Controlling the morphology of ultrathin MoS2/MoO2 nanosheets grown by chemical vapor deposition

The morphology of MoS2 plays an important role in its properties and applications, such as electronics and catalysis. Herein, the morphology of as-grown MoS2/MoO2 freestanding nanosheets and 2D MoS2, as synthesized by chemical vapor deposition using S and MoO3 powders as reactants, was studied by tuning the distances between the MoO3 source and the substrate and between the S and MoO3 powder sources. The distance between the MoO3 source and the substrate was deliberately reduced to obtain a sharp gradient of MoO3 precursor concentration on the growth substrate, and the position of S was changed to obtain various sulfur concentrations and initial reaction temperatures. As a result, morphology evolution, including 2D MoS2 and MoS2/MoO2 freestanding nanosheets was observed. A mechanism was proposed to explain the morphology transformation between horizontal 2D flakes and freestanding nanosheets. Based on this mechanism, synthesis methods to produce dense, ultrathin, large-sized MoS2 freestanding nanosheets were proposed. These results may be further generalized to create novel nanostructured devices.