Fig. 4: Quantification of surface defects and oxidation of monolayer MoS₂ in pristine and aqueous solution.

a Aberration-corrected ADF-STEM image of monolayer MoS₂ in its pristine form and after incubation in aqueous solution. Marked circles show single sulfur vacancies in MoS₂ (Vs). Inset, an example of the marked circle, showing a single sulfur vacancy defect (green arrow). b Histogram and kernel density estimation analysis show two primary defect populations (single sulfur vacancies annotated as Vs and double sulfur vacancies, Vs₂). There is a slight increase in the sulfur defect concentration after treatment on the same order of magnitude at the same imaging conditions. PL spectrum of MoS₂ in aqueous solution the presence of dissolved oxygen (~8 mg L⁻¹) shown in c, and reduced oxygen level (~1 mg L⁻¹) as shown in d. e Chemical structure of pristine MoS₂ showing sulfur vacancies in the basal plane. f Schematic showing oxidative dissolution and etching of monolayer MoS₂ in air-saturated aqueous solution.