First-principles predictions on the ground structures and charge carrier mobility of two-dimensional MoOS monolayers

Abstract

Substitution of elements with the same main group has been proven to be an effective strategy for the functionalization and synthesis of new two-dimensional materials. In this study, we focused on replacing the sulfur elements in the classic two-dimensional material MoS₂ with oxygen elements, resulting in the formation of stable 2D MoOS materials. Using particle-swarm optimization method and density functional theory calculations, we identified nine new two-dimensional MoOS structures with different space groups. Electronic structure calculations reveal that the P21/m phase exhibits metallic characteristics, while all other structures are semiconductors with band gaps ranging from 1.6 to 1.8 eV. Notably, the P3 and P31m phases were identified as direct band-gap semiconductors. In addition, we conducted a detail study on the carrier mobility of semiconductors with the three highest cohesive energy structures Pmm2, P3 and P2. The results show that the hole mobility values of the Pmm2 phase is nearly five times that of MoS₂, which is attributed to the smaller deformation potential of the valence band maximum and moderate hole effective masses. Furthermore, the electron mobility in P3 and P2 phase has also been improved compared to MoS₂ due to the small electron effective masses. Apart from the metallic P21/m MoOS phase, the incorporation of oxygen significantly enhances the Young's modulus and shear modulus of the two-dimensional semiconducting MoOS, indicating stronger Mo–O and Mo-S bonds. Our work shows that oxygenation can significantly alter the physical and chemical properties of two-dimensional MoS₂, forming stable two-dimensional MoOS materials with diverse band-gaps, superior carrier mobility, and improved mechanical properties compared to MoS₂.