title: Atomic-Scale Spectroscopy of Gated Monolayer MoS2.
abstract: The electronic properties of semiconducting monolayer transition-metal dichalcogenides can be tuned by electrostatic gate potentials. Here we report gate-tunable imaging and spectroscopy of monolayer MoS2 by atomic-resolution scanning tunneling microscopy/spectroscopy (STM/STS). Our measurements are performed on large-area samples grown by metal-organic chemical vapor deposition (MOCVD) techniques on a silicon oxide substrate. Topographic measurements of defect density indicate a sample quality comparable to single-crystal MoS2. From gate voltage dependent spectroscopic measurements, we determine that in-gap states exist in or near the MoS2 film at a density of 1.3 × 10(12) eV(-1) cm(-2). By combining the single-particle band gap measured by STS with optical measurements, we estimate an exciton binding energy of 230 meV on this substrate, in qualitative agreement with numerical simulation. Grain boundaries are observed in these polycrystalline samples, which are seen to not have strong electronic signatures in STM imaging.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zhou
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853, United States.
authors.forename: Kibum
authors.initials: K
authors.lastname: Kang
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853, United States.
authors.forename: Saien
authors.initials: S
authors.lastname: Xie
authors.forename: Ali
authors.initials: A
authors.lastname: Dadgar
authors.forename: Nicholas R
authors.initials: NR
authors.lastname: Monahan
authors.forename: X-Y
authors.initials: XY
authors.lastname: Zhu
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853, United States.
authors.forename: Jiwoong
authors.initials: J
authors.lastname: Park
authors.forename: Abhay N
authors.initials: AN
authors.lastname: Pasupathy
keywords: Monolayer molybdenum disulfide; exciton binding energy; grain boundary; scanning tunneling microscopy/spectroscopy; single-particle band gap