Monolayer Tungsten Disulfide (WS₂) via Chlorine‐Driven Chemical Vapor Transport

Abstract

Large-scale production of high-quality tungsten disulfide (WS ) monolayers is a prerequisite for potential device applications using this promising transition metal dichalcogenide semiconductor. The most researched technique is chemical vapor deposition, typically involving the reaction of sulfur vapors with tungsten oxide. Other techniques such as physical vapor deposition have been explored with some success, but low vapor pressures make growth difficult. This study demonstrates a growth process that relies on halide-driven vapor transport commonly utilized in bulk crystal growth. Using a small amount of sodium chloride salt as a source of chlorine, nonvolatile WS can react to form gaseous tungsten chloride and sulfur. With an open tube system, a controlled reaction generates mono and few-layer WS crystals. Optical and physical characterization of the monolayer material shows good uniformity and triangular domains over 50 µm in length. Photoluminescence transient measurements show similar nonlinear exciton dynamics as exfoliated flakes, attributed to multiparticle physics. Requiring only the powder of the desired crystal and appropriate halide salt as precursors, the technique has the potential to realize other layered materials that are challenging to grow with current processes.

Realization of Quantum Hall Effect in Chemically Synthesized InSe

“…Recently, a small amount of NaCl salt has been used as a source of chlorine to facilitate the synthesis of single‐layer transition metal dichalcogenides, due to its lower transport ability. Furthermore, the addition of NaCl played a key role in lowering the growth temperatures, as Na‐containing precursors that condensed on the substrates provided nucleation sites and reduced the energy of the reaction .…”

CVD controlled growth of large-scale WS2 monolayers

“…They suggested that nonvolatile WS 2 reacts with NaCl to form gaseous tungsten chloride and sulfur. 48 Wang et al synthesized MoS 2 -WS 2 in-plane heterostructures by ambient pressure chemical vapor deposition. They suggested Na-containing intermediate product is formed, which reduces the reaction energy.…”

2D Transition Metal Dichalcogenide Thin Films Obtained by Chemical Gas Phase Deposition Techniques

“…The use of NaCl can modify the shape and quality of TMDs, Song et al, for example, employed NaCl as a catalyst, which is effective in comparison with S organic compounds in improving the growth rate (5 min for monolayer MoS 2 ). The MoS 2 synthesized using NaCl presented a large grain size (≈50 µm) and showed conformality on a wafer scale (≈6 in.)…”