The evolution of MoS₂ properties under oxygen plasma treatment and its application in MoS₂ based devices

CVD molybdenum disulfide (MoS₂) is shown to chemically oxidize rapidly after pure oxygen plasma bombardment. Atomic force microscopy (AFM), photoluminescence spectrum (PL), Raman spectrum and X-ray photoelectron spectroscopy (XPS) are employed to characterize the physical and chemical properties and indicate that MoO₃ is easily formed from MoS₂. The result of AFM shows that thickness of the film increases from 0.9 to 1.79 nm after oxygen plasma treatment, which is mainly due to the difference in lattice structure between pristine MoS₂ and generated MoO₃. XPS analysis shows that the intensity of the S2s peak is reduced to 0 after oxygen plasma treatment. Also, the intensities of Mo⁴⁺ peaks disappear at 233.2 eV and 230 eV, leaving only the Mo⁶⁺ peaks at 232.5 eV and 235.65 eV, which strongly proves the transformation of MoS₂ to MoO₃. Further, we use oxygen plasma to treat few-layer MoS₂, and find that the top oxidized layer can protect the lower MoS₂ from further oxidation. Finally, we obtain p-type doped transistors with this method.