Operando Study of Thermal Oxidation of Monolayer MoS₂

Monolayer MoS₂ is a promising semiconductor to overcome the physical dimension limits of microelectronic devices. Understanding the thermochemical stability of MoS₂ is essential since these devices generate heat and are susceptible to oxidative environments. Herein, the promoting effect of molybdenum oxides (MoO ) particles on the thermal oxidation of MoS₂ monolayers is shown by employing operando X-ray absorption spectroscopy, ex situ scanning electron microscopy and X-ray photoelectron spectroscopy. The study demonstrates that chemical vapor deposition-grown MoS₂ monolayers contain intrinsic MoO and are quickly oxidized at 100 °C (3 vol% O₂/He), in contrast to previously reported oxidation thresholds (e.g., 250 °C, t ≤ 1 h in the air). Otherwise, removing MoO increases the thermal oxidation onset temperature of monolayer MoS₂ to 300 °C. These results indicate that MoO promote oxidation. An oxide-free lattice is critical to the long-term stability of monolayer MoS₂ in state-of-the-art 2D electronic, optical, and catalytic applications.