Raman and X‐ray photoelectron spectroscopy investigation of the effect of gamma‐ray irradiation on MoS ₂

Abstract

The effect of gamma‐ray (γ‐ray) irradiation on the material characteristics of nanometre scale films of molybdenum disulphide (MoS 2 ) has been investigated. 3.2, 4.5, and 5.2 nm thick MoS 2 films (measured by atomic force microscopy) were grown on Si by using a two‐step synthesis method (sputtering of Mo, followed by sulphurisation). The samples were subsequently exposed to γ‐ray irradiation (dose of 120 MRad). Dramatic chemical changes in the MoS 2 films after irradiation were characterised by micro‐Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), and optical microscopy. Micro‐Raman spectroscopy showed the disappearance of the E 2 g 1 and A 1g modes after irradiation. XPS revealed that the MoS 2 crystal structure was converted to molybdenum oxide (MoO x ). It is hypothesised that S vacancies are formed due to the γ‐ray irradiation, which subsequently transforms MoS 2 to MoO x .