Electron-injection driven phase transition in two-dimensional transition metal dichalcogenides

Abstract

Two-dimensional transition metal dichalcogenides (TMDs) have attracted considerable attention as potential building blocks for electronic and optoelectronic applications due to their polymorphism that creates the possibility to realize metallic and semiconducting properties in the same material. Here we report the electron-injection driven structural transition from the semiconducting H phase to semimetal T′ phase in MoX₂ (X =S, Se, and Te) nanosheets based on density-functional theory (DFT) calculations. Our results show that the phase stability of MoX₂ highly depends on the arrangement of Mo-4d orbitals and p–d hybridization between the Mo and X atoms. The addition of electrons onto the MoX₂ basal plane increases the orbital occupation degree of d electrons in the T′ phase that enhances the T′-phase stability and reduces the phase-transition barriers, which contributes to the H-to-T′ phase transition. We demonstrate that the electron-driven phase-transition mechanism can be applied to explain broad experimental observations, including the realization of T′-phase MoX₂ nanosheets by the intercalation of Li ions, hydrogen passivation, and defect engineering. The present work offers a basic understanding of semiconductor-to-semimetal transition in TMD nanosheets and opens up more possibilities to control the crystal phase of MoX₂ for device applications.