First-principles Study On The Structural Stability Of 1T-XS2(X=Mo, W) Monolayer By Stress Controlling

Single-layered dichalcogenide XS2(X=Mo, W) have shown their great potential for applications in electrical and optoelectronic devices. For MoS2, 1H phase is the most stable structure at ambient temperature. However, one of the unique features of single-layered MoS2 is polymorphism, with its distinct electronic characteristics. For example, 1H-MoS2 is semiconducting, whereas 1T phase exhibit metallic. In order to widen the applications of single-layered MoS2, we propose an approach to stabilize the 1T-MoS2, with utilizing the compressive strain.Based on density functional theory, we study the lattice stabilities of 1T-MoS2 and 1T-WS2 under various strains. Through analyzing the phonon dispersion curves under different strains, we could get the following conclusions:(i) Under zero strain or tensile strains, the phonon dispersion curves of 1T-MoS2 and 1T-WS2 have imaginary frequencies, indicating the instability of their structures.(ii) Under compressive strains, the imaginary frequencies of the phonon dispersion curves of 1T-MoS2 and 1T-WS2 decrease with increase of the strain. For1T-MoS2, the imaginary frequencies disappear when the compressive strain reaches5.5%, suggesting the structural stability. For 1T-WS2, compressive strain 6.5% could make the imaginary frequencies disappear.(iii) Under compressive strains, the energy bands of 1T-MoS2 and 1T-WS2 show that the metallic characteristic of 1T phase remains.Overall, our results show that the stabilities of single-layered 1T-MS2(M=Mo, W)could be controlled by using strains. And the stable 1T-MS2 could keep its original metallic characteristic. Therefore, our proposed approach is possible from the theoretical point of view.