Mesoscale Imperfections in MoS2AtomicLayers Grown by a Vapor Transport Technique.

The success of isolating small flakesof atomically thin layersthrough mechanical exfoliation has triggered enormous research interestin graphene and other two-dimensional materials. For device applications,however, controlled large-area synthesis of highly crystalline monolayerswith a low density of electronically active defects is imperative.Here, we demonstrate the electrical imaging of dendritic ad-layersand grain boundaries in monolayer molybdenum disulfide (MoS2) grown by a vapor transport technique using microwave impedancemicroscopy. The micrometer-sized precipitates in our films, whichappear as a second layer of MoS2in conventional heightand optical measurements, show ∼2 orders of magnitude higherconductivity than that of the single layer. The zigzag grain boundaries,on the other hand, are shown to be more resistive than the crystallinegrains, consistent with previous studies. Our ability to map the localelectrical properties in a rapid and nondestructive manner is highlydesirable for optimizing the growth process of large-scale MoS2atomic layers. [ABSTRACT FROM AUTHOR]