title: Highly scalable, atomically thin WSe2 grown via metal-organic chemical vapor deposition.
abstract: Tungsten diselenide (WSe2) is a two-dimensional material that is of interest for next-generation electronic and optoelectronic devices due to its direct bandgap of 1.65 eV in the monolayer form and excellent transport properties. However, technologies based on this 2D material cannot be realized without a scalable synthesis process. Here, we demonstrate the first scalable synthesis of large-area, mono and few-layer WSe2 via metal-organic chemical vapor deposition using tungsten hexacarbonyl (W(CO)6) and dimethylselenium ((CH3)2Se). In addition to being intrinsically scalable, this technique allows for the precise control of the vapor-phase chemistry, which is unobtainable using more traditional oxide vaporization routes. We show that temperature, pressure, Se:W ratio, and substrate choice have a strong impact on the ensuing atomic layer structure, with optimized conditions yielding >8 μm size domains. Raman spectroscopy, atomic force microscopy (AFM), and cross-sectional transmission electron microscopy (TEM) confirm crystalline monoto-multilayer WSe2 is achievable. Finally, TEM and vertical current/voltage transport provide evidence that a pristine van der Waals gap exists in WSe2/graphene heterostructures.
authors.affiliation: Department of Materials Science and Engineering, ‡Center for Two-Dimensional and Layered Materials, and ⊥Department of Electrical Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Eichfeld
authors.forename: Lorraine
authors.initials: L
authors.lastname: Hossain
authors.forename: Yu-Chuan
authors.initials: YC
authors.lastname: Lin
authors.forename: Aleksander F
authors.initials: AF
authors.lastname: Piasecki
authors.forename: Benjamin
authors.initials: B
authors.lastname: Kupp
authors.forename: A Glen
authors.initials: AG
authors.lastname: Birdwell
authors.forename: Robert A
authors.initials: RA
authors.lastname: Burke
authors.forename: Ning
authors.initials: N
authors.lastname: Lu
authors.forename: Xin
authors.initials: X
authors.lastname: Peng
authors.forename: Jie
authors.initials: J
authors.lastname: Li
authors.forename: Angelica
authors.initials: A
authors.lastname: Azcatl
authors.forename: Stephen
authors.initials: S
authors.lastname: McDonnell
authors.forename: Robert M
authors.initials: RM
authors.lastname: Wallace
authors.forename: Moon J
authors.initials: MJ
authors.lastname: Kim
authors.forename: Theresa S
authors.initials: TS
authors.lastname: Mayer
authors.forename: Joan M
authors.initials: JM
authors.lastname: Redwing
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Robinson
keywords: WSe2; graphene; metal organic chemical vapor deposition (MOCVD); synthesis; transition-metal dichalcogenide; tungsten diselenide; two-dimensional (2D) materials