo atom sites. A small shoulder peak at a center of around 0.7 is attributed to VS1 sites 43 . The fact that the shoulder peak increases in the plasma-treated samples is consistent with this interpretation.…”

“…We used a ResUNet architecture (Figure c) for both vacancy identification and polymorph detection models. In training FCN models, a sufficiently large set of data with enough diversity and proper quality is crucial. , As shown in Figure a,b and Figure S1, we mainly trained our ResUNet models with simulated STEM images (256 × 256 pixels) generated by Computem . Some experimental images were also incorporated into the training and validation sets for the polymorph model.…”