Strong Photoluminescence Enhancement of MoS sub(2) through Defect Engineering and Oxygen Bonding

We report on a strong photoluminescence (PL) enhancement of monolayer MoS sub(2) through defect engineering and oxygen bonding. Micro-PL and Raman images clearly reveal that the PL enhancement occurs at cracks/defects formed during high-temperature annealing. The PL enhancement at crack/defect sites could be as high as thousands of times after considering the laser spot size. The main reasons of such huge PL enhancement include the following: (1) the oxygen chemical adsorption induced heavy p doping and the conversion from trion to exciton; (2) the suppression of nonradiative recombination of excitons at defect sites, which was verified by low-temperature PL measurements. First-principle calculations reveal a strong binding energy of 2.395 eV for an oxygen molecule adsorbed on a S vacancy of MoS sub(2). The chemically adsorbed oxygen also provides a much more effective charge transfer (0.997 electrons per O sub(2)) compared to physically adsorbed oxygen on an ideal MoS sub(2) surface. We also demonstrate that the defect engineering and oxygen bonding could be easily realized by mild oxygen plasma irradiation. X-ray photoelectron spectroscopy further confirms the formation of Mo-O bonding. Our results provide a new route for modulating the optical properties of two-dimensional semiconductors. The strong and stable PL from defects sites of MoS sub(2) may have promising applications in optoelectronic devices. Keywords: MoS sub(2); photoluminescence; defect engineering; plasma; oxygen bonding; excitons