First-principles calculations integrated with experimental optical and electronic properties for MoS2-graphene heterostructures and MoS2-graphene-Au heterointerfaces

We present a computational and experimental study for various heterostructures and heterointerfaces comprising two-dimensional (2D) molybdenum disulfide (MoS2) and graphene (Gr) supported on gold (Au). These structures are useful for photo-electrochemical and nanophotonic applications, as well as for hydrogen generation. The frequency-dependent dielectric function, the refractive index, and the reflectivity are calculated using light polarization parallel and perpendicular to the respective monolayer c axis. We identify the transitions within MoS2 and graphene, which correspond to peaks in the imaginary part of the frequency-dependent dielectric function. The Gr-MoS2 dielectric function appears as a composition of the corresponding dielectric functions from the isolated monolayers with their peaks being shifted. However, for the Gr-MoS2-Au heterointerfaces, some of these peaks from the isolated monolayers are no longer detected. Charge transfers and work function calculations show that MoS2 and graphene are n and p-type semiconductors, respectively, which agree with our experimental local photoconductivity measurements. The heterojunction behavior for Gr-MoS2 is attributed to the interlayer electronic coupling, while minimizing Fermi level pinning at the MoS2/Au interface and charge transfers from graphene to MoS2. Thus, interfacing MoS2 with graphene signifies substrate engineering, allowing tunable MoS2 physical properties for diverse applications across the electromagnetic spectrum.