Abstract
Two-dimensional layered transition metal dichalcogenides (TMDCs) show great potential for optoelectronic devices due to their electronic and optical properties. A metal-semiconductor interface, as epitaxial graphene - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science, as it constitutes an outstanding platform to investigate the interlayer interaction in van der Waals heterostructures. Here, we study large area MoS2-graphene-heterostructures formed by direct transfer of chemical-vapor deposited MoS2 layer onto epitaxial graphene/SiC. We show that via a direct transfer, which minimizes interface contamination, we can obtain high quality and homogeneous van der Waals heterostructures. Angle-resolved photoemission spectroscopy (ARPES) measurements combined with Density Functional Theory (DFT) calculations show that the transition from indirect to direct bandgap in monolayer MoS2 is maintained in these heterostructures due to the weak van der Waals interaction with epitaxial graphene. A downshift of the Raman 2D band of the graphene, an up shift of the A1g peak of MoS2 and a significant photoluminescence quenching are observed for both monolayer and bilayer MoS2 as a result of charge transfer from MoS2 to epitaxial graphene under illumination. Our work provides a possible route to modify the thin film TDMCs photoluminescence properties via substrate engineering for future device design.
Highlights
The study of graphene, a two dimensional (2D) atomic crystal formed of carbon atoms arranged in a honeycomb structure, is one of the hottest topics in material science due to its unique capabilities[1,2]
Until now there are few works discussing the possibility of growing transition metal dichalcogenides (TMDCs) materials (MoS2 or WS2) on epitaxial graphene/SiC15–18
The possibility to obtain large area TMDCs/ graphene heterostructures is important for a large variety of in situ characterization techniques, and is a basic requirement for realistic applications
Summary
Waals heterostructures received: 15 January 2016 accepted: 03 May 2016 Published: 01 June 2016. Combining different 2D layers with complementary characteristics can lead to new vdW heterostructures with tunable properties leading to an outstanding range of possible applications[7,8] Among these systems, the combination of a transition metal dichalcogenide (TMDCs) such as MoS2 and graphene, forming an heterostructure is very interesting, since it combines the excellent optical properties of MoS2 and the high mobility and transparency of graphene[9,10,11,12]. MoS2 grown by this approach has high crystallinity, with large flakes (between 20–100 μm) and electrical and optical properties comparable to exfoliated material These CVD-grown flakes are suitable for transfer onto epitaxial graphene/SiC substrate in order to obtain large area of MoS2/graphene heterostructures. Using a transfer process (see results and discussion and Fig. 1(a)) we have obtained monolayer and bilayer MoS2/graphene heterostructures, allowing the study of interlayer interaction between TDMCs materials and graphene on a large scale, using several complementary techniques. This work may open a new way in graphene optoelectronics by modulating the graphene photoelectric response through 2D materials interfacing
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