Effect of Ultraviolet-Ozone Treatment on MoS 2 Monolayers: Comparison of Chemical-Vapor-Deposited Polycrystalline Thin Films and Mechanically Exfoliated Single Crystal Flakes

摘要

We report the different oxidation behavior between polycrystalline chemical-vapor-deposited and mechanically exfoliated single crystal MoS~(2)monolayers by ultraviolet-ozone treatment. As ultraviolet-ozone treatment time increased from 0 to 5?min, photoluminescence emission and Raman modes of both MoS~(2)disappeared, suggesting structural degradation by oxidation. Analysis with optical absorbance and X-ray photoelectron spectroscopy suggested the formation of MoO~(3)in both MoS~(2)after ultraviolet-ozone treatment. In addition, ultraviolet-ozone treatment possibly led to the formation of oxygen vacancies, molybdenum oxysulfide, or molybdenum sulfates in chemical-vapor-deposited MoS~(2). The measurement of electrical resistance after ultraviolet-ozone treatment suggested the transformation of chemical-vapor-deposited MoS~(2)into doped MoO~(3)and of mechanically exfoliated MoS~(2)into negligibly doped MoO~(3). These results demonstrate that the crystallinity of monolayer MoS~(2)can strongly influence the effect of ultraviolet-ozone treatment, providing important implications on the device integration of MoS~(2)and other two-dimensional semiconductors.