Raman spectroscopy measurement of MoS$_{2}$ to 43 GPa

MoS$_{2}$ has a typical layered crystal structure. The two-dimensional lattice vibration, in conjunction with the strong (ionic) and weak (Van de Waals) bonding, is a very interesting subject. Among many of the interesting properties of MoS$_{2}$ is the physical performance in response to the substantial reduction of distance between the layers of the MoS$_{2}$ network along with the increase of interaction between them. We compressed MoS$_{2}$ in a diamond anvil cell to 43 GPa and carried out \textit{in situ} Raman spectroscopy measurement. We found that the vibration energy of the A$_{1g}^1 $and E$_{2g}^1 $modes was elevated with increasing pressure. At about 27 GPa, the peak of E$_{2g}^1 $ mode split into two peaks while the A$_{1g}^1 $ peak did not show any abnormality. We believe that this reflects a structural phase transformation due to a minimal distortion of the MoS$_{2}$ network within the layer. We also found that non-hydrostatic compression on the sample lowered the pressure-induced energy elevation of the vibration modes, indicating that the differential stress applied on a MoS$_{2}$ crystal resists the atomic vibration.