Damage Effects of CVD Single-layer MoS₂ Irradiated by ²⁰⁹Bi Ions

The layer number of MoS₂ with different thickness was determined by the optical microscope and Raman spectra. And the damage effect of the CVD (chemical vapor deposition) prepared single-layer MoS₂ sample irradiated by ²⁰⁹Bi ions was analyzed by the combination of Raman analysis and AFM observations. With the increase of irradiation fluence, the Raman characteristic peaks of E_2g¹ and A_1g corresponding to both phonon vibration modes gradually bluely shift, and the intensity of the peaks obviously decreased. This is due to the fact that the ²⁰⁹Bi ion irradiation results in the latent track type lattice defects and they adsorb the oxygen molecules in the air ended with the p-type doping. Meanwhile, from the AFM image of the mono-layer of irradiated MoS₂ under the 5×10¹⁰ ions/cm², it can been seen that latent tracks mainly occur in the form of pits, which different from the hillock tracks observed by mechanical stripping method. The influence of different preparation technology to the track morphology is analyzed. Compared with the Raman and AFM results of MoS₂ prepared by mechanical stripping, it is considered that different preparation methods will affect the electron density in single or few layers of MoS₂.