Proton beam flux dependent work function of mono-layer MoS2

Monolayer (ML)-molybdenum disulfide (MoS2) with a direct band gap of ~1.8 eV exhibits considerable potential for advanced electronic and optical device applications. The surface electronic properties of ML-MoS2 need to be controlled for developing novel MoS2-based devices. In this study, we investigated the work function variation of chemical vapor deposition-grown ML-MoS2 that was controlled by proton irradiation. The crystallinity of the ML-MoS2 was confirmed by micro-Raman and Photoluminescence measurements. The work functions of the ML-MoS2 irradiated with varying proton beam flux were measured by Kelvin probe force microscopy. As the ML-MoS2 were exposed to the proton beam flux ranging from 1 × 1012 to 1 × 1014 protons/cm2 at the same beam energy of 10 MeV, the contact potential difference of the MoS2 increased up to about 0.108 V with increased proton beam flux. Based on the referenced value of the Au work function (≈5.1 eV), the work functions of non-treated ML-MoS2 and proton-irradiated ML-MoS2 with a proton beam flux of 1 × 1014 protons/cm2 were determined to be 5.031 eV and 4.992 eV, respectively. The decrease of the work function of the MoS2 with increased proton beam flux is due to the defect formation induced by proton irradiation. We suggest the possibility of engineering the surface potential and electronic properties of ML-MoS2 through controlling proton irradiation conditions.