MoS2 are two-dimensional (2D) materials that exhibit emerging photoluminescence (PL) at the monolayer level and have potential optoelectronic applications. Monolayers of MoS2 typically achieved by mechanical exfoliation (Me), chemical vapor deposition (CVD), and chemical exfoliation (Ce) via lithium intercalation contain numerous defects that significantly reduce their PL efficiency. Several studies have reported overcoming poor PL in mechanically exfoliated and CVD-grown MoS2, but such studies for chemically exfoliated MoS2 (Ce-MoS2) have not been reported. Here, we report a solution-based method of enhancing the PL of Ce-MoS2 by reacting with molecules with suitable functional groups at high temperatures. Reaction with dodecanethiol (DDT) generates PL that is more intense than mechanically exfoliated MoS2 (Me-MoS2) with high crystallinity and has a significantly broader range of wavelengths. Based on ultraviolet-visible, Fourier transform infrared, X-ray photoemission, and PL spectroscopy as well as transmission electron and PL imaging, we propose that the present method modifies PL properties of Ce-MoS2 by simultaneously annealing, replacing molybdenum-oxygen with molybdenum-sulfur bonds, inducing strain, and generating a nanopolycrystalline structure. This work points to such defect engineering using molecules as an effective means to modify the properties of Ce-MoS2 and layered transition-metal dichalcogenides more generally.
Keywords: chemically exfoliated MoS; functionalization; phase engineering; photoluminescence enhancement; surface chemistry; transition-metal dichalcogenide.