How Does Twist Angle Affect the Conductivity of an MoS₂/Graphene Heterostructure?

So-called Van der Waals heterostructures, which are formed by stacking layers of different 2D materials, offer vast opportunities for next-generation electronics. A variety of heterostructure properties have been shown to depend strongly on the twist angle (relative orientation angle of the layers).

Researchers at Beijing Institute of Technology and the Chinese Academy of Sciences used conductive AFM (CAFM) to measure variations in current across an MoS₂/graphene heterostructure as a function of relative twist angle. The high resolution and high sensitivity of CAFM measurements on the Asylum Research Cypher S AFM were used to confirm the expected 1.18 nm period of the moiré superlattice created by the lattice mismatch.

In this work, the angular dependence of electrical conductivity in MoS₂/graphene heterojunctions was investigated. High-sensitivity imaging of electrical current with the Cypher S AFM by Oxford Instruments Asylum Research revealed that the vertical conductivity varied by almost a factor of five depending on twist angle. The results help inform the design of advanced devices based on MoS₂/graphene heterojunctions.

Instrument used

Cypher S with the ORCA conductive AFM option

Techniques used

Topography was imaged using tapping mode. The low noise of the Cypher S enabled very accurate measurement of the MoS₂ domain height. The nanomanipulation capability of the Asylum AFM software was used to rotate the MoS₂ domains to achieve the desired rotation angles relative to the graphene substrate. Though most of the conductivity measurements were made over 500 nm scan areas, the authors also took advantage of Cypher’s high spatial resolution to capture conductive AFM images at 25 nm scan size. At this scale, the 1.18 nm period of the moiré superlattice was visible in the current image (see supplementary data on the journal site).

Citation: M. Liao, Z. Wu, L. Du et al. Twist angle-dependent conductivities across MoS₂/graphene heterojunctions. Nat. Commun. 9, 4068 (2018). https://doi.org/10.1038/s41467-018-06555-w

Note: The original article featured above was published Open Access. The data shown here is reused under fair use and under the Creative Commons license of the original article, which can be accessed through the article link above.