Integrated density functional theory and experimental study of optical and electronic properties for MoS2/ (Metal=Au, Pt, Ni, Cu) and MoS2/ Graphene/Metal heterointerfaces

We present computational simulations and experimental analyses of various heterointerfaces constructed from two-dimensional molybdenum disulfide (MoS2) and graphene on gold (Au), platinum (Pt), nickel (Ni), and copper (Cu) substrates. We combined density functional theory electronic structure, optical properties, and work function to elucidate heterostructure changes due to metal selection, corroborated with experimentally determined surface electronic properties. Here, we correlate shifts in the metal d-band center relative to the Fermi energy with the MoS2 bandgaps and bandgaps in the Dirac point region of the MoS2/graphene/Metal heterointerfaces. For the Ni heterointerfaces, the upshift of the metal d-band relative to the Fermi energy leads to increased coupling with the MoS2 d-bands and the graphene carbon-sp2 bands, which decreases the MoS2 bandgap and opens a bandgap at the Dirac point. The later bandgap strengthens the pi -> pi* transition, as evidenced by the peaks in out-of-plane components of the imaginary part of the frequency-dependent dielectric function. Sulfur vacancies in MoS2/Au introduce flat bands in the band structure, indicating possible interband and intraband transitions, verified by peaks in the dielectric function imaginary part in the sub eV region. MoS2 is inherently an n-type semiconductor, whereas, for graphene insertion between MoS2 and metal, the direction of the electron transfer flow depends on the metal-yielding semiconducting pn diode-like behavior. The MoS2/Gr/Pt exhibited the highest work function and one of the largest bandgaps among other samples, leading to low electrical conductivity.