Width-dependent phase crossover in transition metal dichalcogenide nanoribbons.

Two-dimensional (2D) transition metal dichalcogenides MX (M = Mo, W; X = S, Se) exhibit two phases: the ground state 2H and the metastable 1T. Here, WSe and MoS monolayers have been studied, and we show by comprehensive first-principles calculations that the stability of the two phases can be switched in MX nanoribbons. The 2H phase is found to have increasingly higher energy than the 1T phase at a smaller ribbon width, and the width for favoring the 1T phase reaches up to 2.50 nm for WSe. The phase crossover is due to higher coordination of edge M atoms in 1T phase than in 2H phase and an interesting electronic reconstruction of 1T lattice in the ribbon interior. The edge configuration of 1T phase diminishes the edge dangling bonds and thereby enhances the stability of MX nanoribbons. Our findings underscore the importance of edges in determining the structures of 2D MX and are crucial for their future scientific studies and potential applications.