The Pressure Response of Bulk and Two−Dimensional MoS2 Crystals Studied by Raman and Photoluminescence Spectroscopy: Dimensionality and Pressure Transmitting Medium Effects

The pressure response of bulk and two−dimensional (2D) MoS2 crystals (monolayer, bilayer, and many–layered), directly transferred to the diamond surface of the diamond anvil cell (DAC) used for high−pressure application, is examined by means of Raman and photoluminescence (PL) spectroscopy. For the high–pressure experiments of 2D MoS2, the Daphne 7474 oil and the 4:1 methanol–ethanol mixture are alternatively used as pressure-transmitting media (PTM), while the former is also used as PTM in the case of bulk MoS2. Characteristic differences are observed in the pressure evolution of the Raman spectral profile and the pressure coefficients of the peak frequencies between the bulk and the 2D MoS2 crystals of various thicknesses, which also depend on the PTM used. These observations, along with the pressure evolution of the PL spectrum of 2D MoS2, are ascribed to the different stress conditions in each case (hydrostatic vs. uniaxial compression perpendicular to the MoS2 layers), the adhesion of the 2D MoS2 crystals on the diamond anvil, as well as the nature of the particular PTM used and its interaction with the studied system.