CVD Synthesis of Intermediate State-Free, Large-Area and Continuous MoS2 via Single-Step Vapor-Phase Sulfurization of MoO2 Precursor

Abstract

The low evaporation temperature and carcinogen classification of commonly used molybdenum trioxide (MoO3) precursor render it unsuitable for the safe and practical synthesis of molybdenum disulfide (MoS2). Furthermore, as evidenced by several experimental findings, the associated reaction constitutes a multistep process prone to the formation of uncontrolled amounts of intermediate MoS2−yOy phase mixed with the MoS2 crystals. Here, molybdenum dioxide (MoO2), a chemically more stable and safer oxide than MoO3, was utilized to successfully grow cm-scale continuous films of monolayer MoS2. A high-resolution optical image stitching approach and Raman line mapping were used to confirm the composition and homogeneity of the material grown across the substrate. A detailed examination of the surface morphology of the continuous film revealed that, as the gas flow rate increased by an order of magnitude, the grain-boundary separation dramatically reduced, implying a transition from a kinetically to thermodynamically controlled growth. Importantly, the single-step vapor-phase sulfurization (VPS) reaction of MoO2 was shown to suppress intermediate state formations for a wide range of experimental parameters investigated and is completely absent, provided that the global S:Mo loading ratio is set higher than the stoichiometric ratio of 3:1 required by the VPS reaction.

Controlled growth of 3D assemblies of edge enriched multilayer MoS2 nanosheets for dually selective NH3 and NO2 gas sensors

“…Herein, the CVD is controlled by a surface reaction. [40][41][42] Therefore, at an argon flow rate of 30 ml min À1 , we have a perfect fit between the surface interaction and the mass transport of precursor molecules, resulting in a suitable morphology for gas sensor fabrication. In fact, it offers a large surface area to volume ratio with enriched exposed edge sites, has plenty of voids for gas diffusion, and has many defects that make it highly reactive with gas molecules.…”

NaCl-Assisted Temperature-Dependent Controllable Growth of Large-Area MoS2 Crystals Using Confined-Space CVD

“…The Raman maps were obtained for both the vibrating modes E 1 2g and A 1g , as shown in Figure b–d. The Raman mapping indicates that the flake is uniform and has high crystallinity …”

Vapor–Liquid–Solid Growth of Site-Controlled Monolayer MoS2 Films Via Pressure-Induc ed Supercritical Phase Nucleation

“…8−11 MoS 2 , as a typical TMDCs, has the most systematic study of its CVD growth mechanism. 12−15 The conventional CVD growth mechanism is a vapor−solid−solid reaction, depending on the evaporation of inorganic volatile powder precursors such as MoO 3 16,17 and MoO 2 18,19 and sulfurization in the gas phase to form MoS 2 , which can deposit on arbitrary substrates. 20 However, the spatial distribution of precursor vapor concentration is inhomogeneous, resulting in monolayer MoS 2 domains with nonuniform sizes on the substrate.…”

“…Therefore, controlled growth of high-quality and large-area TMDC films is crucial. Chemical vapor deposition (CVD) is utilized as the most suitable method for growing two-dimensional films because of its advantages such as low cost, easy operation, and large scale. − MoS 2 , as a typical TMDCs, has the most systematic study of its CVD growth mechanism. − The conventional CVD growth mechanism is a vapor–solid–solid reaction, depending on the evaporation of inorganic volatile powder precursors such as MoO 3 , and MoO 2 , and sulfurization in the gas phase to form MoS 2 , which can deposit on arbitrary substrates . However, the spatial distribution of precursor vapor concentration is inhomogeneous, resulting in monolayer MoS 2 domains with nonuniform sizes on the substrate. , Furthermore, whether the surface sulfurization reaction of precursors , or surface nucleation growth after gas phase sulfurization , is utilized, random nucleation sites are inevitably generated on the substrate or on the monolayer MoS 2 , which degrades the film quality.…”