Determination of the Fermi velocity of graphene on MoS2 using dual mode scanning tunneling spectroscopy

We have measured the Fermi velocity of graphene on MoS2 using dual mode scanning tunneling spectroscopy. In our method, the tunnel current (I) and the derivate of the current to the gap width (dI/dz) are measured simultaneously as a function of sample bias (V) at a constant tip-substrate distance. Owing to the difference in lattice constants between graphene (2.461 A) and MoS2 (3.161 A), a moire structure is found with a periodicity of 1.07 nm and a twist angle of 4°. Our experiments reveal that the electronic band structure of graphene remains intact in the bandgap region of MoS2. The Fermi velocity of graphene on MoS2 is determined to be 1.2 ± 0.1 × 10 6 m / s.