Using ab initio density functional theory calculations, we characterize changes in the electronic structure of MoS2 monolayers introduced by missing or additional adsorbed sulfur atoms. We furthermore identify the chemical and electronic function of substances that have been reported to reduce the adverse effect of sulfur vacancies in quenching photoluminescence and reducing electronic conductance. We find that thiol-group-containing molecules adsorbed at vacancy sites may reinsert missing sulfur atoms. In the presence of additional adsorbed sulfur atoms, thiols may form disulfides on the MoS2 surface to mitigate the adverse effect of defects.
Keywords: 2D materials; ab initio calculations; defects; electronic structure; transition metal dichalcogenides.