Direct Observation of Interlayer Hybridization and Dirac Relativistic Carriers in Graphene/MoS₂ van der Waals Heterostructures

Abstract

Artificial heterostructures assembled from van der Waals materials promise to combine materials without the traditional restrictions in heterostructure-growth such as lattice matching conditions and atom interdiffusion. Simple stacking of van der Waals materials with diverse properties would thus enable the fabrication of novel materials or device structures with atomically precise interfaces. Because covalent bonding in these layered materials is limited to molecular planes and the interaction between planes are very weak, only small changes in the electronic structure are expected by stacking these materials on top of each other. Here we prepare interfaces between CVD-grown graphene and MoS2 and report the direct measurement of the electronic structure of such a van der Waals heterostructure by angle-resolved photoemission spectroscopy. While the Dirac cone of graphene remains intact and no significant charge transfer doping is detected, we observe formation of band gaps in the π-band of graphene, away from the Fermi-level, due to hybridization with states from the MoS2 substrate.

Tuning the electronic structure of monolayer graphene/MoS2van der Waals heterostructures via interlayer twist

“…Another set of ARPES measurements of an MBE-grown MoSe 2 thin film, which was formed on a bilayer of graphene/SiC, also showed no evidence of band hybridization between the MoSe 2 and graphene electronic states [38]. However, a recent ARPES study of CVD-grown graphene on a bulk MoS 2 crystal shows modification of the graphene π-bands by way of hybridization with bulk MoS 2 bands, mostly at higher binding energies than measured here [25]. Presumably, the increase in the number of states with out-ofplane character, as is the case for bulk MoS 2 , increases the possibility for hybridization in comparison to our case of monolayer MoS 2 .…”

“…These theoretical and optical investigations have led to a pressing need for a full understanding of the electronic structure of Gr/MoS 2 vdW heterostructures. Very recently, photoemission measurements of Gr/MoS 2 interface have been attempted [24][25][26]. Thus Coy-Diaz et al examined a twisted interface between polycrystalline graphene and a bulk MoS 2 crystal [24,25], while Miwa et al examined the electronic structure of a multidomain epitaxial MoS 2 -graphene heterostructure, which is laterally averaged over different orientations [26].…”

“…Very recently, photoemission measurements of Gr/MoS 2 interface have been attempted [24][25][26]. Thus Coy-Diaz et al examined a twisted interface between polycrystalline graphene and a bulk MoS 2 crystal [24,25], while Miwa et al examined the electronic structure of a multidomain epitaxial MoS 2 -graphene heterostructure, which is laterally averaged over different orientations [26]. In all, a direct experimental investigation of the evolution of the momentumresolved electronic structure with twist angle in Gr/MoS 2 twisted bilayer has, thus far, been lacking.…”

Dirac Cones in Graphene, Interlayer Interaction in Layered Materials, and the Band Gap in MoS2

“…The changes in electronic structure of graphene caused by interaction with MoS 2 monolayer were suggested to be less pronounced. From ARPES study of this heterostructure Diaz et al [92] concluded that the Dirac cone of graphene remains intact and no significant charge transfer doping was detected. Later, Pierucci et al [93] confirmed that, close to the Fermi level, graphene exhibits a robust, almost perfect, gapless Dirac cone, but suggested the graphene to be n-doped.…”

“…A number of recent papers was devoted to detailed studies of a model 2D heterostructure formed of a single layer of MoS 2 on graphene [88][89][90][91][92][93]. It was found that the electronic structure of two-dimensional (2D) semiconductors can be significantly altered by screening effects.…”