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

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 twodimensional (2D) materials. Especially, local structures in the heterostructures, such as interfaces, edges and point defects, are critical for their wide range of potential application. 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 (STM) and spectroscopy (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 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 interfaces between the MoS2 monolayer and the top layer of the heterobilayer with atomic resolution. Our STS results and density functional theory (DFT) calculations revealed the band gaps of the heterobilayer and the 2 MoS2 monolayer. The finding of the continuous interfaces and the systematic characterizations could have significant impacts on optimizing and designing new 2D heterostructures.

One-Pot Selective Epitaxial Growth of Large WS2/MoS2 Lateral and Vertical Heterostructures

“…Furthermore, the stacked region in the HAADF-STEM image (Figure i) exhibits a clear interface between the MoS 2 monolayer and the WS 2 /MoS 2 bilayer, as marked by the yellow dashed line. The MoS 2 monolayer and the stacked region show a perfect hexagonal atomic structure without atomic defects or W atom alloying. , In addition, the intensity profiles of WS 2 and MoS 2 in Figure S11e and S11f clearly display W, S and Mo, S atomic arrangements, respectively, without the incorporation of Mo into WS 2 or the opposite. The atomically clean and sharp interface further confirms the high quality of the as-grown WS 2 /MoS 2 vertical heterostructures.…”

Convergent ion beam alteration of 2D materials and metal-2D interfaces

“…The scanning tunneling microscopy (STM) measurements were carried out in an ultra-high vacuum (UHV) STM system (Omicron RT-STM). Similar to the previously reported annealing process for 2D MoS 2 [59,60], the sample was annealed at 300 °C for 3 h in the UHV chamber with a base pressure of 4.0 × 10 −10 torr. The STM used a chemically etched tungsten tip.…”

Two-Dimensional Layered Materials Offering Expanded Applications in Flatland

“…Heterostructures can be formed by combining different dimensionalities (for instance, 2D/2D, 1D/2D, and zero-dimensional (0D)/2D) or by connecting different phases of the same stoichiometry (e.g., 1T/1H). 1L–2L lateral heterostructures, where the bilayer (2L) is a vertical heterostructure laterally connected to a monolayer (1L), are less common . Scanning tunneling microscopy and spectroscopy (STM/STS) studies of this type of heterostructures revealed the absence of edge states over the continuous transition region from 1L to 2L .…”