Tailoring the structure of MoS₂ using ball-milled MoO₃ powders: hexagonal, triangular, and fullerene-like shapes

Single and few-layered MoS₂ materials have attracted attention due to their outstanding physicochemical properties with potential applications in optoelectronics, catalysis, and energy storage. In the past, these materials have been produced using the chemical vapor deposition (CVD) method using MoO₃ films and powders as Mo precursors. In this work, we demonstrate that the size and morphology of few-layered MoS₂ nanostructures can be controlled, modifying the Mo precursor mechanically. We synthesized few-layered MoS₂ materials using MoO₃ powders previously exposed to a high-energy ball milling treatment by the salt-assisted CVD method. The MoO₃ powders milled for 30, 120, and 300 min were used to synthesize sample MoS₂-30, MoS₂-120, and MoS₂-300, respectively. We found morphologies mainly of hexagons (MoS₂-30), triangles (MoS₂-120), and fullerenes (MoS₂-300). The MoS₂ nanostructures and MoO₃ powders were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, x-ray diffraction, and thermogravimetric analysis. It was found that MoO₃ milled powders exhibit oxygen loss and decrease in crystallite size as milling time increases. Oxygen deficiency in the Mo precursor prevents the growth of large MoS₂ crystals and a large number of milled MoO_3-x  + NaCl promote greater nucleation sites for the formation of MoS₂, achieving a high density of nanoflakes in the 2H and 3R phases, with diameter sizes in the range of ∼30-600 nm with 1-12 layers. Photoluminescence characterization at room temperature revealed a direct bandgap and exciting trends for the different MoS₂ samples. We envisage that our work provides a route for modifying the structure and optical properties for future device design via precursor engineering.