Width-dependent phase crossover in transition metal dichalcogenide nanoribbons

Abstract

Two-dimensional (2D) transition metal dichalcogenides MX2 (M = Mo, W; X = S, Se) exhibit two phases: the ground state 2H and the metastable 1T. Here, WSe2 and MoS2 monolayers have been studied, and we show by comprehensive first-principles calculations that the stability of the two phases can be switched in MX2 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 WSe2. 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 MX2 nanoribbons. Our findings underscore the importance of edges in determining the structures of 2D MX2 and are crucial for their future scientific studies and potential applications.