Engineering of Oxidized Line Defects on CVD-Grown MoS 2 Flakes.

Defect engineering is a promising means to create patterns on two-dimensional (2D) materials to enable unconventional properties. However, defects usually exist abundantly and randomly on 2D materials, which makes it difficult to tune the properties in a controllable manner. Therefore, it is highly desirable to find out the formation mechanism and controllable fabrication method of defects on 2D materials. In this report, we systematically investigated the line defects on monolayer MoS formed by introducing oxygen during the CVD growth. The line defects were formed due to the overoxidation of the MoS flake along crystal boundaries, which bulged out of the surface and had the same surface potential as the basal plane. Therefore, the MoS flake with line defects maintained the optical and electrical integrity but exhibited distinct properties as compared to the pristine one. By controlling the oxygen concentration during CVD growth, the density of the line defects can be precisely controlled to implement controllable property tuning. Moreover, during the transfer process, the MoS flake was easily broken along the line defects, which increased the active sites to achieve enhanced hydrogen evolution reaction performance. This work is expected to inspire the development of patterned functional 2D materials by defect engineering.