Mesoscale Imperfections in MoS2 Atomic Layers Grown by Vapor Transport Technique

TL;DR

This paper uses microwave impedance microscopy to map electrical properties of MoS2 monolayers grown by vapor transport, revealing defects and grain boundaries crucial for improving large-scale synthesis.

Contribution

It demonstrates a rapid, nondestructive method to image electrical variations and defects in vapor-grown MoS2 monolayers, aiding growth optimization.

Findings

Dendritic ad-layers show 100x higher conductivity than monolayer MoS2.

Grain boundaries are more resistive than crystalline regions.

Microwave impedance microscopy effectively maps local electrical properties.

Abstract

The success of isolating small flakes of atomically thin layers through mechanical exfoliation has triggered enormous research interest in graphene and other two-dimensional materials. For device applications, however, controlled large-area synthesis of highly crystalline monolayers with a low density of electronically active defects is imperative. Here, we demonstrate the electrical imaging of dendritic ad-layers and grain boundaries in monolayer molybdenum disulfide (MoS2) grown by vapor transport technique using microwave impedance microscopy. The micrometer-sized precipitates in our films, which appear as a second layer of MoS2 in conventional height and optical measurements, show 2 orders of magnitude higher conductivity than that of the single layer. The zigzag grain boundaries, on the other hand, are shown to be more resistive than the crystalline grains, consistent with previous studies. Our ability to map the local electrical properties in a rapid and nondestructive manner is highly desirable for optimizing the growth process of large-scale MoS2 atomic layers.