Vapor-phase growth and characterization of Mo sub(1-x)W sub(x)S sub(2) (0 less than or equal to x less than or equal to 1) atomic layers on 2-inch sapphire substrates

• Published in: Nanoscale Vol. 6; no. 1; pp. 624 - 629
• Main Authors: Liu, Hongfei, Antwi, KKAnsah, Chua, Soojin, Chi, Dongzhi
• Format: Journal Article
• Language: English
• Published: 01.12.2013
• Subjects: Atomic force microscopy
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/c3nr04515c

Atomically thin Mo sub(1-x)W sub(x)S sub(2) (0 less than or equal to x less than or equal to 1) ternary compounds have been grown on 2-inch c-plane sapphire substrates with high uniformity by sulfurizing thin Mo sub(1-x)W sub(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 sub(1-x)W sub(x)S sub(2) 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 sub(1-x)W sub(x)S sub(2) is tuned from 1.85 to 1.99 eV by increasing x from 0 to 1. Both E super(1) sub(2g) and A sub(1g) phonon modes of the Mo sub(1-x)W sub(x)S sub(2) 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 sub(1-x)W sub(x)S sub(2) obtained by mechanical exfoliation, thus shedding light on the bottom-up growth of large-scale two-dimensional Mo sub(1-x)W sub(x)S sub(2) ternary alloys.