Core level spectroscopy of MoS2

X-ray photoelectron spectroscopy has been used to study mineral molybdenite, MoS2. The fitted core level spectra of sulphur 2p and molybdenum 3d states reveal several photon energy sensitive components. The high binding energy component in both spectra is proposed to originate from the uppermost sulphur or molybdenum atoms of an S-Mo-S sandwich layer of the hexagonal structure, respectively. The other features are suggested to be caused by the edge structures formed during the sample cleavage. The edge facets have much stronger chemical properties than the basal planes and they are known as the active sites of MoS2 when it is used as a catalyst. The spectral features and the effect of the structure of UHV cleaved MoS2 on them are discussed.