Electronic structure and scanning tunnelling microscope images of missing-atom defects on MoS and MoTe surfaces

Missing-atom defects on the transition metal dichalcogenides MoS and MoTe have been studied using the projector augmented-wave method, based on ab initio density functional theory. The presence of the vacancies results in localized electronic states in the surface band gap which can affect the STM image, and on the basis of our results we believe that the hole and trimer defects such as those observed by Fuchs et al could be explained by single-missing-chalcogen and single-missing-metal-atom defects respectively. It is found that the chalcogen vacancy systems behave in a similar way for both MoS and MoTe; however, the system of MoTe with a metal vacancy is discovered to be a Jahn-Teller system, while the equivalent MoS system is not. The effects that this has on the atomic and electronic structure and the STM images are discussed.