Growth of atomically thick transition metal sulfide films on graphene/6H-SIC(0001) by molecular beam epitaxy

We report the growth and characterization of atomically thick NbS2, TaS2, and FeS films on a 6H-SiC(0001) substrate terminated with monolayer or bilayer epitaxial graphene. The crystal and electronic structures are studied by scanning tunneling microscopy and reflection high-energy electron diffraction. The NbS2 monolayer is solely in the 2H structure, while the TaS2 monolayer contains both 1T and 2H structures. Charge-density waves are observed in all phases. For the FeS films, the tetragonal structure coexists with the hexagonal one and no superconductivity is observed.