Rotationally Commensurate Growth of MoS₂on Epitaxial Graphene

Abstract

Atomically thin MoS2/graphene heterostructures are promising candidates for nanoelectronic and optoelectronic technologies. Among different graphene substrates, epitaxial graphene (EG) on SiC provides several potential advantages for such heterostructures, including high electronic quality, tunable substrate coupling, wafer-scale processability, and crystalline ordering that can template commensurate growth. Exploiting these attributes, we demonstrate here the thickness-controlled van der Waals epitaxial growth of MoS2 on EG via chemical vapor deposition, giving rise to transfer-free synthesis of a two-dimensional heterostructure with registry between its constituent materials. The rotational commensurability observed between the MoS2 and EG is driven by the energetically favorable alignment of their respective lattices and results in nearly strain-free MoS2, as evidenced by synchrotron X-ray scattering and atomic-resolution scanning tunneling microscopy (STM). The electronic nature of the MoS2/EG heterostructure is elucidated with STM and scanning tunneling spectroscopy, which reveals bias-dependent apparent thickness, band bending, and a reduced band gap of ∼0.4 eV at the monolayer MoS2 edges.

Bandgap inhomogeneity of MoS2 monolayer on epitaxial graphene bilayer in van der Waals p-n junction

“…This ratio between the shifts of E 1 2g and A 1g is in accordance with the results reported on the effect of uniform biaxial strain on the Raman spectrum of MoS 2 [29]. Meanwhile, the widths of the peaks, calculated by means of a Lorentzian fitting, are barely unchanged.…”

“…4(c) measured, using a laser spot whose diameter is about 1 mm, in the centers of the small and big MoS 2 flakes (red and blue curves, respectively), we can obviously see that both peaks corresponding to the big flake are red-shifted. These downshifts can be explained based on the difference in the tensile strain sustained by MoS 2 flakes [37,39,40] rather than a difference in the doping levels caused by a dissimilarity in charge transfer for the two systems (if doping occurred, we would observe an up-shift of the A 1g mode while the E 1 2g mode remains unchanged [29,41] since graphene is p-doped, but this not the case here). The atomic displacements of these two modes are illustrated in Fig.…”

“…These values of the bandgap, determined by PL spectroscopy and known as optical bandgap, are different from that determined by electronic transport due to the exciton binding energy [29]. As shown in the graph in Fig.…”

Electrolytic phototransistor based on graphene-MoS2 van der Waals p-n heterojunction with tunable photoresponse

“…As shown in Figure S2(a), this value corresponds to the main transition peak in the spectrum (named A) arising from the direct inter-band recombination at the K-point of the Brillouin zone of the photogenerated electron-hole pairs [42][43][44] . However it should be noted that using STS the obtained electronic band gap is 2 eV 45 , which is 0.17 eV larger than the optical band gap due to the high excitonic binding energy for this 2D system. We then investigated the photoresponse of the electrolytic transistor.…”

Fundamentals of Chemical Vapor Deposited Graphene and Emerging Applications

“…TMDC layers have been combined with graphene and hBN for the fabrication of transistors, photodetectors, solar cell, sensors, [114]. The graphene-MoS 2 heterostructures have also been adopted to demonstrate an extremely high photo-gain and the ultrasensitive sensors fabrication [118,119]. Considering the significant potential, efforts have been made to grow graphene-TMDCs hybrid structures by a CVD technique (Figure 12).…”