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.
Highlights
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
A fundamental limitation of chemical vapor deposition (CVD) growth of TMDs on graphene compared to traditional substrates (i.e. S iO2/Si or sapphire) is the weak adsorption of the precursors on the surface, which results in slow lateral growth rates and a tendency for multilayers to form[29]
The sample was characterized by X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM) and Raman spectroscopy to determine the surface chemistry and morphology
Summary
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. 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. Chemical vapor deposition (CVD) of TMDs has been used to successfully to produce monolayers of MoS2, WS2, MoSe2 and WSe2 at the wafer scale on substrates such as SiO2/Si and sapphire[21,22] Despite these successes there are still some limitations in extending this process to synthesizing large area monolayers on van der Waals substrates such as graphene. Previous studies have demonstrated direct sulfurization of the metal precursor as an effective route to producing large-area TMDs on S iO2/Si30–32 This has the advantage of allowing a control of the layer thickness and morphology directly according to the thickness of the precursor. We have utilized scanning tunneling microscopy (STM), atomic force microscopy (AFM), photoemission spectroscopy and Raman spectroscopy to investigate the surface morphology and composition of the W S2 layers and have presented the electronic band alignment of the van der Waals heterostructure
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