Contrasting Structural Reconstructions, Electronic Properties, and Magnetic Orderings along Different Edges of Zigzag Transition Metal Dichalcogenide Nanoribbons

Two-dimensional transition metal dichalcogenides represent an emerging class of layered materials exhibiting various intriguing properties, and integration of such materials for potential device applications will necessarily invoke further reduction of their dimensionality. Using first-principles approaches, here we investigate the structural, electronic, and magnetic properties along the two different edges of zigzag MX2 (M = Mo, W; X = S, Se) nanoribbons. Along the M edges, we reveal a previously unrecognized but energetically strongly preferred (2 x 1) reconstruction pattern, which is universally operative for all the four systems (and possibly more), characterized by an elegant self-passivation mechanism through place exchanges of the outmost X and M edge atoms. In contrast, the X edges undergo a much milder (2 x 1) or (3 x 1) reconstruction for MoX2 or WX2, respectively. These contrasting structural preferences of the edges can be exploited for controlled fabrication of properly tailored transition metal dichalcogenide nanoribbons under nonequilibrium growth conditions. We further use the zigzag MoX2 nanoribbons to demonstrate that the Mo and X edges possess distinctly different electronic and magnetic properties, which are significant for catalytic and spintronic applications.