Poisoning of MoO_3 Precursor on Monolayer MoS_2 Nanosheets Growth by Tellurium-Assisted Chemical Vapor Deposition

We obtain molybdenum disulfide (MoS_2) nanosheets (NSs) with edge sizes of 18 μm by direct sulfuration of MoO_3 powder spread on the SiO_2/Si substrates. However, the undesirable MoO_3 nanoparticles (NPs) left on the surface of MoS_2 NSs poison the MoO_3 precursor. Introducing Te vapors to react with MoS_2 to form low melting point intermediate MoS_xTe_2-x, the evaporations of MoO_3 precursor recover and MoO_3 NPs disappear. Thus Te vapor is effective to suppress poisoning of the MoO_3 precursor. Selecting the appropriate amount of Te vapor, we fabricate monolayer MoS_2 NSs up to 70 μm in edge length. This finding can be significant to understand the role of Te in the Te-assisted chemical vapor deposition growth process of layered chalcogenide materials.