Raman and X-ray photoelectron spectroscopy investigation of the effect of gamma-ray irradiation on MoS sub(2)

The effect of gamma-ray ( gamma -ray) irradiation on the material characteristics of nanometre scale films of molybdenum disulphide (MoS sub(2)) has been investigated. 3.2, 4.5, and 5.2 nm thick MoS sub(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 gamma -ray irradiation (dose of 120 MRad). Dramatic chemical changes in the MoS sub(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 sub(2g) super(1) and A sub(1g) modes after irradiation. XPS revealed that the MoS sub(2) crystal structure was converted to molybdenum oxide (MoO sub(x)). It is hypothesised that S vacancies are formed due to the gamma -ray irradiation, which subsequently transforms MoS sub(2) to MoO sub(x).