Type of presentation: Oral

MS-1-O-2715 Investigation of Detailed Monolayer MoS2 Edge Structure and Defect Configuration by Atomic Resolution Scanning Transmission Electron Microscopy

Li K.1, Hong J.2, Jin C.2, Zhang X.3
1Imaging and Characterization Core Lab, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia, 2Department of Materials Science and Engineering, Zhejiang University, China, 3Division of Physical Science, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
kun.li@kaust.edu.sa

Recent intense research and development activities in graphene have regained strong research interest in its related two dimensional (2D) counterparts, especially BN and transition metal dichalcogenides (TMDCs), with MoS2 under the focus. The idea has been fortified again that in addition to composition and structure dimensionality also plays a very important role in determining the fundamental properties due to quantum confinement effect. These materials possess exotic properties that are absent in their bulk forms. For MoS2, understanding its edge and defect configuration at atomic level is critical for realizing its application potentials as electronic devices and catalysis, as it affects the electronic band structure of MoS2 and the catalytic behavior.

Here we employ a probe Cs corrected Titan scanning transmission electron microscope (STEM) operated at 80 kV to study the defect and edge structure of monolayer MoS2. Z-contrast STEM technique is used to differentiate between Mo and S atom columns, with Mo showing brighter contrast and S showing darker contrast. Vacancies with different size are found in our study, ranging from mono vacancy to large triangular-shaped vacancies. Fig. 1 shows a triangular-shaped vacancy with a lateral length of 3 unit cells, revealing Mo-terminated Klein edge. Mo-terminated zigzag edge is found in a bigger triangular-shaped vacancy with a lateral length of 4 unit cells, as shown in Fig. 2. The results suggest that S atoms are easier than Mo atoms to be removed under electron beam illumination and Mo-terminated edge is the most often found type. We also find in our experiment that when a nano-ribbons is formed, one side of it is Klein edge, and the other side is zigzag, where removed Mo atoms tend to be absorbed. Based on this observation we believe that for catalysis application, zigzag edge should also be the preferred absorption site for noble catalytic atoms. Dislocation pairs are also found in this study with atomic resolution (Fig. 3) and the Burgers vector is also defined (Fig. 4); it is a 60-degree dislocation.

With no doubt the capability of unambiguously identifying defect and edge configuration at atomic level will facilitate process optimization for realizing the promising applications of MoS2 and its related TMDCs.

Fig. 1: Atomic resolution defect configuration of triangular-shaped vacancies with the lateral length of three unit cell and Mo-terminated Klein edge.

Fig. 2: Atomic resolution defect configuration of triangular-shaped vacancies with the lateral length of four unit cell and Mo-terminated zigzag edge

Fig. 3: Dislocation pairs in MoS2 Monolayer.

Fig. 4: Dislocation in Figure 3 with Burgers vector identified