Theoretical and experimental Raman study of molybdenum disulfide

Abstract

High pressure Raman spectra were measured for 2H–MoS2 at small pressure intervals, including Stokes Raman spectra from 0 to 40 GPa and anti-Stokes Raman spectra from 0 to 31.4 GPa. Analysis of the pressure-dependent frequencies and full width at half maximums for the A1g and E2g1 modes showed that the A1g mode was more sensitive to pressure. The peaks of the E2g1 mode split from 20.0 GPa, thereby indicating the beginning of a phase transition from 2Hc to 2Ha, and the transition was complete near 40.7 GPa. In the same pressure range, density functional theory calculations confirmed the phase transition and the pressure-dependent frequencies were in good agreement with the experimental results. Simulations predicted that the linear growth in the frequency of A1g-2Hc with the pressure was inhibited at 35 GPa by repulsive interlayer interactions, thereby causing frequency splitting from the A1g-2Ha mode. In addition, the in-plane E2g1 mode of the 2Hc phase was annihilated when the pressure reached 40.7 GPa. Based on our results and previous research, we propose that the 2Hc-2Ha phase transition of MoS2 is complete at around 40.7 GPa and this explains the absence of the Raman peak split for the out-of-plane A1g mode.