Interlayer Coupling Affected Structural Stability in Ultrathin MoS₂: An Investigation by High Pressure Raman Spectroscopy

Abstract

Interlayer coupling plays critical roles in determining the lattice vibrations of two-dimensional transition-metal dichalcogenides. When compressed, the effects of interlayer coupling remain ambiguous. Pressure-dependent vibrational properties of trilayer and quadlayer MoS 2 up to 12.7 GPa were investigated through in situ high pressure Raman spectroscopy measurement. The Raman spectrum reveals different responses to pressure in trilayer and quadlayer MoS 2 due to their thickness-dependent interlayer coupling interaction. Combining this data with the first-principles calculations, we demonstrate that the quadlayer MoS 2 transforms into an AB′ stacking configuration above 8.6 GPa, where all Mo atoms sit exactly over the Mo atoms in their neighboring layer and all S atoms sit over the centers of the hexagons, while the trilayer MoS 2 possesses a distorted and wrinkled 2H structure within our studied pressure range. Our study demonstrates that high pressure Raman spectroscopy measurement is an effective method to explore the structural transformation of ultrathin MoS 2 at extreme conditions as well as to explore their complicated interlayer coupling interaction. It should also be of great benefit for the development of nanotechnology, especially for the design and fabrication of different stacking nanometer devices with tailored properties for specific applications.