Atomically Resolved Observation of Continuous Interfaces between As-grown MoS2 Monolayer and WS2/MoS2 Heterobilayer on SiO2

TL;DR

This study uses STM/STS to observe, with atomic resolution, the continuous interface between MoS2 monolayer and WS2/MoS2 heterobilayer on SiO2, revealing smoother surfaces and providing insights into their electronic properties.

Contribution

First direct atomic-resolution observation of a continuous interface between MoS2 monolayer and WS2/MoS2 heterobilayer, contrasting previous reports of open edges.

Findings

Heterobilayer is smoother than monolayer (RMS roughness 0.230 nm vs. 0.329 nm).

Continuous interface observed between MoS2 monolayer and heterobilayer top layer.

Band gaps of heterobilayer and monolayer characterized by STS and DFT.

Abstract

Van der Waals (vdW) heterostructures synthesized through the chemical vapor deposition (CVD) method allow creation and tuning of intriguing electronic and optical properties of two- dimensional (2D) materials, the knowledge of which is critical for a wide range of potential applications. Here we report our scanning tunneling microscopy/spectroscopy (STM/STS) study of as-grown MoS2 monolayer and WS2/MoS2 heterobilayer on SiO2. The heterobilayer appears smoother than the MoS2 monolayer, with root mean square (RMS) roughness of 0.230 +- 0.021 nm in the former and 0.329 +- 0.033 nm in the latter. For the first time, to our knowledge, we directly observed a continuous interface between the MoS2 monolayer and the top layer of the heterobilayer with atomic resolution. This finding contrasts to the previously reported open edges in the top layer of the heterobilayer. Our STS results and density functional theory (DFT) calculations revealed the band gaps of the heterobilayer and the MoS2 monolayer.