Tuning Local Electronic Structure of Monolayer MoS$_{2}$ through Defect Engineering

Two-dimensional molybdenum disulfide (MoS$_{2})$ has shown promising applications in electronics, photonics, energy and electrochemistry, and defects have shown to play an essential role in altering the performance of MoS$_{2}$. However, the mechanism of defects in affecting the MoS$_{2}$ properties is unsettled. In this work, we perform a systematic study on the effect that MoS$_{2}$ defects play on the electronic structure and electrochemical reactivity. Using chemical-vapor deposited monolayer MoS$_{2}$ combined with thermal driving and ion irradiation, we fabricate monolayer MoS$_{2}$ with different defect densities on various substrates. We reveal that the electronic state of MoS$_{2}$ is sensitive to both substrates and defects, supported by our X-ray photoelectron spectroscopy, Raman and photoluminescence spectroscopies, and scanning tunneling microscopy/spectroscopy. We further found that the defect density in MoS$_{2}$ can effectively tune the hydrogen evolution reactivity. Our findings provide useful guidance for defect engineering in MoS$_{2}$ and show the potential application of such defect engineering in using MoS$_{2}$ for a clean and effective energy source.