UV illumination enhanced desorption of oxygen molecules from monolayer MoS2 surface

The oxygen adsorption can drastically alter the electronic properties of the 2D materials, which is usually difficult to be removed. In this work, we report the UV illumination induced desorption of the O-2 molecules from the monolayer MoS2 surface by using the atmosphere dependent transport measurement, Kelvin probe microscopy, photoluminescence spectroscopy and X-ray photoelectron spectroscopy. Obvious increasing of the conductivity, rising of the Fermi level, and red shift of the photoluminescence peaks of the MoS2 were observed after the UV illumination in vacuum, indicating the elimination of the depletion effect from the oxygen adsorption. Such parameter changes can be reversibly recovered by the subsequent O-2 exposure. Furthermore, obvious decreasing of the oxygen concentration after the UV illumination was also observed by X-ray photoelectron spectroscopy. Thus the UV induced O-2 photodesorption effect is evidenced. The photo-excited charge transfer mechanism is proposed to account for the photodesorption effect. These results provide a nondestructive way to clean the MoS2 surface and manipulate the performance of the MoS2 based devices.