  Monolayer transition metal dichalcogenides (TMDCs) are two-dimensional (2D)
materials with many potential applications. Chemical vapour deposition (CVD) is
a promising method to synthesize these materials. However, CVD-grown materials
generally have poorer quality than mechanically exfoliated ones and contain
more defects due to the difficulties in controlling precursors' distribution
and concentration during growth where solid precursors are used. Here, we
propose to use thiol as a liquid precursor for CVD growth of high quality and
uniform 2D MoS2. Atomic-resolved structure characterizations indicate that the
concentration of sulfur vacancies in the MoS2 grown from thiol is the lowest
among all reported CVD samples. Low temperature spectroscopic characterization
further reveals the ultrahigh optical quality of the grown MoS2. Density
functional theory simulations indicate that thiol molecules could interact with
sulfur vacancies in MoS2 and repair these defects during the growth of MoS2,
resulting in high quality MoS2. This work provides a facile and controllable
method for the growth of high-quality 2D materials with ultralow sulfur
vacancies and high optical quality, which will benefit their optoelectronic
applications.
