Tailoring the properties of two dimensional molybdenum disulfide

The ability to tailor the properties of a material is essential to optimize device functionality. In this talk, I will present evidence that the electrical and optical properties two-dimensional (2D) molybdenum disulfide (MoS$_{2})$ can be tuned by controlled exposure to oxygen plasma. We find that the mobility, on-current and resistance of 2D MoS$_{2}$ FETs vary exponentially by up to four orders of magnitude with respect to the plasma exposure time. Photoluminescence (PL) study show a decrease of PL intensity leading a complete quenching. Raman studies show a significant decrease of intensity of MoS$_{2}$ peaks with the creation of new oxidation induced peak, while X-ray photoelectron spectroscopy (XPS) study show peaks associated with MoO$_{3}$ after plasma exposure. We suggest that during exposure to oxygen plasma, the energetic oxygen molecules interact with MoS$_{2}$ and create MoO$_{3}$ rich defected-regions, which are insulating. MoO$_{3}$ defected-regions act as a tunnel barrier for the injected conduction electrons, giving rise to the exponential increase in resistivity as a function of plasma exposure time. Bandstructure calculation shows that the PL quenching upon plasma exposure is due to the creation of MoO$_{3}$ defected-regions which causes a direct to indirect bandgap transition in monolayer MoS$_{2}$.