title: Raman Shifts in Electron-Irradiated Monolayer MoS2.
abstract: We report how the presence of electron-beam-induced sulfur vacancies affects first-order Raman modes and correlate the effects with the evolution of the in situ transmission-electron microscopy two-terminal conductivity of monolayer MoS2 under electron irradiation. We observe a red-shift in the E' Raman peak and a less pronounced blue-shift in the A'1 peak with increasing electron dose. Using energy-dispersive X-ray spectroscopy and selected-area electron diffraction, we show that irradiation causes partial removal of sulfur and correlate the dependence of the Raman peak shifts with S vacancy density (a few %). This allows us to quantitatively correlate the frequency shifts with vacancy concentration, as rationalized by first-principles density functional theory calculations. In situ device current measurements show an exponential decrease in channel current upon irradiation. Our analysis demonstrates that the observed frequency shifts are intrinsic properties of the defective systems and that Raman spectroscopy can be used as a quantitative diagnostic tool to characterize MoS2-based transport channels.
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: William M
authors.initials: WM
authors.lastname: Parkin
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Adrian
authors.initials: A
authors.lastname: Balan
authors.affiliation: Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute , Troy, New York 12180, United States.|Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Liangbo
authors.initials: L
authors.lastname: Liang
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Paul Masih
authors.initials: PM
authors.lastname: Das
authors.affiliation: Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute , Troy, New York 12180, United States.
authors.forename: Michael
authors.initials: M
authors.lastname: Lamparski
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Carl H
authors.initials: CH
authors.lastname: Naylor
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Julio A
authors.initials: JA
authors.lastname: Rodríguez-Manzo
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: A T Charlie
authors.initials: AT
authors.lastname: Johnson
authors.affiliation: Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute , Troy, New York 12180, United States.
authors.forename: Vincent
authors.initials: V
authors.lastname: Meunier
authors.affiliation: Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States.
authors.forename: Marija
authors.initials: M
authors.lastname: Drndić
mesh_terms: D003460:Crystallization; D004220:Disulfides / Q000737:chemistry* / Q000528:radiation effects; D004553:Electric Conductivity; D004583:Electrons; D046529:Microscopy, Electron, Transmission; D008962:Models, Theoretical; D008982:Molybdenum / Q000737:chemistry* / Q000528:radiation effects; D049329:Nanostructures; D055585:Physical Phenomena; D011789:Quantum Theory; D017655:Silicon Compounds / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission; D013059:Spectrum Analysis, Raman
chemical_list: D004220:Disulfides; D017655:Silicon Compounds; D008982:Molybdenum; C032734:silicon nitride; C082964:molybdenum disulfide
keywords: MoS2; Raman; in situ transmission electron microscopy; transition-metal dichalcogenide; two-dimensional material