Coexistence of Anisotropic and Fractal Etching in Monolayer MoS₂ under Ambient Conditions

The stability of chemical vapor deposition (CVD)-grown transition metal dichalcogenide (TMD) films under ambient conditions remains a critical challenge for sustaining the performance of 2D-TMD-based devices. Here we present a systematic study of the degradation behavior of CVD-grown MoS₂ films on Si/SiO₂ substrates under atmospheric conditions. We observe that vacancy defects and domain edges act as the primary sites for natural etching, as confirmed via Raman spectroscopy. Scanning electron microscopy reveals a complex etching mechanism – a rapid anisotropic one-dimensional etching following MoS₂ crystal symmetry and slower fractal etching governed by the diffusion-limited aggregation (DLA) mechanism. Our results provide valuable insights toward improving the durability of TMD-based next-generation electronic and optoelectronic devices.