Structural Stability of Bilayer MoS2 in Ambient Air

It is reported that chemical vapor deposition (CVD) grown bilayer (BL) MoS2 films are significantly more structurally stable in ambient air than CVD-grown monolayer (ML) MoS2 films that have been reported to structurally degrade in ambient air. The authors present atomic force microscopy (AFM) images of preheated and as-grown ML and multilayer MoS2 films after exposure to ambient air for periods of up to 2 years. The AFM images show that, in ambient air, preheated and as-grown BL and thicker-layer MoS2 films do not exhibit the growth of dendrites that is characteristic of ML degradation. Dendrites are observed to stop at the ML-BL boundary. Raman spectra of BLs exposed for up to 2 years are similar to those reported for as-grown BLs. The greater stability of BLs and thicker layers are attributed to their indirect band gaps that suppress Forster resonance energy transfer processes that have been proposed to be responsible for ML degradation. The results show that BL and thicker-layer transition metal dichalcogenides with indirect band gaps may be structurally stable in air and useful for ambient-air applications.