Influence of chemical potential on shape evolution of 2D-MoS2 flakes produced by chemical vapor deposition

Abstract High-quality, ultrathin 2D-MoS 2 layers with large area were grown on SiO 2 /Si substrates by using atmospheric pressure chemical vapor deposition (APCVD) at elevated temperatures. The growth precursors (MoO 3 and S) were placed separately inside the double-zone furnace to control the growth parameters individually for better flexibility in the growth process. In this study, it was found that the shape and edge structure of the evolved MoS 2 flakes were significantly influenced by the chemical potential of the Mo and S precursor concentration. In keeping with the concentration gradient of the Mo precursor (MoO 3 ) on the substrate surface, the shape of MoS 2 flakes changed from hexagonal to truncated triangle and then to triangular shapes, owing to the Mo-rich to S-rich conditions. The surface roughness and thickness of the differently shaped MoS 2 flakes were studied by using atomic force microscope (AFM). Additionally, Raman and photoluminescence (PL) techniques were employed to characterize the crystalline quality, number of grown layers and optical performance of the as-grown MoS 2 layers. Auger electron spectroscopy (AES) analysis and scanning electron microscopy (SEM) confirmed that the equilibrium crystal shape of the MoS 2 was hexagonal under Mo-rich conditions. However, the shape of the MoS 2 crystal changed to a triangle under S-rich conditions. Furthermore, the influence of chemical potential on the edge structure of the monolayer MoS 2 and its effect on the equilibrium shape of the crystal were studied.