Characterization of local non-equilibrium phonons in bulk MoS 2 probed by temperature-dependent Raman scattering

This study presents an experimental implementation to determine the temperature dependence of Raman spectra of bulk 2H-MoS 2 in the temperature range of 300–650 K. In addition, we have measured T AS / S according to the anti-Stokes to Stokes integrated intensity ratio ( I AS / I S ). The results indicate that Raman shift of both the vibration modes E 2 g 1 and A 1 g exhibits a linear temperature-dependent behavior in the heating and cooling processes. It is confirmed that the sample did not deteriorate by oxidization and decomposition at high temperatures. However, above 500 K, the measured phonon temperature T AS / S deviated from the heat bath temperature. It is suggested that the I AS / I S does not correspond to the equilibrium population of optical phonons, thus indicating that the measurement was not in thermal equilibrium but in a thermal steady state under laser irradiation. We conclude that this is caused by the difference in relaxation times in the thermal steady state.