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

van der Waals (vdW) heterostructures synthesized through the chemical vapor deposition (CVD) method allow the creation and tuning of intriguing electronic and optical properties of two-dimensional (2D) materials. Especially, local structures in the heterostructures, such as interfaces, edges, and point defects, are critical for their wide range of potential applications. However, up to now atomic-scale measurements of local structures in as-grown 2D heterostructures on insulating substrates are still rare. Here we report our scanning tunneling microscopy and spectroscopy (STM/STS) study of as-grown MoS2 monolayer and WS2/MoS2 heterobilayer on SiO2. The heterobilayer appears smoother than the MoS2 monolayer, with a root-mean-square roughness of 0.230 nm in the former and 0.329 nm in the latter. For the first time, to our knowledge, we directly observed a novel type of continuous interface between the MoS2 monolayer and the top layer of the heterobilayer with atomic resolution. Our STS results and density f...