Pressure Tuning Resonance Raman Scattering in Monolayer, Trilayer, and Many-Layer Molybdenum Disulfide

We report a pressure-dependent resonance Raman study of mechanically exfoliated one-layer (1L), three-layer (3L), and many-layer MoS2 near the A excitonic transitions by using an excitation energy of 1.96 eV. Our results show a linear blue shift for the majority of phonon modes, except for the second-order phonons LA(K) + TA(K) and 2LA, whose pressure-dependent frequency is non-linear. The pressure dependence of these bands is explained by considering the dispersive scattering process that gives rise to these two modes, where both phonon and exciton energies blue-shift as the pressure increases. In addition, the resonance of the A1g mode in 1L-MoS2 is achieved at ∼7.0 GPa, while for 3L-MoS2 and many-layer MoS2, it occurs at ∼3.4 GPa. This difference is attributed to the smaller pressure coefficient of the A excitonic transition for 1L-MoS2, as compared with that of 3L-MoS2 and the MoS2 bulk. Our findings constitute an important step toward understanding and controlling the optoelectronic properties of few-layer MoS2 by means of strain/pressure, which are relevant in designing new flexible electronic and light-emitting devices.