An effective approach to synthesize monolayer tungsten disulphide crystals using tungsten halide precursor

Abstract

The synthesis of large-area monolayer tungsten disulphide (WS2) single crystal is critical for realistic application in electronic and optical devices. Here, we demonstrate an effective approach to synthesize monolayer WS2 crystals using tungsten hexachloride (WCl6) as a solid precursor in atmospheric chemical vapor deposition process. In this technique, 0.05M solution of WCl6 in ethanol was drop-casted on SiO2/Si substrate to create an even distribution of the precursor, which was reduced and sulfurized at 750 °C in Ar atmosphere. We observed growth of triangular, star-shaped, as well as dendritic WS2 crystals on the substrate. The crystal geometry evolves with the shape and size of the nuclei as observed from the dendritic structures. These results show that controlling the initial nucleation and growth process, large WS2 single crystalline monolayer can be grown using the WCl6 precursor. Our finding shows an easier and effective approach to grow WS2 monolayer using tungsten halide solution-casting, rather than evaporating the precursor for gas phase reaction.

Facile and Controllable Synthesis of Large-Area Monolayer WS2 Flakes Based on WO3 Precursor Drop-Casted Substrates by Chemical Vapor Deposition

“…Due to the differences in the nucleation density and local environment on the substrate, the dimension distribution of the triangular flakes is quite wide, from tens to hundreds of micrometers, while large triangular WS 2 flakes with edge lengths of ~270 μm are readily obtained on the covering SiO 2 /Si substrate, as shown in Figure 2a. In addition, truncated-triangle, hexagon, and butterfly-shaped flakes are formed on the covering SiO 2 /Si substrate as well (as shown in Supplementary Materials Figure S3), which was observed in previous CVD-grown WS 2 and MoS 2 and explained from the point of the changes in the M:S (M = Mo, W) ratio of the precursors within the growth interface [6,31,42,43].…”

Scalable synthesis of WS 2 on graphene and h-BN: an all-2D platform for light-matter transduction

“…No isolated triangular crystal [11,15,20] is observed and the uniform distribution of WS 2 on the flake is confirmed by Raman spectroscopy, which is instrumental in identifying the nature and the thickness of TMDs [21,22]. The intensity ratio of the inplane vibrational mode E 2g 1 and of the out-of-plane vibrational mode A 1g is indicative of the thickness of WS 2 when using specific excitation wavelengths such as that adopted in this work, i.e., 532 nm [21,23,24]. As visible in figure 1(b), the A E 1g 2g…”

“…1 ∼ 1) [23] (see also supporting information). Local monolayer inclusions are observed especially in proximity and within transfer-generated tears of graphene (which are visible in the optical image in panel (c)).…”

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

“…Chemical vapor deposition (CVD) is the most popular, specifically using elemental sulfur and metal oxides (i.e., MoO x or WO x ) as precursors . Other precursors have also been reported, including metal chlorides (e.g., MoCl 5 and WCl 6 ) or carbonyls (e.g., Mo(CO) 6 or W(CO) 6 ) with hydrogen sulfide gas (H 2 S) . Although successful, these methods become challenging for TMDs that are less stable due to rapid oxidation (e.g., NbSe 2 ) .…”