In situ photothermal oxidation kinetics in MoS2

It is important to understand the thermal and chemical stability of mono- and few-layer MoS$_{\mathrm{2}}$ for their use in applications. Oxidative environments are of particular interest due to the potential for use of MoS$_{\mathrm{2}}$ in electronics, sensing and energy storage. Here we present an in situ study of the oxidation kinetics of few-layer MoS$_{\mathrm{2}}$ over a wide range of temperatures. In situ monitoring of the MoS$_{\mathrm{2}}$ Raman spectra under oxidation revealed a decrease in intensity of the peaks following sigmoidal decay kinetics and that was initiated at temperatures as low as 300 \textordmasculine C. Ex situ resonance Raman spectroscopy, scanning electron and atomic force microscopy analysis indicated breaking up and thinning of the MoS$_{\mathrm{2}}$ films down to mono- and bi-layer regions. The process likely originated at defect sites in the film, and based on the Raman peak frequencies, resulted in p-doped islands. From the temperature dependence of the data we extracted a reaction energy of \textasciitilde 0.54 eV, which can be attributed to oxidation of the MoS$_{\mathrm{2}}$ at defect sites. Finally, oxidation of films with varying defect densities revealed a clear dependence of oxidation rate and reaction energy on structural defects.