Chalcogen vacancies in transition metal dichalcogenides are widely
acknowledged as both donor dopants and as a source of disorder. The electronic
structure of sulphur vacancies in MoS2 however is still controversial, with
discrepancies in the literature pertaining to the origin of the in-gap features
observed via scanning tunneling spectroscopy (STS) on single sulphur vacancies.
Here we use a combination of scanning tunnelling microscopy (STM) and STS to
study embedded sulphur vacancies in bulk MoS2 crystals. We observe
spectroscopic features dispersing in real space and in energy, which we
interpret as tip position- and bias-dependent ionization of the sulphur vacancy
donor due to tip induced band bending (TIBB). The observations indicate that
care must be taken in interpreting defect spectra as reflecting in-gap density
of states, and may explain discrepancies in the literature.Comment: 7 pages, 5 figure