Tunable sulfur desorption in exfoliated MoS2 by means of thermal annealing in ultra-high vacuum

The effects of thermal annealing in ultra-high vacuum on the electronic structures of bulk and liquid exfoliated MoS2 have been studied by core level and valence band X-ray photoemission spectroscopy. A quantitative analysis of core level spectra demonstrates, in the case of exfoliated MoS2, that, upon annealing above 200 °C, defect formation occurs in the form of sulfur single and double vacancies. Sulfur vacancies introduce surface states in the band gap (determined by the analysis of the valence band spectra). This determines a rigid shift of the core levels to lower binding energies, as a consequence of an upward band bending.