Investigation on friction force and surface modification of MoS₂ flakes under Ga⁺ ion irradiation

The influence of Ga ion irradiation intensity on the surface of both chemical vapor deposition (CVD) and mechanical exfoliate MoS 2 flakes were studied. By Raman spectroscopy, it was observed that the irradiation-induced defects and strain had an impact on the crystal structure of the MoS 2 . The ion-induced tensile strain initially caused lattice stretched of the MoS 2 flakes to increase the work function. However, when the strain exceeded a few percentages (2%), the work function decreased. Friction force microscopy in contact mode was then used to determine the friction force and surface changes in the samples treated with different irradiation time. The result indicated that the friction force decreases as the exposure time increases. Also, the average mean value of irradiated and non-irradiated areas of the samples showed variation in the surface morphology. Furthermore, the bond between the atomic force microscope (AFM) tip and the sample increased, suggesting that the irradiation had caused a change in the MoS 2 flakes.