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.