Anharmonicity of monolayer MoS2, MoSe2, and WSe2: A Raman study under high pressure and elevated temperature

In this paper, the thermodynamic parameters such as Grüneisen parameters and anharmonicity are investigated utilizing pressure- and temperature-dependent Raman spectroscopy of monolayer transition-metal dichalcogenides MX2 (M = Mo, W; X = S, Se). The result indicates a good stability of these compounds in the pressure range of 0–9.0 GPa and the temperature range of 175–575 K. It is a general trend that Raman mode varies with temperature and pressure linearly for monolayer MX2, and the thermodynamic Grüneisen parameters can be determined from the temperature- and pressure-dependencies of Raman spectra. Based on these measurable parameters, anharmonic parameters are extracted for each active Raman mode. The result shows that the temperature dependencies of the phonon frequencies are well described by considering the contributions from thermal expansion and lattice anharmonicity.