Gas-Source CVD Growth of Atomic Layered WS2 from WF6 and H2S Precursors with High Grain Size Uniformity

Abstract

Two-dimensional (2D) transition-metal dichalcogenides have attracted a considerable amount of attention because of their potential for post-silicon device applications, as well as for exploring fundamental physics in an ideal 2D system. We tested the chemical vapour deposition (CVD) of WS2 using the gaseous precursors WF6 and H2S, augmented by the Na-assistance method. When Na was present during growth, the process created triangle-shaped WS2 crystals that were 10 μm in size and exhibited semiconducting characteristics. By contrast, the Na-free growth of WS2 resulted in a continuous film with metallic behaviour. These results clearly demonstrate that alkali-metal assistance is valid even in applications of gas-source CVD without oxygen-containing species, where intermediates comprising Na, W, and S can play an important role. We observed that the WS2 crystals grown by gas-source CVD exhibited a narrow size distribution when compared with crystals grown by conventional solid-source CVD, indicating that the crystal nucleation occurred almost simultaneously across the substrate, and that uniform lateral growth was dominant afterwards. This phenomenon was attributed to the suppression of inhomogeneous nucleation through the fast and uniform diffusion of the gas-phase precursors, supported by the Na-assisted suppression of the fast reactions between WF6 and H2S.

Two-Step Growth of Uniform Monolayer MoS2 Nanosheets by Metal–Organic Chemical Vapor Deposition

“…Electrical properties of the as-grown film ( Figure S14 ) show no modulation that could arise due to the presence of defects in the as-grown film. 50 The sulfurized film was transferred via a poly(methyl methacrylate) (PMMA)-based wet transfer method using NaOH as the substrate etchant onto the target Si/SiO 2 substrate with alignment mark. Figure 7 a shows PL spectra of a MoS 2 domain before and after transfer.…”

2D WS2: From Vapor Phase Synthesis to Device Applications

“…[ 109 ] Remarkably, Okada et al. introduced NaCl during the CVD synthesis of WS 2 using gaseous precursors of WF 6 and H 2 S. [ 110 ] The size of obtained triangle‐shaped WS 2 crystals was about 10 µm after the introduction of NaCl. Although large WS 2 crystals were obtained, no continuous film was realized.…”

Tungsten disulfide: synthesis and applications in electrochemical energy storage and conversion

“…The nucleation and growth mechanism of CVD differs in each synthetic process as the generation of 2D WS 2 lies in (1) vapor sources, (2) temperature, (3) atomic gas flux and (4) substrates. In case of the vapor sources, metal containing precursors (e.g., WS 2 [59], WO 3 [39,[60][61][62][63], WCl 6 [64], WF 6 [65,66] and W(CO) 6 [67]) are vaporized and then react with sulpur containing elements (S [39,68,69], H 2 S [63,65,66]) through vapor-solid reactions, leading to the growth of 2D WS 2 nanosheets on the substrate downstream. Generally, WO 3 is always the first choice as a cheap and easily handled precursor with relatively low melting and evaporation temperature [70].…”