Spontaneous Curvature of Janus Transition Metal Dichalcogenide Nanoribbons: Effects on Optoelectronic, Magnetic and Mechanical Properties

Janus transition metal dichalcogenides (TMDs) are two-dimensional materials of the form MXY (M = Mo, W; X, Y = S, Se, Te). These materials are similar to traditional TMDs with structure MX₂, but with one chalcogen layer replaced by another chalcogen type. In this work, we study freestanding armchair and zigzag nanoribbons of the Janus materials Mo/WSSe, Mo/WSTe, and Mo/WSeTe using density functional theory. The lattice mismatch between the X and Y sides of the material causes curvature of the unsupported ribbons. We investigate the magnetic and electronic properties of these structures as a function of ribbon width and curvature angle. Zigzag nanoribbons are found to be metallic while armchair nanoribbons are semiconducting with a band gap that depends on the ribbon width. Additionally, all zigzag nanoribbons possess a magnetic moment while armchair ribbons may not. We also study the effects of edge passivation on both armchair and zigzag nanoribbons. Hydrogen passivation was found to increase the band gap, enhance the stability of nanoribbon edge and induce a magnetic moment in the armchair ribbons. This work sheds light on how the spontaneous curvature of the nanoribbons affect/enhance the optoelectronic, magnetic and mechanical properties.