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Rapid ambient degradation of monolayer MoS2 after heating in air

We report that heating chemical vapor deposition grown monolayer MoS2 in air at temperatures as low as 285 °C for 2 h results in rapid degradation of the monolayer within 2.5 weeks of ambient air exposure after heating. We find that the rapid degradation proceeds via the growth of dendrites on the basal plane that have a fractal dimension close to that of diffusion-limited aggregation. We also observe dendrites in unheated samples that have been in ambient air for a year. We explain the rapid degradation after heating to an increase in MoO3. We propose that the mechanism for dendrite growth involves the diffusion of H2O to oxide sites. This results in the liquefication of the oxides. The liquefied oxides do not protect the surface from further oxidation. Putting heated samples in a dry box for 2 weeks immediately after heating prevents the rapid degradation from occurring.