title: Vapor-phase growth and characterization of Mo(1-x)W(x)S2 (0 ≤ x ≤ 1) atomic layers on 2-inch sapphire substrates.
abstract: Atomically thin Mo(1-x)W(x)S2 (0 ≤ x ≤ 1) ternary compounds have been grown on 2-inch c-plane sapphire substrates with high uniformity by sulfurizing thin Mo(1-x)W(x) layers that were deposited at room temperature using a co-sputtering technique. Atomic force microscopy (AFM), Raman scattering, and optical absorbance spectroscopy (OAS) studies reveal that the Mo(1-x)W(x)S2 films consist of crystallites of two-to-four monolayers in thickness. X-ray photoelectron spectroscopy (XPS) shows that the core levels of Mo3d and W4f shift to lower binding energies while that of S2p shifts to higher ones with the increase in W compositions, which can be related to the larger electron affinity of W (0.8163 eV) than that of Mo (0.7473 eV). OAS has also shown that the direct bandgap of Mo(1-x)W(x)S2 is tuned from 1.85 to 1.99 eV by increasing x from 0 to 1. Both E(1/2)(g) and A(1g) phonon modes of the Mo(1-x)W(x)S2 films exhibit a two-mode behavior. The bandgap tuning and the two-mode phonon behaviors are typically the same as those recently observed in monolayer Mo(1-x)W(x)S2 obtained by mechanical exfoliation, thus shedding light on the bottom-up growth of large-scale two-dimensional Mo(1-x)W(x)S2 ternary alloys.
authors.affiliation: Institute of Materials Research and Engineering (IMRE), A*STAR Agency for Science, Technology and Research, 3 Research Link, Singapore 117602, Singapore. liuhf@imre.a-star.edu.sg.
authors.forename: Hongfei
authors.initials: H
authors.lastname: Liu
authors.forename: K K Ansah
authors.initials: KK
authors.lastname: Antwi
authors.forename: Soojin
authors.initials: S
authors.lastname: Chua
authors.forename: Dongzhi
authors.initials: D
authors.lastname: Chi