title: Understanding the Intrinsic Water Wettability of Molybdenum Disulfide (MoS2).
abstract: 2D semiconductors allow for unique and ultrasensitive devices to be fabricated for applications ranging from clinical diagnosis instruments to low-energy light-emitting diodes (LEDs). Graphene has championed research in this field since it was first fabricated; however, its zero bandgap creates many challenges. Transition metal dichalcogenides (TMDCs), e.g., MoS2, have a direct bandgap which alleviates the challenge of creating a bandgap in graphene-based devices. Water wettability of MoS2 is critical to device fabrication/performance and MoS2 has been believed to be hydrophobic. Herein, we report that water contact angle (WCA) of freshly exfoliated MoS2 shows temporal evolution with an intrinsic WCA of 69.0 ± 3.8° that increases to 89.0 ± 3.1° after 1 day exposure to ambient air. ATR-FTIR and ellipsometry show that the fresh, intrinsically mildly hydrophilic MoS2 surface adsorbs hydrocarbons from ambient air and thus becomes hydrophobic.
authors.forename: Andrew
authors.initials: A
authors.lastname: Kozbial
authors.forename: Xiao
authors.initials: X
authors.lastname: Gong
authors.affiliation: ‡Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States.
authors.forename: Haitao
authors.initials: H
authors.lastname: Liu
authors.forename: Lei
authors.initials: L
authors.lastname: Li