Effect of geometry of precursor crucibles on the growth of MoS2 flakes by chemical vapor deposition

Chemical vapor deposition (CVD) employing a furnace with multiple temperature zones is still the best and most widely used method for preparing high-quality MoS2 flakes. In this work, MoO3 powder was chosen as the molybdenum precursor to explore the influence of the size of boat crucibles holding molybdenum precursors on the morphology of resultant MoS2 crystals. It is found that shorter or open-ended boat crucibles are not favorable for the reaction between the vapor of sulfur and molybdenum precursors, i.e. no MoS2 crystals can be produced under these conditions. In contrast, the use of longer boat crucibles as the precursor carrier facilitates the growth of triangular MoS2 crystals. Furthermore, the width of the boat crucibles was also found to have a substantial impact on the structural and optical properties of the as-grown MoS2 crystals. More monolayers, regular shapes, uniform surfaces and better optical properties were evident in MoS2 crystals prepared using narrower boat crucibles, as confirmed by the results of the atomic force microscopy (AFM), Raman spectroscopy and photoluminescence (PL). This work clarifies the critical role of the geometry of the molybdenum precursor container and suggests a facile yet efficient way for obtaining monolayer high-quality MoS2 crystals by the CVD technique.