Synthesis and characterization of WS2/graphene/SiC van der Waals heterostructures via WO3−x thin film sulfurization

Abstract

Van der Waals heterostructures of monolayer transition metal dichalcogenides (TMDs) and graphene have attracted keen scientific interest due to the complementary properties of the materials, which have wide reaching technological applications. Direct growth of uniform, large area TMDs on graphene substrates by chemical vapor deposition (CVD) is limited by slow lateral growth rates, which result in a tendency for non-uniform multilayer growth. In this work, monolayer and few-layer WS2 was grown on epitaxial graphene on SiC by sulfurization of WO3−x thin films deposited directly onto the substrate. Using this method, WS2 growth was achieved at temperatures as low as 700 °C – significantly less than the temperature required for conventional CVD. Achieving long-range uniformity remains a challenge, but this process could provide a route to synthesize a broad range of TMD/graphene van der Waals heterostructures with novel properties and functionality not accessible by conventional CVD growth.

Strain and Spin-Orbit Coupling Engineering in Twisted WS2/Graphene Heterobilayer

“…The possible band structure and bandgap change in single layer WS 2 could be translated by the orientation angle of the flakes with respect to the graphene substrate and may induce a variation of the properties of WS 2 . Thus, despite the clean interface between WS 2 and graphene [8], both the PL and µ-Raman results prove that the two layers are coupled electronically.…”

“…These peaks were redshifted of 1 cm −1 or 2 cm −1 , compared to those of WS 2 /Gr, attributable to a strain between the WS 2 and the graphene substrate. Additional Raman peaks around 296 cm −1 and 323 cm −1 were combination modes, attributed to the 2LA(M) − 2E 2 2g (Γ) and the 2LA(M) − E 2 2g (Γ) modes, respectively [8]. To investigate the optical properties of the WS2 flakes, μ-PL/Raman spectroscopy was carried out at room temperature [22].…”

“…These peaks were redshifted of 1 cm −1 or 2 cm −1 , compared to those of WS2/Gr, attributable to a strain between the WS2 and the graphene substrate. Additional Raman peaks around 296 cm −1 and 323 cm −1 were combination modes, attributed to the 2𝐿𝐴 𝑀 2𝐸 Γ and the 2𝐿𝐴 𝑀 𝐸 Γ modes, respectively [8]. Before transferring Flake 1 (1 ML) and Flake 1b (2 ML) onto graphene, we measured their PL spectra on the SiO2 substrate (see Supplementary Information, Figure S1).…”

“…New variants of twisted hybrid heterostructures have also been proposed, in which the monolayers are made of distinct 2D materials (e.g., TMD/Gr) instead of sibling TMD crystals. In such TMD/Gr heterostructures, several electronic features can be improved with respect to the corresponding TMD monolayer structure, as in the case of WS 2 /Gr heterobilayers, which exhibit remarkable advantages compared to monolayer WS 2 [8][9][10]. While MX 2 monolayers are generally limited by a relatively low carrier mobility and photosensitivity, the MX 2 /Gr heterobilayers often offer much improved values, which leads to direct applications in photodetector and transistor devices [11].…”

Substrate-mediated growth of oriented, vertically aligned MoS2 nanosheets on vicinal and on-axis SiC substrates

“…Although passivation of sulfur vacancies with other atomic species is a possibility [31], we do not believe that to be the case here. Given the growth environment the element mostly likely to passivate defects would be oxygen, however incorporation of oxygen into a MoOxSy compound would result in a shift of the Mo 3d and S 2p electrons to higher binding energies [32,33].…”