Long-Term Exposure of MoS(2) to Oxygen and Water Promoted Armchair-to-Zigzag-Directional Line Unzippings

Understanding the long-term stability of MoS(2) is important for various optoelectronic applications. Herein, we show that the long-term exposure to an oxygen atmosphere for up to a few months results in zigzag (zz)-directional line unzipping of the MoS(2) basal plane. In contrast to exposure to dry or humid N(2) atmospheres, dry O(2) treatment promotes the initial formation of line defects, mainly along the armchair (ac) direction, and humid O(2) treatment further promotes ac line unzipping near edges. Further incubation of MoS(2) for a few months in an O(2) atmosphere results in massive zz-directional line unzipping. The photoluminescence and the strain-doping plot based on two prominent bands in the Raman spectrum show that, in contrast to dry-N(2)-treated MoS(2), the O(2)-treated MoS(2) primarily exhibits hole doping, whereas humid-O(2)-treated MoS(2) mainly exists in a neutral charge state with tension. This study provides a guideline for MoS(2) preservation and a further method for generating controlled defects.