Large-area fabrication of transition metal dichalcogenides via environmentally friendly and efficient processes has been a long-standing issue in the field of two-dimensional (2D) materials. Here, we report that single- to few-layered MoS2 sheets with an average size of the order of micrometers have been successfully synthesized on an ionic liquid surface by a modified low-pressure chemical vapor deposition (LP-CVD) method without the assistance of catalysts. It is found that the MoS2 sheets grown on the liquid substrate exhibit a complete molecular crystal structure, which is confirmed by transmission electron microscopy (TEM), Raman spectroscopy, and photoluminescence (PL) spectroscopy measurements. The interlayer spacing does not change significantly with the increase of the MoS2 layers, corresponding to a layer-by-layer growth pattern. The growth mechanism of the MoS2 sheets is presented according to the experimental results. The work provides a new and simple method of preparing more molecular crystals on liquid substrates and will contribute to further research in this field.
Keywords: CVD method; MoS2; growth mechanism; liquid substrate; molecular crystal.