Band Alignment and Minigaps in Monolayer MoS₂-Graphene van der Waals Heterostructures

Abstract

Two-dimensional layered MoS2 shows great potential for nanoelectronic and optoelectronic devices due to its high photosensitivity, which is the result of its indirect to direct band gap transition when the bulk dimension is reduced to a single monolayer. Here, we present an exhaustive study of the band alignment and relativistic properties of a van der Waals heterostructure formed between single layers of MoS2 and graphene. A sharp, high-quality MoS2-graphene interface was obtained and characterized by micro-Raman spectroscopy, high-resolution X-ray photoemission spectroscopy (HRXPS), and scanning high-resolution transmission electron microscopy (STEM/HRTEM). Moreover, direct band structure determination of the MoS2/graphene van der Waals heterostructure monolayer was carried out using angle-resolved photoemission spectroscopy (ARPES), shedding light on essential features such as doping, Fermi velocity, hybridization, and band-offset of the low energy electronic dynamics found at the interface. We show that, close to the Fermi level, graphene exhibits a robust, almost perfect, gapless, and n-doped Dirac cone and no significant charge transfer doping is detected from MoS2 to graphene. However, modification of the graphene band structure occurs at rather larger binding energies, as the opening of several miniband-gaps is observed. These miniband-gaps resulting from the overlay of MoS2 and the graphene layer lattice impose a superperiodic potential.

Mass inversion in graphene by proximity to dichalcogenide monolayer

“…3c, which show how the low energy spectrum exhibits a finite gap for fully spin polarized bands. This band alignment agrees well with recent experiments in such bilayer system [29].…”

“…The SOC in the valence bands is much larger than in the conduction bands, with strength that varies with the transition metal [26]. Successful growth of graphene on MoS 2 and WS 2 has been demonstrated experimentally [22,[27][28][29][30]. First principles calculations on some of these systems have proved challenging [21][22][23], with reported results that differ qualitatively and quantitatively.…”

“…1, as the voltage changes. The fits are excellent (to less than 1 %) up to an energy 0.3 eV away from the graphene Dirac point, with nearly linear dispersion at higher energies [29]. The effective model describes not only the lowenergy band dispersion, but also the full spin and pseudospin structure of the states, illustrating the generality of the model [39].…”

Moiré-related in-gap states in a twisted MoS2/graphite heterojunction

“…The band profile and morphology have been revealed in previous STM/STS investigations, [22][23][24][25][26] and the opening of a band gap in graphene by overlaying a MoS 2 monolayer has been observed using angle-resolved photoemission spectroscopy. 27,28 However, the detailed connection between the atomic structure of the twisted heterojunction and the corresponding electronic structure is still lacking. Huang et al have visualized the moiré patterns clearly, and also shown using STS that the MoS 2 band gap is tunable by the local strain field.…”

Van Der Waals Heterostructures between Small Organic Molecules and Layered Substrates

“…G, MoS2, and h-BN are all chemically inert, avoiding bonding strongly when integrating with different dimensional crystals at the interface and leading to 2D-2D and 0D-2D (organic molecules-2D) van der Waals (vdW) heterostructures [25][26][27]. For example, MoS2-G vdW heterostructure shows that close to the Fermi level, no significant charge transfer doping is detected from MoS2 to G [28,29]. Besides, organic molecules are able to grow into well-ordered thin film with a high degree of crystallinity on 2D substrates and form vdW heterostructures.…”