Raman spectroscopic investigations on transition-metal dichalcogenides MX2 (M = Mo, W; X = S, Se) at high pressures and low temperature

Transition-metal dichalcogenides have been investigated using Raman spectroscopy both being off-resonance and in resonance. The first-order Raman spectra of MoS2, MoSe2, WS2 and WSe2 single crystal synthesized by vapor transport technique have been studied as a function of hydrostatic pressure (0-20GPa) and temperature (80-300K). Isobaric and isothermal mode-Gruneisen parameters have been determined from the temperature and pressure-dependent Raman spectra. The pressure dependence of the chalcogen-chalcogen and metal-chalcogen force constant has been obtained using a central force model. Separation of the temperature dependence of Raman mode wavenumbers into quasi-harmonic and purely anharmonic contributions using measured high-pressure Raman data allows us to extract the changes in the phonon wavenumbers arising exclusively due to anharmonic interactions. Copyright (c) 2014 John Wiley & Sons, Ltd.