Atomic-layered MoS2 on SiO2 under high pressure: Bimodal adhesion and biaxial strain effects

The stacking effect on the E12g and A1g vibrational modes of mechanically exfoliated MoS2 samples supported on SiO2 was investigated by onresonant Raman spectroscopy at high-pressure conditions. The split of E12g and A1g modes were observed for single- and bilayered samples whereas such splitting disappears for higher numbers of layers. The differences on the E12g pressure coefficients allowed us to interpret the observed splitting as due to the presence of two types of regions corresponding to a high and a low conformation of MoS2 to the substrate roughness. The difference in the pressure coefficient appears then as due to the biaxial stress introduced via the substrate compression. Such effects were not observed for the A1g mode due to its vibration symmetry. This out-of-plane vibration is mainly affected by the normal stress that corresponds to pressure transmitted by the pressure-transmitting medium.