Effects of argon ion bombardment on basal plane and polycrystalline MoS2

Argon ion bombardment effects have been studied for two molybdenum disulphide samples with differing surface crystal orientations. High resolution X-ray photoelectron spectroscopy was used to monitor detailed changes in the core and valence levels. The specimens were dosed using a 2 kV argon ion beam, 45° to the surface at fluences ranging from 1 × 1014 to 1.2 × 1016ionscm2. A basal 〈0001〉 plane of MoS2 dosed to 1 × 1014ionscm4 exhibited a Fermi level shift of −0.55 eV; this is interpreted as a of the level further away from the conduction band minimum as a result of defects introduced by the beam. Pinning at a similar point occurs naturally for the other specimen studied — a polycrystalline thin film of MoS2. Increasingly higher fluences of Ar+ on the basal plane MoS2 resulted in the gradual conversion of MoS2 to one prominent surface product — a molybdenum species with a Mo(3d52) binding energy of 228.1 eV: evidence suggests that this molybdenum species is still associated with the Mo-S lattice framework. Similar doses of Ar+ on a polycrystalline surface results in substantially greater sulphur depletion and a number of different molybdenum-sulphur and molybdenum-oxide species.