Atomic-scale defects and electronic properties of a transferred synthesized MoS2 monolayer

MoS2 monolayer samples were synthesized on a SiO2/Si wafer and transferred to Ir(111) for nanoscale characterization. The samples were extensively characterized during every step of the transfer process, and MoS2 on the final substrate was examined down to the atomic level by scanning tunneling microscopy (STM). The procedures conducted yielded high-quality monolayer MoS2 of milimeter-scale size with an average defect density of 2 x 10(13) cm(-2). The lift-off from the growth substrate was followed by a release of the tensile strain, visible in a widening of the optical band gap measured by photoluminescence. Subsequent transfer to the Ir(111) surface led to a strong drop of this optical signal but without further shifts of characteristic peaks. The electronic band gap was measured by scanning tunneling spectroscopy (STS), revealing n-doping and lateral nanoscale variations. The combined use of STM imaging and density functional theory (DFT) calculations allows us to identify the most recurring point-like defects as S vacancies.