Vapor-phase growth and characterization of Mo1−xWxS2 (0 ≤ x ≤ 1) atomic layers on 2-inch sapphire substrates

• Main Authors: Liu, Hongfei, Antwi, K. K. Ansah, Chua, Soojin, Chi, Dongzhi
• Format: Journal Article
• Language: English; Japanese
• Published: 01.01.2014
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/c3nr04515c

Atomically thin Mo 1− x W x S 2 (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 S 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 1− x W x S 2 is tuned from 1.85 to 1.99 eV by increasing x from 0 to 1. Both E 1 2g and A 1g phonon modes of the Mo 1− x W x S 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 1− x W x S 2 obtained by mechanical exfoliation, thus shedding light on the bottom-up growth of large-scale two-dimensional Mo 1− x W x S 2 ternary alloys. Two-dimensional Mo 1− x W x S 2 alloys with Mo/W atoms randomly mixed in the lattice have been grown on 2-inch sapphire substrates by vapor-phase deposition.