Pressure confinement effect in MoS2 monolayers

Abstract

With ever increasing interest in layered materials, molybdenum disulfide has been widely investigated due to its unique optoelectronic properties. Pressure is an effective technique to tune the lattice and electronic structure of materials such that high pressure studies can disclose new structural and optical phenomena. In this study, taking MoS₂ as an example, we investigate the pressure confinement effect on monolayer MoS₂ by in situ high pressure Raman and photoluminescence (PL) measurements. Our results reveal a structural deformation of monolayer MoS₂ starting from 0.84 GPa, which is evidenced by the splitting of E¹_2g and A_1g modes. A further compression leads to a transition from the 1H-MoS₂ phase to a novel structure evidenced by the appearance of two new peaks located at 200 and 240 cm⁻¹. This is a distinct feature of monolayer MoS₂ compared with bulk MoS₂. The new structure is supposed to have a distorted unit with the S atoms slided within a single layer like that of metastable 1T′-MoS₂. However, unlike the non-photoluminescent 1T′-MoS₂ structure, our monolayer shows a remarkable PL peak and a pressure-induced blue shift up to 13.1 GPa. This pressure-dependent behavior might enable the development of novel devices with multiple phenomena involving the strong coupling of the mechanical, electrical and optical properties of layered nanomaterials.