Characterization of the structural defects in CVD-grown monolayered MoS2 using near-field photoluminescence imaging

Structural defects can critically influence the electrical and optical properties of monolayered molybdenum disulfide (MoS2) grown by chemical vapor deposition (CVD); thus, convenient optical methods that can visualize grain boundaries (GBs) and other structural defects are in great demand. Although photoluminescence (PL) imaging can identify the presence of relatively large defects, the limited spatial resolution of PL imaging prevents the identification of nanosized structural defects in the monolayered MoS2. Additionally, the origin of the PL signal contrast observed at certain types of structural defects, such as GBs, is not yet understood. Here, we present near-field PL images of CVD-grown monolayered MoS2, collected to identify nanosized line defects and adlayer defects in the monolayered MoS2. Our results of correlated scanning electron microscopy imaging and the inspection of near-field PL profiles of line defects and GBs suggest that decreased PL on GBs is due to the local physical damage of the MoS2 film rather than due to the presence of localized states.