Vapour–liquid–solid growth of monolayer MoS2 nanoribbons

Li, Shisheng; Lin, Yung Chang; Zhao, Wen; Wu, Jing; Wang, Zhuo; Hu, Zehua; Shen, Youde; Tang, Dai‐Ming; Wang, Junyong; Zhang, Qi; Zhu, Hai; Chu, Leiqiang; Zhao, Weijie; Liu, Chang; Sun, Zhipei; Taniguchi, Takaaki; Osada, Minoru; Chen, Wei; Xu, Qian; Wee, Andrew Thye Shen; Suenaga, Kazu; Ding, Feng; Eda, Goki

doi:10.1038/s41563-018-0055-z

Cited by 327 publications

(372 citation statements)

References 54 publications

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“…Especially above 730 °C, as time goes on, no solid WO3 grains remain as a result of reaction with NaCl (see Supplementary Movie 2). As reported previously in the literature 11 and as illustrated later in the text, this reaction has a significant role in both VLS and VSS crystal synthesis.…”

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confidence: 75%

Real time optical observation and control of atomically thin transition metal dichalcogenide synthesis

et al. 2019

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Understanding the mechanisms involved in chemical vapour deposition (CVD) synthesis of atomically thin transition metal dichalcogenides (TMDCs) requires the precise control of numerous growth parameters. All the proposed mechanisms and their relation to the growth conditions are inferred from characterising intermediate formations obtained by stopping the growth blindly. To fully understand the reaction routes that lead to the monolayer formation, real time observation and control of the growth are needed. Here, we demonstrate how a custom-made CVD chamber that allows real time optical monitoring can be employed to study the reaction routes that are critical to the production of the desired layered thin crystals in salt assisted TMDC synthesis. Our real time observations reveal the reaction between the salt and the metallic precursor to form intermediate compounds which lead to the layered crystal formation. We identified that both the vapour-solid-solid and vapour-liquid-solid growth routes are in an interplay. Furthermore, we demonstrate the role H2 plays in the saltassisted WSe2 synthesis. Finally, we guided the crystal formation by directing the liquid intermediate compound through pre-patterned channels. The methods presented in this article can be extended to other materials that can be synthesized via CVD. Main Text:Chemical vapour deposition (CVD) synthesis of two-dimensional (2D) transition metal dichalcogenides (TMDCs) involves deposition of gaseous precursors on to a substrate to facilitate the crystallization in the desired crystal structure 1,2,3,4,5 . In a typical CVD synthesis, a transition metal containing precursor is placed in a tube furnace with a chalcogen precursor and a target substrate. Ar/H2 mixture carries the vaporised chalcogen precursor and the metal compounds to form atomically thin layers on the target substrate. Salts are also added to the conventionally used metal oxide precursors to form more volatile intermediate compounds 6,7,8 . This increases the monolayer formation rate and allows the synthesis of otherwise difficult to synthesize 2D TMDCs 9 . The setup described above has been used to produce atomically thin TMDC crystals in various morphologies. However, optimization of the growth parameters requires blind trial and errors, and even the optimized recipes offer limited control in terms of number of layers, crystal phase and morphology.There are two growth modes in CVD synthesis of TMDCs. (1) Vapour-Solid-Solid (VSS): Vaporized precursors are adsorbed on the substrate and form crystals via surface diffusion and bond formation at an elevated temperature 10 , and (2) Vapour-Liquid-Solid (VLS): Supersaturated liquid droplets containing the constituent elements form the crystals 11 . Figure 1a depicts these growth modes. Despite many studies on the CVD growth mechanisms of few layer TMDCs, it is unclear which growth mode prevails under different growth conditions. The

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confidence: 75%

Real time optical observation and control of atomically thin transition metal dichalcogenide synthesis

et al. 2019

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“…The measured on/off ratios for the single‐ and few‐layer MoS 2 reached a maximum value of 6 × 10 6 and the carrier mobilities showed an average of 3.5–5.1 cm 2 V −1 s −1 . Recently, a molten‐salt‐assisted CVD was developed to control the nanostructure of MoS 2 . This improved CVD method also has been demonstrated to be compatible with various other TMDs as well as their alloys …”

Section: D Transition‐metal Dichalcogenidesmentioning

confidence: 99%

Various Structures of 2D Transition‐Metal Dichalcogenides and Their Applications

et al. 2018

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2D transition‐metal dichalcogenides (TMDs), which exhibit fascinating and fantastic properties, have promising applications in future electronic devices and photoelectric devices. Here, the recent research on 2D TMDs is summarized, including single components, 2D doped TMDs, and 2D van der Waals heterostructures. The physical picture, synthetic methods, and optoelectronic properties of these 2D materials are comprehensively described. Opportunities and emerging applications of 2D materials in the future are briefly discussed.

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“…Email addresses: wulx@hdu.edu.cn (Lixiang Wu), yangwh@hdu.edu.cn (Weihuang Yang), gaofeng@hdu.edu.cn (Gaofeng Wang) To enable the direct growth of large single crystals and nanoribbons by CVD [10], the flake alignment of 2D materials can be one of key factors and the growth anisotropy should be intensively investigated, since it has been shown that the waferscale single-crystalline graphene can be grown if the initial graphene nuclei have the same orientation [11] and the alignment of monolayer TMDC nanoribbons is largely determined by the orientation of the crystal substrate. [12,13] Currently [14], in many synthesis approaches, 2D TMDC materials nucleate randomly on substrates, and their orientation cannot be well controlled. Controlled anisotropic growth of large-area or high-aspectratio single crystals is still in the early stage of development, and the detailed mechanism remains unclear, though there have been efforts and attempts on the location-and orientation-controlled growth of monolayer TMDCs.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of substrate-induced anisotropic growth of monolayer WS2 by kinetic Monte Carlo simulations

Yang

Wang

2019

npj 2D Mater Appl

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Controlled anisotropic growth of two-dimensional materials provides an approach for the synthesis of large single crystals and nanoribbons, which are promising for applications as low-dimensional semiconductors and in next-generation optoelectronic devices. In particular, the anisotropic growth of transition metal dichalcogenides induced by the substrate is of great interest due to its operability. To date, however, their substrate-induced anisotropic growth is typically driven by the optimization of experimental parameters without uncovering the fundamental mechanism. Here, the anisotropic growth of monolayer tungsten disulfide on an ST-X quartz substrate is achieved by chemical vapor deposition, and the mechanism of substrate-induced anisotropic growth is examined by kinetic Monte Carlo simulations. These results show that, besides the variation of substrate adsorption, the chalcogen to metal (C/M) ratio is a major contributor to the large growth anisotropy and the polarization of undergrowth and overgrowth; either perfect isotropy or high anisotropy can be expected when the C/M ratio equals 2.0 by properly controlling the linear relationship between gas flux and temperature.Keywords: anisotropic growth, monolayer tungsten disulfide, kinetic Monte Carlo, ST-X quartz substrate, chemical vapor depositionRecently, substrates such as sapphire, mica, graphite [18][19][20][21] have been used in the alignment of as-grown TMDC flakes, which is attributed to the

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Vapour–liquid–solid growth of monolayer MoS2 nanoribbons

Cited by 327 publications

References 54 publications

Real time optical observation and control of atomically thin transition metal dichalcogenide synthesis

Real time optical observation and control of atomically thin transition metal dichalcogenide synthesis

Various Structures of 2D Transition‐Metal Dichalcogenides and Their Applications

Mechanism of substrate-induced anisotropic growth of monolayer WS2 by kinetic Monte Carlo simulations

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