X-ray photoelectron spectroscopy study of MoTe2 single crystals and thin films

XPS spectra of different MoTe2 samples recorded under the same experimental conditions are compared and discussed. For a freshly cleaved single crystal, it is shown that the binding energies are Mo 3d5/2=227.80±0.05 eV and Te 3d5/2=572.40±0.05 eV when C 1s=284.60±0.05 eV is used as reference. Measurements have also been done on samples contaminated by room air: single crystals and thin films obtained by synthesis or co-evaporation. By comparison with the results obtained in the case of freshly cleaved single crystal, it is shown that air contamination induces small, but systematical modifications of the XPS spectra recorded. Moreover, there is some surface oxidation of these samples. This superficial oxidation and the difficulty to achieve stoichiometric samples are discussed with the help of the small electronegativity difference between Mo and Te