Probing defect dynamics in monolayer MoS2 via noise nanospectroscopy

Monolayer molybdenum disulfide (MoS2) has received intense interest as a strong candidate for next-generation electronics. However, the observed electrical properties of monolayer MoS2 exhibit several anomalies: samples universally exhibit unexpectedly low mobilities, ntype characteristics, and large contact resistances regardless of contact metal work function. These anomalies have been attributed to the presence of defects, but the mechanism behind this link has been elusive. Here we report the ionization dynamics of sulfur monovacancy defects in monolayer MoS2 probed via noise nanospectroscopy, realized by combining noise-current analysis with atomic force microscopy. Due to the nanoscale dimension of the in situ channel defined by the tip size, we probe a few monovacancy defects at a time. Monovacancy defects exhibit switching between three distinct ionization configurations, corresponding to charge states 0, -1, and -2. The most probable charge configurations are 0 and -1, providing a plausible mechanism to explain the observed anomalies of MoS2 monolayers.