Abstract
Monolayer WS2 (Tungsten Disulfide) with a direct-energy gap and excellent photoluminescence quantum yield at room temperature shows potential applications in optoelectronics. However, controllable synthesis of large-area monolayer WS2 is still challenging because of the difficulty in controlling the interrelated growth parameters. Herein, we report a facile and controllable method for synthesis of large-area monolayer WS2 flakes by direct sulfurization of powdered WO3 (Tungsten Trioxide) drop-casted on SiO2/Si substrates in a one-end sealed quartz tube. The samples were thoroughly characterized by an optical microscope, atomic force microscope, transmission electron microscope, fluorescence microscope, photoluminescence spectrometer, and Raman spectrometer. The obtained results indicate that large triangular monolayer WS2 flakes with an edge length up to 250 to 370 μm and homogeneous crystallinity were readily synthesized within 5 min of growth. We demonstrate that the as-grown monolayer WS2 flakes show distinctly size-dependent fluorescence emission, which is mainly attributed to the heterogeneous release of intrinsic tensile strain after growth.
Highlights
The isolation and synthesis of atomically thin two-dimensional transition metal dichalcogenides (TMDs), such as MS2 (M = Mo, W), have attracted a lot of interest due to their unprecedented properties compared with their bulk counterparts [1,2,3]
Thin tungsten disulfide (WS2) has a similar structure to MoS2, but exhibits stronger photoluminescence (PL) quantum yield at room temperature and larger spin-orbit coupling compared to MoS2 [18,19,20], which makes it promising for applications in new optoelectronics and spintronics
The morphology, thickness, atomic structure, and light emissions of the as-grown WS2 samples were characterized by various tools, such as an optical microscope (OM), atomic force microscope (AFM), transmission electron microscope (TEM), fluorescence (FL) microscope, PL spectrometer, and Raman spectrometer
Summary
Yue et al [36] reported that uniform triangular monolayer WS2 flakes with a side length of ~233 μm were synthesized on SiO2/Si substrate by carefully adjusting the introduction time of the sulfur precursor and the distance between the sources and substrates. Zhou et al [37] demonstrated that molten-salt-assisted CVD can be used to synthesize large-area triangular monolayer WS2 flakes with an edge length of 300 μm at moderate temperatures due to the reduction of the WO3 melting point by using sodium chloride.
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