Adsorption Behavior of the Hydroxyl Radical and Its Effects on Monolayer MoS₂

Based on first-principles density functional theory calculations, we investigated a modified routine using hydroxyl adsorption that recently demonstrated the controlled growth of MoS₂ monolayers. The new growth approach impedes the deposition of a second MoS₂ layer; however, the hydroxyl adsorption and its effects have been mostly unexplored. Through this study, we first explored the adsorption behaviors of the hydroxyl radical (OH) on monolayer MoS₂ and briefly discussed its effects on the stability and electronic structure. Monolayer MoS₂ repels charged OH^-, whereas the adsorption of the neutral OH radical is energetically favorable; the corresponding adsorption energies are 0.09 eV and -1.35 eV, respectively. The diffusion barrier of the OH radical on MoS₂ is 0.52 eV, indicating that the molecule can quickly diffuse. Next, the study demonstrated that for multiple OH adsorptions, a concerted reaction including OH dissociation and H₂O formation is more energetically favorable than the adsorption of two OH molecules by 2.50 eV, which in turn results in a mixed adsorption configuration of O and OH. In addition, we revealed that the OH adsorption creates a mid-gap state and facilitates the reconstruction of the MoS₂ edge.