Ultraviolet-Ozone Treatment: An Effective Method for Fine-Tuning Optical and Electrical Properties of Suspended and Substrate-Supported MoS 2 .

Ultraviolet-ozone (UV-O 3 ) treatment is a simple but effective technique for surface cleaning, surface sterilization, doping, and oxidation, and is applicable to a wide range of materials. In this study, we investigated how UV-O 3 treatment affects the optical and electrical properties of molybdenum disulfide (MoS 2 ), with and without the presence of a dielectric substrate. We performed detailed photoluminescence (PL) measurements on 1-7 layers of MoS 2 with up to 8 min of UV-O 3 exposure. Density functional theory (DFT) calculations were carried out to provide insight into oxygen-MoS 2 interaction mechanisms. Our results showed that the influence of UV-O 3 treatment on PL depends on whether the substrate is present, as well as the number of layers. Additionally, 4 min of UV-O 3 treatment was found to be optimal to produce p-type MoS 2 , while maintaining above 80% of the PL intensity and the emission wavelength, compared to pristine flakes (intrinsically n-type). UV-O 3 treatment for more than 6 min not only caused a reduction in the electron density but also deteriorated the hole-dominated transport. It is revealed that the substrate plays a critical role in the manipulation of the electrical and optical properties of MoS 2 , which should be considered in future device fabrication and applications.